EN IEC 61400-3-2:2025
(Main)Wind energy generation systems - Part 3-2: Design requirements for floating offshore wind turbines
Wind energy generation systems - Part 3-2: Design requirements for floating offshore wind turbines
IEC 61400-3-2:2025 specifies requirements for assessment of the external conditions at a floating offshore wind turbine (FOWT) site and specifies essential design requirements to ensure the engineering integrity of FOWTs. Its purpose is to provide an appropriate level of protection against damage from all anticipated hazards during the planned lifetime. This document focuses on the engineering integrity of the structural components of a FOWT but is also concerned with subsystems such as control and protection mechanisms, internal electrical systems and mechanical systems. This first edition cancels and replaces IEC TS 61400-3-2, published in 2019. This edition includes the following significant technical changes with respect to IEC TS 61400‑3-2: a) The relevant contents of IEC 61400-3-1 have been migrated into IEC 61400-3-2, making IEC 61400-3-2 a self-standing document that does not have to be read directly in conjunction with IEC 61400-3-1. b) Several modifications have been made regarding metocean conditions in Clause 6 considering the nature of FOWT and the offshore site where FOWT will be installed, including: (1) the importance of wave directional spreading has been highlighted as it may result in larger loads for FOWT, including the addition of the new informative Annex O and Annex P and (2) the characteristic of swell has been explained, which may be relevant for some FOWT projects, including the addition of new informative Annex R regarding the characteristic of swell. c) Subclauses 7.1, 7.2, 7.3, 7.4 and 7.5 have been changed to include a revised DLC table and its related descriptions, including amongst others updated requirements on directionality, wave conditions, redundancy check and damage stability cases, and a robustness check case; further updates are made related to guidance and necessities provided on load calculations and simulation requirements. d) Subclause 7.6 has been updated with guidance on fatigue assessment along with clarifications on serviceability analysis and the applicable material for WSD; related Annex L has been updated and a new Annex M has been added for clarification of the safety factors and load and load effect approach for floating substructures e) The concept of floater control system that will interact with the wind turbine controller has been introduced in Clause 8. f) Clause 11 has been renamed from "Foundation and substructure design" to "Anchor design" and requirements for the transient conditions have been added. g) A more detailed clause regarding concrete design has been added to Clause 16 together with an informative Annex Q. h) Clause 15 has been updated with the aim to improve ease of use, using experience from oil and gas and considering unique wind turbine characteristics; updates included guidance for TLPs, damage stability, dynamic stability, testing and the addition for Annex S regarding how to analyse collision probability.
Windenergieanlagen - Teil 3-2: Auslegungsanforderungen für schwimmende Windenergieanlagen auf offener See
Systèmes de génération d’énergie éolienne - Partie 3-2: Exigences de conception des éoliennes en mer flottantes
l'IEC 61400-3-2:2025 spécifie des exigences d'évaluation des conditions externes sur un site d'éoliennes en mer flottantes (FOWT), ainsi que les exigences essentielles de conception, afin d'assurer l'intégrité technique des FOWT. Elle a pour objet de fournir un niveau de protection approprié contre les dommages provoqués par tous les dangers prévus pendant la durée de vie prévue. Le présent document se concentre sur l'intégrité technique des composants structurels d'une FOWT, mais concerne également les sous-systèmes, tels que les mécanismes de commande et de protection, les systèmes électriques internes et les systèmes mécaniques. Cette première édition annule et remplace l'IEC TS 61400-3-2 parue en 2019. Cette première édition annule et remplace l'IEC TS 61400-3-2 parue en 2019. a) le contenu pertinent de l'IEC 61400-3-1 a été transféré dans l'IEC 61400-3-2, faisant de l'IEC 61400-3-2 un document autonome qui ne doit pas être lu directement conjointement avec l'IEC 61400-3-1; b) plusieurs modifications ont été apportées concernant les conditions océano-météorologiques spécifiées à l'Article 6 en prenant en compte la nature de la FOWT et le site en mer sur lequel la FOWT est installée, notamment: (1) l'importance de la propagation directionnelle des vagues a été soulignée, car elle peut entraîner des charges plus importantes pour la FOWT, y compris l'ajout des nouvelles Annexe O et Annexe P informatives, et (2) la caractéristique de la houle a été expliquée, ce qui peut être pertinent pour certains projets FOWT, y compris l'ajout d'une nouvelle Annexe R informative concernant la caractéristique de la houle; c) les 7.1, 7.2, 7.3, 7.4 et 7.5 ont été modifiés pour inclure un tableau de DLC (Design Load Case, cas de charge pour la conception) révisé et ses descriptions associées, y compris, entre autres, des exigences mises à jour sur la directionnalité, les conditions de vagues, les cas de contrôle de redondance et de stabilité après avarie, et un cas de contrôle de solidité; d'autres mises à jour sont effectuées concernant les recommandations et les éléments nécessaires fournis sur les calculs de charge et les exigences de simulation; d) le 7.6 a été mis à jour avec des recommandations relatives à l'évaluation de la fatigue ainsi que des clarifications sur l'analyse de l'aptitude au service et le matériel applicable pour le WSD. L'Annexe L connexe a été mise à jour et une nouvelle Annexe M a été ajoutée pour la clarification des facteurs de sécurité et l'approche de charge et d'effet de charge pour les sous-structures flottantes; e) le concept de système de commande de flotteur qui interagit avec le régulateur de l'éolienne a été introduit à l'Article 8; f) l'Article 11 "Conception de la fondation et de la sous-structure" a été renommé en "Conception des ancres" et des exigences relatives aux conditions transitoires ont été ajoutées; g) un article plus détaillé sur la conception du béton a été ajouté à l'Article 16 ainsi qu'une Annexe Q informative; h) l'Article 15 a été mis à jour dans le but d'améliorer la facilité d'utilisation, en utilisant l'expérience du pétrole et du gaz et en prenant en compte les caractéristiques uniques des éoliennes. Les mises à jour comprenaient des recommandations pour les TLP, la stabilité après avarie, la stabilité dynamique, les essais et l'ajout de l'Annexe S concernant la manière d'analyser la probabilité de collision.
Sistemi za proizvodnjo energije na veter - 3-2. del: Zahteve za načrtovanje plavajočih vetrnih turbin na morju (IEC 61400-3-2:2025)
Ta del standarda IEC 61400 določa dodatne zahteve za ocenjevanje zunanjih pogojev na območju plavajočih vetrnih turbin na morju (FOWT) in temeljne zahteve za načrtovanje, s katerimi se zagotovi inženirska celovitost plavajočih vetrnih turbin na morju. Njegov namen je zagotoviti ustrezno raven zaščite pred poškodbami zaradi vseh pričakovanih nevarnosti v predvideni življenjski dobi.
Ta dokument se osredotoča na inženirsko celovitost sestavnih delov konstrukcije plavajoče vetrne turbine na morju, obravnava pa tudi podsisteme, kot so nadzorni in zaščitni mehanizmi, notranji električni sistemi ter mehanski sistemi.
Vetrno turbino je treba obravnavati kot plavajočo vetrno turbino na morju, če je plavajoča podkonstrukcija podvržena hidrodinamični obremenitvi ter jo podpirajo sile plovnosti in vzdrževalni sistem. Plavajoča vetrna turbina na morju zajema pet glavnih podsistemov: sklop rotorja in gondole (RNA), steber, plavajočo podkonstrukcijo, vzdrževalni sistem ter stroje, opremo in sisteme na ploščadi, ki niso del sklopa rotorja in gondole.
V kontekstu tega dokumenta so izrecno obravnavane naslednje vrste plavajočih podkonstrukcij:
• konstrukcije in plovila v obliki ladje; • enote, ki so pol pod vodo (Semi); • navigacijske boje (Spar);• navpično zasidrane ploščadi/boje (TLP/TLB).
Ta dokument je mogoče uporabljati tudi za druge vrste konstrukcij, ki niso navedene zgoraj, pri čemer bo morda treba posebno pozornost nameniti podpori novih funkcij, da se doseže enaka ciljna stopnja varnosti.
Te druge konstrukcije se lahko zelo razlikujejo z vidika geometrije, materialov in strukturnih oblik, zato so lahko le delno zajete v zahtevah tega dokumenta.
V drugih primerih posameznih zahtev v tem dokumentu morda ni mogoče uporabiti za celotno načrtovano konstrukcijo ali njen del. V vseh zgoraj navedenih primerih bo za skladnost s tem dokumentom potrebno, da načrtovanje temelji na temeljnih načelih tega dokumenta in doseže stopnjo varnosti, ki je enakovredna ali večja od predvidene stopnje.
Ta dokument se uporablja za plavajoče konstrukcije brez posadke, ki vključujejo turbino z eno horizontalno osjo. Čeprav se splošno uporablja, so lahko potrebni dodatni premisleki, npr. za enote z več turbinami na eni plavajoči podkonstrukciji, vetrne turbine z navpično osjo, plavajoče vetrne turbine na morju s skupnim zasidranjem, vrteče se nosilce, plavajoče konstrukcije brez vzdrževalnega sistema ali kombinirane sisteme vetrne energije/energije valovanja.
Ta dokument je treba uporabljati skupaj z ustreznimi standardi IEC in ISO, navedenimi v točki 2. Ta dokument je v celoti skladen z zahtevami iz standarda IEC 61400-1.
V primeru nasprotujočih si zahtev v tem dokumentu in zvezah s standardi imajo prednost zahteve tega dokumenta.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2025
Sistemi za proizvodnjo energije na veter - 3-2. del: Zahteve za načrtovanje
plavajočih vetrnih turbin na morju (IEC 61400-3-2:2025)
Wind energy generation systems - Part 3-2: Design requirements for floating offshore
wind turbines (IEC 61400-3-2:2025)
Windenergieanlagen - Teil 3-2: Auslegungsanforderungen für schwimmende
Windenergieanlagen auf offener See (IEC 61400-3-2:2025)
Systèmes de génération d’énergie éolienne - Partie 3-2: Exigences de conception des
éoliennes en mer flottantes (IEC 61400-3-2:2025)
Ta slovenski standard je istoveten z: EN IEC 61400-3-2:2025
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN IEC 61400-3-2
NORME EUROPÉENNE
February 2025
EUROPÄISCHE NORM
ICS 27.180
English Version
Wind energy generation systems - Part 3-2: Design
requirements for floating offshore wind turbines
(IEC 61400-3-2:2025)
Systèmes de génération d'énergie éolienne - Partie 3-2: Windenergieanlagen - Teil 3-2: Auslegungsanforderungen
Exigences de conception des éoliennes en mer flottantes für schwimmende Windenergieanlagen auf offener See
(IEC 61400-3-2:2025) (IEC 61400-3-2:2025)
This European Standard was approved by CENELEC on 2025-02-26. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 20252025 All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
CENELEC
Ref. No. EN IEC 61400-3-2:2025 E
European foreword
The text of document 88/1028/FDIS, future edition 1 of IEC 61400-3-2, prepared by TC 88 "Wind
energy generation systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61400-3-2:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-02-28
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-02-29
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document is read in conjunction with EN IEC 61400-1.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61400-3-2:2025 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 61400-24 NOTE Approved as EN IEC 61400-24
ISO 12944-2 NOTE Approved as EN ISO 12944-2
ISO 12944-9 NOTE Approved as EN ISO 12944-9
ISO 13628-5 NOTE Approved as EN ISO 13628-5
ISO 19901-2 NOTE Approved as EN ISO 19901-2
ISO 19901-8 NOTE Approved as EN ISO 19901-8
ISO 19901-10 NOTE Approved as EN ISO 19901-10
IEC 60721-3-3 NOTE Approved as EN IEC 60721-3-3
ISO 12944-2 NOTE Approved as EN ISO 12944-2
ISO 12944-9 NOTE Approved as EN ISO 12944-9
ISO 19902 NOTE Approved as EN ISO 19902
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60721 series Classification of environmental EN 60721 series
IEC 61400-1 2019 Wind energy generation systems - Part 1: EN IEC 61400-1 2019
Design requirements
IEC 61400-3-1 - Wind energy generation systems - Part 3- EN IEC 61400-3-1 -
1: Design requirements for fixed offshore
wind turbines
IEC 61400-13 - Wind turbines - Part 13: Measurement of EN 61400-13 -
mechanical loads
IEC 61400-15-1 - Wind energy generation systems - Part 15- EN IEC 61400-15- -
1: Site suitability input conditions for wind 1
power plants
IEC 61400-24 - Wind energy generation systems - Part 24: EN IEC 61400-24 -
Lightning protection
ISO 2394 - General principles on reliability for - -
structures
ISO 2533 - Standard Atmosphere - -
ISO 18692-1 - Fibre ropes for offshore stationkeeping - - -
Part 1: General specification
ISO 18692-2 - Fibre ropes for offshore stationkeeping - - -
Part 2: Polyester
ISO 18692-3 - Fibre ropes for offshore stationkeeping - - -
Part 3: High modulus polyethylene (HMPE)
ISO 19900 - Petroleum and natural gas industries - EN ISO 19900 -
General requirements for offshore
structures
Under preparation. Stage at the time of publication: IEC/AFDIS 61400-15-1:2023.
Under preparation. Stage at the time of publication: FprEN IEC 61400-15-1:2024.
Publication Year Title EN/HD Year
ISO 19901-1 - Petroleum and natural gas industries - EN ISO 19901-1 -
Specific requirements for offshore
structures - Part 1: Metocean design and
operating considerations
ISO 19901-4 - Petroleum and natural gas industries - EN ISO 19901-4 -
Specific requirements for offshore
structures - Part 4: Geotechnical and
foundation design considerations
ISO 19901-6 - Petroleum and natural gas industries - EN ISO 19901-6 -
Specific requirements for offshore
structures - Part 6: Marine operations
ISO 19901-7 - Petroleum and natural gas industries - EN ISO 19901-7 -
Specific requirements for offshore
structures - Part 7: Stationkeeping systems
for floating offshore structures and mobile
offshore units
ISO 19902 - Petroleum and natural gas industries - EN ISO 19902 -
Fixed steel offshore structures
ISO 19903 - Petroleum and natural gas industries - EN ISO 19903 -
Concrete offshore structures
ISO 19904-1 - Petroleum and natural gas industries - EN ISO 19904-1 -
Floating offshore structures - Part 1: Ship-
shaped, semi-submersible, spar and
shallow-draught cylindrical structures
ISO 19906 - Petroleum and natural gas industries - EN ISO 19906 -
Arctic offshore structures
ISO 29400 - Ships and marine technology - Offshore - -
wind energy - Port and marine operations
IEC/TS 61400-30 2023 Wind energy generation systems - Part 30: - -
Safety of wind turbine generators - General
principles for design
API RP 2T - Planning, Designing, and Constructing - -
Tension Leg Platforms
IMO - International Code on Intact Stability - -
IMO - MODU CODE - -
IEC 61400-3-2 ®
Edition 1.0 2025-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Wind energy generation systems –
Part 3-2: Design requirements for floating offshore wind turbines
Systèmes de génération d’énergie éolienne –
Partie 3-2: Exigences de conception des éoliennes en mer flottantes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-9825-1
– 2 – IEC 61400-3-2:2025 © IEC 2025
CONTENTS
FOREWORD . 8
INTRODUCTION . 11
1 Scope . 12
2 Normative references . 13
3 Terms and definitions . 14
4 Symbols, units and abbreviated terms . 26
4.1 General . 26
4.2 Symbols and units. 26
4.3 Abbreviated terms . 27
5 Principal elements . 28
5.1 General . 28
5.2 Design methods . 28
5.3 Safety level for FOWT . 30
5.4 Safety classes for RNA and tower . 30
5.5 Quality assurance . 30
5.6 Rotor–nacelle assembly markings . 30
5.7 Support structure markings . 31
6 External conditions – definition and assessment . 31
6.1 General . 31
6.2 Wind turbine classes . 31
6.3 Definition of external conditions at a FOWT site . 32
6.3.1 General . 32
6.3.2 Wind conditions . 32
6.3.3 Marine conditions . 33
6.3.4 Electrical power network conditions . 40
6.3.5 Other environmental conditions . 40
6.4 Assessment of external conditions at a FOWT site . 41
6.4.1 General . 41
6.4.2 The metocean database . 41
6.4.3 Assessment of wind conditions . 42
6.4.4 Assessment of marine conditions . 44
6.4.5 Assessment of other environmental conditions . 48
6.4.6 Assessment of electrical network conditions . 49
6.4.7 Assessment of soil conditions . 49
7 Structural design . 50
7.1 General . 50
7.2 Design methodology . 51
7.3 Loads. 51
7.3.1 General . 51
7.3.2 Gravitational and inertial loads . 51
7.3.3 Aerodynamic loads . 51
7.3.4 Actuation loads . 51
7.3.5 Hydrodynamic loads . 52
7.3.6 Sea/lake ice loads . 52
7.3.7 Other loads . 52
7.4 Design situations and load cases . 53
IEC 61400-3-2:2025 © IEC 2025 − 3 −
7.4.1 General . 53
7.4.2 Power production (DLC 1.1 to 1.6) . 63
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 – 2.6) . 64
7.4.4 Start up (DLC 3.1 to 3.3). 66
7.4.5 Normal shutdown (DLC 4.1 to 4.3) . 67
7.4.6 Emergency stop (DLC 5.1) . 68
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.5) . 68
7.4.8 Parked plus fault conditions (DLC 7.1 and 7.2) . 69
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 to 8.4) . 70
7.4.10 Redundancy check and damage stability (DLC F1.1 to F2.3) . 74
7.5 Load and load effect calculations . 75
7.5.1 General . 75
7.5.2 Relevance of hydrodynamic loads . 75
7.5.3 Calculation of hydrodynamic loads . 76
7.5.4 Calculation of sea/lake ice loads . 77
7.5.5 Overall damping assessment for support structure response evaluations . 77
7.5.6 Simulation requirements . 78
7.5.7 Other requirements . 82
7.6 Limit state analysis . 83
7.6.1 Method . 83
7.6.2 Ultimate strength analysis . 86
7.6.3 Fatigue analysis . 87
7.6.4 Serviceability analysis . 88
8 Control system . 89
9 Mechanical systems . 90
10 Electrical system . 91
11 Anchor design . 91
12 Assembly, transport and installation . 91
12.1 General . 91
12.2 Planning . 92
12.3 Environmental conditions . 92
12.4 Documentation . 92
12.5 Transport, receiving, handling and storage . 93
13 Commissioning, operation and maintenance . 93
13.1 General . 93
13.2 Design requirements for safe operation, inspection and maintenance . 93
13.3 Commissioning . 94
13.3.1 General . 94
13.3.2 Energization . 95
13.3.3 Commissioning tests . 95
13.3.4 Records . 95
13.3.5 Post commissioning activities . 95
13.4 Operator’s instruction manual . 95
13.4.1 General . 95
13.4.2 Instructions for operations and maintenance record . 96
13.4.3 Instructions for unscheduled automatic shutdown . 96
13.4.4 Instructions for diminished reliability . 96
– 4 – IEC 61400-3-2:2025 © IEC 2025
13.4.5 Work procedures plan . 96
13.4.6 Emergency procedures plan . 97
13.5 Maintenance manual . 97
14 Stationkeeping systems . 98
14.1 General . 98
14.2 Catenary, semi-taut or taut stationkeeping systems . 98
14.3 Tendon systems . 99
14.4 Synthetic mooring . 99
14.5 Stationkeeping system hardware . 99
14.6 Dynamic power cable . 99
15 Floating stability . 100
15.1 General . 100
15.2 Intact static stability criteria . 101
15.3 Quasi static evaluation . 101
15.4 Dynamic response evaluation . 102
15.5 Damage stability criteria . 102
16 Materials . 103
17 Marine support systems . 103
17.1 General . 103
17.2 Bilge system . 103
17.3 Ballast system . 103
Annex A (informative) Key design parameters for a floating offshore wind turbine
(FOWT) . 104
A.1 Floating offshore wind turbine (FOWT) identifiers. 104
A.1.1 General . 104
A.1.2 Rotor nacelle assembly (machine) parameters . 104
A.1.3 Support structure parameters . 105
A.1.4 Wind conditions (based on a 10-min reference period and including
wind farm wake effects where relevant) . 105
A.1.5 Marine conditions (based on a 3-hour reference period where relevant) . 106
A.1.6 Electrical network conditions at turbine . 107
A.2 Other environmental conditions . 107
A.3 Limiting conditions for transport, installation and maintenance . 108
Annex B (informative) Guidance on calculation of hydrodynamic loads . 109
B.1 General . 109
B.2 Morison’s equation . 109
B.3 Diffraction and radiation theory . 109
B.4 Slam loading . 110
B.5 Vortex-induced vibrations and motions . 110
B.6 Appurtenances and marine growth . 111
B.7 Global analysis and fatigue analysis methods . 111
B.8 Breaking wave loads . 112
B.9 Air gap . 112
Annex C (informative) Floating offshore wind turbine (FOWT) anchor design . 113
Annex D (informative) Statistical extrapolation of operational metocean parameters for
ultimate strength analysis . 114
D.1 General . 114
D.2 Use of IFORM to determine 50-yr significant wave height conditional on
mean wind speed . 114
IEC 61400-3-2:2025 © IEC 2025 − 5 −
D.3 Examples of joint distributions of V and H and approximations to the
s
environmental contour . 116
D.4 Choice of sea state duration . 118
D.5 Determination of the extreme individual wave height to optionally be
embedded in SSS . 119
Annex E (informative) Corrosion protection . 120
E.1 General . 120
E.2 The marine environment . 120
E.3 Corrosion protection considerations . 121
E.4 Corrosion protection systems – Support structures . 121
E.5 Corrosion protection in the rotor-nacelle assembly . 122
Annex F (informative) Prediction of extreme wave heights during tropical cyclones . 123
F.1 General . 123
F.2 Wind field estimation for tropical cyclones . 123
F.3 Wave estimation for tropical cyclones . 124
Annex G (informative) Recommendations for alignment of safety levels in tropical
cyclone regions . 125
G.1 General . 125
G.2 Global robustness level criteria . 125
G.3 Design load cases. 125
Annex H (informative) Earthquakes . 127
Annex I (informative) Model tests . 128
Annex J (informative) Tsunamis . 131
J.1 General . 131
J.2 Numerical model of tsunami [51], [52] . 131
J.3 Evaluation of variance of water surface elevation and current velocity [5] . 134
Annex K (informative) Redundancy of stationkeeping system . 135
Annex L (informative) Differing limit state methods in IEC and ISO standards . 136
Annex M (informative) Application of load and load effect logic to floating substructure
design . 138
M.1 General . 138
M.2 Typical load computation setups . 138
M.3 Applied example . 139
Annex N (informative) Guidance on simulation length and associated parameters . 140
N.1 General considerations . 140
N.1.1 General . 140
N.1.2 Initial transient time . 140
N.1.3 Low-frequency dynamics sampling . 140
N.1.4 Reference period . 140
N.2 Simulations for fatigue limit state analysis . 141
N.2.1 General . 141
N.2.2 Response variance and reference period . 141
N.2.3 Statistical convergence of damage . 141
N.3 Simulations for extreme limit state analysis . 141
N.3.1 General . 141
N.3.2 Characteristic extreme consistency with the reference period . 142
N.3.3 Characteristic value variability . 142
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Annex O (informative) Estimation of wave directional spreading by long wave method /
single point measurement . 143
O.1 Background. 143
O.2 Linear free-wave extraction . 144
O.3 Second-order calculation . 144
Annex P (informative) Direction spreading function . 146
Annex Q (informative) Concrete structures design . 147
Q.1 General . 147
Q.2 Design load cases. 147
Q.2.1 Limit states in reinforced concrete design . 147
Q.2.2 ULS, ALS and FLS load cases . 148
Q.2.3 SLS load cases . 148
Q.2.4 Load factors . 148
Q.3 Design criteria . 149
Q.3.1 Material factors . 149
Q.3.2 ULS, ALS, FLS verifications . 149
Q.3.3 SLS: Watertightness verification . 150
Q.3.4 SLS: Crack-opening verification . 150
Q.3.5 SLS: Limitation of stresses . 150
Annex R (informative) Relationship between peak wave period and significant wave
height in the sea areas affected by swell. 151
R.1 General . 151
R.2 Relationship between wave height and wave period in the sea areas affected
by swell . 151
Annex S (informative) Application of damage stability criteria . 152
S.1 Objective . 152
S.2 Scenario of loss of floating stability . 152
S.3 Flow of application of new damage stability criteria . 152
S.4 Definition of target probability of failure (PS) . 153
S.5 Definition of collision probability (P1) . 154
S.6 Definition of total loss probability by ship collision (P2) . 156
S.6.1 Concept of estimation of P2 and PT . 156
S.6.2 Simplification of FEM analysis . 156
S.6.3 Estimation of P2 by limit curve . 158
S.7 Additional countermeasure to reduce P2 . 159
Bibliography . 160
Figure 1 – Parts of a floating offshore wind turbine (FOWT) . 16
Figure 2 – Rigid-body motion degrees of freedom of a floating substructure; illustration
by Alfred Hicks, National Renewable Energy Laboratory . 17
Figure 3 – Design process for a floating offshore wind turbine (FOWT) . 29
Figure 4 – Definition of water levels . 38
Figure 5 – Top-down view of nacelle yaw and nacelle yaw misalignment in a simulation . 62
Figure 6 – The two approaches to calculate the design load effect . 84
Figure D.1 – Example of the construction of the 50-year environmental contour for a 3-
hour sea state duration . 115
Figure J.1 – The calculated result of Equation (J.8) . 133
IEC 61400-3-2:2025 © IEC 2025 − 7 −
Figure M.1 – Example of load and load effect workflow for a hybrid "beams" and
"nodes" floating substructure model setup . 139
Figure O.1 – A typical 60-min (full-scale) time history spectrum with Hs = 6,18 m and
Tp = 10,36 s recorded at the Ocean Engineering Wide Tank, University of Ulsan,
Korea (South) . 143
Figure R.1 – The relationship between significant wave height and significant wave
period based on the measurement at Fukushima offshore site [2] . 151
Figure S.1 – Concept flow of application of new damage stability criteria . 153
Figure S.2 – Concept image of the approaching frequency . 155
Figure S.3 – Concept of estimation of P2 and PT in a strict way. 156
Figure S.4 – Concept of a limit curve . 158
Figure S.5 – Concept of the probability of total loss probability by ship collision. 158
Table 1 – Conversion between extreme wind speeds of different averaging periods . 42
Table 2 – Design load cases . 56
Table 3 – Safety factor for yield stress . 87
Table G.1 – Additional load cases for tropical cyclone affected regions . 126
Table L.1 – Mapping of limit states in ISO 19904-1 Table 4 and load cases from
IEC 61400-3-2 . 137
Table Q.1 – Partial factors γ for actions for different limit states . 149
F
Table Q.2 – Material factors γ for different limit states and materials . 149
m
Table Q.3 – Allowable crack-width for different exposure zones . 150
Table S.1 – Annual reliability of offshore structures . 154
– 8 – IEC 61400-3-2:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –
Part 3-2: Design requirements for floating offshore wind turbines
FOREWORD
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IEC 61400-3-2 has been prepared by IEC technical committee 88: Wind energy generation
systems. It is an International Standard.
This first edition cancels and replaces IEC TS 61400-3-2, published in 2019. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to
IEC TS 61400-3-2:
a) The relevant contents of IEC 61400-3-1 have been migrated into IEC 61400-3-2, making
IEC 61400-3-2 a self-standing document that does not have to be read directly in
conjunction with IEC 61400-3-1.
IEC 61400-3-
...
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