Research On Bull Whipping And Dynamic Stability Of Large Parachute System

As one of the most important and critical phases of tripping from space to earth, the process of recovery and landing of manned spacecraft requires very high reliability and safety. Considering the practical problems of the recovery system of ShenZhou manned spacecraft, this dissertation focuses on three problems existing in the process of recovery system working, the first problem is the deployment of large main parachute with attached apex drogue and the bull whipping phenomenon, the second problem is the dynamic stability of the system of main parachute and cabin, and the third problem is aerodynamic parameters identification of main parachute in the full inflation state. The main contents in this dissertation are summarized as follows:The dynamic models of deployment process of the main parachute with attached apex drogue and peel off band was researched. Based on the deployment process of the main parachute with attached apex drogue and peel off band of ShenZhou-8 manned spacecraft, the dynamic models of multi-phase, multi-segment, and multi-freedom was built. Considering the improved design of the recovery system of ShenZhou-8 spacecraft, a dynamic model of the connecting band of the main parachute bag and the connecting band of attached apex drogue were built, and the deployment and inflation models of attached apex drogue were presented also. The factors of folding sequence of lines and canopy, deployment process of line segments, restrictions of binding lines were considered in detail, it may simulate the case of non-uniformity and non-continuously deployment process of main parachute. In the end, correctness and validity of the dynamic models and programs were verified through comparative analysis of the statistics dates from airdrop tests kinescope and simulation results.The effects of the attached apex drogue and peel off band on the bull whipping phenomenon were analyzed and evaluated. The improved measurements of the deployment process of main parachute of ShenZhou-8 spacecraft were analyzed and evaluated, and the effects of the attached apex drogue and peel off band were researched in focus. The results indicated that the attached apex drogue and peel off band could minish the velocity, range and radian of bull whipping, reform the distribution of tensile force in the lines and canopy, and restrain the forming of bull whipping phenomenon effectively. The effects of different intensity and length of the peel off band and different drag area of the attached apex drogue on the bull whipping phenomenon were researched also, and the conclusions were used as important evidences for the checking and accepted of ShenZhou-8 recovery system.The characteristics and causes of the bull whipping phenomenon in the deployment process of large parachute were researched. This dissertation defined four status parameters for the bull whipping phenomenon, and dynamic parameters and variety curves of lines and canopy were provided, the influence factors of the bull whipping were analyzed also. Combined with the observation of airdrop video, the viewpoint of forming the bull whipping phenomenon were proposed, one essential factor is the velocity difference between the upper and bottom segment of lines, the other is the linesail phenomenon of lines and canopy, this viewpoint was validated by simulation results also.The dynamic stability of the parachute recovery systems was researched. The conclusion that the attitudes of parachute recovery system were interrelated with the aerodynamic coefficients, especially the lateral force coefficients of parachute were educed through simulate analysis, and the different aerodynamic models of stability and instability for the parachutes were summarized. The different modes of attitudes were analyzed with different wind models and aerodynamic models in simulation, and finally the basic motion patterns of single point suspension and double point suspension were researched and summarized by the airdrop video and experimental data.The problem of aerodynamic coefficients identification of large parachute was researched. For the difficulty in measuring the kinematics parameters of parachute, this dissertation proposed a method to estimate aerodynamic coefficients of the parachute. The validity of the method was verified through simulation analysis, and a method which improved the precision by decreasing the searching space was presented. Combined with the experimental data of airdrop video, a more precise set of aerodynamic coefficients of the main parachute of ShenZhou-8 manned spacecraft was identified, and the result was validated by experiment. The results indicate that the identification results were more precise than the originally ones, and the attitudes of main parachute in simulation were basically consistent with the airdrop video.