Invitation to PhD Defence 'Structural Optimization with Fatigue Constraints' on 20 October, 2017

Abstract

Fatigue is one of the most important causes of mechanical failure. Fatigue can be described as progressive damage to a material subject to repeated loading. Most fatigue-loaded components are exposed to a large amount of repeated loads where the stresses are low and the strains are elastic. This is normally referred to as high-cycle fatigue. This dissemination addresses structural optimization for high-cycle fatigue in metals.

The developed methods take offset in the offshore wind industry, more specifically in the design of a lattice-type of support structure for large wind turbines. These so-called jacket structures are subjected to complex aerodynamic and hydrodynamic loading conditions throughout their lifespan of approximately 20-25 years. The design of these structures is generally driven by fatigue in welded connections, and constitutes a great application for fatigue optimization. Thus, a new approach to optimization of jacket structures has been established. Additionally, this method and other state-of-the-art approaches to gradient-based optimizations of jacket structures are investigated and compared. The sizing optimization of jacket structures is of large interest to the industry, and is an optimization problem with few design variables, many constraints, and very computational costly analyses due to the large multiaxial and non-proportional load cases.

Topology optimization of 2D continua with fatigue constraints is also addressed. This problem differs from structural optimization of jackets, as many design variables are present in topology optimization. An effective formulation is proposed for proportional loading conditions, where finite-life constraints are formulated such that the computational costs of the design sensitivity analysis is comparable to static stress optimization.

Assessment Committee   

Technology Director Claus B. W. Pedersen
Dassault Systemes Deutschland GmbH, Germany

Professor Helder C. Rodrigues
Instituto Superior Técnico, Lisboa

Supervisor

Professor Erik Lund
Aalborg University, Denmark

Co-supervisor