This paper carries out a comprehensive and systematic comparison study on the kinematic performance of four six degrees of freedom(6-DOF)parallel mechanisms with different topologies,i.e.,6-UPS,3-(2-UPR)U,3-(2-UCR)U,a...This paper carries out a comprehensive and systematic comparison study on the kinematic performance of four six degrees of freedom(6-DOF)parallel mechanisms with different topologies,i.e.,6-UPS,3-(2-UPR)U,3-(2-UCR)U,and 3-R(2-RPR)U.The research begins by elaborating in detail the similarities and differences among these four parallel mechanisms.By standardizing the definition of the coordinate system for each mechanism,the inverse kinematics and the Jacobian matrix of these four mechanisms are systematically derived.Employing a set of motion/force transmission indices,which are directly obtained from the Jacobian matrix,the kinematic performances of the four mechanisms are thoroughly analyzed and compared within the given workspaces while maintaining the same dimensional parameters for all cases.The comparison study of these four parallel mechanisms extends beyond local transmission indices to also include global transmission indices,covering both position and orientation workspaces,as well as assessments at both the local and global workspace levels.This comprehensive approach ensures a detailed and fair evaluation of their respective kinematic capabilities.The results indicate that the comprehensive kinematic performances of the four parallel mechanisms are similar,and providing a solid theoretical foundation for innovative design and practical guidance for selecting optimal architectures based on specific application requirements.展开更多
The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The moti...The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The motions of the floating breakwater are assumed to be two-dimensional in sway, heave, and roll. The solution to the fluid motion is derived by transforming the governing differential equation into the integral equation on the boundary in time domain with the Green＇s function method. The motion equations of the floating breakwater are established and solved with the fourth-order Runge-Kutta method to obtain the displacement and velocity of the breakwater. The mooring forces are computed with the static method. The computational results of the wave transmission coefficient, the motion responses, and the mooring forces of the pontoon-plate floating breakwater are given. It is indicated that the relative width of the pontoon is an important factor influencing the wave transmission coefficient of the floating breakwater. The transmission coefficient decreases obviously as the relative width of the pontoon increases. The horizontal plates help to reduce the wave transmission over the floating breakwater. The motion responses and the mooring forces of the pontoon-plate floating breakwater are less than those of the pontoon floating breakwater. The mooring force at the offshore side is larger than that at the onshore side.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.52325501,U24B2047).
文摘This paper carries out a comprehensive and systematic comparison study on the kinematic performance of four six degrees of freedom(6-DOF)parallel mechanisms with different topologies,i.e.,6-UPS,3-(2-UPR)U,3-(2-UCR)U,and 3-R(2-RPR)U.The research begins by elaborating in detail the similarities and differences among these four parallel mechanisms.By standardizing the definition of the coordinate system for each mechanism,the inverse kinematics and the Jacobian matrix of these four mechanisms are systematically derived.Employing a set of motion/force transmission indices,which are directly obtained from the Jacobian matrix,the kinematic performances of the four mechanisms are thoroughly analyzed and compared within the given workspaces while maintaining the same dimensional parameters for all cases.The comparison study of these four parallel mechanisms extends beyond local transmission indices to also include global transmission indices,covering both position and orientation workspaces,as well as assessments at both the local and global workspace levels.This comprehensive approach ensures a detailed and fair evaluation of their respective kinematic capabilities.The results indicate that the comprehensive kinematic performances of the four parallel mechanisms are similar,and providing a solid theoretical foundation for innovative design and practical guidance for selecting optimal architectures based on specific application requirements.
基金supported by the National Natural Science Foundation of China (Grant No. 51009032)the Scientific Research Foundation of Third Institute of Oceanography, SOA (Grant No. 201003)the Open Research Fund Program of Hunan Province Key Laboratory of Water, Sediment Science & Flood Hazard Prevention (Grant No. 2010SS03)
文摘The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The motions of the floating breakwater are assumed to be two-dimensional in sway, heave, and roll. The solution to the fluid motion is derived by transforming the governing differential equation into the integral equation on the boundary in time domain with the Green＇s function method. The motion equations of the floating breakwater are established and solved with the fourth-order Runge-Kutta method to obtain the displacement and velocity of the breakwater. The mooring forces are computed with the static method. The computational results of the wave transmission coefficient, the motion responses, and the mooring forces of the pontoon-plate floating breakwater are given. It is indicated that the relative width of the pontoon is an important factor influencing the wave transmission coefficient of the floating breakwater. The transmission coefficient decreases obviously as the relative width of the pontoon increases. The horizontal plates help to reduce the wave transmission over the floating breakwater. The motion responses and the mooring forces of the pontoon-plate floating breakwater are less than those of the pontoon floating breakwater. The mooring force at the offshore side is larger than that at the onshore side.
