Key Components' Damage Dynamics And Damage-Mitigating Control Techniques For Reusable Liquid-propellant Rocket Engines

In order to develop the concerned techniques about reusable liquid-propellant rocket engines, taking certain LOX/Kerosene rocket engine as the object investigated, some main aspects of engine damage-mitigating control (DMC) such as system dynamics modeling and simulating, critical components'structural dynamics and damage dynamics modeling and simulating, synthesis of the rocket engine DMC law and on-line DMC method based on fuzzy logic have been studied in this dissertation. The theory and techniques developed in the dissertation can be used to improve and enhance engine's system reliability, structural durability of critical components, and service life of the rocket engine. The results can also provide valuable reference for optimizing the scheme of startup process, state regulating process and shutdown process of reusable liquid-propellant rocket engines.The system dynamics model of the LOX/Kerosene rocket engine was built by using standard lumped parameter methods. Based on the model, a universal simulation software for the rocket engine based on Matlab/Simulink was developed which can be applied to simulate the whole process of the rocket engine. Different operating schemes of the startup process, state regulating process and shutdown process were simulated by using the software. The results show that the setup of flow regulator's startup mass flow-rate, flow regulator's change rate and end mass flow-rate has an important influence on characteristics of the transient process of rocket engine. The influence of these factors on the reusable liquid-propellant rocket engine is not only dynamic performance, but also damage evolving process of the critical components.The structural and damage dynamics models of coolant channel ligaments (CCL) and turbine blades (TB) were also built. Based on these models, CCL and TB damage evolution law during the startup process, state regulating process and shutdown process were investigated. Some important results have been obtained. For examples, the damage of CCL and TB evolving is slow during steady state, while the damage accumulation of CCL during startup process, HTL process (a regulating process from high operating condition preseted to low operating condition preseted) and shutdown process is very obvious. In addition, the damage accumulation of TB during startup process and RTH process (a regulating process from rated condition to high working condition preseted) is also obvious. The results indicate that DMC of the rocket engine should put emphasis on the transient processes. The effects of material property and geometrical dimensions of CCL on damage evolution of CCL, the effects of flow regulator's mass flow-rate and change rate on damage evolution of CCL and TB, were all studied. The results show that different schemes of startup and state regulation can make distinct damage accumulation of CCL and TB. Optimizing these schemes is very valuable to improve reliability and structural durability of critical components.It is presented and clarified that analysis and synthesis of DMC law can be dealt as a muti-objectives optimization. For DMC of liquid-propellant rocket engines, three objective functions including performance function, damage of CCL function and damage of TB function can be constructed. The optimized control input sequences are the DMC laws. The theory and methodology of analysis and synthesis on the DMC law based on multi-objective particle swarm optimization is clarified and discussed with simulation computation. The results show that: (i) the optimized control input sequences can reduce the damage accumulation of CCL and TB during the transient process such as startup process, RTH process and HTL process by insignificant sacrifice on the system performance; (ii) appreciable loss on the system performance can considerably reduce damage accumulation of TB during startup process, but it may not work to CCL.In order to develop on-line damage-mitigating control method, the design and realization of the intelligent damage-mitigating controller (DMCer) based on fuzzy logic, which can reduce both CCL and TB's damage accumulation, were also discussed and studied. The results of simulating computation with the DMCer for the rocket engine show that: (i) the DMCer can monitor the damage of the CCL and TB, and take proper DMC law in time if necessary; (ii) the DMCer can reduce the damage accumulation of CCL and TB during startup process, RTH process and HTL process with insignificant loss on system performance, and the effect of damage reduction will be more obvious along with the damage evolving.