Modal analysis of a complex shell structure under operational loads
Keywords:elastic shell, universal finite element, thermo-mechanical load, stress-strain state, natural frequency, mode shapes
The results of calculation of a complex shell structure under the action of operational loads are presented. A three-section cooling tower, called a three-petal cooling tower, is regarded as a complex-shaped structure. Three variants of loads on the shell are considered: wind pressure, heating and load combination. The design model of a shell of a complex shape is based on the developed universal spatial finite element. The universal spatial finite element allows one to take into account the geometric features of structural elements for a thin shell (constant or varying thickness, knees, ribs, cover plates, holes, cavities, channels, inserts, facets) and multilayer structure of the material. According to the method, thin and medium thickness shells of various shapes and structures are considered. The shells are under the action of static mechanical and temperature loads. The finite element method is based on the unified positions of the three-dimensional geometrically nonlinear theory of thermoelasticity and the moment finite element scheme. The method for determining the natural vibrations of thin-walled shell structures is based on an integrated approach. Modal analysis is carried out taking into account the prestressed and deformed states of the shell at each step of thermomechanical loading. Thus, the problem of determining the natural frequencies and vibration modes of the shell is solved by the step method in two stages.
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