optimal topology design of truss structures concerning stress and frictionless unilateral contact displacement constraints is investigated. The existence of ununique optimal solution under contact gaps is found. This ...optimal topology design of truss structures concerning stress and frictionless unilateral contact displacement constraints is investigated. The existence of ununique optimal solution under contact gaps is found. This shows that the contact conditions have an effect on structural topology, and different initial contact gaps may lead to different structural topologies. To avoid the singular optima in structural topology optimization in multiple loading cases, an epsilon-relaxed method is adopted to establish the relaxing topology optimization formulations. The problem is solved by means of a two-level optimization method. In the first sublevel, the solution of the frictionless unilateral contact problem is obtained by solving an equivalent quadratic programming. In the second sublevel, topology optimization of truss is carried out by an epsilon-relaxed method. The validity of the method proposed is verified by computational results.展开更多
To interpret density holes in the solar wind,which are nonlinear structures observed by Cluster and Double Star,we propose an electrostatic ion fluid model.We derive the Sagdeev potential from the magnetohydrodynamic(...To interpret density holes in the solar wind,which are nonlinear structures observed by Cluster and Double Star,we propose an electrostatic ion fluid model.We derive the Sagdeev potential from the magnetohydrodynamic(MHD)equations and study the characteristics of nonlinear structures in our model.The results show that density depletions(or holes)can develop from linear ion acoustic waves or ion cyclotron waves in space plasmas when parameters such as Mach number,initial electric field and ratio of ion to electron temperature satisfy certain conditions.In our model,the relative density depletion(or density holes)is from 0 to 1, and the time duration of density holes is from 2 s to more than 98 s.These are in good agreement with the observations by Cluster and Double Star in the solar wind.Our model also shows that the density holes should be accompanied by bipolar electric field solitary structures,which have also been observed by Cluster in the solar wind.展开更多
基金the Postdoctoral Science and Research Foundation of Shanghai,China
文摘optimal topology design of truss structures concerning stress and frictionless unilateral contact displacement constraints is investigated. The existence of ununique optimal solution under contact gaps is found. This shows that the contact conditions have an effect on structural topology, and different initial contact gaps may lead to different structural topologies. To avoid the singular optima in structural topology optimization in multiple loading cases, an epsilon-relaxed method is adopted to establish the relaxing topology optimization formulations. The problem is solved by means of a two-level optimization method. In the first sublevel, the solution of the frictionless unilateral contact problem is obtained by solving an equivalent quadratic programming. In the second sublevel, topology optimization of truss is carried out by an epsilon-relaxed method. The validity of the method proposed is verified by computational results.
基金supported by the National Natural Science Foundation of China(41074114,40921063,40804031)the Specialized ResearchFund for State Key Laboratories of China
文摘To interpret density holes in the solar wind,which are nonlinear structures observed by Cluster and Double Star,we propose an electrostatic ion fluid model.We derive the Sagdeev potential from the magnetohydrodynamic(MHD)equations and study the characteristics of nonlinear structures in our model.The results show that density depletions(or holes)can develop from linear ion acoustic waves or ion cyclotron waves in space plasmas when parameters such as Mach number,initial electric field and ratio of ion to electron temperature satisfy certain conditions.In our model,the relative density depletion(or density holes)is from 0 to 1, and the time duration of density holes is from 2 s to more than 98 s.These are in good agreement with the observations by Cluster and Double Star in the solar wind.Our model also shows that the density holes should be accompanied by bipolar electric field solitary structures,which have also been observed by Cluster in the solar wind.
