Tailoring the Fatigue Detail Category Class: A Deterministic Implementation of a Probabilistic-Based Approach to Consequence- and Uncertainty-Informed Fatigue Life Prediction of Ships

Abstract

The fatigue life of ship structures is typically based on deterministic methods in which underlying uncertainties are only implicitly taken into account and not explicitly reflected. Guidance for a probabilistic assessment is provided in class documents, but the methodology is too time consuming to apply in design practice. This paper proposes a novel approach based on DNV-CG-0129 to incorporate uncertainties and consequences explicitly. Using a probabilistic model, tailored deterministic FAT classes are derived to be applied in design practice. A tailored FAT class should be selected based on an acceptable probability of failure related to the severity of the consequences of a failure for the ship. Results show that tailored FAT classes are strongly dependent on the uncertainties provided as input when using the calculation method of DNV-CG-0129. This emphasizes the need for careful consideration and specification of the uncertainties. Furthermore, application of the First Order Reliability Method for a sensitivity study shows that the global model uncertainty is governing over other uncertainties considered in DNV-CG-0129. The proposed approach enables a low-effort and transparent probabilistic-based method, leading to optimized and improved designs due to reduction of overdimensioning in non-critical areas.

Keywords

• fatigue reliability
• fatigue design
• uncertainty
• welded joints
• probabilistic fatigue
• S–N curve