Analyse av halvt nedsenkbar offshore vindturbin

Abstract

This master’s thesis describes the evaluation of a semi-submersible offshore wind turbine concept designed by Dr. techn. Olav Olsen. The main purpose of this evaluation is to contribute towards the development and verification of the numerical simulation code 3DFloat. During 2013 a series of experimental tests were performed on a scaled down model of the OO Star Wind Floater. The experiments were carried out at a wave tank located at Ecole Centrale de Nantes, in France. During the initial stage of this project our focus was mainly upon coupling 3Dfloat with theoretical knowledge. When the experimental test results arrived our minds were set on understanding the different test regimes, having boundary conditions for 3Dfloat in mind. Based on analysis of the test results and theoretical considerations 3Dfloat is setup to simulate a specific set of experiments. A main goal has been to recreate the physical movements of the platform represented in the different tests with one single setup. This required altering a series of coefficients and variables in a predefined input-file. During the final stages of this project a simulation setup able to recreate “free decay” tests was achieved. The heave-period was described by an added mass coefficient of 2.65. Our specific setup does not produce simulations with good agreement for cases with wind and wave loading. This seems to be due to a mismatch between global quadratic damping and “Morison” drag. An axial “Morison” drag of 4 is likely to be too sparse. In the feature the damping ratio needs closer inspection. Verification of the mooring system and some alterations to the RNA-geometry is advised. With these subjects in mind a higher simulation quality should be reached.