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2020 Vol. 39, No. 9
Published: 2020-05-15
1
Overpressure distribution on a pseudorandom reticulated shell loaded by explosion shock wave
XIA Ming1,2, ZHOU Fengjun1, LU Fangyun2, ZHANG Ao1, ZHENG Lei1,SUN Yunhou1, WANG Xiaodong1
By scale model explosion experiments and numerical simulations, the distribution of the overpressure on a pseudorandom reticulated shell loaded by explosion shock wave was investigated.A typical pseudorandom 140-sided reticulated shell was selected as an investigated object to carry out model explosion experiments.The shock wave overpressure data at the surface characteristic measuring points were measured.The errors of the experimental and simulation results were compared and its reasons were analyzed.Based on the experimental data, a numerical simulation model for the interaction between the explosion shock wave and the shell was established, which was then used to deal with six different conditions of air explosion and ground explosion at three different distances.The action process of the characteristic surface overpressure on the shell was analyzed, and the experimental results were extended.The distribution of shock wave overpressure on the shell was achieved, and the protecting measures to enhance the safety of the reticulated shell were put forward, which provides a reference to the shock safety design of pseudorandom reticulated shells.The results show that the overpressure peak value distribution on the pseudorandom reticulated shell is more complicated than the traditional symmetric one and the action mechanism is influenced by the pseudorandom characteristic of the structure, while the overpressure peak value is also of obvious difference at the similar position on the surface.The peak values of overpressure at the bottom and middle of the shell are generally higher than at other parts in the blast direction.The method of erecting explosion-proof wall at a certain distance outside the reticulated shell and reinforcing the middle and bottom nodes structure can improve its anti-impact security.
2020 Vol. 39 (9): 1-8 [
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9
EMD-DCS based pseudo-fault feature identification method for rolling bearings
CHI Yongwei1, YANG Shixi1, JIAO Weidong2, LIU Xuekun1
Pseudo-fault feature is the fault feature included in the vibration signals of healthy parts, which is caused by the faulty parts in the system.In the paper, a pseudo-fault feature recognition method based on empirical mode decomposition (EMD) and degree of cyclostationary (DCS) was proposed to identify the pseudo-fault feature of a rotor bearing system.The technical difficulties of rolling bearing fault diagnosis based on the single-channel pseudo-fault signal were analyzed by comparing the healthy and pseudo-fault signals of the rolling bearing.A dynamic model of the rotor-bearing system considering the rolling bearing slipping rate was established.The pseudo-fault feature of the rolling bearing was analyzed by the time-frequency method and the cyclic stationary method.The feature identification process of the rolling bearing pseudo-fault based on EMD-DCS was presented.An experiment of feature identification was carried out by using a rolling bearing fault simulator.The experimental results show that the EMD-DCS based method can effectively distinguish pseudo-fault features of rolling bearings from fault features.The research in the paper has theoretical significance and practical application value to ensure the equipment operation safety.
2020 Vol. 39 (9): 9-16 [
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245
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17
Experimental study on the bird-wing shaped suppression device for the vortex-induced vibration of risers
LI Zifeng,SONG Guangming,CHEN Yanling,LI Yinpeng
Based on the bionics study on trailing-edge serrations of some birds, a vortex-induced vibration suppression device for marine risers was put forward with double bird-wing shaped streamers.The water flow simulation experiment was performed on the model of a bare cylinder model and cylinder models with different trailing edge profiles and different lengths of streamers, and the wake flow field of the model was measured using the particle image velocimetry.By comparing the corresponding wake streamline diagrams and vorticity diagrams, the following conclusions were found.The double streamers structure can effectively reduce the vortex behind the cylindrical model in the water flow, and the trailing edge profiles of streamers can affect the flow field around the cylinder.When using trailing edge serrated streamers, the generation of vortex will lag.When the length of the streamers are about four times the diameter of the cylinder, the effect of vortex suppressing is better.Therefore, the bird-wing shaped vortex-induced vibration suppression device for risers is efficient and of good working performance.
2020 Vol. 39 (9): 17-23 [
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191
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24
Influence of aggrecate size on the dynamic tensile strength and size effect of concrete
JIN Liu,YANG Wangxian,YU Wenxuan,DU Xiuli
Aggregate size is an important factor affecting the mechanical properties and fracture mechanism of concrete.From the microscopic point of view, concrete was considered as a three-phase composite material composed of aggregate particles, mortar matrix and interfacial transition zone.Considering the strain rate effect of meso-components, a meso-mechanical analysis model for the study of dynamic tensile failure behaviors of concrete was established.The dynamic tensile failure behavior of concrete with different aggregate size was simulated and the size effect on the dynamic tensile strength was revealed.The results are as follows: at low strain rate, aggregate does not be destroyed, and aggregate size has a significant effect on the dynamic tensile failure mode and tensile strength of concrete.The size effect on the tensile strength weakens with the decrease of aggregate size.Cracks will penetrate aggregate at high strain rate, so that the effect of aggregate size on the dynamic tensile strength and size effect of concrete can be neglected.Finally, combining with the influence mechanism of strain rate effect, a theoretical formula for the “static and dynamic unified” size effect of concrete tensile strength was established, which can well describe the quantitative relationship between the concrete dynamic tensile strength and specimen size under different aggregate size.
2020 Vol. 39 (9): 24-34 [
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224
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35
Aeroengine fault data tag using on improved BDPCA algorithm
LV Chao1, CHENG Gong2,LIU Yunqing1
As the power core of an aircraft,the aeroengine plays an important role in the safe flight of the aircraft.It is of great significance to ensure the smooth operation of aeroengine for flight safety.While the technology of aeroengine fault diagnosis based on supervised learning has been progressing continuously, how to convert a large number of unlabeled data obtained at ordinary time into labeled data that can be used to train the fault diagnosis model has become a bottleneck restricting the development of the industry.In the paper, the DPCA algorithm based on unsupervised learning was introduced to realize the accurate classification and marking of unmarked data sets.Aiming at some defects of the DPCA algorithm, the algorithm was optimized by using the shared neighborhood algorithm and BIC selection criteria.Finally, the performance of the improved algorithm was verified by applying gas path fault data of some aeroengine, and good results were obtained.
2020 Vol. 39 (9): 35-41 [
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162
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42
On-line model updating method for hybrid testings based on the forgetting factor and LMBP neural network
WANG Yanhua, LV Jing，WU Jing
Recently the application of neural networks to the online model updating of hybrid testings is an important research direction.How to improve the adaptability, stability and anti-noise ability of online model updating algorithm of neural network is a key problem.An on-line model updating method for hybrid testings based on the forgetting factor and LMBP neural network was proposed, namely in each time step the historical experimental data of the test substructure were used to form a dynamic window sample with a forgetting factor.Then the LMBP neural network was trained with the sample set by the incremental training method, and the restoring force of the numerical element with the same constitutive model was predicted synchronously.The model updating hybrid testing on a 2-DOF nonlinear system was simulated and the RMSD of the predicted restoring force of numerical substructure was found to be 0.023 0 finally.The results show that the online model updating method of hybrid testings based on the forgetting factor and LMBP neural network has good adaptability, stability and anti-noise ability.
2020 Vol. 39 (9): 42-48 [
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255
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49
Design and energy-absorbing properties of the everting components of straight corrugated tubes
ZHANG Jianzhuo, LIU Huan, WANG Jie
In order to improve the impact resistance of hydraulic columns,a kind of straight corrugated tube energy-absorbing component for its combined use with the hydraulic columns was designed.The evaluating indexes of energy-absorbing properties were given.The energy method was applied to derive the everting deformation resistance of straight corrugated tubes.The calculation formula for the stable everting deformation resistance of straight corrugated tubes was provided.The deformation process,the resistance trend and energy absorption of the components were studied by numerical simulation.The results show that the everting deformation process,the resistance trend and the energy absorption correspond to each other.When the straight corrugated tubes enter into the stable deformation stage,the resistance is constant and the energy increases linearly.Aiming at the problem that a certain compressing distance is required for the straight corrugated tubes to enter into the stable everting deformation stage, an improved method was proposed.The improved energy-absorbing components have the characteristic of constant resistance.The results by the theoretical formula are in good agreement with the deformation resistance obtained by simulation.Changing the wall thickness is an effective method to obtain the required deformation resistance.Straight corrugated tubes are an ideal energy-absorbing component with stable and repeatable deformation mode.According to the simulation results, the error analysis and the correction of the theoretical formula were carried out.The corrected theoretical formula has guiding significance for the design of straight corrugated tube energy-absorbing components.
2020 Vol. 39 (9): 49-56 [
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57
Numerical analysis on the charge structure optimization under hydraulic blasting and its application
LIU Jiangchao, GAO Wenxue, WANG Lintai, CAO Xiaoli, ZHANG Shenghui, WEI Xiao
Taking the Wen Quan Tunnel as the research background, three kinds of charge structures under hydraulic blasting including the top-water-decking charge structure, two ends-water-decking charge structure and lower-water-decking charge structure were simulated from the views of stress, vibration velocity, dynamic damage and dust after explosion in order to choose the best charge structure.The results show that:（1） The lower-water-decking charge structure is liable to cause rock damage or even breakage at the orifice, resulting in the outflow of explosive gas and reduction of blasting effect.The explosion stress duration in the top-water-decking charge structure and two ends-water-decking charge structure is longer, and it is favorable for surrounding rock fragmentation.Water medium at the bottom of the two ends-water-decking charge structure can protect the surrounding rock of the hole bottom;（2） The blasting vibration speed and stress of the surrounding rock at both ends of the hole can be reduced by using the two ends-water-decking charge structure, so that the energy of the explosive can be fully acted on the surrounding rock of the hole wall to be broken, and explosive consumption can be reduced;（3） The top-water-decking charge structure has the smallest damage to the surrounding rock of the orifice, which causes the larger blocks of rock after breakage.The lower-water-decking charge structure forms the smallest damage area, which results in high explosive consumption.The damage area formed by the two ends-water-decking charge structure is regular, and the rock fragmentation is minimum after blasting;（4） Among the three charg structures, the dust concentration of the lower-water-decking charge structure is the highest after explosion.The dust concentration of the two ends-water-decking charge structure after explosion is slightly higher than that of the top-water-decking charge structure, and the difference is very small.However, the blasting effect of the two ends-water-decking charge structure is better than that of the top-water-decking charge structure.In summary, the two ends-water-decking charge structure is the best and can be used in engineering construction.
2020 Vol. 39 (9): 57-62 [
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181
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63
Lateral vibration characteristics of a rod-fastening rotor considering the tightening force and roughness
WU Jinjun, CHEN Qiang
A micro turbine engine rotor could be considered as a rod fastening rotor, since the disc thickness of its centrifugal impeller is not negligible compared with the rotor length.To gain an insight into the rotor lateral vibration characteristics, a simply supported Bernoulli-Euler beam including connecting surfaces was built.By means of the fractal contacting theory, the mathematical expression for describing the effects of the tightening force and surface roughness on the lateral vibration were derived, and the effect trends were clearly expounded by case studys.It shows that the needed minimal tightening force for connecting surfaces rises exponentially with roughness.Considering only the change of joint stiffness, the rotor natural frequencies vary along an S-shape curve with the increase of exponential tightening force.Furthermore, the more the roughness, the longer the incubation period of the S-shape curve.Considering both the changes of joint stiffness and rotor lateral stiffness, when the roughness and tightening force are small, the natural frequencies increase with the tightening force, on the contrary, the natural frequencies fall with the tightening force.
2020 Vol. 39 (9): 63-70 [
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167
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71
Analysis on the vertical coupled dynamic effect of a crowd-bridge system based on the social force model
ZHANG Qiong1, NAN Nana1, ZHU Qiankun1,2, DU Yongfeng1,2
For more and more structural vibration problems of lightweight flexible footbridges under random crowd loading, it is particularly important to establish a stochastic crowd model considering the crowd-structure interaction in order to obtain more realistic and accurate vibration responses.A moving spring-mass-damping model was used to simulate the dynamical characters of a single pedestrian, and the movement model of a random crowd was established based on the social force model.Then a random crowd load model considering the crowd-structure coupled vibration was built.According to the dynamic balance of the pedestrian bridge and the random crowd at any time, the control equation for the coupled vibration of the crowd and the bridge was established.The variation of footbridge dynamic parameters in pace with the crowd motion was solved by the state space method and the control equation for the coupled vibration was solved by the mode decomposition method.The influence of random crowd load on the modal and vibration responses of the pedestrian bridge considering crowd-structure coupled vibration was discussed.The results show that the modal variation of the coupled system increases along with the increase of pedestrians.The pedestrian-structure interaction and pedestrian randomness are of marked effect on vertical dynamic responses so they should not be ignored while analysing the vibration of light-weight footbridges.Compared with the peak acceleration, the RMS acceleration can weaken the disturbance of random fluctuation, so 1-s RMS acceleration is more reasonable to be used in measuring structural vibration responses.
2020 Vol. 39 (9): 71-79 [
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239
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80
Liquid dynamic equilibrium position during large-amplitude sloshing
MIAO Nan, LIU Zhanhe, WANG Jing, WANG Xiaolu
When large-amplitude liquid sloshing takes place under external excitation, the sloshing characteristics and responses will present certain non-linearity, where traditional equivalent mechanical models cannot be applied immediately.The change of liquid equilibrium position in different configuration tanks during large-amplitude sloshing was studied, providing a basis for its composite equivalent modeling.The dynamic equilibrium positions of liquid in axisymmetric and non-axisymmetric tanks under constant translational excitation were studied.Considering the characteristics of different tanks, the liquid parts following equivalent gravity were modeled, and the descriptions of dynamic equilibrium position were proposed and derived and the results were compared with CFD simulation results.The description effect for the liquid dynamic equilibrium position under time-dependent excitations was examined.The correctness of the resulted dynamic equilibrium position was verified by comparing with the CFD simulations results for different configuration tanks.The method was summarized and the possible improvements were discussed.
2020 Vol. 39 (9): 80-87 [
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175
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88
Perturbation analysis on the dispersion relations of a two-dimensional nonlinear single atom square lattice
WANG Jie1, ZHU Jiang1, HUANG Wenbo1, HE Huan1,2
The dispersion relation of phononic crystals determines the propagation mode of elastic waves.Starting from the wave equation of a two-dimensional infinite periodic structure, a first-order approximate perturbation method for analyzing the dispersion relation of nonlinear discrete phononic crystals was proposed.Based on the Bloch theory and small parametric perturbation expansion method, the first-order dispersion relations and dispersion curves were obtained to analyze the effects of impedance configuration and nonlinear coefficient on the dispersion and group velocity in different directions.Two-dimensional single-atom lattices were used as examples.Their first-order dispersion curves and group velocity contours were presented.The dispersion results reveal that the band gap and direction of propagation are related to the amplitude of waves.Finally, the response of the lattice to the point harmonic force was simulated to verify the effectiveness of the perturbation analysis.
2020 Vol. 39 (9): 88-96 [
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166
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97
Control of accumulated multi-hop synchronous acquisition error based on the cross-layer design of machine vibration WSNs
XIAO Xin, DENG Lei, TANG Baoping, HUANG Yi
Aimed at the problem that the error of synchronous acquisition method based on a cross-layer design would accumulate rapidly with network expansion, a transmission model for synchronous information was established, and its mechanism was analysed.It is found that the low real-time performance of embedded systems, the random jitter of crystal oscillator and the delay jitter of wireless link are the main reasons of error accumulation.Thus, a control method for the accumulated synchronous error based on the cross-layer design was proposed and a multipath cross-layer design was provided to capture synchronous information and trigger timer.A high accuracy crystal oscillator was adopted to suppress the jitter; The mathematical model for the random delay of wireless link was established, and the regression analysis was adopted to calibrate the caused errors such as the random jitter of synchronous information and the calculation error of transmission delay.Finally, a 4-hop network was constructed to evaluate the proposed method, which shows that the accumulated error is suppressed effectively.
2020 Vol. 39 (9): 97-102 [
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105
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103
Experimental research on the aerodynamic characteristics in the critical Reynolds number regime of stay-cables with micro elliptical section
XIAO Bin1, LIU Qingkuan2,3, WANG Xiaojiang1, JA Yaya2,3
In order to study the aerodynamic characteristics of stay-cables with micro elliptical section, a circular section cable and a micro elliptical section cable models were taken as research objects.Different section deformation and wind attack angle were considered in the wind tunnel tests, and the variation of aerodynamic force coefficients with Reynolds numbers under different conditions were analyzed.At the same time, the change of vortex shedding in wake flow around the circular section and the micro elliptical section models at the subcritical, critical and supercritical Reynolds number regimes were obtained by the lift time history and lift spectrum analysis.The results show that the lift coefficient in the subcritical regime of the micro elliptical model is basically unchanged, after entering the critical regime, the lift coefficient increases with the increase of Reynolds number.When the wind attack angle is within the range from 0° to 50°, the Reynolds number corresponding to the maximum lift coefficient increases with the increase of wind attack angle.The lift coefficients time history of the models may display bistable phenomenon during the transition from TrBL0 to TrBL1 and from TrBL1 to TrBL2.The deformation will affect the vortex shedding in the wake area of the cables, and further influence the value of the Strouhal number at different Reynolds numbers.
2020 Vol. 39 (9): 103-111 [
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127
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112
Effects of axial pretension on the detecting accuracy and thermoelastic damping of micro-beam resonant mass sensors
CHEN Siyu, GUO Fenglin
An analytical study was carried out on the evaluation of mass sensitivity, thermoelastic damping and minimum detectable mass for resonant mass sensors of bridge configuration with axial pretension.Explicit expressions for mass sensitivity, thermoelastic damping and minimum detectable mass were derived.Proposed models were applied to examine the effect of axial pretension on the performance of mass sensors.The results of the presented study demonstrate that better device performances can be achieved by axial pretension, i.e., the presence of tensile axial stress could improve mass sensitivity, increase quality factor, and enable the mass sensor to detect ever smaller mass.
2020 Vol. 39 (9): 112-117 [
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119
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118
Seismic vulnerability analysis of small and medium span girder bridges
SONG Shuai1,WANG Shuai1,WU Gang2,XU Baishun3
In order to accurately evaluate the seismic vulnerability of bridge systems, a new vulnerability analysis method of the bridge system based on series-parallel system and Copula function technology is proposed.The pier is a control component in the bridge and is difficult to be repaired after earthquakes.Bridge piers are combined by a series system.For bridge abutments and bearings which are less difficult to be repaired, a parallel system is used to simulate them.The three types of component classes are then connected in the series form, and a series-parallel system of the bridge system is developed.A three-span continuous box girder bridge is used to illustrate the seismic vulnerability analysis method of bridge systems based on the series-parallel system.The results are compared with the system vulnerability based on the series system.The results show that the vulnerability of the small and medium span continuous bridge system is significantly overestimated based on a simple series system.Compared with the series-parallel system, deviations of the vulnerability medians in the longitudinal direction are 22.2%, 20.7%, 20.5% and 24.6% for slight, medium, severe and complete limit states, respectively.The deviations in the transverse direction are respectively 30.0%, 16.1%, 9.8% and 11.3% for the four limit states.The seismic vulnerability of the bridge system based on the series-parallel system is more realistic and reasonable.
2020 Vol. 39 (9): 118-125 [
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162
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126
Influence of dynamic pressure on the optical window in laser interferometry
LI Bo1,2,YANG Jun2,TANG Xiaqing1,HUANG Nan1,3,SHI Yusong2
The optical window is often designed in the pressure chamber when a laser interferometer does the non-contact measurement of dynamic pressure in order to establish optical channels between dynamic pressure and laser interferometer.However, under dynamic pressure environment, optical windows are affected by the internal and external pressure difference, temperature variation, vibration and other factors, which will directly affect the accuracy of optical measurement.To solve the above problem, through simulation analysis, the relationship between the optical window and the pressure, temperature, vibration under dynamic pressure environment was analyzed.At the same time, the optical window was tested under dynamic pressure environment to study the influence of each influential component on the real measurement results, which can modify and compensate for the accuracy of calibration and measurement of dynamic pressure.It also provides a basis for the optical window design under other similar dynamic measurements.
2020 Vol. 39 (9): 126-131 [
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181
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132
Servo compensation technology for the torsional vibration of industry robots
WU Zhenyu1,2,YUAN Huiqun3, LUO Baojia2,ZHAN Mingru2
The dynamic instability of an industry robot is often influenced by the transmission error of its RV reducer.For analysing its mechanism, an electro-mechanical system comprised of motor, RV reducer and load was established.Considering the difficulty of attaching a sensor at the load side of the industry robot, and according to the principle that torque vibration causes rotating speed vibration, the derivative of acceleration at the load side which was derived by a state observer was taken as a feedback variable to compensate for the torque of the motor.The numerical results in time-domain and frequency-domain show that the compensated torque of motor can offset the torque vibration, and the speed vibration at the load side can be suppressed satisfactorily.The proposed system can improve the dynamic precision of industry robots when the working condition is suddenly changed.
2020 Vol. 39 (9): 132-137 [
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157
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138
Technology for detecting bolted joints based on nonlinear damping identification
AI Yanting, LIU Chengming, WANG Zhi, TIAN Jing
Bolt connection quality is the key factor to affect the mechanical structure assembly quality, so it’s important to explore a fast and effective technique for its detection.The definition of high order nonlinear damping ratio was proposed, and a formula for the identification of nonlinear damping on the bolted joints contact surfaces was provided according to the energy conservation law.The dynamic characteristics of the system were obtained through modal experiments, combined with which the empirical mode decomposition (EMD) was used to determine the frequency sensitive to the torsional vibration of the system.Impact response experiments of L-beams under different torques were carried out.The viscous damping ratio and nonlinear damping ratio of the system were identified by using the Hilbert transform and the established nonlinear damping identification formula.The results show that the change of bolt torque has a little effect on the natural frequencies of the system, but has obvious influence on the damping of the system, especially the viscous damping ratio.When the bolt is loose, the viscous damping ratio of the system will change significantly, that is, from 0.122 5 to 0.258 7, a relative increase of 111.18%, which verifies the effectiveness of the method proposed.
2020 Vol. 39 (9): 138-143 [
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185
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144
Feature extraction method for bearing composite faults of a wind turbine
XIANG Ling, LI Ying
Aiming at the problem that the complex fault characteristics of wind turbine bearings under strong background noise are difficult to accurately extract, a method based on adaptive maximum correlation kurtosis deconvolution (AMCKD) for the wind turbine bearing composite fault feature extraction was proposed.Using the artificial fish swarm algorithm (AFSA), and taking the correlated kurtosis of the deconvoluted signal envelope spectrum as an objective function, the influential parameters of the maximum correlation kurtosis deconvolution algorithm (MCKD) were adaptively optimized.Then, the optimized MCKD was used to deconvolute the original fault signal, and an envelope spectrum analysis was performed on the deconvoluted signal.Through the comparison of the dominant frequency components in the envelope spectrum with the fault characteristic frequency of each component of the bearing, the diagnosis of the bearing composite faults was accurately realized.Simulation and engineering application examples verify the effectiveness and practicability of the proposed method.
2020 Vol. 39 (9): 144-151 [
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195
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152
Prediction of transmission line galloping by one class SVM based on the Bagging algorithm for constructing a strong classifier
CHENG Yongfeng, HAN Jingshan, LIU Bin,LI Peng, JI Kunpeng
Considering that the traditional physical analysis method cannot solve the prediction of conductor galloping, a machine learning algorithm was synthetically used to screen and pre-process the existing dance history data.Mining effective information from the selected and preprocessed data, the one class SVM algorithm was used to carry out an unsupervised learning of the galloping history data.In the training of the galloping prediction model, the Bagging algorithm was used in the ensemble learning algorithm to train the classifier.The monitoring data was randomly sampled into different sets of data sets for independent training, which avoids over-fitting and improves the anti-noise ability and generalization ability of the machine learning algorithm.Using the k-fold cross validation algorithm to verify the accuracy of the prediction model and using the F1-score to describe the performance of the traverse galloping early warning model, the effectiveness of the machine learning method in the aspect of galloping prediction was confirmed.
2020 Vol. 39 (9): 152-158 [
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146
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159
Experimental study on the seismic performance of a new type assembled metal energy dissipation composite wallboard
WU Congxiao1,2, XIONG Xiaopeng1, XU Hu1, WU Congyong1
In order to study the seismic performance of a new type prefabricated metal energy dissipation composite wallboard, low cyclic loading experiments were carried out on the new type composite wallboard and the traditional sandwich wallboard respectively.The failure mode, hysteretic energy dissipation, bearing capacity, stiffness and displacement ductility of specimens were compared.The results show that the hysteretic curve of the new type prefabricated metal performance damping composite wallboard presents a configuration of “parallelogram”, which is more full than that of traditional composite wall panels and has good seismic performance.Compared with the traditional sandwich composite wallboard, where X-shaped shear cracks appear mainly in the middle of the wallboard, the cracks of the new wallboard mainly appear at its corners, showing good overall performance.The new wallboard has smaller lateral stiffness and better displacement ductility, which can reduce the constraint effect of the additional stiffness of the clothing wallboard.The new prefabricated metal performance damping composite wallboard can achieve the seismic design goal of “elastic under small earthquake and yielding energy under large earthquake”.
2020 Vol. 39 (9): 159-164 [
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252
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165
Fatigue reliability analysis of a steel crane beam in service
YANG Youfa1, CHEN Qian1, LEI Ming2
Based on the theory of structural reliability, the whole use process of a steel crane beam was considered as a random process.The effect and resistance of the steel crane beam were considered as random variables, and the fatigue dynamic reliability calculation model for the limit stress was studied.The fatigue reliability factors of the steel crane girder were analyzed by using the fatigue dynamic reliability calculation model.Based on the study, the suggestions for fatigue design, operation and maintenance of steel crane beams were put forward.
2020 Vol. 39 (9): 165-172 [
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177
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Track nonlinear energy sink attached to a high-rise building for response mitigation
WANG Jingjing1, LI Haobo2, LIU Zhibin1
Track nonlinear energy sinks (track NESs) are a type of passive structural control devices that can mitigate the vibration of a primary structure with a nonlinear restoring force.This nonlinearity is generated by the motion of the NES mass on a specially designed track.The nonlinear restoring force of track NESs and the equations of motion for control systems were analytically constructed.Parameters optimization was carry out for the track NES when attached to a 32 degrees of freedom primary structure.The optimized track NES performs effectively in response reduction and demonstrates better robustness against the changes of the device stiffness than the conventional TMD.The track NES is, however, sensitive to the changes of the device damping.To address this issue, single-sided vibro-impact track energy sinks（SSVI track NESs）were proposed.The control performance of the SSVI track NES was investigated in consideration of the effects of device stiffness and damping.The results show the SSVI track NES is able to effectively mitigate structural responses with improved robustness against the changes of device stiffness and damping.
2020 Vol. 39 (9): 173-180 [
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Fatigue properties of BFRP bars after temperature damage
KUANG Jinxin1, ZHANG Chuntao1, HAO Zhiming2
The fatigue property of basalt fiber reinforced composites (BFRP) with cumulative thermal damage was studied, which is of great significance for its proper use under high temperature condition.An improved Single Point Group method was proposed to do a regressive analysis on a three-parameter expression of the fatigue S-N curve.The gray theory GM (1,1) model and the extreme value principle were introduced to derive a three-parameter Weibull probability density function varying with corresponding stress level, and the distribution parameters were determined by the maximum likelihood estimation method.A Weibull probabilistic fatigue T-P-S-N model was established through the nonliear fitting, considering the comprehensive effect of temperature and reliability, which was then validated by using the fatigue test of a high temperature affected BFRP bar.The results demonstrate that the downtrend of fatigue life of BFRP bar can be apparently observed when the external temperature and reliability ascend, which corresponds well to the practical situation.The proposed model is able to properly describe the trend of fatigue behavior of BFRP with varied temperature and reliability.
2020 Vol. 39 (9): 181-187 [
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Influences of main controlling factors on the penetration depth of special-shaped head projectiles penetrating metal targets
YU Bin1, DONG Yongxiang2, LI Xiangyu1, SONG Qing2, FENG Shunshan2
In order to study the penetration characteristics of special-shaped head projectiles penetrating metal targets，based on the dimension method, the main controlling factors affecting the penetration depth were analyzed, experiments and numerical simulations on the process of partial penetrating metal targets by special-shaped head projectiles were carried out respectively by using a gas gun and the LS-DYNA software.The influences of the projectile structure, projectile initial velocity, and target thickness on the penetration depth were investigated.The curves of the penetration depth versus the initial projectile velocity and the target thickness were obtained.The results show that the key factors affecting the penetration depth of partial penetrating are the initial velocity of the projectile and the thickness of the target plate.The dimensionless empirical formula for expressing the relation of the initial projectile velocity and the target plate thickness to the penetration depth was derived through fitting.The results provide a reference to the study of partial penetration depth as well as to the engineering calculation of new type penetration problems.
2020 Vol. 39 (9): 188-193 [
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194
Effect of the rotor diameter-length ratio on the rotary lobe pump performance based on numerical simulations and experimental tests
LI Yibin1, GUO Dongsheng1, TANG Yonglin2, DU Jun1
The purpose of the paper is to reveal the influence of the rotor diameter-length ratio on the performance parameter of a kind of rotary lobe pump, to establish a quantitative relationship between the diameter-length ratio and the characteristic curve of the rotary lobe pump and to obtain the radial load distribution characteristics of the shaft system so as to provide a basis for the calculation of the shafting strength of the rotary lobe pump.Based on the FLUENT dynamic mesh and the RNG k-ε turbulence model, the numerical calculation of the 3D transient flow in the rotary lobe pump was carried out.The flow characteristics of rotary lobe pumps with six different kinds of diameter-length ratio were compared, and the influence of the diameter-length ratio on the radial exciting force of the pump rotor was revealed.The results show that the diameter-length ratio has a significant influence on the performance of the rotary lobe pump.With the increase of the diameter-length ratio, the flow pulsation gradually decreases, and the outlet flow increases first and then decreases.The magnitude and direction of the radial force are changed periodically with the rotation of the rotor.The force decreases with the increase of diameter-length ratio, and increases with the increase of pump outlet pressure, which is independent of rotational speed.When the diameter-length ratio is from 0.7 to 1.3, the average volume flows at the outlet reaches the peak area, and the flow pulsation amplitude at the pump outlet is the lowest, meanwhile, the rotor’s force state is better.The results provide a theoretical basis for selecting the diameter-length ratio of rotary lobe pumps.
2020 Vol. 39 (9): 194-200 [
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194
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Analysis and experiment on the vertical vibration characteristics of a disc cutter
LI Jie, HUANG Yuanjun, ZHANG Bin, MA Chao
The vertical vibration of a disc cutter has certain influence on the penetration and rock breaking efficiency of a full-face tunnel boring machine.In order to study the factors affecting the vertical vibration of cutter, a three-degree-of-freedom vertical vibration model for the disc cutter was established, and the equivalent masses and stiffnesses of the disc cutter ring together with cutter body, tapered roller bearing and cutter shaft were presented.The mass and stiffness of the cutter were simulated by using the MATLAB software, and the vibration displacement of each part of the cutter was obtained.The simulated vibration displacement of each part of the cutter is consistent with the experimental results. The results show that the maximum vibration displacement of the cutter’s ring and body is 2.8×10-4 m and the maximum vibration displacement of the bearing is 2.1×10-4 m.When the rigidity of the cutter’s bearing increases by three times, the maximum vibration displacement of each part decreases by about 50%.When the rigidity of the cutter ring and body increases, the maximum vibration displacement of each part decreases by about 12%.To reduce the vibration of the disc cutter it needs to increase the rigidity of the bearing as well as the cutter ring and body. The results provide an effective method for the vibration measurement of disc cutters and have important significance for cutter design.
2020 Vol. 39 (9): 201-206 [
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151
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Equivalent circuit analysis of the galloping-based piezoelectric energy harvester with a passive turbulence control cylinder
JIN Zunlong, LI Guoping, GENG Linfeng, WANG Junlei
In order to better predict the performance of the galloping piezoelectric energy harvester, an equivalent circuit simulation model (ECM) was established and verified by experiments, with a maximum discrepancy of less than 10%, by which the cylindrical galloping piezoelectric energy collection under passive turbulence control (PTC) was analyzed.The parameters of the mass-spring-damping (M-C-K) galloping control equation for the energy conversion system were expressed by the corresponding equivalent circuit electronic elements.Thus, this makes it possible to analyze the DC circuit coupling that cannot be solved by the past simulation means.The variation of the critical wind (Ucr) along with the external connected load and the output voltage and power at different wind speeds and under different external load were analyzed from the perspective of energy harvesting efficiency in AC-DC equivalent circuit.The results show that Ucr increases and then decreases with the increase of load in the AC circuit, and Ucr decreases with the increase of load in the DC circuit.When the wind speed reaches the maximum value of Ucr, the galloping occurs under any resistance.When U≥Ucr, the galloping phenomenon occurs, and the output voltage and power increase with the increase of the wind speed.The growth rate has a decreasing trend at high wind speeds. With the increase of the resistance, the output voltage increases, and the power first increases and then decreases.Comparing to AC circuits, the optimum load of the DC circuit is increased from 1.1 to 2.0 MΩ, while the power peak is reduced from 0.08 to 0.04 mW.
2020 Vol. 39 (9): 207-213 [
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158
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Erosion characteristics of solid-liquid two-phase flow in multi-stage stamping pumps
ZHENG Shuihua, MOU Chengqi, ZHANG Wenqi, ZHANG Fengye, MOU Jiegang
Based on the discrete phase model and the standard k-ε turbulence model, the flow fields in the first and second stages of a multi-stage stamping pump were numerically simulated to calculate the performance and the erosion characteristics of the over-current components under different particle mass concentrations.The particle volume fraction distribution, flow field velocity, and particle motion trajectory were analyzed to study the effects of particle parameter on erosion characteristics.The results show that with the increase of particle concentration, the single stage head and efficiency of the stamping pump are linearly attenuated.When the particle mass concentration is 90 kg/m3, the single stage head decreases by 6.89%, and the efficiency decreases by 6.95%.The erosion rate of the impeller and the vane is exponentially and positively correlated with the particle mass concentration.The erosion rate of the joint between the blade and the rear cover as well as the turning portion of the vane blade is the highest.Higher particle concentration, high impact velocities, and more frequent particle impacts are the main reason for the higher erosion rate in the above regions.
2020 Vol. 39 (9): 214-220 [
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135
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221
Seismic response of a suspension bridge tower installed with composite beam subjected to near-field earthquake
DUAN Jiahong1,CAO Fahui2,LIN Fan1,RAN Zhihong1,LIU Zhenyu2, ZHANG Jing1,YANG Sizhao1
In order to reduce the moment on the tower section under near-field earthquake, a suspension bridge tower was innovatively installed with the corrugated steel web beam.Taking the Dadu river bridge as an example, and based on the pseudo-static test data of the beam, a numerical structural dynamics model was established.The structural seismic responses were calculated under different types of near-field ground motions to investigate the seismic performance of the suspension bridge and its near-field effect.The results show that the bridge tower with corrugated steel web beam has the advantages of light weight and low rigidity, and more conforms to the design idea of strong column weak beam and strong shear weak bend.Under high intensity near-field earthquake, the ductility of corrugated steel web beam is reasonable to the seismic strategy.The pulse effect has a greater influence on the response.Therefore, it suggests that for this type of bridges, the near-field pulse effect should be paid more attention. The response to the hanging wall effect is less than that to a ground motion without near-field effect, so the bridge on the hanging wall is safer.Under transverse seismic excitation, the near-field pulse effect has a greater influence on the displacement and moment of the bridge tower.
2020 Vol. 39 (9): 221-228 [
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271
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Impact spectrum of vehicle-bridge collision
LI Sitong1, QI Xingjun1,YIN Zhuangfei2
Aiming at the shortcomings of nonlinear finite element method such as time-consuming, effort-consuming and narrow applicability when analysing the dynamic time-history responses to vehicle-bridge collision.A calculation method for the impact spectrum of vehicle-bridge collision was proposed with reference to the concept of seismic response spectrum.63 impact force time-history curves were obtained by constructing 7 finite element models of “vehicle-rigid wall” collision systems and solving their key files.By using the method of spectral analysis, the displacement amplification factor of a single-degree-of-freedom system under impact force was solved. The statistical relation between the amplification factor and the structural period of vehicles at different speeds was observed.The mathematical expressions for the impact spectrum of vehicle-bridge collision were thus obtained by fitting the period-displacement amplification factor curves.Finally, the suggestions for the practical use of impact spectrum were proposed.
2020 Vol. 39 (9): 229-234 [
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186
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A large range chaotic system with multiple types of equilibrium points and its topological horseshoe
A new three-dimensional chaotic system was proposed.By adjusting system parameters, the system may have multiple types of equilibrium points, such as an unstable equilibrium point, no equilibrium point, infinite equilibrium points and a stable equilibrium point, while maintaining its chaotic dynamical behaviors.In addition, with the change of parameters and initial values, it is found that the system is a large-scale chaotic system and has coexistence attractors under the condition of asymmetry.The system’s basic dynamic behaviors were analyzed by using the phase diagram, Lyapunov exponent spectrum and bifurcation diagram.By virtue of topological horseshoe theory and by means of numerical calculations, the system’s topological horseshoe and topological entropy were obtained, which further proves its chaotic characteristics in theory.
2020 Vol. 39 (9): 235-241 [
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138
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242
Theoretical analysis on the vibration and sound radiation of a rectangular plate facing finite depth of water
SUN Yao1, SHEN Nawei1, BAO Zhenming1, YANG Tiejun2
The sound radiation impedance matrix of a rectangular plate facing shallow water was derived analytically. By the eigen-value decomposition technique, the sound radiation modes and their radiation efficiencies were obtained and used to study the sound radiation characteristics of the plate in shallow water.The effect of water depth on the sound radiation and modal added mass was discussed.The results show that underwater natural frequencies of the plate are related to the distribution of added mass while the variation of radiation efficiencies of radiation modes in different depth of water will influence the sound radiation.
2020 Vol. 39 (9): 242-247 [
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145
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248
Optimization and performance analysis of a mine rescue cabin filled with aluminum foam based on crash safety
SHEN Jiaxing1,2, XU Ping2, YU Yinghua2
In order to improve the crash safety of the mine rescue cabin, a new type of mine rescue cabin filled with aluminum foam was designed.Using the parameter optimization module of ANSYS Workbench, the acceleration, deformation and energy absorption of the rescue cabin were taken as the optimization objective.The structural parameters of the cabin and material performance parameters of aluminum foam were optimized.The crash safety of the optimized aluminum foam rescue cabin was analyzed.The results show that, under the premise that the mass and maximum stress of the aluminum foam rescue cabin are sure to be somewhat reduced, the maximum deformation and maximum acceleration of the foam aluminum rescue capsule are significantly reduced, and the energy absorbed by the cabin is greatly improved.It is proved that the aluminum foam rescue cabin has better crash safety.
2020 Vol. 39 (9): 248-253 [
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Low frequency broadband sound insulation performance of an acoustic metamaterial panel supported on two sides
ZHANG Songyang1, CHEN Yongyong2, WANG Guangzhou1, WANG Leilei1, WANG Xiaopeng2
Uner the background of the low-frequency sound insulation of power transformers, a kind of simple and lightweight local resonant acoustic metamaterial panel was proposed, which was made by closely bonding high-polymer sheets on the two sides of supporting frames, with a superior low frequency sound insulation capability compared with four-side supported metamaterial panels.Under the normal incident sound wave, the sound insulation performance was studied by finite element analysis (FEA).The results show that there is obvious sound transmission loss (STL) with a peak of 31 dB at 248 Hz.To broaden the STL low-frequency band, mass blocks were arranged on the metamaterial panel.The FEA results show that there are three STL peaks in the range of 152-560 Hz, with the highest STL of 26 dB, thus achieving broadband sound insulation effect to some extent.At the same time, a STL peak of 18 dB appears at 120 Hz.Finally, a sound insulation experiment platform based on small box was built, and it can be found that the experimental test results are in good agreement with the FEA results, which verifies the excellent low-frequency broadband sound insulation ability of the lightweight acoustic metamaterial panel, indicating the acoustic metamaterial panel supported on two sides has broad engineering application prospects.
2020 Vol. 39 (9): 254-259 [
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211
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Mixed lubrication of a linear motion rolling guideway pair
WANG Xiaopeng1,2, ZHAO Xinze2, XU Xiang2, LI Xiang2, HE Kongde2, TIAN Hongliang2
A numerical model for the mixed lubrication of a linear motion rolling guideway pair was proposed considering the factors of contact geometry, preload, real surface roughness and curvature coefficient.The effects of the moving speed, curvature coefficient, load and surface roughness on the lubrication characteristics of the linear motion rolling guideway pair and sub-stress were studied.The results show that the normal working load of the guideway pair, maximum Hertz pressure and Hertz contact radius increase with the rise of the normal total load, however, the average film thickness decreases with the growth of the normal total load.The numerical model can be used to predict the whole lubrication characteristics in a wide range of operating conditions of the guide rail.The linear motion guide rail is mostly working under the mixed lubrication state, and as the moving speed increases, the contact interface performs from the boundary lubrication condition to mixed lubrication condition, the lubrication performance becomes better and better. Appropriately increasing the coefficient of curvature radius will be conducive to the formation and stabilization of oil film.
2020 Vol. 39 (9): 260-266 [
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132
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Dynamic load simulation and fatigue analysis of a pure electric light truck battery bracket based on measured road load spectrum
GE Wentao, HUANG Hui, DUAN Longyang, LIU Zhou, QIU Xing,BI Pengfei,CHEN Weihuan
In order to keep the relevance between the analytical durability analysis of a pure electric light truck battery bracket and its durability test on proving ground, an analysis methodology combining the multi-body dynamics, durability analysis and road spectrum measurement on proving ground was proposed.A rigid-flexible coupled multi-body dynamics model composed of seven channels virtual test-rigs, the battery bracket and the whole frame was built by using ADAMS software.By applying virtual iteration technique and Femfat.lab software, and taking the measured battery bracket acceleration signal on proving ground as a target response signal, the load boundary used for the fatigue analysis of battery bracket was back-calculated.The fatigue life of the battery bracket was analysed by using the fatigue simulation software nCode with the Miner Counting Algorithm. The analysis results show that the fatigue life can satisfy the requirement, and meantime, the battery bracket has ultimately passed the durability validation of proving ground, which verifies the engineering practicability of this methodology.The methodology has important reference value to the fatigue property analysis of electric vehicle battery brackets.
2020 Vol. 39 (9): 267-273 [
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264
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