Experimental and numerical investigation of fatigue damage due to wave-induced vibrations in a containership in head seas

Fatigue cracks have been known to occur in welded ships for several decades. For large ocean-going ships wave-induced vibrations can, depending on trade and design, cause up to 50% of the fatigue damage. The vibrations may be due to springing and whipping effects. In this paper, we address the fatigue damage caused by wave-induced vibrations in a containership of newer design trading in the North Atlantic. The fatigue damage was obtained both experimentally and numerically. The experimental results were found from tests performed with a flexible model of the ship, while the numerical predictions were done using nonlinear hydroelastic strip theory. The measurements showed that the wave-induced vibrations contributed approximately 40% of the total fatigue damage. The numerical method predicted the wave frequency damage well, but was found to overestimate the total fatigue damage by 50%. This was mainly due to an overprediction of the wave-induced vibrations. The discrepancy is partly related to three-dimensional (3D) effects which are not included in the two-dimensional (2D) slamming calculation, and partly to an overprediction of the springing contribution. Moreover, the numerical method does not account for the steady wave due to forward speed. By using a simplified approach we show that high-frequency damage can be significantly reduced by including the steady wave for the relevant vessel, implying better agreement with the experimental results.     

波激振动的理论预报及与实船试验结果的比较

本文研究一艘大型海船的波激振动问题。该船在运行过程中发生了频繁的波激振动，导致严重的结构裂纹。文中对四种预报船体波激振动响应的理论及其计算机程序进行了描述。这些理论在计算水动力载荷和结构振动时具有各自的特点，如：线性、二阶、非线性、频域、时域、二维和三维等。相应的程序(WASIM，SOST，SINO和VERES)对低频波浪诱导响应预报已有较多的验证。文中对各程序在波激振动预报中的前提条件作了说明。计算中进行了参数敏感性分析并给出了主要结果。在与实船试验结果的比较过程中选择了十个不同的工况，对其海况、航向和试验现象给出了简要描述。对低频波浪诱导和高频波激振动响应分别进行了比较，得出了一些有意义的结论。