Analysis Of The Influence Of Structural Uncertainty On The Launch Vehicle Dynamics

The dynamic characteristics of the launch vehicle are the basis for its load calculation,attitude control and POGO analysis.It has a critical effect on the successful launch of the rocket,is a key link in the design of the launch vehicle and of important engineering significance.The launch vehicle is huge in size and complex in structure.The uncertainty errors will inevitably occur during its manufacture,installation and transportation,which would directly affect the accuracy and availability of its dynamic analysis results.So it is necessary to consider the influence of structural uncertainty when carrying out dynamic analysis of the launch vehicle.However,it is very difficult to obtain the overall dynamic characteristics directly,and it takes a lot of human and material resources whether it adopts experimental or simulation methods.In consideration of the above problems,this master thesis uses a component mode synthesis(CMS)method to study the influence of the uncertainty of the various sections of the launch vehicle and the bundle connection structures on the overall frequency of the launch vehicle.Then,a software platform is developed on this basis.CMS method significantly reduces the analysis cost,and the software platform provides convenience for the analysis of the subsequent series of rocket models.The main contents of this thesis are as follows:1)The development process and theoretical content of the fixed interface method and the free interface method are introduced,meanwhile,the principle and implementation of the superelement analysis module in MSC NASTRAN are also explained by examples.Then,an overall simplified and locally refined finite element(FE)model of the launch vehicle is established,and the CMS accuracy between different division schemes are compared.2)The influence of component uncertainty on the overall dynamic characteristics is studied.Firstly,based on the FE model of the launch vehicle,the mode slopes at the key positions are calculated.By modifying the specific order frequencies of the representative structures such as core level and boosters,the effect of frequency deviation of different substructures on the overall dynamic characteristics is studied.This work simplifies the analysis method of the impact of structural uncertainty and has certain guiding significance for the project.3)The uncertainty of the main bundle connection structures is studied.The bar element and ball hinge modeling scheme is adopted to establish the FE model of the main bundle connection structures,and the uncertainty is investigated by random parameters methods.The material properties of the main bundle connection structures are evenly distributed in the specified interval.The CMS results obtained by the Monte-Carlo method illustrate the influence of the main bundle connection structures uncertainty on the overall frequencies.4)The CMS software LVSyn_SiPESC is developed through the PyQt program package to solidify the CMS module and the structural uncertainty influence calculation module.The software is convenient for users to divide the structures and choose CMS forms independently.The software is efficient and concise,and it makes the analysis process streamlined.