Vibration doi: 10.3390/vibration7020016
Authors: Lorenzo Bernardini Andrea Collina Gianluca Soldavini
Bridges connecting islands close to the coast and crossing the sea have been attracting the attention of several researchers working in the field of train–bridge interactions. A runability analysis of a bridge during the event of a ship impact with a pier is one of the most interesting and challenging scenarios to simulate. The objective of the present paper is to study the impact on the running safety of a train crossing a sea bridge as a function of different operational factors, such as the train travelling speed, the type of impacting ship, and the impact force magnitude. Considering train–bridge interactions, a focus is also placed on wheel–rail geometrical contact profiles, considering new and worn wheel–rail profiles. This work is developed considering a representative continuous deck bridge with pier foundations located on the sea bed composed of six spans of 80 m. Time-domain simulations of trains running on the bridge during ship impact events were carried out to quantify the effect of different operating parameters on the train running safety. For this purpose, derailment and unloading coefficients, according to railway standards, were calculated from wheel–rail vertical and lateral contact forces. Maps of the safety coefficients were finally built to assess the combined effect of the impact force magnitude and train speed. The present investigation also showed that new wheel–rail contact geometrical profiles represent the most critical case compared to moderately worn wheel–rail profiles.
]]>Vibration doi: 10.3390/vibration7010015
Authors: Loan Dolbachian Walid Harizi Zoheir Aboura
The goal of this article is to provide a review of the experimental techniques and procedures using vibration methods for the Structural Health Monitoring (SHM) of Polymer-Matrix Composites (PMCs). It aims to be a guide for any researchers to carry out vibration experiments. The linear methods are first introduced. But, as PMC is a complex material, these classic methods show some limits, such as low accuracy for small damages and a high environmental dependency. This is why the nonlinear methods are secondly studied, considering that the complexity of PMCs induces a nonlinear behavior of the structure after damage occurrence. The different damage mechanisms are well-explained in order to evaluate the potential of each vibration method to detect them.
]]>Vibration doi: 10.3390/vibration7010014
Authors: Maria Anna De Rosa Isaac Elishakoff Maria Lippiello
Plates are flat structural elements whose thickness is small in relation to the size of the surface. Their use may include engine foundations, reinforced concrete bridge elements or parts of various floating structures. Consequently, knowledge of their mechanical behavior under static and dynamic loads is of primary importance in engineering applications and of interest from a structural point of view. As a result, numerous works existing in the literature have investigated the mechanical properties of plates using various plate models, such as Reissner’s theory, Levinson’s theory, Kirchhoff’s theory and Mindlin’s theory, and their static and dynamic behavior has been examined. In the present paper the truncated Uflyand–Mindlin plate equation is proposed. According to Uflyand–Mindlin theory, an alternative theoretical formulation is presented for the free-vibration analysis of plates, and the equations of motion and the general corresponding boundary conditions are derived. This paper develops the truncated Uflyand–Mindlin plate equation, i.e., without the fourth-order derivative, by means of the direct method and variational formulation. The first-order shear deformable plate theory developed by Elishakoff, which takes into account rotational inertia and shear deformation and does not include a fourth-order time derivative, is variationally derived here. This derivation complements that performed by Mindlin some 70 years ago. The innovative aspect of the suggested strategy is that variational and direct methods for studying plate dynamics are analogous. Finding the third equation of the reduced Uflyand–Mindlin equations, the accompanying boundary conditions and their mathematical resemblance are the goals of the presented formulations. In order to solve the dynamic equilibrium problem of a truncated Uflyand–Mindlin equation via a variational formulation, it is demonstrated that the differential equations and the corresponding boundary conditions have the same form as those found using the direct technique. This paper successfully completes this task. Finally, in order to validate the effectiveness and correctness of the proposed procedure, a numerical example of the case of a plate simply supported at all four ends is proposed.
]]>Vibration doi: 10.3390/vibration7010013
Authors: Qinkai Han Shuai Gao Fulei Chu
In this paper, the main excitation sources of micro vibration of spacecraft flywheel rotor systems (SFRSs) are briefly described, and then the research progress is systematically reviewed from four perspectives, including modeling methods, suppression means, vibration isolation techniques, and ground simulation tests. Finally, the existing problems of current research and the direction of further research are given to better serve the micro-vibration prediction and sensitivity analysis of existing models, and provide reference points for the micro-vibration suppression and isolation of the next generation of high-precision spacecraft.
]]>Vibration doi: 10.3390/vibration7010012
Authors: Charis J. Gantes Stelios M. Vernardos Konstantina G. Koulatsou Semih Gül
The safe and cost-effective design of wind turbine towers is a critical and challenging aspect of the future development of the wind energy sector. This process should consider the continuous growth of towers in height and blades in length. Among potential failure modes of tubular steel towers, shell local buckling due to static axial compressive stresses from the rotor, blades, and tower weight, as well as dynamic flexural compressive stresses from wind actions on the rotating blades and the tower itself, are dominant as thickness is optimized to reduce weight. As man door and ventilation openings are necessary for the towers’ operation, the local weakening of the tower shell in those areas leads to increased buckling danger. This is compensated for by tower manufacturers by the provision of stiffening frames around the openings. However, the cold-forming and welding of these frames are among the most time-consuming aspects of tower fabrication. Working towards the optimization of this design aspect, the buckling response of tubular steel towers near such openings is investigated by means of nonlinear finite element analysis, accounting for geometrical and material nonlinearity and imperfections (GMNIA), and also considering several wind directions with respect to the openings. The alternatives of stiffened and unstiffened openings are investigated, revealing that a thicker shell section around the opening may be sufficient to restore lost stiffness and strength, while the stiffener frame may also be eliminated, offering substantial benefits in terms of manufacturing effort, time and cost.
]]>Vibration doi: 10.3390/vibration7010011
Authors: Carlo Rosso Fabio Bruzzone Domenico Lisitano Elvio Bonisoli
The measurement of the meshing stiffness in gear pairs is a technological problem. Many studies have been conducted, but a few results are available. A tailored test bench was designed and realized to measure the Static Transmission Error in two mating gears to address this issue. The bench is capable of testing several kinds of gears, e.g., spur, helical, conical, and internal, and it measures the transmission error concerning the applied torque. The Static Transmission Error is due to the variable stiffness of the gear teeth during a mesh cycle. In this paper, a dynamical method for measuring gear mesh stiffness is presented. The tooth stiffness is estimated from the torsional modal behavior of the rotating parts of the test bench. The dynamics of the system are acquired using accelerometers and very precise encoders to measure the angular accelerations and displacements of rotating parts. The torsional mode shapes are identified; those that show a vibrational behavior of the gears that do not follow the transmission ratio’s sign of the mating kinematic condition are selected because they depend on the flexibility of the teeth. In such a way, the engagement stiffness is estimated from the natural frequencies of the selected mode-shapes and the known inertia of gears and shafts. The experimentally identified results are also compared with numerical values computed with a commercial software for mutual validation.
]]>Vibration doi: 10.3390/vibration7010010
Authors: Paulius Ragauskas Raimondas Jasevičius
In studies of structural mechanics, modal analysis, presented in this paper, is an important tool for analyzing the vibration of an object and its frequencies. In modal analysis, different modes of vibration and the frequencies that generate them are considered. The study covers the nondestructive identification of the elastic characteristics of materials, which involves stochastic algorithms and the application of reverse engineering (i.e., the comparison of reference eigenfrequencies with the results of mathematical models). Identification is achieved by minimizing the objective function—the smaller the value of the objective function, the higher the identification accuracy obtained. By changing the parameters of a material’s mathematical model during identification, certain (usually higher order) modes can change places in a natural frequency spectrum. This leads to the comparison of different order eigenfrequencies, slow convergence and poor accuracy of the identification process. The technique involved in this work is the mode-shape recognition of a specimen of material with an “incorrect” set of elastic properties. The results prove that the identification accuracy of a material’s elastic properties can be increased if an “incorrect” set of elastic properties is removed from the identification process. The research covers only numerical research, with a physical experiment simulation.
]]>Vibration doi: 10.3390/vibration7010009
Authors: Péter Zoltán Csurcsia Muhammad Ajmal Tim De Troyer
In this work, an advanced 2D nonparametric correlogram method is presented to cope with output-only measurements of linear (slow) time-varying systems. The proposed method is a novel generalization of the kernel function-based regularization techniques that have been developed for estimating linear time-invariant impulse response functions. In the proposed system identification technique, an estimation method is provided that can estimate the time-varying auto- and cross-correlation function and indirectly, the time-varying auto- and cross-correlation power spectrum estimates based on real-life measurements without measuring the perturbation signals. The (slow) time-varying behavior means that the dynamic of the system changes as a function of time. In this work, a tailored regularization cost function is considered to impose assumptions such as smoothness and stability on the 2D auto- and cross-correlation function resulting in robust and uniquely determined estimates. The proposed method is validated on two examples: a simulation to check the numerical correctness of the method, and a flutter test measurement of a scaled airplane model to illustrate the power of the method on a real-life challenging problem.
]]>Vibration doi: 10.3390/vibration7010008
Authors: Spyros Brezas Evaggelos Kaselouris Yannis Orphanos Michael Tatarakis Makis Bakarezos Nektarios A. Papadogiannis Vasilis Dimitriou
The present study encompasses a thorough analysis of the vibrations in a splash musical cymbal. The analysis is performed using a hybrid methodology that combines experimental measurements with parametric computer-aided design and finite element method simulations. Experimental measurements, including electronic speckle pattern interferometry, and impulse response measurements are conducted. The interferometric measurements are used as a reference for the evaluation of finite element method modal analysis results. The modal damping ratio is calculated via the impulse response measurements and is adopted by the corresponding simulations. Two different approximations are employed for the computer-aided design and finite element method models: one using three-point arcs and the other using lines to describe the non-smooth curvature introduced during manufacturing finishing procedures. The numerical models employing the latter approximation exhibit better agreement with experimental results. The numerical results demonstrate that the cymbal geometrical characteristics, such as the non-smooth curvature and thickness, greatly affect the vibrational behavior of the percussion instrument. These results are of valuable importance for the development of vibroacoustic numerical models that will accurately simulate the sound synthesis of cymbals.
]]>Vibration doi: 10.3390/vibration7010007
Authors: Mahsa Keikha Jalal Taheri Kahnamouei Mehrdad Moallem
Radio frequency (RF) cavities hold a crucial role in Electron Linear Accelerators, serving to provide precisely controlled accelerating fields. However, the susceptibility of these cavities to microphonic interference necessitates the development of effective controllers to mitigate vibration due to interference and disturbances. This paper undertakes an investigation into the modeling of RF cavities, treating them as cylindrical beams. To this end, a pseudo-rigid body model is employed to represent the translational vibration of the beam under various boundary conditions. The model is systematically analyzed using ANSYS software (from Ansys, Inc., Canonsburg, PA, USA, 2022). The study further delves into the controllability and observability of the proposed model, laying the foundation for the subsequent design of an observer-based controller geared towards suppressing longitudinal vibrations. The paper presents the design considerations and methodology for the controller. The performance of the proposed controller is evaluated via comprehensive simulations, providing valuable insights into its effectiveness in mitigating microphonic interference and enhancing the stability of RF cavities in Electron Linear Accelerators.
]]>Vibration doi: 10.3390/vibration7010006
Authors: Chein-Shan Liu Chung-Lun Kuo Chih-Wen Chang
In the paper, we first develop a novel automatically energy-preserving scheme (AEPS) for the undamped and unforced single and multi-coupled Duffing equations by recasting them to the Lie-type systems of ordinary differential equations. The AEPS can automatically preserve the energy to be a constant value in a long-term free vibration behavior. The analytical solution of a special Duffing–van der Pol equation is compared with that computed by the novel group-preserving scheme (GPS) which has fourth-order accuracy. The main novelty is that we constructed the quadratic forms of the energy equations, the Lie-algebras and Lie-groups for the multi-coupled Duffing oscillator system. Then, we extend the GPS to the damped and forced Duffing equations. The corresponding algorithms are developed, which are effective to depict the long term nonlinear vibration behaviors of the multi-coupled Duffing oscillators with an accuracy of O(h4) for a small time stepsize h.
]]>Vibration doi: 10.3390/vibration7010005
Authors: Qi Chen Jinlei Li
The AMB-rotor system is complex and has strong coupling characteristics, which allows multi-harmonic disturbances to enter the system through different ways to produce vibrations with rich spectrum components, which has a great influence on the improvement of micro-vibration accuracy of the rotor system. To further achieve active control of the micro-vibration in the AMB-rotor system, firstly, the mechanism of multi-source disturbance is analyzed according to the working principle of the AMB-rotor system, and the mathematical and physical relationship between the mechanism of disturbance generation and the inducement is deeply studied. Then, the structure of a novel adaptive notch filter, the method of adaptive frequency estimation and analysis of harmonic current suppression in the AMB system are presented. Finally, simulation and experimental research using an MSCMG system demonstrate the feasibility of the proposed method regarding the elimination of harmonic control current.
]]>Vibration doi: 10.3390/vibration7010004
Authors: Ivan Banović Jure Radnić Nikola Grgić Marko Galić
Low-income regions do not have the economic strength to use conventional isolators; therefore, low-cost alternatives are needed. The recent series of earthquakes in Turkey has once again demonstrated the destructive power of this natural disaster and highlighted the need for high-quality earthquake-resistant structures. In this context, a comprehensive experimental parametric study on the use of natural stone pebbles (ASL-1) and stone pebbles in combination with a geogrid layer (ASL-2) as suitable materials for a GSI system is conducted and the main results are presented. The seismic behavior of five different models was tested using four different acceleration diagrams with different peak ground accelerations (PGAs). Characteristic displacements, accelerations, and strains were measured. The results and conclusions presented are based on the integration and synthesis of several previously conducted studies.
]]>Vibration doi: 10.3390/vibration7010003
Authors: Yuli Zhao Mohamed Khayet Xu Wang
A reliable prediction model can greatly contribute to the research of car seating system vibration control. The novelty of this paper lies in the development of a hybrid method of an artificial neural network (ANN) and response surface methodology (RSM) to predict the peak seat-to-head transmissibility ratio of a seating suspension system and to evaluate its ride comfort for different seat design parameters. Additionally, this method can remove the experimental design of the RSM model. In this paper, four seat design parameters are selected as input parameters and arranged using the central composite design method. The peak transmissibility ratio from seat to head at 4 Hz is chosen as the response target output value. To illustrate this hybrid method, the response target output value of the peak transmissibility ratio is calculated from the frequency response of a five-degrees-of-freedom (5-DOF) lumped-parameter biodynamic seating suspension model. The input design parameters and the response target output values are used to train an ANN to establish the relationship between the seat design parameters and the peak transmissibility ratio. At the same time, the input design parameters and the response target output values predicted by the ANN are used to develop the relationship between the seat design parameters and the peak transmissibility ratio using the response surface method and linear regression models. The hybrid of the ANN and response surface methods makes the planning or design of experiments not essential. The hybrid model of the ANN and response surface method is more accurate and convenient than a linear regression model for the study of seating system vibration isolation.
]]>Vibration doi: 10.3390/vibration7010002
Authors: Robert-Gabriel Sultana Achilleas Davrados Dimitrios Dimogianopoulos
The contact-less sensing and fault diagnosis characteristics induced by fixing short Metglas® 2826MB ribbons onto the surface of thin cantilever polymer beams are examined and statistically evaluated in this study. Excitation of the beam’s free end generates magnetic flux from the vibrating ribbon (fixed near the clamp side), which, via a coil suspended above the ribbon surface, is recorded as voltage with an oscilloscope. Cost-efficient design and operation are key objectives of this setup since only conventional equipment (coil, oscilloscope) is used, whereas filtering, amplification and similar circuits are absent. A statistical framework for extending past findings on the relationship between spectral changes in voltage and fault occurrence is introduced. Currently, different levels of beam excitation (within a frequency range) are shown to result in statistically different voltage spectral changes (frequency shifts). The principle is also valid for loads (faults) of different magnitudes and/or locations on the beam for a given excitation. Testing with either various beam excitation frequencies or different loads (magnitude/locations) at a given excitation demonstrates that voltage spectral changes are statistically mapped onto excitation levels or occurrences of distinct faults (loads). Thus, conventional beams may cost-efficiently acquire contact-less sensing and fault diagnosis capabilities using limited hardware/equipment.
]]>Vibration doi: 10.3390/vibration7010001
Authors: Bernhard Heinemann Kai Simanowski Michael Clasen Jan Dreesen Delf Sachau
Shockmounts in naval applications are used to mount technical equipment onto the structure of naval vessels. The insulating effect against mechanical shock is important here, as it can excite the structure in the event of underwater explosions and otherwise cause damage to the equipment. Although knowledge of the dynamic properties of shockmounts is important to naval architects, the dynamic force-displacement characteristics of shockmounts are often tested and measured statically and/or in the harmonic field. Recently, an inertia-based method and a dynamic model for measuring the dynamic force-displacement characteristics of shockmounts was described. This paper presents a full description of a testbench for implementing this method. The testbench incorporates a drop table for excitation. The proposed setup can be configured for measuring the dynamic characteristics of elastomer and wire rope shockmounts, with shock loads in compression, tension, shear and roll directions. The advanced Kelvin–Voigt model for shockmounts is applied, showing that the dynamic force-displacement characteristics measured with this setup are qualified to generate model parameters for further use.
]]>Vibration doi: 10.3390/vibration6040062
Authors: Yuanjing Wang Pengxuan Lei Binbin Lv Yuchen Li Hongtao Guo
The influence of trailing edge deformation on the aerodynamic characteristics of camber morphing wings is an important topic in the aviation field. In this paper, a new memory alloy actuator is proposed to realize trailing edge deformation, and computational fluid dynamics (CFD) and wind tunnel experiments are used to study the influence of trailing edge deformation on the aerodynamic characteristics of the camber morphing wings. The experiments was carried out in a transonic wind tunnel with Mach numbers ranging from 0.4 to 0.8 and angles of attack ranging from 0° to 6°. The external flow fields and aerodynamic force coefficients with and without deformation were calculated using the CFD method. A loose coupled method based on data exchange was used to achieve a fluid–structure interaction (FSI) analysis. The research results indicate that when the trailing edge is deflected downwards, the phenomenon of shock wave forward movement reduces the negative pressure area on the upper wing surface, increases the pressure on the lower wing surface, and ultimately increases the total lift. This work provides a new approach for the implementation of trailing edge deformation and a powerful data reference for the design of camber morphing wings.
]]>Vibration doi: 10.3390/vibration6040061
Authors: Tian Li Yifan Li Lai Wei Jiye Zhang
As the speed of high-speed trains increases, the vehicle’s lateral stability steadily deteriorates. There have been observations of abnormal vibrations in the tail car, particularly on certain sections of the railway line. This study built a high-speed train aerodynamic simulation model for a three-car consist, and a multibody dynamics simulation model for an eight-car consist based on numerical simulations of train aerodynamics and multibody dynamics. It investigated both steady and unsteady aerodynamic loads, flow field characteristics, and the dynamic performance of vehicles under varied aerodynamic loads at 400 km/h. The results indicate that the aerodynamic loads generated during high-speed train operation exhibit highly unsteady characteristics. Steady aerodynamic loads have a relatively minor impact on the vehicle’s dynamic performance, whereas unsteady loads exert a more significant influence. Under unsteady aerodynamic forces, the tail car experiences severe lateral vibrations. The lateral stability index, displacement, velocity, and acceleration of the tail car under unsteady conditions were measured at 2.26, 7.54 mm, and 0.53 m/s2, respectively. These values represent increases of over 17.71%, 148.84%, and 111.24%, respectively, compared to the steady loads. Large oscillation amplitudes result in more significant lateral displacements and accelerations of the vehicle. This phenomenon is a crucial factor contributing to the “tail swing” effect observed in high-speed trains. This study emphasizes the importance of considering unsteady aerodynamic effects in assessing the lateral stability of high-speed trains and highlights the significance of mitigating the adverse impacts of such dynamic responses, particularly in the tail car.
]]>Vibration doi: 10.3390/vibration6040060
Authors: Thomas Kletschkowski
Theoretical and non-dimensional investigations have been performed to study the vibration control potential of approaches that are not only based on viscoelastic but also on endochronic elements. The latter are known from the endochronic theory of plasticity and provide the possibility of establishing rate-independent schemes for vibration control. The main question that has to be answered is: Can rate-independent damping be efficiently used to reduce mechanical vibrations? To answer this question, non-dimensional models for dynamical systems are derived and analyzed numerically in the time domain as well as in the frequency domain. The results are used to compare the performance of an optimally tuned endochronic absorber to the performance of an optimally tuned dynamic absorber with viscoelastic damping. Based on a novel closed-form representation for non-linear systems with endochronic elements, it has been possible to prove that the rate-independent control of vibration results in an overall control profit that is close to the control profit obtained by the application of well-established approaches. It has also been found that the new concept is advantageous if anti-resonances have to be considered in broadband vibration control. Based on these novel findings, a practical realization in the context of active vibration control is proposed in which the rate-independent control law is implemented with an appropriate signal processing hardware.
]]>Vibration doi: 10.3390/vibration6040059
Authors: Farhan Md. Siraj Syed Tasnimul Karim Ayon Jia Uddin
Efficient maintenance in the face of complex and interconnected industrial equipment is crucial for corporate competitiveness. Traditional reactive approaches often prove inadequate, necessitating a shift towards proactive strategies. This study addresses the challenges of data scarcity and timely defect identification by providing practical guidance for selecting optimal solutions for various equipment malfunction scenarios. Utilizing three datasets—Machine Sound to Machine Condition Monitoring and Intelligent Information (MIMII), Case Western Reserve University (CWRU), and Machinery Failure Prevention Technology (MFPT)—the study employs the Short-Time Fourier Transform (STFT) as a preprocessing method to enhance feature extraction. To determine the best preprocessing technique, Gammatone Transformation, and raw data are also considered. The research optimizes performance and training efficiency by adjusting hyperparameters, minimizing overfitting, and using the KERAS Early Halting API within resource constraints. To address data scarcity, which is one of the major obstacles to detecting faults in the industrial environment, Few-shot learning (FSL) is employed. Various architectures, including ConvNeXt Base, Large MobileNetV3, ResNet-18, and ResNet-50, are incorporated within a prototypical network-based few-shot learning model. MobileNet’s lower parameter count, high accuracy, efficiency, and portability make it the ideal choice for this application. By combining few-shot learning, MobileNet architecture, and STFT preprocessing, this study proposes a practical and data-efficient fault diagnosis method. The model demonstrates adaptability across datasets, offering valuable insights for enhancing industrial fault detection and preventive maintenance procedures.
]]>Vibration doi: 10.3390/vibration6040058
Authors: Amalia Moutsopoulou Georgios E. Stavroulakis Markos Petousis Anastasios Pouliezos Nectarios Vidakis
To simulate a lightweight structure with integrated actuators and sensors, two-dimensional finite elements are utilized. The study looks at the optimal location and active vibration control for a piezoelectric smart flexible structure. Intelligent applications are commonly used in engineering applications. In computational mechanics, selecting the ideal position for actuators to suppress oscillations is crucial. The structure oscillates due to dynamic disturbance, and active control is used to try to reduce the oscillation. Utilizing an LQR and Hinfinity controller, optimization is carried out to determine the best controller weights, which will dampen the oscillation. Challenging issues arise in the design of control techniques for piezoelectric smart structures. Piezoelectric materials have been investigated for use in distributed parameter systems (for example airplane wings, intelligent bridges, etc.) to provide active control efficiently and affordably. Still, no full suppression of the oscillation with this approach has been achieved so far. The controller’s order is then decreased using optimization techniques. Piezoelectric actuators are positioned optimally according to an enhanced optimization method. The outcomes demonstrate that the actuator optimization strategies used in the piezoelectric smart single flexible manipulator system have increased observability in addition to good vibration suppression results.
]]>Vibration doi: 10.3390/vibration6040057
Authors: Nurlan Zhangabay Marco Bonopera Akmaral Utelbayeva Timur Tursunkululy Murat Rakhimov
This article analyzes the convergence of the obtained values as a result of the authors’ earlier experimental and theoretical studies. On the basis of the correlations, it was found that the analyses of a traditional cylindrical steel tank without a steel wire strand wrapping and with a filling level of zero by a liquid showed a difference in natural vibration frequencies of 8.4%, while with half and maximal filling by a liquid showed differences equal to 3.2% and 6.2%, respectively. Vice versa, analyses of a cylindrical steel tank with a steel wire strand winding pitch of a = 3d and with a filling level of zero by a liquid showed a difference in natural vibration frequencies of 8.1%, while with half and maximum filling by a liquid and with the same steel wire strand winding pitch showed differences of 10.1% and 5.9%, respectively. Conversely, analyses of a cylindrical steel tank with a steel wire strand winding pitch of a = d and in absence of filling level amounted to a difference of 5.5%, while with half and maximum filling and with the same steel wire strand winding pitch of a = d, differences of 1.6% and 1.4% were, respectively, achieved. Based on the aforementioned results, the general difference between experimental and theoretical vibration frequencies showed up to 10%, which is a satisfactory result of convergence. The obtained findings of this research can be used by engineers and technical workers in the industries of various fields, research institutes and professional companies in designing new earthquake-resistant steel tanks and strengthening existing ones. Conclusions were then mentioned at the end of the article.
]]>Vibration doi: 10.3390/vibration6040056
Authors: Nikolaos M. Papadakis Nikolaos Nikolidakis Georgios E. Stavroulakis
Cretan lyra is a stringed instrument very popular on the island of Crete, Greece, and an important part of its musical tradition. For stringed musical instruments, the air mode resonance plays a vital part in their sound, especially in the low frequency range. For this study, the air mode resonance of a Cretan lyra is investigated with the use of finite element method (FEM). Two different FEM acoustic models were utilized: First, a pressure acoustics model with the Cretan lyra body treated as rigid was used to provide an approximate result. Secondly, an acoustic–structure interaction model was applied for a more accurate representation. In addition, acoustic measurements were performed to identify the air mode resonance frequency. The results of this study reveal that the acoustic–structure interaction model has a 3.7% difference regarding the actual measurements of the resonance frequency. In contrast, the pressure acoustics solution is approximately 13.8% too high compared with the actual measurements. Taken together, the findings of this study support the idea that utilizing the FEM acoustic–structure interaction models could possibly predict the vibroacoustic behavior of musical instruments more accurately, which in turn can enable the determination of key aspects that can be used to control the instrument’s tone and sound quality.
]]>Vibration doi: 10.3390/vibration6040055
Authors: Andrea Dincher
Parkinson’s disease is an incurable neurological disease. Only the symptoms can be treated with medication or exercise therapy. The present analysis is intended to show how whole-body vibration training affects the symptoms of Parkinson’s disease, distinguishing between acute and long-term effects. Methods: online databases (EMBASE, PubMed, PEDro) were searched for reviews, meta-analyses and new studies since the previous most recent review/meta-analysis. Studies with at least a medium methodological quality (PEDro score at least 5 points) were selected. Results were presented as forest plots that indicated standardized mean differences with 95% confidence interval. Results: Sixteen studies were found with a PEDro-score of at least 5 points. Of these, three studies were excluded from the qualitative analysis because the necessary data, such as standard deviation or control group results, were missing. The effect sizes are very mixed. In some parameters there is no effect, in others a very strong effect. The effects in the comparison between single and multiple treatments are similar. Discussion: The different effects may be partly due to the different vibration frequencies or sentence durations, as well as to different valid test procedures. Conclusions: Since the study situation still does not show clear results, further studies must follow that compare different frequencies, sentence durations and vibration types with each other, so that training recommendations can be given on this basis.
]]>Vibration doi: 10.3390/vibration6040054
Authors: Chunyan Deng Lidong He Zhifu Tan Xingyun Jia
Taking a type of test centrifuge as the research object, the finite element model of the test centrifuge was established, the vibration characteristics and aerodynamic performance of the test centrifuge were analyzed, and a structural optimization design of the test centrifuge was carried out. In this paper, the load was applied according to the actual working condition of a type of test centrifuge. The vibration of the mounting seat of the test centrifuge was analyzed, and the structure of the mounting seat was improved. After improvement, the vibration of the mounting seat was 77.38% lower than that of the original mounting seat. Then, the aerodynamic analysis of the test centrifuge was carried out. The analysis results show that the test centrifuge moved more smoothly under the whole-package shell and the fairing, the resistance decreased, and the shaft load decreased. Finally, the fairing of the test centrifuge was optimized. The analysis shows that an increase in the width of the fairing can reduce the resistance coefficient, which is helpful to the stability of the test centrifuge during operation and reduces the unbalanced response of the system caused by air resistance.
]]>Vibration doi: 10.3390/vibration6040053
Authors: Ana Ramos Alexandre Castanheira-Pinto Aires Colaço Jesús Fernández-Ruiz Pedro Alves Costa
Motivated by concerns regarding safety and maintenance, the operational speed of a railway line must remain significantly below the critical speed associated with the track–ground system. Given the large number of track sections within a railway corridor that potentially need to be analyzed, the development of efficient predictive tools is of the utmost importance. Based on that, the problem can be analyzed in a few seconds instead of taking several hours of computational effort, as required by a numerical analysis. In this context, and for the first time, machine learning algorithms, namely artificial neural networks and support vector machine techniques, are applied to this particular issue. For its derivation, a reliable and robust dataset was developed by means of advanced numerical methodologies that were previously experimentally validated. The database is available as supplemental data and may be used by other researchers. Regarding the prediction process, the performance of both models was very satisfactory. From the results achieved, it is possible to conclude that the prediction tool is a novel and reliable approach for an almost instantaneous prediction of critical speed in a high number of track sections.
]]>Vibration doi: 10.3390/vibration6040052
Authors: Koray Kondakcı Safa Bozkurt Coşkun
In this study, an analytical-based numerical approach was proposed for the analysis of the free axial vibration of homogeneous and functionally graded rods with varying cross-sectional areas. The proposed approach is based on analytical approximation techniques, such as the Adomian decomposition method, variational iteration method, and homotopy perturbation method. However, the governing equations of the problems solved in this study were variable coefficient differential equations. These equations provide analytical solutions for strictly limited cases. Analytical approximation methods easily handle problems with uniform material properties and constant cross-sections, whereas with varying cross-sectional areas, the analytical integration process becomes a difficult task for the software. If the rod’s material is functionally graded with varying cross-sectional areas, the analytical integration process becomes a cumbersome task. The proposed approach eliminates all difficulties and requires computation within several seconds. The application of this method is straightforward, and the results obtained in this study are in excellent agreement with the solutions provided in the literature.
]]>Vibration doi: 10.3390/vibration6040051
Authors: Xutao Sun Sinniah Ilanko Yusuke Mochida Rachael C. Tighe
Vibration-based damage detection is a range of methods that utilizes the dynamic response of a structure to evaluate its condition and detect damage. It is an important approach for structural health monitoring and has drawn much attention from researchers. While multiple reviews have been published focusing on different aspects of this field, there has not been a study specifically examining the recent development across the range of methods, including natural frequency, mode shape, modal curvature, modal strain energy, and modal flexibility-based damage detection methods. This paper aims to fill this gap by reviewing the recent application of these methods in civil structures, including beams, plates, trusses, frames, and composite structural members. The merits and limitations of each method are discussed, and research opportunities are presented. This broader review also provides an opportunity for critical comparison across this range of methods. While predominantly reviewing experiment-based studies, this review also considers some numerical studies that may motivate further research.
]]>Vibration doi: 10.3390/vibration6040050
Authors: Weizhuo Wang
Full-field non-contact vibration measurements provide a rich dataset for analysing structural dynamics. However, implementing the identification algorithm directly using high-spatial resolution data can be computationally expensive in modal identification. To address this challenge, performing identification in a shape-preserving but lower-dimensional feature space is more feasible. The full-field mode shapes can then be reconstructed from the identified feature mode shapes. This paper discusses two approaches, namely data-dependent and data-independent, for constructing the feature spaces. The applications of these approaches to modal identification on a curved plate are studied, and their performance is compared. In a case study involving a curved plate, it was found that a spatial data compression ratio as low as 1% could be achieved without compromising the integrity of the shape features essential for a full-field modal. Furthermore, the paper explores the optimal point-wise sensor placement using the feature space. It presents an alternative, data-driven method for optimal sensor placement that eliminates the need for a normal model, which is typically required in conventional approaches. Combining a small number of point-wise sensors with the constructed feature space can accurately reconstruct the full-field response. This approach demonstrates a two-step structural health monitoring (SHM) preparation process: offline full-field identification of the structure and the recommended point-wise sensor placement for online long-term monitoring.
]]>Vibration doi: 10.3390/vibration6040049
Authors: Tommaso Seresini Sevilia Sunetchiieva Helge Pfeiffer Martine Wevers Christ Glorieux
Laser Doppler scanning vibrometry is used for imaging spectral vibration components in a carbon fiber-reinforced composite plate that contains a sub-surface delamination defect caused by hammer impact. The images reveal sideband generation at the location of the defect, reflecting mechanical nonlinearity-induced mixing between a high amplitude, low-frequency vibration that modulates the stress–strain behavior near the defect and a low amplitude, high-frequency probe vibration. In this work, a multifrequency probe is used to tackle the problem that the mixing coefficients are, in practice, frequency dependent. Based on the measured sideband amplitudes, a study is presented on the expected feasibility of detecting defects by a full field imaging scheme based on a photorefractive interferometer that is configured as a vibrometer acting as a bandpass filter around a sideband frequency of interest.
]]>Vibration doi: 10.3390/vibration6040048
Authors: Yimei Wang Hossein Vatandoost Ramin Sedaghati
Human operators in the transportation sector are exposed to whole-body vibration (WBV) while driving. Occupational exposure to WBV, predominant at low frequencies (<20 Hz), has been linked to spinal injuries and reduced functioning. This study aims at the design development of a novel semi-active seat suspension system featuring magneto-rheological elastomers (MREs) to mitigate the WBV. The proposed suspension system allows a greater range of strokes, while ensuring the MRE remains within an acceptable level of deformation. Several MRE samples were fabricated and characterized under shear mode. Afterward, a field- and frequency-dependent phenomenological model was developed to predict the viscoelastic properties of MREs as functions of both the excitation frequency and applied magnetic field. The MRE material model was subsequently used to design and optimize an adaptive seat suspension system incorporating a C-shaped MRE-based isolator in parallel and series with passive springs. The proposed adaptive seat suspension system demonstrated a frequency shift of 29% by increasing the applied current from 0 to 2 A. Finally, a 6-DOF lumped parameter model of a seated human subject combined with the proposed semi-active suspension system featuring the MRE isolator has been formulated to investigate the vibration transmissibility from the floor to the subject’s head.
]]>Vibration doi: 10.3390/vibration6040047
Authors: Ophélie Larivière Delphine Chadefaux Christophe Sauret Patricia Thoreux
Manual wheelchair (MWC) users are daily exposed to vibration during propulsion. The impact of such exposure on the MWC user’s health has yet to be proven. To date, no agreement has been reached, presumably on the account of the wide variety of experimental parameters that need to be controlled. A possible solution relies on the implementation of a User/MWC model to point out the effect of propelling conditions (MWC loads, propulsion methods, speeds, and ground floor types) on the vibration exposure and eventually on the MWC user’s health. To feed such a model, the evaluation of the MWC vibration response during propulsion is required. Following a necessary MWC experimental modal analysis under laboratory conditions, this study presents the vibration response of an MWC under various propelling conditions. For each investigated condition, the identified set of modal parameters was provided and the effect on the MWC response to vibration at the User/MWC interfaces was highlighted. Results mostly underline that the response to vibration is highly dependent on the propelling conditions. The speed and the ground floor type greatly affect the vibration response: doubling speed and increasing ground surface roughness imply threefold and eightfold vibration levels, respectively. Finally, the main outcome is that an empty MWC or an MWC loaded with a dummy generates vibration outside the range measured for an MWC loaded with a human body, resulting in a lower frequency content and an almost two-fold vibration level increase. The findings of this study will help enhance the understanding of the health risks that wheelchair users encounter as a result of vibrations.
]]>Vibration doi: 10.3390/vibration6040046
Authors: Marco Riboli Elisabetta Manconi Dario Fusai Marco Silvestri Alessandra Aimi
Vibration mitigation of moving flexible structures is a key issue in many applications. Examples include antennas, solar arrays, radar reflectors, and manipulator arms, especially in the aerospace sector. These structures typically consist of inter-connected slender and flexible elements moved by external actuators to reach specific configurations and positions. The movements excite vibrations, which lead to the risk of structural and fatigue failures; once in position, residual vibrations can be further amplified by structure lightness, causing bad performance and malfunctioning of onboard sensors. This paper proposes an effective technique to minimise the vibration of moving flexible structures by calculating the control points of a time-parametrised B-spline representing the shape of the motion law. A testing case of a rotating cantilever beam is considered. Validation using multi-flexible-body simulation software has shown the method’s effectiveness in minimising residual vibrations.
]]>Vibration doi: 10.3390/vibration6040045
Authors: Daniel Winarski Kip P. Nygren Tyson Winarski
Six mode shapes, including bending and torsion, were documented for five different basketball rims and backboards at the United States Military Academy, West Point, New York, NY, USA. The frequency and damping ratio of each mode shape were also determined. The empirical process began with the time-domain excitation and response of each rim-backboard system. The impulse of excitation came from an impact hammer separately applied sequentially to each node. The sinusoidal response was gathered from an accelerometer at a fixed location (node 1). Each time-domain excitation response was then converted to a frequency-domain Bode plot for each node by a Brüel & Kjær 2034 Signal Analyzer, giving transfer functions of output/input versus frequency. Structural Measurements System (SMS) StarStruc software was used to fit mode shapes to the Bode plots. Each of the six mode shapes was fitted to the Bode plots of each node at a specific modal frequency. Each of the six mode shapes was a function of the locations of the nodes, and the Bode plots gathered at each node. The first and second modes were critical for showing that the Energy Rebound Testing Device statistically correlated with the energy transferred to the rim and backboard. A known perturbation mass was selectively attached to the rim to help isolate the dynamic masses and spring rates for the rim and backboard and to ascertain that the kinetic energy transferred to the rim had a 95.67% inverse correlation with rim stiffness.
]]>Vibration doi: 10.3390/vibration6030044
Authors: David Eager Imam Hossain Callan Brook
This paper provides an initial investigation of quadruped rotary galloping gait patterns using data from racing greyhounds as they navigate their way around a constant radius bend. This study reviewed actual race data collected over a five month period from 2986 racing greyhounds. Using numerical dynamics modelling and value range analysis important factors were identified and analysed. By cleaning and synthesising simple X and Y data and also processing data for accuracy greyhound motion path dynamics results were produced for analysis. The results show that the galloping path greyhounds took going into the bend was different from the path coming out of the bend. It also shows that more than 50% of the greyhounds naturally optimised their path for a longer transition while minimising jerk when entering and exiting the bend. This research verified that individual greyhounds naturally chose different path transition lengths for accommodating their dynamic conditions. Finally, it was found that the greyhound galloping path dynamics state is less intense during the second half of the bend.
]]>Vibration doi: 10.3390/vibration6030043
Authors: Cédric Maury Teresa Bravo
Broadband noise reduction over the low–mid frequency range in the building and transportation sectors requires compact lightweight sound absorbers of a typical subwavelength size. The use of multi-layered, closely spaced (micro-)perforated membranes or panels, if suitably optimized, contributes to these objectives. However, their elasticity or modal behaviors often impede the final acoustical performance of the partition. The objective of this study is to obtain insights into the vibrational effects induced by elastic limp membranes or panel volumetric modes on the optimized sound absorption properties of acoustic fishnets and functionally graded partitions (FGP). The cost-efficient global optimization of the partitions’ frequency-averaged dissipation is achieved using the simulated annealing optimization method, while vibrational effects are included through an impedance translation method. A critical coupling analysis reveals how the membranes or panel vibrations redistribute the locations of the Hole-Cavity resonances, as well as their cross-coupling with the panels’ first volumetric mode. It is found that elastic limp micro-perforated membranes broaden the pass-band of acoustic fishnets, while smoothing out the dissipation ripples over the FGP optimization bandwidth. Moreover, the resonance frequency of the first panels mode sets an upper limit to the broadband optimization of FGPs, up to which a high dissipation, high absorption, and low transmission can be achieved.
]]>Vibration doi: 10.3390/vibration6030042
Authors: Thomas Provot Samaneh Choupani Maxime Bourgain Laura Valdes-Tamayo Delphine Chadefaux
The estimation of vertical ground reaction forces (VGRFs) during running is necessary to understand running mechanisms. For this purpose, the use of force platforms is fundamental. However, to extend the study of VGRFs to real conditions, wearable accelerometers are a promising alternative to force platforms, whose use is often limited to the laboratory environment. The objective of this study was to develop a VGRF model using wearable accelerometers and a stepwise regression algorithm. Several models were developed and validated using the VGRFs and acceleration signals collected during 100 stances performed by one participant. The validated models were tested on eight participants. In a sensitivity study, the strongest correlations were observed at cut-off frequencies of ≤25 Hz and in models developed with 30 to 90 stances. After the validation phase, the 10 best models had, on average, low relative differences (≤10%) in the estimation of discrete VGRF parameters, i.e., the passive peak (εpp=6.26%), active peak (εap=2.22%), and loading rate (εlr=2.17%). The results indicate that the development of personalized models is more suitable for achieving the best estimates. The proposed methodology opens many perspectives for monitoring VGRFs under real conditions using a limited number of wearable sensors.
]]>Vibration doi: 10.3390/vibration6030041
Authors: Yue Su Kaifu Xu Yongqiang Gao Lu Jin
The support stiffness of the turbopump rotor system with angular contact ball bearing varies with the rotational speed, which leads to the inaccurate prediction of the dynamics of the turbopump rotor system. The model of the rotor bearing system was constructed based on the theoretical model of angular contact ball bearing stiffness, and the dynamics characteristics of the turbopump system were calculated. To verify the accuracy of the stiffness and the dynamics model, a test system of the turbopump rotor with angular contact ball bearings was designed. Since the bearing stiffness cannot be measured directly, a stiffness identification model was introduced, and an unbalanced response test was conducted to verify the dynamics model. It was found that the turbopump bearing stiffness increased dynamically with speed and reduced the unbalance response of the rotor. The results show that the angular contact ball bearing stiffness model and the dynamics model of the rotor support system are accurate and provide support for the dynamics design of the turbopump rotor system with angular contact ball bearings.
]]>Vibration doi: 10.3390/vibration6030040
Authors: Alessandro Viganò Claudia Celletti Giada Giuliani Tommaso B. Jannini Francesco Marenco Ilaria Maestrini Rosaceleste Zumpano Edoardo Vicenzini Marta Altieri Filippo Camerota Vittorio Di Piero Massimiliano Toscano
Despite newly available therapies for acute stroke and innovative prevention strategies, stroke remains the third leading cause of disability-adjusted life-years (DALYs) lost worldwide, mostly because more than half of stroke survivors aged 65 and over exhibit an incomplete functional recovery of the paretic limb. Given that a repeated sensory input is one of the most effective modulators of cortical motor and somatosensory structures, focal muscle vibration (fMV) is gaining growing interest as a safe, well-tolerated, and non-invasive brain stimulation technique to promote motor recovery after stroke with a long-lasting and clinically relevant improvement in strength, step symmetry, gait, and kinematics parameters. In this narrative review, we first summarize the structural (neural plasticity) and functional changes (network relearning) triggered by the stroke lesion and carried out at a brain and spinal cord level in an attempt to recover from the loss of function. Then, we will focus on the fMV’s plasticity-based mechanisms reporting evidence of a possible concurrently acting multisite plasticity induced by fMV. Finally, to understand what the most effective fMV rehabilitation protocol could be, we will report the most recent evidence regarding the different clinical approaches and timing of the fMV treatment, the related open issues, and prospects.
]]>Vibration doi: 10.3390/vibration6030039
Authors: Silvano Donati
Self-mixing interferometry (SMI) is suitable to sense and measure vibrations of amplitudes ranging from picometers to millimeters at frequencies from sub-Hz to MHz’s. As an optical probe, SMI has the advantage of being non-invasive with the ability to measure without any treatment of the target surface and operate from a substantial standoff distance from the target. As an additional advantage, the SMI configuration is much simpler than that of conventional interferometers as it does not require any optical part external to the laser source. After a short introduction to the basics of SMI, we review the development of configurations of SMI instruments for vibration measurements, based on both analog and digital processing, with record performance to cover the range of vibration amplitudes from 0.1 nm to 1 mm, frequencies up to MHz, and stand-off distances up to 100 m. These performances set a benchmark that is unequaled by other approaches reported so far in the literature. The configurations we describe are (i) a simple MEMS-response testing instrument based on fringe counting, (ii) a half-fringe locking vibrometer for mechanical mode analysis and transfer function measurements, with a wide linear response on six decades of amplitude, (iii) a vibrometer with analog switching cancellation for μm-to-mm amplitude of vibrations, and (iv) a long standoff distance vibrometer for testing large structures at distances up to 100 m and with nm sensitivity. Lastly, as the vibrometer will almost invariably operate on untreated, diffusing surfaces, we provide an evaluation of phase-induced speckle pattern errors affecting the SMI measurement.
]]>Vibration doi: 10.3390/vibration6030038
Authors: Mohamed Hamdaoui
The aim of this work is to perform an uncertainty propagation and global sensitivity analysis of a surface acoustic wave (SAW) gas sensor using finite elements and sparse polynomial chaos. The SAW gas sensor is modeled using finite elements (FEM) under COMSOL, and the sensitivity to DCM of its Sezawa mode is considered to be the quantity of interest. The importance of several geometrical (width and PIB thickness), material (PIB Young’s modulus and density), and ambient (pressure, temperature, and concentration) parameters on the sensor’s sensitivity is figured out by means of Sobol’ indices using sparse polynomial chaos expansions. It is shown that when the variability of the input parameters is low (inferior to 5%), the only impacting parameter is the cell width. However, when the variability of the input parameters reaches medium levels (around 10%), all the input parameters except the ambient temperature are impacting the sensor’s sensitivity. It is also reported that in the medium variability case, the sensor’s sensitivity experiences high variations that can lead to a degradation of its performances.
]]>Vibration doi: 10.3390/vibration6030037
Authors: Nobuyuki Shibata
Background: The purpose of this study was to validate the applicability of a new screening parameter of VPTW defined as the difference between the ascending and descending thresholds of vibrotactile perception to evaluation of the increasing risk of the neurological components of hand-arm vibration syndrome (HAVS) for repeated exposure to hand-arm vibration (HAV). Methods: Thirty subjects—10 old exposed (G1), 10 old non-exposed (G2), and 10 young non-exposed subjects (G3)—were required to carry out three 3 min grip tasks with exposure to two intensities of HAV at 10 min intervals. Vibration perception measurements, each of which lasted 90 s, were performed at 5 min intervals at the right index finger. Results: VPTWs calculated from pairs of the vibrotactile ascending and descending thresholds at the fingertips were not significantly affected by repeated HAV exposure. Moreover, the VPTWs measured for non-exposed subjects were almost invariant regardless of the subjects’ age or the time elapsed after repeated exposure to HAV. Residual TTSs at 125 Hz gradually recovered in all subject groups under both HAV exposure conditions. The residual TTSs of non-exposed subject groups significantly increased as the number of iterations of HAV exposure increased. Conclusions: VPTWs measured after exposure to repeated HAV are invariant and independent of the individual neurosensory characteristics of the fingertips, which supports the hypothesis that VPTWs can be used as a screening parameter to detect potential patients only with neurosensory components observed as early signs of HAVS.
]]>Vibration doi: 10.3390/vibration6030036
Authors: Takashi Chujo Hideyuki Sawada
The widespread use of smartphones and smart wearable devices has created a great demand for vibrators with complex vibration patterns driven by simple circuits. In our previous studies, we observed that a filiform shape-memory alloy (SMA) wire will shrink and then return to its initial length, perfectly synchronizing with a given pulse current. Here, we developed a novel vibrator whose structure allows the micro-vibrations of an SMA wire to be amplified up to a recognizable level without directly touching the wire. The vibrator has the advantage of independently controlling its magnitude and frequency together with a simple driving circuit since it is directly driven by a frequency-modulated pulse current with a controlled duty ratio. We measured the power consumption and the acceleration generated by the vibrator. The results showed that the vibrator consumed only 4–77 milliwatts of power with a quick vibration response within 5 milliseconds, and the acceleration increased significantly in a duty ratio range of around 1%. Furthermore, user evaluations demonstrated that differences in the magnitude and frequency of the generated vibrations were sufficiently recognized when the vibrator was driven by different duty ratios and frequencies, and the vibrator provided various tactile and haptic sensations to users.
]]>Vibration doi: 10.3390/vibration6030035
Authors: Harri Hakula
New applications introduced capsule designs with features that have not been fully analysed in the literature. In this study, thin shells of revolution are used to model drug delivery capsules both with closed and open designs including perforations. The effects of internal boundary layers and sensitivity on frequency response are discussed in the special case with symmetric concentrated load. The simulations are carried out using high-order finite element method and the frequency response is computed with a very accurate low-rank approximation. Due to the propagation of the singularities induced by the concentrated loads, the most energetic responses do not necessarily include a pinch-through at the point of action. In sensitive configurations, the presence of regions with elliptic curvature leads to strong oscillations at lower frequencies. The amplitudes of these oscillations decay as the frequencies increase. For efficient and reliable analysis of such structures, it is necessary to understand the intricate interplay of loading types and geometry, including the effects of the chosen shell models.
]]>Vibration doi: 10.3390/vibration6030034
Authors: Angeliki Papalou
An experimental study was performed examining the effectiveness of a multi-compartment damper in attenuating the response of structures under random and earthquake excitations. The damper consisted of four compartments of unequal size; it was mounted on a small one-story steel structure. The same number of steel spherical particles were placed inside each compartment, resulting in filling area ratios (the total area of the squares around the projected particles divided by the area of the compartment) from 40% to 70%. The damper was effective in reducing the response displacement and acceleration of the structure considerably. The use of different filling area ratios enabled the damper to be effective for a wide range of excitation levels.
]]>Vibration doi: 10.3390/vibration6030033
Authors: Maria Mareen Maravich Robert Rosenkranz M. Ercan Altinsoy
Noise and whole-body vibrations (WBV) inside commercial vehicles can lead to annoyance and reduced comfort. As a result, negative effects on the driver can occur even below the legal exposure limits. In order to understand the annoyance perception and the interaction between noise and WBV, two perception experiments were conducted. For both experiments, recorded signals inside different commercial vehicles were used. Sound pressure and acceleration levels varied. In addition, the frequency content of the recorded vertical seat vibrations was reproduced in different modified variants. The varied parameters (sound pressure level, acceleration level and vibration frequency) were investigated within a three-factorial experimental design. It was found that noise and vibration levels, as well as the vibration spectrum, had a significant effect on total annoyance. Furthermore, an interaction between noise and vibration levels in both experiments could be observed. The results show that for the highest noise level, changing vibration exposure influences annoyance ratings less than the lowest noise level. The results also show that despite the same Wk-weighted RMS level of the WBV according to ISO 2631-1, vibration spectra with sinusoidal components or narrowband vibrations below <10 Hz were significantly perceived as more annoying during a ride in a vehicle.
]]>Vibration doi: 10.3390/vibration6030032
Authors: Mădălina Dumitriu Ioana Izabela Apostol Dragoș Ionuț Stănică
The evaluation of the vibration behavior of railway vehicle car bodies based on the results of numerical simulations requires the adoption of an appropriate theoretical model of the suspension which considers the important factors that influence the vibration level of the car body. In this paper, the influence of the secondary suspension model on the vertical vibration behavior of the railway vehicle car body is investigated, based on the results of numerical simulations on the frequency response functions of the acceleration, the power spectral density of the acceleration and the root mean square of the acceleration of the car body. Numerical simulation applications are developed based on a rigid-flexible coupled vehicle model with seven degrees of freedom, corresponding to car body vibration modes: bounce, pitch, and first vertical bending mode, and bogie vibration modes: bounce and pitch. Four different models of secondary suspension are integrated into the vehicle model, namely a reference model and four analysis models. Analysis models include systems through which the pitch vibration of the bogies is transmitted to the car body, influencing its vibration behavior and, respectively, a system that takes the relative angular displacement between the car body and the bogie and a system that models the transmission system of the longitudinal forces between the bogie and the car body are analyzed. The effects of these two systems on the vibration behavior of the railway vehicle car body are analyzed both for each system separately and together. In the conclusions of the paper, the influence of the secondary suspension model on the vibration level at the resonance frequencies of the vertical bending of the car body and the pitch of the bogie is pointed out. It also highlights the important contribution of the transmission system of the longitudinal forces between the bogie and the car body in transmitting pitch vibrations of the bogies to the car body, with effects on the vibration level of the car body at high speeds.
]]>Vibration doi: 10.3390/vibration6030031
Authors: Mehran S. Razzaghi
Steel cylindrical tanks are vital structures for storing various types of liquid in industrial plants or as a component in a water distributing system. As they sometimes are used to store toxic, flammable, and explosive material, their inapt performance during an earthquake may lead to catastrophic consequences. Therefore, practicing engineers, researchers, and industry owners are concerned about their structural safety. Meanwhile, the seismic performance of liquid storage tanks is rather complex. Thus, this subject has garnered many researchers’ interest in the past decades. This paper aims to briefly review the most significant studies on the seismic performance of on-ground steel cylindrical tanks. It focuses on analytical approaches and does not include experimental and on-site ones. Finally, the new horizons for the seismic performance assessment of such structures are presented herein.
]]>Vibration doi: 10.3390/vibration6030030
Authors: William Kaal Jörg Baumgartner Maximilian Budnik Christoph Tamm
In the design of lightweight structures, both the dynamics and durability must be taken into account. In this paper, a methodology for the combined optimization of structural dynamics, lightweight design, and lifetime with discrete vibration engineering measures is developed and discussed using a demonstration structure. A two-sided welded bending beam is excited at the centre and optimal parameters for tuned mass dampers (TMD) are searched, satisfying the requirements for the dynamic behaviour, the overall mass, and the lifetime of the weldings. It is shown that the combination of a reduced order model with the implementation of the structural stress approach at critical welds enables an efficient evaluation of certain design concepts in the time domain. Using this approach, multi-criterial optimization methods are used to identify the best set of parameters of the TMD to reduce the structural vibrations and enhance the durability.
]]>Vibration doi: 10.3390/vibration6030029
Authors: Massimiliano Rossi Marco Frasca
Ultrasonic signals can be conveniently recorded using modern high-speed analog-to-digital converters and analyzed through digital signal processing algorithms. Sometimes, in some applications, such as in bioacoustics, it is necessary to convert digital data to analog signals with a special transformation that allows compressing and translating the spectrum toward audible frequencies. The process is called time expansion and can be conveniently achieved by slowing down the frequency clock of a digital-to-analog converter. This paper analyzes in detail the spectral characteristics of a time-expanded signal.
]]>Vibration doi: 10.3390/vibration6020028
Authors: Xin Song Amel Sassi Kimberly Seaman Chun-Yu Lin Lidan You
Patients undergoing cancer treatments and/or suffering from metastatic bone lesions experience various skeletal-related events (SREs), substantially reducing functional independence and quality of life. Therefore, researchers are working towards developing new interventions by harnessing the bone’s innate anabolic response to mechanical stimulations. Whole body vibration (WBV) has recently gained interest due to its nature of being safe, effective, and easy to perform. In this review, we will summarize the most cutting-edge vibration studies of cancer models and bone-cancer cell interactions. We will also discuss various parameters, including age, vibration settings, and differences between bone sites, which may affect vibration efficacy. Studies have shown that WBV improves bone mineral density (BMD) and bone volume in patients and mice with cancer. WBV also reduces tumor burden and normalizes bone vasculature in mice. At the cellular level, vibration promotes interactions between bone cells and cancer cells, which reduce osteoclastogenesis and inhibit cancer metastatic potential. Hence, WBV could potentially serve as a new intervention or adjuvant treatment to attenuate cancer progression while preserving bone health.
]]>Vibration doi: 10.3390/vibration6020027
Authors: Tobenna D. Uzuegbunam Rodney Forster Terry Williams
Available decision-support tools rarely account for the welfare of technicians in maintenance scheduling for offshore wind farms. This creates uncertainties, especially since current operational limits might make a wind farm accessible but the vibrations from transits might be unacceptable to technicians. We explore technician exposure to vibration in transit based on the levels of discomfort and the likelihood of seasickness occurring on crew transfer vessels (CTVs). Vessel motion monitoring systems deployed on CTVs operating in the North Sea and sea-state data are used in a machine learning (ML) process to model the welfare of technicians based on operational limits applied to modelled proxy variables including composite weighted RMS acceleration (aWRMS) and motion sickness incidence (MSI). The model results revealed poor to moderate performance in predicting the proxies based on selected model evaluation criteria, raising the possibility of more data and relevant variables being needed to improve model performance. Therefore, this research presents a framework for an ML approach towards accounting for the wellbeing of technicians in sailing decisions once the highlighted limitations can be addressed.
]]>Vibration doi: 10.3390/vibration6020026
Authors: Mona Yadi Yoshiharu Morimoto Yasuhiro Takaya
In order to address the issue of vibration, it is crucial to accurately measure the vibration distribution. The authors previously developed the one-pitch phase analysis (OPPA) method, which allows for rapidly capturing the three-dimensional shape of a flat object. By integrating this method into a system, an OPPA vibration distribution measurement system was created, utilizing a line light source consisting of LEDs or optical fibers and also a high-speed camera to measure the vibrations of three-dimensional objects without physical contact. To further extend the application of the OPPA method to larger objects, such as cars, in this paper, a new system is introduced using a commercially available projector using a liquid crystal display (LCD) instead of a liner light source and a glass grating. This new system, which employs an ultra-short throw projector, is highly sensitive in displacement measurements and provides a wide-area analysis. These kinds of projectors produce noises at the frequency of the cooling fan and the refresh rate of the LCD. However, in this study, these noise sources were also examined. The capabilities of the new system are demonstrated through its application to the measurement of vibrations in a car door and an engine head. The measurement system and examples of its application are presented.
]]>Vibration doi: 10.3390/vibration6020025
Authors: Keigo Ikeda Kota Kamimori Ikkei Kobayashi Jumpei Kuroda Daigo Uchino Kazuki Ogawa Ayato Endo Taro Kato Xiaojun Liu Mohamad Heerwan Bin Peeie Hideaki Kato Takayoshi Narita
Mechanical vibrations adversely affect mechanical components, and in the worst case, lead to serious accidents by breaking themselves. To suppress vibrations, various studies have been conducted on vibration isolation, suppression, and resistance. In addition, technologies to actively suppress vibration have been rapidly developed in recent years, and it has been reported that vibrations can be suppressed with higher performance. However, these studies have been conducted mostly for low-order systems, and few studies have employed control models that consider the complex vibration characteristics of multi-degree-of-freedom (DOF) systems. This study is a basic study that establishes a control model for complex control systems, and the vibration characteristics of a 2-DOF system are calculated using the vibration analysis of a multi-DOF system. Furthermore, the vibration suppression performance of the 2-DOF system is investigated by performing vibration experiments.
]]>Vibration doi: 10.3390/vibration6020024
Authors: Francesca Greco Federico Quinzi Katia Folino Marco Spadafora Loretta Francesca Cosco Maria Grazia Tarsitano Gian Pietro Emerenziani
This study analysed the acute effects of whole-body vibration (WBV) on quadriceps isometric muscular endurance. Fifteen healthy middle-aged males performed an endurance isometric strength test after three different warm-up conditions: static half squat plus WBV (HSV), static half squat without WBV (HS), and control condition (CC). The endurance isometric strength test consisted of 10 maximal isometric contractions held for 4 s and interspersed by 2 s of rest between each repetition. Rate of Perceived Exertion (RPE) was assessed after warm-up (RPE1) and at the end of the testing session (RPE2). During each testing session, participant’s heart rate (HR) was continuously recorded. For each trial, the mean force across the 10 repetitions and fatigue index were evaluated. Mean force was significantly higher (p < 0.01) in CC than in the other two conditions. Both RPE1 and RPE2 were significantly lower (p < 0.01) in CC than HSV and HS condition. Warm-up HR and the mean testing session HR were significantly lower in CC than the other two conditions (p < 0.01). No significant differences were observed in fatigue index between conditions (p > 0.05) or in HR during the endurance protocol. Performing half-squat with or without vibration stimuli does not increase isometric muscular endurance and does not influence fatigue index.
]]>Vibration doi: 10.3390/vibration6020023
Authors: Tassilo Schröder Andreas Lindenmann Sven Matthiesen
This manuscript investigates the rotational mechanical impedance of the human hand–arm system with respect to vibration excitation around the gripping axis of the hand under the influence of body posture, gripping force, and push force. Knowledge of rotational mechanical impedance is required for deriving models of hand–arm biodynamics. These models are used in the validation of power tools to predict further vibrational human–machine interactions. In the current state of research, such models exist for translational but not rotational vibration excitation. Consequently, this study investigates the properties of a hand–arm system with respect to rotational vibration excitation. In the study, the rotational impedance of the hand–arm systems of 13 adults was measured at various gripping and push forces applied in different body postures. The setup of the test used in this study consisted of a shaker that applied rotational vibrations at certain frequencies to the subjects’ hand–arm systems via a cylindrical handle. The results of the study indicate a spring–damper dynamic of the hand–arm system. The gripping force strongly influences the magnitude of rotational impedance across the frequency spectrum. Regarding push force and posture, no corresponding influence could be determined. The results suggest that the frictional contact between the hand and handle might confer a damping effect.
]]>Vibration doi: 10.3390/vibration6020022
Authors: Davide Raffaele Emiliano Rustighi Timothy Waters
The Semi-Analytical Finite-Element (SAFE) method represents one of the most established numerical approaches for predicting the propagation of elastic waves in one-dimensional structures of arbitrary cross-sections. Its implementation in the commercial finite-element software COMSOL Multiphysics has been proposed in recent years; however, it is limited to only the free wave propagation for computing dispersion curves. To overcome this limitation, this paper proposes an extension of this approach that combines COMSOL and its Livelink for Matlab tool. This enables the extraction from COMSOL of the assembled mass and stiffness SAFE matrices to solve problems of both free and forced wave propagation in the Matlab environment. The resulting customised software takes advantage of both the potential of commercial FE software and the power of Matlab without worrying about compatibility issues. A model of a simply supported plate strip and that of a more complex geometry are implemented to validate, respectively, the SAFE matrix extraction procedure and the implemented forced response formulation. The results agree well with corresponding analytical and numerical results validating the proposed implementation of the SAFE method.
]]>Vibration doi: 10.3390/vibration6020021
Authors: Junya Tatsuno Setsuo Maeda
This study aims to investigate the effects of whole-body vibration (WBV) exposure on the disturbance of standing balance function assuming that the cause of slip, trip and fall accidents in the land transportation industry is related to WBV exposure when traveling in vehicles. In the experiment, ten participants underwent 60 min of virtual driving in a driving simulator (DS) for WBV exposure. In addition, standing balance measurements were conducted before exposure, immediately after exposure, 2 min after exposure and 4 min after exposure. Four conditions were considered by combining two magnitudes of WBV exposure and the driver and passenger conditions. This study focused on two indexes of standing balance, namely, total length and enveloped area and the rate of change relative to the value before the vibration exposure was calculated. The rate of change remained almost constant at 1.0 in the control condition without vibration exposure, whereas that under vibration exposure conditions varied. Interestingly, the rate of change at 2 min after exposure remained high in the driver condition, but it decreased to almost 1.0 in the passenger condition. Since no difference appeared in the vibration acceleration measured at the seating surface between the driver and passenger conditions, it was believed that the difference between the driving and passenger conditions was related to fatigue caused by the accelerator-pedal operation. As a result of considering the percentage of the standing balance that returned to 1.0 after 4 min in most conditions, this study proposed that a rest period of several minutes be allowed from the experiment in which the participants were exposed to vibration at 0.5m/s2 rms for 60 min at the DS. Further basic experiments will be conducted to introduce another WBV exposure assessment, including loss of standing balance as a health indicator, to ISO 2631-1.
]]>Vibration doi: 10.3390/vibration6020020
Authors: Mahsa Keikha Jalal Taheri Kahnamouei Mehrdad Moallem
Reduction or suppression of microphonic interference in radio frequency (RF) cavities, such as those used in Electron Linear Accelerators, is necessary to precisely control accelerating fields. In this paper, we investigate modeling the cavity as a cylindrical shell and present its free vibration analysis along with an appropriate control scheme to suppress vibrations. To this end, we first obtain an analytical mechanical dynamic model of a nine-cell cavity using a modified Fourier-Ritz method that provides a unified solution for cylindrical shell systems with general boundary conditions. The model is then verified using the ANSYS software in terms of a comparison of eigenfrequencies which prove to be identical to the proposed model. We also present an active observer-based vibration control scheme to suppress the dominant mechanical modes of the cavity. The control system performance is investigated using simulations.
]]>Vibration doi: 10.3390/vibration6010019
Authors: Junjie Zhao Pengfei Liu Dingxin Leng Haoyu Zhan Guangrui Luan Donghong Ning Jianqiang Yu
Seat suspension plays a vital role in improving riding comfort and protecting drivers’ health. This paper develops semi-active seat suspension that equips a controllable electromagnetic damper (EMD) and proposes a prescribed performance control-based semi-active vibration controller with experimental validation. The semi-active EMD mainly consists of a permanent magnet synchronous motor, a ball screw, a three-phase rectifier, and a controllable external resistor, which can vary its damping from 90 to 800 N·s/m by tuning the controllable external resistor in real-time. The EMD is applied to seat suspension, and a semi-active controller is proposed for the EMD seat suspension. In order to control the seat suspension vibration, a prescribed performance method is applied to obtain a desired control force and then a force-tracking strategy is designed to make the EMD track the desired control force. Finally, the semi-active seat suspension with the proposed controller is tested in experiments with different vibration conditions. The semi-active seat suspension performs excellently for the bump, sine wave and random vibration. The root mean square (RMS) acceleration, the frequency-weighted RMS acceleration and the acceleration’s fourth power vibration dose value were reduced by 17.5%, 39.9%, and 25.4%, respectively, in the random vibration, compared with a passive system.
]]>Vibration doi: 10.3390/vibration6010018
Authors: Minoru Sasaki Joseph Muguro Waweru Njeri Arockia Selvakumar Arockia Doss
This paper presents a 2-link, 2-DOF flexible manipulator control using an inverse feedforward controller and an adaptive notch filter with a direct strain feedback controller. In the flexible manipulator, transient and residue vibrations inhibit the full potential of the manipulator. Vibrations caused by abrupt changes in the direction of the links are referred to as transient vibrations, whereas residual vibrations occur when the arm takes too long to settle after engaging in the intended task. The feedforward adaptive notch filter will reduce transient vibration caused by the manipulator arm beginning and halting suddenly, while the strain feedback will assure the quick decay of leftover vibrations. Maple, Maplesim, and MATLAB tools were used to model the manipulator and create the inverse controller and adaptive notch filter. The experiments took place in the dSPACE control desk environment. The experimental results of the spectral power of strain resulting from the two strategies are compared. From the results, the adaptive notch filter control had over an 80% improvement in the reduction in resonant frequencies that contribute to vibration. The results confirmed the feasibility of the approach, characterized by very minimal transient vibrations and a quick settling of the end effector.
]]>Vibration doi: 10.3390/vibration6010017
Authors: Hamid Jafari Ramin Sedaghati
This paper is concerned with the free and forced vibration responses of a magneto/electroactive dielectric elastomer, emphasizing the chaotic phenomena. The dielectric elastomers under external magnetic and electrical excitations undergo large elastic deformation. The magnetodielectric elastomer is modeled based on the Gent–Gent strain energy function to incorporate the influence of the second invariant and the strain stiffening. The viscoelasticity of the active polymer is also considered in the form of Rayleigh’s dissipation function. The equation of motion is governed with the aid of the Lagrangian equation in terms of a physical quantity, namely, the stretch of the elastomer. An energy-based approach is utilized to re-evaluate the static and DC voltage instabilities of the resonator. Time-stretch response (time history behavior), phase plane diagram, Poincaré map, and fast Fourier transform are numerically obtained and presented to explore the chaotic oscillation behavior of the active polymer actuators. The results reveal that the magnetic field may tune the stability and instability regions of the active polymeric membrane. It has also been shown that the applied magnetic field may lead to chaotic vibration responses when a sinusoidal voltage is applied simultaneously to the system. The results presented in this paper can be effectively used to design magnetic and electrical soft robotic actuators and elastomer membranes under electrical and magnetic stimulants.
]]>Vibration doi: 10.3390/vibration6010016
Authors: Chang Lee Brandon Daveler Jorge Candiotti Rosemarie Cooper Sivashankar Sivakanthan Nikitha Deepak Garrett Grindle Rory Cooper
The QLX is a low-profile automatic powered wheelchair docking system (WDS) prototype developed to improve the securement and discomfort of wheelchair users when riding in vehicles. The study evaluates the whole-body vibration effects between the proposed QLX and another WDS (4-point tiedown system) following ISO 2631-1 standards and a systematic usability evaluation. Whole-body vibration analysis was evaluated in wheelchairs using both WDS to dock in a vehicle while riding on real-world surfaces. Also, participants rated the usability of each WDS while driving a wheelchair and while riding in a vehicle in driving tasks. Both WDSs showed similar vibration results within the vibration health-risk margins; but shock values below health-risk margins. Fifteen powered wheelchair users reported low task load demand to operate both WDS; but better performance to dock in vehicles with the QLX (p = 0.03). Also, the QLX showed better usability (p < 0.01), less discomfort (p’s < 0.05), and greater security compared to the 4-point tiedown while riding in a vehicle (p’s < 0.05). Study findings indicate that both WDS maintain low shock exposure for wheelchair users while riding vehicles, but a better performance overall to operate the QLX compared to the 4-point tiedown system; hence enhancing user’s autonomy to dock in vehicles independently.
]]>Vibration doi: 10.3390/vibration6010015
Authors: Dario Friso
In the nursery sector, the transport and planting of trees must occur with the roots wrapped in a ball of the original earth. The cutting of the original soil can be carried out with a semicircular vibrating blade moved by an oscillator mounted on a self-propelled machine. The oscillator produces an excitation torque supplied to the blade together with the soil cutting torque. The advantage of the vibrating blade is a reduction in the cutting torque of up to 70%. However, to correctly design the oscillator, we need to investigate the link between the maximum displacement of the blade, the maximum oscillation velocity, the cutting velocity, the dry friction, the excitation torque, the elastic torque, the cutting torque, the required power, the required energy, and the excitation frequency. The maximum displacement and velocity ratio need to have the right values to minimize the cutting torque and to avoid the springs reaching the end of stroke; otherwise, vibrations are transmitted to the machine and to the operator. Therefore, starting from the forced oscillation differential equation and using an approximate solution method developed by Den Hartog, along with some experimental data, a mathematical model was constructed to optimize the oscillator design. After construction, it was coupled to blades of various diameters (0.6, 0.9, and 1.2 m) to undergo experimental tests. The soil cutting tests highlighted the achievement of the above objectives and, at the same time, confirmed the validity of the Den Hartog equations used to calculate the phase lag and the maximum displacement, resulting in an average error of 4.4% and a maximum error of 6.4%.
]]>Vibration doi: 10.3390/vibration6010014
Authors: Md Roman Bhuiyan Jia Uddin
In order to evaluate final quality, nondestructive testing techniques for finding bearing flaws have grown in favor. The precision of image processing-based vision-based technology has greatly improved for defect identification, inspection, and classification. Deep Transfer Learning (DTL), a kind of machine learning, combines the superiority of Transfer Learning (TL) for knowledge transfer with the benefits of Deep Learning (DL) for feature representation. As a result, the discipline of Intelligent Fault Diagnosis has extensively developed and researched DTL approaches. They can improve the robustness, reliability, and usefulness of DL-based fault diagnosis techniques (IFD). IFD has been the subject of several thorough and excellent studies, although most of them have appraised important research from an algorithmic standpoint, neglecting real-world applications. DTL-based IFD strategies have also not yet undergone a full evaluation. It is necessary and imperative to go through the relevant DTL-based IFD publications in light of this. Readers will be able to grasp the most cutting-edge concepts and develop practical solutions to any IFD challenges they may encounter by doing this. The theory behind DTL is briefly discussed before describing how transfer learning algorithms may be included into deep learning models. This research study looks at a number of vision-based methods for defect detection and identification utilizing vibration acoustic sensor data. The goal of this review is to assess where vision inspection system research is right now. In this respect, image processing as well as deep learning, machine learning, transfer learning, few-shot learning, and light-weight approach and its selection were explored. This review addresses the creation of defect classifiers and vision-based fault detection systems.
]]>Vibration doi: 10.3390/vibration6010013
Authors: Kemajou Herbert Yakeu Happi Bernard Xavier Tchomeni Kouejou Alfayo Anyika Alugongo
This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear system with coexisting defects, specifically pitting and cracking. Numerical simulations and experimental analysis in various scenarios of the system in operation were conducted using the RPM–Frequency mapping technique. To identify fault characteristics, the analysis performed assumed the gear system had been misadjusted by a combination of pitting and cracking on the gear teeth. The correlation of the system-forced responses under regular and chaotic vibrations revealed that the system is far more sensitive to the crack than to the pitting when there are fluctuating harmonic peaks present at high vibration levels.
]]>Vibration doi: 10.3390/vibration6010012
Authors: Yumeng Yao Krishna N. Dewangan Subhash Rakheja
This study investigated the effects of gender and ten different anthropometric parameters on the vertical vibration transmission from seat to the head of the body seated on an elastic seat. The seat-to-head transmissibility (STHT) responses in the vertical and fore-aft directions of 58 participants (31 males and 27 females) were measured under three levels of vertical vibration (root mean square acceleration: 0.25, 0.50, and 0.75 m/s2) in the 0.50–20 Hz range, when sitting on a viscoelastic seat with and without a vertical back support, and with hands on a steering wheel. Apart from the important effects of elastic coupling between the body and seat, the results show distinctly different vertical and fore-aft STHT responses from the two genders. Moreover, the gender effect was strongly coupled with back support and excitation conditions. The primary resonance frequencies of male subjects were higher than those of female subjects, while the peak vertical STHT magnitudes were comparable. Owing to the strong coupled effects of gender and anthropometric dimensions, the study is designed to reduce the coupling by considering datasets for subjects with comparable chosen dimensions. Among the various anthropometric dimensions considered, the body mass and fat mass revealed strong influences on the primary resonance frequency, which was similar for male and female subjects with comparable body mass index and body fat mass. The vertical STHT magnitude of the two genders with the same lean body mass was also nearly identical. The peak fore-aft STHT magnitudes of the male subjects were notably higher than those of the female subjects with comparable anthropometric dimensions with the exception of the body mass.
]]>Vibration doi: 10.3390/vibration6010011
Authors: Marios Filippoupolitis Carl Hopkins
To detect human survivors trapped in buildings after earthquakes by using structure-borne sound it is necessary to have knowledge of vibration transmission in collapsed and fragmented reinforced-concrete buildings. In this paper, statistical energy analysis (SEA) is considered for modelling vibration transmission in seismically damaged, reinforced concrete, beam-to-column junctions where the connection between the beam and the column is made only via the steel reinforcement. An ensemble of 30 randomly damaged beam-to-column junctions was generated using a Monte Carlo simulation with FEM. Experimental SEA (ESEA) is then considered with two or three subsystems to determine the coupling loss factors (CLFs) between the beam and the column with either bending modes or the combination of all mode types. It is shown that bending modes dominate the dynamic response and that the uncertainty of predicting the CLFs using FEM with ESEA is sufficiently low that it should be feasible to estimate the coupling even when the exact angle between the beam and the column is unknown. In addition, the use of two rather than three subsystems for the junction significantly decreases the number of negative coupling loss factors with ESEA. An initial analysis of the results in this paper was presented at the 50th International Congress and Exposition on Noise Control Engineering.
]]>Vibration doi: 10.3390/vibration6010010
Authors: Vibration Editorial Office Vibration Editorial Office
High-quality academic publishing is built on rigorous peer review [...]
]]>Vibration doi: 10.3390/vibration6010009
Authors: Zuzana Dimitrovová
This article presents a comparison between layered models of a railway track. All analyses are based on semianalytical approaches to show how powerful they can be. Results are presented in dimensionless form, making them applicable to a wide range of possible real-world scenarios. The main results and conclusions are obtained using repeated exact calculations of the equivalent flexibility of supporting structure related to each model by contour integration. New terms and a fundamentally different approach with respect to other published works underline the scientific contribution to this field. Semianalytical methods demonstrate that the intended results can be obtained easily and accurately. However, this benefit cannot be extended to a large number of models due to the simplifications that must be introduced in order to apply such methods. It turns out that even though the one-layer model is the furthest away from reality, it is easy to handle analytically because it has a regular and predictable behavior. The three-layer model, on the other hand, has many unpredictable properties that will be detailed in this article.
]]>Vibration doi: 10.3390/vibration6010008
Authors: Panagiota S. Katsimpini George A. Papagiannopoulos
This work investigates and discusses the effectiveness of the seesaw system when installed in an older, non-ductile reinforced concrete (RC) building for seismic upgrading purposes. In particular, two different configurations of the seesaw system are assumed in a two-storey 3D RC framed building which was designed according to older seismic provisions and, thus, is susceptible to flexural and shear failures. To check if there is any merit in employing the seesaw system in this RC building, non-linear time-history (NLTH) analyses are conducting using 11 seismic motions. Peak values for inter-story drift ratios (IDR), residual inter-story drift ratios (RIDR) and floor accelerations (FA) are computed, and the sequence and cause (i.e., due to surpass of flexural or shear strength) of plastic hinge formations are monitored. Leaving aside any issues related to fabrication and cost, interpretation of the results obtained by the aforementioned seismic response indices for the RC building under study leads to the conclusion that the seesaw system can be a retrofitting scheme for the seismic upgrading of older, non-ductile RC framed buildings.
]]>Vibration doi: 10.3390/vibration6010007
Authors: Kadir Gunaydin Ahmet Yavuz Aykut Tamer
This paper presents a modal analysis of honeycomb and re-entrant lattice structures to understand the change in natural frequencies when multi-material configuration is implemented. For this purpose, parallel nylon ligaments within re-entrant and honeycomb lattice structures are replaced with chopped and continuous carbon fibre to constitute multi-material lattice configurations. For each set, the first five natural frequencies were compared using detailed finite element models. For each configuration, three different boundary conditions were considered, which are free–free and clamping at the two sides that are parallel and perpendicular to the vertical parts of the structure. The comparison of the natural frequencies was based on mode-shape matching using modal assurance criteria to identify the correct modes of different configurations. The results showed that the natural frequency of the multi-material configurations increases from 4% to 18% depending on the configuration and material.
]]>Vibration doi: 10.3390/vibration6010006
Authors: Pasakorn Sengsri Sakdirat Kaewunruen
Bridge bearings are one of the most important components in bridge systems. Typical bearings are extensively used in small- to medium-span highway bridges since they are economical and offer a good performance at service-level conditions. On the other hand, common bridge bearings possess a low performance-to-weight ratio under combined compression and shear loading conditions (low crashworthiness and specific energy absorption), due to their heavy weight, high costs, and the non-recyclability of steel and elastomer materials. With the help of a relatively higher ratio of a 3D-printed triply periodic minimal surface (TPMS) structure, this method can potentially be used for bridge bearing applications. However, the cyclic responses of this TPMS structure used in bearings have never been completely investigated. This study is the world’s first to investigate the effects of normal pressure on the cyclic responses of novel 3D-printed TPMS bridge bearings. A numerical TPMS unit cell model considering the effects of normal pressure on cyclic responses of a novel TPMS bridge bearing is developed and validated with experimental data. The numerical results reveal new insights related to the nonlinear effects of normal pressure on the cyclic behaviours of 3D-printed TPMS bearings. Higher normal pressures result in a higher degree of nonlinearity in the dynamic cyclic responses of the 3D-printed TPMS bearings.
]]>Vibration doi: 10.3390/vibration6010005
Authors: Danila A. Prikazchikov
This paper deals with the Rayleigh wave, propagating on a nonlocally elastic, linearly isotropic half-space, excited by a prescribed surface loading. The consideration develops the methodology of hyperbolic–elliptic models for Rayleigh and Rayleigh-type waves, and relies on the effective boundary conditions formulated recently, accounting for the crucial contributions of the nonlocal boundary layer. A slow-time perturbation scheme is established, leading to the reduced model for the Rayleigh wave field, comprised of a singularly perturbed hyperbolic equation for the longitudinal wave potential on the surface, acting as a boundary condition for the elliptic equation governing the decay over the interior. An equivalent alternative formulation involving a pseudo-differential operator acting on the loading terms, with parametric dependence on the depth coordinate, is also presented.
]]>Vibration doi: 10.3390/vibration6010004
Authors: Yahya Sumayli Ying Ye
The purpose of this study was to investigate the effect of two views on motion sickness caused by low-frequency roll motion in the laboratory. Fifteen healthy male subjects participated in the study and were exposed to 30 min of 0.25 Hz roll oscillation at an angle of rotation (±5°). Subjects sat on a rigid seat with one of two visual scenes each session: (i) viewing 360° videos through virtual reality (VR) head-mounted display (HMD) device and (ii) reading articles on a monitor in a closed cabin. Ratings of motion sickness were obtained at 1 min intervals. The mean illness ratings of subjects for all visual conditions increased over the 30 min exposure to motion. There was significantly less sickness in the HMD condition than in the monitor condition. The findings suggest a beneficial effect of the HMD view on the severity of sickness. However, the HMD view had no effect on the sickness experienced by those vulnerable to sickness caused by exposure to motion or use of VR. It was concluded that the visual activity had a significant influence on motion sickness induced by 0.25 Hz roll oscillation with an angle of rotation (±5°), and the applications of VR could be implemented to further reduce motion sickness.
]]>Vibration doi: 10.3390/vibration6010003
Authors: Péter Zoltán Csurcsia Muhammad Faheem Siddiqui Mark Charles Runacres Tim De Troyer
This work discusses the experimental challenges and processing of unsteady experiments for a pitching wing in the low-speed wind tunnel of the Vrije Universiteit Brussel. The setup used for unsteady experiments consisted of two independent devices: (a) a position control device to steer the pitch angle of the wing, and (b) a pressure measurement device to measure the aerodynamic loads. The position control setup can pitch the wing for a range of frequencies, amplitude, and offset levels. In this work, a NACA-0018 wing profile was used with an aspect ratio of 1.8. The position control and the pressure measurement setups operate independently of each other, necessitating advanced signal processing techniques to synchronize the pitch angle and the lift force. Furthermore, there is a (not well-documented) issue with the (sampling) clock frequency of the pressure measurement setup, which was resolved using a fully automated spectral analysis technique. The wing was pitched using a simple harmonic sine excitation signal at eight different offset levels (between 6° and 21°) for a fixed amplitude variation (std) of 6°. At each offset level, the wing was pitched at five different frequencies between 0.1 Hz and 2 Hz (that correspond to reduced frequencies k ranging from 0.006 to 0.125). All the experiments were conducted at a fixed chord-based Reynolds number of 2.85 × 105. The choice of operating parameters invokes the linear and nonlinear behavior of the wing. The linear unsteady measurements agreed with the analytical results. The unsteady pressure measurements at higher offset levels revealed the nonlinear aerodynamic phenomenon of dynamic stall. This confirms that a nonlinear and dynamic model is required to capture the salient characteristics of the lift force on a pitching wing.
]]>Vibration doi: 10.3390/vibration6010002
Authors: Taher Saghi Danyal Bustan Sumeet S. Aphale
Finding a reliable approach to detect bearing faults is crucial, as the most common rotating machine defects occur in its bearings. A convolutional neural network can automatically extract the local features of the mechanical vibration signal and classify the patterns. Nevertheless, these types of networks suffer from the extraction of the global feature of the input signal as they utilize only one scale on their input. This paper presents a method to overcome the above weakness by employing a combination of three parallel convolutional neural networks with different filter lengths. In addition, a bidirectional gated recurrent unit is utilized to extract global features. The CWRU-bearing dataset is used to prove the performance of the proposed method. The results show the high accuracy of the proposed method even in the presence of noise.
]]>Vibration doi: 10.3390/vibration6010001
Authors: Keigo Ikeda Jumpei Kuroda Daigo Uchino Kazuki Ogawa Ayato Endo Taro Kato Hideaki Kato Takayoshi Narita
The deterioration of ride comfort in ultra-compact vehicles has recently become an increasing concern. Active seat suspension was proposed to improve the ride comfort of ultra-compact vehicles. An active seat suspension is a vibration control device that is easily installed. The general vibration control system of the active seat suspension is fed back to the displacement and velocity by integrating the measured seat acceleration. This control has problems, such as control delay and deviation by integration. In this study, we focused on vibration control using acceleration directly. First, we established a control model that feeds back the acceleration to terminate the error occurring in the integral process and investigated the change in vibration characteristics in the case where the feedback gain of acceleration was changed. Second, the control system was analyzed to investigate the performance of the control based on the frequency characteristics. As a result, it was confirmed that the frequency response changes when the feedback gain is changed. In acceleration feedback control, ride comfort was improved by selecting a proper feedback gain because the characteristics of frequency were changed by the gain.
]]>Vibration doi: 10.3390/vibration5040054
Authors: Ayato Endo Rintaro Itoyama Jumpei Kuroda Daigo Uchino Kazuki Ogawa Keigo Ikeda Taro Kato Takayoshi Narita Hideaki Kato
Flexible steel plates are generally transported by rollers; however, the contact between the rollers and the steel plate degrades the surface quality of the plate. To solve this problem, noncontact transportation of steel plates using electromagnetic force has been proposed. However, ultrathin flexible steel plates can easily fall owing to deflection. A magnetic levitation system using electromagnets installed in the horizontal direction has also been proposed to improve the levitation performance of a conventional system. However, it is difficult to control vibrations with such a system because flexible steel plates are elastically deformed into complex shapes by gravity. Therefore, an electromagnetic levitation system was proposed, wherein electromagnets were installed near the edge of the steel plate such that it could be controlled with noncontact grip, such as by allowing one side of the steel plate to hang. This system is expected to improve levitation stability because the moment of inertia increases with vertical levitation and simplifies the control system. In addition, this system actively uses gravity acting on a steel plate to decrease its deflection. The use of gravity to suppress deflection is novel. In this study, the feasibility of magnetic levitation using the proposed system was investigated using magnetic field analysis. Its usefulness was investigated experimentally using a constructed magnetic levitation system. In addition, it was found that a magnetic levitation system that maintains the standing position generates a peculiar vibration.
]]>Vibration doi: 10.3390/vibration5040053
Authors: Chein-Shan Liu Chung-Lun Kuo Chih-Wen Chang
For the free vibrations of multi-degree mechanical structures appeared in structural dynamics, we solve the quadratic eigenvalue problem either by linearizing it to a generalized eigenvalue problem or directly treating it by developing the iterative detection methods for the real and complex eigenvalues. To solve the generalized eigenvalue problem, we impose a nonzero exciting vector into the eigen-equation, and solve a nonhomogeneous linear system to obtain a response curve, which consists of the magnitudes of the n-vectors with respect to the eigen-parameters in a range. The n-dimensional eigenvector is supposed to be a superposition of a constant exciting vector and an m-vector, which can be obtained in terms of eigen-parameter by solving the projected eigen-equation. In doing so, we can save computational cost because the response curve is generated from the data acquired in a lower dimensional subspace. We develop a fast iterative detection method by maximizing the magnitude to locate the eigenvalue, which appears as a peak in the response curve. Through zoom-in sequentially, very accurate eigenvalue can be obtained. We reduce the number of eigen-equation to n−1 to find the eigen-mode with its certain component being normalized to the unit. The real and complex eigenvalues and eigen-modes can be determined simultaneously, quickly and accurately by the proposed methods.
]]>Vibration doi: 10.3390/vibration5040052
Authors: Angus Ewan Peters Vitomir Racic Stana Živanović John Orr
The increased ambition of architects coupled with advancements in structural materials, as well as the rapidly increasing pressure on civil engineering sector to reduce embodied carbon, have resulted in longer spans and more slender pedestrian structures. These structures often have one or more low natural frequencies in the range of human walking accompanied with low modal masses and damping ratios. Thus, they are prone to excessive and often resonant vibrations that may compromise the serviceability limit state. Principally the uncertainty in prediction of the vibration serviceability limit state mainly originates from unreliable estimates of pedestrian loading. The key rationale behind this situation is the limited mathematical characterisation featuring in current design codes and guidelines pertinent to pedestrian-induced loading. The Fourier approximation is typically used to describe individual walking forces. Historically, such models are based on limited experimental data and deterministic mathematical descriptions. Current industry used load models featured in design codes and guidelines have been shown to incorporate inherent bias through limited intra-subject variation and poor correlation with real walking loads. This paper presents an improved Fourier model of vertical walking force across multiple harmonics, presented in a Bayesian and Frequentist statistical parameterisation. They are derived using the most comprehensive dataset to date, comprising of over ten hours of continuous vertical walking force signals. Dissimilar to previous Fourier models, the proposed models attempt to encapsulate the surround energy leakage around harmonic integers with a singular value. The proposed models provide consistently lower force amplitudes than any previous model and is shown to be more representative of real walking. The proposed model provides a closer approximation of a structural acceleration than any other similar Fourier-based model. The proposed model provides further evidence to combine the so called high and low frequency load models.
]]>Vibration doi: 10.3390/vibration5040051
Authors: K. N. Dewangan Yumeng Yao S. Rakheja
This study investigated the seat-to-head vibration transmissibility (STHT) responses of 58 subjects (31 males and 27 females) seated on three different elastic seats with (WB) and without back support (NB) and under three levels of vertical vibration (0.25, 0.50 and 0.75 m/s2 RMS) in the 0.50–20 Hz range. The STHT responses with elastic seats were significantly different from the widely reported responses with rigid seats, irrespective of sitting and excitation conditions. The peak STHT magnitudes with elastic seats were relatively higher than those obtained with a rigid seat. Moreover, the transmission of seat vibration showed a strong dependence on the elastic properties of the body-seat coupling. The primary resonance frequencies were also significantly different among the elastic seats. Compared to NB conditions, the peak STHT magnitudes and the primary resonance frequencies obtained with WB conditions were significantly lower. An increase in excitation magnitude resulted in a statistically significant (p < 0.001) decrease in the primary resonance frequency.
]]>Vibration doi: 10.3390/vibration5040050
Authors: Adedayo K. Babarinde Sumeet S. Aphale
This paper presents a method to extend the eigenstructure assignment based design of the Positive Position Feedback (PPF) damping controller to the family of well-known second-order Positive Feedback Controllers (PFC) namely: (i) the Positive Velocity and Position Feedback (PVPF) and (ii) the Positive Acceleration Velocity and Position Feedback (PAVPF) using appropriate eigenstructure assignment. This design problem entails solving a set of linear equations in the controller parameters using Linear Matrix Inequalities (LMI) to specify a convex design constraint. These damping controllers are popularly used in tandem with a tracking controller (typically an integrator) to deliver high-bandwidth nanopositioning performance. Consequently, the closed-loop performance of all three controllers (PPF, PVPF and PAVPF) employed in tandem with suitably gained integral tracking loops is thoroughly quantified via relevant performance metrics, using measured frequency response data from one axis of a piezo-stack actuated x-y nanopositioner.
]]>Vibration doi: 10.3390/vibration5040049
Authors: Aires Colaço Pedro Alves Costa Cecília Parente Ahmed M. Abouelmaty
The present paper addresses the problem of generating and propagating vibrations induced by low-impact loading on a driven pile. In this context, an experimental test site was selected and characterized, where ground-borne vibrations induced by the application of a low dynamic loading on the pile head were measured using accelerometers placed at the ground surface. At the same time, a new numerical approach, based on a coupled FEM-PML (Finite Element Method-Perfectly Matched Layer) formulation, to model the pile–ground system was presented. A very satisfactory agreement was observed between the experimental data collected in these experiments and the prediction performed by the numerical model. The experimental data can be also used by other authors for the experimental validation of their or other prediction models.
]]>Vibration doi: 10.3390/vibration5040048
Authors: Kazuki Ogawa Riku Miyazaki Yamato Uchida Ikkei Kobayashi Jumpei Kuroda Daigo Uchino Keigo Ikeda Taro Kato Ayato Endo Takayoshi Narita Hideaki Kato
Recently, research on non-contact conveyance systems using electromagnetic levitation technology has accelerated. We have constructed an electromagnetic levitation control system that keeps the relative distance between the electromagnet and steel plate constant. To investigate the levitation stability of thin steel plates, we performed magnetic levitation experiments on a thin steel plate with curvature. A physical disturbance was applied to the electromagnet units by vibrators. The electromagnet units were vibrated up and down by a vibrator. We investigated whether the bending magnetic levitation improved the levitation performance even if the magnetic levitation system was in a vibrating environment. We determined that it was possible to realize stable levitation for a steel plate under external disturbances during levitation at the optimal bending angle.
]]>Vibration doi: 10.3390/vibration5040047
Authors: Nobuyuki Shibata
Background: The aim of this study was to propose and validate a novel indicator that characterizes the potential effects of exposure to hand–arm vibration (HAV) and evaluates the increasing risk of neurosensory components of hand–arm vibration syndrome (HAVS). The author focused on a quantity calculated from ascending and descending thresholds and residual shifts in vibrotactile perception thresholds (VPTs) observed at the fingertips in the recovery process after exposure to HAV. Methods: Thirty subjects—10 old exposed (G1), 10 old non-exposed (G2), and 10 young non-exposed subjects (G3)—were required to perform a series of grip tasks with exposure to two intensities of HAV, which was followed by 90 s of vibration perception measurements at the tip of each subject’s right index finger. Vibrotactile perception was measured every 5 min for 30 min. Results: Mean differences between ascending and descending thresholds (VPTWs) for G2 and G3 remained nearly unchanged over time after exposure to HAV. In contrast, the mean VPTWs for G1 gradually increased over time after exposure to HAV. The mean VPTWs for G1 were always larger than those for G2 and G3. TTS recovery was observed at 125 Hz under both of the HAV exposure conditions in each group. TTSs of nearly zero were observed for the low-HAV condition in G3. TTS recovery after exposure to HAV was not observed at 31.5 Hz in any of the subject groups. Regardless of elapsed time, the mean TTSs for G2 and G3 were smaller than those for G1. Negative TTS values showing a lower TTS than the baseline were sometimes observed for the low-HAV condition in G3. Conclusions: VPTWs can be a screening parameter that detects potential patients with only neurosensory components observed as an early sign of HAVS.
]]>Vibration doi: 10.3390/vibration5040046
Authors: Kyle Dunno Purushottam Chavan
Crowdsourced logistics has emerged as a delivery channel for many single-parcel packages. As a result, this logistics network has introduced personal passenger vehicles as a means to transport parcels during last mile delivery segments. To understand this network’s vibration levels and cargo capacity restraints, four vehicle types (a sedan, sports sedan, compact SUV and full-size SUV) commonly used in crowdsourced logistics deliveries were selected for measurement and analysis. This study shows that the vibration levels were significantly higher in the vertical axis and that the overall vibration energy increased as vehicle speed increased, except in the sedan. The sedan and SUV vehicles showed power spectral density peak frequencies in the low-frequency range, occurring at approximately 2 Hz, matching previous studies using similar vehicles. The vibration levels were greatest in the sports sedan and lowest in the sedan. The recorded vibration events showed a right-skewed heavy-tailed distribution and were non-Gaussian.
]]>Vibration doi: 10.3390/vibration5040045
Authors: Roberta Fátima Neumeister Adriane Prisco Petry Sergio Viçosa Möller
The present study aims to investigate the dominant frequency ranges of a cylinder free to vibrate transversally to the flow positioned in the first, the second or in both positions of the tandem assembly for L/D = 1.26, 1.4, 1.6, and 3.52 with the increase in the flow velocity. Accelerometers and hot wire anemometers were the experimental tools applied in this study. The range of study encompassed the reduced velocity with values from 6 to 72 and Reynolds number from 7.1 × 103 to 2.4 × 104. Fourier transform, continuous wavelet transform, magnitude-square coherence, and wavelet coherence were applied to analyze the cylinder acceleration results for all L/D and wake velocity values studied. The results show that the amplitudes of vibration are below 1.5% of the diameter for all the cases, except for the lower L/D, where the amplitude increases. The first cylinder free to vibrate presents the highest amplitudes observed. Fourier and continuous wavelet analysis showed high energy associated with the two natural frequencies of the system and a third frequency, which may be associated with the flow excitation. In the second cylinder free to vibrate, energy spreads across the monitored spectrum, justifying the smaller amplitudes but the energy level increases with increasing L/D and may be associated with wake-induced vibration. The cases with both cylinders free to vibrate show that the relation between the assembly parameters of each cylinder is relevant to the vibration response and the excitation frequency range. The results showed that even with a clear excitation in a higher frequency, the main energy in the vibration signals is in the natural frequency range.
]]>Vibration doi: 10.3390/vibration5040044
Authors: Jelte Bos Cyriel Diels Jan Souman
Motion sickness is known under several names in different domains, such as seasickness, carsickness, cybersickness, and simulator sickness. As we will argue, these can all be considered manifestations of one common underlying mechanism. In recent years, it has received renewed interest, largely due to the advent of automated vehicles and developments in virtual reality, in particular using head-mounted displays. Currently, the most widely accepted standard to predict motion sickness is ISO 2631-1 (1997), which is based on studies on seasickness and has limited applicability to these newer domains. Therefore, this paper argues for extending the ISO standard to cover all forms of motion sickness, to incorporate factors affecting motion sickness, and to consider various degrees of severity of motion sickness rather than just emesis. This requires a dedicated standard, separate from other effects of whole-body vibration as described in the current ISO 2631-1. To that end, we first provide a sketch of the historical origins of the ISO 2631-1 standard regarding motion sickness and discuss the evidence for a common mechanism underlying various forms of motion sickness. After discussing some methodological issues concerning the measurement of motion sickness, we outline the main knowledge gaps that require further research.
]]>Vibration doi: 10.3390/vibration5040043
Authors: Jocelyn Kluger Lynn Crevier Martin Udengaard
Accurate, computationally efficient simulations enable engineers to design high-performing, cost-efficient, lightweight machines that can leverage models of predictive controls and digital twin predictive maintenance schedules. This study demonstrates a new speed-dependent eigenmode method for accurately and efficiently simulating shaft transverse vibrations. The method involves first independently computing shaft eigenmodes over a range of operating speeds, then correlating the eigenmodes across the different speeds during compilation, and finally adjusting modal properties gradually in accordance with a lookup method during simulation. The new method offers several distinct advantages over the traditional static eigenmodes and Craig-Bampton methods. The new method maintains accuracy over a large range of shaft rotation speeds whereas the static eigenmodes method does not. The new method typically requires fewer modal degrees of freedom than the Craig-Bampton method. Whereas the Craig-Bampton method is limited to modeling changes at the boundaries, the new method is suitable for modeling changing body properties as well as boundary-based changes. For this paper, a fluid-bearing-supported 10 MW direct-drive wind turbine drive shaft is tested virtually in a simulation model developed in Simscape™ Driveline™. Using the simulation statistics, this study compares the accuracy and computational efficiency of the speed-dependent eigenmode method to the traditional finite lumped element, static eigenmode, and Craig–Bampton methods. This paper shows that the new method simulates the chosen system 5 times faster than the traditional lumped mass method and 2.4 times faster than the Craig-Bampton method.
]]>Vibration doi: 10.3390/vibration5040042
Authors: Jingchao Guan Jingshun Zuo Wei Zhao Nobuyuki Gomi Xilu Zhao
Hydraulic dampers for the vibration damping of industrial machinery and building structures are typically cylindrical. This study proposes a novel, axially free-folding hydraulic damper of the origami type to improve the structural characteristics of the conventional cylinder shape with restricted effective stroke in relation to the overall length. First, the basic design equation of the proposed origami hydraulic damper was derived by demonstrating that the fold line cylinders on the sidewalls will always meet the foldable condition of the origami hydraulic damper, that is, α=π/n and π/2n≤β≤π/n. Next, the fluid flow characteristics inside the origami hydraulic damper and in the flow path were analyzed; it was determined that the actual damping force exerted on the origami damper was proportional to the square of the velocity of motion. Equations of motion were developed considering the derived damping force equation, and a vibration analysis method using the Range–Kutta numerical analysis technique was established. A validation test system with an origami hydraulic damper in a mass-spring vibration system was developed, and vibration tests were performed with actual seismic waves to verify the damping characteristics and effectiveness of the origami hydraulic damper. Furthermore, the orifice hole diameter at the end of the origami structure as well as the type of internal fluid, were varied in the vibration tests. The effect of the main components of the origami hydraulic damper on the damping effect was analyzed, revealing that the orifice hole diameter had a more significant effect than the internal fluid.
]]>Vibration doi: 10.3390/vibration5040041
Authors: Jennifer M. Vojtech Claire L. Mitchell Laura Raiff Joshua C. Kline Gianluca De Luca
Silent speech interfaces (SSIs) enable speech recognition and synthesis in the absence of an acoustic signal. Yet, the archetypal SSI fails to convey the expressive attributes of prosody such as pitch and loudness, leading to lexical ambiguities. The aim of this study was to determine the efficacy of using surface electromyography (sEMG) as an approach for predicting continuous acoustic estimates of prosody. Ten participants performed a series of vocal tasks including sustained vowels, phrases, and monologues while acoustic data was recorded simultaneously with sEMG activity from muscles of the face and neck. A battery of time-, frequency-, and cepstral-domain features extracted from the sEMG signals were used to train deep regression neural networks to predict fundamental frequency and intensity contours from the acoustic signals. We achieved an average accuracy of 0.01 ST and precision of 0.56 ST for the estimation of fundamental frequency, and an average accuracy of 0.21 dB SPL and precision of 3.25 dB SPL for the estimation of intensity. This work highlights the importance of using sEMG as an alternative means of detecting prosody and shows promise for improving SSIs in future development.
]]>Vibration doi: 10.3390/vibration5040040
Authors: Janik Habegger Marwan Hassan Michele Oliver
Vibration isolation across the frequency spectrum is a challenge in many applications, particularly at low frequencies where linear oscillators amplify excitation forces. To overcome this, nonlinear high static low dynamic (HSLD) stiffness oscillators have been proposed with the aim of reducing the resonant frequency while maintaining the high load capacities of much stiffer linear systems. A two-degree of freedom (2DOF) HSLD stiffness system is proposed to investigate the effectiveness of such systems. Experiments reveal that a 2DOF non-linear HSLD stiffness system outperforms a similar single-degree of freedom (SDOF) HSLD stiffness system, as well as similar SDOF and 2DOF linear systems. Three performance criteria are used to assess these systems, including (1) minimizing the resonant frequency and maximizing the isolation zone, (2) minimizing the magnitude of amplification at resonance, and (3) maximizing the ability to isolate large input frequencies. Exact numerical and approximate analytical simulations are validated using these experimental data. A sensitivity analysis of system parameters reveals that it is necessary to incorporate adjustability into the geometry of a design to counteract unavoidable manufacturing tolerances. Changes of less than 2% to the stiffness or geometry of a system can drastically change its dynamic response.
]]>Vibration doi: 10.3390/vibration5040039
Authors: Mădălina Dumitriu Ioana Izabela Apostol
This paper investigates the dynamic behaviour of a two-axle bogie under the influence of interference between the vertical vibrations of bounce and pitch—generated by the track irregularities—and the roll horizontal vibrations—excited by the asymmetry in the suspension damping that can be caused by the failure of a damper during exploitation. For this purpose, the results of numerical simulations are being used, as developed on the basis of two original models of the bogie-track system, namely the model of the bogie with symmetrical damping of the suspension—track and the model of the bogie with asymmetrical damping of the suspension—track, respectively. The dynamic behaviour of the bogie with symmetrical/asymmetrical damping is evaluated in five reference points of the bogie regime of vibrations, based on the Root Mean Square of acceleration (RMS acceleration). The results thus obtained highlight the characteristics regarding the symmetry/asymmetry of the regime of vibrations in the bogie reference points and the location of the critical point of the bogie regime of vibrations. The influence of the suspension asymmetry upon the dynamic behaviour of the bogie is analysed in an original manner, hence leading to conclusions that might establish themselves as the starting point of a new fault detection method of the dampers in the primary suspension of the railway vehicle.
]]>Vibration doi: 10.3390/vibration5040038
Authors: James MacLean Majid Aleyaasin Sumeet S. Aphale
Designers of Positive Feedback Controllers (PFCs) arbitrarily place poles into the left-hand half-plane of the complex plane without any detailed understanding of where to stop. This works aims to clearly demonstrate, via rigorous mathematical derivation, the conditions for which pole–placement becomes possible. It also highlights the design limits for the family of second–order PFCs—the most popular PFC group. To this end, the complete family of PFCs, namely, Positive Acceleration Velocity Position Feedback and its derivatives, are analysed in great depth with respect to pure damping and also with respect to combined damping and tracking applications. To showcase the practical value and validity of this work, experimental results on a piezoelectric nanopositioner are also presented and discussed.
]]>Vibration doi: 10.3390/vibration5030037
Authors: Ján Ďungel Juraj Grenčík Peter Zvolenský
Railway transport is considered relatively environmentally friendly in terms of energy consumption and air pollution, but it is relatively unfriendly in terms of noise pollution. Noise and vibrations propagating to railroad surrounding areas are disturbing populations. In order to minimize this noise, legislation and regulations such as TSI NOI have been adopted and research of noise and vibrations generated by railway transport has been carried out. Such research has been carried out also by our team focused on experimental investigation of noise generated by railway wagons, in this particular case on tank wagons. We simulated the structural eigenfrequencies of both bogies and tanks using FEM models to find vibrations and corresponding noise levels generated by these vibrations. Theoretical results have been compared with results of measurements of noise generated by impact hammer and visualization of noise fields using a digital acoustic camera Soundcam. Based on the simulation and measurements, principal frequency noise domains of fundamental noise sources were determined—rolling (40–63 Hz), tank (200–1000 Hz), bogie (400–1600 Hz), and wheel (800–10,000 Hz). Measurements on the railway line under real operational conditions at two train speeds have been carried out, too, to see the actual external noise levels.
]]>Vibration doi: 10.3390/vibration5030036
Authors: Ahmed Fathy Abouzeid Fritz Felix Trimpe Sönke Lück Markus Traupe Juan Manuel Guerrero Fernando Briz
Torsional vibration is an oscillation phenomenon occurring at driven railway vehicle wheelsets. As the resulting dynamic stresses can be significantly larger than the maximum static motor torque, axle and press fit are at risk of failure. To prevent dangerous vibration events and with these, press fit and axle from failure, traction drive manufactures nowadays used to implement vibration suppression algorithms in drive controls. In this paper, the effectiveness of such suppression algorithms is analyzed. Furthermore, as a pilot survey, we analyze to what extend traction controls influence the excitation of torsional vibration.
]]>Vibration doi: 10.3390/vibration5030035
Authors: Mortaza Aliasghary Saber Azizi Hadi Madinei Hamed Haddad Khodaparast
In this paper, we propose an active control method to adjust the resonance frequency of a capacitive energy harvester. To this end, the resonance frequency of the harvester is tuned using an electrostatic force, which is actively controlled by a voltage source. The spring softening effect of the electrostatic force is used to accommodate the dominant frequency of the ambient mechanical vibration within the bandwidth of the resonance region. A single degree of freedom is considered, and the nonlinear equation of motion is numerically integrated over time. Using a conventional proportional–integral–derivative (PID) control mechanism, the results demonstrated that our controller could shift the resonance frequency leftward on the frequency domain and, as a result, improve the efficiency of the energy harvester, provided that the excitation frequency is lower than the resonance frequency of the energy harvester. Application of the PID controller in the resonance zone resulted in pull-in instability, adversely affecting the harvester’s performance. To tackle this problem, we embedded a saturation mechanism in the path of the control signal to prevent a sudden change in motion amplitude. Outside the pull-in band, the saturation of the control signal resulted in the reduction of harvested power compared to the non-saturated signal; this is a promising improvement in the design and analysis of energy harvesting devices.
]]>Vibration doi: 10.3390/vibration5030034
Authors: Hedieh Badkoobehhezaveh Reza Fotouhi Qianwei Zhang Douglas Bitner
In this paper, dynamic and vibration characteristics of a newly developed 5-degrees-of-freedom (5-DOF) long-reach robotic arm for farm applications is studied through finite element analysis (FEA), as well as experimentally. The new manipulator is designed to be light and compact enough that it can be mounted on a small vehicle for farm applications. A finite element model of this novel manipulator was established using a commercial FEA software. FEA was carried out for two different configurations of the manipulator (fully-extended and vertical half-extended). The fully-extended configuration provides the longest reach of the arm and is one of the most commonly used poses in farm applications; vibrations of this configuration are highly affected by its base excitation. The FEA results indicated that the first six natural frequencies of the manipulator for the two configurations considered were between 4.4 to 41.6 (Hz). Modal analysis on the fully-extended configuration was completed using experimental modal analysis to verify the finite element results. In the experiments, acceleration data were obtained utilizing sensors, and were post-processed using Fast-Fourier Transforms. The first six natural frequencies and their corresponding mode shapes were obtained using FEA and also experimentally, and the results were compared; the comparison showed good agreement, with less than 10% difference. Our verified FE model provides a reliable basis for future vibration control for the newly developed robotic arm for different applications. A harmonic response simulation was also carried out using an experimentally corrected FE model; this provides a good understanding of the dynamic behavior of the newly developed arm under base excitation. This paper offers an experimentally corrected FEA model for a large manipulator with base excitation for farm applications.
]]>Vibration doi: 10.3390/vibration5030033
Authors: Salah M. Zaidan Hamad M. Hasan
This work presents an analytical study of the parametric instability of cylindrical panels containing functionally graded porous exposed to static and dynamic periodic axial loads under simply supported boundary conditions. Based on Hamilton’s principle, the governing equation of motion by using first-order shear deformation theory (FSDT) has been obtained. By applying the Galerkin technique, an excitation frequency expression is derived, which helps identify areas of instability of functionally graded porous cylindrical panels. Numerical simulations are used to validate the analytical results. Eventually, the impacts of the porosity coefficient, porosity distribution method, static and dynamic periodic axial loads, panel angle, circumferential wave number, and cylindrical panel characteristics on the region of instability are displayed in the section of results and discussions. The findings show that when the porosity is further from the surface, the more stable the structure is. Furthermore, a small angle of the cylindrical panels gives a better dynamic response than a large angle. In addition, increased static and dynamic loads lead to an expansion of areas of instability.
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