Research

17 pages, 5038 KiB

Open AccessArticle

Nonlinear Vibration Characteristics and Bifurcations of a Rotor System Subjected to Brush Seal Forces

by Yingyong Zou, Mukai Wang, Duhui Lu, Yongde Zhang, Zili Xu and Yeyin Xu

Appl. Sci. 2023, 13(20), 11539; https://doi.org/10.3390/app132011539 - 21 Oct 2023

Viewed by 597

In the paper, nonlinear vibration characteristics of a rotor system are investigated. Such a nonlinear rotor system is subjected to brush seal forces, which are obtained by integrating the bristle force along the entire ring. The nonlinear brush seal rotor system is constructed [...] Read more.

In the paper, nonlinear vibration characteristics of a rotor system are investigated. Such a nonlinear rotor system is subjected to brush seal forces, which are obtained by integrating the bristle force along the entire ring. The nonlinear brush seal rotor system is constructed by merging a flexible rotor with nonlinear seal forces. The research is aimed at studying the nonlinear vibration characteristics and bifurcations of the motions under a variety of eccentricity circumstances. Different kinds of bifurcations are successfully obtained by mathematical discretization and mapping manipulation. Such a discrete mapping method successfully predicts the stable and unstable motions accurately. The period-doubling bifurcations and saddle node bifurcations of the rotor system are obtained. The sole unstable solutions are obtained, which are special, and a normal numerical integration method cannot solve this problem, which provides advantages in rotor design and motion control. According to the results, nonlinear resonances are found between the stable and unstable motions. The greater the eccentricity of the rotor, the greater the number of bifurcation points that occur during the rotor’s nonlinear motions, as well as the larger the ranges of speeds where the motions are unstable. Saddle node bifurcations generate unstable nonlinear motions and non-smooth motions, which may bring damage to the mechanical rotors. The period-doubling bifurcations produce the route from period-1 to period-2 motions in the nonlinear rotor system. The research provides a new perspective to study the bifurcations and stability of the nonlinear rotor systems. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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15 pages, 2931 KiB

Open AccessArticle

Experimental Stability Analysis of Vertical Takeoff and Landing System Based on Robust Control Strategy

by Muhammad Ilyas, Shahid Aziz, Imran Shah, Awais Khan and Dong-Won Jung

Appl. Sci. 2023, 13(20), 11209; https://doi.org/10.3390/app132011209 - 12 Oct 2023

Viewed by 956

Abstract

The Vertical Take-Off and Landing (VTOL) system is a multi-variable system subjected to harsh weather conditions, which creates challenges in proving the stability of the system before takeoff, which is essential for a flight dynamics system. The presented research work is based on [...] Read more.

The Vertical Take-Off and Landing (VTOL) system is a multi-variable system subjected to harsh weather conditions, which creates challenges in proving the stability of the system before takeoff, which is essential for a flight dynamics system. The presented research work is based on the experimental results of the VTOL system to investigate and prove the stability using Lyapunov theory. This is achieved by tracking the pitch along the x-axis using cascaded control and integral super twisting sliding mode control (ISTSMC) algorithms. The motor current of the propeller assembly is regulated based on proportional integral (PI) and proportional integral derivative (PID) controllers. The cascaded control shows the maximum tracking error due to high-frequency fluctuations in the controller input signal, which lead to expensive mechanical losses for the actuators. The comparison of the results shows that ISTSMC outperforms the cascaded control strategy by reducing the tracking error to less than 1% percent and reducing the high-frequency fluctuations in the controller input signal. The hardware results show a minor delay in the transient response during vertical takeoff due to the inertia of the system and the tracking error due to air friction, etc., of the external environment, compared to the simulation results obtained in MATLAB. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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16 pages, 3035 KiB

Open AccessArticle

Acoustic Characteristics Analysis of Double-Layer Liquid-Filled Pipes Based on Acoustic–Solid Coupling Theory

by Jin Yan, Jiangfeng Li, Lvlong Zou, Dapeng Zhang, Cheng Wang and Zhi Tang

Appl. Sci. 2023, 13(19), 11017; https://doi.org/10.3390/app131911017 - 06 Oct 2023

Viewed by 683

Abstract

Based on the theory of acoustic–solid coupling, the phase velocity-thickness product of a double-layer liquid-filled pipeline is analyzed, and the dispersion relationship between angular frequency and wavenumber–thickness product is analyzed, providing a theoretical basis for ultrasonic guided wave detection. The wave number analytical [...] Read more.

Based on the theory of acoustic–solid coupling, the phase velocity-thickness product of a double-layer liquid-filled pipeline is analyzed, and the dispersion relationship between angular frequency and wavenumber–thickness product is analyzed, providing a theoretical basis for ultrasonic guided wave detection. The wave number analytical expression of the double-layer liquid-filled pipeline is constructed, and the dispersion relationship of the double-layer liquid-filled pipeline under different frequency–thickness products and wavenumber–thickness products is calculated through parameter scanning. The dispersion curves of the double-layer liquid-filled pipeline are numerically analyzed in the domains of pressure acoustics, solid mechanics, and acoustic–solid coupling. The numerically simulated dispersion curves show high consistency with the analytically calculated dispersion curves. The analysis of the phase velocity frequency–thickness product indicates that the axial mode dispersion curves of the pipe wall decrease with the increase in frequency–thickness product in the coupling domain, and then tend to be flat and intersect with the radial mode dispersion curves in the coupling domain; these intersection points cannot be used for ultrasonic guided wave detection. The T(0,1) mode dispersion curve in the coupling domain of the pressure acoustics domain remains smooth from low frequency to high frequency. It is found that the dispersion curves of the phase velocity frequency–thickness product, angular frequency wavenumber–thickness product, and the acoustic pressure distribution map of the double-layer liquid-filled pipeline based on acoustic–solid coupling can provide theoretical support for ultrasonic guided wave detection of pipelines. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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16 pages, 1398 KiB

Open AccessArticle

Linear and Nonlinear Modes and Data Signatures in Dynamic Systems Biology Models

by Joseph DiStefano III

Appl. Sci. 2023, 13(17), 9772; https://doi.org/10.3390/app13179772 - 29 Aug 2023

Viewed by 534

Abstract

The particulars of stimulus–response experiments performed on dynamic biosystems clearly limit what one can learn and validate about their structural interconnectivity (topology), even when collected kinetic output data are perfect (noise-free). As always, available access ports and other data limitations rule. For linear [...] Read more.

The particulars of stimulus–response experiments performed on dynamic biosystems clearly limit what one can learn and validate about their structural interconnectivity (topology), even when collected kinetic output data are perfect (noise-free). As always, available access ports and other data limitations rule. For linear systems, exponential modes, visible and hidden, play an important role in understanding data limitations, embodied in what we call dynamical signatures in the data. We show here how to circumscribe and analyze modal response data in compartmentalizing model structures—so that modal analysis can be used constructively in systems biology mechanistic model building—for some nonlinear (NL) as well as linear biosystems. We do this by developing and exploiting the modal basis for dynamical signatures in hypothetical (perfect) input–output (I-O) data associated with a (mechanistic) structural model—one that includes inputs and outputs explicitly. The methodology establishes model dimensionality (size and complexity) from particular I-O datasets; helps select among multiple candidate models (model distinguishability); helps in designing new I-O experiments to extract “hidden” structure; and helps to simplify (reduce) models to their essentials. These modal analysis tools are introduced to NL enzyme-regulated and protein–protein interaction biosystems via nonlinear normal mode (NNM) and quasi-steady state approximation (QSSA) analyses and unified with linear models on invariant 2-dimensional manifolds in phase space, with properties similarly informative about their dominant dynamical properties. Some automation of these highly technical aspects of biomodeling is also introduced. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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23 pages, 12578 KiB

Open AccessArticle

Dynamics Modeling and Load-Sharing Performance Optimization of Concentric Face Gear Split-Torque Transmission Systems

by Fei Gong, Rupeng Zhu and Qibo Wang

Appl. Sci. 2023, 13(7), 4352; https://doi.org/10.3390/app13074352 - 29 Mar 2023

Viewed by 1429

Abstract

The concentric face gear split-torque transmission system (CFGSTTS) has the advantages of a large reduction ratio and high power density. The CFGSTTS has considerable potential to be applied in helicopter main reducers. As such, in this study, we analyzed the load distribution characteristics [...] Read more.

The concentric face gear split-torque transmission system (CFGSTTS) has the advantages of a large reduction ratio and high power density. The CFGSTTS has considerable potential to be applied in helicopter main reducers. As such, in this study, we analyzed the load distribution characteristics of a dual input–dual output concentric face gear split-torque transmission system. A load-dependent time-varying meshing stiffness surrogate model was designed based on a feedforward neural network. The difference in the meshing stiffness between the pinion driving and face gear driving was analyzed. The coupled lumped parameter dynamic model of the bending–torsion–axis–pendulum was developed through Newton’s second law, and the influences of the time-varying meshing stiffness, backlash, comprehensive transmission error, support stiffness, and damping were considered. Finally, the impact of the support stiffness on the load-sharing coefficient was analyzed. An optimization model was constructed with the objective function of minimizing the sum of the load-sharing coefficients and was solved by the marine predator algorithm. In addition, the validity of the optimization results was verified with a finite element model. The results indicate that (1) smaller support stiffnesses of input gears benefit the corresponding load balance; (2) the support stiffnesses of the face gears have different laws of influence on the load-sharing coefficient at the input gear and idler, and the support stiffnesses of the other gears need to be comprehensively considered; (3) the larger supporting stiffnesses of the idler gears and tail gear are beneficial for decreasing the load-sharing coefficient at the input gear; and (4) the optimized load-sharing coefficients at Input Gears 1 and 2 and the idler gear decrease by 23.7%, 24.2%, and 4.6%, respectively. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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27 pages, 8659 KiB

Open AccessArticle

Modeling and Analysis of Drill String–Casing Collision under the Influence of Inviscid Fluid Forces

by Bernard Xavier Tchomeni Kouejou, Desejo Filipeson Sozinando and Alfayo Anyika Alugongo

Appl. Sci. 2023, 13(6), 3557; https://doi.org/10.3390/app13063557 - 10 Mar 2023

Cited by 1 | Viewed by 1552

Abstract

The current study aims to study the drill string–casing system operating in an inviscid fluid under imbalanced and rubbing damage types. The Navier–Stokes equations were linearized to establish the hydrodynamic forces surrounding the drill string and resulted in a five-dimensional system of nonlinear [...] Read more.

The current study aims to study the drill string–casing system operating in an inviscid fluid under imbalanced and rubbing damage types. The Navier–Stokes equations were linearized to establish the hydrodynamic forces surrounding the drill string and resulted in a five-dimensional system of nonlinear differential equations. To ensure the accurate acquisition of friction characteristics in a fluid medium, a nonlinear wavelet synchronized transform (NWSST) technique was enhanced based on the denoised wavelet hard thresholding algorithm to extract the features of the rubbing system. The developed model was verified through various test conditions, and the extracted data tests show that the frictional impact proves sufficient to modify the dynamic behavior of the drill string throughout the energy concentration with a slight shift above and below the resonant frequency. It was shown by simulation that the vibration of the submerged drill string system potentially enhanced highly undesirable hidden vibrational frequencies that led to a disturbed and chaotic 3D orbit pattern vibrational response. The experimental results show how vibration analysis combined with the synchrosqueezed technique can identify the condition of the drill string system even under harsh operating conditions and demonstrate that fluid enables the drill string system to rotate with minimum friction. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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15 pages, 11854 KiB

Open AccessArticle

Research on Automatic Recognition Method of Artificial Ground Target Based on Improved HED

by Wei Zhong, Yueqiu Jiang and Xin Zhang

Appl. Sci. 2023, 13(5), 3163; https://doi.org/10.3390/app13053163 - 01 Mar 2023

Viewed by 1133

Abstract

Automatic target recognition technology is an important research direction in the field of machine vision. Artificial ground targets, such as bridges, airports and houses, are mostly composed of straight lines. The ratio of geometric primitive lines to the triangle area formed by their [...] Read more.

Automatic target recognition technology is an important research direction in the field of machine vision. Artificial ground targets, such as bridges, airports and houses, are mostly composed of straight lines. The ratio of geometric primitive lines to the triangle area formed by their combination is used as the feature quantity to describe the group of lines, so as to characterize the artificial ground target. In view of the shortcomings of traditional edge detection methods, such as background suppression, non-prominent targets, missing positions, etc., this paper proposed an image edge detection method based on depth learning. By combining the traditional edge detection algorithm with the edge detection algorithm based on an improved HED network, the real-time target image edge detection was completed. An automatic target recognition method based on template matching was proposed. This method solved the problem of both homologous template matching and heterogeneous template matching, which has important theoretical value. First, the lines were combined to form the geometric primitives of the line group, and then the relationship of the lines in the group was determined by using the characteristic quantity of the line group. The best line group matching the target template was found in the image edge, and the homonymous points in the real-time image and the target template were calculated. The affine transformation matrix between the two images was obtained according to the homonymous points, and then the accurate position of the target in the real-time image was found. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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29 pages, 43181 KiB

Open AccessArticle

Time-Frequency Feature-Based Seismic Response Prediction Neural Network Model for Building Structures

by Peng Zhang, Yiming Li, Yu Lin and Huiqin Jiang

Appl. Sci. 2023, 13(5), 2956; https://doi.org/10.3390/app13052956 - 25 Feb 2023

Viewed by 1460

Abstract

Currently, machine learning techniques are widely used in structural seismic response studies. The developed network models for various types of seismic response provide new ways to analyse seismic hazards. However, it is not easy to balance the applicability of the input, accuracy, and [...] Read more.

Currently, machine learning techniques are widely used in structural seismic response studies. The developed network models for various types of seismic response provide new ways to analyse seismic hazards. However, it is not easy to balance the applicability of the input, accuracy, and computational efficiency for existing network models. In this paper, a neural network model containing an efficient self-adaptive feature extraction module (AFEM) is designed. It can recognize time-frequency features from ground motion (GM) inputs for structural seismic response prediction tasks while considering the model’s computational accuracy and computational cost. The self-adaptive feature extraction module is constructed based on the MFCCs feature extraction process in NLP. AFEM recognizes time-frequency features closely related to structures’ behaviour and response under dynamic loads. Taking the seismic response prediction of a typical building as the target task, the neural network configuration, including a baseline model

M_{0}

and three comparison models (

M_{1}

,

M_{2}

, and

M_{3}

) with AFEM, is systematically analysed. The results demonstrate that the proposed

M_{1}

model with initial AFEM, the

M_{2}

model with combined amplitude and phase features, and the

M_{3}

model with a complex-valued network are more adaptable than the baseline model to the target task. The extracted amplitude and phase features by the

M_{3}

model’s AFEM significantly improve model validation accuracy by 8.6% while reducing computation time by 11.4%. It could provide the basis for future research on regional earthquake damage intelligence assessment systems. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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12 pages, 1758 KiB

Open AccessArticle

Prediction Research on Irregularly Cavitied Components Volume Based on Gray Correlation and PSO-SVM

by Xin Zhang, Yueqiu Jiang and Wei Zhong

Appl. Sci. 2023, 13(3), 1354; https://doi.org/10.3390/app13031354 - 19 Jan 2023

Cited by 2 | Viewed by 846

Abstract

The use of a micro-compressed air-volume-detection method to detect the volume of irregularly cavitied components has the characteristics of multi-variable coupling and nonlinearity. To solve this problem, a volume-prediction model of irregularly cavitied components based on gray correlation and a particle-swarm-optimization support-vector machine [...] Read more.

The use of a micro-compressed air-volume-detection method to detect the volume of irregularly cavitied components has the characteristics of multi-variable coupling and nonlinearity. To solve this problem, a volume-prediction model of irregularly cavitied components based on gray correlation and a particle-swarm-optimization support-vector machine is proposed. In this paper, the gray-correlation method was used to extract the detection parameters that have the greatest correlation with the cavity volume. On the basis of the obtained detection parameters, the SVM algorithm was used to build an irregularly cavitied components volume-prediction model. During model training, since the regression accuracy and generalization performance of the SVM model depend on the proper setting of its two parameters (the penalty-parameter C and the kernel-parameter

σ

), and especially on the interaction of the parameters, this paper presents an optimal-selection approach towards the SVM parameters, based on the particle-swarm-optimization (PSO) algorithm. Experiments showed that the prediction model can better predict the volume of irregularly cavitied components, and the prediction accuracy was high, which played a guiding role in intellectual nondestructive testing of the volume of the irregularly cavitied components. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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17 pages, 17797 KiB

Open AccessArticle

Study on Dynamic Characteristics of the Bistable Nonlinear Damper

by Yunan Liu, Xianhui Li, Min Yang, Junjuan Zhao and Wenjiang Wang

Appl. Sci. 2023, 13(2), 878; https://doi.org/10.3390/app13020878 - 09 Jan 2023

Cited by 2 | Viewed by 1560

Abstract

A conventional dynamic vibration absorber based on resonance effect can hardly satisfy the requirement for low-frequency and broadband vibration control in actual engineering. Combined with passive and nonlinear vibration absorption strategy, this study employed nonlinear characteristics of the magnetic force, bistable structure to [...] Read more.

A conventional dynamic vibration absorber based on resonance effect can hardly satisfy the requirement for low-frequency and broadband vibration control in actual engineering. Combined with passive and nonlinear vibration absorption strategy, this study employed nonlinear characteristics of the magnetic force, bistable structure to establish the dynamic model of the main system with a bistable vibration absorber. The nonlinear motion states of the structure under different excitation conditions were analyzed to explore the inherent relation between the chaotic and large amplitude motion and the vibration absorber’s operating performance. The effect laws of the structural parameters on the dynamic characteristics of the nonlinear vibration absorber and the main system were developed to obtain the optimal parameter settings in the case of resonance and off-resonance of the main system. These results provide an insightful theoretical foundation for the optimal design of the nonlinear vibration absorber. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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18 pages, 12596 KiB

Open AccessArticle

Nonlinear Dynamics Analysis of Disc Brake Frictional Vibration

by Hongyuan Zhang, Jiayu Qiao and Xin Zhang

Appl. Sci. 2022, 12(23), 12104; https://doi.org/10.3390/app122312104 - 26 Nov 2022

Cited by 3 | Viewed by 1875

Abstract

The brake system is a key component to ensuring the safe driving and riding comfort of the vehicle, and the friction between the brake disc and the friction plate is the main source of vibration and noise. Therefore, in order to improve the [...] Read more.

The brake system is a key component to ensuring the safe driving and riding comfort of the vehicle, and the friction between the brake disc and the friction plate is the main source of vibration and noise. Therefore, in order to improve the stability of the braking system and reduce the generation of vibration, a six-degree-of-freedom nonlinear dynamics model was established, and using the Stribeck friction model and related parameters, the dynamic equation was solved by the Runge-Kutta method. The bifurcation diagram, Lyapunov diagram, time domain diagram, frequency spectrum diagram, and phase plane diagram of the brake pad and brake disc during friction braking were obtained, and the vibration characteristics of both under different braking pressure, braking speed, brake pad support stiffness, and brake disc support stiffness were analyzed. The results show that brake pressure is an important factor in triggering nonlinear vibration; increasing the braking speed will increase the amplitude of vibration, but will shorten the time to enter the stable motion state, and increasing the support stiffness brake pad and disc will reduce the amplitude of system vibration. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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16 pages, 4916 KiB

Open AccessArticle

Contact Analysis and Friction Prediction of Non-Gaussian Random Surfaces

by Jinzhao Ren and Huiqun Yuan

Appl. Sci. 2022, 12(21), 11237; https://doi.org/10.3390/app122111237 - 05 Nov 2022

Cited by 5 | Viewed by 1747

Abstract

Engineering surfaces exhibit asymmetrical height distributions due to certain types of surface finishing and running-in process. This non-Gaussian surface reflects different contact performances and tribological properties. In this paper, the influence of non-Gaussian surface parameters on contact performance and friction is investigated. First, [...] Read more.

Engineering surfaces exhibit asymmetrical height distributions due to certain types of surface finishing and running-in process. This non-Gaussian surface reflects different contact performances and tribological properties. In this paper, the influence of non-Gaussian surface parameters on contact performance and friction is investigated. First, the computer program for generating rough surfaces with given parameters is developed; then, contact analysis for rough surfaces are conducted through a deterministic contact model; finally, friction coefficient can be derived from friction model using the results of the contact model. The simulation analyses indicate that the skewness and amplitude of non-Gaussian surface have significant effects on contact performance and friction. The contact characteristic parameters and friction coefficient become slightly changed when kurtosis becomes relatively large. Full article

(This article belongs to the Special Issue Advances in Nonlinear Dynamics and Mechanical Vibrations)

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