Study on High Cycle Vibration of Ship Structure

船体结构是由许多加劲钢板组成的复杂钢结构。船舶结构中的高周期振动是由螺旋桨和主机等推进装置引起的，并且很容易传递到上部结构和水箱等局部结构。疲劳损伤有时也可以在这些储罐中观察到，这似乎是由共振引起的。为了预防这些问题，进行了以下研究。采用子结构法分析船体与主机之间的动力相互作用，考虑发动机运动部件的影响，分析振动响应，以及分析激振力对振动响应的贡献。结果表明，轴向激振力的特性受到较大影响。研究了加筋板的振动特性，研究了几种主要的振动模态。在多级优化中，提出的简化方程改变了加筋板的动力特性。结果表明，该方法对加筋板动力特性的优化修正是有效的。位于发动机或螺旋桨附近的薄壁舱受到所增加的水质量的强烈影响。我们开发了一种振动分析的数值工具，用有限元分析板的振动，用边界元分析流体的振动。数值研究了含水附加质量和板间结构约束对结构振动特性的影响。重点研究了水箱呼吸模式的固有频率和动水压力。

A ship hull structure is a much complicated steel structure which consists of many stiffened this plates. High cycle vibrations in the ship structure are originated by the propulsion such as a propeller and a main engine and are easily transmitted to the local structures such as a superstructure and water tanks. Fatigue damages can also be sometimes observed in these tanks which seemed to be caused by resonance. In order to make prevention of these problems, following studies have been carried out.1. We developed new method that is to analyze (1) Dynamic interaction between ship hull and main engine by means of substructure approach, (2) Vibratory response considering the influence of moving parts in engine, and (3) Contribution of exciting forces to the vibratory response. We proved that the characteristics of the exciting force from the shaft is much influenced.2. The vibration characteristics of the stiffened plate is examined, and some main vibration modes are studied. In the mult-level optimization, the dynamic characteristics of the stiffened plate is changed by the proposed simplified equation. It is shown that the results are effective in the optimum modification for dynamic characteristics of the stiffened plate.3. Thin walled tank located near the engine or propeller are strongly affected by the added mass of containing water. We have developed a numerical tool of vibration analysis using finite elements for plates and boundary elements for fluid. The effect of added mass of containing water and structural constraint between panels on the vibration characteristics are investigated numerically. Especially natural frequencies and hydrodynamic pressure of breath mode of the water tank are focused on and clarified.