The main purpose of this project is to investigate different methods for performing a size optimization of offshore wind turbine support structures w.r.t. fatigue. A generic jacket model and a load case have been provided and it is desired to minimize the mass with fatigue as a constraint by using gradient based optimization methods. The main focus is a development of analytical Design Sensitivity Analysis (DSA) for fatigue constraints with non-proportional load spectra.
A 3D MATLAB FE program is developed in order to perform the structural analysis and determine the accumulated damage.
Small benchmark examples are used to investigate and determine the most suitable methods for damage estimation, optimization, and the analytical DSA.
The DSA is made both numerically and analytically by the adjoint- and direct differentiation method in order to obtain the gradients of the fatigue constraint functions w.r.t. design changes.
Parametric studies and optimization have been performed with the selected methods. A SLP algorithm is used and an adaptive move limit strategy is developed to obtain successful results.
It can be concluded, that the developed methods have a great potential for use in structural optimization since they performed well for the optimization of the jacket structure.
Furthermore, the optimization and analytical DSA of fatigue have proven its potential for future work.