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2019 Vol. 38, No. 24
Published: 2019-12-15
1
A study on vibration reduction of a flexible manipulator based on the saturation principle
ZHANG Ge,GAO Zhihui,BIAN Yushu
this paper, a rigid-flexible coupling flexible manipulator was studied.A semi-active internal resonance vibration absorber with nonlinear coupling term was established.By adjusting the parameters of the vibration absorber, a 2:1 internal resonance between the first-order vibration mode of the flexible manipulator and the vibration mode of the vibration absorber was formed.As a result, an energy path between the two vibration modes was established.The nonlinear dynamic equations of the flexible manipulator equipped with the internal resonance absorber were established by using the Kane method.The approximate steady-state solutions of the nonlinear dynamic equations were obtained by using the multi-scale method.With the analysis of the existence of steady-state solutions, the saturation phenomenon of the system was proved to be existed; the existence of saturation phenomenon and effectiveness of the vibration absorber were verified by numerical simulation.
2019 Vol. 38 (24): 1-7 [
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312
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Contact damping characteristics of delaminated composite plates
HE Yi1,XIAO Yi1,SU Zhongqing2
Damping performance is a high-sensitivity dynamic parameter that can be utilized to identify delamination.The damping of the delaminated composite plates contains material damping and contact damping, material damping was calculated based on the strain energy method, and contact damping was analyzed by a static-slip-integrated friction energy-dissipated model.The finite element models (FEMs) were developed by using the Abaqus software to simulate the dynamic responses of delaminated composite plates, in which, the normal contact stiffness and contact damping were introduced via the penalty stiffness method and equivalent viscous damping, respectively.The free decay test was set up to measure the dynamic parameters of the plates with different delamination sizes and locations in thickness direction.The results show that the higher the delamination ratio is, the more the first-order modal damping of the laminate rises, and the contact damping plays a major role in the rising.The experimental results are in good agreement with the FEMs' results, which verifies the rationality and accuracy of the FEMs.
2019 Vol. 38 (24): 8-17 [
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234
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18
Accurate location and degree identification of wind turbine blade cracks based on natural frequency
WU Qiqiang,GUO Shuaiping,WANG Gang,LI Xuejun
The structure health condition of a wind turbine blade is closely related to public safety.Cracks in wind turbine blades affect safe operation of wind turbines.The diagnosis of blade cracks is of paramount importance.The cracks influence the natural frequency of the blades.In wind turbine blades, the natural frequency variation of the structure caused by the crack is related to its position.In terms of the ratio of the adjacent two-order natural frequency variation, it was found that the ratio is related to the crack position alone.Based on the ratio parameters, the blade can be fictitiously divided into multiple connected regions.The crack is implanted at each joint point of regions to establish the database of the ratio parameters for crack locating.The region where the crack exists can be ascertained.Then, a new position parameter in the region was proposed, and the mapping between this parameter and the detail position within the region was established.The crack can be located more accurate in the regions.In order to identify the degree of the crack, a parameter of crack degree, which is defined as the ratio of the variation of the natural frequency to the natural frequency itself, was proposed.Based on simulation and data analysis, the correlation between the parameter and the degree of crack was established.Based on the correlation, the degree of crack can be ascertained by the correlation after crack locating.Numerical simulation analysis and tests for blade with different cross-sectional shapes were performed, and the results all show that the method is effective and accurate.
2019 Vol. 38 (24): 18-27 [
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296
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28
Primary investigation on site classification for high speedrailway seismic stations in China using a spectral ratio method
HUANG Jun1,2,CHEN Zhigao1,2,YANG Jiang1,2,XIA Jiening1,2
High-speed railway seismic stations in China had not carried out site classification, which limits the use of strong earthquake records.The mianshock-aftershock of Menyuan Ms6.4 earthquake were record by Lanzhou-Xinjiang high-speed railway seismic statons.The average curve of aftershocks (Peak Ground Acceleration, PGA<35 cm/s2) were calculated as the linear site response reference.The seismic station site nonlinear site response degree was assessed to screen out strong earthquake records (PGA>35 cm/s2) that were used for sites classification.Then four high-speed railway seismic stations were finished site classification by using the empirical site classification scheme for National Strong Motion Observation Network System station.It shows that the near and far high-speed rail monitoring points are identified as the same site classification, which proves the high-speed railway seismic station construction method in China is reasonable.Finally, the reason of the larger PGA difference of the two monitoring points in mainshock was analyzed.
2019 Vol. 38 (24): 28-33 [
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199
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34
Stiffness matching relationship between constrained edge members and embedded steel plates of steel plate shear wall
WANG Wei,XIANG Zhaoxing,LIANG Yujian,WANG Jun,HUANG Sikao
In order to study corrugated steel plate shear mechanical properties and energy dissipation capacity, three specimens were designed and conducted quasi-static tests.The experimental results show that the hysteretic performance, bearing capacity and ductility of the corrugated steel plate shear wall are better than those of the flat steel plate shear wall, and the mechanical properties of the transverse wave steel plate is the best.At the same time, it can be obtained from the failure mode of the experiment that the three specimens were unsteady due to the out-of-plane deformation of the restrained edge member H-shaped steel column, which failed to give full play to the mechanical properties of the embedded steel plate.In order to study the stiffness matching relationship between constrained edge members and embedded steel plates, 12 finite element models were established for numerical analysis by the ABAQUS software, and the geometrical dimensions of 3 models were consistent with the experimental specimens.Comparing the numerical analysis results with the experimental results, it indicatess that the finite element analysis results are in good agreement with the experimental results.The remaining 9 models changed the stiffness matching relationship between the restrained edge member and the embedded steel plate by changing the flange width-to-thickness ratio of H-shaped steel column.The results show that when the flange width-to-thickness ratio of H-shaped column is 13.9, the stiffness matching between the restrained edge member and the embedded steel plate is optimum.
2019 Vol. 38 (24): 34-40 [
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190
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41
Planetary gearbox fault diagnosis via current signature analysis based on ICEEMDAN and frequency demodulation
GUAN Yichen,TONG Pan,FENG Zhipeng
In order to accurately extract gear fault feature of planetary gearboxes from current signals, a fault diagnosis method was proposed based on improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) and frequency demodulation analysis.Firstly, the complex multi-component induction motor current signal was adaptively decomposed into a series of intrinsic mode functions (IMF) by ICEEMDAN.Then, based on the characteristics of fault frequency modulating supply frequency and the principle of the instantaneous frequency fluctuation around supply frequency, the IMF containing fault information was preferably selected as the sensitive component.Finally, the planetary gearbox fault was diagnosed according to the frequency demodulated spectrum of the sensitive components.The gearbox experiment collected the induction motor current signal with sun, planet and ring partial fault, respectively.The analysis result shows that this method can not only reduce the influence of the noise in stator current, but can also extract the fault frequency feature in complex signals effectively.
2019 Vol. 38 (24): 41-47 [
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181
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48
The strut-and-tie mode for shear performance of a RC frame internal joint based on crack distribution
DONG Junhong1,YANG Hong1,2,ZHAO Wentong1
A large number of reinforced concrete beam-column subassemblage seismic experimental results indicate that under high shear compression ratio, beam-column joint concrete may generate obvious nonlinear shear deformation at the later stage of loading.When utilizing finite element methods to simulate the mechanics performance of a joint, correct calculation for stress-strain hysteretic curve is the base or precondition for reasonable finite model or nonlinear deformation calculation.Based on the development and distribution of joint cracks in beam-column subassemblage seismic experiments, a crack-based strut-and-tie model and a method for calculating the shear stress-strain skeleton curve were proposed.Based on the super joint element (beam-column joint element) in the OpenSees software, the simulation results of the model were used in the finite element analysis of the seismic tests of several typical beam-column subassemblages.By comparing the simulation results of joint shear block shear stress-strain hysteresis curves, load-displacement hysteresis curves at the beam end with that of the test results, the applicability and effectiveness of the crack-based strut-and-tie model was verified.
2019 Vol. 38 (24): 48-55 [
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145
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A calculation method of structural response considering dynamic characteristics of damping materials
LIU Lan1,LIU Yunong1,2,LIU Chao1,LIU Geng1,WU Liyan1 YUE Yanjiong3
In order to accurately calculate the vibration response of an additional damping structure, a structural response calculation method which considers the dynamic characteristics of the damping materials was proposed, which can accurately extract the modal parameters and calculate the vibration responses of the additional damping structure.The material properties of damping materials are affected by the excitation frequency, which may cause the calculation of the vibration response inaccurate.Based on the traditional modal strain energy method, an improved modal strain energy method considering the dynamic characteristics of materials was established.The modal parameters of the composite structure were extracted accurately, which were verified by a modal test.Then the modal parameters were accurately substituted into the structural vibration response calculation.By comparing the acceleration frequency response curves of the observation points in simulation and experiment, the accuracy of the response calculation method was verified.The results show that the modal parameters of the additional damping structure can be accurately extracted and the vibration response of the structure can be calculated by this method.
2019 Vol. 38 (24): 56-62 [
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190
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63
Shaking table tests on transverse pounding effect of high-speed railway simply-supported girder bridges under earthquake excitations
MENG Dongliang,GAO Qiong,YANG Menggang
The pounding occurs when the earthquake-induced transverse relative displacement between superstructures and substructures exceeds the initial gap between shear keys and girders or between shear keys and bearing bases.In order to investigate the transverse pounding effect of high-speed railway simply-supported girder bridges under earthquake excitations, taking a 32 m standard-span simply-supported girder bridge as the research object, a single-span bridge model was designed and made with the scale ratio of 1∶6.The influence of the spectral characteristic of the ground motion, peak ground acceleration (PGA), and the initial gap between shear keys and bearing bases on transverse pounding effects was studied through shaking table tests.And the anti-collision effect and isolation mechanism of rubber bumpers were also discussed.The results show that: shaking table tests could reproduce the transverse seismic pounding process of the bridge structure; the fixed bearings were not damaged under the low-level earthquake excitations, and there was no collision phenomenon between the shear keys and the bearing bases; however, the fixed bearings were damaged and most of the test cases collided under the excitations of the design and high-level earthquakes.The pounding between the shear keys and the bearing bases significantly limited the development of the transverse relative displacement between the superstructure and the substructure, but it also aroused high-frequency response of the structure, and hence, amplified the bending moment response at the bottom of the pier.The installation of the rubber bumpers would reduce the pounding stiffness and weaken the high-frequency response of the bridge structure caused by the pounding, thus reduced the seismic responses of the bridge structure.
2019 Vol. 38 (24): 63-73 [
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163
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74
A study on firing dynamics of a glass/carbon hybrid filament winding composite launch canister
SUN Tongsheng1,WANG Qi2,YU Cungui1
In order to simulate the motion process of projectile in bore accuracy, the two-dimensional transient distribution characteristics of the propellant gas pressure in a glass/carbon hybrid filament winding composite launch canister was considered.Based on the contact collision theory and considering the strong dynamic impact of propellant gas, a numerical analysis model for the nonlinear coupling problems between the projectile and the launch canister was built.A user-defined subroutine was used to reconstruct the correlation kinetic process between the temporal and spatial variation of propellant gas pressure and the projectile motion.Numerical analysis results were compared with test data.The results show that the established numerical analysis model can reproduce the physical field changes in the actual launching process and the dynamics stress response of launch canister can be simulated more actually, providing a theoretical support for the design, optimization ,and launch safety evaluation of the fiber composite launch canister.
2019 Vol. 38 (24): 74-80 [
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150
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A simplified analytical method for ship plating subjected to lateral impact by a wedge indenter
ZHANG Min1.2,3，LIU Jingxi2,3，ZHAO Yao2,3，HUANG Shiwen4
Ship plating can experience large plastic deformation and even tearing under lateral impact by a wedge.In this paper, theoretical and experimental studies on the response of large plastic deformation were conducted.Based on the upper bound theorem, a simplified analytical method for the resistance of a clamped rectangular plate subjected to line or rectangular area load was proposed.Analytical calculation formulae were derived and verified with model tests.The results show that the analytical method can provide a guidance for crashworthiness design of ship plating.
2019 Vol. 38 (24): 81-84 [
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141
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85
A stochastic response surface method for probability analysis of critical speeds of a rotor systems
ZUO Yanfei1，JIANG Zhinong1，FENG Kun1，WANG Jianjun2
In order to analyze the probability distribution of the critical speeds of rotor systems influenced by uncertainties, a method based on stochastic response surface was proposed.The implicit function relationship between the critical speed and the uncertain parameters of the rotor system was approximated.By using stochastic response surface of the critical speed, the Campbell diagram was replaced to avoid the difficulties of directly using it to perform the stochastic critical speed analysis.The analysis of stochastic critical speed of a typical dual-rotor system verified the accuracy and efficiency of the proposed method.
2019 Vol. 38 (24): 85-90 [
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178
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91
A study on the seismic performance optimization of a 1 000 kV capacitor voltage transformer
LIN Sen，CHENG Yongfeng，MENG Xianzheng，SUN Yuhan，LU Zhicheng，ZHANG Qian
For ensuring the seismic safety of an important electrical equipment in an ultra high voltage power transformation project, improving the seismic withstand capability of theporcelain equipment, the seismic performances of a 1000 kV capacitor voltage transformer(CVT) with and without mental dampers were investigated by shaking table tests.The test result shows that the application of dampers reduces peak stress at the bottom of the equipment and peak acceleration at the top of the equipment by 59% and 54%, respectively.Considering the disadvantage in seismic performance for the equipment displayed in test, a finite element model was established to further explorer structure defect of equipment.A structural remolding optimization scheme improving the equipment as monolithic tower-type and adjusting outer diameter difference between the middle and bottom section of bushing to 5 mm locally by reducing material was proposed.After optimization, the maximum stress of the equipment reduces from 32.46 MPa to 20.18 MPa.The maximum stress ratio of the bottom bushing to the top bushing reduces from 7.92 to 2.33, which indicates that stress distribution is more balanced.The seismic precautionary requirement which the equipment can meet is increased from 0.2g to 0.3g.For different seismic optimization targets from 0.3—0.5g, corresponding strategies for improving the seismic performance of the 1 000 kV capacitor voltage transformer, which combine modification in construction with energy absorption, were proposed.
2019 Vol. 38 (24): 91-100 [
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103
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101
An orthogonal experiment study on dynamic characteristics of a swing polishing grinding head
YE Youdong，WANG Kai，ZHOU Zhebo
An experimental platform of dynamic characteristics of a swinging polishing grinding head was designed and built.The vibration signals of the grinding head were measured by an acceleration sensor.Based on the factors affecting the vibration of the grinding head, orthogonal experiments were carried out based on three parameters of grinding spindle speed, grinding head pressure, and grinding block size.By analyzing and comparing the experimental data and the waterfall chart, optimum matching polishing parameters were obtained for suppressing the vibration.The experimental results provide a useful reference for the application of the swing polishing grinding head on polishing machines.
2019 Vol. 38 (24): 101-106 [
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162
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107
An experimental study on the damage effects of the concrete slabs under low-velocity impact
GU Song1,2，PENG Feng1，YU Zhixiang3，LI Jinxing1,2,4
In order to investigate the damage effect of concrete slabs under low velocity impact, six groups of concrete slabs were tested by a drop hammer tester, and the effects of different impact velocities, concrete slab strength, and length-thickness ratio on the impact damage of concrete slabs were analyzed.A high-speed camera records the whole process of crack occurrence, development, and destruction of each test piece during the impact process.The test shows that under the impact load, the crack distribution of the concrete slab has a clear trend with the impact velocity increasing to the impact point.At higher energy, the concrete slab is punched and damaged near the impact point; and the board is deduced based on the experimental phenomenon.The calculation method of the impact force of the overall deformation of the structure was compared with the experimental results, which shows that the error of the calculation method are within 25%.
2019 Vol. 38 (24): 107-114 [
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155
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115
Anti-progressive collapse analysis for steel concentrically braced frame under vierendeel action
QIAO Huiyun1,2，WEI Jianpeng3，TIAN Limin3
Multi-story frame structures exhibit different anti-collapse mechanisms after key components failed.The Vierendeel action is one of the important anti-progressive collapse mechanisms.The dynamic non-linear analysis considering damage and strain rate was used to simulate column-removal tests by other scholars on multi-story frames, and a theoretical model of the Vierendeel action was proposed.Then, the steel concentrically braced frame commonly used in seismic design was improved, and horizontal bracing was arranged on the top story.Finally, the horizontal bracing system was applied to the Ohio Union building.The results show that the Vierendeel action is the result of the internal forces redistribution among the vertical members, which reflects the overall stress characteristics of the frame structure.The Vierendeel action and other anti-collapse mechanisms together resist the unbalanced load.The top horizontal bracing can significantly reduce the displacement at the failure point, play the role of Vierendeel action, and improve the progressive collapse resistance of the structure.After two middle-column of the Ohio Union building fail, the bracing system transfers most of the gravity of the failed span to the adjacent structure.
2019 Vol. 38 (24): 115-121 [
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172
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122
Wind-induced effects and leeward flow patterns of a CAARC standard tall building model
DONG Xin1,2，YE Jihong3，ZOU Yunfeng4，ZUO Taihui4
Through wind tunnel test, PIV experiment, and dynamic response calculation, wind pressure distribution, surrounding flow field, and wind-induced responses of a CAARC model under wind directions of 0° and 90° were investigated.Firstly, the wind pressure distribution and the total forces were compared.Results indicate that major difference of wind pressure distributions between the two wind directions is on the side face.Smaller drag and lift force, along with larger torque, is obtained under wind direction of 90°.Secondly, the flow field behind the model was displayed.A vortex pair in the horizontal plane was observed under two wind directions.Recirculation zone in the vertical plane appears only at wind direction of 0°.The vortex size and its reverse flow velocity are larger at wind direction of 0°.In addition, the transverse motion of fluid around the vortex is more vigorous.Thirdly, the variation of top displacement and acceleration with reduced velocity was explored.The along-wind and across-wind responses vary with reduced velocity to a power of 2—2.6 and 3—3.5, respectively.For wind direction of 90°, the amplification of across-wind displacement and across-wind acceleration with reduced velocity are twice and 2.6 times those under wind direction of 0°.
2019 Vol. 38 (24): 122-130 [
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175
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131
Broken area evolution characteristics and crack propagation rules of concrete under high pressure water jet crushing
LIU Jialiang1,2,3，LI Kunyuan1，ZHANG Di1
The internal crack propagation rules in concrete under high pressure water jet impingement are the fundamental issue of hydraulic breaking concrete mechanism.Through the similar material and model method and the high speed photography technology, an erosion hole and crack propagation detection system of the high pressure water jet impacting transparent similar-concrete material was built.A detailed study on the evolution process of the erosion zone and the crack propagation mode was performed.The results show that the high pressure water jet erosion can be divided into three typical evolution processes: the expansion in the water hammer compression zone, the expansion in the non compression zone, and the extension after penetration.In the water hammer compression zone, the erosion hole expands to the free surface in the form of a "petal" shape, and there is a significant plastic yield zone and staggered crack network in front of the erosion hole.The critical criterion for the evolution of the erosion hole was proposed theoretically.In the non compression zone, the plastic yield zone near the erosion hole has a sharp decrease and the material removal has evolved into the completely brittle fracture mode, and the axial evolution velocity of the erosion hole presents periodical stagnations.After penetrating, the radial dimension of the erosion hole continues to increase, and the discontinuous and micro hemispherical crack region appears near the hole wall.When the erosion hole diameter extends to about two times of the initial hole, the main erosion hole will tend to be stable.
2019 Vol. 38 (24): 131-137 [
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162
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138
A study on the effects of particle impact forms on energy dissipation of dampers
SONG Xiaoyu，YIN Zhongjun，CHEN Bing
In order to reveal the dependence between the impact forms and the loss power, the motion patterns of the particles in cylinder and conical containers were reproduced through the discrete element method, and the difference between the impact forms and the energy loss caused by different forms of particle motion was explored.The results show that compared with a cylinder container, the movement of the particles in a conical container has obvious regional characteristics.This special form of motion has a certain inhibitory effect on the impact subharmonic bifurcations, so that the impact form on the system is expressed as “Small and dense” type.The energy consumption results show that the energy loss caused by this “small and dense” impact mode is higher than that of the “large and sparse” type of impact in the cylinder container, and the energy consumption difference between the two increases with the vibration intensity.The significant effect of the impact form on the power loss is further verified by analyzing the gradual process of the container inclination.
2019 Vol. 38 (24): 138-143 [
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151
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144
Transient lubrication analysis of UHMWPE bearings during start-up with vibration and shock
XIE Yinong，WANG Youqiang，SONG Xiaoping，ZHAO Jingjing，ZHANG Ping
An elastohydrodynamic lubrication model of the ultra-high molecular weight polyethylene (UHMWPE) bearing during the start-up was established.The acceleration with vibration and shock coupled time-dependent effect was comprehensively considered.The lubrication condition of the UHMWPE bearing under different working conditions was numerically simulated for reference to ensure safe operation.The results show that the effect of impact on pressure is greater, and the vibration has a greater influence on film thickness.When the normal vibration of the shaft and the impact of the waves are in the same period and both changes are the same, there will be a synergetic effect of superposition, and vice versa.The effect of negative sinusoidal vibration on pressure and film thickness is even more pronounced.As the acceleration increases, the pressure decreases, the film thickness increases, and the effect of vibration on the pressure and film thickness becomes smaller.
2019 Vol. 38 (24): 144-149 [
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134
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150
Visual identification and diagnosis based on IC engine vibration signals
CAI Yanping1,2，XU Guanghua1,3，ZHANG Heng2，FAN Yu2，LI Aihua2
In order to improve the accuracy and real-time of IC engine fault identification and diagnosis, and solve the difficulty of feature extraction for IC engine multi-component and non-stationary vibration signals effectively, a visual fault diagnosis method for IC engine vibration signals based on improved local binary pattern(ILBP) and two directional-two dimensional principal component analysis(TD-2DPCA) was proposed.Firstly，aiming at the problem of low time-frequency resolution and cross-interference in the analysis of IC engine vibration signals by the traditional method, the empirical wavelet transform(EWT) and synchro-squeezing wavelet transform(SST) were applied to the time-frequency representation of IC engine vibration signals.Secondly, the texture feature of the image was extracted by ILBP and TD-2DPCA was used to reduce the dimension of an ILBP texture image.The feature parameters of the image were obtained by vectorizing the coding matrix.Last, the feature vectors were trained and tested by support vector machine(SVM) and nearest neighbor classifier(NNC) respectively to realize the fault diagnosis of the IC engine.In the identification and diagnosis test of cylinder head vibration signals under 8 working conditions of the IC engine, higher classification accuracy was obtained.Through reasonable optimization of the parameters, the classification rate is guaranteed and the highest recognition rate reaches 96.67%.Compared with other methods, the effectiveness of this method in IC engine fault diagnosis was fully demonstrated.
2019 Vol. 38 (24): 150-157 [
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218
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158
Coupling mechanism analysis between shaft whirling and transient oil film force of journal bearings under dynamical load
LI Qiang1，ZHANG Shuo1，WANG Yujun1，XU Weiwei2，WANG Zhenbo1
Transient oil film force is the main damping source of a rotor-bearing system, and also an important reason for instability.Firstly, a new structured dynamic mesh method was presented for mesh updating.Based on this method, a CFD model for nonlinear transient oil film force under dynamical load was established.The cavitation was described by the "full cavitation model".Then the coupling mechanism between shaft whirling and transient oil film force was analyzed for circular and multi-wedge journal bearings.Results indicate that the deviation between the calculated results of the static equilibrium position and the experimental results is less than 2.5%.Under the support of nonlinear oil film force, the dynamic load has an obvious influence on the stability of the rotor.When the dynamic load is small, the oil tank seriously weakens the radial and tangential oil film force in the shaft whirling process.With the increase of dynamic load, the influence of the oil wedge decreases, the radial and tangential oil film force increase gradually, and the half speed whirling can be suppressed.For multi-wedge bearings, the influence of the oil tank is relatively small, so the oil film force can provide enough stiffness and damping to maintain stability.
2019 Vol. 38 (24): 158-164 [
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124
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165
Numerical simulation of vibration response of pipe conveying fluid based on a generalized finite difference method
ZHANG Ting1,LIN Zhenhuan1,GUO Xiaomei1,ZHANG Heng1,FAN Jiaming2
In this study, a high-order accuracy numerical model of the meshless method, called generalized finite difference method (GFDM), was generalized to analyze the transverse vibration problem of pipe conveying fluid.Based on the differential equation of transverse vibration, the GFDM and the Houbolt methods were adopted to discretize the partial differential items in space and time, respectively.The consistent with good results of natural frequency and the amplitude time range was compared with the theoretical solution and other numerical results reported in literature.Meanwhile, the numerical model proposed in this paper has good stability and robustness in solving the vibration response of pipe conveying fluid by comparing with the vibration amplitude at the midpoint with different total number of points N, time step Δt and sub-region selection points ns, respectively.Furthermore, detailed analysis of the vibration response characteristics with several typical boundary conditions indicates that the vibration amplitude at the midpoint of the pined-pined pipe is much large than that of two other boundary conditions, and the vibration frequency of the clamped-clamped pipe is more fast than that of others.Besides, the position of the maximum amplitude of the vibration is shifted to the weak constraint when the end of restrictive condition is asymmetric.
2019 Vol. 38 (24): 165-171 [
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170
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172
A study on longitudinal displacements and damage control of expansion joints of long-span steel bridges under stochastic traffic loads
HAN Dazhang1,GUO Tong2,HUANG Lingyu2,LIU Zhongxiang2
An expansion joint is one of the vulnerable bridge parts, and for long-span steel bridges, which are vibration sensitive due to high flexibility, their expansion joints encounter more significant damage.To control the damage of expansion joints of long-span steel bridges, an approach for analyzing the displacements of expansion joints under stochastic traffic flow was established, based on the stochastic vehicle model and finite element analysis.The influence of speed, vehicle-induced vibration frequency, traffic volume and heavy traffic on longitudinal displacements was investigated, and it is found that with higher vehicle speed and vibration frequency, larger traffic volume and more heavy vehicles, the cumulative displacements of expansion joints significantly increase.Two kinds of traffic limit measures and installing viscous dampers at beam ends are suggested, so as to control the damage of expansion joints.Analysis results show that the vehicle-type based measure is more effective than the time-based measure.After the use of viscous dampers at beam ends, there is a significant reduce in displacement amplitude, cumulative displacement and high-frequency displacements.
2019 Vol. 38 (24): 172-178 [
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198
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179
A modification for the PSD envelope of ground microtremor considering non-stationary modification
HAO Yu,CHEN Xueqian,FAN Xuanhua,WANG Yujun,DU Qiang,HU Shaoquan
Ground microtremor is an important factor for stability of large precise equipments.Determination of the envelope of power spectral density (PSD) is one of the preliminaries for the stability design of a structure.Combining the numerical characteristics of a ground microtremor, a modification method was proposed considering the non-stationarity of the ground mircotremor signal.The modified PSD envelope can avoid the problem that large-amplitude vibrations may be hided in the traditional stationary or locally stationary assumptions, yielding an envelope that fully reflects the most dangerous part of the ground microtremor load, which is independent to the selection of time length of a PSD curve.The PSD envelopes of the ground microntremor of the Huagai monitoring station in 2015—2016 were calculated, founding basis for the design of large opto-mechanical structures.
2019 Vol. 38 (24): 179-182 [
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167
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183
A method of incipient fault diagnosis of bearings based on autocorrelation analysis and MCKD
ZHU Xiaoyan,WANG Yongjie
Rolling bearing early faults often present a non-stationary signal, weak regulation.The fault feature component is not outstanding and there is strong background noise, which makes effective extraction of bearing fault features very difficult.To solve this problem, a fault diagnosis method of rolling bearings based on autocorrelation analysis and MCKD was proposed in this paper.First of all, the use of the biased estimate autocorrelation analysis method of the bearing signal makes a preliminary analysis, realizes the inhibition effect of noise in the signal component, then MCKD solution of the convolution algorithm of the signals was used for further analysis, highlighting the original impact signal components and further de-noising.The signal-to-noise ratio was further improved.Finally, signal envelope spectrum analysis was used to determine the bearing fault location.The simulations and the analysis results of the measured data show that the proposed method can effectively extract the characteristic information of the fault signal and has certain validity.
2019 Vol. 38 (24): 183-188 [
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218
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189
Analysis of perforation liquid pressure pulsation law considering complex boundary conditions at the bottom of a well
LI Mingfei,DOU Yihua,CAO Yinping,YU Yang,CAO Ting
Perforation detonation shock and pressure pulsation often lead to accidents, such as bend and break of the column of the emission hole because of vibration.The high pressure of the perforating liquid and the narrow casing boundary that affect the shock wave propagation, and the influence of interference caused by the dense arrangement of perforating bullets were considered.Furthermore, continuity of shock wave propagation at phase change interface was also considered.An initial pressure analysis method of the shock wave was established according to the Tait equation.The law of shock wave propagation was clarified and an analytical method of direct shock wave was established, which both consider the narrow boundary conditions of casings.According to the principle of shock wave reflection, the approximate graphic method was used for solving the parameters of the perforation liquid and the casing interface.The pressure pulsation analysis method was established by applying the superposition principle of direct and reflected waves.After actual perforation verification, the results show that the reflected wave pressure is significantly larger than the incident wave pressure, and the reflected wave pressure decreases with the explosion distance.When perforating bullets are arranged in 16 holes/m, the four nearby bombs affect the shock wave generated by a certain bomb, and the rest can be neglected.The pressure decay is increased by the initial pressure time of the perforating liquid by 30 μs.
2019 Vol. 38 (24): 189-196 [
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128
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197
A study on sound field prediction of underwater vehicles based on a modal superposition method
ZHOU Sitong1,2,3,SHUAI Changgeng1,2,YANG Jiaxuan4
In order to predict the radiation sound field of a finite cylinder through discrete sound pressure or velocity data on a cylindrical surface, a sound field prediction algorithm based on the modal superposition method was proposed.In the method, the radial vibration of the finite cylindrical shell was represented by axial and circumferential modes, and then a transfer function matrix was built between each mode and holographic surface.The modal coefficients were determined by matching the holographic surface sound pressure or vibration velocity.In addition, small amount of far-field sound pressure data was used to perform parameter matching in the sense of least-squares to obtain the optimal axial and circumferential modal order, and finally the prediction of the radiation sound field was realized.Numerical simulations and experiments of point source, cylinder source and ship model were used to demonstrate the validity and applicability of the approach.Results of both the numerical simulations and the anechoic chamber experiment show that compared with the statistically optimized near-field acoustical holography, the proposed technology can realize the sound field prediction outside the holographic aperture, which is suitable for the radiation acoustic field analysis of the finite long cylinder.
2019 Vol. 38 (24): 197-202 [
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189
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203
Recognition of battlefield acoustic target based on morphological multifractal of double changed dimensions
ZHANG Kun1,DI Yi1,2,GU Xiaohui1
An acoustic recognition method based on morphological multifractal of double dimensions changed was proposed according to the multifractal characteristics of the battlefield acoustic target.The method defined double dimensions changed distributed function.Regression analysis was used to show that the accuracy of fitting with the function was high and the slope of two points could be used as the fractal dimension.Based on speed and recognition rate, the best scale group was selected.The simulation results show that the algorithm is faster than the traditional method of measurement in morphological multifractal obviously.The multifractal dimension calculated by them was used as the feature input.The support vector machine was used for acoustic target recognition, and also the acoustic target recognition rate is increased by 23.5% compared with the existed method.Therefore, the method proposed in this work can be a better choice for battlefield acoustic target recognition using the nonlinear characteristic of the signal.
2019 Vol. 38 (24): 203-208 [
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94
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209
A multi-level performance SMA-based isolation system in girder bridges
CAO Sasa1,WU Suiwen2,SUN Zhuo1,WANG Huan1,YANG Jun1
During the near-fault earthquake action, isolated bridges experience significant in-plane displacement and residual displacements, which may cause the bridge girders to unseating and even complete collapse.In this paper, a multi-level performance SMA-based isolation system was proposed.This device consists of 3-levels of SMA cables and conventional isolators, which are assembled in parallel.With the intensity of earthquake increasing, each level of SMA cables will be activated in a sequence to meet different performance requirements.Based on OpenSees and Sap2000 platforms, the lateral restoring force-displacement relationship and the hysteresis model of a specific SMA-based isolator was explored.The effectiveness of the two platforms for simulating the isolator was also investigated.Furthermore, a case study of a continuous bridge was conducted and parameter analysis about effective sectional area was conducted to testify the effectiveness of the isolation system in multi-level aseismic design.It turns out that this device has better displacement reduction, restoration, and energy dissipation capability.In addition, it has the advantages of multi-level performances, which ensures itself a bright prospect in application.
2019 Vol. 38 (24): 209-217 [
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158
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218
A study on dynamic responses properties of packaged products under different spectral excitation
WANG Zhiwei1,2,3, FANG Shugai1,2,3
Two types of acceleration random vibration power spectral density (PSD) excitations were set up according to the results of sine sweep vibration experiments, which had the same spectrum in the vicinity of the resonance frequency and different spectrum in the vicinity of the non-resonance frequency.The acceleration responses of product and dynamic contact force responses of packaged product were investigated with three kinds of constraints and input intensities for the nonlinear packaging system.The results indicate that under the same constraint and vibration intensity condition, the acceleration response PSDs of product and dynamic contact force response PSDs of package were basically consistent around the resonance frequencies; when the vibration intensity was higher, the acceleration response PSD of product and dynamic contact force response PSD of package under the two types of spectral excitations had a certain deviation in the small range of the resonance point due to the influence of the damping; the probability density function (PDF) of acceleration responses almost showed no difference under the different spectral excitations, and the values of mean, standard deviation, skewness and kurtosis were close; there were some differences between the PDF of the peak of dynamic contact force, and the distributions in the spectrum 1 were narrower and higher than that in the spectrum 2; however, the values of mean and standard deviation, number of mean value crossings and number of maxima of dynamic contact force, and bandwidth coefficient were close.Excitation of resonant region controls the responses of the whole nonlinear packaging system.
2019 Vol. 38 (24): 218-226 [
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113
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Instantaneous impact force decomposition of underwater self-excited inspiration pulse jet device
YU Xiaolong1,2, LIU Xinyang2, XU Hongzeng1, CHEN Hao2, WANG Shunsheng2, GAO Chuanchang2
In order to study the time-varying impact and fluctuation impact force in the instantaneous impact force of the underwater self-excited inspiration pulsed jet device, discrete orthogonal wavelet transform and EMD were used to denoise and decompose for the instantaneous impact force of the device.The wavelet basis function and the number of decomposition layers for the wavelet transform and the number of intrinsic mode functions (IMF) for EMD were determined for time-varying impact force extraction.The influence of confining pressure on the pulsed amplitude and pulsed period of the time-varying impact and the fluctuation strength of fluctuation impact were analyzed.The results show that under different confining pressure, the discrete orthogonal wavelet transform is better than EMD in extracting the time-varying impact force, but the choice of wavelet basis function needs to consider the variation characteristics of instantaneous impact force under different confining pressure.Confining pressure has little effect on the pulsed period of the time-varying impact force after the device inspiration, but it has a great influence on the pulsed amplitude.Confining pressure and inspiration have a great influence on the time-varying value of the instantaneous impact force and the fluctuation strength of the fluctuation impact force, but the influence of the inspiration on the two is different under different confining pressure.
2019 Vol. 38 (24): 227-234 [
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156
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Fault feature extraction of rotating machinery based on EWT and a weighted multi neighborhood rough set
WU Yaochun1,2, ZHAO Rongzhen1, JIN Wuyin1
In the use of attribute reduction with a neighborhood rough set (NRS), the neighborhood radius was needed to be adjusted for several times iteratively.And it was not determined automatically.In order to solve this inconvenience, a feature selection method based on weighted multi neighborhood rough set (WMNRS) was proposed.Combined with the method of empirical wavelet transform (EWT) in rotating machinery, a fault feature extraction method for rotating machinery was proposed.Firstly, the vibration signal of rotating machinery with nonlinear and strong noise was reconstructed with a group of EWT’ optimal modal component selected by correlation, and a high dimensional original feature set was constructed with time domain characteristics of the reconstructed signal.Then, a feature subset was obtained from the original feature dataset by NRSin different neighborhood radius.Last, the probability of occurrence for each feature in the attribute reduction with multiple neighborhood rough sets was counted as feature weight, which was weighted with feature value as sensitive feature set.A characteristic of this method was that it can extract feature automatically in neighborhood rough sets, and the extracted features were more distinguishable.A rotor experiment shows that this method can extract the characteristics of vibration signals effectively, and the fault types of the rotor can be identified correctly according to feature vectors.It provides a theoretical base for solving the classification problem of nonlinear, strong noise, and high-dimensional fault dataset.
2019 Vol. 38 (24): 235-242 [
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159
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243
Deviation caused by circular arc in axis orbit measurement and its modification
MA Huifang, WAN Zhao
Analysis on deviation caused by circular arc in axis orbit measurement was conducted, and the effects of the radius in the measurement plane and the displacements in the radial direction on the deviation were discussed.The results show that the smaller the radius in the measurement plane is, the more the deviation is; and the more the displacement in the radius direction is, the more the deviation is.Based on the analysis on the deviation, a modification method was presented, which was able to compute the real displacements of the axis orbit based on the measured displacements, with the radius in the measurement plane as an input.By using the proposed modification method, the deviation caused by circular arc can be eliminated, and improvement on measurement accuracy is made.The modification method has a significant engineering application value, which is suitable for both real-time testing systems and offline systems.
2019 Vol. 38 (24): 243-248 [
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111
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249
The influence of grinding ball on the vibration-impact crushing properties of wheat bran
CHENG Min1,2, LIU Baoguo2, LIU Yanxu2
On the basis of fully considering the movement modes of the grinding ball in a vibration mill grinding tube, a bilateral impact calculation model named "grinding medium-wheat bran-grinding medium" was proposed based on the similarity principle.This model overcomes the shortage of the single side impact calculation model which can not simulate impact shear.At the same time, the material parameters of the model and the solution setting of the finite element simulation calculation were given.On this basis, the finite element numerical simulation was carried out on the movement characteristics, quality characteristics and crushing forms of wheat bran breaking properties by using the LS-DYNA.The results show that the effect of milling medium on the crushing properties of wheat bran is significant.In terms of the motion characteristics, the higher the impact speed of the grinding ball, the better the crushing performance of wheat bran.However, the greater the impact angles of the grinding ball, the worse the crushing performance of wheat bran.In terms of quality characteristics, the greater the density parameters of the grinding ball, the better the crushing performance of wheat bran; the greater the diameter of the ball, the greater the contact force; the greater the contact area of the wheat bran, but the contact number will be reduced.In the aspect of crushing form, the difference between impact shear and impact extrusion in contact force, contact time and contact area is small，but the effective plastic strain of bran center unit caused by impact extrusion is greater than that of impact shear.For large size bran, impact extrusion should be applied as the main form of crushing; and for small size bran, impact shear should be used.The above research preliminarily found out the effect of grinding ball on the crushing performance of wheat bran, and provided a new way to explore the influence law of material crushing performance of vibration mill comprehensively.
2019 Vol. 38 (24): 249-256 [
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137
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Characteristics of shock load and initial stress unloading in blasting of compressed brittle medium
YAO Yingkang1,2, SUN Jinshan1, JIA Yongsheng2, WU Liang3, NI Mingliang1, MING Sheng1, CHEN Yang3
In order to study the blasting mechanism of brittle medium containing compress strain energy, the filed blasting experiments of the first-floor columns of high buildings were conducted, and the strain of the reserved part of the columns was monitored.The strain monitoring result shows that during the blasting process, when explosive in blasting hole is initiated, the time history curve of blasting load far from the blasting hole is approximately in the shape of triangle, and the strain rate in load increasing stage is higher than that in load decreasing stage.If the charge length is about 20 cm, the time of the explosion shock is about 1 ms.After the explosion shock wave disappears, the bearing capacity of the blasted medium can be maintained for several milliseconds after the detonation, because the moving speed of the fragment is much lower than the shock wave and the stress wave propagation speed.At this time, the medium is mainly affected by the explosive gas and the additional dynamic strain far from blasting holes is low.When the medium is completely destroyed, the fragments are thrown at a high initial velocity, and its bearing capacity disappears rapidly, then the initial strain rapidly releases to 0.The monitoring results show that the time history curve of strain relief is close to a straight line.The mechanical model of one-dimensional bar is deduced to analyze the explosion shock and initial stress relieving process.Through the superposition of the loading and unloading process of the straight bar in the time domain, the strain history of the reserved zone in the compression column blasting was simulated.The simulation of the blasting experiment shows that the initial stress began to unload after a few milliseconds of explosive shock.
2019 Vol. 38 (24): 257-266 [
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165
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A study on dropping impact characteristics and damage regularity of potato tubers during harvest
FENG Bin1,2, SUN Wei1, SUN Bugong1, ZHANG Tao1, WU Jianmin1, SHI Linrong1
In order to reduce damages in potato mechanical harvest, there is a need to reveal the damage mechanism of potatoes’ tuber dropping impact.This article took “Gansu potato 7” as experimental material, and carried out a lot of experiments to study potato dropping impact under different factors and conditions.We studied the influence of the impact feature and the damage index of potatoes and analyzed the damage rules by testing the falling height, the collision material, the moisture content and the dropping directions of potatoes.Results show that the collision material, the falling height, and the moisture content have a significant impact on the collision characteristics, but the drop direction was insignificant; the maximum deformation and the damage index show significantly positive correlation, and the restitution coefficient and the damage index are significantly negative correlated, and a linear regression model for the restitution coefficient and the maximum deformation was obtained ,respectively.There is no correlation between the acceleration peak and the damage index.When the potato bumps with the collision materials, the linear correlation exists between the damage index and the falling height.The results of the study can be used to evaluate the collision damage of potatoes during harvest.
2019 Vol. 38 (24): 267-274 [
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211
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An adaptive active control method based on frequency estimation
YANG Lihua1, SUN Junzhong1, ZHANG Haipeng1, LIU Shuyong2,YANG Qingchao2
Active control is an effective way to isolate mechanical vibration of underwater vehicles.Because of limiting factors such as installation space and equipments coupling complex excitation, it is difficult to effectively pick up or obtain a higher SNR reference signal, which seriously affects the application and effect of active control algorithms based on reference signals.Therefore, based on the filtered-x adaptive control algorithm, an adaptive control strategy without reference signal was proposed using the frequency identification and signal digital synthesis theory, and it was applied to active control for the double-layer vibration isolation system of a rotating equipment.The results show that the two algorithms can effectively reduce the residual signal of the vibration isolation system, the filtered-x adaptive algorithm has better ability to control the fundamental line spectrum, while the other one has better performance in multi-line spectrum control, and the steady-state control force of the former is basically the same as the latter, which also illustrates that the same amount of secondary vibration source energy is required to consume the same external incentives.In addition, the frequency estimation and digital synthesis method can obtain a stable and effective reference signal, which can be applied to active vibration control of rotating machinery in complex installation environment.
2019 Vol. 38 (24): 275-282 [
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