Shock and Vibration The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Energy-Based Optimal Ranking of the Interior Modes for Reduced-Order Models under Periodic Excitation Tue, 24 Nov 2015 12:02:00 +0000 This paper introduces a novel method for ranking and selecting the interior modes to be retained in the Craig-Bampton model reduction, in the case of linear vibrating systems under periodic excitation. The aim of the method is to provide an effective ranking of such modes and hence an optimal sequence according to which the interior modes should be progressively included to achieve a desired accuracy of the reduced-order model at the frequencies of interest, while keeping model dimensions to a minimum. An energy-based ranking (EBR) method is proposed, which exploits analytical coefficients to evaluate the contribution of each interior mode to the forced response of the full-order system. The application of the method to two representative systems is discussed: an ultrasonic horn and a vibratory feeder. The results show that the EBR method provides a very effective ranking of the most important interior modes and that it outperforms other state-of-the-art benchmark techniques. Ilaria Palomba, Dario Richiedei, and Alberto Trevisani Copyright © 2015 Ilaria Palomba et al. All rights reserved. Study on Fluid-Lining-Rock Coupling Interaction of Diversion Tunnel under Seismic Load Mon, 23 Nov 2015 09:26:02 +0000 Fluid-lining-rock coupling interaction of diversion tunnel under seismic load is a critical problem in seismic research which should be solved urgently. Based on the explicit finite element method for dynamic analysis of single-phase fluid and solid medium and combining with the boundary conditions of coupling interface, a dynamic explicit finite element solving format of diversion tunnel considering fluid-lining coupling interaction is established. In light of the basic theory of dynamic contact force method and applying the nonlinear hyperbolic constitutive model of contact surface, a dynamic explicit finite element time-domain integral equation of combined bearing of lining and surrounding rocks, which takes the bond-slip behavior of the contact surface into account, is put forward. Meanwhile, considering the dynamic interaction process of inner water and lining, lining and surrounding rocks, an explicit finite element numerical simulation analysis method of fluid-lining-rock coupling interaction of diversion tunnel under seismic load is presented. The calculation results of case study reasonably reflect the seismic response characteristics of diversion tunnel, and an effective analysis method is provided for the aseismic design of hydraulic tunnel. Jian Deng, Ming Xiao, Juntao Chen, Bingbing Xie, and Yang Yang Copyright © 2015 Jian Deng et al. All rights reserved. Effects of a Group of High-Rise Structures on Ground Motions under Seismic Excitation Mon, 23 Nov 2015 08:40:05 +0000 A three-dimensional simulation was created to determine the seismic performance of coupled systems with a group of up to 100 pile-high-rise structures resting on soil layers using system modal, harmonic, and time domain analysis. The results demonstrated that the existence of a structural group mitigates the structural responses with respect to the single-structure-soil interaction (SSI) and results in significantly nonuniform ground seismic motions. Due to the influence of a structural group, adjacent structures can exhibit fully alternating mechanical behavior, and buildings in the urban fringe are subjected to stronger shaking than downtown buildings. The overall trend of the influence of structural groups is that ground motions are lessened inside an urban area, and ground motions at the locations between structures differ from those at the locations of the structures. Moreover, the effective distance of a structural group on ground motions is associated with the urban width. Less distance between structures enhances the interaction effect. In addition, the soil properties can greatly influence the system’s seismic responses and can even completely change the effect trends. The results in our paper are consistent with the phenomena observed in the Mexico City earthquake and the 1976 earthquake in Friuli, Italy. Qing-jun Chen and Wen-ting Li Copyright © 2015 Qing-jun Chen and Wen-ting Li. All rights reserved. Design and Experimental Implementation of a Beam-Type Twin Dynamic Vibration Absorber for a Cantilevered Flexible Structure Carrying an Unbalanced Rotor: Numerical and Experimental Observations Mon, 23 Nov 2015 07:32:25 +0000 This paper presents experimental and numerical results about the effectiveness of a beam-type twin dynamic vibration absorber for a cantilevered flexible structure carrying an unbalanced rotor. An experimental laboratory prototype setup has been built and implemented in our laboratory and numerical investigations have been performed through finite element analysis. The proposed system design consists of a primary cantilevered flexible structure with an attached dual-mass cantilevered secondary dynamic vibration absorber arrangement. In addition, an unbalanced rotor system is attached to the tip of the flexible cantilevered structure to inspect the system response under harmonic excitations. Numerical findings and experimental observations have revealed that significant vibration reductions are possible with the proposed dual-mass, cantilevered dynamic vibration absorber on a flexible cantilevered platform carrying an unbalanced rotor system at its tip. The proposed system is efficient and it can be practically tuned for variety of design and operating conditions. The designed setup and the results in this paper can serve for practicing engineers, researchers and can be used for educational purposes. Abdullah Özer, Mojtaba Ghodsi, Akio Sekiguchi, Ashraf Saleem, and Mohammed Nasser Al-Sabari Copyright © 2015 Abdullah Özer et al. All rights reserved. Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology Mon, 23 Nov 2015 06:54:31 +0000 Novel accelerated random vibration fatigue test methodology and strategy are proposed, which can generate a design of the experimental test plan significantly reducing the test time and the sample size. Based on theoretical analysis and fatigue damage model, several groups of random vibration fatigue tests were designed and conducted with the aim of investigating effects of both Gaussian and non-Gaussian random excitation on the vibration fatigue. First, stress responses at a weak point of a notched specimen structure were measured under different base random excitations. According to the measured stress responses, the structural fatigue lives corresponding to the different vibrational excitations were predicted by using the WAFO simulation technique. Second, a couple of destructive vibration fatigue tests were carried out to validate the accuracy of the WAFO fatigue life prediction method. After applying the proposed experimental and numerical simulation methods, various factors that affect the vibration fatigue life of structures were systematically studied, including root mean squares of acceleration, power spectral density, power spectral bandwidth, and kurtosis. The feasibility of WAFO for non-Gaussian vibration fatigue life prediction and the use of non-Gaussian vibration excitation for accelerated fatigue testing were experimentally verified. Yu Jiang, Gun Jin Yun, Li Zhao, and Junyong Tao Copyright © 2015 Yu Jiang et al. All rights reserved. Cyclostationary Analysis for Gearbox and Bearing Fault Diagnosis Mon, 23 Nov 2015 06:03:47 +0000 Gearbox and rolling element bearing vibration signals feature modulation, thus being cyclostationary. Therefore, the cyclic correlation and cyclic spectrum are suited to analyze their modulation characteristics and thereby extract gearbox and bearing fault symptoms. In order to thoroughly understand the cyclostationarity of gearbox and bearing vibrations, the explicit expressions of cyclic correlation and cyclic spectrum for amplitude modulation and frequency modulation (AM-FM) signals are derived, and their properties are summarized. The theoretical derivations are illustrated and validated by gearbox and bearing experimental signal analyses. The modulation characteristics caused by gearbox and bearing faults are extracted. In faulty gearbox and bearing cases, more peaks appear in cyclic correlation slice of 0 lag and cyclic spectrum, than in healthy cases. The gear and bearing faults are detected by checking the presence or monitoring the magnitude change of peaks in cyclic correlation and cyclic spectrum and are located according to the peak cyclic frequency locations or sideband frequency spacing. Zhipeng Feng and Fulei Chu Copyright © 2015 Zhipeng Feng and Fulei Chu. All rights reserved. Feature Extraction of Faulty Rolling Element Bearing under Variable Rotational Speed and Gear Interferences Conditions Sun, 22 Nov 2015 14:20:31 +0000 In the field of rolling element bearing fault diagnosis, variable rotational speed and gear noise are main obstacles. Even though some effective algorithms have been proposed to solve the problems, their process is complicated and they may not work well without auxiliary equipment. So we proposed a method of faulty bearing feature extraction based on Instantaneous Dominant Meshing Multiply (IDMM) and Empirical Mode Decomposition (EMD). The new method mainly consists of three parts. Firstly, IDMM is extracted from time-frequency representation of original signal by peak searching algorithm, which can be used to substitute the bearing rotational frequency. Secondly, resampled signal is obtained by an IDMM-based resampling algorithm; then it is decomposed into a number of Intrinsic Mode Functions (IMFs) based on the EMD algorithm. Calculate kurtosis values of IMFs and an appropriate IMF with biggest kurtosis value is selected. Thirdly, the selected IMF is analyzed with envelope demodulation method which can describe the fault type of bearing. The effectiveness of the proposed method has been demonstrated by both simulated and experimental mixed signals which contain bearing and gear vibration signal. Dezun Zhao, Jianyong Li, and Weidong Cheng Copyright © 2015 Dezun Zhao et al. All rights reserved. Structural Dynamical Monitoring and Fault Diagnosis Tue, 17 Nov 2015 07:14:32 +0000 Jiawei Xiang, Yaguo Lei, Yanxue Wang, Yumin He, Changjun Zheng, and Haifeng Gao Copyright © 2015 Jiawei Xiang et al. All rights reserved. Damage Detection Technique for Cold-Formed Steel Beam Structure Based on NSGA-II Tue, 17 Nov 2015 07:04:05 +0000 Cold-formed steel is uniform in quality, suitable for mass production, and light in weight. It is widely used for both structural and nonstructural members in buildings. When it is used in a bending structural member, damage such as local buckling is considered to be more important than general steel members in terms of failure mode. However, preceding studies on damage detection did not consider the failure characteristics of cold-formed beam members. Hence, this paper proposes a damage detection technique that considers the failure mode of local buckling for a cold-formed beam member. The differences between the dynamic characteristics from vibration-based measurements and those from finite element model are set to error functions. The error functions are minimized by the optimization technique NSGA-II. In the damage detection, the location of local damage and the severity of damage are considered variables. The proposed technique was validated through a simulation of damage detection for a cold-formed steel beam structure example. Byung Kwan Oh, Se Woon Choi, and Hyo Seon Park Copyright © 2015 Byung Kwan Oh et al. All rights reserved. Identification of Incipient Damage Using High-Frequency Vibrational Responses Mon, 16 Nov 2015 16:15:15 +0000 Maosen Cao, Wiesław Ostachowicz, Gang Li, Wei Xu, and Mohammad Reza Ashoory Copyright © 2015 Maosen Cao et al. All rights reserved. Two General Architectures for Intelligent Machine Performance Degradation Assessment Mon, 16 Nov 2015 13:36:41 +0000 Markov model is of good ability to infer random events whose likelihood depends on previous events. Based on this theory, hidden Markov model serves as an extension of Markov model to present an event from observations rather than states in Markov model. Moreover, due to successful applications in speech recognition, it attracts much attention in machine fault diagnosis. This paper presents two architectures for machine performance degradation assessment, which can be used to minimize machine downtime, reduce economic loss, and improve productivity. The major difference between the two architectures is whether historical data are available to build hidden Markov models. In case studies, bearing data as well as available historical data are used to demonstrate the effectiveness of the first architecture. Then, whole life gearbox data without historical data are employed to demonstrate the effectiveness of the second architecture. The results obtained from two case studies show that the presented architectures have good abilities for machine performance degradation assessment. Yanwei Xu, Aijun Xu, and Tancheng Xie Copyright © 2015 Yanwei Xu et al. All rights reserved. Vibration Response Prediction of Plate with Particle Dampers Using Cosimulation Method Mon, 16 Nov 2015 13:17:44 +0000 The particle damping technology is a passive vibration control technique. The particle dampers (PDs) as one of the passive damping devices has found wide use in the field of aeronautical engineering, mechanical engineering, and civil engineering because it has several advantages compared with the forms of viscous damping, for example, structure simplicity, low cost, robust properties, and being effective over a wide range of frequencies. In this paper, a novelty simulation method based on multiphase flow theory (MFT) is developed to evaluate the particle damping characteristics using FEM combining DEM with COMSOL Multiphysics. First, the effects of the collisions and friction between the particles are interpreted as an equivalent nonlinear viscous damping based on MFT of gas particle. Next, the contribution of PDs is estimated as equivalent spring-damper system. Then a cantilever rectangular plate treated with PDs is introduced in a finite element model of structure system. Finally frequency response functions (FRFs) of the plate without and with particle dampers are predicted to study characteristics of the particle damping plates under forced vibration. Meanwhile, an experimental verification is performed. Simulation results are in good agreement with experiment date. It is concluded that the simulation method in this paper is valid. Dongqiang Wang and Chengjun Wu Copyright © 2015 Dongqiang Wang and Chengjun Wu. All rights reserved. Experimental and Theoretical Study on Influence of Different Charging Structures on Blasting Vibration Energy Sun, 15 Nov 2015 14:10:41 +0000 As an important parameter in blasting design, charging structure directly influences blasting effect. Due to complex conditions of this blasting and excavating engineering in Jiangsu, China, the authors carried out comparative researches with coupling structure, air-decoupling structure, and water-decoupling structure. After collecting, comparing, and analyzing produced signals on blasting vibration, the authors summarized that when proportional distances are the same, water-decoupling structure can reduce instantaneous energy of blasting vibration more effectively with more average rock fragmentation and less harm of dust. From the perspective of impedance matching, the present paper analyzed influence of charging structure on blasting vibration energy, demonstrating that impedance matching relationship between explosive and rock changes because of different charging structures. Through deducing relationship equation that meets the impedance matching of explosive and rock under different charging structures, the research concludes that when blasting rocks with high impedance, explosive with high impedance can better transmits blasting energy. Besides, when employing decoupling charging, there exists a reasonable decoupling coefficient helping realize impedance matching of explosive and rock. Wenbin Gu, Zhenxiong Wang, Jianghai Chen, Jianqing Liu, and Ming Lu Copyright © 2015 Wenbin Gu et al. All rights reserved. In Situ Measurement of Seeking Speed and Seeking Induced Head-Disk Interface Instability in Hard Disk Drives Sun, 15 Nov 2015 14:02:43 +0000 This paper investigated the instability of head-disk interface caused by the voice coil motor (VCM) end crashing the crash stop during the seeking of magnetic head. To make the whole process of that clear, an in situ measurement method based on maximum likelihood estimation and extended Kalman filter for seeking speed at component level was developed first and was then calibrated by a high speed camera. Given a crash between VCM end and crash stop that may be a consequence of the continuous increasing seeking speed, the seeking speed was carefully controlled by using our developed method to find a critical value that may induce vigorous head-disk interface instability. Acoustic emission sensor and laser Doppler vibrometer were used to capture the transient dynamic behaviors of magnetic head when the crash is happening. Damage analysis and mode identification were carried out to reveal the relationship between the damage patterns on disk surface and head dynamics. The results of this study are helpful to optimize the track seeking profile during the HDD operation, as well as the design of components such as head and head arm. Yu Wang, Xiongfei Wei, Yanyang Zi, and Kwok-Leung Tsui Copyright © 2015 Yu Wang et al. All rights reserved. A New Transmissibility Based Indicator of Local Variation in Structure and Its Application for Damage Detection Tue, 10 Nov 2015 07:26:19 +0000 The presence of damage in engineering structures could usually cause local variation in stiffness or damping, and therefore it is meaningful to detect the variation as early as possible for protecting the engineering structure from serious damage. In the study, a novel method is developed to detect and locate the local variation in stiffness and damping for structures based on transmissibility. Some important properties of transmissibility are first analytically revealed and, further, a variation detection indicator is proposed to locate the variation. The effectiveness of the proposed method is verified by numerical studies and the usefulness of it is demonstrated by application for detecting crack position in beam structures. The results show that the proposed new method has better performance than the three conventional transmissibility based methods when considering different frequency bands and noise. X. Z. Li, Z. K. Peng, X. J. Dong, W. M. Zhang, and G. Meng Copyright © 2015 X. Z. Li et al. All rights reserved. Nondestructive Damage Assessment of Composite Structures Based on Wavelet Analysis of Modal Curvatures: State-of-the-Art Review and Description of Wavelet-Based Damage Assessment Benchmark Tue, 10 Nov 2015 07:24:33 +0000 The application of composite structures as elements of machines and vehicles working under various operational conditions causes degradation and occurrence of damage. Considering that composites are often used for responsible elements, for example, parts of aircrafts and other vehicles, it is extremely important to maintain them properly and detect, localize, and identify the damage occurring during their operation in possible early stage of its development. From a great variety of nondestructive testing methods developed to date, the vibration-based methods seem to be ones of the least expensive and simultaneously effective with appropriate processing of measurement data. Over the last decades a great popularity of vibration-based structural testing has been gained by wavelet analysis due to its high sensitivity to a damage. This paper presents an overview of results of numerous researchers working in the area of vibration-based damage assessment supported by the wavelet analysis and the detailed description of the Wavelet-based Structural Damage Assessment (WavStructDamAs) Benchmark, which summarizes the author’s 5-year research in this area. The benchmark covers example problems of damage identification in various composite structures with various damage types using numerous wavelet transforms and supporting tools. The benchmark is openly available and allows performing the analysis on the example problems as well as on its own problems using available analysis tools. Andrzej Katunin Copyright © 2015 Andrzej Katunin. All rights reserved. A Comparative Study on Multiwavelet Construction Methods and Customized Multiwavelet Library for Mechanical Fault Detection Tue, 10 Nov 2015 07:23:46 +0000 Inner product transform principle reveals that the basis functions most relevant or similar to the fault features are pivotal to the meaningful fault detection. Customized multiwavelet methods and practices have continued to improve over the recent years, focused on two-scale similarity transform (TST), lifting transform (LT), and lifting scheme (LS). Due to the respective advantages and disadvantages, a comparative study on the multiwavelet construction methods by TST, symmetric and dissymmetric LT, and LS is discussed in the paper, covering the differences of construction theories, the synthetic analyses of construction strategies, and the comparison of waveform characteristics along with their applicable occasions. Comprehensively utilizing the capabilities of the construction methods, a novel customized multiwavelet library is established for the accurate fault detection. The proposed method is applied to incipient fault detection of rolling bearing for electric locomotive to verify the effectiveness and feasibility. Jing Yuan, Chenjun Wei, Bo Zou, Jun Zhu, Ying Wei, Yanyang Zi, and Yu Zhou Copyright © 2015 Jing Yuan et al. All rights reserved. Enhanced DET-Based Fault Signature Analysis for Reliable Diagnosis of Single and Multiple-Combined Bearing Defects Tue, 10 Nov 2015 07:22:25 +0000 To early identify cylindrical roller bearing failures, this paper proposes a comprehensive bearing fault diagnosis method, which consists of spectral kurtosis analysis for finding the most informative subband signal well representing abnormal symptoms about the bearing failures, fault signature calculation using this subband signal, enhanced distance evaluation technique- (EDET-) based fault signature analysis that outputs the most discriminative fault features for accurate diagnosis, and identification of various single and multiple-combined cylindrical roller bearing defects using the simplified fuzzy adaptive resonance map (SFAM). The proposed comprehensive bearing fault diagnosis methodology is effective for accurate bearing fault diagnosis, yielding an average classification accuracy of 90.35%. In this paper, the proposed EDET specifically addresses shortcomings in the conventional distance evaluation technique (DET) by accurately estimating the sensitivity of each fault signature for each class. To verify the efficacy of the EDET-based fault signature analysis for accurate diagnosis, a diagnostic performance comparison is carried between the proposed EDET and the conventional DET in terms of average classification accuracy. In fact, the proposed EDET achieves up to 106.85% performance improvement over the conventional DET in average classification accuracy. In-Kyu Jeong, Myeongsu Kang, Jaeyoung Kim, Jong-Myon Kim, Jeong-Min Ha, and Byeong-Keun Choi Copyright © 2015 In-Kyu Jeong et al. All rights reserved. Transverse Free Vibration of Axially Moving Stepped Beam with Different Length and Tip Mass Tue, 10 Nov 2015 06:33:41 +0000 Axially moving stepped beam (AMSB) with different length and tip mass is represented by adopting Euler-Bernoulli beam theory, and its characteristics and displacements of transverse free vibration are calculated by using semianalytical method. Firstly, the governing equation of the transverse free vibration is established based on Hamilton’s principle. The equation is cast into eigenvalue equation through the complex modal analysis. Then, a scheme is proposed to derive the continuous condition accordingly as the displacement, rotation, bending moment, and shear force are all equal at the connections of any two segments. Another scheme is to derive frequency equation from the given boundary conditions which contain a tip mass in the last segment. Finally, the natural frequency and modal function are calculated by using numerical method according to the eigenvalue equation and frequency equation. Due to the introduction of modal truncation, displacement and, the free vibration solution can be obtained by adopting modal superposition after Hilbert transform. The numerical examples illustrate that length, velocity, mass, and geometry affect characteristics and displacements significantly; the series of methods are effective and accurate to investigate the vibration of the AMSB with different length and tip mass after comparing several results. Guoliang Ma, Minglong Xu, Liqun Chen, and Zengyong An Copyright © 2015 Guoliang Ma et al. All rights reserved. Numerical and Experimental Studies on Nonlinear Dynamics and Performance of a Bistable Piezoelectric Cantilever Generator Sun, 08 Nov 2015 14:03:12 +0000 A piezo-magneto-elastically coupled distributed-parameter model of a bistable piezoelectric cantilever generator is developed by using the generalized Hamilton principle. The influence of the spacing between two adjacent magnets on the static bifurcation characteristics of the system is studied and the range of magnet spacing corresponding to the bistable states is obtained. Numerical and experimental studies are carried out to analyze the bifurcation, response characteristics, and their impact on the electrical output performance under varying external excitations. Results indicate that interwell limit cycle motion of the beam around the two centers corresponds to optimum power output; interwell chaotic motion and multiperiodic motion including intrawell oscillations are less effective. At a given frequency, the phenomena of symmetric-breaking and amplitude-phase modulation are observed with increase of base excitation. Both period-doubling bifurcation and intermittency routes to chaotic motion in the bistable system are found. It can be observed that the power output is not proportional to the excitation level because of the bifurcation behaviours. Kangkang Guo, Shuqian Cao, and Shiyu Wang Copyright © 2015 Kangkang Guo et al. All rights reserved. Nonlinear Dynamics Analysis of the Semiactive Suspension System with Magneto-Rheological Damper Sun, 08 Nov 2015 13:56:08 +0000 This paper examines dynamical behavior of a nonlinear oscillator which models a quarter-car forced by the road profile. The magneto-rheological (MR) suspension system has been established, by employing the modified Bouc-Wen force-velocity (F-v) model of magneto-rheological damper (MRD). The possibility of chaotic motions in MR suspension is discovered by employing the method of nonlinear stability analysis. With the bifurcation diagrams and corresponding Lyapunov exponent (LE) spectrum diagrams detected through numerical calculation, we can observe the complex dynamical behaviors and oscillating mechanism of alternating periodic oscillations, quasiperiodic oscillations, and chaotic oscillations with different profiles of road excitation, as well as the dynamical evolutions to chaos through period-doubling bifurcations, saddle-node bifurcations, and reverse period-doubling bifurcations. Hailong Zhang, Enrong Wang, Fuhong Min, Ning Zhang, Chunyi Su, and Subhash Rakheja Copyright © 2015 Hailong Zhang et al. All rights reserved. An Experimental Study on Dynamics of a Novel Dual-Belt Continuous Variable Transmission Based on a Newly Developed Test Rig Wed, 04 Nov 2015 07:32:12 +0000 A novel dual-belt Van Doorne’s continuous variable transmission (DBVCVT) system, which is applicable to heavy-duty vehicles, has been previously proposed by the authors in order to improve the low torque capacity of traditional single-belt CVT. This DBVCVT is a novel design among continuously variable transmissions and is necessary to be prototyped for experimental study, and the analytical dynamic model for this DBVCVT also needs to be experimentally validated. So, this work originally fabricated a prototype of DBVCVT and integrates this prototype to a light-load hardware-in-the-loop test rig by replacing the engine and load equipment with the AC motor and magnetic powder dynamometer. Moreover, with the use of this newly developed test rig, this work implements the experimental study of this DBVCVT for the first time. The comparison of experimental and simulation results validates the previously proposed analytical model for DBVCVT, and some basic characteristics of the DBVCVT in terms of the reliability, speed ratio, and transmission efficiency are also experimentally studied. In all, this developed test rig with the analytical model lays the foundation for further study on this novel DBVCVT. Pak Kin Wong, Zhengchao Xie, and Yueqiao Chen Copyright © 2015 Pak Kin Wong et al. All rights reserved. The Effect of the Parameters of a Vibration-Based Impact Mode Piezoelectric Power Generator Tue, 03 Nov 2015 07:24:35 +0000 This study reports the effects of the parameters of a vibration-based impact mode piezoelectric power generator. First, an evaluation of the effects of the impact parameters, the mass, and the impact velocity is presented. It is found that the output voltage of the piezoelectric device in impact mode is directly proportional to the velocity, whereas the output power is equal to a quadratic function of the same variable. For the same impact momentum, the effect of the velocity in generating a higher peak output is dominant compared with the mass. Second, the vibration-based impact mode piezoelectric power generator is discussed. The experimental results show that a wider operating frequency bandwidth of the output power can be achieved with the preloading configuration. However, regarding magnitude, due to the high velocity of impact, the configuration with a gap between the tip and the piezoelectric device produces a higher output. Amat A. Basari, S. Awaji, S. Sakamoto, S. Hashimoto, B. Homma, K. Suto, H. Okada, H. Okuno, K. Kobayashi, and S. Kumagai Copyright © 2015 Amat A. Basari et al. All rights reserved. Fatigue Life Analysis of Rolling Bearings Based on Quasistatic Modeling Tue, 03 Nov 2015 07:23:28 +0000 Rolling bearings are widely used in aeroengine, machine tool spindles, locomotive wheelset, and so forth. Rolling bearings are usually the weakest components that influence the remaining life of the whole machine. In this paper, a fatigue life prediction method is proposed based on quasistatic modeling of rolling bearings. With consideration of radial centrifugal expansion and thermal deformations on the geometric displacement in the bearings, the Jones’ bearing model is updated, which can predict the contact angle, deformation, and load between rolling elements and bearing raceways more accurately. Based on Hertz contact theory and contact mechanics, the contact stress field between rolling elements and raceways is calculated. A coupling model of fatigue life and damage for rolling bearings is given and verified through accelerated life test. Afterwards, the variation of bearing life is investigated under different working conditions, that is, axial load, radial load, and rotational speed. The results suggested that the working condition had a great influence on fatigue life of bearing parts and the order in which the damage appears on bearing parts. Wei Guo, Hongrui Cao, Zhengjia He, and Laihao Yang Copyright © 2015 Wei Guo et al. All rights reserved. Modal Parameter Identification from Output Data Only: Equivalent Approaches Mon, 02 Nov 2015 07:11:44 +0000 The problem of modal parameter identification from output data only is presented. To identify the modal parameters different algorithms are presented: the block Hankel matrix and its shifted version and the block observability and block controllability matrices and their shifted version. These algorithms are derived from properties of the subspace approach. It is shown in the paper that these algorithms give the same results even in the noisy data case. Numerical and experimental results are presented showing the effectiveness of the procedure. In particular a microsystem constituted of a perforated microplate is analysed. Joseph Lardies Copyright © 2015 Joseph Lardies. All rights reserved. Identification of Modal Parameters of Bridges Using Ambient Vibration Measurements Mon, 02 Nov 2015 06:26:43 +0000 The paper provides an overview of ambient vibration tests and numerical analysis performed in the framework of Project NATO SfP 983828. The aim of the research is the definition of the dynamic characteristics of bridges on the examples. The paper considers three case studies: two older existing bridges and one newly constructed bridge. A comparative analysis of natural frequencies and mode shapes, obtained by ambient vibration measurements (AVM) and mathematical models (AMs), was carried with the aim to demonstrate the usefulness of ambient vibration tests for identification of the modal parameters of the tested bridge structure. Agreement between AVM and AMs results is very good. The mode shapes are very similar. Some differences between computed and measured frequencies were obtained, which can be attributed to the real nature of the boundary conditions, the uncertainty in the material properties of structure elements, and the mathematical models assumptions. Damir Zenunovic, Mirsad Topalovic, and Radomir Folic Copyright © 2015 Damir Zenunovic et al. All rights reserved. Nonlinear Parameters for Monitoring Gear: Comparison Between Lempel-Ziv, Approximate Entropy, and Sample Entropy Complexity Sun, 01 Nov 2015 09:09:40 +0000 Vibration analysis is the most used technique for defect monitoring failures of industrial gearboxes. Detection and diagnosis of gear defects are thus crucial to avoid catastrophic failures. It is therefore important to detect early fault symptoms. This paper introduces signal processing methods based on approximate entropy (ApEn), sample entropy (SampEn), and Lempel-Ziv Complexity (LZC) for detection of gears defects. These methods are based on statistical measurements exploring the regularity of vibratory signals. Applied to gear signals, the parameter selection of ApEn, SampEn, and LZC calculation is first numerically investigated, and appropriate parameters are suggested. Finally, an experimental study is presented to investigate the effectiveness of these indicators and a comparative study with traditional time domain indicators is presented. The results demonstrate that ApEn, SampEn, and LZC provide alternative features for signal processing. A new methodology is presented combining both Kurtosis and LZC for early detection of faults. The results show that this proposed method may be used as an effective tool for early detection of gear faults. Mourad Kedadouche, Marc Thomas, Antoine Tahan, and Raynald Guilbault Copyright © 2015 Mourad Kedadouche et al. All rights reserved. Machinery Fault Diagnosis Using Two-Channel Analysis Method Based on Fictitious System Frequency Response Function Sun, 01 Nov 2015 09:02:39 +0000 Most existing techniques for machinery health monitoring that utilize measured vibration signals usually require measurement points to be as close as possible to the expected fault components of interest. This is particularly important for implementing condition-based maintenance since the incipient fault signal power may be too small to be detected if a sensor is located further away from the fault source. However, a measurement sensor is often not attached to the ideal point due to geometric or environmental restrictions. In such a case, many of the conventional diagnostic techniques may not be successfully applicable. In this paper, a two-channel analysis method is proposed to overcome such difficulty. It uses two vibration signals simultaneously measured at arbitrary points in a machine. The proposed method is described theoretically by introducing a fictitious system frequency response function. It is then verified experimentally for bearing fault detection. The results show that the suggested method may be a good alternative when ideal points for measurement sensors are not readily available. Kihong Shin and Sang-Heon Lee Copyright © 2015 Kihong Shin and Sang-Heon Lee. All rights reserved. Vibration and Long-Term Performance Analysis of Pile-Plank-Supported Low Subgrade of Ballastless Track under Excitation Loads Wed, 28 Oct 2015 06:57:40 +0000 Pile-plank structures are widely applied for high-speed railway built in soft ground in China. It can be used as a reinforcement to improve the behavior of subgrade by providing vertical confinement to increase their stiffness and strength and reduce the subgrade settlement of ballastless track. However, the use of pile-board structure for soft ground reinforcement of high-speed railway is hindered by the existing gap between applications and theories. To verify vibration characteristics and long-term performance of pile-plank-supported low subgrade of ballastless track and the benefit of pile-board structure, an experimental study was conducted on low subgrade of pile-board under excitation loads using both in situ frequency sweeping and cyclic loading experiments. The frequency sweeping experimental results show that the pile-plank-supported low subgrade has smooth stiffness along the longitudinal subgrade and can effectively control the progressive effects of train speed on dynamic stiffness of the subgrade, which ensures driving safety and comfort. The cycle loading experimental results show that the pile-plank-supported low subgrade has favorable long-term dynamic stability, and its dynamic response is uniform along the longitudinal subgrade. Junjie Huang, Qian Su, Ting Liu, and Xun Wang Copyright © 2015 Junjie Huang et al. All rights reserved. Performance Improvement of Ensemble Empirical Mode Decomposition for Roller Bearings Damage Detection Wed, 28 Oct 2015 06:56:38 +0000 Ensemble empirical mode decomposition (EEMD) is a noise assisted method widely used for roller bearing damage detection. However, to successfully handle this technique still remains a great challenge: identification of two effective parameters (the amplitude of added noise and the number of ensemble trials), which affect the performances of the EEMD. Although a number of algorithms or values have been proposed, there is no robust guide to select optimal amplitude and the ensemble trial number yet, especially for early damage detection. In this study, a reliable method is proposed to determine the suitable amplitude and the proper number of trials is investigated as well. It is shown that the proposed method (performance improved EEMD) achieves higher damage detection success rate and creates larger Margin than the original algorithm. It leads to a substantially low trial numbers required to achieve perfect labelling of samples; in turn this fact leads to considerably less computational cost. The number of real vibration signals is analysed to verify effectiveness and robustness of the proposed method in discriminating and separating the faulty conditions. Ali Akbar Tabrizi, Luigi Garibaldi, Alessandro Fasana, and Stefano Marchesiello Copyright © 2015 Ali Akbar Tabrizi et al. All rights reserved.