Analysis of the dynamic characteristics of three-layer shells with discrete filler
The problem is posed to study dynamic characteristics of a three-layer cylindrical shell with the discrete filler, which is a regular system of cone-shaped (or pyramidal) cells arranged in a checkerboard pattern. Three-layer structures in various technical objects often have a honeycomb filler’s structure are widely used. Despite the obvious advantages of honeycomb filler (low weight, high rigidity), there are circumstances that prevent their wider use. The closed cellular structure prevents the removal of condensate entering the internal space. And the complexity of ensuring and controlling reliable connection of the aggregate with the bearing layers (especially on curved surfaces) increases their labor intensity and cost. The proposed discrete structure largely allows you to solve the above problems. The design features influence of the of this three-layer shells type on the stress-strain state and stability under static loading has been studied in sufficient detail earlier. A complete solid-state and FE-model of the investigated shell has been constructed. A modal analysis of the cell design was carried out as a next step, and then, having selected the zones of interest, the frequency response of the structure was investigated in order to plot the frequency response and frequency response. The NASTRAN solver is used to calculate eigen-modes and frequencies, the analysis type is set to Normal Modes / Eigenvalue. The geometry of the model was built using PLATE elements. In three-layer structures, the dynamic characteristics can be changed by varying the thickness of the bearing layers or filler and, thus, to obtain the optimal weight, damping, and also radio-technical parameters. To determine the frequency response, a harmonic Frequency / Harmonic Response analysis is performed. It allows you to evaluate the response of the structure with a sinusoidal action. To assess the considering filler structure feasibility a comparative analysis of the dynamic characteristics between smooth and three-layer shells of equal dimensions material, was carried out. Based on the obtained results, it can be concluded that with an thickness increase, and, accordingly, the filler rigidity, the natural frequency decreases, however, with an increase in the bearing layers thickness, an increase in the values of the natural frequencies is observed. Also noted that main vibrations emanating from gas turbine engines are in the range up to 5000 Hz, and the cone-shaped structure is preferable for use in places subject to dynamic loads.