A RESPONSE SURFACE APPROACH TO FATIGUE RELIABILITY OF SHIP STRUCTURES

Abstract eng:
Today ship designers are facing ever more stringent safety and environmental requirements as well as economic ones. With the advancement of rules and procedures in the classification societies and the tail wind of modern computing technology spectral fatigue based on first principles has become a commonplace in ship design. So far the centerpiece of such a process is by and large a deterministic acceptance criterion despite the highly uncertain nature of the problem. As a result the observed damage in a fatigue prone area is often significantly inconsistent with the predicted one, making client-facing a daunting task. As a small step towards reliability-based solution the paper attempts to introduce structural uncertainties in established fatigue design assessment process such as ShipRight FDA3 procedure and the supporting software by Lloyd’s Register. Key design parameters are randomized in a spectral fatigue model, where pseudo-excitation method is used to reflect the nonlinear effect of inertial loads and external wave pressure in the splash zone. Step-wise response surface method is used in tandem with t by t fine mesh FE analysis to obtain the probability of failure. The calculation is demonstrated in an oil tanker example.

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