INTEGRATING CONSTRAINED RANDOM WAVES IN ENDURANCE TIME ANALYSIS of OFFSHORE STRUCTURS SUBJECTED TO SEA WAVES

This paper introduces a novel methodology for design and assessment of offshore structures exposed to irregular sea waves. For this, Constrained New Wave (CNW) is integrated with the Endurance Time Analysis (ETA) methodology, which is basically developed for the performance based analysis of onshore structures to earthquake loads. In this approach, the offshore structure is simulated in time-domain under a set of calibrated intensifying wave functions. They are devised to represent a gradually increasing roughness of the sea state by time. A performance index such as base shear, drift or stress in a critical structural members are monitored until they reach to a predefined maximum value. A higher endurance time (corresponding to a higher wave height) is to be interpreted as a better performance of structure. Ability to consider spectral features of waves, waves' irregularity, the wave-in-deck impacts, utilizing a relatively simple approach, requiring relatively low computational times and capability to consider any desirable damage indices are the advantages of this novel method. The method can be used in the design stage, collapse analysis and for the assessment of existing offshore platforms. In this paper the effectiveness of this method has been examined on offshore jacket platforms. The results obviously have highlighted the potentials of this approach for the dynamic, time-domain, non-linear analysis and assessment of offshore platforms.