Shock and Vibration The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Research on Fatigue Damage of Compressor Blade Steel KMN-I Using Nonlinear Ultrasonic Testing Thu, 19 Oct 2017 00:00:00 +0000 The fatigue damage of compressor blade steel KMN-I was investigated using nonlinear ultrasonic testing and the relation curve between the material nonlinearity parameter β and the fatigue life was obtained. The results showed that the nonlinearity parameter increased first and then decreased with the increase of the fatigue cycles. The microstructures were observed by scanning electron microscopy (SEM). It was found that some small defects like holes and pits appeared in the material matrix with the increase of the fatigue cycles, and the nonlinearity parameter increased correspondingly. The nonlinearity parameter reached the peak value when the microcracks initiated, and the nonlinearity parameter began to decrease when the microcracks further propagated to macrocracks. Therefore, it is proved that the nonlinearity parameter can be used to characterize the initiation of microcracks at the early stage of fatigue, and a method of evaluating the fatigue life of materials by nonlinear ultrasonic testing is proposed. Pengfei Wang, Weiqiang Wang, and Jianfeng Li Copyright © 2017 Pengfei Wang et al. All rights reserved. A Framework for Extension of Dynamic Finite Element Formulation to Flexural Vibration Analysis of Thin Plates Thu, 19 Oct 2017 00:00:00 +0000 Dynamic Finite Element formulation is a powerful technique that combines the accuracy of the exact analysis with wide applicability of the finite element method. The infinite dimensionality of the exact solution space of plate equation has been a major challenge for development of such elements for the dynamic analysis of flexible two-dimensional structures. In this research, a framework for such extension based on subset solutions is proposed. An example element is then developed and implemented in MATLAB® software for numerical testing, verification, and validation purposes. Although the presented formulation is not exact, the element exhibits good convergence characteristics and can be further enriched using the proposed framework. Mohammad M. Elahi and Seyed M. Hashemi Copyright © 2017 Mohammad M. Elahi and Seyed M. Hashemi. All rights reserved. Identification of Loss Factor of Fiber-Reinforced Composite Based on Complex Modulus Method Thu, 19 Oct 2017 00:00:00 +0000 The identification of the loss factor of fiber-reinforced composite based on complex modulus method is presented. Firstly, the damping model of fiber-reinforced composite plate is established, and the relation between each loss factor and modal damping ratio is deduced based on the complex modulus method. Then, the least square relative error function is formed by using the modal damping ratio obtained in the experimental test, and the appropriate step-size is selected in the range of 0~10% to calculate the loss factor. Next, the identification procedure of loss factor of such composite material is summarized, and the corresponding identification procedure is realized based on self-designed MATLAB program. Finally, TC300 carbon/epoxy composite plate is taken as an example to carry out a case study, and its loss factors along the longitudinal, transverse, and shear direction are identified by the complex modulus method. By comparing the measured damping results obtained in this paper and the calculated damping results based on the Adams-Bacon model with the same loss factor, it is found that the corresponding maximum deviation between them is less than 15%, so the correctness of such identification method has been verified indirectly, which can be used to identify loss factor of fiber-reinforced composite with high precision and efficiency. Hui Li, Yi Niu, Chao Mu, and Bangchun Wen Copyright © 2017 Hui Li et al. All rights reserved. Experimental Study of Vibrational Acceleration Spread and Comparison Using Three Citrus Canopy Shaker Shaking Tines Thu, 19 Oct 2017 00:00:00 +0000 The goal of this article is to experimentally study how the vibrational acceleration spreads along the branch shaken by PVC tine, steel tine, and nylon tine for citrus canopy shaking harvesting and to compare the difference. PVC tine and steel tine have potential to be used as shaking rod for citrus canopy shaking harvesting. Nylon tine is a commonly used shaking rod. A tractor-mounted canopy shaker was developed to do the trial. The shaking frequency was set at 2.5 and 5 Hz. Experimental results showed that the vibrational acceleration at the shaking spot is not the highest. Spreading from shaking spot to the stem, it increases evidently. When spreading from stems of the outside subbranch to stems of the nearest inside subbranch, its average decrease percentage is 42%. The overall vibrational acceleration of shaking at 5 Hz is 1.85 times as high as shaking at 2.5 Hz. The overall vibrational acceleration exerted by straight PVC tine and steel tine is 1.77 and 1.97 times as high as that exerted by straight nylon tine, respectively. It is indicated that replacing nylon tine with steel tine or PVC tine helps remove the fruits inside the canopy. Replacing with steel tine is more effective than with PVC tine. Tian-Hu Liu, Reza Ehsani, Arash Toudeshki, Xiang-Jun Zou, and Hong-Jun Wang Copyright © 2017 Tian-Hu Liu et al. All rights reserved. Research and Analysis of Quasi-Zero-Stiffness Isolator with Geometric Nonlinear Damping Wed, 18 Oct 2017 07:52:43 +0000 This paper presents a novel quasi-zero-stiffness (QZS) isolator designed by combining a tension spring with a vertical linear spring. In order to improve the performance of low-frequency vibration isolation, geometric nonlinear damping is proposed and applied to a quasi-zero-stiffness (QZS) vibration isolator. Through the study of static characteristics first, the relationship between force displacement and stiffness displacement of the vibration isolation mechanism is established; it is concluded that the parameters of the mechanism have the characteristics of quasi-zero stiffness at the equilibrium position. The solutions of the QZS system are obtained based on the harmonic balance method (HBM). Then, the force transmissibility of the QZS vibration isolator is analyzed. And the results indicate that increasing the nonlinear damping can effectively suppress the transmissibility compared with the nonlinear damping system. Finally, this system is innovative for low-frequency vibration isolation of rehabilitation robots and other applications. Qingguo Meng, Xuefeng Yang, Wei Li, En Lu, and Lianchao Sheng Copyright © 2017 Qingguo Meng et al. All rights reserved. Research on the Field Dynamic Balance Technologies for Large Diesel Engine Crankshaft System Wed, 18 Oct 2017 00:00:00 +0000 In order to reduce the unbalancing mass and the accompanying unbalancing vibration of diesel engine crankshaft system, the field dynamic balancing method and its key technologies are presented in the paper. In order to separate the unbalancing vibration signal from the total vibration signal of crankshaft system, the fundamental frequency signal fitting principle based on the least square method was introduced firstly, and then wavelet noise reduction method was applied to improve the signal fitting precision of least square method. Based on the unbalancing vibration signal analysis and assessment of crankshaft system, the influence coefficient method was applied to calculate the value and phase of the equivalent unbalancing mass in flywheel. To easily correct the unbalancing condition of crankshaft system, the unbalancing adjustment equipment was designed based on the flywheel structure. The balancing effect of field dynamic balancing system designed for the large diesel engine has been verified by field experiments. Shihai Zhang and Zimiao Zhang Copyright © 2017 Shihai Zhang and Zimiao Zhang. All rights reserved. A Numerical Approach to the Dynamic Response of the Deployment System during a Circular Cylinder Crossing through the Wave Zone Wed, 18 Oct 2017 00:00:00 +0000 The dynamic response of the deployment system while deploying a circular cylinder crossing wave surface and the following submerging process are investigated numerically. The present numerical approach is based on the combination of solution methods of cable dynamics and computational fluid dynamics (CFD). For the implementation of the numerical approach, a cosimulation platform based on a CFD code and MATLAB is developed to study the fluid-solid interaction problem in the process. To generate regular waves, a numerical wave tank is built based on a piston-type wave generation method and a wave damping method applying porous media. Numerical simulations are performed based on the cosimulation platform. The sensitivities of cable tension, velocity, and acceleration of deployed body to different input parameters are investigated, including phase angles, wave heights, and periods of regular waves and deploying velocities, and the effects of those input parameters on dynamic responses of the deployment system are also discussed. Xiaozhou Hu, Daojun Cai, and Yiyao Jiang Copyright © 2017 Xiaozhou Hu et al. All rights reserved. Design and Experimental Study of an L Shape Piezoelectric Energy Harvester Wed, 18 Oct 2017 00:00:00 +0000 Piezoelectric energy harvesters of cantilevered beam type are studied in various fields due to simplicity. In general, these systems obtain electrical energy from mechanical strain by bending of cantilevered beam. However, conventional systems have disadvantages that they have low efficiency in frequency regions other than resonance frequency. To overcome the limitations, various energy harvesters to apply performance enhancement strategies are proposed and investigated. In this paper, a frequency-changeable L shape energy harvester which is form connected cantilever beam and rigid arm is proposed and investigated. The conventional piezoelectric energy harvester exhibits the principal frequency in the simple bending mode whereas the proposed system features the twisting mode resulting in a higher output voltage than the conventional system. The proposed energy harvester is simplified to a two-degree-of-freedom model and its dynamics are described. How the length of a rigid bar affects its natural frequencies is also studied. To evaluate the performance of the system, experiments by using a vertical shaker and numerical simulation are carried out. As a result, it is shown that the natural frequency for a twisting mode decreases as the arm length increased, and the higher output voltage is generated comparing with those of the conventional energy harvester. In-Ho Kim, Seon-Jun Jang, and Hyung-Jo Jung Copyright © 2017 In-Ho Kim et al. All rights reserved. Effects of Heating Rate on the Dynamic Tensile Mechanical Properties of Coal Sandstone during Thermal Treatment Wed, 18 Oct 2017 00:00:00 +0000 The effects of coal layered combustion and the heat injection rate on adjacent rock were examined in the process of underground coal gasification and coal-bed methane mining. Dynamic Brazilian disk tests were conducted on coal sandstone at 800°C and slow cooling from different heating rates by means of a Split Hopkinson Pressure Bar (SHPB) test system. It was discovered that thermal conditions had significant effects on the physical and mechanical properties of the sandstone including longitudinal wave velocity, density, and dynamic linear tensile strength; as the heating rates increased, the thermal expansion of the sandstone was enhanced and the damage degree increased. Compared with sandstone at ambient temperature, the fracture process of heat-treated sandstone was more complicated. After thermal treatment, the specimen had a large crack in the center and cracks on both sides caused by loading; the original cracks grew and mineral particle cracks, internal pore geometry, and other defects gradually appeared. With increasing heating rates, the microscopic fracture mode transformed from ductile fracture to subbrittle fracture. It was concluded that changes in the macroscopic mechanical properties of the sandstone were result from changes in the composition and microstructure. Ming Li, Xianbiao Mao, Hai Pu, Yanlong Chen, Yu Wu, and Lianying Zhang Copyright © 2017 Ming Li et al. All rights reserved. Study on the Stiffness Correction Method of Novel Antivibration Bearing for Urban Rail Transit Viaduct Wed, 18 Oct 2017 00:00:00 +0000 A novel antivibration bearing is developed to reduce the train-induced vibrations for urban rail transit viaduct. It adopts four high-damping thick rubber blocks stacking slantingly to reduce the vibration and provide large lateral stiffness. But the existing stiffness calculation method of laminated rubber bearing aimed at horizontal seismic isolation is unsuitable for thick rubber bearing designed for vertical vibration reduction. First, the stiffness correction method has been proposed based on the characteristics of the novel bearing. Second, to validate the design method, mechanical property tests are performed on a specimen of the novel bearing with design frequency at 8 Hz and with 3500 kN bearing capacity. Third, damping effects of the novel bearing are investigated through impulse vibration tests on scaled models. Results show that the mechanical property of the novel bearing can satisfy the engineering demand, and the proposed method for calculating the stiffness agrees well with the test results. The overall insertion loss of the novel bearing is 13.49 dB which is 5.32 dB larger than that of steel bearing, showing that the novel bearing is very promising to be used in the field to mitigate train-induced vibrations. Weiping Xie, Youfu Du, Liangming Sun, Agostino Marioni, and Xu Liang Copyright © 2017 Weiping Xie et al. All rights reserved. Effects of Transverse Deformation on Free Vibration of 2D Curved Beams with General Restraints Wed, 18 Oct 2017 00:00:00 +0000 An efficient modified Fourier series-based sampling surface approach is proposed for the analytical evaluation of the vibration characteristics of thick curved beams subjected to general restraints. The theoretical models of the beams are formulated by the theory of elasticity in two dimensions, which allows arbitrary thickness configurations to be tackled. As an innovation of this work, the approach is based upon the sampling surface method combined with the use of modified Fourier series approximation. In particular, the transverse beam domain is discretized by a set of sampling surfaces with unequal spaces, and the displacement components in beam domain coinciding with these surfaces are mathematically described as a set of modified Fourier series in which certain supplementary functions are included to remove all the relevant discontinuities with the displacements and their derivatives at the boundaries to form a mathematically complete set and guarantee the results convergent to the exact solutions. The final results are numerically solved using a modified variational principle by means of Lagrange multipliers and penalty method for the sake of arbitrary boundary conditions. The influences of transverse normal and shear deformation on the vibration characteristics with respect to the geometrical dimension and boundary conditions are systematically evaluated. Xueren Wang, Xuhong Miao, Di Jia, and Shengyao Gao Copyright © 2017 Xueren Wang et al. All rights reserved. A Semiactive and Adaptive Hybrid Control System for a Tracked Vehicle Hydropneumatic Suspension Based on Disturbance Identification Wed, 18 Oct 2017 00:00:00 +0000 The riding conditions for a high-speed tracked vehicle are quite complex. To enhance the adaptability of suspension systems to different riding conditions, a semiactive and self-adaptive hybrid control strategy based on disturbance velocity and frequency identification was proposed. A mathematical model of the semiactive, self-adaptive hybrid suspension control system, along with a performance evaluation function, was established. Based on a two-degree-of-freedom (DOF) suspension system, the kinematic relations and frequency zero-crossing detection method were defined, and expressions for the disturbance velocity and disturbance frequency of the road were obtained. Optimal scheduling of the semiactive hybrid damping control gain (,,) and self-adaptive control gain () under different disturbances were realized by exploiting the particle swarm multiobjective optimization algorithm. An experimental study using a carefully designed test rig was performed under a number of typical riding conditions of tracked vehicles, and the results showed that the proposed control strategy is capable of accurately recognizing different disturbances, shifting between control modes (semiactive/self-adaptive), and scheduling the damping control gain according to the disturbance identification outcomes; hence, the proposed strategy could achieve a good trade-off between ride comfort and ride safety and efficiently increase the overall performance of the suspension under various riding conditions. Shousong Han, Zhiqiang Chao, and Xiangbo Liu Copyright © 2017 Shousong Han et al. All rights reserved. A New Vibration Absorber Design for Under-Chassis Device of a High-Speed Train Tue, 17 Oct 2017 00:00:00 +0000 To realize the separation of vertical and lateral stiffness of the under-chassis device, a new type of vibration absorber is designed by using the negative stiffness of the disc spring in parallel with the rubber component. To solve its transmission characteristics, harmonic transfer method was used. A rigid-flexible coupling multibody dynamic model of a high-speed train with an elastic car body is established, and the vertical and lateral optimal stiffness of the under-chassis device are calculated. The Sperling index and acceleration PSD of the vehicle with the new vibration absorber and the vehicle with traditional rubber absorber are compared and analyzed. The results show that, with the new vibration absorber, vehicle’s running stability and vibration of the car body are more effective than the vehicle with the traditional rubber absorber. Yu Sun, Jinsong Zhou, Dao Gong, Wenjing Sun, and Zhanghui Xia Copyright © 2017 Yu Sun et al. All rights reserved. A Robust Vibration Control of a Magnetorheological Damper Based Railway Suspension Using a Novel Adaptive Type 2 Fuzzy Sliding Mode Controller Tue, 17 Oct 2017 00:00:00 +0000 This work proposes a novel adaptive type 2 fuzzy sliding controller (AT2FC) for vibration control of magnetorheological damper- (MRD-) based railway suspensions subjected to uncertainty and disturbance (UAD). The AT2FC is constituted of four main parts. The first one is a sliding mode controller (SMC) for specifying the main damping force supporting the suspension. This controller is designed via Lyapunov stability theory. The second one is an interpolation model based on an interval type 2 fuzzy logic system for determination of optimal parameters of the SMC. The third one is a nonlinear UAD observer to compensate for external disturbances. The fourth one is an inverse MRD model (T2F-I-MRD) for specifying the input current. In the operating process, an adaptively optimal structure deriving from the SMC is created (called the Ad-op-SMC) to adapt to the real status. Working as an actuator, the input current for MRD is then determined by the T2F-I-MRD to generate the required damping force which is estimated by the Ad-op-SMC and the nonlinear observer. It is shown that the obtained survey results reflect the AT2FC’s excellent vibration control performance compared with the other controllers. Sy Dung Nguyen, Dongsoo Jung, and Seung-Bok Choi Copyright © 2017 Sy Dung Nguyen et al. All rights reserved. A Study on the Dynamic Behaviour of Lightweight Gears Mon, 16 Oct 2017 00:00:00 +0000 This paper investigates the dynamic effects of mass reduction on a pair of spur gears. A one-Degree-of-Freedom (DOF) model of a mechanical oscillator with clearance-type nonlinearity and linear viscous damping is used to perform the investigations. One-dimensional (1D) gear pair models aim at studying the torsional gear vibrations around the rotational axes and can be used to simulate either gear whine or gear rattle phenomena. High computational efficiency is reached by using a spring-damper element with variable stiffness to model the gear meshing process. The angle-dependent mesh stiffness function is computed in a preparation phase through detailed Finite Element (FE) simulations and then stored in a lookup table, which is then interpolated during the dynamic simulation allowing for high computational efficiency. Nonlinear contact effects and influence of material discontinuities due to lightweighting are taken into account by FE simulations with high level of detail. Finally, the influence of gear body topology is investigated through a sensitivity analysis, in which analytical functions are defined to describe the time-varying mesh stiffness. Shadi Shweiki, Antonio Palermo, and Domenico Mundo Copyright © 2017 Shadi Shweiki et al. All rights reserved. Investigation of Axial Strengthened Reinforced Concrete Columns under Lateral Blast Loading Mon, 16 Oct 2017 00:00:00 +0000 Different factors can affect blast response of structural components. Hence, experimental tests could be the best method for evaluating structures under blast loading. Therefore, an experimental explosion loading has been done on RC members by the authors. Four RC components, with identical geometry and material, with and without axial load were imposed to air blast. Observed data of the members’ response under blast loading was used for validation of finite element modeling process using ABAQUS software. With respect to complexity, limitations, and high costs of experimental tests, analytical studies and software modeling can be good alternatives. Accordingly, in this paper, the behavior of 6 different models of normal and strengthened RC columns under blast loading was evaluated using ABAQUS. Strengthening configurations considered here were designed for enhancing axial capacity of RC columns. Therefore, we can investigate the effectiveness of axial strengthening of column on its blast resistance capacity and residual axial strength. The considered strengthening methods were different steel jacket configurations including steel angle, channel, and plate sections. The results showed that retrofitting significantly improves blast performance of the columns. Moreover, residual strength capacity of the columns strengthened with steel channel is higher than the other models. Mohammad Esmaeilnia Omran and Somayeh Mollaei Copyright © 2017 Mohammad Esmaeilnia Omran and Somayeh Mollaei. All rights reserved. Dynamic Response Analysis of Cable of Submerged Floating Tunnel under Hydrodynamic Force and Earthquake Sun, 15 Oct 2017 00:00:00 +0000 A simplified analysis model of cable for submerged floating tunnel subjected to parametrically excited vibrations in the ocean environment is proposed in this investigation. The equation of motion of the cable is obtained by a mathematical method utilizing the Euler beam theory and the Galerkin method. The hydrodynamic force induced by earthquake excitations is formulated to simulate real seaquake conditions. The random earthquake excitation in the time domain is formulated by the stochastic phase spectrum method. An analytical model for analyzing the cable for submerged floating tunnel subjected to combined hydrodynamic forces and earthquake excitations is then developed. The sensitivity of key parameters including the hydrodynamic, earthquake, and structural parameters on the dynamic response of the cable is investigated and discussed. The present model enables a preliminary examination of the hydrodynamic and seismic behavior of cable for submerged floating tunnel and can provide valuable recommendations for use in design and operation of anchor systems for submerged floating tunnel. Zhiwen Wu and Guoxiong Mei Copyright © 2017 Zhiwen Wu and Guoxiong Mei. All rights reserved. Acoustic Emission Characteristics and Failure Mechanism of Fractured Rock under Different Loading Rates Sun, 15 Oct 2017 00:00:00 +0000 To study the loading rate dependence of acoustic emissions and the failure mechanism of fractured rock, biaxial compression tests performed on granite were numerically simulated using the bonded particle model in Particle Flow Code (PFC). Uniaxial tests on a sample containing a single open fracture were simulated under different loading rates ranging from 0.005 to 0.5 m/s. Our results demonstrate the following. (1) The overall trends of stress and strain changes are not affected by the loading rate; the loading rate only affects the strain required to reach each stage. (2) The strain energy rate and acoustic emission (AE) events are affected by the loading rate in fractured rock. With an increase in the loading rate, AE events and the strain energy rate initially increase and then decrease, forming a fluctuating trend. (3) Under an external load, the particles within a specimen are constantly squeezed, rotated, and displaced. This process is accompanied by energy dissipation via the production of internal tensile and shear cracks; their propagation and coalescence result in the formation of a macroscopic rupture zone. Yongzheng Zhang, Gang Wang, Yujing Jiang, Shugang Wang, Honghua Zhao, and Wenjun Jing Copyright © 2017 Yongzheng Zhang et al. All rights reserved. Drilling Performance of Rock Drill by High-Pressure Water Jet under Different Configuration Modes Sun, 15 Oct 2017 00:00:00 +0000 In the rock drilling progress, the resistant force results in tools failure and the low drilling efficiency; thus, it is necessary to reduce the tools failure and enhance the drilling efficiency. In this paper, different configuration modes of drilling performance assisted with water jet are explored based on the mechanism and experiment analysis of rock drilling assisted with water jet. Moreover, the rotary sealing device with high pressure is designed to achieve the axial and rotation movement simultaneously as well as good sealing effect under high-pressure water jet. The results indicate that the NDB and NFB have better effects on drilling performance compared with that of NSB. Moreover, the high-pressure water jet is helpful not only to reduce the drill rod deflection, but also to reduce the probability of drill rod bending and improve the drill rod service life. Songyong Liu, Hongsheng Li, and Huanhuan Chang Copyright © 2017 Songyong Liu et al. All rights reserved. Numerical Analysis on Chaotic Vibration of Drive System for a Movable Tooth Piezoelectric Motor Thu, 12 Oct 2017 00:00:00 +0000 The nonlinear dynamic equations of the drive system for movable tooth piezoelectric motor are established. Using these equations, the chaotic vibrations of the system are investigated. The results show that chaotic vibrations occur in the movable tooth drive system under some parameters. The average mesh stiffness, theoretical radius, and wave generator offset significantly influence the nonlinear chaotic vibrations of the drive system of the movable tooth piezoelectric motor. The ranges for the system parameters that lead to a motor with bad dynamics are shown. The results can be used to predict the dynamic load and optimize power density of the proposed piezoelectric motor. Chong Li, Jichun Xing, Jiwen Fang, and Zhong Zhao Copyright © 2017 Chong Li et al. All rights reserved. Dynamic of Friction Coupling Independently Rotating Wheels for High Speed Thu, 12 Oct 2017 00:00:00 +0000 A new lateral coupling structure with independently rotating wheels (IRW) is proposed, and longitudinal creepage is obtained by replacing the gear pair with the friction pair to synchronize the rotation speed of left and right wheels. The auxiliary wheelset made up of two friction wheels can be placed either under the primary suspension or on the frame. Vehicles dynamics models with three different kinds of bogies are developed, including friction coupling bogie with independently rotating wheels (FCIRW-bogie), bogie with independently rotating wheels (IRW-bogie), and bogie with rigid wheelsets, and their guiding and resetting capability when negotiating large-radius curves are compared and analyzed. Results show that FCIRW has the advantages of both IRW and rigid wheelset. On the straight track, FCIRW has sufficient wheel-rail longitudinal creep force to assist the reset; its critical speed is much higher than that of the rigid wheelset. On the curved track, the whole vehicle wear power of FCIRW-bogie vehicle is about 2/3 of the rigid axle level. Yan Shi, Miao Li, Weihua Ma, and Kang Chen Copyright © 2017 Yan Shi et al. All rights reserved. Time-Varying Wind Load Identification Based on Minimum-Variance Unbiased Estimation Thu, 12 Oct 2017 00:00:00 +0000 A minimum-variance unbiased estimation method is developed to identify the time-varying wind load from measured responses. The formula derivation of recursive identification equations is obtained in state space. The new approach can simultaneously estimate the entire wind load and the unknown structural responses only with limited measurement of structural acceleration response. The fluctuating wind speed process is investigated by the autoregressive (AR) model method in time series analysis. The accuracy and feasibility of the inverse approach are numerically investigated by identifying the wind load on a twenty-story shear building structure. The influences of the number and location of accelerometers are examined and discussed. In order to study the stability of the proposed method, the effects of the errors in crucial factors such as natural frequency and damping ratio are discussed through detailed parametric analysis. It can be found from the identification results that the proposed method can identify the wind load from limited measurement of acceleration responses with good accuracy and stability, indicating that it is an effective approach for estimating wind load on building structures. Huili Xue, Kun Lin, Yin Luo, and Hongjun Liu Copyright © 2017 Huili Xue et al. All rights reserved. Mechanical Properties and Acoustic Emission Properties of Rocks with Different Transverse Scales Wed, 11 Oct 2017 00:00:00 +0000 Since the stability of engineering rock masses has important practical significance to projects like mining, tunneling, and petroleum engineering, it is necessary to study mechanical properties and stability prediction methods for rocks, cementing materials that are composed of minerals in all shapes and sizes. Rocks will generate acoustic emission during damage failure processes, which is deemed as an effective means of monitoring the stability of coal rocks. In the meantime, actual mining and roadway surrounding rocks tend to have transverse effects; namely, the transverse scale is larger than the length scale. Therefore, it is important to explore mechanical properties and acoustic emission properties of rocks under transverse size effects. Considering the transverse scale effects of rocks, this paper employs the microparticle flow software PFC2D to explore the influence of different aspect ratios on damage mechanics and acoustic emission properties of rocks. The results show that the transverse scale affects uniaxial compression strength of rocks. As the aspect ratio increases, uniaxial compression strength of rocks decreases initially and later increases, showing a V-shape structure and although it affects the maximum hit rate and the strain range of acoustic emission, it has little influence on the period of occurrence. As the transverse scale increases, both damage degree and damage rate of rocks decrease initially and later increase. Xi Yan, Li Jun, Liu Gonghui, and Guo Xueli Copyright © 2017 Xi Yan et al. All rights reserved. Deep Learning Enabled Fault Diagnosis Using Time-Frequency Image Analysis of Rolling Element Bearings Mon, 09 Oct 2017 08:44:13 +0000 Traditional feature extraction and selection is a labor-intensive process requiring expert knowledge of the relevant features pertinent to the system. This knowledge is sometimes a luxury and could introduce added uncertainty and bias to the results. To address this problem a deep learning enabled featureless methodology is proposed to automatically learn the features of the data. Time-frequency representations of the raw data are used to generate image representations of the raw signal, which are then fed into a deep convolutional neural network (CNN) architecture for classification and fault diagnosis. This methodology was applied to two public data sets of rolling element bearing vibration signals. Three time-frequency analysis methods (short-time Fourier transform, wavelet transform, and Hilbert-Huang transform) were explored for their representation effectiveness. The proposed CNN architecture achieves better results with less learnable parameters than similar architectures used for fault detection, including cases with experimental noise. David Verstraete, Andrés Ferrada, Enrique López Droguett, Viviana Meruane, and Mohammad Modarres Copyright © 2017 David Verstraete et al. All rights reserved. Impact Dynamics of a Percussive System Based on Rotary-Percussive Ultrasonic Drill Mon, 09 Oct 2017 00:00:00 +0000 This paper presents an impact dynamic analysis of a percussive system based on rotary-percussive ultrasonic drill (RPUD). The RPUD employs vibrations on two sides of one single piezoelectric stack to achieve rotary-percussive motion, which improves drilling efficiency. The RPUD’s percussive system is composed of a percussive horn, a free mass, and a drill tool. The percussive horn enlarges longitudinal vibration from piezoelectric stack and delivers the vibration to the drill tool through the free mass, which forms the percussive motion. Based on the theory of conservation of momentum and Newton’s impact law, collision process of the percussive system under no-load condition is analyzed to establish the collision model between the percussive horn, the free mass, and the drill tool. The collision model shows that free mass transfers high-frequency small-amplitude vibration of percussive horn into low-frequency large-amplitude vibration of drill tool through impact. As an important parameter of free mass, the greater the weight of the free mass, the higher the kinetic energy obtained by drill tool after collision. High-speed camera system and drilling experiments are employed to validate the inference results of collision model by using a prototype of the RPUD. Yinchao Wang, Qiquan Quan, Hongying Yu, He Li, Deen Bai, and Zongquan Deng Copyright © 2017 Yinchao Wang et al. All rights reserved. Numerical Study on the Seismic Response of Structure with Consideration of the Behavior of Base Mat Uplift Tue, 03 Oct 2017 09:31:26 +0000 The foundation might be separated from the supporting soil if the earthquake is big enough, which is known as base mat uplift. This paper proposed a simplified calculation model in which spring element is adopted to simulate the interaction between soil and structure. The load-deformation curve (- curve) of the spring element can be designated to represent the base mat uplift, in which the pressure can be applied while tensile forces are not allowed. Key factors, such as seismic wave types, seismic wave excitation directions, seismic wave amplitudes, soil shear velocities, structure stiffness, and the ratio of structure height to width (), were considered in the analysis. It is shown that () seismic wave type has significant influence on structure response due to different frequency components it contained; () the vertical input of seismic wave greatly affected structure response in vertical direction, while it has little impacts in horizontal direction; () base mat uplift is easier to take place in soil with higher shear velocity; () structure value has complicated influence on base mat uplift. The outcome of this research is assumed to provide some references for the seismic design of the structure due to base mat uplift. Guo-Bo Wang, Xin Zhou, Xian-Feng Ma, and Jun Wu Copyright © 2017 Guo-Bo Wang et al. All rights reserved. Experimental Study and Engineering Practice of Pressured Water Coupling Blasting Tue, 03 Oct 2017 06:50:25 +0000 Overburden strata movement in large space stope is the major reason that induces the appearance of strong mining pressure. Presplitting blasting for hard coal rocks is crucial for the prevention and control of strong pressure in stope. In this study, pressured water coupling blasting technique was proposed. The process and effect of blasting were analyzed by orthogonal test and field practice. Results showed that the presence of pressure-bearing water and explosive cartridges in the drill are the main influence factors of the blasting effect of cement test block. The high load-transmitting performance of pore water and energy accumulation in explosive cartridges were analyzed. Noxious substances produced during the blasting process were properly controlled because of the moistening, cooling, and diluting effect of pore water. Not only the goal of safe and static rock fragmentation by high-explosive detonation but also a combination of superdynamic blast loading and static loading effect of the pressured water was achieved. Then the practice of blasting control of hard coal rocks in Datong coal mine was analyzed to determine reasonable parameters of pressured water coupling blasting. A good presplitting blasting control effect was achieved for the hard coal rocks. J. X. Yang and C. Y. Liu Copyright © 2017 J. X. Yang and C. Y. Liu. All rights reserved. Research on the Vibration Characteristics of a Compounded Periodic Strut Used for Helicopter Cabin Noise Reduction Tue, 03 Oct 2017 00:00:00 +0000 A special periodic strut is developed to reduce the helicopter cabin noise in this paper. The strut exhibits unique dynamic characteristics which can isolate the gearbox vibrations from transferring to the fuselage and radiating noise. Modeling, simulation, and experimental research are carried out to explore its characteristics and performance. A theoretical model of the strut is firstly established, with particular emphasis on correlating the passband and stop band behaviors with the damping and a series of boundary conditions. Then, through simulations, it is shown that both the damping and boundary conditions have significant influences on the stop band, including the beginning and end frequencies and attenuation effects. Based on these analytical simulations, experimental analyses are conducted with the newly developed strut. Inspiring performances are validated under different conditions. Considering that the helicopter vibration in practical applications is much more complex, further experimental investigations are carried out on a helicopter model, which generates prominent gear mesh tones similar to a real helicopter. The experimental results show that the compounded periodic strut can significantly attenuate the vibrations transmitted to the fuselage. Compared with the plain strut, attenuations in excess of 40 dB are measured in the frequency range from 300 to 2000 Hz. Yang Lu, Fengjiao Wang, and Xunjun Ma Copyright © 2017 Yang Lu et al. All rights reserved. Projectile Penetration into Sandy Soil Confined by a Honeycomb-Like Structure Tue, 03 Oct 2017 00:00:00 +0000 HPS (Honeycomb-like Protective Structure) is a newly proposed protective structure filled with sandy soil. In order to investigate the penetration resistance of the structure, numerical simulations based on SPH method had been carried out by using LS-DYNA, which are corresponding to the experiments. The calibrated model leads to reasonable predictions of the dynamic responses and damage modes of the HPS. More situations were carried out taking factors influencing the penetration into consideration, including point of impact, angle of impact, and projectile caliber. Penetration mode was established by analyzing the energy dissipation and investigating the mechanism from the phenomenological viewpoint. Simulation results show that the resisting forces and the torque that act on the long rod projectile would be greater than those acting on the short one when instability occurred. Besides, approximate 45° angle of impact was formed in the case of off-axis, which has a certain influence on the ballistic stability, resulting in more kinetic energy of projectile dissipating in HPS and less depth of penetration. The kinetic energy of projectile dissipated in sandy soil largely and the strip slightly, and the former was greater than the sum of the latter. Weiming Luo, Shaoqing Shi, Zipeng Chen, Jianhu Sun, and Wenkang Wang Copyright © 2017 Weiming Luo et al. All rights reserved. Experimental Study of Bilinear Initiating System Based on Hard Rock Pile Blasting Sun, 01 Oct 2017 07:43:22 +0000 It is difficult to use industrial explosives to excavate hard rock and achieve suitable blasting effect due to the low energy utilization rate resulting in large rocks and short blasting footage. Thus, improving the utilization ratio of the explosive energy is important. In this study, a novel bilinear initiation system based on hard rock blasting was proposed to improve the blasting effects. Furthermore, on the basis of the detonation wave collision theory, frontal collision, oblique reflection, and Mach reflection during detonation wave propagation were studied. The results show that the maximum detonation pressure at the Mach reflection point where the incident angle is 46.9° is three times larger than the value of the explosive complete detonation. Then, in order to analyze the crack propagation in different initiation forms, a rock fracture test slot was designed, and the results show that bilinear initiating system can change the energy distribution of explosives. Finally, field experiment was implemented at the hard rock pile blasting engineering, and experimental results show that the present system possesses high explosive energy utilization ratio and low rock fragments size. The results of this study can be used to improve the efficiency in hard rock blasting. Yusong Miao, Xiaojie Li, HongHao Yan, Xiaohong Wang, and Junpeng Sun Copyright © 2017 Yusong Miao et al. All rights reserved.