Fatigue reliability of ship structures.
PhD thesis, University of Glasgow.
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Today we are sitting on a huge wealth of structural reliability theory but its application in
ship design and construction is far behind. Researchers and practitioners face a daunting
task of dove-tailing the theoretical achievements into the established processes in the
industry. The research is aimed to create a computational framework to facilitate fatigue
reliability of ship structures. Modeling, transformation and optimization, the three key
elements underlying the success of computational mechanics are adopted as the basic
methodology through the research. The whole work is presented in a way that is most
suitable for software development.
The foundation of the framework is constituted of reliability methods at component level.
Looking at the second-moment reliability theory from a minimum distance point of view
the author derives a generic set of formulations that incorporate all major first and second
order reliability methods (FORM, SORM). Practical ways to treat correlation and non-
Gaussian variables are discussed in detail. Monte Carlo simulation (MCS) also accounts
for significant part of the research with emphasis on variance reduction techniques in a
proposed Markov chain kernel method. Existing response surface methods (RSM) are
reviewed and improved with much weight given to sampling techniques and determination
of the quadratic form. Time-variant problem is touched upon and methods to convert it to
nested reliability problems are discussed.
In the upper layer of the framework common fatigue damage models are compared.
Random process simulation and rain-flow counting are used to study effect of wide-banded
non-Gaussian process. At the center of this layer is spectral fatigue analysis based on SN
curve and first-principle stress and hydrodynamic analysis. Pseudo-excitation is introduced
to get linear equivalent stress RAO in the non-linear ship-wave system. Finally response
surface method is applied to this model to calculate probability of failure and design
sensitivity in the case studies of a double hull oil tanker and a bulk carrier.
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