Degtyarev K. Static and dynamic characteristics of structure elements in space technologies considering plasticity and hydro-elasticity effects

The thesis is devoted to solution of the scientific and practical problem that consists in developing methods for estimation of destructive loads on shell structures taking into account plastic deformations of materials and methods for simulating tank vibration frequencies taking into account the effects of hydro-elasticity under different operating conditions. Based on equations of continuous medium motion, a unified approach to solving boundary value problems has been developed by using the method of weighted residuals and receiving the resolving relations based on finite and boundary element methods. In the obtained relations different dependences between stresses and strains or strain rates are used. Continuous and discrete models are obtained to determine the frequencies and modes of free vibrations of shell structures with compartments partially filled with compressible viscous fluid, taking into account the elasticity of walls, liquid sloshing, different levels of filling and overloads. The fuel tank of the launch vehicle’s second stage was studied in order to determine the natural frequencies of structures and sloshing of the liquid free surface under different operating conditions. The dependences of the frequencies on the level of gravity in the flight of the first stage, and depending on the flight time in the flight of the second stage, taking into account the elasticity of the walls and different levels of overload, are received. The strength of pressure vessels under the simultaneous action of internal pressure and compressive force on the tank lid was studied. The method for determining the destructive load has been developed. The computer virtual test reproduced the scheme and methodology of the field experiment. Various finiteelement calculation schemes were proposed in order to take into account the design features and the possibility of simplifying both the virtual and field model of the tank. The calculation results on the refined three-dimensional model almost coincide with ones for simplified models. That allowed us to conclude about possibility of using simplified models not only in virtual but also in field full-scale tests. The estimate of the stress-strain state of the cylindrical shell with the periodic system of holes is given, destructive loads are obtained and the moment of cracking is determined. With the help of computer simulation, a design of the smallest thickness that can withstand the specified intense short-term loads was proposed.