Shock and Vibration The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Study on Shale’s Dynamic Damage Constitutive Model Based on Statistical Distribution Thu, 23 Apr 2015 16:51:18 +0000 The dynamic constitutive model of shale is basic for shale gas reservoir reforming. In order to investigate the dynamic mechanism of shale, a new dynamic damage constitutive model of shale under uniaxial impact load was established based on the statistical damage theory and the laboratory test results of deformation and the damage characteristics under the action of SHPB impact. Compared with the theoretical results, the model can describe shale’s mechanical attributes and reveal the fracture damage mechanism as well. The results will provide theoretical basis for hydraulic fracturing on shale and other dynamic reforming technics. Jianjun Liu, Yuan Li, and Huijuan Zhang Copyright © 2015 Jianjun Liu et al. All rights reserved. Study on Elastic Dynamic Model for the Clamping Mechanism of High-Speed Precision Injection Molding Machine Tue, 21 Apr 2015 08:14:41 +0000 This work centered on the double-toggle clamping mechanism with diagonal-five points for the high-speed precise plastic injection machine. Based on Lagrange equations, the differential equations of motion for the beam elements are established, in a rotating coordinate system and an absolute coordinate system, respectively. 43 generalized coordinates and a model matrix for the mechanism are created and some coordinate matrices are derived. By coupling the coordinate transformation and matrix manipulation, a high nonlinear and strong time-variant elastic dynamic model is obtained. Based on the dynamic model, a Kineto-Elasto Dynamics (KED) analysis and a Kineto-Elasto Static (KES) analysis are carried out, respectively. By comparing and analyzing the simulation results of KED and KES, the regularity of elastic vibration of the clamping mechanism in high-speed clamping process has been revealed. Xue-feng Chen, Jian-guo Hu, Yan-sheng Xu, Zhong-ming Xu, and Hong-bo Wang Copyright © 2015 Xue-feng Chen et al. All rights reserved. Seismic Response Analysis of Continuous Multispan Bridges with Partial Isolation Mon, 20 Apr 2015 06:38:50 +0000 Partially isolated bridges are a particular class of bridges in which isolation bearings are placed only between the piers top and the deck whereas seismic stoppers restrain the transverse motion of the deck at the abutments. This paper proposes an analytical formulation for the seismic analysis of these bridges, modelled as beams with intermediate viscoelastic restraints whose properties describe the pier-isolator behaviour. Different techniques are developed for solving the seismic problem. The first technique employs the complex mode superposition method and provides an exact benchmark solution to the problem at hand. The two other simplified techniques are based on an approximation of the displacement field and are useful for preliminary assessment and design purposes. A realistic bridge is considered as case study and its seismic response under a set of ground motion records is analyzed. First, the complex mode superposition method is applied to study the characteristic features of the dynamic and seismic response of the system. A parametric analysis is carried out to evaluate the influence of support stiffness and damping on the seismic performance. Then, a comparison is made between the exact solution and the approximate solutions in order to evaluate the accuracy and suitability of the simplified analysis techniques for evaluating the seismic response of partially isolated bridges. E. Tubaldi, A. Dall’Asta, and L. Dezi Copyright © 2015 E. Tubaldi et al. All rights reserved. A New Improved Kurtogram and Its Application to Bearing Fault Diagnosis Sun, 19 Apr 2015 14:32:41 +0000 A new improved Kurtogram was proposed in this paper. Instead of Kurtosis, correlated Kurtosis of envelope signal extracted from the wavelet packet node was used as an indicator to determine the optimal frequency band. Correlated Kurtosis helps to determine the fault related impulse signals not affected by other unrelated signal components. Finally, two simulated and three experimental bearing fault cases are used to validate the effectiveness of proposed method and to compare with other similar methods. The results demonstrate it can locate resonant frequency band with a high reliability than two previous developed methods by Lei et al. and Wang et al. especially for the incipient faults under low load. Xinghui Zhang, Jianshe Kang, Lei Xiao, Jianmin Zhao, and Hongzhi Teng Copyright © 2015 Xinghui Zhang et al. All rights reserved. Seismic Performance of Midstory Isolated Structures under Near-Field Pulse-Like Ground Motion and Limiting Deformation of Isolation Layers Sun, 19 Apr 2015 06:11:23 +0000 Excessive deformation of the isolation layer in midstory isolated structures may occur under strong near-field pulse-like ground motion, which would result in the overturning collapse of the superstructure. The objective of the present research is to limit excessive deformation of the isolation layer and to reduce nonlinear response of midstory isolated structures. To this end, a protective system is presented to limit deformation of the isolation layer by soft pounding. Based on the Kelvin pounding model, a mechanical model is put forward for this protective system. In addition, a new method has been proposed that synthesizes artificial near-field pulse-like ground motion by combining the real near-field nonpulse ground motion with simple equivalent pulses. Also, the impact of artificial near-field pulse-like ground motion on the nonlinear response of midstory isolated structures and the deformation of the isolation layer has been investigated. The effectiveness of the midstory isolation with the protective system has been validated. The results show that the maximum deformation of the isolation layer significantly exceeds the allowable deformation of lead-rubber bearings when subjected to near-field pulse-like ground motion, and it causes the lead-rubber bearings destruction. The proposed protective system is effective in restricting the excessive deformation of the isolation layer and reducing nonlinear responses of the isolated structure, preventing collapse of the superstructure. Guiyun Yan and Fuquan Chen Copyright © 2015 Guiyun Yan and Fuquan Chen. All rights reserved. Investigation of Effect on Vibrational Behavior of Giant Magnetostrictive Transducers Wed, 08 Apr 2015 08:25:02 +0000 Resonant magnetostrictive transducers are used for generating vibrations in the sonic and ultrasonic range of frequency. As the mechanical properties of magnetostrictive materials change according to different operating conditions (i.e., temperature, mechanical prestress, and magnetic bias), the vibrational behavior of the transducer changes too. effect is the change in the Young modulus of the ferromagnetic material and it has to be considered as it leads to changes in the dynamics of the transducer. This paper deals with the study of such effect from both theoretical and experimental point of view. effect on behavior of the transducer based on Terfenol-D is analytically described as a function of different operating conditions focusing on effects on resonance frequency, mode shape, and moreover experimentally the quality factor. Results of resonance frequency prediction have been validated with experiments and good agreement has been seen. M. Sheykholeslami, Y. Hojjat, M. Ghodsi, K. Kakavand, and S. Cinquemani Copyright © 2015 M. Sheykholeslami et al. All rights reserved. Application of LCD-SVD Technique and CRO-SVM Method to Fault Diagnosis for Roller Bearing Tue, 07 Apr 2015 16:59:36 +0000 Targeting the nonlinear and nonstationary characteristics of vibration signal from fault roller bearing and scarcity of fault samples, a novel method is presented and applied to roller bearing fault diagnosis in this paper. Firstly, the nonlinear and nonstationary vibration signal produced by local faults of roller bearing is decomposed into intrinsic scale components (ISCs) by using local characteristic-scale decomposition (LCD) method and initial feature vector matrices are obtained. Secondly, fault feature values are extracted by singular value decomposition (SVD) techniques to obtain singular values, while avoiding the selection of reconstruction parameters. Thirdly, a support vector machine (SVM) classifier based on Chemical Reaction Optimization (CRO) algorithm, called CRO-SVM method, is designed for classification of fault location. Lastly, the proposed method is validated by two experimental datasets. Experimental results show that the proposed method based LCD-SVD technique and CRO-SVM method have higher classification accuracy and shorter cost time than the comparative methods. Songrong Luo, Junsheng Cheng, and HungLinh Ao Copyright © 2015 Songrong Luo et al. All rights reserved. Dynamic Analysis of Three-Layer Sandwich Beams with Thick Viscoelastic Damping Core for Finite Element Applications Tue, 07 Apr 2015 12:48:26 +0000 This paper presents an analysis of the dynamic behaviour of constrained layer damping (CLD) beams with thick viscoelastic layer. A homogenised model for the flexural stiffness is formulated using Reddy-Bickford’s quadratic shear in each layer, and it is compared with Ross-Kerwin-Ungar (RKU) classical model, which considers a uniform shear deformation for the viscoelastic core. In order to analyse the efficiency of both models, a numerical application is accomplished and the provided results are compared with those of a 2D model using finite elements, which considers extensional and shear stress and longitudinal, transverse, and rotational inertias. The intermediate viscoelastic material is characterised by a fractional derivative model, with a frequency dependent complex modulus. Eigenvalues and eigenvectors are obtained from an iterative method avoiding the computational problems derived from the frequency dependence of the stiffness matrices. Also, frequency response functions are calculated. The results show that the new model provides better accuracy than the RKU one as the thickness of the core layer increases. In conclusion, a new model has been developed, being able to reproduce the mechanical behaviour of thick CLD beams, reducing storage needs and computational time compared with a 2D model, and improving the results from the RKU model. Fernando Cortés and Imanol Sarría Copyright © 2015 Fernando Cortés and Imanol Sarría. All rights reserved. Transversal Vibration of Chain Ropeway System Having Support Boundary Conditions with Polygonal Action Mon, 06 Apr 2015 08:10:27 +0000 The purpose of this paper is to characterize the modal parameters and transverse vibrations of a monochain ropeway system for hilly orchards. The moving chain is modeled with uniform distribution and concentrated inertial loads. In order to study the dynamical behavior of the moving chain, Hamilton’s principle is applied to obtain the homogenous differential equation of transverse vibration. With the boundary conditions subjected to the polygonal action caused by chain-support engagement, the coupling effect of concentrated load, variable tension, and time-dependent speed on transverse vibration is investigated. The contribution of residue of singularity to total vibrations in phase space is numerically analyzed by using the Laplace transform method. The influence of the boundary condition considering the polygonal action is investigated in terms of excitation frequency and amplitude coupled with transport speed. The transverse vibrations are calculated numerically and measured experimentally. The numerical results are in agreement with the experimental data, which suggest that the amplitude and frequency of vibration are proportional to the value of propagation speed. The analytical solution to the moving chain problem provides a feasible reference for its stability analysis and wind-induced vibration control. Zhou Yang, Xue-Ping Li, Jun Li, Tian-Sheng Hong, and Kun-Peng Xue Copyright © 2015 Zhou Yang et al. All rights reserved. Damage Detection and Quantification Using Transmissibility Coherence Analysis Sun, 05 Apr 2015 07:13:23 +0000 A new transmissibility-based damage detection and quantification approach is proposed. Based on the operational modal analysis, the transmissibility is extracted from system responses and transmissibility coherence is defined and analyzed. Afterwards, a sensitive-damage indicator is defined in order to detect and identify the severity of damage and compared with an indicator developed by other authors. The proposed approach is validated on data from a physics-based numerical model as well as experimental data from a three-story aluminum frame structure. For both numerical simulation and experiment the results of the new indicator reveal a better performance than coherence measure proposed in Rizos et al., 2008, Rizos et al., 2002, Fassois and Sakellariou, 2007, especially when nonlinearity occurs, which might be further used in real engineering. The main contribution of this study is the construction of the relation between transmissibility coherence and frequency response function coherence and the construction of an effective indicator based on the transmissibility modal assurance criteria for damage (especially for minor nonlinearity) detection as well as quantification. Yun-Lai Zhou, E. Figueiredo, N. Maia, and R. Perera Copyright © 2015 Yun-Lai Zhou et al. All rights reserved. Analysis of a Low-Angle Annular Expander Nozzle Thu, 02 Apr 2015 11:04:44 +0000 An experimental and numerical analysis of a low-angle annular expander nozzle is presented to observe the variance in shock structure within the flow field. A RANS-based axisymmetric numerical model was used to evaluate flow characteristics and the model validated using experimental pressure readings and schlieren images. Results were compared with an equivalent converging-diverging nozzle to determine the capability of the wake region in varying the effective area of a low-angle design. Comparison of schlieren images confirmed that shock closure occurred in the expander nozzle, prohibiting the wake region from affecting the area ratio. The findings show that a low angle of deflection is inherently unable to influence the effective area of an annular supersonic nozzle design. Kyll Schomberg, John Olsen, and Graham Doig Copyright © 2015 Kyll Schomberg et al. All rights reserved. Dynamic Analysis of a High-Static-Low-Dynamic-Stiffness Vibration Isolator with Time-Delayed Feedback Control Tue, 31 Mar 2015 08:19:02 +0000 This paper proposes the time-delayed cubic velocity feedback control strategy to improve the isolation performance of High-Static-Low-Dynamic-Stiffness (HSLDS) vibration isolator. Firstly, the primary resonance of the controlled HSLDS vibration isolator is obtained by using multiple scales method. The equivalent damping ratio and equivalent resonance frequency are defined to study the effects of feedback gain and time delay on the primary resonance. The jump phenomenon analysis of the controlled system without and with time delay is investigated by using Sylvester resultant method and optimization method, respectively. The stability analysis of the controlled system is also considered. Then, the 1/3 subharmonic resonance of the controlled system is studied by using multiple scales method. The effects of feedback gain and time delay on the 1/3 subharmonic resonance are also presented. Finally, force transmissibility is proposed to evaluate the performance of the controlled system and compared with an equivalent linear passive vibration isolator. The results show that the vibration amplitude of the controlled system around the resonance frequency region decreases and the isolation frequency band is larger compared to the equivalent one. A better isolation performance in the high frequency band can be achieved compared to the passive HSLDS vibration isolator. Yong Wang, Shunming Li, Chun Cheng, and Xingxing Jiang Copyright © 2015 Yong Wang et al. All rights reserved. Analysis of Closure Characteristics of a MEMS Omnidirectional Inertial Switch under Shock Loads Tue, 31 Mar 2015 07:56:35 +0000 A preliminary theoretical method for calculating contact time of a dual mass-spring system applied to shock acceleration was proposed based on the MEMS omnidirectional inertial switch. The influence of relevant parameters on the contact time was analyzed, and the theoretical results were in agreement with the simulation predictions. The theoretical method could provide the design of MEMS inertial switch for prolonged contact time. The system stiffness of the mass-spring system in all directions was obtained by using the FE method. Dynamic contact simulation results of contact time in typical directions under the applied shock acceleration indicate that the switch has a contact time within the range of 33 μs to 95 μs and has an enhanced contact effect with the dual mass-spring system in the MEMS inertial switch. The fabricated switches were tested by a shock test device. The results show that the switch can be reliably closed in all directions under the applied shock acceleration and has a long contact time, which is basically in accordance with the theoretical results. Yun Cao, Zhanwen Xi, Jiong Wang, and Weirong Nie Copyright © 2015 Yun Cao et al. All rights reserved. Stability Evaluation on Surrounding Rocks of Underground Powerhouse Based on Microseismic Monitoring Mon, 30 Mar 2015 11:26:59 +0000 To study the stability of underground powerhouse at Houziyan hydropower station during excavation, a microseismic monitoring system is adopted. Based on the space-time distribution characteristics of microseismic events during excavation of the main powerhouse, the correlation between microseismic events and blasting construction is established; and the microseismic clustering areas of the underground powerhouse are identified and delineated. The FLAC3D code is used to simulate the deformation of main powerhouse. The simulated deformation characteristics are consistent with that recorded by microseismic monitoring. Finally, the correlation between the macroscopic deformation of surrounding rock mass and microseismic activities is also revealed. The results show that multiple faults between 1# and 3# bus tunnels are activated during excavation of floors V and VI of the main powerhouse. The comprehensive method combining microseismic monitoring with numerical simulation as well as routine monitoring can provide an effective way to evaluate the surrounding rock mass stability of underground caverns. Feng Dai, Biao Li, Nuwen Xu, Yongguo Zhu, and Peiwei Xiao Copyright © 2015 Feng Dai et al. All rights reserved. Topology Optimization for Minimizing the Resonant Response of Plates with Constrained Layer Damping Treatment Wed, 25 Mar 2015 06:54:30 +0000 A topology optimization method is proposed to minimize the resonant response of plates with constrained layer damping (CLD) treatment under specified broadband harmonic excitations. The topology optimization problem is formulated and the square of displacement resonant response in frequency domain at the specified point is considered as the objective function. Two sensitivity analysis methods are investigated and discussed. The derivative of modal damp ratio is not considered in the conventional sensitivity analysis method. An improved sensitivity analysis method considering the derivative of modal damp ratio is developed to improve the computational accuracy of the sensitivity. The evolutionary structural optimization (ESO) method is used to search the optimal layout of CLD material on plates. Numerical examples and experimental results show that the optimal layout of CLD treatment on the plate from the proposed topology optimization using the conventional sensitivity analysis or the improved sensitivity analysis can reduce the displacement resonant response. However, the optimization method using the improved sensitivity analysis can produce a higher modal damping ratio than that using the conventional sensitivity analysis and develop a smaller displacement resonant response. Zhanpeng Fang and Ling Zheng Copyright © 2015 Zhanpeng Fang and Ling Zheng. All rights reserved. Static and Dynamic Experiment Evaluations of a Displacement Differential Self-Induced Magnetorheological Damper Tue, 24 Mar 2015 12:17:15 +0000 This paper presents the development of a novel magnetorheological damper (MRD) which has a self-induced ability. In this study, a linear variable differential sensor (LVDS) based on the electromagnetic induction mechanism was integrated with a conventional MRD. The structure of the displacement differential self-induced magnetorheological damper (DDSMRD) was developed, and the theory of displacement differential self-induced performance was deduced. The static experiments of the DDSMRD under different displacement positions were carried out by applying sine excitation signals to the excitation coils, and the experimental results show that the self-induced voltage is proportional to the damper piston displacement. Meanwhile, the dynamic experiments were also carried out using the fatigue test machine to investigate the change of the self-induced voltage under the typical direct current inputs and the different piston rod displacements; the experimental results also show that the self-induced voltage is proportional to the damper piston displacements. Additionally, the dynamic mechanical performance of the DDSMRD was evaluated. The theory deduction and the experimental results indicate that the proposed DDSMRD has the ability of the integrated displacement sensor in addition to the output controllable damping force. Guoliang Hu, Wei Zhou, Mingke Liao, and Weihua Li Copyright © 2015 Guoliang Hu et al. All rights reserved. Active Structural Acoustic Control of Clamped Flat Plates Using a Weighted Sum of Spatial Gradients Sun, 22 Mar 2015 13:44:28 +0000 The weighted sum of spatial gradients (WSSG) control minimization parameter is developed for use in active structural acoustic control (ASAC) on a clamped flat rectangular plate. The WSSG minimization parameter is measured using four accelerometers grouped closely together on the test structure. In previous work, WSSG was developed on a simply supported flat rectangular plate and showed promise as a control metric. The displacement on the clamped plate has been modeled using an approximate analytical solution assuming shape functions corresponding to clamped-clamped beams. From the analytical formulation, weights, which were found to be the reciprocal of the wave number squared, have been derived to produce a uniform WSSG field across the plate. In active control simulations, this quantity has been shown to provide better global control of acoustic radiation than volume velocity. Analysis is presented which shows that comparable control, regardless of the sensor location, can be achieved using WSSG. Experimental results are presented which demonstrate that WSSG works effectively in practice, with results similar to the simulations. The results show that minimization of WSSG can be used as an effective control objective on clamped rectangular plates to achieve attenuation of acoustic radiation. William R. Johnson, Daniel R. Hendricks, Scott D. Sommerfeldt, and Jonathan D. Blotter Copyright © 2015 William R. Johnson et al. All rights reserved. Viability Analysis of Waste Tires as Material for Rail Vibration and Noise Control in Modern Tram Track Systems Wed, 18 Mar 2015 14:03:14 +0000 This research study focused on the effect of using damping chamber elements made from waste tires on railway noise reduction. First, the energy absorption characteristics of damping chamber elements with various gradation combinations and compaction indices were measured in the laboratory using compression testing. The laboratory compression results demonstrated that the optimal gradation combination of damping chamber elements is as follows: the content of fine rubber particles is 10%, the content of coarse granules is 90%, and the optimal compaction index is 0.98. Next, the findings from the laboratory compression-test studies were used to produce damping chamber elements that were applied to a full-scale modern track model in the laboratory. The measurements of the dynamic properties indicated that the damping chamber elements could significantly reduce the vibration levels of the rail head. Finally, the damping chamber elements, which had been proven effective through laboratory dynamic tests, were widely applied to test rail sections in the field. The field tests demonstrated that damping chamber elements can significantly increase the track vibration decay rate in the frequency range of 200–10000 Hz. Therefore, damping chamber elements made from waste tires are able to control rail vibration and noise in modern tram track systems. Caiyou Zhao, Ping Wang, Qiang Yi, and Duo Meng Copyright © 2015 Caiyou Zhao et al. All rights reserved. A New Approach for Studying Nonlinear Dynamic Response of a Thin Plate with Internal Resonance in a Fractional Viscoelastic Medium Wed, 18 Mar 2015 13:22:40 +0000 In the previous analysis, the dynamic behaviour of a nonlinear plate embedded into a fractional derivative viscoelastic medium has been studied by the method of multiple time scales under the conditions of the internal resonances two-to-one and one-to-one, as well as the internal combinational resonances for the case when the linear parts of nonlinear equations of motion occur to be coupled. A new approach proposed in this paper allows one to uncouple the linear parts of equations of motion of the plate, while the same method, the method of multiple time scales, has been utilized for solving nonlinear equations. The influence of viscosity on the energy exchange mechanism between interacting nonlinear modes has been analyzed. It has been shown that for some internal resonances there exist such particular cases when it is possible to obtain two first integrals, namely, the energy integral and the stream function, which allows one to reduce the problem to the calculation of elliptic integrals. The new approach enables one to solve the problems of vibrations of thin bodies more efficiently. Yury A. Rossikhin, Marina V. Shitikova, and Jean Claude Ngenzi Copyright © 2015 Yury A. Rossikhin et al. All rights reserved. Aeroservoelastic Pitch Control of Stall-Induced Flap/Lag Flutter of Wind Turbine Blade Section Wed, 18 Mar 2015 11:34:29 +0000 The aim of this paper is to analyze aeroelastic stability, especially flutter suppression for aeroelastic instability. Effects of aeroservoelastic pitch control for flutter suppression on wind turbine blade section subjected to combined flap and lag motions are rarely studied. The work is dedicated to solving destructive flapwise and edgewise instability of stall-induced flutter of wind turbine blade by aeroservoelastic pitch control. The aeroelastic governing equations combine a flap/lag structural model and an unsteady nonlinear aerodynamic model. The nonlinear resulting equations are linearized by small perturbation about the equilibrium point. The instability characteristics of stall-induced flap/lag flutter are investigated. Pitch actuator is described by a second-order model. The aeroservoelastic control is analyzed by three types of optimal PID controllers, two types of fuzzy PID controllers, and neural network PID controllers. The fuzzy controllers are developed based on Sugeno model and intuition method with good results achieved. A single neuron PID control strategy with improved Hebb learning algorithm and a radial basic function neural network PID algorithm are applied and performed well in the range of extreme wind speeds. Tingrui Liu Copyright © 2015 Tingrui Liu. All rights reserved. Artificial Neural Network Model for Monitoring Oil Film Regime in Spur Gear Based on Acoustic Emission Data Tue, 17 Mar 2015 13:45:22 +0000 The thickness of an oil film lubricant can contribute to less gear tooth wear and surface failure. The purpose of this research is to use artificial neural network (ANN) computational modelling to correlate spur gear data from acoustic emissions, lubricant temperature, and specific film thickness (λ). The approach is using an algorithm to monitor the oil film thickness and to detect which lubrication regime the gearbox is running either hydrodynamic, elastohydrodynamic, or boundary. This monitoring can aid identification of fault development. Feed-forward and recurrent Elman neural network algorithms were used to develop ANN models, which are subjected to training, testing, and validation process. The Levenberg-Marquardt back-propagation algorithm was applied to reduce errors. Log-sigmoid and Purelin were identified as suitable transfer functions for hidden and output nodes. The methods used in this paper shows accurate predictions from ANN and the feed-forward network performance is superior to the Elman neural network. Yasir Hassan Ali, Roslan Abd Rahman, and Raja Ishak Raja Hamzah Copyright © 2015 Yasir Hassan Ali et al. All rights reserved. A Multiple-Kernel Relevance Vector Machine with Nonlinear Decreasing Inertia Weight PSO for State Prediction of Bearing Tue, 17 Mar 2015 06:11:57 +0000 The scientific and accurate prediction for state of bearing is the key to ensure its safe operation. A multiple-kernel relevance vector machine (MkRVM) including RBF kernel and polynomial kernel is proposed for state prediction of bearing in this study; the proportions of RBF kernel and polynomial kernel are determined by a controlled parameter. As the selection of the parameters of the kernel functions and the controlled parameter has a certain influence on the prediction results of MkRVM, nonlinear decreasing inertia weight PSO (NDIWPSO) is used to select its kernel parameters and controlled parameter. The RBF kernel RVM model with NDIWPSO (NDIWPSO-RBFRVM) and the polynomial kernel RVM model with NDIWPSO (NDIWPSO-PolyRVM) are used, respectively, to compare with the multiple-kernel RVM model with NDIWPSO (NDIWPSO-MkRVM). The experimental results indicate that NDIWPSO-MkRVM is more suitable for the state prediction of bearing than NDIWPSO-RBFRVM and NDIWPSO-PolyRVM. Sheng-wei Fei and Yong He Copyright © 2015 Sheng-wei Fei and Yong He. All rights reserved. Vibration Properties of a Steel-PMMA Composite Beam Thu, 12 Mar 2015 13:32:32 +0000 A steel-polymethyl methacrylate (steel-PMMA) beam was fabricated to investigate the vibration properties of a one-dimensional phononic crystal structure. The experimental system included an excitation system, a signal acquisition system, and a data analysis and processing system. When an excitation signal was exerted on one end of the beam, the signals of six response points were collected with acceleration sensors. Subsequent signal analysis showed that the beam was attenuated in certain frequency ranges. The lumped mass method was then used to calculate the bandgap of the phononic crystal beam to analyze the vibration properties of a beam made of two different materials. The finite element method was also employed to simulate the vibration of the phononic crystal beam, and the simulation results were consistent with theoretical calculations. The existence of the bandgap was confirmed experimentally and theoretically, which allows for the potential applications of phononic crystals, including wave guiding and filtering, in integrated structures. Yuyang He and Xiaoxiong Jin Copyright © 2015 Yuyang He and Xiaoxiong Jin. All rights reserved. Modelling the Environmental Effects of Railway Vibrations from Different Types of Rolling Stock: A Numerical Study Wed, 11 Mar 2015 13:39:54 +0000 This paper analyses the influence of rolling stock dynamics on ground-borne vibration levels. Four vehicle types (Thalys, German ICE, Eurostar, and Belgian freight trains) are investigated using a multibody approach. First, a numerical model is constructed using a flexible track on which the vehicles traverse at constant speed. A two-step approach is used to simulate ground wave propagation which is analysed at various distances from the track. This approach offers a new insight because the train and track are fully coupled. Therefore rail unevenness or other irregularity on the rail/wheel surface can be accurately modelled. Vehicle speed is analysed and the frequency spectrums of track and soil responses are also assessed to investigate different excitation mechanisms, such as carriage periodicities. To efficiently quantify train effects, a new (normalised) metric, defined as the ratio between the peak particle velocity and the nominal axle load, is introduced for a comparison of dynamic excitation. It is concluded that rolling stock dynamics have a significant influence on the free field vibrations at low frequencies, whereas high frequencies are dominated by the presence of track unevenness. Georges Kouroussis, David P. Connolly, Konstantinos Vogiatzis, and Olivier Verlinden Copyright © 2015 Georges Kouroussis et al. All rights reserved. Inverse Shape Reconstruction of Inner Cavities Using Guided SH-Waves in a Plate Tue, 10 Mar 2015 11:34:20 +0000 The paper proposes an inverse reconstruction method for inner cavities in a 2D plate using guided SH-waves. When a pure incident wave mode is sent toward the flaw area, reflected waves are observed at the far field due to mode conversion. From wave scattering theory, the reflected wave field is expressed by an integral over the unknown flaw surface concerning the total wave field. By the introduction of Born approximation and far-field expressions of Green’s function, it is found that the reflection coefficient for the mode of the same order as that of the incident mode is related to the unknown shape of the cavity by Fourier transform relations. By mathematical deduction, we show that if the basic (0th-order) symmetric and the 1st-order antisymmetric modes are used as incident waves, the locations and shapes of upper and lower boundaries of the cavity can be reconstructed. Numerical examples are illustrated in the paper, and a proper condition for applying this method is discussed. The research can act as a basis of nondestructive inspection for latent flaws within more complicated structures. Bin Wang, Zhenghua Qian, and Sohichi Hirose Copyright © 2015 Bin Wang et al. All rights reserved. Modeling of Magnetorheological Dampers under Various Impact Loads Tue, 10 Mar 2015 09:40:40 +0000 Magnetorheological (MR) damper has received great attention from structural control engineering because it provides the best features of both passive and active control systems. However, many studies on the application of MR dampers to large civil structures have tended to center on the modeling of MR dampers under seismic excitations, while, to date, there has been minimal research regarding the MR damper model under impact loads. Hence, this paper investigates nonlinear models of MR dampers under a variety of impact loads and control signals. Two fuzzy models are proposed for modeling the nonlinear impact behavior of MR dampers. They are compared with mechanical models, the Bingham and Bouc-Wen models. Experimental studies are performed to generate sets of input and output data for training, validating, and testing the models: the deflection, acceleration, velocity, and current signals. It is demonstrated that the proposed fuzzy models are effective in predicting the complex nonlinear behavior of the MR damper subjected to a variety of impact loads and control signals. The proposed fuzzy model resulted in an accuracy of 99% to predict the impact forces of the MR damper. K. Sarp Arsava and Yeesock Kim Copyright © 2015 K. Sarp Arsava and Yeesock Kim. All rights reserved. Theoretical Research Progress in High-Velocity/Hypervelocity Impact on Semi-Infinite Targets Mon, 09 Mar 2015 08:43:32 +0000 With the hypervelocity kinetic weapon and hypersonic cruise missiles research projects being carried out, the damage mechanism for high-velocity/hypervelocity projectile impact on semi-infinite targets has become the research keystone in impact dynamics. Theoretical research progress in high-velocity/hypervelocity impact on semi-infinite targets was reviewed in this paper. The evaluation methods for critical velocity of high-velocity and hypervelocity impact were summarized. The crater shape, crater scaling laws and empirical formulae, and simplified analysis models of crater parameters for spherical projectiles impact on semi-infinite targets were reviewed, so were the long rod penetration state differentiation, penetration depth calculation models for the semifluid, and deformed long rod projectiles. Finally, some research proposals were given for further study. Yunhou Sun, Cuncheng Shi, Zheng Liu, and Desheng Wen Copyright © 2015 Yunhou Sun et al. All rights reserved. Flutter Instability Speeds of Guided Splined Disks: An Experimental and Analytical Investigation Thu, 05 Mar 2015 14:21:21 +0000 “Guided splined disks” are defined as flat thin disks in which the inner radius of the disk is splined and matches a splined arbor that provides the driving torque for rotating the disk. Lateral constraint for the disk is provided by space fixed guide pads. Experimental lateral displacement of run-up tests of such a system is presented, and the flutter instability zones are identified. The results indicate that flutter instability occurs at speeds when a backward travelling wave of a mode meets a reflected wave of a different mode. Sometimes, the system cannot pass a flutter zone, and transverse vibrations of the disk lock into that flutter instability zone. The governing linear equations of transverse motion of such a spinning disk, with assumed free inner and outer boundary conditions, are derived. A lateral constraint is introduced and modeled as a linear spring. Rigid body translational and tilting degrees of freedom are included in the analysis of the total motion of the spinning disk. The eigenvalues of the system are computed numerically, and the flutter instability zones are defined. The results show that the mathematical model can predict accurately the flutter instability zones measured in the experimental tests. Ahmad Mohammadpanah and Stanley G. Hutton Copyright © 2015 Ahmad Mohammadpanah and Stanley G. Hutton. All rights reserved. Embedded Electromechanical Impedance and Strain Sensors for Health Monitoring of a Concrete Bridge Mon, 02 Mar 2015 11:55:05 +0000 Piezoelectric lead zirconate titanate (PZT) is one of the piezoelectric smart materials, which has direct and converse piezoelectric effects and can serve as an active electromechanical impedance (EMI) sensor. The design and fabrication processes of EMI sensors embedded into concrete structures are presented briefly. Subsequently, finite element modeling and modal analysis of a continuous rigid frame bridge are implemented by using ANSYS and MIDAS and validated by the field test results. Uppermost, a health monitoring technique by employing the embedded EMI and strain sensors is proposed in this paper. The technique is not based on any physical model and is sensitive to incipient structural changes for its high frequency characteristics. A practical study on health monitoring of the continuous rigid frame bridge is implemented based on the EMI and strain signatures. In this study, some EMI and strain sensors are embedded into the box-sectional girders. The electrical admittances of distributed EMI active sensors and the strains of concrete are measured when the bridge is under construction or in operation. Based on the electrical admittance and strain measurements, the health statuses of the continuous rigid frame bridge are monitored and evaluated successfully in the construction and operation stages using a root-mean-square deviation (RMSD) index. Dansheng Wang, Junbing Zhang, and Hongping Zhu Copyright © 2015 Dansheng Wang et al. All rights reserved. Dynamic Instability Analysis of a Rotating Ship Shaft under a Periodic Axial Force by Discrete Singular Convolution Mon, 02 Mar 2015 09:40:43 +0000 Dynamic instability of a rotating ship shaft subjected to a periodic axial force is studied by using discrete singular convolution (DSC) with regularized Shannon’s delta kernel. The excitation frequency is related to the spinning speed and the number of blades on the propeller. Effects of number of blades, constant term in the periodic force, and damping on dynamic instability regions are investigated. The results have shown that the increase of number of blades and damping could improve the dynamic stability of rotating shaft with damping. The increase of constant term in the periodic force leads to dynamic instability regions shifting to lower frequencies, making the shaft more sensitive to periodic force. Those dynamic instability regions obtained by DSC method have been compared with those by Floquet’s method to verify the application of DSC method to dynamic instability analysis of rotating ship shaft. Wei Li, Zhiwei Song, Xuexia Gao, and Zhigang Chen Copyright © 2015 Wei Li et al. All rights reserved.