Study on High Cycle Vibration of Ship Structure

船舶船体结构是由许多加筋板组成的复杂钢结构。船舶结构中的高循环振动由推进器（例如螺旋桨和主机）引起，并且容易传递到局部结构（例如上层建筑和水箱）。在这些坦克中有时也可以观察到疲劳损伤，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：1.本文提出了一种新的分析方法：（1）用子结构法分析船体与主机的动力相互作用，（2）考虑主机运动部件影响的振动响应，（3）激振力对振动响应的贡献。证明了轴向激振力的特性对系统的性能有很大的影响.分析了加筋板的振动特性，研究了加筋板的几种主要振型。在多级优化中，通过所提出的简化方程改变加筋板的动力特性。结果表明，本文的研究结果对加筋板的动力特性优化修改是有效的.位于发动机或螺旋桨附近的薄壁贮箱受到所含水的附加质量的强烈影响。我们已经开发了一个振动分析的数值工具，使用有限元板和流体边界元。通过数值计算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。重点分析了水箱呼吸模态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.