Comparison of methods for the computation of wave forcing

The resulting motion of a slender offshore floating structure

Presentation slides , 2014 , 14 Pages , Grade: 1,0

Engineering - Civil Engineering

Unlike fossil fuels (e.g. oil, coal and natural gas), wind energy is a renewable energy resource. Since winds at sea are stronger and more consistent than onshore winds, the demand for offshore wind turbines has increased over the last years. As energy can be produced more efficient in deeper water, several floating offshore wind turbine constructions, such as the OC3 Hywind spar-buoy, have been proposed. The design of floating wind turbines depends on the simulation of the system behavior caused by exciting forces.

This thesis deals with the comparison between different methods for calculating wave forces and resulting platform motions of a floating offshore wind turbine. On the one hand, wave exciting loads computed with Morison’s equation are compared to the hydrodynamic forces simulated by the open source code FAST on the basis of the diffraction theory. On the other hand, response motions of the floating structure are simulated by the commercial offshore software SESAM in the frequency domain and compared with the motions calculated by FAST in the time domain.

Table of Contents

Introduction

Floating Offshore Wind Turbine Model

Calculation of Wave Loads

Modified Morison Formulation

SESAM

FAST

Comparison of the Methods

Summary

Conclusion and Outlook

Background

Most of the energy worldwide is obtained by nonrenewable resources, e.g. coal, oil, natural gas, nuclear power Fossil fuels are limited in supply and are harmful to the environment Wind is a renewable energy resource Onshore wind power has been the fastest growing energy source Increasing demand of offshore wind turbines Higher wind energy production stronger and more constant winds at sea than onshore No interference with life on land

Comparison of methods for computation of wave forcing and resulting motion of a slender offshore floating structure

Background

Several prototypes of floating substructures were developed The most economical constructions for generating electricity in the open sea are the Spar-buoy the Tension Leg Platform the Barge Design of floating wind turbines depends on the simulation of the system behavior

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Goal of this thesis:

Presentation and comparison of different methods for calculating wave forces and resulting platform motions of a floating offshore wind turbine

Floating Offshore Wind Turbine Model - OC3 Hywind -

First full-scale floating platform for offshore wind turbines in deep water

The support platform is developed by the Norwegian oil corporation Statoil

Development within the so-called Hywind-project

In water depths from 120 m to 700 m

FOWT used in this thesis is the Hywind spar-buoy (OC3 Phase IV)

OC3 Hywind system is characterized by a deeply-drafted, slender spar-buoy with three mooring lines

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Source: Jonkman (2007)

OC3 Hywind System

Comparison of methods for computation of wave forcing and resulting motion of a slender offshore floating structure

structural Properties of Tower and Platform Total height of 207.6 m Draft of the platform is 120 m Total mass of 7,716.048 tons Location of the COG at 89.9 m below MSL Thickness between 0.019 m and 0.027 m

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• College: University of Hannover
• Grade: 1,0
• Author: Olga Glöckner (Author)
• Publication Year: 2014
• Pages: 14
• Catalog Number: V425814
• ISBN (eBook): 9783668706149
• ISBN (Book): 9783668706156
• Language: English
• Tags: Offshore, Floating Platform, Wind Turbine, SESAM DNV, Morrison, wave forces, Platform motions