Shock and Vibration The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Forced Responses of the Parametric Vibration System for the Electromechanical Integrated Magnetic Gear Thu, 30 Jul 2015 09:46:03 +0000 Considering the magnetic fields modulating in the electromechanical integrated magnetic gear (EIMG), the electromagnetic coupling stiffnesses vary periodically and the expressions are given by the finite element method. The parametric vibration model and the dynamic differential equations are founded. The expressions of forced responses of EIMG system are deduced when the main resonances and the combination resonances occur. And then, the time and frequency responses are figured out. The dynamic characteristics of EIMG system are discussed. The results show that the dominant frequencies in the resonances are always the natural frequency of EIMG system. The relative amplitudes of the components have great difference and the components amplitudes of the main resonances are much bigger than the components amplitudes of the combination resonances. The time-varying meshing stiffness wave between the inner stator and the inner ferromagnetic pole-pieces has little influence on EIMG system. Xiu-hong Hao and Xue-jun Zhu Copyright © 2015 Xiu-hong Hao and Xue-jun Zhu. All rights reserved. Classical Flutter and Active Control of Wind Turbine Blade Based on Piezoelectric Actuation Wed, 29 Jul 2015 16:09:34 +0000 The aim of this article is to analyze classical flutter and active control of single-cell thin-walled composite wind turbine blade beam based on piezoelectric actuation. Effects of piezoelectric actuation for classical flutter suppression on wind turbine blade beam subjected to combined transverse shear deformation, warping restraint effect, and secondary warping are investigated. The extended Hamilton’s principle is used to set up the equations of motion, and the Galerkin method is applied to reduce the aeroelastic coupled equations into a state-space form. Active control is developed to enhance the vibrational behavior and dynamic response to classical aerodynamic excitation and stabilize structures that might be damaged in the absence of control. Active optimal control scheme based on linear quadratic Gaussian (LQG) controller is implemented. The research provides a way for rare study of classical flutter suppression and active control of wind turbine blade based on piezoelectric actuation. Tingrui Liu Copyright © 2015 Tingrui Liu. All rights reserved. Identifying the Mechanical Parameters of Hard Coating with Strain Dependent Characteristic by an Inverse Method Wed, 29 Jul 2015 13:20:20 +0000 The mechanical parameters of hard coating, such as storage modulus and loss factor, are affected by preparation technology significantly and have the strain dependent characteristic. So the effective identification of these mechanical parameters becomes a challenge task. In this study, a hard-coating cantilever thin plate under base excitation was taken as the research object, and an inverse method was developed to identify these mechanical parameters. Firstly, the principles of identifying storage modulus and loss factor of hard coating were presented according to the inverse method. Then, from the need of parameters identification, the analytical model and calculation formula of equivalent strain for the hard-coating composite plate were derived. Next, also for parameter identification, the vibration experiments about the cantilever plate coated with NiCoCrAlY+ yttria-stabilised zirconia (YSZ) hard coating were performed. Finally, the mechanical parameters of NiCoCrAlY+YSZ hard coating with strain dependent characteristic were identified by the proposed method. The identification results show that the change rules of storage modulus and loss factor of hard coating with the strain amplitude are almost consistent with the results listed in the other similar references. However, the identification results herein can more directly serve for the dynamic modeling of hard-coating plate-shape composite structure. Wei Sun, Zhuo Wang, Mingwei Zhu, and Guangyu Du Copyright © 2015 Wei Sun et al. All rights reserved. Shock Analysis on a Packaged Washing Machine from Damage Boundary: Shock Response Spectrum to Component Failure Wed, 29 Jul 2015 13:15:20 +0000 Both analyses of the damage boundary and shock response spectrum (RSR) are the basis for the development of the protective packaging system. The shock analysis through lab test and numerical simulation found that the root cause of packaging failure was due to the stress of the critical component beyond the yield limit of the material. Lab shock test data showed that the packaging design based on the damage boundary is conservative, and the RSR could be helpful and provide support to develop more effective packaging system. Furthermore, numerical simulation can accurately analyze the component and the entire product packaging system in great detail. Jing Qian, Heping Cai, Weiwei Ma, and Zhiwei Hao Copyright © 2015 Jing Qian et al. All rights reserved. Experimental and Numerical Analysis of Hull Girder Vibrations and Bow Impact of a Large Ship Sailing in Waves Wed, 29 Jul 2015 09:45:08 +0000 It is of great importance to evaluate the hull structural vibrations response of large ships in extreme seas. Studies of hydroelastic response of an ultra large ship have been conducted with comparative verification between experimental and numerical methods in order to estimate the wave loads response considering hull vibration and water impact. A segmented self-propelling model with steel backbone system was elaborately designed and the experiments were performed in a tank. Time domain numerical simulations of the ship were carried out by using three-dimensional nonlinear hydroelasticity theory. The results from the computational analyses have been correlated with those from model tests. Jialong Jiao, Huilong Ren, and Christiaan Adika Adenya Copyright © 2015 Jialong Jiao et al. All rights reserved. The Time-Varying Characteristics of Overhead Electric Transmission Lines Considering the Induced-Ice-Shedding Effect Tue, 28 Jul 2015 11:55:12 +0000 More ice deposits accreted on conductors or ground wires may be shed off when an overhead electric transmission line is responding to shocks initiated by natural ice shedding. Ice shedding causes the global mass, stiffness, and damping of the tower-line system to vary with time, and the successive shedding effect beyond a trigger event has not been taken into account in previous studies due to the lack of an adequate ice detachment model. In this paper, the ice shedding effect induced by initial shocks was considered in finite element (FE) analysis. An ice detachment criterion, in the way of user-defined element rupture subroutine, was implemented into the main commercial nonlinear FE program ADINA, making it possible to consider the induced-ice-shedding effect numerically. The incremental FE form of the system’s governing equations of motion is presented where the variations in the mass and stiffness matrices of the system are taken into consideration. Taking a transmission line section following natural ice shedding as a case study, the results indicate that neglecting successive ice shedding underestimates the adverse influence of natural ice shedding. The proposed method can help to improve the design and evaluation of transmission lines in cold regions and to ensure their mechanical security. Kunpeng Ji, Xiaoming Rui, Lin Li, Chao Zhou, Chen Liu, and Ghyslaine McClure Copyright © 2015 Kunpeng Ji et al. All rights reserved. Nonlinear Dynamic Characteristics and Optimal Control of SMA Composite Wings Subjected to Stochastic Excitation Tue, 28 Jul 2015 07:44:38 +0000 A kind of high-aspect-ratio shape memory alloy (SMA) composite wing is proposed to reduce the wing’s fluttering. The nonlinear dynamic characteristics and optimal control of the SMA composite wings subjected to in-plane stochastic excitation are investigated where the great bending under the flight loads is considered. The stochastic stability of the system is analyzed, and the system’s response is obtained. The conditions of stochastic Hopf bifurcation are determined, and the probability density of the first-passage time is obtained. Finally, the optimal control strategy is proposed. Numerical simulation shows that the stability of the system varies with bifurcation parameters, and stochastic Hopf bifurcation appears in the process; the reliability of the system is improved through optimal control, and the first-passage time is delayed. Finally, the effects of the control strategy are proved by experiments. The results of this paper are helpful for engineering applications of SMA. Zhi-Wen Zhu, Xin-Miao Li, and Jia Xu Copyright © 2015 Zhi-Wen Zhu et al. All rights reserved. Hybrid Stochastic Finite Element Method for Mechanical Vibration Problems Mon, 27 Jul 2015 11:49:34 +0000 We present and analyze a new hybrid stochastic finite element method for solving eigenmodes of structures with random geometry and random elastic modulus. The fundamental assumption is that the smallest eigenpair is well defined over the whole stochastic parameter space. The geometric uncertainty is resolved using collocation and random material models using Galerkin method at each collocation point. The response statistics, expectation and variance of the smallest eigenmode, are computed in numerical experiments. The hybrid approach is superior to alternatives in practical cases where the number of random parameters used to describe geometric uncertainty is much smaller than that of the material models. Harri Hakula and Mikael Laaksonen Copyright © 2015 Harri Hakula and Mikael Laaksonen. All rights reserved. Applications of Magnetorheological Technology to Semiactive Vibration Control Systems Mon, 27 Jul 2015 09:53:28 +0000 Miao Yu, Seung-Bok Choi, Norman M. Wereley, Weihua Li, Jeong-Hoi Koo, and Xinchun Guan Copyright © 2015 Miao Yu et al. All rights reserved. Dropping Impact Characteristics Analysis of a Cubic Nonlinear Packaging System with a Cantilever Beam Type Elastic Critical Component with Concentrated Tip Mass Mon, 27 Jul 2015 08:23:04 +0000 A mathematical model for a cubic nonlinear packaging system with a cantilever beam type critical component with concentrated tip mass is proposed. The finite element method and the implicit finite difference method together with the Rung-Kutta method are applied to study the dropping impact dynamics of the critical component and the effect of system parameters, such as the value of the concentrated tip mass and the frequency of the main component, is discussed. The results show that the relative displacement and acceleration change remarkably with the length of the cantilever beam, and the maximum internal stress occurs at the joint end of the critical component. With the increase of the value of the concentrated tip mass and/or a higher frequency of the main component, the amplitudes of the responses increase obviously. Meng Hao and An-Jun Chen Copyright © 2014 Meng Hao and An-Jun Chen. All rights reserved. Indirect Inverse Substructuring Method for Multibody Product Transport System with Rigid and Flexible Coupling Mon, 27 Jul 2015 07:18:13 +0000 The aim of this paper is to develop a new frequency response function- (FRF-) based indirect inverse substructuring method without measuring system-level FRFs in the coupling DOFs for the analysis of the dynamic characteristics of a three-substructure coupled product transport system with rigid and flexible coupling. By enforcing the dynamic equilibrium conditions at the coupling coordinates and the displacement compatibility conditions, a closed-form analytical solution to inverse substructuring analysis of multisubstructure coupled product transport system is derived based on the relationship of easy-to-monitor component-level FRFs and the system-level FRFs at the coupling coordinates. The proposed method is validated by a lumped mass-spring-damper model, and the predicted coupling dynamic stiffness is compared with the direct computation, showing exact agreement. The method developed offers an approach to predict the unknown coupling dynamic stiffness from measured FRFs purely. The suggested method may help to obtain the main controlling factors and contributions from the various structure-borne paths for product transport system. Jun Wang, Li-xin Lu, Pengjiang Qian, Li-qiang Huang, Yan Hua, and Guang-yi Pu Copyright © 2015 Jun Wang et al. All rights reserved. Effect of Fatigue Damage on Energy Absorption Properties of Honeycomb Paperboard Mon, 27 Jul 2015 07:02:57 +0000 The effect of fatigue damage (FD) on the energy absorption properties of precompressed honeycomb paperboard is investigated by fatigue compression experiments. The constitutive relations of honeycomb paperboard have been changed after the fatigue damage. The results show that FD has effect on plateau stress and energy absorption capacity of honeycomb paperboard after fatigue cycles but has no significant effect on densification strain. Energy absorption diagram based on the effect of FD is constructed from the stress-strain curves obtained after fatigue compression experiments. FD is a significant consideration for honeycomb paperboard after transports. The results of this paper could be used for optimization design of packaging materials. Zhi-geng Fan, Li-xin Lu, and Jun Wang Copyright © 2015 Zhi-geng Fan et al. All rights reserved. Design of a Real-Time Adaptively Tuned Dynamic Vibration Absorber with a Variable Stiffness Property Using Magnetorheological Elastomer Sun, 26 Jul 2015 14:14:43 +0000 An elastomer composite with controllable stiffness, known as a magnetorheological elastomer (MRE), is used in a dynamic vibration absorber whose natural frequency is tuned adaptively to the disturbance frequency through the application of an external magnetic field. The field-dependent property test of the fabricated MRE sample shows that the stiffness changes by more than six times compared to the baseline property value at a 40% iron powder volume concentration. The MRE is then used to fabricate a frequency-tunable dynamic absorber for mitigating transient vibrations of a one-degree-of-freedom system. Investigations show that the proposed absorber outperforms a conventional passive-type absorber throughout the tunable frequency range. Toshihiko Komatsuzaki and Yoshio Iwata Copyright © 2015 Toshihiko Komatsuzaki and Yoshio Iwata. All rights reserved. Variational Iteration Method of Dropping Shock Response for the Suspension Spring Packaging System Sun, 26 Jul 2015 12:46:07 +0000 In accordance with dropping shock dimensionless cubic nonlinear dynamic equation of suspension spring system, by variational iteration method, a first-order approximate solution of the system was obtained. The nondimensional peak of displacement, the nondimensional peak of acceleration, and the dropping shock extended period were compared with the results of the Runge-Kutta method, at which relative errors were less than 4%. The influence of suspension angle on peaks of response were discussed. It shows that the maximum response nondimensional acceleration decreases with decrease of the suspension angle under condition of the same nondimensional dropping shock velocity. Conditions for resonance were obtained by applying the variational iteration method, which should be avoided in the packaging design. The results provide reference for suspension spring system design. Shuang Song and An-Jun Chen Copyright © 2015 Shuang Song and An-Jun Chen. All rights reserved. Wavelet Adaptive Algorithm and Its Application to MRE Noise Control System Sun, 26 Jul 2015 12:44:49 +0000 To address the limitation of conventional adaptive algorithm used for active noise control (ANC) system, this paper proposed and studied two adaptive algorithms based on Wavelet. The twos are applied to a noise control system including magnetorheological elastomers (MRE), which is a smart viscoelastic material characterized by a complex modulus dependent on vibration frequency and controllable by external magnetic fields. Simulation results reveal that the Decomposition LMS algorithm (D-LMS) and Decomposition and Reconstruction LMS algorithm (DR-LMS) based on Wavelet can significantly improve the noise reduction performance of MRE control system compared with traditional LMS algorithm. Zhang Yulin and Zhao Xiuyang Copyright © 2015 Zhang Yulin and Zhao Xiuyang. All rights reserved. Magnetic Circuit Analyses and Turning Chatter Suppression Based on a Squeeze-Mode Magnetorheological Damping Turning Tool Sun, 26 Jul 2015 12:43:15 +0000 As a smart material, magnetorheological fluid (MRF) has been utilized in fields including civil engineering and automotive engineering, and so on. In this study, the MR damping turning tool based on the squeeze-mode was developed to improve the vibration resistance of the tool system on the lathe. The 3D magnetic circuit simulations of the damper were performed. The influences of damper structural parameters, such as coil positions, plate thicknesses, and others, on the magnetic induction strength were investigated. Orthogonal experiments were carried out and the optimal combination of damper parameters was determined. The chatter suppressive experiments were carried out to evaluate the performance of the MR damping turning tool. Yongliang Zhang, Norman M. Wereley, Wei Hu, Ming Hong, and Wei Zhang Copyright © 2015 Yongliang Zhang et al. All rights reserved. Nonlinear Regression Based Health Monitoring of Hysteretic Structures under Seismic Excitation Sun, 26 Jul 2015 12:03:59 +0000 This paper presents a health monitoring method using measured hysteretic responses. Acceleration and infrequently measured displacement are integrated using a multirate Kalman filtering method to generate restoring force-displacement hysteresis loops. A linear/nonlinear regression analysis based two-step method is proposed to identify nonlinear system parameters. First, hysteresis loops are divided into loading/unloading half cycles. Multiple linear regression analysis is applied to separate linear and nonlinear half cycles. Preyielding stiffness and viscous damping coefficient are obtained in this step and used as known parameters in the second step. Then, nonlinear regression analysis is applied to identified nonlinear half cycles to yield nonlinear system parameters and two damage indicators: cumulative plastic deformation and residual deformation. These values are closely related to structural status and repair costs. The feasibility of the method is demonstrated using a simulated shear-type structure with different levels of added measurement noise and a suite of ground motions. The results show that the proposed SHM method effectively and accurately identifies physical system parameters with up to 10% RMS added noise. The resulting damage indicators can robustly and clearly indicate structural condition over different earthquake events. C. Xu, J. Geoffrey Chase, and Geoffrey W. Rodgers Copyright © 2015 C. Xu et al. All rights reserved. Damping Force Tracking Control of MR Damper System Using a New Direct Adaptive Fuzzy Controller Sun, 26 Jul 2015 11:38:28 +0000 This paper presents a new direct adaptive fuzzy controller and its effectiveness is verified by investigating the damping force tracking control of magnetorheological (MR) fluid based damper (MR damper in short) system. In the formulation of the proposed controller, a model of interval type 2 fuzzy controller is combined with the direct adaptive control to achieve high performance in vibration control. In addition, (H infinity) tracking technique is used in building a model of the direct adaptive fuzzy controller in which an enhanced iterative algorithm is combined with the fuzzy model. After establishing a closed-loop control structure to achieve high control performance, a cylindrical MR damper is adopted and damping force tracking results are obtained and discussed. In addition, in order to demonstrate the effectiveness of the proposed control strategy, two existing controllers are modified and tested for comparative work. It has been demonstrated from simulation and experiment that the proposed control scheme provides much better control performance in terms of damping force tracking error. This leads to excellent vibration control performance of the semiactive MR damper system associated with the proposed controller. Xuan Phu Do, Kruti Shah, and Seung-Bok Choi Copyright © 2015 Xuan Phu Do et al. All rights reserved. Adaptive Vibration Control System for MR Damper Faults Sun, 26 Jul 2015 08:20:58 +0000 Several methods have been proposed to estimate the force of a semiactive damper, particularly of a magnetorheological damper because of its importance in automotive and civil engineering. Usually, all models have been proposed assuming experimental data in nominal operating conditions and some of them are estimated for control purposes. Because dampers are prone to fail, fault estimation is useful to design adaptive vibration controllers to accommodate the malfunction in the suspension system. This paper deals with the diagnosis and estimation of faults in an automotive magnetorheological damper. A robust LPV observer is proposed to estimate the lack of force caused by a damper leakage in a vehicle corner. Once the faulty damper is isolated in the vehicle and the fault is estimated, an Adaptive Vibration Control System is proposed to reduce the fault effect using compensation forces from the remaining healthy dampers. To fulfill the semiactive damper constraints in the fault adaptation, an LPV controller is designed for vehicle comfort and road holding. Simulation results show that the fault observer has good performance with robustness to noise and road disturbances and the proposed AVCS improves the comfort up to 24% with respect to a controlled suspension without fault tolerance features. Juan C. Tudón-Martínez and Ruben Morales-Menendez Copyright © 2015 Juan C. Tudón-Martínez and Ruben Morales-Menendez. All rights reserved. Thermodynamic Behaviors of a Kind of Self-Decoupling Magnetorheological Damper Sun, 26 Jul 2015 08:12:08 +0000 A theoretical model of temperature change on a kind of self-decoupling magnetorheological (SDMR) damper was established based on conservation of energy, and the constraint equation for structural design parameters of the SDMR damper was improved to satisfy heat dissipation requirements in this work. According to the theoretical model and improved constraint equation, the main structure parameters of SDMR damper were obtained and the damper was tested. The temperature performance test results indicate that the rising temperature makes the damping force decline, and the main affection factors of temperature variation are excitation methods and input current. The results also show that the improved constraint equation and design method introduced are correct and efficient in the engineering. Guojun Yu, Chengbin Du, and Tiger Sun Copyright © 2015 Guojun Yu et al. All rights reserved. Frequency Dependent Spencer Modeling of Magnetorheological Damper Using Hybrid Optimization Approach Sun, 26 Jul 2015 07:38:02 +0000 Magnetorheological dampers have been widely used in civil and automotive industries. The nonlinear behavior of MR fluid makes MR damper modeling a challenging problem. In this paper, a frequency dependent MR damper model is proposed based on Spencer MR damper model. The parameters of the model are identified using an experimental data based hybrid optimization approach which is a combination of Genetic Algorithm and Sequential Quadratic Programming approach. The frequency in the proposed model is calculated using measured relative velocity and relative displacement between MR damper ends. Therefore, the MR damper model will be function of frequency. The mathematical model is validated using the experimental results which confirm the improvement in the accuracy of the model and consistency in the variation damping with the frequency. Ali Fellah Jahromi, Rama B. Bhat, and Wen-Fang Xie Copyright © 2015 Ali Fellah Jahromi et al. All rights reserved. In-Structure Shock of Surface Structures: A Theoretical Approach Wed, 22 Jul 2015 13:21:26 +0000 Metal foam cladding emerges as a promising measure for structure protection against close range blast. With proper cladding design, a considerable amount of energy can be absorbed while the load transmitted to the protected structure can be lowered to a controllable level, leading to less damage of the protected structure. However, it is not clear whether the in-structure shock can be mitigated by attaching foam cladding. The present study theoretically investigates the response of a structural member subjected to a close range blast, for both scenarios with and without attaching foam cladding. Subsequently, shock response spectra are employed to assess the in-structure shock of both situations. It is found that applying foam cladding does not effectively mitigate in-structure shock of surface structures. Hongyuan Zhou and Xiaojuan Wang Copyright © 2015 Hongyuan Zhou and Xiaojuan Wang. All rights reserved. Off-Road Motorbike Performance Analysis Using a Rear Semiactive EH Suspension Wed, 22 Jul 2015 06:39:37 +0000 The topic of this paper is the analysis of a control system for a semiactive rear suspension in an off-road two-wheeled vehicle. Several control methods are studied, as well as the recently proposed Frequency Estimation Based (FEB) algorithm. The motorcycle dynamics, as well as the passive, and semiactive dampers, and the algorithm controlled shock absorber models are loaded into BikeSim, a professional two-wheeled vehicle simulation software, and tested in several road conditions. The results show a detailed comparison of the theoretical performance of the different control approaches in a novel environment for semiactive dampers. Jorge de-J. Lozoya-Santos, Damián Cervantes-Muñoz, Juan Carlos Tudón-Martínez, and Ricardo A. Ramírez-Mendoza Copyright © 2015 Jorge de-J. Lozoya-Santos et al. All rights reserved. Experimental Investigation of Dynamic Response and Deformation of Aluminium Honeycomb Sandwich Panels Subjected to Underwater Impulsive Loads Thu, 16 Jul 2015 10:54:06 +0000 The response of aluminium sandwich panels with three thicknesses’ core subjected to different underwater loading levels has been studied in the fluid-structure interaction (FSI) experiments. The transient response of the panels is measured using a three-dimensional (3D) Digital Image Correlation (DIC) system, along with high-speed photography. The full-field shape and displacement profiles of dry face sheets were recorded in real time compared with those of monolithic plate. The out-of-plane deflection and in-plane strain were quantified and analyzed. Three typical deformation modes of sandwich panel were identified. The results show that the core structure is crushed resulting in an initial large circular shape of deformation in the center area of panels. From this moment on, the panel is starting to act as a free vibration beam with initial velocities. The deformation modes consisted of homogeneous large deformation for both face sheets, obvious deformation border on wet face sheet, core node imprinting, remarkable wrinkled skin of deformation border, and a partial delamination and partial tear failure of the dry face. The blast-resistance of sandwich panel can be highly efficiently improved by increasing the thickness of core structure. Da-Lin Xiang, Ji-Li Rong, and Xuan He Copyright © 2015 Da-Lin Xiang et al. All rights reserved. Finite Element Simulation of Medium-Range Blast Loading Using LS-DYNA Thu, 16 Jul 2015 08:03:58 +0000 This study investigated the Finite Element simulation of blast loading using LS-DYNA. The objective is to identify approaches to reduce the requirement of computation effort while maintaining reasonable accuracy, focusing on blast loading scheme, element size, and its relationship with scale of explosion. The study made use of the recently developed blast loading scheme in LS-DYNA, which removes the necessity to model the explosive in the numerical models but still maintains the advantages of nonlinear fluid-structure interaction. It was found that the blast loading technique could significantly reduce the computation effort. It was also found that the initial density of air in the numerical model could be purposely increased to partially compensate the error induced by the use of relatively large air elements. Using the numerical approach, free air blast above a scaled distance of 0.4 m/kg1/3 was properly simulated, and the fluid-structure interaction at the same location could be properly duplicated using proper Arbitrary Lagrangian Eulerian (ALE) coupling scheme. The study also showed that centrifuge technique, which has been successfully employed in model tests to investigate the blast effects, may be used when simulating the effect of medium- to large-scale explosion at small scaled distance. Yuzhen Han and Huabei Liu Copyright © 2015 Yuzhen Han and Huabei Liu. All rights reserved. A Vibration Control Method for the Flexible Arm Based on Energy Migration Wed, 15 Jul 2015 08:40:34 +0000 A vibration control method based on energy migration is proposed to decrease vibration response of the flexible arm undergoing rigid motion. A type of vibration absorber is suggested and gives rise to the inertial coupling between the modes of the flexible arm and the absorber. By analyzing 1 : 2 internal resonance, it is proved that the internal resonance can be successfully created and the exchange of vibration energy is existent. Due to the inertial coupling, the damping enhancement effect is revealed. Via the inertial coupling, vibration energy of the flexible arm can be dissipated by not only the damping of the vibration absorber but also its own enhanced damping, thereby effectively decreasing vibration. Through numerical simulations and analyses, it is proven that this method is feasible in controlling nonlinear vibration of the flexible arm undergoing rigid motion. Yushu Bian, Zhihui Gao, and Ming Fan Copyright © 2015 Yushu Bian et al. All rights reserved. An Exact Analytical Solution to Exponentially Tapered Piezoelectric Energy Harvester Wed, 15 Jul 2015 08:28:14 +0000 It has been proven that tapering the piezoelectric beam through its length optimizes the power extracted from vibration based energy harvesting. This phenomenon has been investigated by some researchers using semianalytical, finite element and experimental methods. In this paper, an exact analytical solution is presented to calculate the power generated from vibration of exponentially tapered unimorph and bimorph with series and parallel connections. The mass normalized mode shapes of the exponentially tapered piezoelectric beam with tip mass are implemented to transfer the proposed electromechanical coupled equations into modal coordinates. The steady states harmonic solution results are verified both numerically and experimentally. Results show that there exist values for tapering parameter and electric resistance in a way that the output power per mass of the energy harvester will be maximized. Moreover it is concluded that the electric resistance must be higher than a specified value for gaining more power by tapering the beam. H. Salmani, G. H. Rahimi, and S. A. Hosseini Kordkheili Copyright © 2015 H. Salmani et al. All rights reserved. Study on Load Characteristics of Underwater Explosion Using RKDG-LS-DGF and BEM Wed, 15 Jul 2015 06:21:07 +0000 This study numerically investigates the underwater explosion bubble dynamics during the process from detonation to bubble jet with a hybrid algorithm based on Runge Kutta Discontinuous Galerkin-Level Set-Direct Ghost Fluid method (RKDG-LS-DGF) and boundary element method (BEM). RKDG-LS-DGF method is used to simulate the physical process from the detonation of a column charge at one end to the formation of a nonspherical initial bubble and the process of bubble jet. And BEM is adopted to simulate bubble pulsing characteristics. In addition, the numerical results are compared with the experimental results to verify the feasibility of the numerical method. It is found that, during the detonation process of a column charge, the detonation product experiences a shape change from an initial ellipsoid into a sphere during expansion. After the detonation, the bubble experiences expansion and contraction and develops a jet. The jet threads through the bubble in the opposite direction to gravity and induces a high-pressure region. Subsequently, the pressure of this region decreases when the bubble reexpands after being penetrated by the jet. The numerical results agree well with the experimental data, which proves that axisymmetric RKDG-LS-DGF method and BEM are successfully combined to simulate the whole process of underwater explosion. Longkan Wang, Hailong Chen, Xi Ye, and Xiongliang Yao Copyright © 2015 Longkan Wang et al. All rights reserved. Principal Components of Superhigh-Dimensional Statistical Features and Support Vector Machine for Improving Identification Accuracies of Different Gear Crack Levels under Different Working Conditions Tue, 14 Jul 2015 08:58:33 +0000 Gears are widely used in gearbox to transmit power from one shaft to another. Gear crack is one of the most frequent gear fault modes found in industry. Identification of different gear crack levels is beneficial in preventing any unexpected machine breakdown and reducing economic loss because gear crack leads to gear tooth breakage. In this paper, an intelligent fault diagnosis method for identification of different gear crack levels under different working conditions is proposed. First, superhigh-dimensional statistical features are extracted from continuous wavelet transform at different scales. The number of the statistical features extracted by using the proposed method is 920 so that the extracted statistical features are superhigh dimensional. To reduce the dimensionality of the extracted statistical features and generate new significant low-dimensional statistical features, a simple and effective method called principal component analysis is used. To further improve identification accuracies of different gear crack levels under different working conditions, support vector machine is employed. Three experiments are investigated to show the superiority of the proposed method. Comparisons with other existing gear crack level identification methods are conducted. The results show that the proposed method has the highest identification accuracies among all existing methods. Dong Wang, Kwok-Leung Tsui, Peter W. Tse, and Ming J. Zuo Copyright © 2015 Dong Wang et al. All rights reserved. Failure Diagnosis System for a Ball-Screw by Using Vibration Signals Tue, 14 Jul 2015 08:31:59 +0000 Recently, in order to reduce high maintenance costs and to increase operating ratio in manufacturing systems, condition-based maintenance (CBM) has been developed. CBM is carried out with indicators, which show equipment’s faults and performance deterioration. In this study, indicator signal acquisition and condition monitoring are applied to a ball-screw-driven stage. Although ball-screw is a typical linearly reciprocating part and is widely used in industry, it has not gained attention to be diagnosed compared to rotating parts such as motor, pump, and bearing. First, the vibration-based monitoring method, which uses vibration signal to monitor the condition of a machine, is proposed. Second, Wavelet transform is used to analyze the defect signals in time-frequency domain. Finally, the failure diagnosis system is developed using the analysis, and then its performance is evaluated. Using the system, we estimated the severity of failure and detect the defect position. The low defect frequency (≈58.7 Hz) is spread all over the time in the Wavelet-filtered signal with low frequency range. Its amplitude reflects the progress of defect. The defect position was found in the signal with high frequency range (768~1,536 Hz). It was detected from the interval between abrupt changes of signal. Won Gi Lee, Jin Woo Lee, Min Sung Hong, Sung-Ho Nam, YongHo Jeon, and Moon G. Lee Copyright © 2015 Won Gi Lee et al. All rights reserved.