At the stage of design load analysis for offshore installations such as wave energy systems, a critical step is the determination of environmental cases to be evaluated for the definition of the characteristic design load. A commonly used methodology for load case selection, applied in multiple studies and recommended by technical specifications and guidelines, is the environmental contour approach. Here, 50-year environmental contours were generated for four study sites located in the North Sea, Skagerrak and the Baltic Sea by considering both observations and hindcast (model) data. For the construction of the contours, the well-established inverse first-order method (I-FORM) and a modified version using principal component analysis (PCA) were both examined. Furthermore, a 2-dimensional peaks-over-threshold (2D POT) method was evaluated. It was found that a version of the regular I-FORM was able to produce satisfactory contours which properly accounted for the highest waves. When using PCA, the dependency in the data was not properly captured by the probability functions under consideration. The 2D POT method, where applicable, was found to underestimate the extreme sea states. Comparisons between contours obtained from observations and hindcast data showed that the contours may differ substantially depending on the site and method, and thus care must be exercised when using hindcast data for such purposes.

中文翻译：

---

估计波罗的海和北海近海设施极端波浪的环境轮廓方法的比较分析

在诸如波浪能系统等海上设施的设计负荷分析阶段，关键步骤是确定要评估的环境工况，以定义特征设计负荷。环境轮廓法是一种用于载荷工况选择的常用方法，该方法在多项研究中得到应用，并得到了技术规范和指南的推荐。在这里，通过同时考虑观测和后预报（模型）数据，为位于北海，斯卡格拉克和波罗的海的四个研究地点生成了50年的环境轮廓。对于轮廓的构造，都检查了完善的逆一阶方法（I-FORM）和使用主成分分析（PCA）的改进版本。此外，还评估了二维阈值峰值（2D POT）方法。结果发现，常规I-FORM的一种版本能够产生令人满意的轮廓，该轮廓适当地占了最大的波浪。使用PCA时，所考虑的概率函数无法正确捕获数据中的依存关系。发现适用时的2D POT方法低估了极端海况。从观测值获得的等高线与后播数据之间的比较表明，等高线可能会因地点和方法的不同而有很大差异，因此在将后播数据用于此类目的时必须格外小心。在适用的情况下，人们发现其低估了极端海洋状况。从观测值获得的等高线与后播数据之间的比较表明，等高线可能会因地点和方法的不同而有很大差异，因此在将后播数据用于此类目的时必须格外小心。在适用的情况下，人们发现其低估了极端海洋状况。从观测值获得的等高线与后播数据之间的比较表明，等高线可能会因地点和方法的不同而有很大差异，因此在将后播数据用于此类目的时必须格外小心。