Ultimate- and Fatigue Limit State Analysis of a Rigid Offshore Aquaculture Structure

Abstract

Marine fish farming is in rapid development, dimensions are expected to increase, and locations are being moved to areas exposed to more energetic waves and stronger currents. New and extreme loading scenarios need to be properly designed for by means of "first principles" methods to meet the required safety levels and performance. By use of the nonlinear finite element software USFOS, ULS and FLS analyses have been conducted on Ocean Farming's rigid offshore aquaculture structure. ULS analyses have been run on 7 directions inside a quadrant of the model based on received estimated 100-year values for waves and current. Members have been checked according to API-WSD, were the highest 100-year utilization was found to be 0.82, thus being within the requirements. FLS analyses have resulted in a parametric study of limiting SCF values based on the calculated total fatigue damage. A factor of 4.39 was found as the limiting upper value of the stress concentration factor at the worst connection (saddle point on chord) that gives a Miner sum equal to 1.