Numerical and experimental studies on impact dynamics of a planar flexible multibody system

In this paper a computational methodology on impact dynamics of the flexible multibody system is presented. First, the floating frame of reference approach and nodal coordinates on the basis of finite element formulation are used to describe the kinematics of planar deformable bodies. According to the kinematic description of contact conditions, the contact constraint equations of planar flexible bodies are derived. Based on the varying topology technique the impact dynamic equations for a planar multibody system are established. Then the initial conditions of the equations in each contact stage are determined according to the discontinuity theory in continuum mechanics. The experiments between the aluminum rods are performed to check the correctness of the proposed method. Through the comparison between the numerical and experimental results the proposed method is validated. Experimental results also show that the impulse momentum method cannot accurately predict the complex impact dynamic phenomena and the continuous model may lead to a serious error when used to simulate the impact problems with significant wave propagation effects.

Simulation of Hertz Transient Contact/Impact of Flexible Bodies

The transient response to longitudinal impact of flexible rods with Hertz contact is closely related to the extent of deformations with different impact parameters. By means of LS-DYNA, for different radius and different speeds, the longitudinal impact of a hammer with a rounded end on a drill rod is numerically simulated in this article. Simulations demonstrate that there is an obvious dif-ference between analytical solution and numerical solution on condition of short curvature radius. In the circumstance contact pressure increases, the boundary of the yield zone exceeds that of the contact zone, and the significant plastic deformation reduces the intensity of contact pressure pulse. Contact force-time curves in loading and unloading phases shift down. The numerical solution is in good agree-ment with analytical solution on condition of large curvature radius and impact speeds. The deforma-tion of yield region is constrained by the surrounding elastic region and no significant plastic deforma-tion appears.

Renminbi's New Flexibility May Exert Impact on Textile Exports

People’s Bank of China over the weekend said it was abandoning its peg to the US dollar, a move taken to shelter the China economy

Speed Planning Algorithm Based on Improved S-Type Acceleration and Deceleration Model

The acceleration saltation of the traditional S-type acceleration model in the speed planning of the NURBS curve will result in the vibration and flexible impact of the machine tool.It will affect the surface quality of the components.The high speed smooth S-type acceleration and deceleration model deals with flexible impact,but the calculation is tedious.Aimed at the above problems,the traditional S-type acceleration and deceleration model is improved to make the jerk change linearly at a certain slope to reduce the flexible impact.Before the speed planning,it is needed to find the arc length and curvature of each point on the NURBS curve with a tiny step,and to determine the speed sensitivity point on the curve accordingly.According to the speed sensitive point,the NURBS curve is segmented.The attribute parameters of each section are determined by adaptive speed planning.Then,the speed planning can be performed on the NURBS curve according to the speed characteristics classification.The simulation results show that the algorithm can effectively reduce the flexible impact,improve the machining precision and efficiency,and simplify the classification of speed characteristics.