First arrival travel time tomography has achieved wide application. However, tomographic resolution is insufficient because geometry constraints cause rays to be unevenly distributed in the velocity model. The variabl...First arrival travel time tomography has achieved wide application. However, tomographic resolution is insufficient because geometry constraints cause rays to be unevenly distributed in the velocity model. The variable damping constraint method adopts uneven priori information to match uneven data distribution which can lessen the correlation between velocity correction values and ray coverage density. In this paper, we combine the variable damping constraint with a smoothness constraint which is added into the regularization equations in velocity inversion to avoid instability caused by only using the variable damping constraint method. The alpha-trimmed-mean filter is used to smooth and denoise intermediate results in the velocity inversion process. We use the LSQR algorithm to enhance the convergence rate and suppress error propagation in solving linear equations. In this paper, we apply the proposed tomographic method to perform velocity inversion using VSP data. The application in recovery test of the checkerboard model and velocity inversion of real VSP data show that the variable damping constraint method can improve tomographic quality because it can solve the effects of uneven ray coverage. In addition, the examples show that the tomographic result near geophones is much more reliable than other areas in the velocity model.展开更多
Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force...Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.展开更多
In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,ef...In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.展开更多
A new type of isolator, the electrorheology (ER) isolator, is mainly described. Through theoretical analysis, a simplified physical model is established under some hypotheses and a series of motion equations are deduc...A new type of isolator, the electrorheology (ER) isolator, is mainly described. Through theoretical analysis, a simplified physical model is established under some hypotheses and a series of motion equations are deduced. According to the transmissibility curve simulation under different electric field strengths, the main factors influencing ER isolator’s working properties have been ascertained. Finally, it proves that ER isolator works well in both low and high frequency zones, it can decrease the force transmitted and enlarge the isolation frequency domain efficiently.展开更多
A new tamping device which is driven by an electrohydraulic exciter was proposed to overcome the limitations of mechanically driven devices.The double-rod oscillation cylinder drives the tamping arm to realize vibrati...A new tamping device which is driven by an electrohydraulic exciter was proposed to overcome the limitations of mechanically driven devices.The double-rod oscillation cylinder drives the tamping arm to realize vibration.A new spin valve was designed in order to fulfill dynamic state requirements of the oscillation cylinder.Parametric analysis was carried out by establishing mathematic model.Then,the relationships among the structure of valve port and the frequency,amplitude,output shock force of the cylinder were researched.An experimental device of the electrohydraulic exciter was established to validate the theoretical results.The signals were acquired by AVANT dynamic signal analyser of vibration.The results show that new tamping device can satisfy all kinds of complex working conditions with the flexible adjustment of frequency and amplitude.展开更多
The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtu...The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtual inertia and virtual damping.An optimal coordination control strategy of micro-grid inverter and energy storage based on variable virtual inertia and damping is proposed to mitigate this conflict.With the integrated optimal constraint of the VSG frequency variation and the energy storage capacity,the virtual inertia and damping of VSG are configured dynamically,adopting linear quadratic optimal control.It can suppress the oscillations of the active power and frequency to improve the stability of VSG and optimally configure the energy storage capacity of VSG simultaneously.The proposed strategy aims to improve the control performance of micro-grid inverter and the system economy.The simulation and experimental results verify the effectiveness of the strategy.展开更多
In this paper, a new hybrid control technique, based on a combination of base-isolation and semi-active variable stiffness/damping in a superstructure, is presented. To illustrate the efficiency of the proposed contro...In this paper, a new hybrid control technique, based on a combination of base-isolation and semi-active variable stiffness/damping in a superstructure, is presented. To illustrate the efficiency of the proposed control system, model tests on a mini-electromagnetic shaking table and a numerical simulation were performed. The test and numerical calculation results indicate that this new hybrid control mode with additional damping and smaller additional stiffness can achieve a better control efficiency.展开更多
基金supported by the China Important National Science and Technology Specific Projects (No2011ZX05024-001-02)
文摘First arrival travel time tomography has achieved wide application. However, tomographic resolution is insufficient because geometry constraints cause rays to be unevenly distributed in the velocity model. The variable damping constraint method adopts uneven priori information to match uneven data distribution which can lessen the correlation between velocity correction values and ray coverage density. In this paper, we combine the variable damping constraint with a smoothness constraint which is added into the regularization equations in velocity inversion to avoid instability caused by only using the variable damping constraint method. The alpha-trimmed-mean filter is used to smooth and denoise intermediate results in the velocity inversion process. We use the LSQR algorithm to enhance the convergence rate and suppress error propagation in solving linear equations. In this paper, we apply the proposed tomographic method to perform velocity inversion using VSP data. The application in recovery test of the checkerboard model and velocity inversion of real VSP data show that the variable damping constraint method can improve tomographic quality because it can solve the effects of uneven ray coverage. In addition, the examples show that the tomographic result near geophones is much more reliable than other areas in the velocity model.
基金Supported by National Key Basic Research Program of China(973 Program,Grant No.2014CB046405)State Key Laboratory of Fluid Power and Mechatronic Systems(Zhejiang University)Open Fund Project(Grant No.GZKF-201502)Hebei Military and Civilian Industry Development Funds Projects of China(Grant No.2015B060)
文摘Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.
文摘In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.
文摘A new type of isolator, the electrorheology (ER) isolator, is mainly described. Through theoretical analysis, a simplified physical model is established under some hypotheses and a series of motion equations are deduced. According to the transmissibility curve simulation under different electric field strengths, the main factors influencing ER isolator’s working properties have been ascertained. Finally, it proves that ER isolator works well in both low and high frequency zones, it can decrease the force transmitted and enlarge the isolation frequency domain efficiently.
基金Projects(50975252,51275499)supported by the National Natural Science Foundation of ChinaProject(2013CB035404)supported by the National Basic Research Program of ChinaProject(GZKF-201312)supported by Open Foundation of the State Key Laboratory of Fluid Power Transmission and Control,China
文摘A new tamping device which is driven by an electrohydraulic exciter was proposed to overcome the limitations of mechanically driven devices.The double-rod oscillation cylinder drives the tamping arm to realize vibration.A new spin valve was designed in order to fulfill dynamic state requirements of the oscillation cylinder.Parametric analysis was carried out by establishing mathematic model.Then,the relationships among the structure of valve port and the frequency,amplitude,output shock force of the cylinder were researched.An experimental device of the electrohydraulic exciter was established to validate the theoretical results.The signals were acquired by AVANT dynamic signal analyser of vibration.The results show that new tamping device can satisfy all kinds of complex working conditions with the flexible adjustment of frequency and amplitude.
基金Supported by National Key R&D Program of China(2016YFB0900300)National Natural Science Foundation of China(51677049).
文摘The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtual inertia and virtual damping.An optimal coordination control strategy of micro-grid inverter and energy storage based on variable virtual inertia and damping is proposed to mitigate this conflict.With the integrated optimal constraint of the VSG frequency variation and the energy storage capacity,the virtual inertia and damping of VSG are configured dynamically,adopting linear quadratic optimal control.It can suppress the oscillations of the active power and frequency to improve the stability of VSG and optimally configure the energy storage capacity of VSG simultaneously.The proposed strategy aims to improve the control performance of micro-grid inverter and the system economy.The simulation and experimental results verify the effectiveness of the strategy.
基金Societal Commonweal Fund Project (2001DIB20098) Earthquake Science Associate Fund (603011)
文摘In this paper, a new hybrid control technique, based on a combination of base-isolation and semi-active variable stiffness/damping in a superstructure, is presented. To illustrate the efficiency of the proposed control system, model tests on a mini-electromagnetic shaking table and a numerical simulation were performed. The test and numerical calculation results indicate that this new hybrid control mode with additional damping and smaller additional stiffness can achieve a better control efficiency.
