Application Of Multi-body System Dynamics On The Spreading Net System

The Spreading Net System (SNS) is a kind of equipment that spreads a long rectanglenet on target ground area with a rocket as the propulsion. The research of spreading processof the system is crucial for the system design. As it is difficult to conduct a lot ofexperiments of such large and complex net system, modeling and numerical simulations ofthe SNS are important to research the dynamic behavior of the system. Both of the largedisplacement of the flexible parts and coupling movement of multi bodies make it diiffcultto model the spreading process. Whereas, the methods of multi-body dynmiics can solvethese problems simultaneously.Three different SNS dynamic models are established with different multi-bodydynamics methods. Three models consider different factors affecting the spreadingrespectively, and the dynamic equations are established. Firstly, based on the analysis of thestructure and the movement behavior of the SNS, the2D hypothesis is proposed to simplifythe net to be a "cable" moving in the plane. Based on the2D hypothesis, the2D rigid modeland dynamic equations are built with Kane’s method. The spreading motion is analyzedaccording to the numerical solutions of the dynamic equations. After that, the axialdisplacement of the cables and the initial conditions of the SNS are taken in toconsideration to establish the2D elasticity model. The dynamic equations are solved andthe calculation results are analyzed as well. In order to analyze the3D motions and theaffect of the real structure of the net, the3D rigid-flexible-mixed net model is establishedwith the absolute coordinate method. The dynamic equation of the3D model is establishedand solvedBased on the analysis of the SNS，a simulated experiment of the SNS is conducted.The results of the experiment prove the feasibility of the spreading method. Calculationscoincide well with experiments. The reasons result to the calculation error are analyzed.Both experimental and calculated results show that the current design of the SNS has someinstability factors. As a result, some improvements are proposed based on the analysisresults.