Shock and Vibration http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Detection and Localization of Tooth Breakage Fault on Wind Turbine Planetary Gear System considering Gear Manufacturing Errors Tue, 19 Aug 2014 12:11:30 +0000 http://www.hindawi.com/journals/sv/2014/692347/ Sidebands of vibration spectrum are sensitive to the fault degree and have been proved to be useful for tooth fault detection and localization. However, the amplitude and frequency modulation due to manufacturing errors (which are inevitable in actual planetary gear system) lead to much more complex sidebands. Thus, in the paper, a lumped parameter model for a typical planetary gear system with various types of errors is established. In the model, the influences of tooth faults on time-varying mesh stiffness and tooth impact force are derived analytically. Numerical methods are then utilized to obtain the response spectra of the system with tooth faults with and without errors. Three system components (including sun, planet, and ring gears) with tooth faults are considered in the discussion, respectively. Through detailed comparisons of spectral sidebands, fault characteristic frequencies of the system are acquired. Dynamic experiments on a planetary gear-box test rig are carried out to verify the simulation results and these results are of great significances for the detection and localization of tooth faults in wind turbines. Y. Gui, Q. K. Han, Z. Li, and F. L. Chu Copyright © 2014 Y. Gui et al. All rights reserved. Dynamical Jumps in a Shape Memory Alloy Oscillator Mon, 18 Aug 2014 07:38:00 +0000 http://www.hindawi.com/journals/sv/2014/656212/ The dynamical response of systems with shape memory alloy (SMA) elements presents a rich behavior due to their intrinsic nonlinear characteristic. SMA’s nonlinear response is associated with both adaptive dissipation related to hysteretic behavior and huge changes in properties caused by phase transformations. These characteristics are attracting much technological interest in several scientific and engineering fields, varying from medical to aerospace applications. An important characteristic associated with dynamical response of SMA system is the jump phenomenon. Dynamical jumps result in abrupt changes in system behavior and its analysis is essential for a proper design of SMA systems. This paper discusses the nonlinear dynamics of a one degree of freedom SMA oscillator presenting pseudoelastic behavior and dynamical jumps. Numerical simulations show different aspects of this kind of behavior, illustrating its importance for a proper understanding of nonlinear dynamics of SMA systems. H. S. Oliveira, A. S. de Paula, and M. A. Savi Copyright © 2014 H. S. Oliveira et al. All rights reserved. Design of Hybrid Dynamic Balancer and Vibration Absorber Sun, 17 Aug 2014 06:25:19 +0000 http://www.hindawi.com/journals/sv/2014/397584/ This study proposed a novel hybrid dynamic balancer and vibration absorber that is cheaper than active dampers and more effective than passive dampers. The proposed damping system does not need to be altered structurally to deal with different damping targets. Rather, the proposed vibration absorber is capable of self-adjustment to the optimal damping location in order to achieve balance and, thereby, optimize damping effects. The proposed device includes a groove under the damping target with inertial mass hung from a coil spring beneath. This allows the device to bounce vertically or rotate in order to reduce vibrations in the main body. The coil spring vibration absorber can also slide along the groove in order to adjust its location continuously until the vibrations in the system are minimized and the main body is balanced. Experiments verify the efficacy of the proposed device in improving damping performance beyond what has been achieved using conventional devices. We also provide an explanation of the theoretical underpinnings of the design as well as the implications of these findings with regard to future developments. Y. R. Wang and C. Y. Lo Copyright © 2014 Y. R. Wang and C. Y. Lo. All rights reserved. Determination of Optimal Drop Height in Free-Fall Shock Test Using Regression Analysis and Back-Propagation Neural Network Sun, 17 Aug 2014 06:03:54 +0000 http://www.hindawi.com/journals/sv/2014/264728/ The primary purpose of this study is to provide methods that can be used to determine the most suitable drop height for shock testing military equipment, in an efficient and cost ineffective manner. Shock testing is widely employed to assess the performance of electronic systems, including military devices and civilian systems. Determining the height of the drop for a test item is an important step prior to performing the test. Dropping a test item from excessive height leads high G-peak values to damage the test equipment. On the other hand, dropping an item from a low height may not generate the required G-peak value and duration. Therefore, prior to performing shock tests, an optimal drop height must be established to ensure that the resulting G-peak value and duration time match the required test values. The traditional trial-and-error methods are time-consuming and cost-ineffective, often requiring many attempts. To improve the conventional approaches, this study proposes the application of regression analysis and back-propagation neural network for determining the most suitable drop height for free-fall shock tests. A new method is suggested for determining the drop test height. The results of the model are verified, using the results of a series of experiments that are conducted to verify the accuracy of the suggested approaches. The results of the study indicate that both approaches are equally effective in providing an effective guideline for performing drop tests from heights that would result in the peak Gs and duration needed for testing electronic devices. Chao-Rong Chen, Chia-Hung Wu, and Hsin-Tsrong Lee Copyright © 2014 Chao-Rong Chen et al. All rights reserved. Vibration and Instability of Rotating Composite Thin-Walled Shafts with Internal Damping Sun, 17 Aug 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/123271/ The dynamical analysis of a rotating thin-walled composite shaft with internal damping is carried out analytically. The equations of motion are derived using the thin-walled composite beam theory and the principle of virtual work. The internal damping of shafts is introduced by adopting the multiscale damping analysis method. Galerkin’s method is used to discretize and solve the governing equations. Numerical study shows the effect of design parameters on the natural frequencies, critical rotating speeds, and instability thresholds of shafts. Ren Yongsheng, Zhang Xingqi, Liu Yanghang, and Chen Xiulong Copyright © 2014 Ren Yongsheng et al. All rights reserved. Numerical Simulation of Vertical Random Vibration of Train-Slab Track-Bridge Interaction System by PEM Tue, 12 Aug 2014 12:07:45 +0000 http://www.hindawi.com/journals/sv/2014/304219/ The paper describes the numerical simulation of the vertical random vibration of train-slab track-bridge interaction system by means of finite element method and pseudoexcitation method. Each vehicle is modeled as four-wheelset mass-spring-damper system with two-layer suspension systems. The rail, slab, and bridge girder are modeled by three-layer elastic Bernoulli-Euler beams connected with each other by spring and damper elements. The equations of motion for the entire system are derived according to energy principle. By regarding rail irregularity as a series of multipoint, different-phase random excitations, the random load vectors of the equations of motion are obtained by pseudoexcitation method. Taking a nine-span simply supported beam bridge traveled by a train consisting of 8 vehicles as an example, the vertical random vibration responses of the system are investigated. Firstly, the suitable number of discrete frequencies of rail irregularity is obtained by numerical experimentations. Secondly, the reliability and efficiency of pseudoexcitation method are verified through comparison with Monte Carlo method. Thirdly, the random vibration characteristics of train-slab track-bridge interaction system are analyzed by pseudoexcitation method. Finally, applying the 3σ rule for Gaussian stochastic process, the maximum responses of train-slab track-bridge interaction system with respect to various train speeds are studied. Zhi-ping Zeng, Zhi-wu Yu, Yan-gang Zhao, Wen-tao Xu, Ling-kun Chen, and Ping Lou Copyright © 2014 Zhi-ping Zeng et al. All rights reserved. Vibration Mitigation without Dissipative Devices: First Large-Scale Testing of a State Switched Inducer Tue, 12 Aug 2014 11:38:55 +0000 http://www.hindawi.com/journals/sv/2014/135767/ A new passive device for mitigating cable vibrations is proposed and its efficiency is assessed on 45-meter long taut cables through a series of free and forced vibration tests. It consists of a unilateral spring attached perpendicularly to the cable near the anchorage. Because of its ability to change the cable dynamic behaviour through intermittent activation, the device has been called state switched inducer (SSI). The cable behaviour is shown to be deeply modified by the SSI: the forced vibration response is anharmonicc and substantially reduced in amplitude whereas the free vibration decay is largely sped up through a beating phenomenon. The vibration mitigation effect is mainly due to the activation and coupling of various vibration modes, as evidenced in the response spectra of the equipped cable. This first large-scale experimental campaign shows that the SSI outperforms classical passive devices, thus paving the way to a new kind of low-cost vibration mitigation systems which do not rely on dissipation. Daniel Tirelli Copyright © 2014 Daniel Tirelli. All rights reserved. Mobility Matrix of a Thin Circular Plate Carrying Concentrated Masses Based on Transverse Vibration Solution Thu, 07 Aug 2014 06:44:52 +0000 http://www.hindawi.com/journals/sv/2014/284367/ When calculating the vibration or sound power of a vibration source, it is necessary to know the point mobility of the supporting structure. A new method is presented for the calculation of point mobility matrix of a thin circular plate with concentrated masses in this paper. Transverse vibration mode functions are worked out by utilizing the structural circumferential periodicity of the inertia excitation produced by the concentrated masses. The numerical vibratory results, taking the clamped case as an instance, are compared to the published ones to validate the method for ensuring the correctness of mobility solution. Point mobility matrix, including the driving and transfer point mobility, of the titled structure is computed based on the transverse vibration solution. After that, effect of the concentrated masses on the mechanical point mobility characteristics is analyzed. Desheng Li and Junhong Zhang Copyright © 2014 Desheng Li and Junhong Zhang. All rights reserved. 3 DOF Spherical Pendulum Oscillations with a Uniform Slewing Pivot Center and a Small Angle Assumption Mon, 04 Aug 2014 07:32:27 +0000 http://www.hindawi.com/journals/sv/2014/203709/ The present paper addresses the derivation of a 3 DOF mathematical model of a spherical pendulum attached to a crane boom tip for uniform slewing motion of the crane. The governing nonlinear DAE-based system for crane boom uniform slewing has been proposed, numerically solved, and experimentally verified. The proposed nonlinear and linearized models have been derived with an introduction of Cartesian coordinates. The linearized model with small angle assumption has an analytical solution. The relative and absolute payload trajectories have been derived. The amplitudes of load oscillations, which depend on computed initial conditions, have been estimated. The dependence of natural frequencies on the transport inertia forces and gravity forces has been computed. The conservative system, which contains first time derivatives of coordinates without oscillation damping, has been derived. The dynamic analogy between crane boom-driven payload swaying motion and Foucault’s pendulum motion has been grounded and outlined. For a small swaying angle, good agreement between theoretical and averaged experimental results was obtained. Alexander V. Perig, Alexander N. Stadnik, Alexander I. Deriglazov, and Sergey V. Podlesny Copyright © 2014 Alexander V. Perig et al. All rights reserved. Vibration and Modal Analysis of Low Earth Orbit Satellite Sun, 03 Aug 2014 06:27:47 +0000 http://www.hindawi.com/journals/sv/2014/740102/ This paper presents design, modeling, and analysis of satellite model used for remote sensing. A detailed study is carried out for the design and modeling of the satellite structure focusing on the factors such as the selection of material, optimization of shape and geometry, and accommodation of different subsystems and payload. The center of mass is required to be kept within the range of (1-2) cm from its geometric center. Once the model is finalized it is required to be analyzed by the use of Ansys, a tool for finite element analysis (FEA) under given loading and boundary conditions. Static, modal, and harmonic analyses in Ansys are performed at the time of ground testing and launching phase. The finite element analysis results are also validated and compared with the theoretical predictions. These analyses are quite helpful and suggest that the satellite structure does not fail and retains its structural integrity during launch environment. Asif Israr Copyright © 2014 Asif Israr. All rights reserved. A Numerical Study for Flow Excitation and Performance of Rampressor Inlet considering Rotor Motion Thu, 24 Jul 2014 07:04:15 +0000 http://www.hindawi.com/journals/sv/2014/963234/ A unique supersonic compressor rotor with high pressure ratio, termed the Rampressor, is presented by Ramgen Power Systems, Inc. (RPS). In order to obtain the excitation characteristic and performance of Rampressor inlet flow field under external excitation, compression inlet flow of Rampressor is studied with considering Rampressor rotor whirling. Flow excitation characteristics and performance of Rampressor inlet are analyzed under different frequency and amplitude of Rampressor rotor whirling. The results indicate that the rotor whirling has a significant effect for flow excitation characteristics and performance of Rampressor inlet. The effect of rotor whirling on the different inlet location excitation has a definite phase difference. Inlet excitation becomes more complex along with the inlet flow path. More frequency components appear in the excitation spectrum of Rampressor inlet with considering Rampressor rotor whirling. The main frequency component is the fundamental frequency, which is caused by the rotor whirling. Besides the fundamental frequency, the double frequency components are generated due to the coupling between inlet compression flow of Rampressor rotor and rotor whirling, especially in the subsonic diffuser of Rampressor rotor inlet. With the increment of rotor whirling frequency and whirling amplitude, the complexity of Rampressor inlet excitation increases, and the stability of Rampressor inlet performance deteriorates. Weijia Kang, Zhansheng Liu, Jiangbo Lu, Yu Wang, and Yanyang Dong Copyright © 2014 Weijia Kang et al. All rights reserved. Influence of the Wave Form on the Material Response Delay Thu, 24 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/538127/ To model damping effects in structural dynamics, the literature provides a wide range of alternatives. The different models claim different advantages and fields of use where they are useful but, in the end, the compliance of the model with the experimental results, within a given tolerance, is the ultimate criterion for assessing its quality. In the present paper, the behaviour of a simple steel specimen is studied, taking as a focus the time response of the material. Since the harmonic response is well established, the authors propose to submit the specimen to a trapezoidal periodic load and study the behaviour of the response to the load changes. A simple setup was used, using a steel specimen loaded in the linear regime. A carefull test procedure was carried out in order to characterize the dissipation in a quasi-static periodic load. The experimental results show that the response delay to a ramp load depends on the durations of both the previous flat and the ramp itself. J. R. Azinheira, L. Reis, and A. M. R. Ribeiro Copyright © 2014 J. R. Azinheira et al. All rights reserved. A Simplified Flexible Multibody Dynamics for a Main Landing Gear with Flexible Leaf Spring Wed, 23 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/595964/ The dynamics of multibody systems with deformable components has been a subject of interest in many different fields such as machine design and aerospace. Traditional rigid-flexible systems often take a lot of computer resources to get accurate results. Accuracy and efficiency of computation have been the focus of this research in satisfying the coupling of rigid body and flex body. The method is based on modal analysis and linear theory of elastodynamics: reduced modal datum was used to describe the elastic deformation which was a linear approximate of the flexible part. Then rigid-flexible multibody system was built and the highly nonlinearity of the mass matrix caused by the limited rotation of the deformation part was approximated using the linear theory of elastodynamics. The above methods were used to establish the drop system of the leaf spring type landing gear of a small UAV. Comparisons of the drop test and simulation were applied. Results show that the errors caused by the linear approximation are acceptable, and the simulation process is fast and stable. Zhi-Peng Xue, Ming Li, Yan-Hui Li, and Hong-Guang Jia Copyright © 2014 Zhi-Peng Xue et al. All rights reserved. A Numerical Study on the Performance of Nonlinear Models of a Microvibration Isolator Tue, 22 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/531013/ A non-Newton fluid microvibration isolator is studied in this paper and several nonlinear models are firstly presented to characterize its vibration behaviors due to the complicated effects of internal structure, external excitation, and fluid property. On the basis of testing hysteretic loops, the generalized pattern search (GPS) algorithm of MATLAB optimization toolbox is used to identify the model parameters. With the use of the fourth-order Runge-Kutta method, the performance of these nonlinear models is further estimated. The results show that, in the cases of force excitation (FE), the generalized nonlinear model (GNM) and the complicated model (CM) can properly characterize the physical vibration in the frequency band of 5–20 Hz. However, in the frequency band of 30–200 Hz, the Maxwell model shows more excellent performance. After the application of orthogonal testing method, several important factors, for example, damping coefficient and flow index, are obtained; then a parametric analysis is carried out with the purpose of further studying the influences of nonlinear model parameters. It can be seen that only the GNM and CM can consider the above nonlinear effects in both the FE cases and the foundation displacement excitation (FDE) cases, but the CM is not convenient to use in practice. Jie Wang, Shougen Zhao, and Dafang Wu Copyright © 2014 Jie Wang et al. All rights reserved. A Novel Double-Piston Magnetorheological Damper for Space Truss Structures Vibration Suppression Tue, 22 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/864765/ The design, fabrication, and testing of a new double-piston MR damper for space applications are discussed. The design concept for the damper is described in detail. The electromagnetic analysis of the design and the fabrication of the MR damper are also presented. The design analysis shows that the damper meets the weight and size requirements for being included in a space truss structure. The prototype design is tested in a damper dynamometer. The test results show that the damper can provide nearly 80 N of damping force at its maximum velocity and current. The test results also show that the seal drag could contribute significantly to the damping forces. Additionally, the test results indicate that both the work by the damper and damping force increase rapidly with increasing current at lower currents and taper off at higher currents as the damper starts to saturate. The damper force versus velocity plots show hysteresis in both pre- and postyield regions and asymmetric forces in jounce and rebound. A model is proposed for representing the force-displacement, force-velocity, and asymmetric forces observed in test results. A comparison of the modeling results and test data indicates that the model accurately represents the force characteristics of the damper. Qiang Wang, Mehdi Ahmadian, and Zhaobo Chen Copyright © 2014 Qiang Wang et al. All rights reserved. A Contrast on Conductor Galloping Amplitude Calculated by Three Mathematical Models with Different DOFs Mon, 21 Jul 2014 09:41:15 +0000 http://www.hindawi.com/journals/sv/2014/781304/ It is pivotal to find an effective mathematical model revealing the galloping mechanism. And it is important to compare the difference between the existing mathematical models on the conductor galloping. In this paper, the continuum cable model for transmission lines was proposed using the Hamilton principle. Discrete models of one DOF, two DOFs, and three DOFs were derived from the continuum model by using the Garlekin method. And the three models were compared by analyzing the galloping vertical amplitude and torsional angle with different influence factors. The influence factors include wind velocity, flow density, span length, damping ratio, and initial tension. The three-DOF model is more accurate at calculating the galloping characteristics than the other two models, but the one-DOF and two-DOF models can also present the trend of galloping amplitude change from the point view of qualitative analysis. And the change of the galloping amplitude relative to the main factors was also obtained, which is very essential to the antigalloping design applied in the actual engineering. Bin Liu, KuanJun Zhu, XiaoQin Sun, Bing Huo, and XiJun Liu Copyright © 2014 Bin Liu et al. All rights reserved. Spatial Information in Autonomous Modal Parameter Estimation Thu, 17 Jul 2014 10:30:03 +0000 http://www.hindawi.com/journals/sv/2014/404132/ Recent work with autonomous modal parameter estimation has shown great promise in the quality of the modal parameter estimation results when compared to results from traditional methods by experienced users. While autonomous modal parameter estimation means slightly different things to different researchers and practitioners, for the purpose of this discussion, autonomous will require an automated procedure which sorts and processes a large number of possible modal parameter solutions to yield one consistent estimate with no user interaction after initial thresholds are chosen. In the work discussed, this final, consistent set of modal parameters is identifiable due to the combination of temporal and spatial information in a domain state vector of relatively high order (5–10). Since this domain state vector has both complex modal frequency and modal vector information as embedded content, sorting consistent estimates from the multitude of possible solutions is relatively trivial. Because this domain state vector can be developed from the results of any modal parameter estimation method, possible solutions from different traditional methods can be utilized in the autonomous procedure to yield one consistent set of modal parameters. Randall J. Allemang and Allyn W. Phillips Copyright © 2014 Randall J. Allemang and Allyn W. Phillips. All rights reserved. Reduction of Structural Vibrations by Passive and Semiactively Controlled Friction Dampers Thu, 17 Jul 2014 10:00:59 +0000 http://www.hindawi.com/journals/sv/2014/870564/ Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines, and increasing structure durability. Besides optimization of the mechanical design or various types of passive damping treatments, active structural vibration control concepts are efficient means to reduce unwanted vibrations. In this contribution, two different semiactive control concepts for vibration reduction are proposed that adapt to the normal force of attached friction dampers. Thereby, semiactive control concepts generally possess the advantage over active control in that the closed loop is intrinsically stable and that less energy is required for the actuation than in active control. In the chosen experimental implementation, a piezoelectric stack actuator is used to apply adjustable normal forces between a structure and an attached friction damper. Simulation and experimental results of a benchmark structure with passive and semiactively controlled friction dampers are compared for stationary narrowband excitation. For simulations of the control performance, transient simulations must be employed to predict the achieved vibration damping. It is well known that transient simulation of systems with friction and normal contact requires excessive computational power due to the nonlinear constitutive laws and the high contact stiffnesses involved. However, commercial finite-element codes do not allow simulating feedback control in a general way. As a remedy, a special simulation framework is developed which allows efficiently modeling interfaces with friction and normal contact by appropriate constitutive laws which are implemented by contact elements in a finite-element model. Furthermore, special model reduction techniques using a substructuring approach are employed for faster simulation. L. Gaul and J. Becker Copyright © 2014 L. Gaul and J. Becker. All rights reserved. Free-Interface Modal Synthesis Based Substructural Damage Detection Method Tue, 15 Jul 2014 09:58:43 +0000 http://www.hindawi.com/journals/sv/2014/741697/ Free-interface modal synthesis method is applied to civil structure, and a substructure method is proposed by introducing the method into global sensitivity method. The substructure expression of the derivatives of eigenvalues and eigenvectors with respect to elemental parameters is obtained. The accuracy of the application of free-interface modal synthesis method is evaluated with different retained modes in substructure, and then the effectiveness of the proposed substructure sensitivity method is illustrated through an 11-storey building under both single- and multidamage cases. Both the damage locations and the extent can be effectively identified. By comparing it with the identical results of global sensitivity method, the proposed method can be faster in detecting the damage location and more stable under multidamage cases. Since this substructure sensitivity method only needs to update sensitivity matrix in the substructure with relative small number of DOFs, it may save much computation effort and become more efficient. Shanghong Chen, Wei Lin, Jiexin Yu, and Ai Qi Copyright © 2014 Shanghong Chen et al. All rights reserved. Chaotic Motions of the Duffing-Van der Pol Oscillator with External and Parametric Excitations Tue, 15 Jul 2014 09:34:48 +0000 http://www.hindawi.com/journals/sv/2014/131637/ The chaotic motions of the Duffing-Van der Pol oscillator with external and parametric excitations are investigated both analytically and numerically in this paper. The critical curves separating the chaotic and nonchaotic regions are obtained. The chaotic feature on the system parameters is discussed in detail. Some new dynamical phenomena including the controllable frequency are presented for this system. Numerical results are given, which verify the analytical ones. Liangqiang Zhou and Fangqi Chen Copyright © 2014 Liangqiang Zhou and Fangqi Chen. All rights reserved. Fully Equipped Dynamic Model of a Bus Tue, 15 Jul 2014 07:45:32 +0000 http://www.hindawi.com/journals/sv/2014/201952/ Nowadays, the time to market a new vehicle is crucial for every company as it is easier to meet the customers’ needs and expectations. However, designing a new vehicle is a long process which needs to take into account different performances. The most difficult is to predict a dynamic behavior of a vehicle especially when such a big vehicles as urban buses are considered. Therefore, there is a necessity to use a virtual model to investigate different performances. However, there is a lack of urban bus models that can fully reflect a dynamic behavior of the bus. This paper presents a fully equipped urban bus model which can be used to study a dynamic behavior of such vehicles. The model is based on innovative technique called cosimulation, which connects different modeling techniques (3D and 1D). Such a technique allows performing different analyses that require small deformations and large translations and rotations in shorter time and automatic way. The work has been carried out in a project EUREKA CHASING. I. Kowarska, J. Korta, K. Kuczek, and T. Uhl Copyright © 2014 I. Kowarska et al. All rights reserved. Developing Dynamic Digital Image Correlation Technique to Monitor Structural Damage of Old Buildings under External Excitation Tue, 15 Jul 2014 06:49:57 +0000 http://www.hindawi.com/journals/sv/2014/954840/ The capacity of buildings to resist external excitation is an important factor to consider for the structural design of buildings. When subject to external excitation, a building may suffer a certain degree of damages, and its residual capacity to resist external excitation cannot be evaluated. In this research, dynamic digital image correlation method combined with parameter evaluation available in system identification is used to evaluate the structural capacity to resist external excitation. The results reveal possible building latent safety problems so that timely structural reinforcement or dismantling of the building can be initiated to alleviate further damages. The results of experiments using the proposed method conform to the results obtained using the conventional method, but this method is more convenient and rapid than the latter in the subsequent procedure of data processing. If only the frequency change is used, the damages suffered by the building can be detected, but the damage location is not revealed. The interstory drift mode shape (IDMS) based on the characteristic of story drift has higher sensitivity than the approximate story damage index (ADSI) method based on modal frequency and vibration type; however, both indices can be used to determine the degree and location of building damages. Ming-Hsiang Shih and Wen-Pei Sung Copyright © 2014 Ming-Hsiang Shih and Wen-Pei Sung. All rights reserved. On the Seismic Response of Protected and Unprotected Middle-Rise Steel Frames in Far-Field and Near-Field Areas Tue, 15 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/393870/ Several steel moment-resisting framed buildings were seriously damaged during Northridge (1994); Kobe (1995); Kocaeli, Turkey (1999), earthquakes. Indeed, for all these cases, the earthquake source was located under the urban area and most victims were in near-field areas. In fact near-field ground motions show velocity and displacement peaks higher than far-field ones. Therefore, the importance of considering near-field ground motion effects in the seismic design of structures is clear. This study analyzes the seismic response of five-story steel moment-resisting frames subjected to Loma Prieta (1989) earthquake—Gilroy (far-field) register and Santa Cruz (near-field) register. The design of the frames verifies all the resistance and stability Eurocodes’ requirements and the first mode has been determined from previous shaking-table tests. In the frames two diagonal braces are installed in different positions. Therefore, ten cases with different periods are considered. Also, friction dampers are installed in substitution of the braces. The behaviour of the braced models under the far-field and the near-field records is analysed. The responses of the aforementioned frames equipped with friction dampers and subjected to the same ground motions are discussed. The maximum response of the examined model structures with and without passive dampers is analysed in terms of damage indices, acceleration amplification, base shear, and interstory drifts. Dora Foti Copyright © 2014 Dora Foti. All rights reserved. Updating Finite Element Model of a Wind Turbine Blade Section Using Experimental Modal Analysis Results Tue, 15 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/684786/ This paper presents selected results and aspects of the multidisciplinary and interdisciplinary research oriented for the experimental and numerical study of the structural dynamics of a bend-twist coupled full scale section of a wind turbine blade structure. The main goal of the conducted research is to validate finite element model of the modified wind turbine blade section mounted in the flexible support structure accordingly to the experimental results. Bend-twist coupling was implemented by adding angled unidirectional layers on the suction and pressure side of the blade. Dynamic test and simulations were performed on a section of a full scale wind turbine blade provided by Vestas Wind Systems A/S. The numerical results are compared to the experimental measurements and the discrepancies are assessed by natural frequency difference and modal assurance criterion. Based on sensitivity analysis, set of model parameters was selected for the model updating process. Design of experiment and response surface method was implemented to find values of model parameters yielding results closest to the experimental. The updated finite element model is producing results more consistent with the measurement outcomes. Marcin Luczak, Simone Manzato, Bart Peeters, Kim Branner, Peter Berring, and Maciej Kahsin Copyright © 2014 Marcin Luczak et al. All rights reserved. Free Vibration Analysis of Moderately Thick Rectangular Plates with Variable Thickness and Arbitrary Boundary Conditions Mon, 14 Jul 2014 09:46:29 +0000 http://www.hindawi.com/journals/sv/2014/572395/ A generalized Fourier series solution based on the first-order shear deformation theory is presented for the free vibrations of moderately thick rectangular plates with variable thickness and arbitrary boundary conditions, a class of problem which is of practical interest and fundamental importance but rarely attempted in the literatures. Unlike in most existing studies where solutions are often developed for a particular type of boundary conditions, the current method can be generally applied to a wide range of boundary conditions with no need of modifying solution algorithms and procedures. Under the current framework, the one displacement and two rotation functions are generally sought, regardless of boundary conditions, as an improved trigonometric series in which several supplementary functions are introduced to remove the potential discontinuities with the displacement components and its derivatives at the edges and to accelerate the convergence of series representations. All the series expansion coefficients are treated as the generalized coordinates and solved using the Rayleigh-Ritz technique. The effectiveness and reliability of the presented solution are demonstrated by comparing the present results with those results published in the literatures and finite element method (FEM) data, and numerous new results for moderately thick rectangular plates with nonuniform thickness and elastic restraints are presented, which may serve as benchmark solution for future researches. Dongyan Shi, Qingshan Wang, Xianjie Shi, and Fuzhen Pang Copyright © 2014 Dongyan Shi et al. All rights reserved. Analysis of Critical Velocities for an Infinite Timoshenko Beam Resting on an Elastic Foundation Subjected to a Harmonic Moving Load Mon, 14 Jul 2014 09:25:15 +0000 http://www.hindawi.com/journals/sv/2014/848536/ Critical velocities are investigated for an infinite Timoshenko beam resting on a Winkler-type elastic foundation subjected to a harmonic moving load. The determination of critical velocities ultimately comes down to discrimination of the existence of multiple real roots of an algebraic equation with real coefficients of the 4th degree, which can be solved by employing Descartes sign method and complete discrimination system for polynomials. Numerical calculations for the European high-speed rail show that there are at most four critical velocities for an infinite Timoshenko beam, which is very different from those gained by others. Furthermore, the shear wave velocity must be the critical velocity, but the longitudinal wave velocity is not possible under certain conditions. Further numerical simulations indicate that all critical velocities are limited to be less than the longitudinal wave velocity no matter how large the foundation stiffness is or how high the loading frequency is. Additionally, our study suggests that the maximum value of one group velocity of waves in Timoshenko beam should be one “dangerous” velocity for the moving load in launching process, which has never been referred to in previous work. Bin Zhen, Wei Luo, and Jian Xu Copyright © 2014 Bin Zhen et al. All rights reserved. Optimization of Sound Transmission Loss through a Thin Functionally Graded Material Cylindrical Shell Mon, 14 Jul 2014 07:39:07 +0000 http://www.hindawi.com/journals/sv/2014/814682/ The maximizing of sound transmission loss (TL) across a functionally graded material (FGM) cylindrical shell has been conducted using a genetic algorithm (GA). To prevent the softening effect from occurring due to optimization, the objective function is modified based on the first resonant frequency. Optimization is performed over the frequency range 1000–4000 Hz, where the ear is the most sensitive. The weighting constants are chosen here to correspond to an A-weighting scale. Since the weight of the shell structure is an important concern in most applications, the weight of the optimized structure is constrained. Several traditional materials are used and the result shows that optimized shells with aluminum-nickel and aluminum-steel FGM are the most effective at maximizing TL at both stiffness and mass control region, while they have minimum weight. Ali Nouri and Sohrab Astaraki Copyright © 2014 Ali Nouri and Sohrab Astaraki. All rights reserved. On the Vibration of Single-Walled Carbon Nanocones: Molecular Mechanics Approach versus Molecular Dynamics Simulations Mon, 14 Jul 2014 07:26:39 +0000 http://www.hindawi.com/journals/sv/2014/410783/ The vibrational behavior of single-walled carbon nanocones is studied using molecular structural method and molecular dynamics simulations. In molecular structural approach, point mass and beam elements are employed to model the carbon atoms and the connecting covalent bonds, respectively. Single-walled carbon nanocones with different apex angles are considered. Besides, the vibrational behavior of nanocones under various types of boundary conditions is studied. Predicted natural frequencies are compared with the existing results in the literature and also with the ones obtained by molecular dynamics simulations. It is found that decreasing apex angle and the length of carbon nanocone results in an increase in the natural frequency. Comparing the vibrational behavior of single-walled carbon nanocones under different boundary conditions shows that the effect of end condition on the natural frequency is more prominent for nanocones with smaller apex angles. R. Ansari, A. Momen, S. Rouhi, and S. Ajori Copyright © 2014 R. Ansari et al. All rights reserved. Investigation of Seismic Behavior of Container Crane Structures by Shake Table Tests and Mathematical Modeling Sun, 13 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/sv/2014/682647/ This paper is concerned with the verification of mathematical modeling of the container cranes under earthquake loadings with shake table test results. Comparison of the shake table tests with the theoretical studies has an important role in the estimation of the seismic behavior of the engineering structures. For this purpose, a new shake table and mathematical model were developed. Firstly, a new physical model is directly fixed on the shake table and the seismic response of the container crane model against the past earthquake ground motion was measured. Secondly, a four degrees-of-freedom mathematical model is developed to understand the dynamic behaviour of cranes under the seismic loadings. The results of the verification study indicate that the developed mathematical model reasonably represents the dynamic behaviour of the crane structure both in time and frequency domains. The mathematical model can be used in active-passive vibration control studies to decrease structural vibrations on container cranes. C. Oktay Azeloglu, Ayse Edincliler, and Ahmet Sagirli Copyright © 2014 C. Oktay Azeloglu et al. All rights reserved. International Conference on Acoustics and Vibration 2012 Thu, 10 Jul 2014 07:05:18 +0000 http://www.hindawi.com/journals/sv/2014/340285/ Hamid Mehdigholi, Hamid Ahmadian, and Abdolreza Ohadi Copyright © 2014 Hamid Mehdigholi et al. All rights reserved.