Environmental Contours for SAfe DEsign of Ships and other marine structures

Ships and other marine structures are continuously exposed to the forces from the wave and wind environment throughout its operating life. These forces impose loads on the structures that need to be accounted for in the structural design. In particular, extreme environmental conditions may lead to extreme stresses and responses from the vessels. In order to ensure safe and reliable operations, the effect of such extreme conditions on the structures needs to be assessed in structural reliability analyses. However, in order to be able to do this there is a need for a realistic long-term description of the environmental conditions. Environmental contours are a tool for identifying dimensioning environmental conditions as input to structural reliability assessment. It separates the environmental conditions from the structural response so that computational intensive loads and response calculations need only be carried out on a limited number of realistic environmental conditions. The ECSADES project has further developed a new approach to environmental contours and assessed its strengths and weaknesses as well as compared its mathematical and statistical properties to existing approaches. By performing carefully selected case studies, the practical consequences of the choice of method have been investigated in order to gain a deeper understanding of the effect of method on the design and reliability levels. Moreover, the project has developed models for the statistical description of extreme ocean environments. Such models should be able to incorporate the non-stationary effects of various factors such as directionality, seasonality and spatial dependence. Moreover, the project has studied and developed contour-methods for a number of special cases, and it has also developed alternative approaches to long-term extreme structural response analysis by applying response emulators based on Machine Learning algorithms. The project has developed and delivered software packages (in MatLab and R) and a web app for doing simple calculations with the developed methods for the users.

The main impact from this project, for the project partners and the industry at large, is an improved understanding and knowledge of environmental contour methods. A balanced, common understanding of theory and practice of contours from different operators, regulators, academia and within offshore, maritime and coastal communities has been developed. Moreover, additional software tools have been made available for estimating contour in simple cases, making it easier for anyone to make such calculations. Moreover, DNV GL's recommended practice on environmental conditions and environmental loads and has been updated with the developed method. Project results have been widely disseminated at international conferences and published in top journals, with a branding effect for the partners. For University of Oslo, topics from the project have been incorporated as a main part of one of the courses taught at the department of mathematics, and several Master projects have been defined.

The ECSADES project will address important and pertinent issues related to the safe design and operation of ships and other marine structures. Such structures need to be designed according to tolerable risk levels. However, in order to understand the risks, the understanding of the extreme ocean environments and their interaction with fixed and floating structures is critical. In this regard, design contours are useful in describing the joint behavior of various environmental parameters, structural loading and response variables. Currently, there are different approaches to establishing environmental contours, and they all have certain strengths and weaknesses and different mathematical and statistical properties. One main objective in this project is to further develop one of the novel approaches to estimating environmental contours with clearly understood probabilistic properties. Moreover, a detailed comparison study involving climate descriptions from different important ocean regions and various structural problems will be performed in order to better understand the effect of the estimation method on the resulting design and reliability levels. Furthermore, some interesting and challenging special cases will be investigated, and methods for contour estimation in non-trivial cases will be explored. These spacial cases include the multidimensional case, non-stationary case with the effect of covariates and the case of bimodal environmental distributions. It is anticipated that the results from this project will be directly relevant to the design of ships and other marine structures, and that the results will be incorporated in standards, recommended practices and guidelines from DNV-GL. Furthermore, project results will be implemented in the Riscue software.