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2020 Vol. 39, No. 8
Published: 2020-04-28
1
Early fault diagnosis of rolling bearings based on adaptive variational mode decomposition and the Teager energy operator
GU Ran1，CHEN Jie1，HONG Rongjing1，PAN Yubin1，LI Yuanyuan2
It is difficult to extract early fault information of rolling bearings because the signal is mixed with abundant compounded background noise.An adaptive variational mode decomposition (AVMD) with the Teager energy operator method was proposed.Firstly, the minimum mean envelope entropy (MMEE) was used to search the optimal value of parameters.Subsequently, the weighted kurtosis (WK) was adopted to select the effective modal components for signal reconstruction.Finally, the reconstructed signal was analyzed by Teager energy spectrum to identify fault frequency.The analysis of vibration signals of bearings with weak fault shows that the proposed method improves the decomposition accuracy, and has stronger noise robustness and fault identification ability than ensemble empirical mode decomposition and local mean decomposition.
2020 Vol. 39 (8): 1-7 [
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478
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8
Roller bearing operation reliability prediction based on Relevance Vector Machine and normalized wavelet decomposition information entropy
CHEN Fafa1，LIU Lili1，LIU Furong1，XIAO Wenrong1，CHEN Baojia1，YANG Yong2
Aimed at traditional methods are difficult to achieve reliability evaluation and prediction for a single serving machine, an operation reliability evaluation and prediction method based on normalized wavelet information entropy and Relevance Vector Machine was proposed in this paper.This method mainly includes the establishment of an operational reliability index and the construction of a Relevance Vector Machine prediction model.Firstly, the vibration signals of roller bearings in the operation process were acquired in a test experiment.The features which reflected roller bearings running status were extracted from the vibration signals using wavelet packet decomposition.Then, the operation reliability index was established based on information entropy theory.Finally, a Relevance Vector Machine prediction model was constructed to predict the operation reliability index and its changing trend for the actual roller bearing.The experiment results show that the operation reliability evaluation and prediction method by using the normalized wavelet information entropy and Relevance Vector Machine, can effectively overcome the traditional calculation problem with probability statistics, and obtain the better operation reliability result for a single serving machine.
2020 Vol. 39 (8): 8-14 [
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193
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15
Minimization of beam response using inerter-based dynamic vibration absorber with negative stiffness
CHEN Jie1，SUN Weiguang2，WU Yangjun1，ZHANG Limin1，HE Xiaolong3
Two new types of passive vibration control structures were proposed, namely the vibration control structure of the dynamic vibration absorber with inerter and negative stiffness, and the transverse vibration of the beam was suppressed.In the case of considering only the first-order modal function, the analytical expressions of the optimal control parameters of the two new dynamic absorbers can be derived using the fixed point theory.On this basis, two kinds of new dynamic absorbers based on inerter and negative stiffness (model 1 and model 2) were compared with the traditional dynamic absorbers under different mass ratios.The numerical results show that the dynamic absorber based on inerter and negative stiffness is more effective than the traditional dynamic absorber in vibration control of beams.For the case of small mass ratio, model 2 has better vibration reduction effect than model 1.However, when the mass ratio or inerter mass ratio is large, the optimum negative stiffness ratio of model 2 is greater than 0, and the optimum parameters of model 2 will not be available.In addition, the effects of mass ratio and inerter mass ratio on the optimal system parameters are briefly discussed.
2020 Vol. 39 (8): 15-22 [
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250
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23
Nonparametric restoring force and mass identification approach using limited acceleration measurement
DENG Baichuan1，GUO Yurong1，XU Bin2,3
Identification of nonlinear structures using traditional extended Kalman filter (EKF) usually requires structure mass and the parametric model of restoring force are known.In this paper, to identify structural parameters, mass and nonlinear restoring force (NRF), a two-steps identification approach using limited acceleration response and nonparametric model was provided.Firstly, memory fading extended Kalman filter (MF-EKF) combining with the equivalent linear model was provided to identify the location of nonlinearities in order to improve calculation efficiency.Secondly, the unscented Kalman filter (UKF) combining with the double Chebyshev polynomial model was provided to identify the mass, structural parameters (stiffness，damping) and NRF.The feasibility of the proposed approach was illustrated via numerical simulation with a multi-degree-of-freedom (MDOF) structure equipped with a Shape Memory Alloy (SMA) damper.Finally, a dynamic experiment with a four-DOFs frame equipped with an SMA damper was designed to illustrate the feasibility of the method.
2020 Vol. 39 (8): 23-32 [
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169
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33
A study on wind-induced vibration characteristics of stay cables under surface-damaged state
LIU Qingkuan1,2，SUN Yifei3，JIA Yaya1,2，ZHANG Leijie3，MA Wenyong1,2，LIU Xiaobing1,2
During production, transportation, installation and operation, stay cables may surfer scratches and cracks.Studying wind-induced vibration characteristics of stay cables under surface damage is of great significance for accurately evaluating the aerodynamic stability of stay cables during their service life.Through wind tunnel tests of a smooth model and other models with 2 sizes of dent, the influences on wind-induced vibration characteristics of Reynolds number, wind direction and the size of dents were studied.And the vibration state was initially judged.Results show that the vibration characteristics with Reynolds number curve of the dent cable model is similar to that of the smooth model, but the maximum amplitudes of the dent cable model are larger than that of the smooth model in the worst wind directions.At the same wind direction, there are lower starting Reynolds number and wider Reynolds number interval of wind-induced vibration of dent models.Also, the size of dent influences wind-induced vibration characteristics prominently during test Reynolds number range, not a simple monotonous relation, but related to wind direction closely.This wind-induced vibration is initially judged to be galloping, not vortex-induced vibration, based on vibration frequency and Den Hartog criterion.
2020 Vol. 39 (8): 33-39 [
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214
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40
Vibration behaviors of the boom luffing of aerial work platform
WANG Hao，JI Aimin，ZHANG Lei，DENG Ming
In the current research for vibration behaviors of boom luffing in a straight boom aerial work platform, the boom was simplified to a stepped cantilever beam, that is, the triangle region that the boom, the luffing cylinder and the turntable hinged together was regarded as a rigid body.This simplification inevitably causes resultant errors.Considering the actual connection and support of the boom, the telescopic boom was treated as a stepped beam with concentrated parameters, pinned at the end and flexibly supported in the middle.Based on the Hamiltonian principle, the differential equation of the boom’s vibration during luffing movement was established, and then the natural frequency and mode shape of the boom’s vibration were obtained.On this basis, by using the orthogonality between modes of vibration and the particular solution, the state space equations of vibration in the Hilbert space were built.The dynamic response of boom’s tip was simulated by using Matlab/Simulink with the change of boom elevation angle.The results show that the vibration amplitude of the boom’s tip obtained in this study was more than 29% compared with the current research.This study can provide a more accurate theoretical reference for the vibration control of aerial work platforms.
2020 Vol. 39 (8): 40-46 [
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193
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47
A study on the FIV load of reactor internals-radial support key
AI Weijiang
In the design of CAP1400 Reactor Vessel Internals (RVI), because of systemic and non-linear properties, it is difficult to predict the flow induced vibration (FIV) load of Radical Support Key.The traditional way is to get the FIV load of Radical Support Key by over conservative methods, based on the linear PSD analysis for single component.A new simplified method to calculate the FIV load of CAP1400 Reactor Internals-Radial Support Key was proposed in this work, which considers the non-linear effects such as gap, stiffness, and friction, and thus gets more accurate results.A simplified beam model was developed for the CAP1400 lower internals, and has was verified by a CAP1400 RVI 1/6 scale model dynamic property test.The downcomer PSD load was transferred to time history load.The time-history analysis method was verified by scale model test results.The time-history downcomer turbulence load was then applied to the beam model to calculate the FIV load of CAP1400 Radial Support Key in various gap conditions.
2020 Vol. 39 (8): 47-50 [
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209
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51
A study on liquid shock of energy-absorbing anti-impact hydraulic column
ZHANG Jianzhuo，ZHANG Jialin
According to the problem of liquid shock on hydraulic column with energy-absorbing component under impact load, the deformation behavior and characteristics of a diameter-expanding energy-absorbing component under different loads were analyzed, and the energy absorption model of energy-absorbing component based on the LuGre model was established.Then, based on the general equation of determining solution of liquid shock problem, theoretical and simulation analysis of liquid shock of roof weighting for the energy-absorbing component and hydraulic column system were carried out, and the effect of characteristics of energy-absorbing components on liquid shock of hydraulic column was obtained.The results show that the maximum static friction force and coulomb friction force correspond to the peak bearing capacity and the reaction force in stable deformation stage of the energy-absorbing component respectively.The bristle stiffness and micro-damping coefficient influence the force-displacement characteristic of energy-absorbing component when the elastic deformation transits to the plastic deformation.With deformation process of diameter-expanding energy-absorbing component, the influence of energy-absorbing component on liquid shock of hydraulic column can be divided into approximate elasticity, flexible giving way to absorpt energy and rigidity three stages.
2020 Vol. 39 (8): 51-57 [
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201
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58
Inverse identification of the pipeline support stiffness and damping of the hoop based on the measured sweep frequency response
GAO Ye1,2，SUN Wei1,2，MA Hui1,2
To establish the dynamic model of a pipeline system and analyze the vibration characteristics, it is necessary to obtain mechanical characteristic parameters of the hoop such as the support stiffness and damping under dynamic load.In this paper, a response surface method for identifying the parameters above was proposed, which was based on the measured sweep response.Firstly, an identification algorithm based on response surface was proposed to identify the stiffness and damping of the pipeline hoop.The dynamic model of the pipe-hoop system was created by the developed finite element method, and the vibration response of pipeline system was deduced.Then on the basis of response surface method, the polynomial fitting of stiffness and damping about frequency and corresponding response was carried out by the matching calculation, and the simple genetic algorithm was used for optimization.Finally, a case study was carried, and the support stiffness and damping with frequency-dependent characteristic were identified by the proposed method.By including identified values into the analysis model, the relative errors between predicted and measured resonance frequency and response are both less than 3% and then the reliability of the identified results was proved.
2020 Vol. 39 (8): 58-63 [
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113
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64
Vibration reduction effect of a novel rubber anti-vibration bearing for rail transit viaduct
SUN Liangming，HU Zhen，DU Youfu，XIE Weiping
A novel rubber anti-vibration bearing was developed to reduce the environmental vibration caused by train running on the rail transit viaduct.This novel bearing adapts a design of arranging high damping thick rubber block with slope, which can reduce vertical vibration and provide a large horizontal stiffness.The finite element model of the upper mass block-rubber bearing-pier system was established to study the vibration reduction effect of the novel bearing through vertical sweep excitation.Then, a series of working conditions were designed to analyze the factors which can influence the vibration reduction effect of the novel bearing.Results indicate that the amplitude of excitation force has no effect on the vibration insertion loss of the novel bearing, but the vibration insertion loss will be reduced if the pier height increases; when the excitation force is 140 kN and the pier height is 6 m, the vibration insertion loss of the novel bearing is 17.53 dB; when the bearing capacity is met, increasing the inclination angle of rubber blocks and the total thickness of rubber layer, and reducing the number of rubber layer, can reduce the compression stiffness of the novel bearing and then improve the vibration reduction effect.
2020 Vol. 39 (8): 64-71 [
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197
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72
Impact dynamic test and simulation analysis on main force transmission structures of carrier-based aircraft fuselage
ZHANG Haocheng1，LIU Xiaoming1，LI Chonglun2，YAO Xiaohu3，XIONG Wenqiang3，ZHANG Run3
The fuselage structures were subjected to complex dynamic loads through the arresting hook, in the process of arresting of a Carrier-based Aircraft.In order to avoid impact damage to the structure, it was necessary to obtain the dynamic response characteristics of the main force transmission structures and find out the propagation and response law of the dynamic load on the structures.In this paper, the dynamic response in the main force transmission structures during the process of arresting the Carrier-based Aircraft was studied through the simulation of ground arresting impact tests.Meanwhile, a rigid-flexible coupling dynamic model was established to simulate the real test state.The structural response characteristics of impact acceleration and stress-strain were obtained, as well as the distribution of acceleration and stress-strain peak along the main force transmission structures, which can be used as a reference for structural strength design of the Carrier-based Aircraft.The results show that the peak of impact acceleration decreases along the main force transmission path, showing an obvious attenuation trend.It will not cause damage to the structures due to short impact time and small strain response, although the impact acceleration peak near the blocking joint is high.The stress concentration effect will be caused by the arresting load at the position of the wing isolation frame, and the corresponding structure should be strengthened locally in the structural design.
2020 Vol. 39 (8): 72-78 [
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260
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79
Seismic response analyses of a single-layer spherical lattice shell structure with a multifunctional FPB system
ZHUANG Peng1,2,3，JI Guangyu1，LIU Pei1，HAN Miao1,2,3
This study proposed a new type of multifunctional friction pendulum bearing (MFPB) and examined its effectiveness in reducing and controlling seismic response of spherical lattice shell with surrounding columns.The MFPB consists of friction pendulum bearing (FPB), shape memory alloy (SMA) cables and sleeve restrainers.To investigate the mechanism of isolation and energy dissipation, the mechanical model of the new isolator were described.Furthermore, the hysteresis behavior of the MFPB was investigated with numerical simulations and the characteristics of such an isolation device were analyzed.Next, the MFPB devices were introduced in a single-layer spherical lattice shell structure with surrounding columns.An analytical model of the controlled structure was constructed through ABAQUS software.Finally, nonlinear time-history analyses were conducted to evaluate seismic performance of controlled and uncontrolled lattice shells using a set of dynamic response indices.The results show that the developed isolation system can effectively control structural responses under horizontal and vertical seismic excitations and possess the potential in disaster resistance under strong earthquakes, which assists high-position isolated spatial lattice shell structures in improving their comprehensive seismic behavior.
2020 Vol. 39 (8): 79-87 [
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213
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88
A study on combined effect of earthquake and scour of bridge in high earthquake-intensity and soft soil site
ZHOU Mi1，ZHAO Wei2，SHI Xiongwei3，ZHU Guoqiang1
Scour leads bridge foundation to be exposed, which weakens the constraint function of soil to the pile foundation and increases the damage risk of the foundation under earthquake.Therefore, it is significant to establish the failure probability model of a bridge under the combined effect of scour and earthquake, and to analyze the combined component coefficient of the scour action of the continuous rigid frame bridges in an earthquake zone.In this paper, based on a continuous rigid frame bridge built in the area with seismic basic intensity of VIII degree, the distribution function of the scour depth was determined by the Monte-Carlo method, and the dynamic finite element models of the entire bridge under different scouring depth were established by CSIBridge software.Forty-eight seismic waves were used for incremental dynamic analysis (IDA), and the distribution function of seismic action effects with different scouring depth was calculated.The failure probability and reliability index of bridge foundation at different scouring depths were obtained by the direct integration method.The results show that the nonlinear relationship between the scouring depth and the earthquake failure probability can be established by the failure probability analysis under the framework of combined effect of erosion and earthquake.This method can reasonably determine the partial combination coefficient of loading combination including erosion and seismic action.
2020 Vol. 39 (8): 88-98 [
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211
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99
Fault feature extraction of a wind turbine gearbox using adaptive parameterless empirical wavelet transform
DING Xian1，XU Jin1，TENG Wei2，WANG Wei2
Wind turbines operate as an equipment cluster, bringing massive vibration signals due to their complex structures and multiply vibration measures.Only analysing the vibration signals to detect fault by human is challenging.In this paper, a fault feature extraction method for wind turbine gearboxes was proposed on the basis of the parameterless empirical wavelet transform.The scale space method and empirical law were utilized to automatically split the Fourier spectrum of the vibration signal, and different frequency bands were obtained.A series of empirical wavelet filters were designed based on the split frequency bands to decompose the signal into multiply empirical modes.The metric of margin factor was adopted to sort the empirical modes, and the empirical mode with maximum margin factor was recognized as the most sensitive one to fault.The proposed method is adaptive without any presented parameters.The fault signals from an experimental platform and a real wind turbine gearbox verified the proposed method.
2020 Vol. 39 (8): 99-105 [
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169
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106
Adaptive fuzzy compensator based CNF control for uncertain robot manipulators
JIANG Yuan1,2,3，GONG Chenglong1，L Ke2，DAI Jiyang1,3
In order to solve the influence of uncertain factors on a robot system and realize the ability of the uncertain robot system to track the reference input accurately, the strategy of combining adaptive fuzzy control and composite nonlinear feedback (CNF) control was studied, and a robot CNF controller based on adaptive fuzzy compensation was proposed.The core is to systematically use the adaptive fuzzy control to approach the uncertainty of the system and use it as a compensation item of the CNF controller to fully utilize the advantages of the two control methods to reduce the impact of uncertainties on the system performance.Through feedback linearization and the Lyapunov theory, the convergence of the closed-loop system was proved.The final simulation results confirm the effectiveness of the method.
2020 Vol. 39 (8): 106-111 [
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148
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112
Dynamic analysis of a flexible robotic arm carrying a moving end effector
ZHAO Liang
Robotic arm is widely used in industrial and space exploration.Dynamic analysis of a flexible robotic arm carrying a moving end effector was investigated.The system was modeled as a translating and rotating flexible cantilever beam with a moving mass.For the convenience purpose, two coordinate systems were introduced: a local coordinate system that rotates with the cantilever beam, and a fixed global coordinate system.The physical quantities of the structure in the local coordinate system were transformed into the global coordinate system, and the total kinetic energy and potential energy of the structure were given.Then the equations of the structure were derived by the Lagrange's equation with the assumed mode method.When the robotic arm rotates at a uniform angular velocity the system dynamic equation is linear, while it rotates at a variable angular velocity the system dynamic equation is nonlinear.Finally, the dynamic responses of the robotic arm and the moving end effector under different motion states were analyzed by numerical examples.Moreover, the influences of frictional force on vibration characteristics of the robotic arm were also discussed.The obtained conclusions provide theoretical basis for the design of robots and their equipments.
2020 Vol. 39 (8): 112-117 [
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159
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118
Vibration isolation control and an experimental study of magnetorheological elastomer isolators
MA Weijia，HUANG Xuegong，WANG Huixing，ZHANG Guang，WANG Jiong
In order to study the vibration isolation performance and control strategy of a magnetorheological elastomer isolator.The frequency shift characteristic of a magnetorheological elastomer isolator was tested by experiments based on sweep excitation.It is proved that the magnetorheological elastomer isolator possesses a wide frequency shift range.Based on the frequency shift characteristic curve of the magnetorheological elastomer isolator, an on-off control strategy for sweeping excitation was proposed.The on-off control strategy based on variable damping and stiffness was applied to harmonic and random excitation.The experimental results prove that the magnetorheological elastomer isolator has great vibration isolation effect for different forms of excitation under control strategy.The above works lay a foundation for the engineering application of magnetorheological elastomer isolators.
2020 Vol. 39 (8): 118-122 [
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212
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123
A study on buffeting force test and correlation based on active grid turbulence field
XIANG Dan1，ZHU Lishan2，NIU Huawei1
In order to study the correlation of buffeting forces on a bluff body, a rectangular cylinder was taken as an example.In the pulsating flow field of active grids, a pressure measurement method was applied to study the span-wise buffeting force under turbulent flow, combined with different correlation model fitting methods.The spatial correlation of buffeting force was compared with static and moving states to analyze the influence of the self-excited force on the correlation of the buffeting force, by decomposing the two forces with matlab.Two different force measurement methods (synchronous pressure measurement) were compared by a balance force test.The results show that the span-wise correlation of buffeting force decreases with the frequency and span spacing.Under the influence of aerodynamic self-excited force, the correlation was improved and larger than that of turbulence.
2020 Vol. 39 (8): 123-130 [
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139
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131
Analysis of the influence of ductility factor and amplitude modulation coefficient on the constant-ductility strength spectra
LAI Qinghui1,HU Jinjun1,FAN Yuan2,XIE Lili1
Abstract:In current structural seismic design, it is very common to match amplitude-modulated ground motion records with the standard spectra.To analyze the influence of ductility coefficient and amplitude modulation factor on the constant-ductility strength spectra, in this paper, the influence of ductility factor and amplitude modulation factor on the constant-ductility yield strength spectra and constant-ductility seismic resistance spectra was analyzed by calculating the dynamic time-history inelastic response of a single-degree-of-freedom system.Through research and analysis, the change regulation of constant-ductility yield strength spectra and constant-ductility seismic resistance spectra under different ductility coefficient and amplitude modulation factor conditions was obtained.When the period was determined, the constant-ductility seismic resistance spectra value increased and decreased when the amplitude of ground motion was modulated, but the constant-ductility yield strength spectra did not change; When the ductility coefficient increased gradually, the constant-ductility yield strength spectra values and constant-ductility seismic resistance spectra values decreased gradually.The results explain and illustrate the influence of ductility coefficient and amplitude modulation factor on constant-ductility intensity spectra and the relationship between complex seismic action and structural dynamic characteristics, which provide a basis for seismic research and design of structures.
2020 Vol. 39 (8): 131-135 [
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180
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136
Effect of electrostatic force nonlinearity on resonant frequency and sensitivity stability of double sense-mode micro gyroscopes
HAO Shuying1,2,3,LI Weixiong1,2,3,LI Huijie1,2,3,ZHANG Qichang4,5,FENG Jingjing1,2,3,ZHANG Kunpeng1,2,3
Abstract:To avoid the influence of electrostatic forces nonlinearity，this article applied the offset of nonlinearity at high voltage and microbeam geometrical nonlinearity to achieve high stability and sensitivity in micro gyroscope’s design.Moreover, The regularities of structural parameters on the dynamic performance of the dual-detection micro-gyro were simultaneously investigated when the nonlinearity of the electrostatic force and the stiffness-cubic nonlinearity both existed under the edge effect.It was shown that the smaller comb-finger non-overlapping length and the greater the DC bias voltages, the greater resonance frequency offsets and the more obvious the effect of electrostatic force softening will be produced.There is a threshold value for non-overlapping length of comb-fingers.Above this value, the nonlinearity weakens to zero and the effect on the amplitude is saturated.This feature could maintain sensitivity’s stability of the double sense-mode micro gyroscope.The softening characteristics from the electrostatic force are balanced by microbeam’s geometrically nonlinear design and the adjustment of hardening characteristics caused by stiffness nonlinearity.The amplitude-frequency curve shows an ideal linear state.The phenomenon of frequency instability and amplitude jump caused by the hardening and softening of electrostatic force is avoided, and the micro-gyro has higher sensitivity and stability.
2020 Vol. 39 (8): 136-142 [
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154
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63
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143
Dynamic monitoring and prediction for vortex induced vibration of a sea crossing bridge
ZHANG Yong1,CAO Sugong1,2MA Rujin2,TIAN Hao1,3,HU Hao1,XU Shiqiao2
Abstract:Vortex-induced vibration of long-span suspension bridges occurs frequently, which seriously affects driving safety and comfort.In order to predict the vortex induced vibration of a long-span suspension bridge in time, a cross sea bridge was taken as an example.Based on the long-term monitoring data of a structural monitoring system, wind velocity, wind direction angle, energy concentration coefficient and acceleration RMS were selected as the characteristic parameters of vortex induced vibration.According to the correlation between the characteristic parameters and the vortex excited vibration, a dynamic monitoring and prediction model of vortex-induced vibration of a cross-sea bridge was constructed, and an independent dynamic monitoring and control system of vortex-induced vibration was established.The results show that: the wind direction is mainly between 300°—330°and 120°—150°, and the energy concentration coefficient (the ratio of power spectral density WP2/WP1) is less than 0.1; the acceleration RMS of the main bridge is more than 5 cm/s2; the prediction recognition rate of the system model is 72%, and the identification accuracy of the vortex induced vibration dynamic monitoring system is 93%.At the same time, the vortex-induced vibration early warning app which is perfectly useful for work has been developed, and it can provide reference for the prediction of vortex-induced vibration of similar bridges.
2020 Vol. 39 (8): 143-150 [
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103
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151
An experimental study on stress wave propagation and attenuation of sandstone during stress unloading process
CHENG Yun1,SONG Zhanping1,2,JIN Jiefang3,WANG Junbao1,2,YANG Tengtian2,4
Abstract:Due to the complexity of excavation and unloading of rock mass and redistribution of original rock stress, surrounding rock mass was usually in complex stress unloading environment.For the purpose of investigating the propagation and attenuation characteristics of stress wave in sandstone during stress unloading process, a strip specimen with length to diameter ratio L/D≈65 was designed, and small disturbance impact tests under different axial unloading stresses were carried out by dynamic and static combined loading test devices.The stress wave signals of sandstone were measured, and the effects of different unloading stress on wave waveform, P-wave velocity, temporal-spatial attenuation characteristics, wave peak, and attenuation rate of wave peak were studied, and the empirical models were established.The results show that whether the sandstone had unloading stress or not had significant effect on waveforms.With the stress unloading, the P-wave velocities attenuated in the form of “approximately linearly stage+nonlinear stage”, and wave peak and its attenuation rate were exponentially changed.With the increase of distance and time, the wave peaks show an exponential attenuation, and temporal-spatial attenuation of wave peaks at different unloading stress stages had different sensitivity.
2020 Vol. 39 (8): 151-158 [
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173
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159
A discrimination algorithm of nuclear electromagnetic pulse based on characteristic parameters in time domain
WANG Tao1,CHEN Fugui2,LIU Ming2,SHI Xiaolei2,CHEN Weihui2,ZHU Wanhua1,HUANG Ling1,FANG Guangyou1
Abstract:In order to discriminate nuclear electromagnetic pulse (NEMP) and lightning electromagnetic pulse (LEMP), an automatic time-domain algorithm at a range of 500 km was proposed.First, for time series of multiple stations emitted by identical source, a method combined of threshold triggering and correlation operation was developed to choose start time of each series.In addition, end time was located according to the height of reflecting layer in the ionosphere, which was estimated through the time difference of direct wave and reflected wave at about 1 000 km distance.Then four parameters were defined to character waveforms.By fitting statistics result with proper probability density function, the four parameters’ distribution of LEMP was drawn.Contrasting the distribution with parameters calculated from NEMP data, finally, a discrimination algorithm was obtained.A test was performed to verify the algorithm, which can identify NEMP data and more than 99% of LEMP data at a range of 500 km.
2020 Vol. 39 (8): 159-164 [
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130
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165
Dynamic fracture experiments of specimens containing inclined crack under impact load
ZHENG Changda1,YANG Liyun1,DING Chenxi1,CHEN Cheng1,XIAO Chenglong1,ZHAO Yong2
Abstract:In order to clearly investigate the mechanism of radical cracks around a roadway under dynamic loading, dynamic fracture tests of PMMA specimens containing inclined crack were studied by using an impact loading platform of a drop hammer and the test system of digital laser dynamic caustics.The effect of changing the pre-crack angle α on the dynamic mechanical behavior was recorded.Through the caustics method and the fractal dimension method, the results show that: ① The pre-crack angle affects the speed of accumulation and release of the strain energy at the crack tip.As the angle increases, the crack initiation time becomes shorter, crack initiation becomes easier and the strain energy at the crack tip accumulates faster.② The releasing law of the strain energy at the crack tip are different on each side of α=45°.③The tendency of KdI-t is similar, but there is a difference in the maximum.④ The growth trajectory of cracks at different angles satisfies a certain fractal law.
2020 Vol. 39 (8): 165-171 [
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140
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172
An adaptive life prediction method for rolling bearings based on improved HMM and similarity calculation
QU Jiaming1,ZHOU Yiwen1,WANG Heng1,HUANG Xi1,JIANG Jie2
Abstract:Based on the idea of data driven, a life prediction method for rolling bearing under the same working conditions was proposed.According to the bearing life monitoring data, the bearing operation state space was divided according to the K-means clustering algorithm, and based on the improved hidden Markov model, a full-life state duration time distribution model was established.The description state information and observation data were retained.On the basis of the chain structure, the description of the change law of bearing life is more suitable for actual situation.For the observation bearing data, based on state clustering, spatial translation and threshold matching, Pearson similarity analysis was performed in real time with the modeling data, and the life proportion adjustment coefficients were constructed according to the similarity analysis.Finally the hidden Markov life model parameters were dynamically modified to predict the observation of bearing life adaptively.Application research was carried out using the bearing test data of the University of Cincinnati Experimental Center.Through a set of bearing life data, the prediction of different stages and lifespan of other bearings was realized.Compared with the gray model prediction results, the proposed algorithm has better prediction accuracy and generalization of the model.
2020 Vol. 39 (8): 172-177 [
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191
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A study on boundary transition of a terrain model for wind field characteristics measurement
JING Hongmiao1,LIAO Haili1,2,MA Cunming1,2,LI Zhiguo1,2
Abstract:Aiming at boundary transition of a terrain model for wind field characteristics measurement, referring to the design theory of an aerospace vehicle, the continuity principle applying for the boundary transition of the terrain model was proposed, namely coordinate continuity, first-order continuity, and second-order continuity.Depending on this principle, a kind of transitional curve based on the hyperbolic tangent function was also proposed and compared with slope transition and first-order transition (vidosinsky curve) using the CFD (computational fluid dynamics) numerical simulation method.Meanwhile, the proposed boundary transition with different lengths was studied, and the results indicate that with the increase of transitional length, the air flows over the boundary transition more fluently.The continuity principle and second-order curve proposed in this paper are of great significance for the design of boundary transition of a terrain model.
2020 Vol. 39 (8): 178-185 [
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172
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186
Frequency analysis on the nonlinear free vibration of a tri-cross string system
PAN Bo1,2,XU Zili3,ZHAO Bo1, 2,GE Xiang2
Abstract:Theoretical analysis on the nonlinear free vibration of a tri-cross string system was presented in this work, which is an element of space net-antennas.The governing equations were derived from the Hamilton’s principle and a linearized solution was obtained by the standard perturbation method.The semi-analytical solutions of the governing equations has not been provided referring to the solution of the plate vibrating problem.This analysis reveals that natural frequencies of the tri-cross string depend on the vibration amplitude due to geometrical nonlinearity in the constitutive equation.The geometric parameters, such as the diameters and the lengths of the constituent strings, also affect the frequency through the nonlinearity of the tri-cross string.The nonlinear natural frequency shows coupled characteristic, i.e. the natural frequency of the tri-cross string varies with that of the constituent strings, but the contribution of each constituent string to the natural frequency is in different proportions.
2020 Vol. 39 (8): 186-192 [
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166
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193
The influence of key structural parameters of main beam TBM on its dynamic characteristics
XIA Yimin1,2,MA Jiesong1,2,LI Zhengguang1,2,MEI Yongbing2,3,JI Zhiyong2,3
Abstract:Full-face rock tunnel boring machine (TBM) bears changing large thrust, torque and overturning moment in the process of excavation, which causes mainframe vibration response.In order to reduce fatigue failure of mainframe and improve tunneling efficiency, a dynamic model of the main beam TBM mainframe was based on the dynamics simulation software, the dynamic response of mainframe and the influence law of main beam structural parameters on the dynamic characteristics of TBM were investigated.The results show that an increase in the length of the first main beam will cause its vibration to increase, and the vibration of the second main beam and saddle will decrease.An increase in the thickness of the first main beam will cause its vibration to decrease, the vibration of the second main beam increases slowly, and the vibration of the saddle first increases and then decreases.When the thickness of the upper and lower webs is 50 mm, the thickness of the side plates is 40 mm, and the thickness of the front and rear flanges is 105 mm, the vibration reaches maximum.The acceleration RMS of the cutterhead in the tunneling direction is 1.1g, and the acceleration RMS of the main beam is 0.21g, and as the vibration transferred backward gradually weakened, the frequency of varies is mainly between 0—50 Hz; According to the simulation results, the relevant parameters of the main beam were determined.The TBM has been applied for 2 years in a water diversion project, and the project has been successfully completed.Field test results show, the error between the three-way vibration test data and the simulation results is basically less than 20%.
2020 Vol. 39 (8): 193-201 [
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176
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47
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202
A study on the pressure characteristic curve of a high frequency reversing valve based on the lattice Boltzmann method combined with LES
WU Wanrong1,LONG Guorui1,HAO Qianhua1,2
Abstract:In order to study the pressure characteristic curve of a high frequency reversing valve and reduce pressure loss, the lattice Boltzmann method (LBM) combined with large Eddy simulation (LES) was used to simulate high-Re flow.A lattice evolution model based on LBM-LES was established for high frequency reversing valve.The valve port characteristics under different size parameters of valve were simulated.It can be concluded that the volume of oil inlet chamber and the maximum flow area have great influence on the pressure of the valve port.For a certain maximum flow area, the opening has the greatest impact on the pressure of the valve.The results show that the LBM has the advantages of accuracy and high computational efficiency and so on.Thus it can be applied to the analysis and research of complex hydraulic exciting systems.
2020 Vol. 39 (8): 202-207 [
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128
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468
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208
The analytical solution of the modeling and vibration characteristics of elastic propeller-shaft
KANG Wei1,2,ZHANG Zhenguo1,2,CHEN Yong1,2
Abstract:In order to consider the influence of the propeller elasticity on vibration characteristics of a propeller-shafting system, an analytical solution was developed based on the Timoshenko theory.The propeller blades and shaft were all modeled by a Timoshenko beam.According to the continuous condition of joint and boundary condition, the control equation of the transverse and longitudinal free vibration of system was deduced.Contrasted the solution of a finite-element model and the analytical solution, they were in good agreement.The effect of propeller elasticity on the mode and force transmission characteristics of the system was explored.The results show that the deformation of both the blades and shafting of the true elastic propeller-shafting system can be seen and their vibration is coupled.The bending mode of blades can aggravate the vibration of shafting.The longitudinal force transmitted by bearing was amplified by the bending mode of propeller and longitudinal mode of shafting, while the transverse force was mainly controlled by bending modes of propeller and shafting under the excitation at the blade.
2020 Vol. 39 (8): 208-214 [
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210
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215
Modelling and experimental study of vertical moving magnetic piezoelectric vibration energy harvester
RUI Xiaobo1， LI Yibo1， LIU Yue1， ZHENG Xiaolei1， QI Lei1,2， ZENG Zhoumo1
In this paper, a vertical moving magnetic piezoelectric vibration energy harvester was presented.The performance of the single cantilever harvester was improved with the nonlinear force introduced by the vertical magnets.In order to carry out the analysis and parameter optimization of the structure, a lumped-parameter theoretical model was established, and various modes were studied via simulation.This paper focuses on the repulsive low-frequency mode, and future studies were carried out with experiments.An experimental platform was built with aluminum alloy and piezoelectric fiber material MFC, and the energy harvesting performance was verified.The experimental results show that the numerical simulation can effectively predict the performance within the error tolerance range, and the performance can be effectively improved by the structure.Based on simulations and experiments, the magnet spacing and magnetic flux density parameters were studied and optimized.Under the optimal parameters, the bandwidth can be increased by 40.6% and the peak power can be increased by 42.7%.
2020 Vol. 39 (8): 215-221 [
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200
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139
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222
The influence of Alford force and active magnetic bearing on the dynamic behavior of a rotor system
WANG Xiaohu, YAN Guangrong, HU Yaoyao, TANG Rui
The dynamic characteristics of a rotor system incorporating flow induced Alford forces and electromagnetic forces of active magnetic bearings (AMBs) were studied, based on a simplified model high-pressure rotor of an aero engine supported by AMBs.The Timoshenko beam theory and a finite element method were utilized to model the rotor.Electromagnetic forces of the AMBs controlled by differential PID methods and flow induced Alford forces at the tip of the compressor vanes were introduced, before the dynamic responses of the rotor system were calculated through the Newmark-β method.The results reveal complex dynamic behaviors of the rotor system simultaneously excited by the nonlinear Alford forces and bearing electromagnetic forces.Control parameters of the AMBs show remarkable influences on the rotor system dynamics, by changing it into period 1, multi-period and quasi-period motions with different values.Therefore, for rotors supported by AMBs and with axial compressors, effects of the flow induced Alford forces and electromagnetic forces need to be considered before determining control parameters.
2020 Vol. 39 (8): 222-229 [
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181
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230
Flow mechanism investigation on interference effect of two square cylinders in tandem arrangement
FAN Xiaoyu1, QIN Hao1, SHANG Jingmiao2, HU Shuai1
The present paper is aimed at studying the flow field around the building group and reducing the loss caused by the interference effect in the engineering.The particle image velocimetry (PIV) and numerical simulation were used to study the flow characteristics and spatial structure of the flow field when the flow field of two square cylinders were disturbed under large Reynolds number and different spacing conditions.Characteristic parameters of flow field, such as lift and drag coefficient, vortex shedding frequency and Strauhal number, were analyzed to study the effects of different spacing on the two cylinders in a tandem arrangement.When Re=3.42×104, there is a critical spacing ratio of G=4, causing a sudden change in the flow field structure of two cylinders in the tandem arrangement.A bistable phenomenon appears in the flow field.When G<4, the average drag coefficient of the downstream square cylinder is negative, which is smaller than that of the single cylinder.The shielding effect is obvious at this point.The vortex shedding behind the upstream square cylinder was suppressed, and the average drag coefficient has a significant decrease, with a maximum drop of around 10%.When G>4, both the upstream and downstream square cylinders have seen vortexes shedding.Thse results can serve as references for engineering application.
2020 Vol. 39 (8): 230-238 [
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174
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239
A study on nonlinear aerodynamic effect of a vibrating thin plate section in windless condition
YING Xuyong1,2, ZHANG Zhe3
Based on an arbitrary lagrange-euler (ALE) method and a weak coupled method, a numerical model for calculating the wind-induced response of section was developed.The mathematical expression of aerodynamic forces for vibrating section in windless condition is proposed.The free vibration response of a thin plate section in windless condition was simulated, and the nonlinear vibration frequency and damping ratio were calculated.The results indicate that the unsteady aerodynamic forces acting on vibrating section in windless condition can be effectively described by the presented aerodynamic force model.For the vibrating section in windless condition, the interference to the ambient air for the vertical motion is larger than that for torsional motion.The aerodynamic effect of vibrating section in windless condition cannot be neglected; otherwise, the error will be increased.The free vibration response of thin plate section in windless condition is significantly influenced by initial excitation.
2020 Vol. 39 (8): 239-244 [
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149
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245
Model parameter updating study consideration of welding residual stress distribution
CHEN Luyun, GUO Yongjin, YI Hong
A structural model parameter updating method was proposed in present research.To improve the accuracy for the finite element model, the welding residual stress distribution problem was considered.The pre-stress matrix function was established based on the pre-stress distribution model, the influence of welding residual stress on structural stiffness and structural dynamic characteristic were discussed.In order to eliminate the influence of welding residual stress on the calculation scale and calculation?precision of complex structure, the structural model parameter updating was carried out by using the structural optimization strategy, in which to minimize the residual value of natural frequency parameter was defined as objective function.Finally, a cylindrical shell structure for example, the optimization calculation based on model parameter updating was carried out, and the feasible of the proposed method was verified.
2020 Vol. 39 (8): 245-249 [
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146
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31
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250
Topology optimization of attached damping layers on thin plate structures for vibration attenuation under non-stationary stochastic excitations
LI Xueping, LIN Mengfeng, WEI Peng, SU Cheng
This paper investigates the optimal distribution of damping material on thin-plate structures under non-stationary stochastic excitation.In the topology optimization model, the relative densities of the damping material were taken as design variables, and the design objective is to minimize the structural displacement variances at specified positions under a given volume constraint of damping material.Since the structure was subjected to non-stationary stochastic force, the stochastic responses were solved rapidly based on an explicit time domain method (ETDM).The analysis of the displacement variance sensitivity was implemented by using the ETDM based on an adjoint variable method.Then the topology optimization problem was solved with an optimal criteria (OC) method.Numerical examples illustrate the feasibility and effectiveness of the proposed method for vibration attenuation of structures through dynamic topology optimization of damping layer under non-stationary stochastic excitation.
2020 Vol. 39 (8): 250-257 [
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196
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258
A reverberation chamber-anechoic room experimental method design based on SEA analysis and STL research
ZHANG Lei1,2, ZHENG Xu1, CHEN Jun2, HAO Zhiyong1
Different from the theoretical and empirical design, a structure sound coupling method of low frequency and a SEA method of mid-high frequency were used to analyze the reverberant sound field to increase the reverberation level.The reverberant chamber was designed and made based on virtual result.The entity was placed into the anechoic room to be tested, which shows that the reverberation time meets the request and the SPL in different positions of the sound field only has gap within 2 dB between each other.The STL result of the SEA method for panel was compared with the test result by using the reverberation chamber-anechoic room method, which shows good agreement.The experiment method thus can realize great STL effect.By using this method to test sound insulation of single layer panel and sandwich panel rapidly, it was found that coincidence frequency effect has a significant impact on STL performance.The above findings offer meaningful reference to the engineering application.
2020 Vol. 39 (8): 258-263 [
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203
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264
Dynamic characteristics analysis of rubber components based on an overlay model
LI Sijie, LUO Shihui, WANG Bo, MA Weihua
Based on the theory of an overlay model, the dynamic characteristics of rubber components were studied.A one-dimensional multi-parameter rubber constitutive model was established by using the time-step method in MATLAB.The model consists of elastic element, viscoelastic element, and elastoplastic element in parallel.The viscoelastic element uses Abel dashpot to characterize the frequency dependence of rubber components.The elastoplastic element uses a multilinear perfectly elastoplastic model to characterize the amplitude dependence of rubber components.The comparison with the test results show that: when the force of rubber spring based on overlay model was calculated with the harmonic excitation, the calculation results of the force-displacement hysteresis curves agree with the test results well, and the stiffness frequency amplitude dependence and damping frequency dependence were well characterized.When the force of the rubber isolator based on the overlay model was calculated with the random excitation, the calculation results of the model can match the test data with the high frequency excitation and has a certain degree of deviation with the low frequency excitation, but the calculation accuracy is within the acceptable range of engineering.The overlay model proposed can better characterize the dynamic characteristics of rubber components and improve the accuracy of the dynamic model.
2020 Vol. 39 (8): 264-270 [
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182
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271
Research on dynamic performance of tail skid shock absorber based on multi-body dynamics
FENG Yunwen1, ZHU Zhengzheng1, PAN Wenting2, ZHU Xianfei1
In order to obtain the energy absorption characteristics of tail skid shock absorber of civil aircraft, the systematic analysis method combining theoretical analysis, co-simulation and test verification was proposed.Firstly, based on the theoretical analysis model of shock absorber, a co-simulation model of shock absorberwas established, which included mechanical dynamics and hydraulic system.Then, the drop test was planned and implemented.The validity of the simulation model and the feasibility of the analysis method were verified by comparing the simulation and experimental results.Finally, the influence of key parameters such as different inflation pressure and height on the dynamic performance of the shock absorber was discussed in detail.The variation law of amount of work, maximum stroke and maximum axial force with relevant parameters were summarized.The analysis method and conclusion can be used to guide the design and selection of tail skid shock absorber, which has certain reference value for the flight test of civil aircraft.
2020 Vol. 39 (8): 271-276 [
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153
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