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. Alternatively, environmental contours provide an approximate 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 demonstrate a methodology for efficient fully probabilistic analysis of structural failure. From this, we estimate the joint conditional probability density of the environment (CDE), given the occurrence of an extreme structural response. We use CDE as a diagnostic to highlight the deficiencies of environmental contour methods for design; none of the IFORM environmental contours considered characterise CDE well for three example structures.

翻译：极值分析利用数据估算长期极端环境条件，如有效波高与周期，为海洋结构物设计提供依据。结合海洋环境短期演变模型及波浪-结构相互作用模型，极值分析为全概率设计分析奠定基础。作为替代方案，环境等值线方法提供了一种无需结构知识的结构完整性近似评估途径。此类等值线方法同样采用包括极值分析在内的统计模型，但通过对环境空间中结构失效边界形状作出假定保守的假设，规避了结构建模需求。然而这些假设可能并不总是合理的，或可能因过度设计导致不必要的资源浪费。本文提出一种高效的结构失效全概率分析方法，据此估算给定极端结构响应发生时环境变量的联合条件概率密度。我们将该条件密度作为诊断工具，揭示环境等值线方法在设计中的缺陷：针对三个示例结构，所考察的IFORM环境等值线均未能有效表征该条件密度特征。