Research On Aerodynamic Thermal Ablation Prediction And Control For Hypersonic Vehicle

Hypersonic vehicle as a high order nonlinear system has the characteristics of strongcoupling, uncertainty, time-varying and unique aerodynamics. So it is a severe challengeto predict and control ablation during reentry flight. However, hypersonic’s special char-acteristics such as complex reentry environment, Serious aerodynamic thermal ablation,multidisciplinary cross and higher flight control requirements make it attracts the exten-sive research of scholars at home and abroad, and also has focused on significant strategicvalue and application prospect for military applications in the countries. Therefore, thereentry flight modeling and characteristic analysis of hypersonic vehicle, aerodynamicthermal ablation prediction and ablation control strategy is introduced and in-depth re-search in this dissertation. The main research content and primary innovation of thisdissertation can be summarized as follows:1. Based on the research contributions at home and abroad, the background of thehypersonic vehicle is introduced. And then, the research status of the aerodynamic abla-tion, fault and ablation control and advanced flight control technology is mainly describedand analyzed.2. A very specific analysis of the kinetic equation and aerodynamic characteristicsof the hypersonic vehicle is given, then a six degree of freedom nonlinear mathematicalmodel and reduced-order model of reentry flight is established, and then a three degree offreedom nonlinear mathematical model of ballistic reentry flight is also built. The resultsof simulation verify that the establishment of the model has the characteristics of thecomplex nonlinear, coupling and time-varying, and so on.3. By using the established mathematical model, the predicted problem of thermalprotection material subject to the dynamic change of the ablative depth and tempera-ture is presented in the reentry process. According to the designed geometric parameterof the heat shield, the engineering prediction method for calculating the ablation mass,the aerodynamic heating and thermal radiation is studied, and then the algorithm ofdynamic analytic ablation is proposed based on the Newton-Raphson and TDMA, anda one dimensional nonlinear heat conduction model is employed to simulate the processof the ablation. Furthermore, The influence of control surface on the ablation and the optimization method of the building a new aerodynamic blance under the fault conditionis elucidated. The results of the proposed method are reliable and reasonable by compar-ing with heat balance integral method, and is able to realize that the dynamic change ofsurface protection material ablation and surface temperature in the whole reentry, andalso provides more accurate prediction for the estimation of the ablation mass and thereal-time ablation control of dynamic control surface.4. It is studied on the basis of reconstitution aerodynamic balance under the condi-tion of actuator fault, the combination of ablation prediction and fault-tolerant controlmethod subject to unpredictable ablation problem result from the fault of the uncon-strained control surface is considered. A adaptive output feedback controller is presentedbased on control surface fault model. By this controller, the non-parametric time-varyingfailures can be realized by the way of adaptive process, and then the estimated gain canbe directly used in the feedback loop. Therefore, The stability and robustness of theclosed-loop system is enhanced. In order to solve the problem of disturbance decoupledfault, the disturbance observer and fault reconstruction control is designed. This ap-proach can be beneficial to evaluate the severity of the fault and provides an efcientobservation method to implement fault accommodation. Simulation results show thatthe combination of adaptive output feedback controller, reconfiguration aerodynamic co-efcients and ablation prediction can ensure the dynamic ablation to track the predictivetrajectory, efectively reduce the ablation increment caused by faults, and also verify thatthis ablation control framework is a kind of passive ablation control method.5. The unpredictable of dynamic ablation increment in time is because that thesaltation of reentry trajectory resulting from the fault of unconstraint control surface.But, constraint control surface is equivalent to limit the ablation increment. Hence, themethod of ablation prediction combined with robust model predictive control with on-line control allocation is proposed. This approach is capable of redistributing the controlsurface among healthy actuators in a stable manner by control allocation scheme, and theof-line robust observer is applied to improve the ability against disturbances of the closed-loop system. By designing the ofset-free model predictive controller, the constraints ofsystem states and the control surface can be realized and the model mismatch problemis also resolved. This control framework can not only guarantee the robustness andstability of the system, but also by limiting the maximum-minimum angular deflection of the control surface to avoid the unpredictability ablation cased by faults, and achievethe purpose of active control with online correction ablation increment.Finally, the main results of the dissertation are concluded and some issues for futureresearch and exploration are proposed.