This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/planesymmetric acoustic wave problems.The half-space fundamental solution is employed in the boundary integral equations s...This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/planesymmetric acoustic wave problems.The half-space fundamental solution is employed in the boundary integral equations so that the tree structure required in the fast multipole algorithm is constructed for the boundary elements in the real domain only.Moreover,a set of symmetric relations between the multipole expansion coefficients of the real and image domains are derived,and the half-space fundamental solution is modified for the purpose of applying such relations to avoid calculating,translating and saving the multipole/local expansion coefficients of the image domain.The wideband adaptive multilevel fast multipole algorithm associated with the iterative solver GMRES is employed so that the present method is accurate and efficient for both lowand high-frequency acoustic wave problems.As for exterior acoustic problems,the Burton-Miller method is adopted to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method.Details on the implementation of the present method are described,and numerical examples are given to demonstrate its accuracy and efficiency.展开更多
The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanic...The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanically deployable aerodynamic decelerators(MDADs)that utilize an umbrella-like mechanism and proposes a new mechanism of MDADs through this method.The proposed method utilizes plane-symmetric 7R(R:revolute joint)linkages,and the kinematics of these linkages are systematically analyzed using the product of exponentials method.The 7R linkage kinematics are equated to an equivalent joint,the foundation for constructing umbrella-like deployable mechanisms.Three distinct types of mechanisms are synthesized using this methodology.Subsequently,their kinematics are analyzed based on the equivalent joint,and the configurations are experimentally validated through 3D-printed models and kinematic simulations.Trajectory simulations and structural analyses are conducted to assess the performance of the deployable mechanisms and provide valuable insights into their capabilities.This research contributes to advancing deployable aerodynamic decelerator technology and offers a promising avenue for future planetary entry,descent,and landing applications.展开更多
We have obtained exact static plane-symmetric solutions to the spinor field equations with nonlinear terms which are arbitrary functions of invariant , taking into account their own gravitational field. It is shown th...We have obtained exact static plane-symmetric solutions to the spinor field equations with nonlinear terms which are arbitrary functions of invariant , taking into account their own gravitational field. It is shown that the initial set of the Einstein and spinor field equations with a power-law nonlinearity have regular solutions with a localized energy density of the spinor field only if m=0 (m is the mass parameter in the spinor field equations). Equations with power and polynomial nonlinearities are studied in detail. In this case, a soliton-like configuration has negative energy. We have also obtained exact static plane-symmetric solutions to the above spinor field equations in flat space-time. It is proved that in this case soliton-like solutions are absent.展开更多
基金supported by the National Natural Science Foundation of China (11172291)the National Science Foundation for Post-doctoral Scientists of China (2012M510162)the Fundamental Research Funds for the Central Universities (KB2090050024)
文摘This paper presents a novel wideband fast multipole boundary element approach to 3D half-space/planesymmetric acoustic wave problems.The half-space fundamental solution is employed in the boundary integral equations so that the tree structure required in the fast multipole algorithm is constructed for the boundary elements in the real domain only.Moreover,a set of symmetric relations between the multipole expansion coefficients of the real and image domains are derived,and the half-space fundamental solution is modified for the purpose of applying such relations to avoid calculating,translating and saving the multipole/local expansion coefficients of the image domain.The wideband adaptive multilevel fast multipole algorithm associated with the iterative solver GMRES is employed so that the present method is accurate and efficient for both lowand high-frequency acoustic wave problems.As for exterior acoustic problems,the Burton-Miller method is adopted to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method.Details on the implementation of the present method are described,and numerical examples are given to demonstrate its accuracy and efficiency.
基金supported by the National Natural Science Foundation of China(Grant No.52175010)the Self-Planned Task of the State Key Laboratory of Robotics and Systems,Harbin Institute of Technology,China(Grant No.SKLRS202202B).
文摘The surging interest in planetary exploration underscores the need for deployable aerodynamic decelerators with a low ballistic coefficient.This study introduces a novel approach to designing and constructing mechanically deployable aerodynamic decelerators(MDADs)that utilize an umbrella-like mechanism and proposes a new mechanism of MDADs through this method.The proposed method utilizes plane-symmetric 7R(R:revolute joint)linkages,and the kinematics of these linkages are systematically analyzed using the product of exponentials method.The 7R linkage kinematics are equated to an equivalent joint,the foundation for constructing umbrella-like deployable mechanisms.Three distinct types of mechanisms are synthesized using this methodology.Subsequently,their kinematics are analyzed based on the equivalent joint,and the configurations are experimentally validated through 3D-printed models and kinematic simulations.Trajectory simulations and structural analyses are conducted to assess the performance of the deployable mechanisms and provide valuable insights into their capabilities.This research contributes to advancing deployable aerodynamic decelerator technology and offers a promising avenue for future planetary entry,descent,and landing applications.
文摘We have obtained exact static plane-symmetric solutions to the spinor field equations with nonlinear terms which are arbitrary functions of invariant , taking into account their own gravitational field. It is shown that the initial set of the Einstein and spinor field equations with a power-law nonlinearity have regular solutions with a localized energy density of the spinor field only if m=0 (m is the mass parameter in the spinor field equations). Equations with power and polynomial nonlinearities are studied in detail. In this case, a soliton-like configuration has negative energy. We have also obtained exact static plane-symmetric solutions to the above spinor field equations in flat space-time. It is proved that in this case soliton-like solutions are absent.
