Dynamic Reduced Order Model Of Complex Slender Structures

With the advancement of aerospace technology,the launch vehicle technology has also developed rapidly.In the overall design stage of the launch vehicle,structural dynamics design is an important part of the overall design stage,and it is the basis for the design of the dynamic load design and mechanical environment design of the launch vehicle.In the structural design stage,the combination of computer-aided engineering(CAE)and experiment is generally used to make the data confirm each other and shorten the development cycle.For the general model of the launch vehicle,it has the characteristics of slender structure and complex internal structure,which is prone to bending deformation during the flight phase,which brings control problems to the rocket.Moreover,the mass of the liquid in the internal tank of the launch vehicle accounts for more than 80% of the total mass of the structure,which brings problems such as fluidsolid coupling stability and hydrodynamic elasticity to the flight.In view of the above problems,it is of great significance to study the reduction and simplification of the launch vehicle and the fluid-solid coupling analysis.In this paper,the fluid-solid coupling analysis of the liquid tank of the launch vehicle and the simplification and reduction of the dynamic model of the complex slender structure are studied.Firstly,the virtual mass method and the acoustic-solid coupling method are combined and the liquid-solid coupling simulation is realized in MSC.NASTRAN,which reflects the coupling characteristics of the propellant liquid sloshing and the tank,and analyzes the difference and relationship between the two methods.Then,According to the method of physical reduction,the elongate rocket is reduced to a one-dimensional beam model,which not only achieves the purpose of reducing structural freedom,but also reflects the important beam deformation during the flight of the launch vehicle.Finally,the application of the component modal synthesis(CMS)reduces the computational complexity of the three-dimensional finite element model analysis and improves the computational efficiency.Modal analysis,transient analysis,and steady-state analysis of the overall structure.The specific work is:1)Fluid-solid coupling analysis of liquid tank based on virtual mass method and acoustic-solid coupling method.Firstly,a finite element model of the carrier rocket structure and its internal liquid coupling is established.Then,combining the theory of acoustic-solid coupling and virtual mass theory,the differences and connections between the two are pointed out and implemented in MSC.NASTRAN.Finally,a numerical example is used to analyze the virtual mass method and the acoustic-solid coupling method to verify and compare the differences and connections between the two.2)One-dimensional equivalent reduction of the launch vehicle finite element model based on the local rigid body method.First,the launch vehicle geometry model and the finite element model are established.Then,it is proposed to equivalent the carrier rocket with structural slender characteristics into a one-dimensional beam model.Finally,the results of the reduced beam model are compared with the results of the original finite element model,and the correctness of the reduced order method is verified by the vibration mode correlation.3)Based on the component modal synthesis,the modal,transient and steady state analysis of the launch vehicle.First,the component modal synthesis is implemented in MSC.NASTRAN.Then,the modal synthesis method is used to analyze the sub-structure modal analysis and transient analysis of the launch vehicle finite element model.Finally,the modal synthesis method results are compared with the original model calculation results to highlight the advantages of the substructure.4)Calculating the fluid-solid coupling problem based on the virtual mass method is more efficient and accurate than the acoustic-solid coupling method.The virtual mass method is used to analyze the modal frequency of the launch vehicle under the condition of tank filling,and compared with the calculation result of the unloaded launch vehicle model,it is concluded that the liquid has a greater influence on the overall modal frequency change.The conclusion that the rocket cannot be ignored in the finite element analysis.