Research On Wheel Mounted Artillery Airdrop System Dynamic Simulation

With distinctive features of high cost performance ratio and high mobility,wheel mounted artillery for airdrop can also implement campaign and strategy maneuvering through aircraft.Therefore,the equipment is developed by many countries.As one of the key technologies in wheel mounted artillery,the airdrop deceleration system will have a direct influence on the combat mission once it malfunctions.As a result,mechanics design and simulation analysis on airdrop system is a critical part for airdrop system development and wheel mounted artillery design.Airdrop system consists of key parts including extractor chute,pilot chute,drogue chute,drag parachute,artillery cargo,airbag and so on.The whole airdrop process includes the wheel mounted artillery extraction phase,the main parachute deployment phase,the main parachute inflation phase,the steady descent phase and the airbag execution phase.However,what should be noted is that there exits plenty of fluid structure interaction simulations to carry out during the phases of deployment、inflation and steady descent.Above all,there exist great challenges in simulation and analysis which are as follows.For one thing,the structure and motion patterns of the parachute are constantly changing.For another,the cost of analyzing and computing on the whole fluid structure interaction is considerable,and it will be quite difficult to preprocess and solve.With the problems mentioned,the following are the main contents of the research.First of all,during deployment phase,the length of the main parachute is constantly changing,which belongs to the problem of variable structure.Due to the fact that the fundamental principles of mechanics are primarily conceived for constant-mass systems,an absolute nodal coordinate variable length cable element is developed and discussed to study the dynamic feature of deploying parachute.It is found that the prevailing variable finite cable element formulation may lead to the divergence of rigid motion.Finally,the divergence analysis is performed and numerical examples are presented to study the divergence effect and its application scope.Second,during the inflation phase,the volume of the main parachute undergoes huge change,meanwhile the parachute interacts with the air fluid,which belongs to fluid structure interaction(FSI).As a result,an axi-symmetric parachute inflation model based on FSI is presented,which means that an axi-symmetric absolute nodal coordinate formulation(ANCF)membrane element is applied to coupling with the incompressible Navier-Stokes solver.In addition,the structure model uses a criterion that becomes active at consecutive nodes on the taut and wrinkle surfaces.The criterion is obtained through three dimensional finite element method.Special C1 continuum techniques are employed to improve numerical stability of this computational module without adding artificial damping.The numerical solutions have been compared with the available experimental images and data,and there are good agreements in the opening forces.It also turns out that the newly-built model has many advantages such as less calculation and easier to build.It also make it possible to analyze the control process of parachute reefing.Third,during the steady descent phase,elasticity deformation of the main parachute is quite limit,and under the influence of random loadit features rigid motion.Therefore,it is necessary to observe the response of the parachute with the random load.Since the wind effects have a significant impact on the land site distribution of this passive decelerator system during steady descent phase and it is difficult to obtain the exact wind profile in practice,major features of parachute payload system are studied via the randomized wind gusts formulation.It is considered that the wind is composed of mean velocity wind and random wind gust which is generated through random sequence.In order to avoid encountering singularity in solution space,a method combining group propagator and Runge Kutta method is proposed.With the proposed method,there will be no singularity in solution space and it becomes possible to always keep the rotating matrix belonging to rotating group S03 during integration with large integrating step size.Fourth,carry out the fluid structure interaction modeling research on wheel mounted artillery airdrop system.Due to the fact that the airdrop platform will undergo severe oscillation during the deployment and inflation phases,a platform-sling model is established to study the dynamic response of the airdrop platform.A uniform equivalence point Newton-Rapshon iteration method is presented and is applied to the dynamic practice.In order to study the unsteady fluid behavior,the time domain is discretized and an ALE base finite volume method is used to solve the NS equations.The aero-force is obtained and imposed on the platform.The equivalence point method is validated through commercial software RECURDYN.The results manifest that the equivalence point method can well represent the slack-taut cases of the sling system.It can also be found that the layer model fits the experiment well at low Reynolds number cases.Finally,the comparisons are made between the steady and unsteady FSI models.The time history of unsteady fluid force displays severe oscillation while the steady fluid force varies evenly.Finally,model and simulate the whole process of airdrop.Depending on the states of the main parachutes,the airdrop process is analyzed through five phases,including the wheel mounted artillery extraction phase,the main parachute deployment phase,the main parachute inflation phase,the steady descent phase and the airbag execution phase.The governing equations are given through these five phases.Finally,the airdrop process is simulated and the results are given and discussed.