fixed wind turbine website

8/7/2019 Fixed Wind Turbine Website

http://slidepdf.com/reader/full/fixed-wind-turbine-website 1/32

Wave loads on fixed offshore windturbines

Johan Peeringa en Erik-Jan de Ridder



2

Foundation types in 30 MW+ offshore wind farms

– 14 Monopiles

– 7 gravity bases

– 1 Tripod andJacket

List of offshore wind farms - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/List_of_offshore_wind_farms








3

Dowec 6MW

– Pitch regulated variablespeed

– Rated power 6MW

– Rotor diameter 129 m

– Hub height 91.4 m

– Monopile 6 m diameter



4

Selected frequencies of the Dowec 6MW

[Hz] [rad/s]

Tower for aft 0.242 1.521

Blade flat wise 0.675 4.241

Blade edge wise 1.107 6.956



5

Offshore wind turbine standards

Organisations

– GL – DNV

– IEC

Design situation IEC61400-3

– Power production (+ fault) – Start up

– Normal shut down

– Emergency shut down

– Parked (+ fault)

– Transport assemblymaintenance and repair



6

Linear and nonlinear waves



7

Wave models and wave loads

– Irregular linearwaves

– Nonlineardeterministicstreamfunction wave

–

Morison equation

Source: www.noordzeewind.nl

dz x x D

C dz x D

C dF D M

24

2



8

Breaking waves

– Blyth

– Wienke

Source: Jan v/d Tempel 2006

Source: Wienke 2001

IMDwave_break F F F F



9

Need for validation of wave load models onoffshore wind turbines

– Code to Code Comparison

– Lack of (public) full scale measurements

– Lack of model tests including hydroelasticity



10

Introduction

– ComFlow

– Linear wave theory vs stream function andComFlow

– Effect relative fluid velocity due to towermotions

– 1st

model tests – ..



11

ComFlow

– Volume of fluid CFD code

– Used at MARIN for: – Green water on deck

– Wave impacts

– Sloshing



12

ComFlow: example



13

Non linear wave forces using ComFlow



14

12m 8s @ 30m waterdepth



15

Influence of hydroelasticity

– Simple bending model

– Linear wave theory – Morison loading, including

relative velocities due totower velocity



16

ComFlow (CFD) does not (yet) include relativefluid velocity due to tower motions



17

Existing MARIN knowledge on segmentedmodels



18



19

1st step by MARIN

– Model tests with a flexible model

– No detailed modelling of the proto type (DOWEC6MW)

– The clamping flexibility of the foundation is partlytaken into account

– The 1st

and 2nd

natural frequencies are modelled, bytuning the weight distribution over the height



20

Full scale model

– DOWEC 6 MW turbine

– Tower 80 m – Support 30 m

– Water depth 21 m



21

FE analyses of model

– FE package ANSYS

– Analyses of model (scale 1:30) – 11 beam & 6 mass elements

– Clamping flexibility included

Tower

support

E , m , I1 2 2

E , m , I1 1 1

M2

M3

M4

M5

M6

EI

M1



22



23



24

Natural frequencies

Natural mode FE analyses Model testing

1st mode 0.26 Hz (1.4 Hz model) 0.59 Hz

2nd mode 1.77 Hz (9.7 Hz model) 2.23 Hz



25

– Accelerations at5 location

– Pressuremeasurementsat five location

– Forces andmoments at the

bottom

– Wave height atthree locationsaround the tower



26

Model set-up in the basin



27

Picture model tests of wave impact



28

First results model tests

– Acceleration at the top of the towerWave:

Hs= 5 m

Tp= 12s



29

First results model tests

– Acceleration at the top of the towerWave:

H= 14 m



30

2nd possible (step)tests

– The results can be used to validate numerical

software: – Which than can be used to optimise the control

system

– Optimised the turbine for specifiek locations

(waves point of view)



31

4th step full scale measurements

fixed wind turbine website

Documents