Shock and Vibration The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Research on High-Frequency Combination Coding-Based SSVEP-BCIs and Its Signal Processing Algorithms Wed, 30 Sep 2015 09:33:55 +0000 This study presents a new steady-state visual evoked potential (SSVEP) paradigm for brain computer interface (BCI) systems. The new paradigm is High-Frequency Combination Coding-Based SSVEP (HFCC-SSVEP). The goal of this study is to increase the number of targets using fewer stimulation frequencies, with diminishing subject’s fatigue and reducing the risk of photosensitive epileptic seizures. This paper investigated the HFCC-SSVEP high-frequency response (beyond 25 Hz) for 3 frequencies (25 Hz, 33.33 Hz, and 40 Hz). HFCC-SSVEP produces with high stimulation frequencies through Time Series Combination Code. Furthermore, The Improved Hilbert-Huang Transform (IHHT) is adopted to extract time-frequency feature of the proposed SSVEP response. Lastly, the differentiation combination (DC) method is proposed to select the combination coding sequence in order to increase the recognition rate; as a result, IHHT algorithm and DC method for the proposed SSVEP paradigm in this study increase recognition efficiency so as to improve ITR and increase the stability of the BCI system. Furthermore, SSVEPs evoked by high-frequency stimuli (beyond 25 Hz) minimally diminish subject’s fatigue and prevent safety hazards linked to photo-induced epileptic seizures. This study tests five subjects in order to verify the feasibility of the proposed method. Feng Zhang, Chengcheng Han, Lili Li, Xin Zhang, Jun Xie, and Yeping Li Copyright © 2015 Feng Zhang et al. All rights reserved. Bridge Damage Severity Quantification Using Multipoint Acceleration Measurement and Artificial Neural Networks Wed, 30 Sep 2015 09:28:50 +0000 The deterioration of bridges as a result of ageing is a serious problem in many countries. To prevent the failure of these deficient bridges, early damage detection which helps us to evaluate the safety of bridges is important. Therefore, the present research proposed a method to quantify damage severity by use of multipoint acceleration measurement and artificial neural networks. In addition to developing the method, we developed a cheap and easy-to-make measurement device which can be made by bridge owners at low cost and without the need for advance technical skills since the method is mainly intended to apply to small to midsized bridges. In addition, the paper gives an example application of the method to a weathering steel bridge in Japan. It can be shown from the analysis results that the method is accurate in its damage identification and mechanical behavior prediction ability. Pang-jo Chun, Hiroaki Yamashita, and Seiji Furukawa Copyright © 2015 Pang-jo Chun et al. All rights reserved. Stayed-Cable Bridge Damage Detection and Localization Based on Accelerometer Health Monitoring Measurements Tue, 29 Sep 2015 08:22:10 +0000 In situ damage detection and localization using real acceleration structural health monitoring technique are the main idea of this study. The statistical and model identification time series, the response spectra, and the power density of the frequency domain are used to detect the behavior of Yonghe cable-stayed bridge during the healthy and damage states. The benchmark problem is used to detect the damage localization of the bridge during its working time. The assessment of the structural health monitoring and damage analysis concluded that (1) the kurtosis statistical moment can be used as an indicator for damage especially with increasing its percentage of change as the damage should occur; (2) the percentage of change of the Kernel density probability for the model identification error estimation can detect and localize the damage; (3) the simplified spectrum of the acceleration-displacement responses and frequencies probability changes are good tools for detection and localization of the one-line bridge damage. Mosbeh R. Kaloop and Jong Wan Hu Copyright © 2015 Mosbeh R. Kaloop and Jong Wan Hu. All rights reserved. Theoretical Analysis and Experimental Verification of Particle Damper-Based Energy Dissipation with Applications to Reduce Structural Vibration Tue, 29 Sep 2015 08:19:06 +0000 Particle damping technology can greatly reduce vibration of equipment and structure through friction and inelastic collisions of particles. An energy dissipation model for particle damper has been presented based on the powder mechanics and the collision theory. The energy dissipation equations of friction and collision motion are developed for the particle damper. The rationality of energy dissipation model has been verified by the experiment and the distributions for the energy dissipation of particles versus acceleration are nonlinear. As the experiment process includes lots of factors of energy dissipation, such as the noise and the air resistance, the experimental value is about 7% more than the simulation value. The simulation model can provide an effective method for the design of particle damper. And the particle parameters for damper have been investigated. The results have shown that choosing an appropriate particle density, particle size, and particle filling rate determined based on the simulation model will provide the optimal damping effect for the practical application of particle damping technology. Wangqiang Xiao, Lina Jin, and Binqiang Chen Copyright © 2015 Wangqiang Xiao et al. All rights reserved. Model Updating of Spindle Systems Based on the Identification of Joint Dynamics Tue, 29 Sep 2015 08:06:01 +0000 In order to simulate the cutting performance of a spindle mounted in the machine tool, the finite element (FE) model of spindles is required to be coupled with machine tool. However, the unknown joint dynamics (e.g., bolts) between the spindle and machine tool column limit the accuracy of the model. In this paper, an FE model updating method is proposed based on the identification of joint dynamics in both translational and rotational degrees-of-freedom (DOF). The receptance coupling (RC) technique is enhanced to estimate frequency response functions (FRFs) corresponding to rotational DOFs. The joint stiffness is identified through the iteration process by minimizing the difference between the simulated FRF and the measured FRF of the assembly. The proposed method is verified with a machine-tool spindle system. The good agreement between simulation and experiment shows the effectiveness of the method. Hongrui Cao, Songtao Xi, and Wei Cheng Copyright © 2015 Hongrui Cao et al. All rights reserved. Automatic Condition Monitoring of Industrial Rolling-Element Bearings Using Motor’s Vibration and Current Analysis Mon, 28 Sep 2015 09:12:09 +0000 An automatic condition monitoring for a class of industrial rolling-element bearings is developed based on the vibration as well as stator current analysis. The considered fault scenarios include a single-point defect, multiple-point defects, and a type of distributed defect. Motivated by the potential commercialization, the developed system is promoted mainly using off-the-shelf techniques, that is, the high-frequency resonance technique with envelope detection and the average of short-time Fourier transform. In order to test the flexibility and robustness, the monitoring performance is extensively studied under diverse operating conditions: different sensor locations, motor speeds, loading conditions, and data samples from different time segments. The experimental results showed the powerful capability of vibration analysis in the bearing point defect fault diagnosis. The current analysis also showed a moderate capability in diagnosis of point defect faults depending on the type of fault, severity of the fault, and the operational condition. The temporal feature indicated a feasibility to detect generalized roughness fault. The practical issues, such as deviations of predicted characteristic frequencies, sideband effects, time-average of spectra, and selection of fault index and thresholds, are also discussed. The experimental work shows a huge potential to use some simple methods for successful diagnosis of industrial bearing systems. Zhenyu Yang Copyright © 2015 Zhenyu Yang. All rights reserved. A Novel Rotor Profile Error Tracing and Compensation Strategy for High Precision Machining of Screw Rotor Based on Trial Cutting of Limited Samples Sun, 27 Sep 2015 07:01:52 +0000 The machining precision plays an important role in the operation reliability and service life of screw rotors. However, the actual machined rotor profile of screw rotors is different from its theoretical profile due to the errors of the machine tool. This paper proposes a novel method of error tracing and compensation to reduce the machined errors of rotor profile on the basis of the limited sample trials, and the method is based on a matrix of error compensation. The errors of rotor profile are obtained based on limited sample trials machining of screw rotors,and fitted into piecewise smooth data. A matrix of error compensation is established to compute the errors of rotor profile to generate a compensated rotor profile. The compensated rotor profile is then used to regenerate forming tool and a new rotor product is processed on the same machine tool. And the errors of new rotor profile are smaller and can be reduced within (−0.01 mm, 0.01 mm) after compensations. Finally, the actual machining examples illustrate that the method of error compensation can not only satisfy the machining requirement of high-precision rotors, but also has the characteristics of good stability and applicability. ZhiHuang Shen, Bin Yao, BinQiang Chen, Wei Feng, and XiangLei Zhang Copyright © 2015 ZhiHuang Shen et al. All rights reserved. Acoustical Source Tracing Using Independent Component Analysis and Correlation Analysis Mon, 21 Sep 2015 09:18:40 +0000 Acoustical signals from mechanical systems reveal the operating conditions of mechanical components and thus benefit for machinery condition monitoring and fault diagnosis. However, the acoustical signals directly measured by the sensors in essential are the mixed signals of all the sources, and normally it is very difficult to be used for source identification or operating feature extraction. Therefore, this paper studies the acoustical source tracing problem using independent component analysis (ICA) and identifies the sources using correlation analysis: the measured acoustical signals are separated into independent components by independent component analysis method, and thus all the independent information of all the sources is obtained; these independent components are identified based on the prior information of the sources and correlation analysis. Therefore, all the source information contained in the measured acoustical signals can be independently separated and traced, which can provide more purer source information for condition monitoring and fault diagnosis. Wei Cheng, Zhousuo Zhang, Jie Zhang, and Jiantao Lu Copyright © 2015 Wei Cheng et al. All rights reserved. Fault Diagnosis for Gearbox Based on Improved Empirical Mode Decomposition Mon, 21 Sep 2015 07:42:04 +0000 The application of the improved empirical mode decomposition (EMD) theory in gearbox fault diagnosis has been studied in this paper, and the transient features of gearbox vibration signals are shown. Based on using EMD, an improved algorithm of orthogonal empirical mode decomposition (OEMD) is put forward and is applied to extract the fault feature. Finally, fault diagnosis application in a gearbox is used as an example to prove the feasibility of the proposed method. Ling Zhao, Darong Huang, and Yi Qin Copyright © 2015 Ling Zhao et al. All rights reserved. A Method Combining Order Tracking and Fuzzy C-Means for Diesel Engine Fault Detection and Isolation Mon, 21 Sep 2015 06:40:13 +0000 Diesel engine works under variable speed conditions; fault symptoms are clearer in the angular/order domains than in the common time/frequency ones. In this paper, firstly, the acceleration signal of diesel engine is resampled by order tracking, in which the rotating speed is computed in every working cycle, and the order tracking spectrum is created in each interval’s speed; then different order band accumulated energy is computed as feature vector. After standardizing these features, the fuzzy c-means (FCM) is introduced to use them as input vector; the optimized classified matrix and clustering centers can be obtained using FCM iteration method; then the fault can be detected by calculating the approach degree between the unknown samples and the known ones. To validate the method, some experiments have been performed; the results show that the signal can be reconstructed, and the features of order band accumulated energy can reflect the information of different wear conditions in crank-shaft bearing; then the fault can be detected accurately. The method of nonentire work cycle is also introduced as a comparison with our method; the result shows our method has more accuracy classification. Ruili Zeng, Lingling Zhang, Yunkui Xiao, Jianmin Mei, Bin Zhou, Huimin Zhao, and Jide Jia Copyright © 2015 Ruili Zeng et al. All rights reserved. Study on Fault Diagnosis of Rolling Bearing Based on Time-Frequency Generalized Dimension Sun, 20 Sep 2015 12:41:01 +0000 The condition monitoring technology and fault diagnosis technology of mechanical equipment played an important role in the modern engineering. Rolling bearing is the most common component of mechanical equipment which sustains and transfers the load. Therefore, fault diagnosis of rolling bearings has great significance. Fractal theory provides an effective method to describe the complexity and irregularity of the vibration signals of rolling bearings. In this paper a novel multifractal fault diagnosis approach based on time-frequency domain signals was proposed. The method and numerical algorithm of Multi-fractal analysis in time-frequency domain were provided. According to grid type J and order parameter q in algorithm, the value range of J and the cut-off condition of q were optimized based on the effect on the dimension calculation. Simulation experiments demonstrated that the effective signal identification could be complete by multifractal method in time-frequency domain, which is related to the factors such as signal energy and distribution. And the further fault diagnosis experiments of bearings showed that the multifractal method in time-frequency domain can complete the fault diagnosis, such as the fault judgment and fault types. And the fault detection can be done in the early stage of fault. Therefore, the multifractal method in time-frequency domain used in fault diagnosis of bearing is a practicable method. Yu Yuan, Xing Zhao, Jiyou Fei, Yulong Zhao, and Jiahui Wang Copyright © 2015 Yu Yuan et al. All rights reserved. Rotating Machine Fault Diagnosis Based on Optimal Morphological Filter and Local Tangent Space Alignment Sun, 20 Sep 2015 12:33:46 +0000 In order to identify the fault of rotating machine effectively, a new method based on the morphological filter optimized by particle swarm optimization algorithm (PSO) and the nonlinear manifold learning algorithm local tangent space alignment (LTSA) is proposed. Firstly, the signal is purified by the morphological filter; the filter’s structure element (SE) is selected by PSO method. Then the filtered signals are decomposed by the empirical mode decomposition (EMD) method, and the extract features are mapped into the LTSA to extract the character features; then the support vector machine (SVM) model is used to achieve the rotating machine fault diagnosis. The proposed method is evaluated by vibration signals measured from bearings with faults. Results show that the method can effectively remove the noise and extract the fault features, so the rotating machine fault diagnosis can be achieved effectively. Shaojiang Dong, Lili Chen, Baoping Tang, Xiangyang Xu, Zhengyuan Gao, and Juan Liu Copyright © 2015 Shaojiang Dong et al. All rights reserved. Lightweight Investigation of Extended-Range Electric Vehicle Based on Collision Failure Using Numerical Simulation Sun, 20 Sep 2015 12:33:01 +0000 The total weight of Extended-Range Electric Vehicle (E-REV) is too heavy, which affects rear-end collision safety. Using numerical simulation, a lightweight method is designed to reduce E-REV body and key parts weight based on rear-end collision failure analysis. To calculate and optimize the performance of vehicle safety, the simulation model of E-REV rear-end collision safety is built by using finite element analysis. Drive battery pack lightweight design method is analyzed and the bending mode and torsional mode of E-REV before and after lightweight are compared to evaluate E-REV rear-end collision safety performance. The simulation results of optimized E-REV safety structure are verified by both numerical simulation and experimental investigation of the entire vehicle crash test. Jiangqi Long, Wenhao Huang, and Wuhu Zhang Copyright © 2015 Jiangqi Long et al. All rights reserved. Modeling and Simulation of Process-Machine Interaction in Grinding of Cemented Carbide Indexable Inserts Sun, 20 Sep 2015 11:14:54 +0000 Interaction of process and machine in grinding of hard and brittle materials such as cemented carbide may cause dynamic instability of the machining process resulting in machining errors and a decrease in productivity. Commonly, the process and machine tools were dealt with separately, which does not take into consideration the mutual interaction between the two subsystems and thus cannot represent the real cutting operations. This paper proposes a method of modeling and simulation to understand well the process-machine interaction in grinding process of cemented carbide indexable inserts. First, a virtual grinding wheel model is built by considering the random nature of abrasive grains and a kinematic-geometrical simulation is adopted to describe the grinding process. Then, a wheel-spindle model is simulated by means of the finite element method to represent the machine structure. The characteristic equation of the closed-loop dynamic grinding system is derived to provide a mathematic description of the process-machine interaction. Furthermore, a coupling simulation of grinding wheel-spindle deformations and grinding process force by combining both the process and machine model is developed to investigate the interaction between process and machine. This paper provides an integrated grinding model combining the machine and process models, which can be used to predict process-machine interactions in grinding process. Wei Feng, Bin Yao, BinQiang Chen, DongSheng Zhang, XiangLei Zhang, and ZhiHuang Shen Copyright © 2015 Wei Feng et al. All rights reserved. An Algorithm of Quantum Restricted Boltzmann Machine Network Based on Quantum Gates and Its Application Tue, 15 Sep 2015 08:26:12 +0000 We present an algorithm of quantum restricted Boltzmann machine network based on quantum gates. The algorithm is used to initialize the procedure that adjusts the qubit and weights. After adjusting, the network forms an unsupervised generative model that gives better classification performance than other discriminative models. In addition, we show how the algorithm can be constructed with quantum circuit for quantum computer. Peilin Zhang, Sheng Li, and Yu Zhou Copyright © 2015 Peilin Zhang et al. All rights reserved. Resonance Analysis of High-Frequency Electrohydraulic Exciter Controlled by 2D Valve Tue, 15 Sep 2015 08:02:38 +0000 The resonant characteristic of hydraulic system has not been described yet because it is necessarily restricted by linear assumptions in classical fluid theory. A way of the resonance analysis is presented for an electrohydraulic exciter controlled by 2D valve. The block diagram of this excitation system is established by extracting nonlinear parts from the traditional linearization analysis; as a result the resonant frequency is obtained. According to input energy from oil source which is equal to the reverse energy to oil source, load pressure and load flow are solved analytically as the working frequency reaches the natural frequency. The analytical expression of resonant peak is also derived without damping. Finally, the experimental system is built to verify the theoretical analysis. The initial research on resonant characteristic will lay theoretical foundation and make useful complement for resonance phenomena of classical fluid theory in hydraulic system. Guojun Pan, Yan Ren, and Jian Ruan Copyright © 2015 Guojun Pan et al. All rights reserved. Identification of Crack Location in Beam Structures Using Wavelet Transform and Fractal Dimension Tue, 15 Sep 2015 07:59:12 +0000 Identification of structural crack location has become an intensely investigated subject due to its practical importance. In this paper, a hybrid method is presented to detect crack locations using wavelet transform and fractal dimension (FD) for beam structures. Wavelet transform is employed to decompose the mode shape of the cracked beam. In many cases, small crack location cannot be identified from approximation signal and detailed signals. And FD estimation method is applied to calculate FD parameters of detailed signals. The crack locations will be detected accurately by FD singularity of the detailed signals. The effectiveness of the proposed method is validated by numerical simulations and experimental investigations for a cantilever beam. The results indicate that the proposed method is feasible and can been extended to more complex structures. Yong-Ying Jiang, Bing Li, Zhou-Suo Zhang, and Xue-Feng Chen Copyright © 2015 Yong-Ying Jiang et al. All rights reserved. Effects of Contraction Joints on Vibrational Characteristics of Arch Dams: Experimental Study Mon, 14 Sep 2015 10:10:44 +0000 This study experimentally investigates the effects of contraction joints on the vibrational characteristics of high arch dams. Three scale models of the world’s second highest dam, the Xiaowan Arch Dam, are used as experimental specimens identified by zero, one, and two contraction joints. When a scale model vibrates harmonically at a specific frequency, its operating deflection shape is acquired by using a scanning laser vibrometer to scan the side surface of the model. The effects of contraction joints on the vibrational characteristics of arch dams are studied by examining the changes in operating deflection shapes. Experimental results demonstrate that (i) contraction joints can significantly affect the vibrational characteristics of arch dams, (ii) the operating deflection shape intuitively illustrates the vibrational characteristics of arch dams, and (iii) a scanning laser vibrometer has marked advantages over traditional equipment in accurately and efficiently acquiring full-field dynamic responses of a structure. S. S. Wang, Y. F. Zhang, M. S. Cao, and W. Xu Copyright © 2015 S. S. Wang et al. All rights reserved. Estimation of Modal Properties of Low-Rise Buildings Using Ambient Excitation Measurements Mon, 14 Sep 2015 09:16:55 +0000 Continuous wavelet transform (CWT) has recently emerged as a promising tool for identification of modal properties through ambient excitation measurements of structures. However, it is difficult to obtain an accurate estimation of damping ratio directly from time-frequency decomposition of ambient vibration measurements using CWT. The main objective of this study is to introduce a new method called two-step procedure in the estimation of damping ratios using ambient vibration measurements. The two-step procedure involves the development of random decrement (RD) signature from the ambient vibration measurements, which is equivalent to the damped free vibration response of a structure under a given initial displacement and subsequently decomposition of time domain RD signature into time-frequency domain using CWT. The secondary objective of the study is to show that CWT is capable of identifying the natural periods and mode shapes of low-rise buildings using ambient vibration measurements. Furthermore, the two-step procedure is validated with two practical applications in a five-storey reinforced concrete structure with masonry infill walls and a three-storey masonry structure. Finally, a conclusion can be drawn that the two-step procedure yields a reasonably good estimation of damping ratio. K. K. Wijesundara, C. Negulescu, and E. Foerster Copyright © 2015 K. K. Wijesundara et al. All rights reserved. Reliability Analysis of Damaged Beam Spectral Element with Parameter Uncertainties Mon, 14 Sep 2015 08:39:58 +0000 The paper examines the influence of uncertainty parameters on the wave propagation responses at high frequencies for a damaged beam structure in the structural reliability context. The reliability analyses were performed using the perturbation method, First-Order Reliability Method (FORM), and response surface method (RSM) which were compared with Monte Carlo simulation (MCS) under the spectral element method environment. The simulated results were performed to investigate the effects of material property and geometric uncertainties on the response at high frequency modes, such as the computational efficiency of reliability methods. For the first time, the spectral element method is used in the context of reliability analysis at medium and high frequency bands applied to damage detection. It has shown the effects of parameters uncertainty on the dynamic beam response due on an impulsive load and the robustness of each method. Numerical examples in a bending vibrating beam with random parameters are performed to verify the computational efficiency of the present study. M. R. Machado and J. M. C. Dos Santos Copyright © 2015 M. R. Machado and J. M. C. Dos Santos. All rights reserved. An Energy-Based Safety Evaluation Index of Blast Vibration Sun, 13 Sep 2015 13:09:08 +0000 The combined peak particle velocity (PPV) and frequency safety criterion for blast vibration is widely used in blasting engineering. However, some field investigations are inconsistent with this criterion. On the basis of field investigations, it is found that there are two failure modes of structures subjected to blasting seismic waves, that is, first-excursion failure and cumulative plastic damage failure. Moreover, the nature of structural responses under blast vibrations is a process of energy input, transformation, and dissipation. Therefore, an energy-based dual safety standard is proposed in this work to more comprehensively explain all failure modes of structures under blast vibrations. To this end, structures are simplified into elastic-plastic single degree of freedom (SDOF) systems with bilinear restoring force models, and energy responses of SDOF systems are then determined using the Newmark-β method. From the energy responses, the maximum instantaneous input energy and hysteretic energy are selected as the basis of the dual safety criterion, because they can reflect first-excursion failure and cumulative plastic damage failure, respectively. Finally, field investigations in a blasting site in Zunyi, Guizhou province, China, are used to prove that compared to the PPV-frequency criterion the proposed energy-based dual safety criterion is more capable of assessing the damage potential of blast vibrations. Mingsheng Zhao, Dong Huang, Maosen Cao, En-an Chi, Jun Liu, and Qiang Kang Copyright © 2015 Mingsheng Zhao et al. All rights reserved. On the Design of High-Rise Buildings for Multihazard: Fundamental Differences between Wind and Earthquake Demand Thu, 10 Sep 2015 13:33:50 +0000 In the past few decades, high-rise buildings have received a renewed interest in many city business locations, where land is scarce, as per their economics, sustainability, and other benefits. Taller and taller towers are being built everywhere in the world. However, the increased frequency of multihazard disasters makes it challenging to balance between a resilient and sustainable construction. Accordingly, it is essential to understand the behavior of such structures under multihazard loadings, in order to apply such knowledge to design. The results obtained from the dynamic analysis of two different high-rise buildings (54-story and 76-story buildings) investigated in the current study indicate that earthquake loads excite higher modes that produce lower interstory drift, compared to wind loads, but higher accelerations that occur for a shorter time. Wind-induced accelerations may have comfort and serviceability concerns, while excessive interstory drifts can cause security issues. The results also show that high-rise and slender buildings designed for wind may be safe under moderate earthquake loads, regarding the main force resisting system. Nevertheless, nonstructural components may present a significant percentage of loss exposure of buildings to earthquakes due to higher floor acceleration. Consequently, appropriate damping/control techniques for tall buildings are recommended for mitigation under multihazard. Aly Mousaad Aly and Srinivasa Abburu Copyright © 2015 Aly Mousaad Aly and Srinivasa Abburu. All rights reserved. Identification of Structural Damage in Bridges Using High-Frequency Vibrational Responses Thu, 10 Sep 2015 10:59:12 +0000 The present research aims to develop an effective and applicable structural damage detection method. A damage identification approach using only the changes of measured natural frequencies is presented. The structural damage model is assumed to be associated with a reduction of a contribution to the element stiffness matrix equivalent to a scalar reduction of the material modulus. The computational technique used to identify the damage from the measured data is described. The performance of the proposed technique on numerically simulated real concrete girder bridge is evaluated using imposed damage scenarios. To demonstrate the applicability of the proposed method by employing experimental measured natural frequencies this technique is applied for the first time to a simply supported reinforced concrete beam statically loaded incrementally to failure. The results of the damage identification procedure show that the proposed method can accurately locate the damage and predict the extent of the damage using high-frequency (here beyond the 4th order) vibrational responses. Ivana Mekjavić Copyright © 2015 Ivana Mekjavić. All rights reserved. Nonlinear Dynamic Behaviors of a Marine Rotor-Bearing System Coupled with Air Bag and Floating-Raft Thu, 10 Sep 2015 10:01:43 +0000 To understand the nonlinear dynamic mechanism of a rotor-bearing system coupled with air bag and floating-raft, the dynamic characteristics of the system are investigated. This work has two key objectives. First, the vibration mechanism of rotor-bearing system coupled with air bag and floating-raft is investigated by developing a numerical model. Then, the nonlinear dynamics of the system and the effect of several parameters are studied, which includes the steady-state response and its spectrum, the orbit and its Poincaré map, the bifurcation diagram, and largest Lyapunov exponent (LLE). The results show that at low speed the dynamic behavior appears in a single periodic motion, and, with the increase of the speed, the motion becomes quasi-periodic and chaotic. These performances indicate that the air bag and floating-raft introduce some dynamic effects of marine rotor-bearing system. W. Zhao, M. Li, and L. Xiao Copyright © 2015 W. Zhao et al. All rights reserved. Dynamics of the Bogie of Maglev Train with Distributed Magnetic Forces Mon, 07 Sep 2015 06:39:40 +0000 A dynamic model of the bogie of maglev train with distributed magnetic forces and four identical levitating controllers is formulated. The vertical, pitching, and rolling degree of freedom of the electromagnet modules and their coupling are considered. The frequency responses of the bogie to track irregularity are investigated with numerical simulation. The results tell us that there are resonances related to the first electromagnetic suspension whose frequencies are determined by the control parameters. A comparative analysis has been carried out between the models with distributed or concentrated magnetic forces. The comparison indicates that simplifying the distributed magnetic force to concentrated one degenerates the dynamic behavior of the maglev bogie, especially resulting in overestimated resonances of the first electromagnetic suspension of maglev trains. The results also indicate that those resonances only occur on specific wavelengths of irregularity that relate to the length of the electromagnets. Yaozong Liu, Wenxi Deng, and Pu Gong Copyright © 2015 Yaozong Liu et al. All rights reserved. Pattern Recognition of Signals for the Fault-Slip Type of Rock Burst in Coal Mines Mon, 07 Sep 2015 06:26:36 +0000 The fault-slip type of rock burst is a major threat to the safety of coal mining, and effectively recognizing its signals patterns is the foundation for the early warning and prevention. At first, a mechanical model of the fault-slip was established and the mechanism of the rock burst induced by the fault-slip was revealed. Then, the patterns of the electromagnetic radiation, acoustic emission (AE), and microseismic signals in the fault-slip type of rock burst were proposed, in that before the rock burst occurs, the electromagnetic radiation intensity near the sliding surface increases rapidly, the AE energy rises exponentially, and the energy released by microseismic events experiences at least one peak and is close to the next peak. At last, in situ investigations were performed at number 1412 coal face in the Huafeng Mine, China. Results showed that the signals patterns proposed are in good agreement with the process of the fault-slip type of rock burst. The pattern recognition can provide a basis for the early warning and the implementation of relief measures of the fault-slip type of rock burst. X. S. Liu, J. Tan, Y. L. Tan, and S. C. Hu Copyright © 2015 X. S. Liu et al. All rights reserved. Numerical Analysis and Demonstration: Transmission Shaft Influence on Meshing Vibration in Driving and Driven Gears Sun, 06 Sep 2015 07:59:45 +0000 The variable axial transmission system composed of universal joint transmission shafts and a gear pair has been applied in many engineering fields. In the design of a drive system, the dynamics of the gear pair have been studied in detail. However few have paid attention to the effect on the system modal characteristics of the gear pair, arising from the universal joint transmission shafts. This work establishes a torsional vibration mathematical model of the transmission shaft, driving gear, and driven gear based on lumped masses and the main reducer system assembly of a CDV (car-based delivery vehicle) car. The model is solved by the state space method. The influence of the angle between transmission shafts and intermediate support stiffness on the vibration and noise of the main reducer is obtained and verified experimentally. A reference for the main reducer and transmission shaft design and the allied parameter matching are provided. Xu Jinli, Su Xingyi, and Peng Bo Copyright © 2015 Xu Jinli et al. All rights reserved. An Improved Shock Factor to Evaluate the Shock Environment of Small-Sized Structures Subjected to Underwater Explosion Sun, 06 Sep 2015 06:50:11 +0000 Shock factor is conventionally used to assess the effect of an underwater explosion on a target. The dimensions of some structures are much smaller than the wavelength of incident wave induced by the underwater explosion. The conventional shock factor may be excessively severe for small-sized structures because it neglects the effect of scattering; so it is necessary to study the shock factor for small objects. The coupled mode method is applied to study the scattering field surrounding the cylindrical shells. A nonlinear relation differential is derived from the impact received by the cylindrical shells and the ratio between the diameters of the shells and the wavelength of the incident wave. An improved shock factor is developed based on the fitted curve, considering the scattering effect caused by the diameters of the submerged cylindrical shells. A set of numerical simulations are carried out to validate the accuracy of the proposed approach. The results show that the cylindrical shells and spherical shells under different conditions, but with the same shock factor, have almost the same shock responses. Wenzheng Zhang and Weikang Jiang Copyright © 2015 Wenzheng Zhang and Weikang Jiang. All rights reserved. Vibration and Stability of Variable Cross Section Thin-Walled Composite Shafts with Transverse Shear Thu, 03 Sep 2015 11:29:10 +0000 A dynamic model of composite shaft with variable cross section is presented. Free vibration equations of the variable cross section thin-walled composite shaft considering the effect of shear deformation are established based on a refined variational asymptotic method and Hamilton’s principle. The numerical results calculated by Galerkin method are analyzed to indicate the effects of ply angle, taper ratio, and transverse shear deformation on the first natural frequency and critical rotating speed. The results are compared with those obtained by using finite element package ANSYS and available in the literature using other models. Ma Jing-min and Ren Yong-sheng Copyright © 2015 Ma Jing-min and Ren Yong-sheng. All rights reserved. Experimental Study on the Measurement of Water Bottom Vibration Induced by Underwater Drilling Blasting Wed, 02 Sep 2015 07:53:25 +0000 Due to the lack of proper instrumentations and the difficulties in underwater measurements, the studies about water bottom vibration induced by underwater drilling blasting are seldom reported. In order to investigate the propagation and attenuation laws of blasting induced water bottom vibration, a water bottom vibration monitor was developed with consideration of the difficulties in underwater measurements. By means of this equipment, the actual water bottom vibration induced by underwater drilling blasting was measured in a field experiment. It shows that the water bottom vibration monitor could collect vibration signals quite effectively in underwater environments. The followed signal analysis shows that the characteristics of water bottom vibration and land ground vibration induced by the same underwater drilling blasting are quite different due to the different geological environments. The amplitude and frequency band of water bottom vibration both exceed those of land ground vibration. Water bottom vibration is mainly in low-frequency band that induced by blasting impact directly acts on rock. Besides the low-frequency component, land vibration contains another higher frequency band component that induced by followed water hammer wave acts on bank slope. Gu Wenbin, Chen Jianghai, Wang Zhenxiong, Wang Zhihua, Liu Jianqing, and Lu Ming Copyright © 2015 Gu Wenbin et al. All rights reserved.