Environmental contours

Environmental contours are used as a basis for e.g., ship designs. The traditional approach to environmental contours is based on the well-known Rosenblatt transformation. However, due to the effects of this transformation the probabilistic properties of the resulting environmental contour can be difficult to interpret. An alternative approach to environmental contours uses Monte Carlo simulations on the joint environmental model, and thus obtain a contour without the need for the Rosenblatt transformation. This contour have well-defined probabilistic properties, but may sometimes be overly conservative in certain areas. In this paper we give a precise definition of the concept of the exceedance probability which is valid for all types of environmental contours. Moreover, we show how to estimate the exceedance probability of a given environmental contour, and use this to compare different approaches to contour constructions. The methods are illustrated by numerical examples based on real-life data. For comparison of environmental contours and finding the best contour for the given application, we have also included a third type of environmental contours, the Iso contours. We adjust the contours so that they get the same desired exceedance probability, which makes it possible to compare the contours graphically. We find that the best contour is the one with the lowest area as we want as little requirements for the construction of the design as possible as well as we want it to be as little conservative as possible