Editorial

5 pages, 191 KiB

Open AccessEditorial

by Francisco G. Montoya, Raúl Baños, Alfredo Alcayde and Francisco Manzano-Agugliaro

Symmetry 2020, 12(7), 1077; https://doi.org/10.3390/sym12071077 - 01 Jul 2020

Cited by 2 | Viewed by 1426

Symmetry can be understood in two different ways: as a property or as a principle. As Plato said, the symmetry that can be seen in nature is not random in itself, because it is a result of the symmetries of the physical laws. [...] Read more.

Symmetry can be understood in two different ways: as a property or as a principle. As Plato said, the symmetry that can be seen in nature is not random in itself, because it is a result of the symmetries of the physical laws. Thus, the principles of symmetry have been used to solve mechanical problems since antiquity. Today, these principles are still being researched; for example, in chemical engineering, the spatial symmetry properties of crystal lattices are being studied, or in electrical engineering, the temporal symmetry of the periodic processes of oscillators can be observed. This Special Issue is dedicated to symmetry in engineering sciences (electrical, mechanical, civil, and others) and aims to cover both engineering solutions related to symmetry and the search for patterns to understand the phenomena observed. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

Research

Jump to: Editorial

22 pages, 1580 KiB

Open AccessArticle

The Rayleigh Birnbaum Saunders Distribution: A General Fading Model

by Emilio Gómez-Déniz and Luis Gómez

Symmetry 2020, 12(3), 389; https://doi.org/10.3390/sym12030389 - 03 Mar 2020

Cited by 3 | Viewed by 2964

Abstract

A new compound non-symmetric distribution for modeling arbitrary fading-shadowing wireless channels is introduced and studied here. This distribution has some advantages in front of other well-known non-symmetric fading distributions such as the Rayleigh–lognormal distribution and the K distribution especially in the tails. We [...] Read more.

A new compound non-symmetric distribution for modeling arbitrary fading-shadowing wireless channels is introduced and studied here. This distribution has some advantages in front of other well-known non-symmetric fading distributions such as the Rayleigh–lognormal distribution and the K distribution especially in the tails. We give closed-form expressions for the average BER of DPSK and MSK when the new distribution is used. Applications to compare how the new distribution works in comparisons with the Rayleigh–lognormal, K distributions and others recently proposed in the literature of fading channel are also provided. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

16 pages, 628 KiB

Open AccessArticle

A Kinematic Calibration Method of a 3T1R 4-Degree-of-Freedom Symmetrical Parallel Manipulator

by Fengxuan Zhang, Silu Chen, Yongyi He, Guoyun Ye, Chi Zhang and Guilin Yang

Symmetry 2020, 12(3), 357; https://doi.org/10.3390/sym12030357 - 02 Mar 2020

Cited by 9 | Viewed by 2773

Abstract

This paper proposes a method for kinematic calibration of a 3T1R, 4-degree-of-freedom symmetrical parallel manipulator driven by two pairs of linear actuators. The kinematic model of the individual branched chain is established by using the local product of exponentials formula. Based on this [...] Read more.

This paper proposes a method for kinematic calibration of a 3T1R, 4-degree-of-freedom symmetrical parallel manipulator driven by two pairs of linear actuators. The kinematic model of the individual branched chain is established by using the local product of exponentials formula. Based on this model, the model of the end effector’s pose error is established from a pair of symmetrical branched chains, and a recursive least square method is applied for the parameter identification. By installing built-in sensors at the passive joints, a calibration method for a serial manipulator is eventually extended to this parallel manipulator. Specifically, the sensor installed at the second revolute joint of each branched chain is saved, replaced by numerical calculation according to kinematic constraints. The simulation results validate the effectiveness of the proposed kinematic error modeling and identification methods. The procedure for pre-processing compensation on this 3T1R parallel manipulator is eventually given to improve its absolute positioning accuracy, using the inverse of the calibrated kinematic model. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

22 pages, 5292 KiB

Open AccessArticle

Elastic-Plastic-Damaged Zones around a Deep Circular Wellbore under Non-Uniform Loading

by Xiaoji Shang and Zhizhen Zhang

Symmetry 2020, 12(2), 323; https://doi.org/10.3390/sym12020323 - 24 Feb 2020

Cited by 4 | Viewed by 3340

Abstract

Wellbores are largely constructed during coal mining, shale gas production, and geothermal exploration. Studying the shape and size of the disturbed zone in surrounding rock is of great significance for wellbore stability control. In this paper, a theoretical model for elastic-plastic-damage analysis around [...] Read more.

Wellbores are largely constructed during coal mining, shale gas production, and geothermal exploration. Studying the shape and size of the disturbed zone in surrounding rock is of great significance for wellbore stability control. In this paper, a theoretical model for elastic-plastic-damage analysis around a deep circular wellbore under non-uniform compression is proposed. Based on the elastoplastic softening constitutive model and Mohr-Coulomb strength criterion, the analytical expressions of stresses in the elastic, plastic and damaged zones around a circle wellbore are derived. Further, the boundary line equations among the three zones are obtained according to the conditions of stress continuity. Then, the influence rules of non-uniform in-situ stress and mechanical parameters on the stress distribution and plastic zone size in surrounding rock mass are analyzed. The plastic and the damaged zones are both approximately elliptical in shape. When the lateral stress coefficient of the in-situ stress field takes the value 1, the model degenerates into the Yuan Wenbo’s Solution. If the brittleness coefficient of the surrounding rock is 0, the model degenerates into the Kastner’s Equation. Finally, the results are compared with those under two special cases (in the elastoplastic softening rock under a uniform stress field, in the ideal elastoplastic rock under a non-uniform stress field) and a common approximation method (the perturbation method). Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

15 pages, 6255 KiB

Open AccessArticle

Mechanical Behavior of Tunnel Lining with Cracks at Different Positions

by Jie Su, Yinming Jie, Xiaokai Niu, Chang Liu and Xuan Liu

Symmetry 2020, 12(2), 194; https://doi.org/10.3390/sym12020194 - 27 Jan 2020

Cited by 13 | Viewed by 3693

Abstract

Cracks in the lining significantly reduce the safety of a tunnel during operation. It is urgent to figure out the influence of cracks on tunnel carrying capacity. In this paper, three-dimensional model tests were conducted to investigate deformation, internal force, and deterioration laws [...] Read more.

Cracks in the lining significantly reduce the safety of a tunnel during operation. It is urgent to figure out the influence of cracks on tunnel carrying capacity. In this paper, three-dimensional model tests were conducted to investigate deformation, internal force, and deterioration laws of the lining with prefabricated cracks at different positions. The main conclusions were obtained as follows: (1) The carrying capacity of the lining structure with prefabricated cracks was reduced, and the deformation of the lining structure increased. The penetration of the vault crown crack accelerated the damage of the lining structure, and structural failure occurred when the crack went through at the left arch spring. (2) The internal force of the lining was greatly affected by the positions of prefabricated cracks. The internal forces of the lining structure decreased with the existence of prefabricated cracks. Whether or not there were prefabricated cracks, tension cracks appeared in the inside fiber of the vault and inverted arch. (3) The deformation of the lining structure with the existence of prefabricated cracks increased. When the prefabricated crack was located at the vault, the deformation was the largest, followed by the arch spring, side wall, and arch shoulder. (4) The analysis shows that prefabricated cracks at the vault are the most damaging under stress and deformation of the lining structure, so longitudinal cracks at the vault should be strengthened. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

12 pages, 2177 KiB

Open AccessFeature PaperArticle

3D Printed Personalized Corneal Models as a Tool for Improving Patient’s Knowledge of an Asymmetric Disease

by Jose S. Velázquez, Francisco Cavas, José M. Bolarín and Jorge L. Alió

Symmetry 2020, 12(1), 151; https://doi.org/10.3390/sym12010151 - 11 Jan 2020

Cited by 19 | Viewed by 4627

Abstract

Additive manufacturing is a vanguard technology that is currently being used in several fields in medicine. This study aims to evaluate the viability in clinical practice of a patient-specific 3D model that helps to improve the strategies of the doctor-patient assistance. Data obtained [...] Read more.

Additive manufacturing is a vanguard technology that is currently being used in several fields in medicine. This study aims to evaluate the viability in clinical practice of a patient-specific 3D model that helps to improve the strategies of the doctor-patient assistance. Data obtained from a corneal topographer were used to make a virtual 3D model by using CAD software, to later print this model by FDM and get an exact replica of each patient’s cornea in consultation. Used CAD and printing software were open-source, and the printing material was biodegradable and its cost was low. Clinic users gave their feedback by means of a survey about their feelings when perceiving with their senses their own printed cornea. There was 82 surveyed, 73.8% (9.74; SD: 0.45) of them considered that the model had helped them a lot to understand their disease, expressing 100% of them their intention of taking home the printed model. The majority highlighted that this new concept improves both quality and clinical service in consultation. Custom-made individualized printed models allow a new patient-oriented perspective that may improve the communication strategy from the ophthalmologist to the patient, easing patient’s understanding of their asymmetric disease and its later treatment. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

20 pages, 3282 KiB

Open AccessArticle

Spring Effects on Workspace and Stiffness of a Symmetrical Cable-Driven Hybrid Joint

by Shan Zhang, Zheng Sun, Jili Lu, Lei Li, Chunlei Yu and Dongxing Cao

Symmetry 2020, 12(1), 101; https://doi.org/10.3390/sym12010101 - 05 Jan 2020

Cited by 3 | Viewed by 3343

Abstract

This paper aims to investigate how to determine the basic parameters of the helical compression spring which supports a symmetrical cable-driven hybrid joint (CDHJ) towards the elbow joint of wheelchair-mounted robotic manipulator. The joint design of wheelchair-mounted robotic manipulator needs to consider lightweight [...] Read more.

This paper aims to investigate how to determine the basic parameters of the helical compression spring which supports a symmetrical cable-driven hybrid joint (CDHJ) towards the elbow joint of wheelchair-mounted robotic manipulator. The joint design of wheelchair-mounted robotic manipulator needs to consider lightweight but robust, workspace requirements, and variable stiffness elements, so we propose a CDHJ which becomes a variable stiffness joint due the spring under bending and compression provides nonlinear stiffness characteristics. Intuitively, different springs will make the workspace and stiffness of CDHJ different, so we focus on studying the spring effects on workspace and stiffness of CDHJ for its preliminary design. The key to workspace and stiffness analysis of CDHJ is the cable tension, the key to calculate the cable tension is the lateral bending and compression spring model. The spring model is based on Castigliano’s theorem to obtain the relationship between spring force and displacement. The simulation results verify the correctness of the proposed spring model, and show that the spring, with properly chosen parameters, can increase the workspace of CDHJ whose stiffness also can be adjusted to meet the specified design requirements. Then, the modelling method can be extended to other cable-driven mechanism with a flexible compression spring. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

27 pages, 4548 KiB

Open AccessArticle

Detection of Communities within the Multibody System Dynamics Network and Analysis of Their Relations

by Daniel García-Vallejo, Alfredo Alcayde, Javier López-Martínez and Francisco G. Montoya

Symmetry 2019, 11(12), 1525; https://doi.org/10.3390/sym11121525 - 17 Dec 2019

Cited by 6 | Viewed by 2993

Abstract

Multibody system dynamics is already a well developed branch of theoretical, computational and applied mechanics. Thousands of documents can be found in any of the well-known scientific databases. In this work it is demonstrated that multibody system dynamics is built of many thematic [...] Read more.

Multibody system dynamics is already a well developed branch of theoretical, computational and applied mechanics. Thousands of documents can be found in any of the well-known scientific databases. In this work it is demonstrated that multibody system dynamics is built of many thematic communities. Using the Elsevier’s abstract and citation database SCOPUS, a massive amount of data is collected and analyzed with the use of the open source visualization tool Gephi. The information is represented as a large set of nodes with connections to study their graphical distribution and explore geometry and symmetries. A randomized radial symmetry is found in the graphical representation of the collected information. Furthermore, the concept of modularity is used to demonstrate that community structures are present in the field of multibody system dynamics. In particular, twenty-four different thematic communities have been identified. The scientific production of each community is analyzed, which allows to predict its growing rate in the next years. The journals and conference proceedings mainly used by the authors belonging to the community as well as the cooperation between them by country are also analyzed. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

17 pages, 3604 KiB

Open AccessArticle

An Equivalent Damping Numerical Prediction Method for the Ring Damper Used in Gears under Axial Vibration

by Shuai Wang, Xiaolei Wang, Yanrong Wang and Hang Ye

Symmetry 2019, 11(12), 1469; https://doi.org/10.3390/sym11121469 - 02 Dec 2019

Cited by 8 | Viewed by 2918

Abstract

In aircraft gas turbine engines, gears in the transmission system are typically cyclic in structure and inevitably encounter large dynamic loads, such as meshing excitation, resulting in high vibration loads in resonance. To prevent gear resonance failure, a ring damper is employed to [...] Read more.

In aircraft gas turbine engines, gears in the transmission system are typically cyclic in structure and inevitably encounter large dynamic loads, such as meshing excitation, resulting in high vibration loads in resonance. To prevent gear resonance failure, a ring damper is employed to reduce the resonance response. As relative motion between the gear and the ring damper occurs, vibration loads can be reduced by friction energy dissipation. Moreover, the gears in the aircraft engine are thin-walled and their axial stiffness is much smaller than radial stiffness; thus, it is easier for axial vibration to cause resonance failure. This paper proposes an equivalent damping numerical prediction method for a ring damper under axial vibration, which greatly shortens the calculation time and prevents the forced response analysis of nonlinear structures. Via this method, the influence of ring damper structural parameters on friction damping in gears under axial vibration is investigated. The results indicate that the friction coefficient and mass of the ring damper have a great influence on damping performance. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

17 pages, 7162 KiB

Open AccessArticle

Angle Tracking Observer with Improved Accuracy for Resolver-to-Digital Conversion

by Haoye Qin and Zhong Wu

Symmetry 2019, 11(11), 1347; https://doi.org/10.3390/sym11111347 - 01 Nov 2019

Cited by 5 | Viewed by 5898

Abstract

A resolver is an absolute shaft sensor which outputs pair signals with ortho-symmetric amplitudes. Ideally, they are sinusoidal and cosinusoidal functions of the shaft angle. In order to demodulate angular position and velocity from resolver signals, resolver-to-digital conversion (RDC) is necessary. In software-based [...] Read more.

A resolver is an absolute shaft sensor which outputs pair signals with ortho-symmetric amplitudes. Ideally, they are sinusoidal and cosinusoidal functions of the shaft angle. In order to demodulate angular position and velocity from resolver signals, resolver-to-digital conversion (RDC) is necessary. In software-based RDC, most algorithms mainly employ a phase-locked loop (PLL)-based angle tracking observer (ATO) to form a type-II system. PLL can track the detected angle by regulating the phase error from the phase detector which depends on the feature of orthogonal symmetry in the resolver outputs. However, a type-II system will result in either steady-state errors or cumulative errors in the estimation of angular position with constant accelerations. Although type-III ATOs can suppress these errors, they are still vulnerable to high-order acceleration signals. In this paper, an improved PLL-based ATO with a compensation model is proposed. By using dynamic compensation, the proposed ATO becomes a type-IV system and can reduce position estimation errors for high-order acceleration signals. In addition, the parameters of ATO can be tuned according to the bandwidth, noise level and capability of error suppression. Simulation and experimental results demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

27 pages, 4061 KiB

Open AccessArticle

Topological Design Methods for Mecanum Wheel Configurations of an Omnidirectional Mobile Robot

by Yunwang Li, Sumei Dai, Lala Zhao, Xucong Yan and Yong Shi

Symmetry 2019, 11(10), 1268; https://doi.org/10.3390/sym11101268 - 10 Oct 2019

Cited by 31 | Viewed by 10932

Abstract

A simple and efficient bottom-roller axle intersections approach for judging the omnidirectional mobility of the Mecanum wheel configuration is proposed and proved theoretically. Based on this approach, a sub-configuration judgment method is derived. Using these methods, on the basis of analyzing the possible [...] Read more.

A simple and efficient bottom-roller axle intersections approach for judging the omnidirectional mobility of the Mecanum wheel configuration is proposed and proved theoretically. Based on this approach, a sub-configuration judgment method is derived. Using these methods, on the basis of analyzing the possible configurations of three and four Mecanum wheels and existing Mecanum wheel configurations of robots in practical applications, the law determining wheel configuration is elucidated. Then, the topological design methods of the Mecanum wheel configurations are summarized and refined, including the basic configuration array method, multiple wheels replacement method, and combination method. The first two methods can be used to create suitable multiple-Mecanum-wheel configurations for a single mobile robot based on the basic Mecanum wheel configuration. Multiple single robots can be arranged by combination methods including end-to-end connection, side-by-side connection, symmetrical rectangular connection, and distributed combination, and then, the abundant combination configurations of robots can be obtained. Examples of Mecanum wheel configurations design based on a symmetrical four-Mecanum-wheel configuration and three centripetal configurations using these topological design methods are presented. This work can provide methods and a reference for Mecanum wheel configurations design. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

18 pages, 7670 KiB

Open AccessArticle

Basket-Handle Arch and Its Optimum Symmetry Generation as a Structural Element and Keeping the Aesthetic Point of View

by Alfredo Alcayde, Cristina Velilla, Carlos San-Antonio-Gómez, Araceli Peña-Fernández, Antonio Pérez-Romero and Francisco Manzano-Agugliaro

Symmetry 2019, 11(10), 1243; https://doi.org/10.3390/sym11101243 - 04 Oct 2019

Cited by 5 | Viewed by 8153

Abstract

The arches were a great advance in construction with respect to the rigid Greek linteled architecture. Its development came from the hand of the great Roman constructions, especially with the semicircular arch. In successive historical periods, different types of arches have been emerging, [...] Read more.

The arches were a great advance in construction with respect to the rigid Greek linteled architecture. Its development came from the hand of the great Roman constructions, especially with the semicircular arch. In successive historical periods, different types of arches have been emerging, which in addition to their structural function was taking aesthetic characteristics that are used today to define the architectural style. When, in the construction of a bow, the rise is less than half the springing line, the semicircular arch is no longer used and the segmental arch is used, and then on to another more efficient and aesthetic arch, the basket-handle arch. This study examines the classic geometry of the basket-handle arch also called the three-centered arch. A solution is proposed from a constructive and aesthetic point of view, and this is approached both geometrically and analytically, where the relationship between the radius of the central arch and the radius of the lateral arch is minimized. The solution achieved allows the maximum springing line or clear span to be saved with the minimum rise that preserves the aesthetic point of view, since the horizontal thrust of a bow is greater than the relationship between the springing line of the arch and the rise. This solution has been programmed and the resulting software has made it possible to analyse existing arches in historic buildings or constructions to check if their solutions were close or not from both points of view. Thus, it has been possible to verify that in most of the existing arches analyzed, the proposed solution is reached. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Graphical abstract

21 pages, 1897 KiB

Open AccessArticle

Research Methodology: Application of Railway Luggage and Package Transportation Scheme Formulation Based on a Dynamic Time–Space Service Network

by Kaige Niu, Jun Liu and Ying Wang

Symmetry 2019, 11(10), 1226; https://doi.org/10.3390/sym11101226 - 01 Oct 2019

Cited by 2 | Viewed by 2245

Abstract

In the current market environment, the formulation of a railway luggage and package transport scheme (RLPTS) is often affected by the specific requirements of the transport organization, the complex composition of the transport service network, and the dynamic changes of transport demands, which [...] Read more.

In the current market environment, the formulation of a railway luggage and package transport scheme (RLPTS) is often affected by the specific requirements of the transport organization, the complex composition of the transport service network, and the dynamic changes of transport demands, which make it very difficult. In this paper, a two-stage RLPTS formulation method is proposed that can meet not only transport demands with dynamic changes, but also the requirements of transport timeliness. It is used to solve the problem of current RLPTS formulation. First, a dynamic service network for railway luggage and package transport (RLPT) is constructed based on passenger train schedules, and based on this network, an improved A* algorithm is designed to generate feasible path sets for RLPT demand. Then, based on feasible path sets, a flow distribution model aiming at maximizing the total profit of transportation is established to solve the model in order to enable the flow allocated on the path. Finally, an example calculation shows that the method can implement the RLPTS formulation rapidly. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

12 pages, 4452 KiB

Open AccessArticle

Rainfall Runoff Analysis and Sustainable Soil Bed Optimization Engineering Process: Application of an Advanced Decision-Making Technique

by Muhammad Hamza Hanif, Muhammad Adnan, Syyed Adnan Raheel Shah, Nasir Mahmood Khan, Mehwish Nadeem, Jahanzeb Javed, Muhammad Waseem Akbar, Ali Farooq and Muhammad Waseem

Symmetry 2019, 11(10), 1224; https://doi.org/10.3390/sym11101224 - 01 Oct 2019

Cited by 3 | Viewed by 3575

Abstract

Sustainable engineering practices always provide an opportunity for engineers to produce long-term solutions. In the fields of construction and irrigation, soil bed formation symmetry is very important, especially in the case of its behavior with reference to water runoff, whether natural or artificial. [...] Read more.

Sustainable engineering practices always provide an opportunity for engineers to produce long-term solutions. In the fields of construction and irrigation, soil bed formation symmetry is very important, especially in the case of its behavior with reference to water runoff, whether natural or artificial. In this study, different soil bed formations were tested with the help of advanced hydrology apparatus under severe rainfall conditions. A major focus was to observe the water retention and volume discharge with reference to soil combinations and slope level change. Furthermore, an advanced decision-making technique incorporating artificial neural networks (ANNs) was used to predict and explore the interrelationship behavior of different parameters. It was observed that ST-1 (100% clay) performed well as it tried to retain a large quantity of water (7.28 L/min), making it suitable for irrigation, while ST-2 (100% sand) performed better for structures, as sand tries to quickly drain water, thus retaining less water (0.16 L/min). Change of slope was also another factor; at a 3% slope level along with 100% clay, water resistance was higher as compared to sand. Soil type-3 (ST-3) helped in the retention of water even at a 3% soil bed slope. This study will help engineers and designers in the optimization of soil bed formation for construction and irrigation purposes. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Graphical abstract

14 pages, 719 KiB

Open AccessArticle

Study on Stiffness-Oriented Cable Tension Distribution for a Symmetrical Cable-Driven Mechanism

by Kaisheng Yang, Guilin Yang, Si-Lu Chen, Yi Wang, Chi Zhang, Zaojun Fang, Tianjiang Zheng and Chongchong Wang

Symmetry 2019, 11(9), 1158; https://doi.org/10.3390/sym11091158 - 11 Sep 2019

Cited by 10 | Viewed by 3335

Abstract

In this paper, we focus on the issues pertaining to stiffness-oriented cable tension distribution for a symmetrical 6-cable-driven spherical joint module (6-CSJM), which can be employed to construct modular cable-driven manipulators. Due to the redundant actuation of the 6-CSJM, three cables are employed [...] Read more.

In this paper, we focus on the issues pertaining to stiffness-oriented cable tension distribution for a symmetrical 6-cable-driven spherical joint module (6-CSJM), which can be employed to construct modular cable-driven manipulators. Due to the redundant actuation of the 6-CSJM, three cables are employed for position regulation by adjusting the cable lengths, and the remaining three cables are utilized for stiffness regulation by adjusting the cable tensions, i.e., the position and stiffness can be regulated simultaneously. To increase the range of stiffness regulation, a variable stiffness device (VSD) is designed, which is serially connected to the driving cable. Since the stiffness model of the 6-CSJM with VSDs is very complicated, it is difficult to directly solve the cable tensions from the desired stiffness. The stiffness-oriented cable tension distribution issue is formulated as a nonlinear constrained optimization problem, and the Complex method is employed to obtain optimal tension distributions. Furthermore, to significantly improve the computation efficiency, a decision variable elimination technique is proposed to deal with the equality constraints, which reduces decision variables from 6 to 3. A comprehensive simulation study is conducted to verify the effectiveness of the proposed method, showing that the 6-CSJM can accurately achieve the desired stiffness through cable tension optimization. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

11 pages, 1227 KiB

Open AccessArticle

Routing for Hazardous Materials Transportation in Urban Areas

by Lukai Zhang, Xuesong Feng, Yan Yang and Chuanchen Ding

Symmetry 2019, 11(9), 1091; https://doi.org/10.3390/sym11091091 - 01 Sep 2019

Cited by 5 | Viewed by 2735

Abstract

Hazardous materials (HAZMAT) are important for daily production in cities, which usually have a high population. To avoid the threat to public safety and security, the routes for HAZMAT transportation should be planned legitimately by mitigating the maximum risk to population centers. For [...] Read more.

Hazardous materials (HAZMAT) are important for daily production in cities, which usually have a high population. To avoid the threat to public safety and security, the routes for HAZMAT transportation should be planned legitimately by mitigating the maximum risk to population centers. For the objective of min-max local risk in urban areas, this study has newly proposed an optimization model where the service of a link for HAZMAT transportation was taken as the key decision variable. Correspondingly, the symmetric problem of min-max optimization takes significant meanings. Moreover, in consideration of the work load of solving the model under a lot of decision variables, a heuristic algorithm was developed to obtain an optimal solution. Thereafter, a case study was made to test the proposed model and algorithm, and the results were compared with those generated by deterministic solving approaches. In addition, this research is able to be an effective reference for authorities on the management of HAZMAT transportation in urban areas. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

24 pages, 4209 KiB

Open AccessArticle

High-Precision Authentication Scheme Based on Matrix Encoding for AMBTC-Compressed Images

by Guo-Dong Su, Chin-Chen Chang and Chia-Chen Lin

Symmetry 2019, 11(8), 996; https://doi.org/10.3390/sym11080996 - 03 Aug 2019

Cited by 13 | Viewed by 2382

Abstract

In this paper, a high-precision image authentication scheme for absolute moment block truncation coding (AMBTC)-compressed images is presented. For each block, two sub-bitmaps are conducted using the symmetrical separation, and the six-bit authentication code is symmetrically assigned to two sub-codes, which is virtually [...] Read more.

In this paper, a high-precision image authentication scheme for absolute moment block truncation coding (AMBTC)-compressed images is presented. For each block, two sub-bitmaps are conducted using the symmetrical separation, and the six-bit authentication code is symmetrically assigned to two sub-codes, which is virtually embedded into sub-bitmaps using the matrix encoding later. To overcome distortion caused by modifications to the bitmap, the corresponding to-be-flipped bit-location information is recorded instead of flipping these bits of the bitmap directly. Then, the bit-location information is inserted into quantization levels based on adjusted quantization level matching. In contrast to previous studies, the proposed scheme offers a significantly improved tampering detection ability, especially in the first hierarchical tampering detection without remediation measures, with an average tampering detection rate of up to 98.55%. Experimental results show that our approach provides a more stable and reliable tampering detection performance and sustains an acceptable visual quality. Full article

(This article belongs to the Special Issue Symmetry in Engineering Sciences II)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Symmetry in Engineering Sciences II

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (17 papers)

Editorial

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI