Short-duration design waves for modelling of extreme second-order surge response with spar substructure test case

IF 4.3 2区 工程技术 Q1 ENGINEERING, OCEAN
D.R. Lande-Sudall , P.K. Stansby
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引用次数: 0

Abstract

This work aims to determine the wave conditions that generate maximum surge response excited predominantly by second-order difference frequency forces. Standard narrow-band wave conditions have random phase components and obtaining the maximum surge response requires long sea-state durations to cover all combinations and correspondingly long computation times using second-order diffraction–radiation models. Multiple 3-hour random sea-states are typically used to evaluate the expected extreme response. The maximum force may be obtained by shifting phases to be equal between component pairs with a frequency difference equal to the structure’s surge natural frequency. However, this work shows that such an approach gives a highly transient force and the lightly damped surge displacement response does not approach a representative maximum value. The larger motion responses may be achieved by sequential wave groups and here we use a genetic algorithm to optimise the phase distribution to give more regular low-frequency excitation in relatively short sea-state durations, less than 1 h. This is demonstrated with a one degree-of-freedom Fourier model. The method is applied to a lightly-moored spar substructure and compared with an experimentally validated standard six degree-of-freedom time domain model (Orcaflex) showing satisfactory agreement.

用短时设计波模拟极端二阶浪涌响应的下部结构试验案例
这项工作旨在确定主要由二阶差频力激发的产生最大浪涌响应的波浪条件。标准窄带波浪条件具有随机相位成分,要获得最大浪涌响应,需要较长的海况持续时间以涵盖所有组合,使用二阶衍射辐射模型的计算时间也相应较长。通常使用多个 3 小时的随机海况来评估预期的极端响应。通过将频率差等于结构浪涌固有频率的部件对之间的相位相等来获得最大力。然而,这项工作表明,这种方法得到的是一个高度瞬态的力,而轻度阻尼的浪涌位移响应并不接近具有代表性的最大值。较大的运动响应可通过连续波群实现,在此我们使用遗传算法来优化相位分布,以便在相对较短的海况持续时间(小于 1 小时)内获得更有规律的低频激励。将该方法应用于轻型系泊支柱下部结构,并与经过实验验证的标准六自由度时域模型(Orcaflex)进行比较,结果显示两者的一致性令人满意。
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来源期刊
Applied Ocean Research
Applied Ocean Research 地学-工程:大洋
CiteScore
8.70
自引率
7.00%
发文量
316
审稿时长
59 days
期刊介绍: The aim of Applied Ocean Research is to encourage the submission of papers that advance the state of knowledge in a range of topics relevant to ocean engineering.
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