모드합성법과 수학적 방법을 이용한 연결보 진동해석 연구

Abstract

In accordance with the recent trend of eco-friendly systems in the shipbuilding market, new equipment such as tanks for LNG propulsion, SCR (Selective Catalytic Reduction), and EGR (Exhaust Gas Recirculation) systems that can treat harmful elements of exhaust gas are arranged in hull structure near the ship's main engine. And equipment and structures are inevitably exposed to vibration due to the main exciting force during ship operation. If a vibration problem occurs after construction or delivery, there is a large loss in terms of ship quality such as reinforcement cost and delivery delay. Therefore, it is necessary to review the anti-vibration design to prevent such vibration problems in the design stage. Analytical method using Rayleigh-Ritz method has not been widely used recently due to intensive use of FEM. However, analytical method is still useful, if suitable mode functions can be provided. Vibration analysis of many local structures in ships such as tanks and supports for equipment can be simplified by breaking up into smaller sub systems which are related through geometrical conditions and natural conditions at junctions. In this study, Polynomials for simple supports and fixed supports are suggested to represent each subsystem. It is found that suggested mode functions improve convergence so that component mode synthesis together with suggested mode functions can widely be used. Frequently, only specific sub-component is more concerned for vibration analysis. In this case, the suitable boundary conditions to consider the static and dynamic coupling from the other sub-component through junctions should be provided. However, the suggestions for such boundary conditions are hardly found. In this study, a boundary condition that can be easily calculated through elimination of generalized coordinates by imposing the satisfaction of each mode at junctions as a constraint condition is proposed.