Analysis Of Structure Vibration Characteristics Of A New Type Of Engine

The liquid rocket engine studied in this paper is a new generation of heavy thrust vehicle core three-stage engine being developed in China.In this paper,the engine is taken as the research object,the finite element model of the whole engine is established,and the vibration characteristics of the whole engine are studied.In order to ensure the accuracy of the model and modeling method,this paper uses Abaqus software to build a finite element model of an upper stage engine,and to carry out modal analysis.By comparing the results of modal calculation with the results of modal test,it is found that the error of modal frequency is less than 15%,which meets the requirements of overall modeling.It is considered that the modeling method is feasible and applied to the liquid rocket engine.The liquid rocket engine studied in this paper is modeled by finite element method and modal analysis is carried out.The results show that the first-order frequency of the engine is low(about 6Hz),and it is easy to couple with the longitudinal vibration frequency of the rocket and the actuation frequency of the servo mechanism.In order to avoid coupling vibration,it is necessary to improve the first-order frequency of the engine.The overall frequency of the engine is mainly determined by the main structure including frame,thrust chamber and nozzle.Since the performance parameters of the engine are determined by the thrust chamber and nozzle,it is difficult to change the structure once the overall scheme is determined.Therefore,this paper proposes to improve the design of the frame only.Combining the docking schemes between engine and rocket abroad,the force transmission structure schemes of frame abroad,three kinds of frame improvement schemes,namely truss type,shell type and shell-beam type,are proposed.The modal calculation of the engine with three types of frame is carried out.Through comparative analysis,the optimum frame improvement scheme is selected,and the static strength of the improved frame is checked.According to the requirements of the rocket and the strength of engine itself,the engine needs to be tested for vibration.In this paper,according to the predicted vibration environment test conditions of the engine,the whole engine’s harmonic response is analyzed by using the improved frame,and the vibration response of each component under low frequency sinusoidal excitation within 100 Hz is obtained.Due to the limitation of the computational hardware,the random vibration of a single engine is analyzed,and the random vibration response of each component of a single engine is obtained.Through the above analysis,the response of each component under vibration excitation is obtained,the weak links in the design and the key points in the subsequent vibration test are found out,which provides a basis for improving the design.The static and dynamic strength analysis and random vibration fatigue analysis methods of liquid hydrogen pipe I and gas hydrogen pipe II on the engine are studied.The influence of mesh density on strength calculation is analyzed.On the basis of static and dynamic strength analysis,random vibration fatigue analysis of pipes is carried out by frequency domain analysis,and the engineering feasibility of this fatigue analysis method in fatigue life prediction of pipes is discussed.