In offshore renewable energy design procedures, accurate predictions of extreme responses are required in order to design for survivability whilst minimising associated costs. At present, the established method for predicting extreme responses is to conduct a large number of long-duration simulations, which is practical only in cases where the structural behaviour is captured by a computationally efficient linear approach. Many applications, however, will require a nonlinear approach, which significantly increases the computational cost, and hence the time required to analyse a problem. Should high-fidelity numerical approaches be the appropriate analysis tool, the long-duration simulations are likely to be impractical and in many cases infeasible. Laboratory testing can be utilised to address this to some extent, but this still time-consuming and expensive from a financial perspective. Consequently, there has been considerable interest in the use of short design waves as an alternative method for speeding up the design process. Currently, standards advise that short design waves can be utilised in the design of fixed offshore structures, but application to floating offshore structures needs verification before it becomes an established procedure. This study considers application of single and constrained short design waves to a floating hinged-raft wave energy converter using a 1:50 scale physical modelling approach, and compares with equivalent irregular sea states. The single wave approaches considered here are “NewWave” and the “Most Likely Extreme Response” wave, which are derived from the frequency content of the wave spectrum and response spectrum, respectively. The constrained approach considered in this study is the “Conditional Random Response Wave,” where the Most Likely Extreme Response wave is embedded within a random short irregular background. Results show that the single wave approaches under-estimate the extreme loading for the hinge-angle and mooring system compared with the irregular and constrained approaches. The discrepancy between single and constrained waves implies that memory effects are non-negligible, and hence it is critical that they are accounted for when utilising short design waves for floating applications.

中文翻译：

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浮式铰筏式波浪能转换器短设计波浪极端响应的实验室研究

在海上可再生能源设计程序中，需要对极端响应进行准确预测，以便设计生存能力，同时最大限度地降低相关成本。目前，用于预测极端响应的既定方法是进行大量长时间模拟，这仅适用于通过计算高效的线性方法捕获结构行为的情况。然而，许多应用程序将需要非线性方法，这会显着增加计算成本，从而增加分析问题所需的时间。如果高保真数值方法是合适的分析工具，那么长时间的模拟可能不切实际，在许多情况下也不可行。可以利用实验室测试在某种程度上解决这个问题，但从财务角度来看，这仍然是费时且昂贵的。因此，人们对使用短设计波作为加速设计过程的替代方法产生了相当大的兴趣。目前，标准建议短设计波可用于固定海上结构的设计，但在浮动海上结构的应用需要验证才能成为既定程序。本研究考虑使用 1:50 比例的物理建模方法将单一和受约束的短设计波应用于浮动铰接筏波能转换器，并与等效的不规则海况进行比较。这里考虑的单波方法是“NewWave”和“Most Likely Extreme Response”波，它们源自波谱和响应谱的频率内容，分别。本研究中考虑的约束方法是“条件随机响应波”，其中最可能的极端响应波嵌入随机的短不规则背景中。结果表明，与不规则和受限方法相比，单波方法低估了铰链角和系泊系统的极端载荷。单波和约束波之间的差异意味着记忆效应是不可忽略的，因此在为浮动应用程序使用短设计波时考虑到它们是至关重要的。结果表明，与不规则和受限方法相比，单波方法低估了铰链角和系泊系统的极端载荷。单波和约束波之间的差异意味着记忆效应是不可忽略的，因此在将短设计波用于浮动应用程序时考虑到它们是至关重要的。结果表明，与不规则和受限方法相比，单波方法低估了铰链角和系泊系统的极端载荷。单波和约束波之间的差异意味着记忆效应是不可忽略的，因此在为浮动应用程序使用短设计波时考虑到它们是至关重要的。