Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural...Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural frequencies of soil deposit, nor simulate a damping of frequency independence. This research develops a new discrete model for onedimensional viscoelastic response analysis of layered soil deposit based on the mode equivalence method. The new discrete model is a one-dimensional equivalent multi-degree-of-freedom（MDOF） system characterized by a series of concentrated masses, springs and dashpots with a special configuration. The dynamic response of the equivalent MDOF system is analytically derived and the physical parameters are formulated in terms of modal properties. The equivalent MDOF system is verified through a comparison of amplification functions with the available theoretical solutions. The appropriate number of degrees of freedom（DOFs） in the equivalent MDOF system is estimated. A comparative study of the equivalent MDOF system with the existing discrete models is performed. It is shown that the proposed equivalent MDOF system can exactly present the natural frequencies and the hysteretic damping of soil deposits and provide more accurate results with fewer DOFs.展开更多
An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivati...An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivatives are introduced.Secondly,the linear sliding surface and the equivalent sliding mode controller are constructed,and the sufficient conditions for the stability of the damaged aircraft motion model are given by using the Lyapunov technique.The damage-tolerant controller is designed based on an adaptive sliding mode control for analyzing damaged aircraft systems.Furthermore,the hyperbolic tangent function is utilized to replace the symbolic function in the controller.The feasibility of the hyperbolic tangent function as the switching function is analyzed theoretically.Finally,the Boeing-747100/200 model is taken as an example to demonstrate the efficiency of theoretical results by recognizing the structural fault of aircraft.Numerical results show that the control law has a positive impact on the performance of the closed-loop system,and it also has a better fault tolerance and robustness towards external disturbance compared with traditional methods of damaged aircraft stabilization control.展开更多
In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index ve...In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index vector is introduced to determine the correlation coefficient between two failure modes, and then, the reliability index vector of a series system can be obtained. Several numerical cases and an analysis on offshore platform are performed, and the results show that this scheme provided here has better computational accuracy, and its calculation process is simpler for the series systems reliability calculations compared with the other methods. Also this scheme is more convenient for the engineering applications.展开更多
All the possible equivalent barotropic (EB) laminar solutions are firstly explored,and all the possible non-EB elliptic circulations and hyperbolic laminar modes of rotating stratified fluids are discovered in this pa...All the possible equivalent barotropic (EB) laminar solutions are firstly explored,and all the possible non-EB elliptic circulations and hyperbolic laminar modes of rotating stratified fluids are discovered in this paper.The EB circulations (including the vortex streets and hurricane like vortices) possess rich structures,because either the arbitrary solutions of arbitrary nonlinear Poisson equations can be used or an arbitrary two-dimensional stream function is revealed which may be broadly applied in atmospheric and oceanic dynamics,plasma physics,astrophysics and so on.The discovery of the non-EB modes disproves a known conjecture.展开更多
基金National Natural Science Foundation of China(51208296&51478343)Shanghai Committee of Science and Technology(13231200503)+2 种基金Fundamental Research Funds for the Central Universities(2013KJ095&101201438)Shanghai Educational Development Foundation(13CG17)National Key Technology R&D Program(2012BAK24B04)
文摘Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural frequencies of soil deposit, nor simulate a damping of frequency independence. This research develops a new discrete model for onedimensional viscoelastic response analysis of layered soil deposit based on the mode equivalence method. The new discrete model is a one-dimensional equivalent multi-degree-of-freedom（MDOF） system characterized by a series of concentrated masses, springs and dashpots with a special configuration. The dynamic response of the equivalent MDOF system is analytically derived and the physical parameters are formulated in terms of modal properties. The equivalent MDOF system is verified through a comparison of amplification functions with the available theoretical solutions. The appropriate number of degrees of freedom（DOFs） in the equivalent MDOF system is estimated. A comparative study of the equivalent MDOF system with the existing discrete models is performed. It is shown that the proposed equivalent MDOF system can exactly present the natural frequencies and the hysteretic damping of soil deposits and provide more accurate results with fewer DOFs.
基金The National Natural Science Foundation of China(No.61973172,61973175)the Key Technologies R&D Program of Tianjin(No.19JCZDJC32800).
文摘An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivatives are introduced.Secondly,the linear sliding surface and the equivalent sliding mode controller are constructed,and the sufficient conditions for the stability of the damaged aircraft motion model are given by using the Lyapunov technique.The damage-tolerant controller is designed based on an adaptive sliding mode control for analyzing damaged aircraft systems.Furthermore,the hyperbolic tangent function is utilized to replace the symbolic function in the controller.The feasibility of the hyperbolic tangent function as the switching function is analyzed theoretically.Finally,the Boeing-747100/200 model is taken as an example to demonstrate the efficiency of theoretical results by recognizing the structural fault of aircraft.Numerical results show that the control law has a positive impact on the performance of the closed-loop system,and it also has a better fault tolerance and robustness towards external disturbance compared with traditional methods of damaged aircraft stabilization control.
文摘In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index vector is introduced to determine the correlation coefficient between two failure modes, and then, the reliability index vector of a series system can be obtained. Several numerical cases and an analysis on offshore platform are performed, and the results show that this scheme provided here has better computational accuracy, and its calculation process is simpler for the series systems reliability calculations compared with the other methods. Also this scheme is more convenient for the engineering applications.
基金Project supported by the National Natural Science Foundation of China (Nos.11175092,10735030)the National Basic Research Program of China (973 Program) (No.2007CB814800)+1 种基金the Natural Science Foundation of Shanghai (No.09ZR1413600)the K.C.Wong Magna Fund of Ningbo University
文摘All the possible equivalent barotropic (EB) laminar solutions are firstly explored,and all the possible non-EB elliptic circulations and hyperbolic laminar modes of rotating stratified fluids are discovered in this paper.The EB circulations (including the vortex streets and hurricane like vortices) possess rich structures,because either the arbitrary solutions of arbitrary nonlinear Poisson equations can be used or an arbitrary two-dimensional stream function is revealed which may be broadly applied in atmospheric and oceanic dynamics,plasma physics,astrophysics and so on.The discovery of the non-EB modes disproves a known conjecture.
