Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequenci...Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequencies are applied to the excavation face.The pattern of the excess pore pressure ratio with frequency,as well as the dynamic response of soil mass under different frequency loads before excavation,is analyzed.When the velocity sinusoidal wave acts on the excavation surface of the shield tunnel with a single sand layer,soil liquefaction occurs.However,the ranges and locations of soil liquefaction are different at different frequencies,which proves that the vibration frequency influences the liquefaction location of the stratum.For sand-clay composite strata with liquefiable layers,the influence of frequency on the liquefaction range is different from that of a single stratum.In the frequency range of 5-30 Hz,the liquefaction area and surface subsidence decrease with an increase in vibration frequency.The research results in this study can be used as a reference in engineering practice for tunneling liquefiable strata with a shield tunneling machine.展开更多
In order to study the disturbance of the liquefiable stratum caused by the vibration induced by construction of the shield machine,the construction process of the shield tunnel was simulated based on the finite differ...In order to study the disturbance of the liquefiable stratum caused by the vibration induced by construction of the shield machine,the construction process of the shield tunnel was simulated based on the finite difference software FLAC 3 D.A sinusoidal velocity boundary that simulates the vibration of shield construction is applied in the horizontal direction of the excavation surface,and dynamic response analysis is carried out to analyze the excess pore water pressure,acceleration,and vertical effective stress time-history curves.The research results show that in the liquefiable stratum,the vibration induced by shield construction will form a certain liquefaction area in the soil in front of the excavation face.The area has not developed to the ground.The area where the vibration induced by shield construction has a great influence on the excess pore water pressure of the soil is below the excavation surface.This area is vortex-shaped.The excess pore water pressure of the overlying soil layer on the excavation surface increases,and the vertical effective stress decreases.The horizontal vibration wave induced by shield construction has no obvious attenuation in the horizontal direction,but has obvious attenuation during the propagation to the ground surface.In the area where the peak value of soil acceleration is large,the soil liquefaction is serious.展开更多
The optimal control problem of the multibody dynamics of a spacecraft in space, modeled as a central body with one-sided connected deployable solar arrays, is investigated. The dynamical equations of motion of the spa...The optimal control problem of the multibody dynamics of a spacecraft in space, modeled as a central body with one-sided connected deployable solar arrays, is investigated. The dynamical equations of motion of the spacecraft with solar arrays are derived using the multibody dynamics method. The control of the attitude motion of a spacecraft system can be transformed into the motion planning problem of nonholonomic system when the initial angular momentum is zero. These are then used to investigate the motion planning of the spacecraft during solar arrays deployment via particle swarm optimization (PSO) and results are obtained with the optimal control input and the optimal trajectory. The results of numerical simulation show that this approach is effective for the control problem of the attitude of a spacecraft during the deployment process of its solar arrays.展开更多
An optimal motion planning of a free-falling cat based on the spline approximation is investigated.Nonholonomicity arises in a free-falling cat subjected to nonintegrable velocity constraints or nonintegrable conserva...An optimal motion planning of a free-falling cat based on the spline approximation is investigated.Nonholonomicity arises in a free-falling cat subjected to nonintegrable velocity constraints or nonintegrable conservation laws.The equation of dynamics of a free-falling cat is obtained by using the model of two symmetric rigid bodies.The control of the system can be converted to the motion planning problem for a driftless system.A cost function is used to incorporate the final errors and control energy.The motion planning is to determine control inputs to minimize the cost function and is formulated as an infinite dimensional optimal control problem.By using the control parameterization,the infinite dimensional optimal control problem can be transformed to a finite dimensional one.The particle swarm optimization(PSO) algorithm with the cubic spline approximation is proposed to solve the finite dimension optimal control problem.The cubic spline approximation is introduced to realize the control parameterization.The resulting controls are smooth and the initial and terminal values of the control inputs are zeros,so they can be easily generated by experiment.Simulations are also performed for the nonholonomic motion planning of a free-falling cat.Simulated experimental results show that the proposed algorithm is more effective than the Newtoian algorithm.展开更多
基金Research Grants for Returned Students of China under Grant No.2020-038the National Natural Science Foundation of China under Grant No.51408392。
文摘Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequencies are applied to the excavation face.The pattern of the excess pore pressure ratio with frequency,as well as the dynamic response of soil mass under different frequency loads before excavation,is analyzed.When the velocity sinusoidal wave acts on the excavation surface of the shield tunnel with a single sand layer,soil liquefaction occurs.However,the ranges and locations of soil liquefaction are different at different frequencies,which proves that the vibration frequency influences the liquefaction location of the stratum.For sand-clay composite strata with liquefiable layers,the influence of frequency on the liquefaction range is different from that of a single stratum.In the frequency range of 5-30 Hz,the liquefaction area and surface subsidence decrease with an increase in vibration frequency.The research results in this study can be used as a reference in engineering practice for tunneling liquefiable strata with a shield tunneling machine.
基金Scientific and Technological Innovation Project for Excellent Talents of Shanxi Province(201605D211037)Scientific Research Fund for Returned Scholars of Shanxi Province(2020038)。
文摘In order to study the disturbance of the liquefiable stratum caused by the vibration induced by construction of the shield machine,the construction process of the shield tunnel was simulated based on the finite difference software FLAC 3 D.A sinusoidal velocity boundary that simulates the vibration of shield construction is applied in the horizontal direction of the excavation surface,and dynamic response analysis is carried out to analyze the excess pore water pressure,acceleration,and vertical effective stress time-history curves.The research results show that in the liquefiable stratum,the vibration induced by shield construction will form a certain liquefaction area in the soil in front of the excavation face.The area has not developed to the ground.The area where the vibration induced by shield construction has a great influence on the excess pore water pressure of the soil is below the excavation surface.This area is vortex-shaped.The excess pore water pressure of the overlying soil layer on the excavation surface increases,and the vertical effective stress decreases.The horizontal vibration wave induced by shield construction has no obvious attenuation in the horizontal direction,but has obvious attenuation during the propagation to the ground surface.In the area where the peak value of soil acceleration is large,the soil liquefaction is serious.
基金supported by the National Natural Science Foundation of China (Grant No. 11072038)
文摘The optimal control problem of the multibody dynamics of a spacecraft in space, modeled as a central body with one-sided connected deployable solar arrays, is investigated. The dynamical equations of motion of the spacecraft with solar arrays are derived using the multibody dynamics method. The control of the attitude motion of a spacecraft system can be transformed into the motion planning problem of nonholonomic system when the initial angular momentum is zero. These are then used to investigate the motion planning of the spacecraft during solar arrays deployment via particle swarm optimization (PSO) and results are obtained with the optimal control input and the optimal trajectory. The results of numerical simulation show that this approach is effective for the control problem of the attitude of a spacecraft during the deployment process of its solar arrays.
基金supported by the National Natural Science Foundation of China (Grant No. 11072038)the Municipal Key Programs of Natural Science Foundation of Beijing,China (Grant No. KZ201110772039)
文摘An optimal motion planning of a free-falling cat based on the spline approximation is investigated.Nonholonomicity arises in a free-falling cat subjected to nonintegrable velocity constraints or nonintegrable conservation laws.The equation of dynamics of a free-falling cat is obtained by using the model of two symmetric rigid bodies.The control of the system can be converted to the motion planning problem for a driftless system.A cost function is used to incorporate the final errors and control energy.The motion planning is to determine control inputs to minimize the cost function and is formulated as an infinite dimensional optimal control problem.By using the control parameterization,the infinite dimensional optimal control problem can be transformed to a finite dimensional one.The particle swarm optimization(PSO) algorithm with the cubic spline approximation is proposed to solve the finite dimension optimal control problem.The cubic spline approximation is introduced to realize the control parameterization.The resulting controls are smooth and the initial and terminal values of the control inputs are zeros,so they can be easily generated by experiment.Simulations are also performed for the nonholonomic motion planning of a free-falling cat.Simulated experimental results show that the proposed algorithm is more effective than the Newtoian algorithm.
