On the fatigue performance prediction of ship structural details

Violette, Franck Luc Marcel (1997) On the fatigue performance prediction of ship structural details. University of Southampton, Doctoral Thesis.

Abstract

This objective of this thesis has been the development of methodologies to attain and maintain the fatigue performance of ship structural details during the ship's lifetime. The evaluation of the fatigue performance of ship structural details is a very complex subject, which involves several areas of knowledge. This thesis has proposed new techniques to address several of these areas, and has provided a consistent and rational approach to produce a comprehensive and integrated methodology en compassing design, construction and in service monitoring of ship structural details with a view to maximise their fatigue performance. The result of which is a set of rational and complementary fatigue design assessment procedures, which can be viewed as a multi-level integrated fatigue design code. The main aspects covered in this thesis are:

• The development of a fatigue strength estimation procedure based on the hot spot stress approach with normalised notch parameters, and a reference S-N curve for welded material. The proposed approach permits to determine the S-N fatigue strength characteristics for any geometries using a parametric formulation of the geometrical stress concentration factors derived from systematic finite element analysis. Fatigue stress criteria for finite element analysis based on the concept of critical fracture plane have also been proposed. The proposed model has been verified by large scale fatigue tests of ship structural details.
• The development of a parametric ship loads and motions model based on the systematic analysis of first principles direct calculation results. The verification of the applicability of the inertia pressure load model for prismatic tank to non-prismatic tanks with internal structures by computational fluid dynamics simulations.
• The formulation of a model based on the concept of equivalent amplitude in regular waves for the load effect combination of multiple non-linear and non-harmonic processes, and its verification by numerical simulations of irregular sea-states. A voyage simulation model has been proposed to determine a more realistic estimate of the long term fatigue damage. The concept of the 100 A1 fatigue wave environment standard has been proposed as a suitable model to perform a fatigue design assessment.
• A Fatigue Control Plan methodology has been developed to monitor the workmanship and construction tolerances during construction, and provide a basis for inspection of the fatigue critical areas during the service life.

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