Studies On Structure Dynamics Design Technology Of The Large Thrust Liquid Rocket Engines

The liquid rocket engines with large thrust are the main powers for the momentous space activities of manned lunar and deep space exploration,its performance and reliability are directly related to the development of China aerospace industry.The large thrust engine has complex structures and harsh service environment,which cause prominent structural dynamics problems.It has an extremely important impact on the reliability and safety of the engine itself and the rocket.The structural dynamics problems in engine have always been one of the hotspots and difficulties in carrying propulsion system researches,and the structural dynamics becomes a fundamental science for solving the key technology problems of the engines.Therefore,the paper focuses on the engineering requirements of structural dynamics design in the engine development process,the studies on the dynamic characteristics,dynamic response and dynamic optimization design of engine structures were carried out,and the work has important theoretical significance and engineering application value.Aiming at the complexity of the engine structure,the harshness of the working environment,and the unpredictability of the dynamics characteristics and the dynamic response,the high-precision and high-efficiency dynamics modeling,model updating,optimization design,startup shock response and acoustic-vibration coupled intense vibration for the large and complex structures,thus studies were carried out.A more precise,efficient and practical structural dynamics design technology for the large-scale liquid rocket engine was proposed.The main work and conclusions are as follows:(1)Based on the modal synthesis theory of Craig-Bampton(C-B)fixed interface and a multi-level dynamic substructure method,an engineering realization method were proposed to use the external superelement technology for dynamics modeling and analysis of the complex large system.Through the modal comprehensive analysis of structural dynamics of a four parallel connected liquid rocket engines and the modal test verification of the whole machine structure,the reliability of the multilevel dynamic substructure method for dealing with complex structural dynamics was proved.Research shows that the multi-stage dynamic substructure method is convenient and flexible,and it can improve the modeling and solution efficiency greatly under the precise of ensuring the analysis accuracy.The technology is an effective method to study the dynamics problems of large complex structures.(2)A finite element model updating method for large-scale complex structure based on an improved simulated annealing algorithm(ISAA)was proposed.A process of finite element model updating was established,which includes model matching,correlation analysis,objective function construction,updating parameters selection based on sensitivity analysis,updating effect evaluation,etc.The ISAA was adopted by setting a memory and linking a local search process after the algorithm.The model updating software of structural dynamics,ZDXZ-V1.0,was developed based on MSC Patran/Nastran software platform.The analysis results show that the proposed model updating method meets the requirements of the model updating standard and has high quality and efficiency.It indicates that the present method is suitable for model updating of large complex structures.(3)An intelligent fast combination optimization strategy was proposed,which is based on combination of the hierarchical Kriging model to the multi-island genetic algorithm(MISA)and the nonlinear quadratic programming(NLPQL).The hierarchical Kriging model based on Kriging model theory,experimental design method,model validity test and update criterion,and MISA+NLPQL algorithm combination optimization strategy were studied.Through dynamics optimization and modal test of the engine structure,it was proved that the optimization method can improve the optimization efficiency greatly under the premise of ensuring the accuracy of the results.The proposed modeling strategy and optimization ideas have universality and superiority in engineering applications,and can provide some novel insights for dynamics optimization problems of large complex structures.(4)Based on the direct transient response analysis method and the Johnson-Cook(J-C)material constitutive model,an analytical method of starting impact dynamics for engine structure was established.The impact dynamics theory based on direct method and modal transient response analysis was studied,the shock load environment of engine starting was analyzed,the J-C material constitutive model was established.The impact dynamics of the engine structure was also studied.The results show that the direct transient response analysis can accurately simulate the impact dynamic response behavior of the engine structure.The J-C material constitutive model has a true characterization for the response process of material.The dynamic response behaviors of engine structure to strong impact load excitation were obtained.The analysis method of impact dynamics can predict the dynamics response characteristics of the engine structure accurately,and provide a reference for the explosion impact test and experimental simulation of other engineering structures.(5)An analytical method of acoustic-vibration coupling and an acoustic-vibration optimization design were proposed for high-amplitude vibration problem in the combustion chambers of large-thrust liquid rocket engines.A vibro-acoustic coupling analysis model for the combustor was established.Through the research,the combustion chamber acoustics,structural vibration,dynamics characteristics and dynamic response laws of acoustic-vibration coupling were obtained.The analysis results reveal the mechanism of intense vibration under the coupled resonance of acoustics and vibration.Finally,a technology of acoustic vibration optimization design was proposed for suppressing intense vibration of engine thrust chamber structure,and it was achieved by decoupling the acoustic-vibration coupling mode in combustion chamber.The results show that the anti-resonance margin of the improved structure become lager than 7.5% and the simulation indicates that the maximum frequency division amplitude of the vibration acceleration in the test state can be reduced by about 60%,which verify the effectiveness of the improvement measures.Furthermore,the results can provide theoretical support for the structural dynamics and acoustics design of combustion chambers of liquid rocket engine.