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Simplified estimation of stress transfer function taking account of phase difference between stress components caused by internal and external pressures in fatigue strength design of ship structure

船舶结构疲劳强度设计中考虑内外压力应力分量相位差的应力传递函数简化估计

基本信息

批准号：
13650973
负责人：
FUKASAWA Toichi
金额：
$ 2.18万
依托单位：
Kanazawa Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

In the fatigue strength evaluation of a ship structure, the crack growth analysis tends to be adopted recently instead of the cumulative fatigue damage analysis such as the Miner's law. The crack propagation can be simulated by means of the stress time history of a certain structural member of a ship in waves. The time history of stress can be obtained by using the stress transfer function, however, there exist some practical difficulties to calculate the stress transfer function.Since the stress of a certain structural member is resulted by multiple loads due to hull girder bending, internal pressure of cargo or ballast water, external sea pressure caused by wave, and so on, it is necessary to superpose the stress caused by each load taking into account of the phase lag between each stress component caused by each load. It is, however, not easy to calculate both the amplitude and phase of stress transfer function. Therefore, several simplified methods to predict the stress transfer function were proposed, but the phase information cannot be obtained in these methods.In the present paper, a simplified procedure to estimate the stress transfer function caused by internal pressure and external pressures is proposed. The representative phase angle of internal pressure and external pressure is introduced, and the stress transfer function caused by internal pressure and external pressure are superposed with the use of the representative phase angle. The effect of the choice of the representative phase angle is investigated in the case of internal pressure, and the accuracy of the method is discussed. Calculated results shows the estimated stress transfer function and the short-term parameter (standard deviation) agree with the exact ones.

在船舶结构的疲劳强度评估中，目前倾向于采用裂纹扩展分析来代替疲劳累积损伤分析，如Miner定律。利用波浪作用下船体构件的应力时程，可以模拟裂纹的扩展。利用应力传递函数可以得到应力的时程，但应力传递函数的计算存在一定的实际困难，由于某一结构构件的应力是由船体梁弯曲、货物或压载水内压、波浪引起的外海压力等多种载荷共同作用的结果，考虑到由每个载荷引起的每个应力分量之间的相位滞后，有必要叠加由每个载荷引起的应力。然而，应力传递函数的幅值和相位都不容易计算。因此，人们提出了几种简化的应力传递函数预测方法，但这些方法不能获得相位信息。本文提出了一种简化的方法来估计由内压和外压引起的应力传递函数。引入了内压和外压的代表相位角，并利用该代表相位角对内压和外压引起的应力传递函数进行了叠加。研究了内压情况下代表相位角选择的影响，并讨论了该方法的准确性。计算结果表明，所估计的应力传递函数和短期参数（标准差）与精确值相吻合。