A new kind of quadrilateral assumed stress hy- brid membrane element with drilling degrees of freedom and a traction-free inclined side has been developed based on an extended Hellinger-Reissner principle which is est...A new kind of quadrilateral assumed stress hy- brid membrane element with drilling degrees of freedom and a traction-free inclined side has been developed based on an extended Hellinger-Reissner principle which is established by expanding the essential terms of the assumed stress field as polynomials in the natural coordinates of the element. The homogeneous equilibrium equations are imposed in a variational sense through the internal displacements which are also expanded in the natural coordinates, while the tractionfree conditions along the inclined side are satisfied exactly. The use of such special element in the finite element solution is shown to be highly accurate when only a very coarse element mesh is used for plates with V-shaped rounded notches or inclined sides.展开更多
Liang Qichao 's analysis of "freedom "in On Freedom is mainly focused on revealing the evolution and variation of the term "freedom "in modern Chinese society. In his view,freedom is not only a...Liang Qichao 's analysis of "freedom "in On Freedom is mainly focused on revealing the evolution and variation of the term "freedom "in modern Chinese society. In his view,freedom is not only an indispensable element of an individual's life,but also fully applicable to the course of social and historical developm ent. Liang Qichao 's liberalism originates directly from the West,but is deeply influenced by the Chinese traditional discourse system and the overwhelming reality context of saving the nation in modern tim es.What is different from Western liberalism is that the dim ensions of Liang Qichao 's freedom are developed at two levels,one is the individual level,the other is the national level. The form er has the significance of enlightenm ent,while the latter has the significance of saving lives. Enlightenm ent and salvation are not only the"double variations"of modern C hina,but also the dual responsibility of modern Chinese enlightenm ent thinkers,which is dem-onstrated in Liang Qichao 's thought of freedom.展开更多
With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture...With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture process,such as excessive collision and fast tumbling of targets,manipulator with redundant Degrees of Freedom(DOFs)can be used to improve the compliance and therefore solve these problems.The Rope-Driven Snake Manipulator(RDSM)is a combina-tion of hyper-redundant DOFs and better compliance,and therefore it is suitable for capturing mis-sion.In this paper,a snake manipulator mechanism is designed,and the complete kinematic model and system dynamic model considering RDSM,target and contact is established.Then,to obtain the configuration of joint with hyper-redundant DOFs,an improved motion dexterity index is pro-posed as the joint motion optimization target.Besides,the force-position collaborative optimization index is designed to adjust active stiffness,and the impedance control method based on the modified index is used to capture the space target.Finally,the proposed force-position collaborative opti-mization method is verified by virtual prototype co-simulation.The results demonstrate that based on the proposed method,the collision force is reduced by about 25%compared to normal impe-dance control,showing higher safety.展开更多
文摘A new kind of quadrilateral assumed stress hy- brid membrane element with drilling degrees of freedom and a traction-free inclined side has been developed based on an extended Hellinger-Reissner principle which is established by expanding the essential terms of the assumed stress field as polynomials in the natural coordinates of the element. The homogeneous equilibrium equations are imposed in a variational sense through the internal displacements which are also expanded in the natural coordinates, while the tractionfree conditions along the inclined side are satisfied exactly. The use of such special element in the finite element solution is shown to be highly accurate when only a very coarse element mesh is used for plates with V-shaped rounded notches or inclined sides.
文摘Liang Qichao 's analysis of "freedom "in On Freedom is mainly focused on revealing the evolution and variation of the term "freedom "in modern Chinese society. In his view,freedom is not only an indispensable element of an individual's life,but also fully applicable to the course of social and historical developm ent. Liang Qichao 's liberalism originates directly from the West,but is deeply influenced by the Chinese traditional discourse system and the overwhelming reality context of saving the nation in modern tim es.What is different from Western liberalism is that the dim ensions of Liang Qichao 's freedom are developed at two levels,one is the individual level,the other is the national level. The form er has the significance of enlightenm ent,while the latter has the significance of saving lives. Enlightenm ent and salvation are not only the"double variations"of modern C hina,but also the dual responsibility of modern Chinese enlightenm ent thinkers,which is dem-onstrated in Liang Qichao 's thought of freedom.
文摘With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture process,such as excessive collision and fast tumbling of targets,manipulator with redundant Degrees of Freedom(DOFs)can be used to improve the compliance and therefore solve these problems.The Rope-Driven Snake Manipulator(RDSM)is a combina-tion of hyper-redundant DOFs and better compliance,and therefore it is suitable for capturing mis-sion.In this paper,a snake manipulator mechanism is designed,and the complete kinematic model and system dynamic model considering RDSM,target and contact is established.Then,to obtain the configuration of joint with hyper-redundant DOFs,an improved motion dexterity index is pro-posed as the joint motion optimization target.Besides,the force-position collaborative optimization index is designed to adjust active stiffness,and the impedance control method based on the modified index is used to capture the space target.Finally,the proposed force-position collaborative opti-mization method is verified by virtual prototype co-simulation.The results demonstrate that based on the proposed method,the collision force is reduced by about 25%compared to normal impe-dance control,showing higher safety.
