The effects of the initial conditions of impact dynamics equations are investigated numerically and experimentally.The inadequacies of previous studies on initial conditions are pointed out.Then a coefficient of velocity jump at the moment of impact is introduced,and the experiments for the mental rods are implemented to validate the appending constraints modeling methods for impact process.The comparisons between the experimental and simulated results at different coefficients are used to study the effects of the velocity jump conditions to the numerical simulation.The results indicate that the physical velocity response of bodies during impact is smooth;the different values of velocity jump only have small effects on numerical oscillation of velocity response,and they have no effects on the time history of impact force.
Most of exiting model updating methods based on the substructure matrices did not consider the effect of model reduction process on model updating which led to the updating results could not become more and more accurate with the improvement of the model reduction precision and the convergence rate was greatly reduced.In order to solve this problem,this paper analyses the basic reason about this problem,and proposes an improved model updating method of reduced-models,named as improved reduced cross-model cross-mode(IRCMCM) method.The proposed method eliminates the disadvantageous effect by adding a correction term to the model updating formula and employing an iterative process.The results obtained by the referenced method and IRCMCM method are compared by numerical examples of satellite's plates,which indicate the model updating results are more accurate by using the proposed method,and the model updating precision becomes better with the precision of the model reduction upgraded and the convergence rate is improved to a large extent at the same time.
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.
