Study on High Cycle Vibration of Ship Structure

船体结构是由多个加筋板组成的复杂的钢结构。船舶结构的高周振动是由螺旋桨和主机等推进器引起的，很容易传递到上层建筑和水箱等局部结构中。在这些储罐中有时也可以观察到疲劳损坏，这似乎是由共振引起的。为了预防这些问题，开展了以下研究。提出了一种新的分析方法：(1)用子结构方法分析船体与主机之间的动力相互作用；(2)考虑发动机运动部件的影响；(3)激振力对振动响应的贡献。证明了竖井激振力的特性对其有很大的影响。分析了加筋板的振动特性，研究了加筋板的主要振型。在多层优化中，本文提出的简化方程改变了加筋板的动力特性。结果表明，计算结果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储罐受到附加质量的水的强烈影响。我们开发了一种用板的有限元和流体的边界元进行振动分析的数值工具。通过数值模拟，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。重点研究和阐明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.