Apply of Explicit Finite Element in Seismic Ground Motion Computation

In this paper, we will use the explicit finite element to compute ground motion due to Tangshan earthquake. The explicit finite-element method uses one integration point and an hourglass control scheme. We implement the coarse-grain method in a structured finite-element mesh straightforwardly. At the same time, we also apply the coarse-grain method to a widely used, slightly unstructured finite-element mesh, where unstructured finite elements are only used in the vertical velocity transition zones. By the finite-element methods, we can compute the ground velocity with some distance to the seismogenic fault in Tangshan earthquake. Through the computation, we can find the main character of ground motion for the strike slip earthquake events and the high frequency vibration motion of ground motion.

Extrusion deformation process of ground surface during the Lushan earthquake in China

Based on finite element method, the extrusion deformation process of ground surface during the Lushan earthquake （April 20, 2013） is investigated in this work. In order to construct the finite element model of Lushan earthquake structure, the geophysical layer model of Lushan area, the frictional characteristic of slip-weaken along the fault surface, and the Coulomb failure criterion are considered. Through the computation and the comparison with achievement on the Lushan focal dynamics, our researches indicate that： （1） The most extrusion deformation of ground surface occurred in the initial phase of earthquake procession, i.e., between the fourth and sixth seconds after the earthquake occurred. （2） Between the first and sixth seconds after the earthquake, the extrusion deformation concentrates on the surface projection of earthquake fault. （3） Between the first and third seconds after the earthquake, the extrusion deformation of ground surface is very tiny. Meanwhile, the extrusion deformation reaches maximum at the sixth second after earthquake. （4） After 6 s of Lushan earthquake, the extrusion deformation spread out of earthquake structure projection. （5） During the earthquake, the maximum of extrusion deformation on ground surface is larger than the final deformation of the post-earthquake, in other words, the ground extrusion deformation will lastly reach a relatively small value after the Lushan earthquake occurred.

Qualitative Analyses of Correlations between Strong Ground Motions of the Three Large Earthquakes and Landslide Distributions

In this work,the correlations between spatial distributions of landslide point density(LPD)and strong ground motions of the three strong earthquakes are qualitatively investigated.Meanwhile the qualitative relationship between the distribution of LPD and the fault rupture process is also characterized.Three strong events are the Lushan,Wenchuan,and Jiuzhaigou earthquakes.In order to reconstruct the near filed strong ground motions and the fault processes of these earthquakes,the broadband ground simulation method of University of California Santa Barbara(UCSB)and the simplified crustal layer structures are applied.To show the rationality of the UCSB method,the fault slip distributions of the three earthquakes reconstructed by the kinematic rupture generator model in the UCSB method are compared with those by inversed.Furthermore,the validation of the UCSB method for the three earthquakes is also carried according to the validation exercise of the Southern California Earthquake Center(SCEC)Broadband Platform(BBP).Lastly,the fields of peak ground acceleration(PGA)and peak ground velocity(PGV)in three mutually perpendicular directions of the three earthquakes are achieved.Generally,the landslide distribution length of large LPD values along the fault strike is less than the fault strike length.Therefore,the slip modes of earthquake faults affect the distributions of landslides.For the strike slip earthquakes,the distributions of large LPD values relate well to PGA and PGV components of the parallel and normal to the fault strike.For the reverse slip earthquakes,distributions of LPD relate to ground motion components in all directions.Moreover,distributions of landslides in near fields of earthquakes are significantly affected by the focus parameters and fault scales.

Gaussian mixture model based adaptive control for uncertain nonlinear systems with complex state constraints

This paper addresses an uncertain nonlinear control system problem with complex state constraints and mismatched uncertainties.A novel Gaussian Mixture Model(GMM)based adaptive PID-Nonsingular Terminal Sliding Mode Control(NTSMC)(GMM-adaptive-PID-NTSMC)method is proposed.It is achieved by combining a GMM based adaptive potential function with a novel switching surface of PID-NTSMC.Next,the stability of the closed-loop system is proved.The main contribution of this paper is that the GMM method is applied to obtain the analytic description of the complex bounded state constraints,ensuring that the states'constraints are not violated with GMM-based adaptive potential function.The developed potential function can consider the influence of uncertainties.More importantly,the GMM-adaptive-PID-NTSMC can be generalized to control a more representative class of uncertain nonlinear systems with constrained states and mismatched uncertainties.In addition,the proposed controller enhances the robustness,and requires less control cost and reduces the steady state error with respect to the Artificial Potential Function based Nonsingular Terminal Sliding Mode Control(APF-NTSMC),GMM-NTSMC and GMM-adaptive-NTSMC.At last,numerical simulation is performed to validate the superior performance of the proposed controller.

Spacecraft formation reconfiguration with multi-obstacle avoidance under navigation and control uncertainties using adaptive artificial potential function method

In this paper,an adaptive artificial potential function(AAPF)method is developed for spacecraft formation reconfiguration with multi-obstacle avoidance under navigation and control uncertainties.Furthermore,an improved Linear Quadratic Regular(ILQR)is proposed to track the reference trajectory and a Lyapunov-based method is employed to demonstrate the stability of the overall closed-loop system.Compared with the traditional APF method and the equal-collision-probability surface(ECPS)method,the AAPF method not only retains the advantages of APF method and ECPS method,such as low computational complexity,simple analytical control law and easy analytical validation progress,but also proposes a new APF to solve multi-obstacle avoidance problem considering the influence of the uncertainties.Moreover,the ILQR controller obtains high control accuracy to enhance the safe performance of the spacecraft formation reconfiguration.Finally,the effectiveness of the proposed AAPF method and the ILQR controller are verified by numerical simulations.