Extreme value analysis (EVA) uses data to estimate long-term extreme environmental conditions for variables such as significant wave height and period, for the design of marine structures. Together with models for the short-term evolution of the ocean environment and for wave-structure interaction, EVA provides a basis for full probabilistic design analysis. Environmental contours provide an alternate approach to estimating structural integrity, without requiring structural knowledge. These contour methods also exploit statistical models, including EVA, but avoid the need for structural modelling by making what are believed to be conservative assumptions about the shape of the structural failure boundary in the environment space. These assumptions, however, may not always be appropriate, or may lead to unnecessary wasted resources from over design. We introduce a methodology for full probabilistic analysis to estimate the joint probability density of the environment, conditional on the occurrence of an extreme structural response, for simple structures. We use this conditional density of the environment as a basis to assess the performance of different environmental contour methods. We demonstrate the difficulty of estimating the contour boundary in the environment space for typical data samples, as well as the dependence of the performance of the environmental contour on the structure being considered.

翻译：极值分析（EVA）利用数据估计用于海洋结构设计的长期极端环境条件变量（如有效波高和周期）。结合海洋环境短期演化模型及波-结构相互作用模型，EVA为全概率设计分析提供了基础。环境等值线法提供了一种无需结构知识即可评估结构完整性的替代方法。这类等值线方法同样利用包括EVA在内的统计模型，但通过假设环境空间中结构失效边界形状的保守性来避免结构建模需求。然而，这些假设可能并非始终适用，或导致因过度设计而造成资源浪费。本文针对简单结构，提出了一种全概率分析方法，以估计在极端结构响应发生条件下环境的联合概率密度。我们以此条件密度为基础，评估不同环境等值线方法的性能。研究揭示了典型数据样本下环境等值线边界估计的困难性，以及环境等值线性能对所考虑结构的依赖性。