Offshore wind turbine foundation design issues

8/17/2019 Offshore wind turbine foundation design issues

1/42

Dynamics and Fatigue of Offshore Wind

Turbine FoundationsA linear approach to a non-linearproblem

Laszlo Arany Department of Engineering Mathematics

May 6, 2016

1Dynamics and Control rou! "eminar


2/42

# Dynamics# Random vibrations

# Fatigue

# Control# Vibration

suppression

Dynamics and Control rou! "eminar 2

May 6, 2016

What do $ %or& on'

YES NOT REALLY…

(ong term beha)iour of offshore %indturbines and su!!ort structures*


3/42

Why %or& on offshore %ind turbines'

Dynamics and Control rou! "eminar +

6 May 2016

Source: EWEA report on offshore wind in Europe (2015)Source: Gijs van der Veen !dentificationof wind ener"# s#ste$s

irbus +-0 .largest!assenger !lane/

The economics The engineering

10 - load cycles


4/42

Why %or& on offshore %ind turbines'

Dynamics and Control rou! "eminar

6 May 2016

n)ironment andsustainability

Source: Various studies co%%ected the Wor%d 'uc%ear Association


5/42

Why %or& on su!!ort structures'

Dynamics and Control rou! "eminar

6 May 2016

Onshore OffshoreSource: nre% "ov


6/42

"tructure of the !resentation

I. Excitations o o!shore "ind turbinesII. Current oundation designIII. #ong term issuesIV. Fatigue in the re$uency domain

V. Integrated designVI.An unsolved problem % ideas "elcome&


May 6, 2016


7/42

# 'ind

# 'aves# Currents# ()# *)# +hip impact,

earth$ua e, etc


May 6, 2016

$* 4citations of offshore%ind turbines


8/42


9/42

The aerodynamics is non8linear

Dynamics and Control rou! "eminar :

May 6, 2016

Source: E 'Windener"ie

Source: S$art*%ade G$&+


10/42

Wa)es are non8linear


May 6, 2016

Source: ,#ushu-niversit# we& pa"e


11/42

"oil is non8linear


May 6, 2016

Source: o. (201/)


12/42

;o% does the load !rocess actually loo&'

12

6 May 2016


13/42

$$* Current load analysis of offshore %ind turbines ime domain analysis(.Create time history o "ind and "aves

/.0se it as input or multibody so t"are 1aero-hydro-servo-elastic simulation "ith +oil-+tructureInteraction 1++I22

*.3btain time history o loads or all re$uiredload scenarios 1hundreds o scenarios24.Fatigue5 rain6o" counting 7 linear damageaccumulation % a terthought

Dynamics and Control rou! "eminar 1+

6 May 2016


14/42

Design of foundations


May 6, 2016

M

;


15/42

Current design of offshore %ind turbines


May 6, 2016


16/42

Current design of offshore %ind turbines


May 6, 2016

# Diameter'

# Foundation de!th'# mount of steel'# $nstallation

!rocedure'# Fatigue life'# Cost of nergy'

Optimal?


17/42

$$$* (ong term issues


6 May 2016


18/42

ffect of load cycles on fre5uency and dam!ing

Dynamics and Control rou! "eminar 1-

6 May 2016

Different beha)iour for sand and clay


19/42

=atural fre5uency change %ith time

Dynamics and Control rou! "eminar 1:

6 May 2016

"isted 8ac et in 9ornsea :#o"e1/;(/2<

eference7>alleha)e and Thilsted .2012/


20/42

9ile head deflection and tilt .1/# #ong term tilt =has to be> predicted

1according to standards2

# Very e" studies available on ho" to do itAchmus et. al. 1/;;?2, #e@lanc 1/;(;2, Cox et. al. 1/;(42

# Virtually no measurement data are

available# ilt is not monitored on existing o!shore"ind turbines


6 May 2016


21/42

9ile head deflection and tilt .2/# +trict re$uirements increase

oundation costs# aximum ;./B 1or ;.B 2

# Re$uirements are arbitrarynumbers originating romonshore "ind technology = or

the sa e operation o theturbine> and =visual concerns># Cox et. al. 1/;(42


6 May 2016


22/42


23/42

$?* linear a!!roach to a non8linear !roblem(. Determine trans er unction bet"een "ind spectrum and

mudline moment spectrum./. Determine trans er unction bet"een "ave spectrum and

mudline moment spectrum.*. Calculate natural re$uency using simpli ed model.4. Apply Dynamic Ampli cation Factors to "ind and "ave loads.B. Combine bending moment spectra rom "ind and "aves.

. 0se bending moment spectrum to determine stress

spectrum.. 0se stress spectrum to estimate damage rate using

re$uency domain atigue damage estimation methods.

Dynamics and Control rou! "eminar 2+

6 May 2016


24/42

# 'ind load model basedon $uasi-static e$uation

# urbulent "indcomponent replaced byGaimal spectrum oturbulence

# 'ave spectrum5 83H+'A) spectrum

# #inear 1Airy2 "aves areused

# orison s e$uation orthe "ave load


6 May 2016

182* Transfer functions .1/


25/42

182* Transfer functions .2/


6 May 2016


26/42








6 May 2016


27/42

+* =atural Fre5uency


6 May 2016


28/42

+* =atural fre5uency

Dynamics and Control rou! "eminar 2-

6 May 2016

of the to%er


29/42

* "ystem ain .D F/

Dynamics and Control rou! "eminar 2:

6 May 2016

Source: Su *hattachar#a presentation

# =atural fre5uency determined using linear s!rings as foundation stiffness# !!ro4imate em!irical formulae fitted to 9D solutions# Dynamic m!lification by using a!!ro4imate dam!ing as in Cam! et* al* .200 /


30/42

86* Mudline @ending Moment "!ectrum .1/

Dynamics and Control rou! "eminar +0

6 May 2016


31/42

86* Mudline @ending Moment "!ectrum .2/


6 May 2016

;o% does a theoretical s!ectrum measure u! to reality'

9"D

Fre5uency


32/42








6 May 2016


33/42

Dynamics and Control rou! "eminar ++

6 May 2016

3* Fre5uency domain methods .1/

Power spectral densityof moment / stress:

Pro a ility density ofstress amplit!des:

"ama#e rate:

$ati#!e life:

!oint on the "8= cur)e and in)erse slo!e


34/42


6 May 2016

3* Fre5uency domain methods .2/


35/42


6 May 2016

3* "im!le, em!irical e4!ressions


36/42


6 May 2016

3* ;o% do they measure u! to reality'

easonable accuracyconsidering the

general accuracy offatigue estimations.failure any%herebet%een 0*3 and 1* /

O)erestimation ty!ical


37/42

?* $ntegrated design benefits .1/# urbine componentsJparameters5

# +ingle speed, double speed, variable speedK# Direct drive or gearboxK 9o" many stepsK# Lenerator typeK# @lade designK

# Can impact natural re$uency,oundation siMe, li etime and settlement


6 May 2016


38/42

?* $ntegrated design benefits .2/# +erviceability re$uirements 1tilt and

de6ection25# o"er stri eK# Na" motor or ya" brea diOcultiesK# Cooling 6uid problemsK# @earing li etimeK

# Costs can be reduced

Dynamics and Control rou! "eminar +-

6 May 2016


39/42


40/42

n unsol)ed !roblem A $deas %elcome .2/# 9o" to treat it statisticallyK


6 May 2016

Wind

Wa)es


41/42

?$* n unsol)ed !roblem A $deas %elcome .+/# #ong term tilt and de6ection "ith

# di!erent "ind and sea states 1'eibull

distribution2,# di!erent load combinations 1one-"ay and

t"o-"ay2,

# three dimensional problem,# directionality o "ind and "aves.


6 May 2016


42/42

Than& you

6 May 2016

Documents

Offshore wind turbine foundation design issues