Abstract

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests.

Highlights

  • To decarbonise the energy system and combat climate change, offshore wind turbines (OWTs) are currently being constructed around the world, including in seismic areas

  • The analysis and design of foundations for offshore wind turbines is challenging due to complex load conditions arising from the environmental loads and possible seismic loads in the presence of active seismic faults

  • This change may be significant in the presence of loose deposits, which may liquefy as a result of cyclic loadings [26,35,36,37]

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Summary

Introduction

To decarbonise the energy system and combat climate change, offshore wind turbines (OWTs) are currently being constructed around the world, including in seismic areas. One of the most important distinctions is that offshore wind turbines are extremely sensitive to dynamic loads arising from wind, waves, and earthquakes They have stringent Serviceability Limit State (SLS) criteria when compared to other structures due to the presence of vibration-sensitive electrical components, notably gear boxes. Eng. 2021, 9, x FOR PEERaRnEdVIlEoWading), the example of wind farm development in China is taken. Example 1: Monopile–caisson hybrid foundation: At the Fujian province offshore wind farm site (Putan Pinhhai Phase II) in China, engineers faced a daunting challenge of installing monopiles due to the presence of rock formations at a shallow depth. SSoommee eexxaammpplelse:sgg: rrgaavrvaiittvyy-i-btbyaa-ssbeedadsfefooduunnfdodauattinioodnnsast(i(GoGBnBFsF))((G(ii,,BiiiFi,,)iiiii(i))i;;, ii, iii); asymmeaatrssiyycmmfmmraeemttrrieiccoffrrnaammsueecootnniossnuucccttaiiooinsnsccoaaniissss(oiovnn,v((iivvs,,evvesseeFeeigFFuiiggruuerree55b5bbffofoorrrmmmooorree dddeeettataaiillissl))s;;)tt;eettreraatprpaoopdd/o/ttdrrii/pptoroiddpooonndssohhnaalllsloohwwalfflooouuwnnddfaaottiuioonndssa((iitvvi,o,vvn));;s (iv,v); twisted jttawwckiissetteetdd(vjjaaicc)kk; heette((lvvicii))a;; lhhmeelliioccaanllommpooilnneoospp(iivlleeissi)((;vvwiiii))i;;nwwgiienndggeepddippleiillseess(v((vviiiiiii)ii););;cccooollllllaaarrreeedddmmmooonnnooppoiiplleei,,leccaa, iicssassooisnns+o+nmm+oonnmoopopinilleeo(p(iixxi)l);e;hh(yyixbbr)ri;iddhmymboornniodoppmiilleeo,, nopile, monopilmme oownniootpphiillpeelwwatiitethh(pxpl)laa;tteset(i(xfx)f);e;snsttieifffdfeenmneedodmnmooopnnoilopepili(elxe(ix)(xi.)i.()b.(b()b)A)AAssysymmmmmmeeterttirrciiccrirgriihggth-hat-tna-ganlngelgdeldterditpriotprdoi.pd(.oc()dcI).nI(nncon)voIanvtianotoniosvnoasftoinofennwsewfoofufonnudenawdtiaoftnoiosuninsdations in ChinaifCno(hauCinnihsdaiana(taaiWo(inasiadiseWa[SSiWoduueicrdtSceieuo:ScnuticoBhtniutotcBpnksuB:ec/u/ktw)cektaw)entwa)dn.aodHnffdHsighHigohihrgeRhR-ieiRsnseieesrPegiPyleei.bleCiCzCa/apfapip.r.s.TtTTr-marrnaaonsnnpssopopporotirlatreatt-itacoiatoniinososnofofntoht-hfheetychcbaaerisiisdcssoa-ofnionsuasannonddndaiatinninosstdntaa-lililnlnaaststtiitoaoalnnllelooadfft-iattohht-neechhhoiyynfbbetrrshiiedde- hybrid foundatiofoofnfusnhdoar[eSti-owuninr[cSdeo-f:uarrcmeh:/t]ht(ptatscp:cs/e/:s/ws/ewwdwdaw.ote.fof3fsfFhsheoborrreue--aeernnye2r0gg2yy1.b.)b.iziz//fifrisrts-tm-monoonpoilpei-lcea-icsasoisns-ohny-bhriydb-froidun-fdoautinodn-aitnisotnal-liends-taatl-lcehdin-aest-ec-hineseoffshore-owffsihnodr-ef-awrmind/]-f(aarcmc/es] s(aecdcedssaetde d3aFteeb3rFueabruya2ry02210)2.1)

Foundations for Offshore Wind Turbines
For floating turbines in non-seismic conditions
Physical Modelling of Offshore Wind Turbine Foundations
Requirements of Foundation Testing for Offshore Wind Turbine Foundations
Suitability on Different Methods of Testing
STEPS in Designing Scaled Mode Tests
Measurement of Dynamic Response and Type 2 Technique
Verification of Failure Modes of Anchor Foundations for Spar Type
Example of Scaled Test on Biofouling on Monopiles
Centrifuge Modelling
Findings
Earthquake Response of Wind Turbine Structures

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