25 February 2011, Volume 30 Issue 2
    

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  • Ju Ping-hua;Qin Shu-ren;Zhao-lin
    . 2011, 30(2): 1-4.
    Abstract ( 1051 ) Download PDF ( 986 )   Knowledge map   Save
    Local mean decomposition (LMD) is an effective time-frequency analysis method for decomposing the multi-component AM-FM signal into a number of mono-component AM-FM signals. An energy operator demodulating approach based on LMD is proposed for extracting the characteristics of the faulty signal. LMD is used to decompose the complex multi-component AM-FM signal into a linear combination of a finite number of production functions (PF), then the energy operator demodulation is applied to extract the amplitudes and frequencies of each PF so as to obtain the time-frequency distribution of the faulty signal and extract the fault characteristics. In order to improve the precision of analysis, a data extension method based on trend character of sine function is proposed to overcome end effect. The application results show that the proposed energy operator demodulating approach based on LMD can extract the characteristics of mechanical fault vibration signal effectively.
  • ZHAO Yang;WU Yue;DUAN Zhongdong;CAO Shuyang;TAMURA Yukio;OZONO. S
    . 2011, 30(2): 5-9.
    Abstract ( 1685 ) Download PDF ( 641 )   Knowledge map   Save
    The method of non-stationary signal analysis is a major issue in the field of signal analysis. Taking the signal of non-stationary wind pressure and lift coefficient obtained from wind tunnel experiment as research objects, time frequency analysis of the signal was presented by the method of HHT. Based on the method of HHT, the meaningful instantaneous frequency was obtained, as well as exact expression of frequency which changes with time; signal was finally expressed as the energy distribution in the time frequency plane as Hilbert spectral; this method can be applied to analyzing a large amount of nonlinear and non-stationary signals whose frequency change with time, and complex signal can be decomposed into a number of intrinsic mode functions from high- to low-frequency. However, analysis results do not show significant characteristics of special distribution, it is different from previous intrinsic mode function extracted by HHT; if intrinsic mode extracted from non-stationary signal obtained in this experiment is residual signal in the low-frequency part and high frequency signal is neglected, the curve of residual signal of time history of wind pressure and lift coefficient can regress a linear function and a sine function separately. It also shows that the components of this non-stationary signal are mostly stationary signal, and the time history of non-stationary signal can be analyzed by the method of stationary signal analysis.
  • XU Fuyou;ZHANG Zhe;WANG Hui-li;HUANG Cai-liang
    . 2011, 30(2): 10-14.
    Abstract ( 953 ) Download PDF ( 518 )   Knowledge map   Save
    Through wind tunnel tests in smooth and turbulent flows, the vortex-induced vibration responses of large-span steel arch rib rectangular aeroelastic model are investigated. Three kinds of attack angles (-3º, 0º, +3º), multiple yaw angles (0º~90º) cases are incorporated. The results show that: in smooth flows, stable 1st anti-symmetric vertical bending and symmetric vertical bending vortex vibration can be observed, which are not found in turbulent flows. The 1st anti-symmetric vertical bending vortex vibration amplitude is very small, with low wind speed and narrow lock-in area. Whereas the 1st symmetric vertical bending vortex vibration amplitude is large, with higher wind speed and wider lock-in area. Vortex vibration amplitude at 1/4 section is greater than that of the vaulted section. When the yaw angle is greater than 10º, vortex vibration does not appear for the rectangular rib.
  • WANG Jun;ZHANG Jing-hui;NING Wei
    . 2011, 30(2): 15-18.
    Abstract ( 1085 ) Download PDF ( 1202 )   Knowledge map   Save
    Based on the coupled finite element and boundary element method, the numerical implementation for computing simultaneously the structural vibration and the associated acoustic field is presented. This paper presents a new approach for integrating discrete structural-acoustic methods with stochastic analysis for computing the vibro-acoustic behavior of the cabin structural subjected to random excitation from a shaker plus reverberant acoustic field. By the mathematical formulation deduced we can calculate nodal response power spectrum density (PSD) of the coupling model under random vibro-acoustic combined environment, it solved the problem that SYSNOISE cannot calculate at the situation when the structure is suffering two different kinds of random excitations simultaneously. The results show that: the effect of structural-acoustic coupling is equivalent to an added damping effect in low frequency, with the increase of frequency, the effect becomes obvious. For the case of vibro-acoustic combined environment, in low frequency, response is mainly caused by random vibration, while in high frequency by reverberant field, modes excited by reverberant field are more than by random vibration, especially in high frequency.
  • HUANG Xiao-ming;ZHU Xi;MU Jin-lei;LI Hai-tao
    . 2011, 30(2): 19-23.
    Abstract ( 994 ) Download PDF ( 432 )   Knowledge map   Save
    A close range underwater explode test on two box-beam models was made in blast cube. High speed photography was applied to capture the sagging damage process of the model subjected to bubble movement. Experimental results show that when bubble shrink, close range hull bottom boundary blocked the fluid movement and form cavities area up the bubble, enhanced the bubble’s negative pressure effect in intension and duration. The close range boundary effect is the first cause of model’s sagging damage. And when the model’s vertical vibrate frequency nearby the frequency of bubble pulsation, the model’s vertical vibration caused by shock wave superposed with bubble’s negative pressure effect, enhanced the possibility of sagging damage of model. The influence of blast distance to bubble’s negative pressure effect and vertical vibrate induced by shock wave are made. The results indicated that only when the blast distance was less than twice bubble’s maximum radiuses, the close range boundary effect cannot be ignored.
  • Qiao Dongsheng;Ou Jinping;
    . 2011, 30(2): 24-31.
    Abstract ( 1185 ) Download PDF ( )   Knowledge map   Save
    The deepwater catenary mooring line damping mainly includes hydrodynamic drag damping, internal damping and friction damping caused by seabed interaction. Hydrodynamic drag and friction damping is significantly affected by a floating platform besides the internal damping caused by material properties. The dissipated energy by a mooring line from the floating platform as a result of its oscillation is applied to calculate the mooring-induced damping. The mooring line and seabed interaction is based on the hypothesis of rigid seabed. The fluid drag force and inertia force on the mooring line are calculated according to the Morrison formula. Under the various current velocity distribution conditions, the non-liner dynamic analysis of mooring line is executed in the time-domain based on the finite element method. Moreover, the wave drift oscillation and the wave frequency oscillation excitation of floating platform are specified. The maximum tension of mooring line and the viscous damping are obtained from the results. Considering the contact friction between the mooring line and seabed, the maximum tension of mooring line is compared under various friction coefficients and the friction damping is calculated.
  • JIANG Xin-liang;WANG Fei
    . 2011, 30(2): 32-38.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve computational efficiency, constrained mode synthesis method is discussed and a linear space consists of displacement vectors calculated by different mode cut-off numbers is defined. A function is also defined and verified to be a norm of this linear space mathematically. Then adopt the maximum value of that norm as the potential energy criterion. The relationship between potential energy criterion and mode cut-off number is derived. Consequently, the mode cut-off criterion based on potential energy criterion is proposed. In addition, the situation of adopting mechanical energy as the criterion of constrained mode synthesis method is considered. It is proved that mechanical energy is not a monotonic function towards mode cut-off number, so it is not suitable for constrained mode synthesis method. Finally, the proposed potential energy criterion is applied to seismic analysis of soil and multi-story buildings interaction system and the results are compared with method without mode synthesis. It shows that the proposed mode cut-off criterion based on potential energy criterion is effective while that based on mechanical energy criterion which generally used in superposition method is not suitable for constrained mode synthesis method.
  • HUANG You-qin;GU Ming
    . 2011, 30(2): 39-43.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A single-layer cylindrical reticulated shell was taken as an example to study the dynamic instability of spatial structures by the Budiansky-Roth criterion. The Budiansky-Roth criterion was explained and the wind tunnel test of the single-layer cylindrical reticulated shell was conducted to obtain the fluctuating wind loads on it. Then, its dynamic instability under fluctuating wind loads was studied, in which the influence of initial geometrical imperfections, wind directions and coefficients of wind pressure were discussed and comparisons with stability analysis results from the Chinese standard and the gust response factor (GRF) method were made. The results show that study on the dynamic instability of spatial structures under fluctuating wind loads is necessary.
  • ZHAO Ming-sheng;ZHANG Jian-hua;YI Chang-ping
    . 2011, 30(2): 44-47.
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    The objective of time-frequency analysis on blasting vibration signal is to obtain the distribution of signal energy with both time and frequencies comprehensively and accurately. The RSPWVD quadratic time-frequency analysis method has high accumulation and can suppress the cross-term preferably, but part signal information will loss inevitably in the process, which induce that the details of blasting vibration signal information can’t be got. RSPWVD quadratic time-frequency analysis method and wavelet analysis method are combined to analyze the blasting vibration signal in this paper, the results show that this method increases the precision of time-frequency characteristics of blasting vibration signal and can obtain its detail information. Employing this method can get more intuitive, reasonable, higher-resolution time-frequency characteristics of signal.
  • Zhou Yun;Liu Chun;Wang Dayang
    . 2011, 30(2): 48-54.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In this paper, wind-induced vibration responses of high-rise building with steel tower protrusion are studied. AR model is introduced and adopted to simulate fluctuating wind time-series. Dynamic characteristics of main structure, steel tower protrusion and structure with the protrusion in along-wind action are discussed. Influences of six kinds of parameters, such as wind power spectrum, frequency ratio, basic wind pressure and so on, to structural steel tower protrusion are also discussed. Control effects of velocity-dependent dampers to wind–induced vibration responses of the steel tower protrusion are studied comparatively. The study results show that natural frequency of the steel protrusion should be away from the first three frequencies of the main structure so as to reduce whiplash effect. The wind-induced vibration responses of the steel tower protrusion are greater than that of the main structure and will be increase with rise of basic wind-pressure and height of the protrusion, but decrease with rise of span of the protrusion. Velocity-dampers can reduce wind responses of the protrusion effectively. The vibration effect of viscous dampers to the wind responses of the protrusion is better than that of viscoelastic dampers and the vibration effect of nonlinear viscous dampers is better than that of linear viscous dampers.
  • SHI Lian-hui;WANG An-wen
    . 2011, 30(2): 55-59.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The axial disturbance on the head of supercavitation vehicles is considered, and the governing equations for dynamic stability of submarine vehicles are derived, then the numerical calculation for the dynamic instability problem of submarine vehicles is performed by Bolotin’s method, corresponding curves of the critical frequency are obtained and the effects of the load parameters and the vehicle parameters on the primary unstable region are analyzed, the results provided a sort of theory foundation for the security evaluation of supercavitation vehicles.
  • ZHENG Xiao-mei;XU Zhi-hong;TANG Wen-hui;RAN Xian-wen
    . 2011, 30(2): 60-64.
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    A second-order Godunov-scheme SPH method is proposed to achieve higher accuracy and steeper representation of wave fronts than that calculated by first-order Godunov-scheme SPH method. The distribution of physical variables inside each particle is represented with linear functions in new method. Therefore physical values at particle boundaries which are calculated through linear interpolation are used as initial values of Riemann problem between interacting particles. Riemann solvers and Taylor series are then introduced into the SPH method. One-dimensional problems of stress wave propagation are simulated by both first-order and second-order Godunov-scheme SPH methods. The results show that the new method has effectively improved the solution accuracy and is stable both in tension and compression.
  • HuZebin;XuJinyu;XiFeng;DingGuobo
    . 2011, 30(2): 65-68.
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    Mechanical behavior of Styropor concrete(EPSC) added with various volumetric fractions of EPS subjected to high strain rates were studied by using the Large-Diameter-SHPB. The infection of volumetric fractions and average strain rate to dynamic properties of EPSC were investigated. A nonlinear viscoelastic constitutive model for EPSC was established with experimental data. The experimental results show that under high strain rate condition, the dynamic strength and limit strain of EPSC are strain rate dependent, the strain rate effect can be expressed by linear approximations. With the addition of volumetric fractions of EPS, the impact compressive strength and elastic modulus of EPSC declines, and the toughness of EPSC is reinforced. Comparison of model output with experimental data indicates that this nonlinear viscoelastic constitutive model is able to describe high-strain-rate mechanical behavior of EPSC reasonably.
  • Liu De-shun;He Xian-ke;Duan Kai
    . 2011, 30(2): 69-72.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The force-penetration relationship curver of rocks reflect interaction mechanism beteen the drill bit and rocks in the percussive drilling mechanical system,but the varable characteristics impedamce of a drill bit is essential to obtain the .A new impedance of a drill bit is essential to obtain the curves.new inverse method is proposed to estimate variable characteristics imperamce of the dill bit from the strains in a drill rod using two-point strain measurement and characteristic lines.Firstly,this paper describes stresswave propagation on a rod with variable characteristics impedance and establishes fht time and space analysis equations using a grid of chatacteristics lines.Secondly,a new inversion principle is proposed to calculate the variable characteristics impedance of drill bit in turn,according to a state vector at one point of the rod,and a method is introduced to calculate the state vector at any point suing two-point strain of the rod.Finally,the inversion meahod using two point steain of the rod and characteristic lines is validated and discussed,which can estimate variable characteristics impedance of the bit.
  • DUAN Shao-wei;XIANG Xiang-lin;SHEN Pu-sheng
    . 2011, 30(2): 73-76.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Dampuing ratio is critical to dynamic analysis of complex structures.However,because of the specifcity of damping model of complex structure,there are no perfect theory and methods to determine damping ratios and so on.A damping model,which is based on the conversion modal damping ratios,is applied to the complex structures constructed of materials of different damping properties.With the procedure,the conversion modal damping ratios can be obtained by use of complex damping theory and modal strain energy method,and the relationship between the conversion modal damping ratios and the damping ratios of materials have been analyzed in this paper.The vibration responses of an engineering structure,investigated with the proposed method,are more accurate than the substruture method of rayleigh damping and agree well with the elemental damping method,and the proposed method is more reasonable.Because the proposed method has a simple mathematical expression and a clear physical,it can be widely used in complex structure dynamical analysis.
  • JIANG Ai-Hua;ZHANG Zhi-Yi;ZHANG Yi;HUA Hong-Xin
    . 2011, 30(2): 77-84.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Researches on noise of centrifugal pump are reviewed. Firstly, noise sources of centrifugal pump are summed up. And researches on noise sources of centrifugal pump are also classified by noise from mechanism, including volute with different geometry shapes and impeller, and by noise from hydrodynamics, including cavitation, fluid-structure interaction and turbulence. Then methods used in these researches are summarized by three aspects, namely theoretical deduction of simplified model, numerical model by PC and experiment. At last, some opening issues at present and new fields in future in the researches of noise of centrifugal pump are putted forward.
  • WANG Da-yang;ZHOU Yun;WANG Shao-he
    . 2011, 30(2): 85-92.
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    Vibration control of a 288m super-tall building is studied in this study. Six vibration control schemes with viscous dampers and lead-viscoelastic dampers are proposed to control structural dynamic responses under wind and earthquake excitations. Fluctuating wind time series of the structure in 10-year frequency are simulated by modified AR model. The dynamic responses of the structure with the proposed control schemes in wind and earthquake excitations are investigated and their vibration control effects are analyzed comparatively. The study results show that the excessive dynamic responses induced by wind and earthquake excitations can be controlled effectively by the proposed schemes. The peak acceleration of top story can be reduced by almost 40% for the proposed control schemes in wind excitation. The additional safety reserve of the structure under minor and major earthquakes can also be added by the proposed control schemes. So, the validity and feasibility of the proposed schemes in reducing structural vibration responses can be fully approved. Some suggestions about structural analysis and design under wind and earthquake excitations are proposed.
  • He Shaohua;Wu Xinyue
    . 2011, 30(2): 93-98.
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    A new method was proposed for shock response modeling and computing of planar multi-rigid-flexible body systems by integrating transfer matrix method with its flexibility and high computational efficiency. Adopting Newmark-β algorithm to linearizing high order terms in dynamic equations and modes to express flexible body deformation, extended transfer matrixes of general rigid-body and special rigid bodies (rigid homogeneous rectangular plate, rectangular sheet plate with elastic support), general flexible-body and special flexible bodies (Euler-Bernouni beam) in systems under base-transferred shock were established. The shock excitations include both translational and rotational components. Numerical iterative algorithm program based on Newmark-β was also given. With an engineering example, the accuracy of this proposed method was verified by a comparison with the finite element method. The results also show that rotational component of shock excitations’ contribution to the overall response can not be ignored. Although this study is objected planar multi-rigid-flexible system, it can easily be extended to three-dimensional case.
  • WANG Guoxin;CHEN Guangxiong;WU Pingbo
    . 2011, 30(2): 99-103.
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    According to Brockley’s theory that friction-induced vibration causes rail corrugation, an elastic vibration model of a wheelset-track system when a vehicle negotiates a tight curve at a steady state is established, which includes a wheelset, two rails and a series of sleeper support springs and dampers. In the model, the creep forces between the wheels and rails are assumed to be saturated and equal to the normal contact forces multiplied by a friction coefficient. The motion stability of the model is analyzed using ABAQUS package. It is found that when the friction coefficient μ>0.28, there are propensities of unstable self-excited vibration which is a possible mechanism for the short-pitch corrugation occurred on the low rail. The influence of the sleeper support stiffness and damping on rail corrugation is studied by use of the model. The results show that softer sleeper support stiffness and appropriate damping may suppress rail corrugation. It is also found that similar to the discrete sleeper support, the continuous sleeper support can not eliminate wear-type rail corrugation.
  • ZHOU Jing;CHEN Kailiang;Huang Liang
    . 2011, 30(2): 104-109.
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    Nonlinear displacement biases in response of single-degree-freedom-systems (SDOF) are studied, which are resulted from scaling the velocity pulse-like ground motion records. Based on dynamic time (history) analysis of SDOF systems subjected to 30 pulse-like ground motions, this work investigates the variation rules of the nonlinear displacement biases versus structural vibration period (T) and strength reduction factor (R) after scaling the earthquake records to the levels of target spectral acceleration (Sa), peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD). The variation trends of displacement biases are determined by log-linear regression of scattered points, and the stability of the biases under the condition of scaling different ground motion intensity measures are comparatively analyzed. The results demonstrate that the amount of displacement biases greatly depend on the scaling factor, the first-mode period of vibration, and overall strength of the structure. Reasonable scaling factor and reasonable ground motions intensity measuring parameter of the velocity pulse-like ground motion records can effectively reduce the calculated displacement bias in structural earthquake responses.
  • WEI Biao;LI Jian-zhong
    . 2011, 30(2): 110-114.
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    Based on the basic concept of modal pushover analysis (MPA), details of MPA estimating irregular continuous bridges’ seismic displacement demand were investigated. Analyzing on bridge’s displacement monitoring point’s selection, capacity spectrum form, inelastic demand spectrum’s building process and modal combination rules produced a MPA procedure for irregular continuous bridges. The lateral seismic displacement demand of four irregular continuous bridges estimated by the MPA procedure was compared with rigorous inelastic time-history analysis. Results show, although irregular continuous bridges’ important modes couple with each other after piers yield, the MPA procedure can estimate reasonable seismic displacement demand.

  • ZHANG Xiao-dong;ZHANG Pei-lin;FU Jian-ping;WANG Cheng
    . 2011, 30(2): 115-118.
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    Presently, the recoil shock motion computation of gun is based on one-dimensional quasi-steady theory. It leads to the hydraulic resistance obtained by the method not accord with the actual condition and can’t show the flow field distribution and the fluid flow characteristics. Based on two-dimensional model according with actual structure, through the collaborative simulation method with MATLAB and FLUENT the complete motion simulation under gun recoil and counter-recoil shock is realized. Comparing simulation data with test data, the results proves the feasibility and validity. The method applies a new idea for improving the shock motion computation of gun.
  • WU Tao-jing;LI Jian-zhong;GUAN Zhong-guo
    . 2011, 30(2): 119-123.
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    The bi-directional coupled interaction of FPS under two horizonta1 orthogonal directional excitations was investigated. Based on a nonlinear numerical model of a typical continuous long span bridge isolated with FPS, the seismic responses taking into account or ignoring the bi-directional coupled interaction of bearing restoring force were compared at different levels of parameters such as pier height, yield strength and bearing radius. The results show that the bi-directional coupled interaction has considerable effects on the seismic responses of the isolated bridge. If these effects are ignored, the peak bearing displacements will be greatly underestimated, which is crucial for isolated bridges from the design point of view.
  • HUANG You-qin;;ZHOU Xuan-yi
    . 2011, 30(2): 124-129.
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    A single-layer cylindrical reticulated shell was taken as an example to study the influence of snow-drifing on the dynamic stability of spatial structures under coupled wind and snow loads by the Budiansky-Roth criterion. Stochastic wind loads on the structure were obtained from the wind tunnel test, and the snow-drifting on the structure under wind actions was simulated by the numerical method based on FLUENT with added C++ code. The results show that snow erodes on the top of the shell while deposits on the windward and lee side of the shell. The angle of the dividing line between the erosion area and the deposition area is identical to the corresponding wind direction. The snow-drifting on the shell debases its dynamic stability in all typical wind directions. The longer the duration of snow-drifting the worse the dynamic stability of the shell, but the influence of snow-drifting decreases with its duration. Also, the dynamic stability of the shell recedes with the increment of original snow depth on the shell.
  • Xinchun Guana;Yonghu Huanga;Shaohua Hua;Jinping Ou a;b;
    . 2011, 30(2): 130-133.
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    ABSTRACT
    Compared to the double ended magnetorheological (MR) dampers, single-ended MR dampers are more suitable in
    limited-space required fields for their larger strokes. An accumulator is needed for a single-ended MR damper to balance the
    volume changes as the piston pushed out and into of the cylinder. Since an accumulator has a great influence on the damper's
    performances, this influence should be taken into account in the damper's designing procedure. In this paper, damping force
    formula is deduced for the single-ended MR damper with spring accumulator. Then both the method of determination main
    parameters of regular spring accumulator and its inherent drawbacks are presented. Finally, by utilizing the super elastic
    character of shape memory alloy (SMA), a SMA spring accumulator is proposed and its design method is given as well.
  • ZhangJie;LinJianhui
    . 2011, 30(2): 134-137.
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    Current spectral analysis for track irregularity is based on sampling data at a uniform interval, but the train is of fluctuation velocity, therefore the accuracy of routine spectral analysis is in doubt. A nonuniform sampling sequence was studied to set up the power spectral density(PSD) formula of nonuniform sampling signal. The new formula was applied to analysis the nonuniform sampling cases when the sampling interval is of the Gaussian distribution probability density function. The result shows that the PSD formula of nonuniform sampling signal includes the classic uniform sampling signal’s PSD formula, which verifies the accuracy of the new formula. Finally a method was put forward to measure the probability density function of the sampling interval for the track irregularity spectral analysis.
  • Zhang Nan;Xia He;Guo Weiwei;Cheng Qian
    . 2011, 30(2): 138-143.
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    The analysis method of vehicle-structure interacted system under breaking force is studied. The vehicle subsystem is modeled by the rigid-body dynamics method, the structure subsystem is modeled by the modal superposition method. The longitudinal, lateral and vertical wheel-rail interacted forces are defined by the given breaking acceleration history, the simplified Kalker Creep Theory and the Wheel-rail Corresponding Assumption, respectively. The equations of motion are solved by the history integral method and the force-motion iterations within time steps. As a case study, the dynamic responses of the Shenzhen North Station under the braking of the Metro Line 4 and Line 6 trains are calculated, and the vibration properties of some key structural parts in the station building are analyzed and evaluated.
  • HU Bao-lin;YAO Wen-juan;LI Guo-qiang
    . 2011, 30(2): 144-148.
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    Basing on the buckling-restrained braced frame under severe earthquakes, and from the point of additional effective damping ratio and energy principle, a simplified calculation method to solving elastic-plastic displacement of the buckling-restrained braced frame under severe earthquakes has been systematically analyzed. In this paper, the detailed calculating method and steps are presented. Moreover, the comparing analysis between the calculation result of simplified calculation method and the mean of the results of ten seismic waves’ elastoplastic time-history analysis has been carried out. The outcome shows that the simplified calculation method is an exact and valid method.
  • ZHANG Yong-bo;GUO Hai-yan;MENG Fan-shun;LIU Xiao-chun
    . 2011, 30(2): 149-154.
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    In order to research the Vortex-Induced Vibration (VIV) characteristics of top tension riser subjected to marine current, modal tests of VIV were conducted in a large wave-current flume. The model riser with changing top tension was attached vertically to the supporting structure and different external current velocities acting on the model. The cylinder model was equipped with six measured stations which are distributed averagely along the riser and each was formed by two strain gauges to measure both in-line direction and cross-flow direction oscillation responses. Through wavelet transform analysis, VIV frequencies, amplitudes of oscillation and coupling vibration rule between X and Y motions were obtained. The effect of varying top tensions on the natural frequency and VIV response were investigated.
  • Guo Yuanjun;Yin Jiong;He Jianxiong;Hu Hui;Hu Binliang;Huang Weijiu
    . 2011, 30(2): 155-158.
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    Using slanting impact contact model of rigid spherical surface and elastic coating, considering coupling function of normal and shear surface force caused by particles in the impacting process ,the contact dynamic stress of elastic coating surface are analyzed ; The results indicate that the primary factor of abrasion sharp growth is the contact tensile stress of the elastic coating surface, the high speed impact of particles stream may results Surface debacle of elastic coating because the stress wave can not disseminate promptly in elastic coating . According to the analysis conclusion, corresponding different jet angle ,the limit velocity that causes abrasion sharp growth of elastic coating is computed in the scope of 39-68m/s, the difference between theoretical analysis and experimental results about 10%.
  • CHEN Jian-guo;XIA He;YAO Jin-bao
    . 2011, 30(2): 159-163.
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    Field measurements were carried out at Beijing No.5 Metro Line to study the ground vibrations subjected to moving trains on viaduct, Time-domain and frequency-domain analysis were executed on measured ground acceleration. It was found that, the lateral vibration level of ground under trains running on common track is 58-100dB, and the vertical vibration level is 55-91dB. However, the lateral vibration level of ground under trains running on ladder track is 62-85dB, and the vertical vibration level is 60-83dB. The attenuation of lateral vibration grows to a peak at the distance of 15m, and then reduces fluctuant with the distance. The vertical vibration reduces with the distance, and has a rebound region at the distance of 15m. The rebound value increases with the vibration level. The ladder track can reduce vibration level by filtering some frequency component, but also magnify vibration level at some frequency which is similar with the ladder track’ natural frequency. The attenuation level of high frequency is fast than low frequency. The vibration of far field is induced mainly by low frequency.
  • LIU Yong-hui;ZHANG Yin
    . 2011, 30(2): 164-166.
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    The dropping simulation and design improvement of a washing machine are realized based on the FEM (Finite Element Method) analysis. An initial design model for a washing machine is established using the CAD software Unigraphics. Then the FE model is set up and the dropping analysis is performed on the design model by applying the software Abaqus. The simulation results show that wrinkling and deformation will occur on the frame part in the process of dropping. The predicted results are in good agreement with the experimental ones. The initial design of the washing machine is modified and the analysis is performed again. The improved design model possesses enough strength and has passed the physical dropping experiment. This ‘Simulation-Based’ design approach provides a new and effective way for the new product design in the field of household electric appliances.
  • CAI Yan-ping;LI Ai-hua;SHI Lin-suo;BAI Xiang-feng;SHEN Jin-wei
    . 2011, 30(2): 167-172.
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    According to the modulation characteristics of roller bearing fault vibration signals,the limitation of the traditional envelope analysis,a roller bearing fault diagnosis method using improved envelope analysis based on empirical mode decomposition(EMD) and spectrum kurtosis (SK) was proposed in this paper. Firstly, roller bearing fault vibration signals were decomposed into a finite number of intrinsic mode functions(IMFs); secondly, using fft transformation to make each IMF into complex signal and calculatting these complex signal absolute value, then, spectrum kurtosis value was calculated of each IMF spectrum square envelope; finally, using the filter function of spectrum kurtosis, the best frequency band for demodulation was automatically choseen by the criterion of IMFs spectrum kurtosis. The proposed method has been applied into simulated signal and actual signal, the analysis results demonstrated the effectiveness of the proposed method.
  • Shao Yuying;Xu Jian;Rao Zhushi;Jin Zhijian;Jiang Yimin;Fu Jian
    . 2011, 30(2): 173-176.
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    It is important for maintaining the safe operation of power transformer to monitor the states of transformer winding on the real-time basis. The winding’s states can be reflected by its vibration signal, which can be measured by the accelerometers located on the transformer tank. In a short-circuit experiments for one large power transformer, the state of winding of every phase can be initially detected by the change of transformer vibration intensity for every short-circuit shock. The method of time-frequency analysis is further used to analyze the shock signal in order to confirm the winding’s states. Compared with the traditional method based on short-circuit reactance measurement, the time-frequency analysis can exactly show the fault characteristics of the winding.
  • YUE Gui-ping;ZHANG Yi-min
    . 2011, 30(2): 177-180.
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    Based on the theory of pipeline acoustics, the method of noise simulation of intake systems of an engine——no-source-method has been brought forward; based on the parameterized model of quarter wave tuner, the method of dynamic optimization design of intake systems of an engine has been studied. Applying no-source-method, while the emulation model of an engine could not be provided, the acoustic property DOE analysis of intake systems could be carried through however, and applying response-face method the design parameters of quarter wave tuner could be optimized, this provides a reference for acoustic property optimization of intake systems.
  • Wang Zhili;Liu Guoxi;Guo Yanli
    . 2011, 30(2): 181-185.
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    Abstract: The vibration process of the double-faced gas film seal in counter-rotating shafts was studied in this article; two stiffness and damping of the seal were calculated with finite element method; the vibration process of the seal caused by transient force was analyzed; then the effects of the system mass and pressure on vibration of the system was studied. The results declared: free vibration frequency of the system is mainly decided by the mass of the seal racetrack, and the effect of the primary seal ring mass on free vibration frequency is neglected; the different ratio of the system mass with the same racetrack mass has little influence on the convergent time of the vibrating system; as pressure increase, the force that system can endure become small and the system is apt to unstable. The calculation and analysis above may be helpful for the analysis of the dynamic response of the gas film seal in counter-rotating shafts.
  • HUANG Xiao-guo;LI Jian-zhong;LIU Xiao-feng
    . 2011, 30(2): 186-191.
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    Firstly,review of dry friction model is sumarrized.Based on Coulomb friction model,Sliding displacement of rigid blocks under harmonic base excitation is deducted. it is analyzed that exact calculation of transition time from stick to slip have more influence on relative displacement between rigid blocks and base. Difference of Relative displacement based on Coulomb friction model and friction force-displacement model is compared. Then, Based on Coulomb friction model,Sliding displacement of rigid blocks under any base excitation is deducted by Newmark linear acceleration method. Under El-centro earthquake,Difference of Relative displacement based on Coulomb friction model and friction force-displacement model is contrasted.
  • Sun Dong-zhe;XuPeng;Zhang Hong-yan
    . 2011, 30(2): 192-195.
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    In the vehicle-loaded environment, the transmission of data would be interrupted and the working disk would be damaged by the vibration and shock. The device may work stably by using hard disk with strong anti-vibration performance and reasonable damper. This article tests out the exciting frequency range of a hard disk which can activate the active protection by experiments, chooses wire rope shock absorber according to the experimental data and its application environment. This paper designs simple structure and adaptable vibration isolation system of hard disk by simplifying the dynamics model, figuring out the efficiency of the absorber and using seasonable installation.
  • Gu Taiping;He Lin;Fu Yu
    . 2011, 30(2): 196-198.
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    Based on air wave theory and shell equilibrium analysis, a proximate analytic approach of mechanical impedance for bellows type air spring is presented by calculation of air pressure and shell stress field. The approach is the way that air spring is divided into several calculable regular simple regions according to superposition principle, then each region’s analytic solution is achieved combined with boundary and joint conditions and assembled to form parameterized expressions of air spring mechanical impedance. Finally an application instance of mechanical impedance calculation of marine air spring is given. And it shows that the method is feasible and provides a new idea of air spring dynamic characteristic analysis.
  • YANG Yang;ZHOU Xiyuan;JIN Guofang;LIU He(M. ASCE)
    . 2011, 30(2): 199-204.
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    An improvement to the Direct Stiffness Calculation (DSC) method for bending-type frame structures, which can be used to carry out damage assessment, and corresponding System Identification toolbox in platform of OpenSees is proposed in this paper. The proposed improvement is a simple, but apparently quite effective, the modification of the DSC method for damage detection, and the System Identification toolbox could be applicable to practical bending-type frame structures. Research on the benchmark test of a 12-story reinforced concrete frame model on shaking table in Tongji University, a simulation model for the benchmark test under excitation of several seismic waves was evaluated to verify the modified DSC technique and the System Identification toolbox. The results show that the preliminary assessment using the improved direct stiffness method and the corresponding System Identification toolbox are feasible and efficient in the damage detection of bending-type structures.
  • HAN Shao-qing;SONG Zi-biao;WU Hai-jun
    . 2011, 30(2): 205-209.
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    The effectiveness of the traditional P-wave complexity in the discrimination between nuclear explosions and earthquakes is validated. Two improved algorithms of P-wave complexity in time domain are proposed and the recognition accuracy is increased a little. The traditional computation of complexity is generalized to time-frequency domain and a framework for the computation of complexity based on short time Fourier transform is given. Under the simplification form of the framework, seismic features are extracted based on Fisher methods. Classification results show that the proposed algorithm is better than other existing algorithms.
  • Wang Jian-hong;Wang Dao-bo
    . 2011, 30(2): 210-213.
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    In this paper, we extend the biased compensated least-squares method (CLS) to get the nonlinear separable least squares (NSLS) when the observed input-output data are corrupted with noise. The nonlinear separable least square algorithm is adopted for aircraft flutter modal parameter identification under noisy environment. Combing with a rational transfer function model, the identification of system with noisy data is transformed into a nonlinear separable least square problem. Using this algorithm, the noise variance parameters and the model parameters can be obtained separately. The simulation with real flight test data shows the efficiency of the algorithm.
  • Yao Shiwei;Yang Jun;Zhang Xuebing;Wang Juan;Rao Zhushi
    . 2011, 30(2): 214-216.
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    Water-lubricated rubber bearings have a lot of superiorities in a certain environment but the noise issue can’t be avoided. In this paper, the theory of bearings noise generation is analyzed first, then a series experiments are designed to find disciplinarian between correlative factors and noise generation.
  • DONG Jian-hua;ZHU Yan-peng
    . 2011, 30(2): 217-221.
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    Based on shear beam theory, the seismic response of the slope is obtained under the condition of horizontal earthquake excitation. Because mass of soil nailing is small compared to one of soil, inertia force can be ignored. The movement of soil nailing and soil is nearly in phase and damage of soil nailing depends on the size of the deformation to withstand but not inertia force, so the soil nailing is simplified for one dimension elastic rod without mass. The seismic response of soil nailing is derived through compatibility of deformation and Hooke’s law. The method is applied to a project case to carry out seismic analysis and design. Using finite element software (ADINA) to verify the proposal method the results show that the design and the analysis are safe and credible. The calculation method provides theoretical basis for earthquake analysis and seismic design of soil nailing supporting structure.
  • TAN Jun;HAN Xu;LIU Xin
    . 2011, 30(2): 222-225.
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    In the manned equipment airdropping process, in order to improve the ability of manned airdrop protection, an airbag chair to protect the human body has been designed. This paper establishes the numerical model of airdrop chair and simulates the buffer process of the airbag chair to the human in airdrop landing through MADYMO. A multi-objective optimization method based on the micro multi-objective genetic algorithm for the dynamic characteristics of airbag have been proposed. An optimization procedure based on the micro multi-objective genetic algorithm is proposed to search the key parameters such as air quality of the airbag chair, venting area of the airbag chair, venting pressure of the airbag chair and air quality of the airbag for neck. The optimal design of airbag chair can not only gives an optimal design of airbag chair with reducing experimental times and cutting down experimental cost, but also can be used in the field of other manned airdrop protections.
  • LIU Ai-guo;LU Dao-gang;WEN Jia-liang;WEN Fu-yue
    . 2011, 30(2): 226-232.
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    Thyristor valve is a key device of HVDC transmission system, the seismic performance of which can directly affect the seismic safety of the whole DC system, whilst seismic behavior can be an important factor when designing valves. Valves structure used shock absorber design. Based on considering the impact of hinged rotating stiffness, three dimensional finite element models of ideal and improved valves were constructed. Used two procedures in order to calculate the ideal model for mutual authentication their calculation results, and the seismic time history of the system was generated based on the IEEE Recommended Practice for Seismic Design of Substations. First, the dynamic character of two models were calculated. The influencing factors of their dynamic characters were discussed subsequently. Secondly, the response of them were analyzed based upon time history analysis method on horizontal and vertical excitation. The result indicates that the valves had good shock absorbers capacity, and under horizontal seismic, valves may occur oscillation phenomenon at low frequency, and also the improved valve structure model can improve displacement deformation of the valves structure.
  • Huang Wei;Zhang Chenghua;Yao Qianfeng;;CHEN Guoxin;;Jing Gang;Hou Lina
    . 2011, 30(2): 233-237.
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    The multi-ribbed slab structure consists of various materials and components nesting each other, which makes the entities calculation model of the structure extremely complicated. Therefore, it is necessary to present the elasto-plastic model for the whole stressing process of structure under strong seismic action. According to different analysis aims, the rigid frame-equivalent diagonal strut model and the rigid frame-whole bracing model of the eco-composite wall structure in elastic-plastic stage are presented. According to the previous results of pseudo-dynamic test on the walls, the rigid frame -equivalent diagonal strut model is employed to perform push-over and dynamic response analysis , therefore, the validity of the model is verified. Based on the previous results of 1 / 10 ratio of shaking table test, the rigid frame-whole bracing mode is employed to perform the time-history analysis, therefore, the validity of the model is verified. Theoretical researches and experimental analysis show that the rigid frame -equivalent diagonal strut model characterized by calculation accuracy and practicability is suitable for nonlinear analysis of multi-ribbed composite wall. The rigid frame-whole bracing mode giving consideration to accuracy and efficiency is applicable to structural elastic-plastic time-history analysis under strong seismic action.
  • LV Zhao;WU Xiao-pei;LI Mi
    . 2011, 30(2): 238-242.
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    To suppress the interference of convolutive noise on speech features and improve the rate of speech recognition, a speech features enhancement algorithm based on frequency-domain ICA (Independent Component Analysis) is presented in this paper. In the proposed algorithm, noise short-time spectrum is estimated by the frequency-domain ICA algorithm, and then noise reduction is achieved by subtracting the estimated noise short-time spectrum from the noisy speech short-time spectrum to be enhanced in the Mel-scale filter bank domain. As a result, robust MFCC (Mel Frequency Cepstral Coefficients) are acquired. Simulation and real environment experiential results reveal that the recognition ratio of the proposed algorithm obtains the relative increasing of 38.2% and 35.8% compared with conventional MFCC, which reveal that the mismatch between training features and testing features in convolutive noise environment can be suppressed effectively.
  • Chen Bo;Zheng Jin;Qu Weilian
    . 2011, 30(2): 243-245.
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    The wind-induced vibration control of a high-rise television tower is actively carried out in this study by using passive friction dampers. The three dimensional finite element model and two dimensional simplified dynamic model of the television tower are established respectively. The motion of equation of the controlled tower is developed and wind loading is numerically simulated. The Hefei television tower is taken as an example to investigate the feasibility of the proposed control approach based on passive friction dampers. The observations made from numerical investigation indicate that the wind-induced vibration of the television tower can be substantially suppressed by using passive friction dampers with optimal damper parameters.
  • Deng xuesong;Wu Congxiao;Zhou Yun;Wu Congyong
    . 2011, 30(2): 248-251.
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    Based on the limited demand of inter-story drift and equivalent lateral rigidity ratio of high-level transfer story structure in Technical Specification for Concrete Structures of Tall Building and Code for seismic design of buildings, the calculation model that the high-level transfer story structure with BRBs is decomposed to frame with BRBs -shear wall structure below the transfer story and shear wall structure above the transfer story of equivalent lateral rigidity ratio has been adopted. Then, based on the above model, the calculating formula of elastic stiffness and simplified design method for BRB of the high-level transfer story structure with BRBs is derived. Finally, a sample structure is studied utilizing the above method, analysis results indicate that the proposed formula and method is valid and may be as a reference to the high-level transfer story structure with BRBs.
  • Qin Boyin;Lin Xiankun;Zhang Lingmi;Guo Qintao
    . 2011, 30(2): 252-257.
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    In order to dispose sensors to reasonable freedom degrees, and reflect adequately the dynamic characteristics of tested structure, the sensor placements of dynamic testing must be optimized. In this paper, taking MAC matrix, Fisher information matrix, and their combinations as optimization criteria respectively, the integer‐coded genetic algorithm was applied to single-objective or multi-objective optimal sensor placement problem. compared with three existing optimal sensor placement method, which are modal kinetic energy, effective independence, and cumulative method based on QR decomposition, their results of the optimal sensor placements indicated that the integer‐coded genetic algorithm is better than three existing method.
  • JI Shao-bo;CHENG Yong;TANG Juan;MA Zong-zheng;HUANG Wan-you
    . 2011, 30(2): 258-262.
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    Cylinder head vibration acceleration signals are measured from a 195 type diesel engine by changing torque, speed and injection timing. The signals are analyzed and results show that amplitude of maximum fluctuation and frequency components under 2kHz of acceleration are related with combustion status in the same speed, while both the amplitude of maximum fluctuation and frequency components under 2kHz of acceleration have no corresponding relation with combustion status in different speed. The influence of pretightening forces and material stiffness is studied using a finite element modal of the engine. Results show that the oscillation frequency of the engine will reduce along with decrease of stiffness and pretightening forces, this will increase the amplitude of maximum fluctuation and frequency components under 2kHz of vibration acceleration.
  • ZHANG Yuanyuan;LI Shunming;Miao Xiaodong
    . 2011, 30(2): 263-266.
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    Based on the spectral analysis of noise signal and sound-intensity test identifying the noise source on the motorcycle, The result indicates that the exhaust noises of engine are the major reasons in whole motorcycle noise. Using the methods of experiment and FEM, the exhaust muffler’s performance of aerodynamics and acoustic are realized and analyzed, three projects of improved muffler are proposed, and validated by experiment. The past-by noise of motorcycle in improved muffler state can ultimately reduce by 1-2 dB at the most.