Endurance Wave Analysis (EWA) and its application for assessment of offshore structures under extreme waves

Abstract

The aim of this paper is to introduce a novel approach, called Endurance Wave Analysis (EWA), for non-linear dynamic analysis and assessment of offshore structures subjected to irregular wave forces. This is, in fact, an extension of the Endurance Time Analysis (ETA) already presented by previous researchers for the seismic assessment of onshore structures. With the EWA method, the offshore structure is simulated under a predefined Intensifying Wave Train Function (IWTF), corresponding to a gradually deteriorating sea state at a specific site. The function is designed so that the roughness of the sea state represented by them increases over the time and even goes well beyond the design sea state. The IWTF is then used for the non-linear dynamic analysis of the structure. Using EWA, damage indices or any other desirable parameters, from the linear elastic range of behavior to permanent deformation or complete collapse level, can be studied directly in terms of the sea state roughness. Structural integrity can then be evaluated based on the EWA results. In this paper the concept of the EWA is presented and the method is examined on sample offshore platforms. Different irregular IWTFs are generated and employed to evaluate the integrity of the three two-dimensional example steel jacket type platforms. The results clearly show that the proposed method is very effective for the dynamic non-linear analysis and assessment of offshore structures subjected to sea loads.