Bashliy I. The oscillations of a complex shell structure with a liquid in the problem of launch vehicle longitudinal stability

The research subject is the longitudinal oscillations of a complex shell structure of fuel tanks of liquid launch vehicle at the acting part of the launch vehicle flight. The objective is to development of a method of determining the parameters of oscillations and stressed-strained state of the shell elements of launch vehicle stage structures under longitudinal instability. The research method is a finite element method, numerical methods of linear algebra, methods of automatic control theory and theory of oscillations mechanical system. The study developed the scientific and methodic support for theoretical determining the dynamical loading on the liquid launch vehicle structure during longitudinal oscillations. Practical importance of the results obtained. Received results can be applying during designing modern hauling unit inclusive tanks with a liquid and during optimization its structure. Research novelty. The method of determining the stressed-strained state and dynamical loading on the shell elements of launch vehicle structures under longitudinal instability during working time of first stage propulsion system. Feature of proposed method is the determining of the forces, acting on the stage structure of liquid launch vehicle during longitudinal oscillations subject to non-steady-state of dynamical system propulsion system - structure of launch vehicle and non-linearity of dynamical units of propulsion system are due to cavitation phenomena in the propulsion system pumps. Mathematical modeling of space oscillation liquid launch vehicle upper-stage with spheroconical configuration fuel tanks, which is the complex system shell structure with liquid, was executed. The parameter of natural longitudinal oscillations of stage with different liquid levels in tanks and the stressed-strained state of the shell elements of the tanks structure during longitudinal oscillations. For the first time for complex shell structure with liquid the dependences of oscillations amplitudes of liquid pressure at the tank's bottom on frequency of longitudinal structure excitation was determined taking into account dynamic interaction of conjugate tanks and liquid oscillations decrement. The quantitative assessment of influence of design features spheroconical fuel tanks developed upper-stage (conjugation of surface of tank shell structure, existence of additional cylindrical inserts) on parameters of natural longitudinal stage oscillations was determined. Applications: designing of modern hauling unit inclusive tanks with a liquid and optimization its structure.