RECOFF

This is the home page of the research and development project 'Recommendations for Design of Offshore Wind Turbines' financially supported by the European Community (contract no. ENK5-CT-2000-00322, acronym RECOFF) under the Energy, Environment and Sustainable Development Programme, a Fifth Framework Programme (1998-2002). The project has been coordinated by Risø National Laboratory, Denmark, and has run over the period from 1^st of January 2001 to the 31^st of August 2004.

The purpose of this home page is to report on the projects results. The documents on the page may be downloaded in pdf-format. The page is maintained by Niels Jacob Tarp-Johansen (The Danish National Research Laboratory, Risø, phone: +45 4677 5078) and has been updated Jan 24 2007.

Contents

Project Summary

Technical Summary Report and Project Documents

Links to project partners and person contacts

Links and material relevant to the project

Internal Home Page (Authorisation required)

Project Summary

Project Objectives

The objective has been to prepare guidelines and recommendations for design of offshore wind turbines. The main intended use of the project results has been the provision of recommendations for European and national standards for offshore wind turbines and the develop-ment of certification rules for offshore wind turbines. The success of the project will be marked by the delivery of reliable and robust design methods and certification rules needed for the safe development of offshore wind farms. This will have direct impact on the readiness to invest in offshore wind energy projects and cut objections connected with project safety.

Main Results

Readily available information has been reviewed and utilisation to the extent possible has been made. In several areas a need for research was identified and generic results were ob-tained. Specifically, we emphasize the following subjects where recommendations have been obtained:

• External conditions: review of existing standards, regulations and literature resulting in recommendations for good practice.

• Analysis methods: methods for lumping, mainly with respect to wave loading, of fa-tigue load cases.

• Analysis methods: principle of synthesizing load cases for different wind directions, wind speeds, and sea states in order to obtain extreme response during normal operation.

• Design load cases: drafting, partially based on project results, proposals for a suitable, i.e. limited and representative, DLC table for offshore turbines.

• Probabilistic methods: review of general methods and application of probabilistic cali-bration methods to the combined action of wind and wave loads in the storm event.

• Structural integrity: based on discussions about reliability levels onshore and offshore and based on comparisons with current practise proposals for safety factors in fatigue and extreme load events are given.

• Operation and maintenance: documents with recommendations regarding labour safety, and monitoring of turbine performance have been prepared.

Implementation of Results

The RECOFF project has run in parallel with a working group (TC88-WG03) set up by the IEC (International Electro-technical Commission) and assigned the task of preparing a separate international standard for design of offshore wind turbines. Several of the RECOFF part-ners are members of the IEC-TC88-WG03, which has caused a strong interaction with current international standardisation work, and a rapid implementation of the findings of the RECOFF project in terms of obtaining the status of being standards’ material. Once, approx. one year from now, the IEC standard 61400-3 has been accepted it will shortly afterwards become a European CENELEC standard. Thus the intended aim of the project has been achieved. Already some project results have been applied in the IEC standard 61400-1, which is the general standard for design requirements for wind turbines to which 61400-3 refers.

Technical Summary Report and Project Documents

The technical summary report is obtained from this link below:

       Technical Summary Report

Further the RECOFF documents are below listed and organised by subject. The number in the second column refers to the original working numbering applied in the project. The numbering may be useful when contacting project partners, and because some references are made by number. Immediately below follow links to each subject. After that come links for each original RECOFF document number and finally links to the documents by title.

      Subject:

1 Existing Standards
2 External Conditions

3 Analysis Methods and Design Load Cases

4 Structural Reliability Methods and Safety Factor Calibration

5 Structural integrity

6 Operation and maintenance

7 Presentations and Miscellaneous

RECOFF doc. no.:

2, 4, 5, 6, 9, 11, 11a, 12, 13, 14, 15, 15a, 16, 16a, 17, 19, 23, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90

1 Existing Standards

  

Title	No.
1.1 List of rules and regulations for offshore wind turbines	4
1.2 Relevant British Standards	9

2 External Conditions

  

Title	No.
2.1 External conditions, state of the art of existing regulations.	26
2.2 Guidelines for identifying, measuring and modelling of external conditions	67
2.3 Re-calculation of std(U)	56
2.4 Recommendations for design of offshore wind turbines External Conditions, A paper	82

3 Analysis Methods and Design Load Cases

  

Title	No.
3.1 Wind and wave misalignment effect on fatigue loading	11
3.2 Wind and wave misalignment effect on fatigue loading (in continuation of document 11)	11a
3.3 Tidal level effects on support structure loading	12
3.4 Mean Water Depth and Support Structure Stiffness Effects on Support Structure Loading	13
3.5 Tidal current effects on support structure loading	14
3.6 Fatigue Load Parametric Studies; Wave Effects and Simulation Length requirements	15
3.7 Simulation Length Requirements for Offshore Fatigue Load Calculations (in continuation of document 15)	15a
3.8 'Lumping' of Fatigue Load Cases	16
3.9 'Lumping' of Fatigue Load Cases (in continuation of document 16)	16a
3.10 Collated sensitivity studies	27
3.11 Extrapolation Including Wave Loads; Replacing the Distribution of HS by a Suitable Percentile	19
3.12 The Influence of the Dependency of Mean Wind Speeds on the Extreme Response of Wind Turbines in the Operational Range	40
3.13 Extreme Response During Operation; Comparing the use of an extreme turbulence model and proper extrapolation	85
3.14 Investigation into IEC Offshore draft standard Design Load Case (DLC) 1.1	59
3.15 Collated Sensitivity Studies II: focus on draft load cases.	70
3.16 Draft IEC 61400-3, Annex C, (informative), Shallow water hydrodynamics and breaking waves	35
3.17 Draft Annex C for draft standard prepared by IEC-TC88-WG03. Based on IEC-TC88-WG03 document 10160	64
3.18 Draft Annex D for draft standard prepared by IEC-TC88-WG03	63
3.19 Additional loads, boat impact; Other maintenance loads	69
3.20 Spatially average of turbulence intensity inside large wind turbine arrays, presented at 2003 OWEMES	68
3.21 Presentation of the DLC table proposed for the IEC 61400-3 standard	72
3.22 Effect of Waves On Ultimate Loads Produced by IEC load cases DLC 1.4 & 1.5	60
3.23 Study of DLC 1.4 and DLC 1.5, background document for document no. 60	62
3.24 Approximate Maximum Value Distribution for Narrow Banded Gaussian Processes with Linearly Varying Mean Value	84
3.25 Peak Factors for the Sum Process of two Independent Stationary Gaussian Processes, Some Analytical Results	58
3.26 Derivation of tower top acceleration due to hydrodynamic loading	61
3.27 Approximate tower top acceleration	42
3.28 Frequency Domain Analysis of Offshore Wind Turbines	81
3.29 Verification Simulations of DLC 1.2 and 6.1 a,b,c	90
3.30 HAWC Load Simulation of Generic 5MW Offshore Wind Turbine Model	87
3.31 Final report from CRESS on test calculations	88

4 Structural Reliability Methods and Safety Factor Calibration

  

Title	No.
4.1 Partial Safety Factors for Extreme Load Effects in Wind Turbines.	6
4.2 Note: updated safety level evaluations relative to the background document for Partial Safety Factors in the 3rd Ed. of IEC 61400-1: Wind Turbine Generator Systems: Safety Requirements	77
4.3 Partial Safety Factors and Characteristic Values for Combined Extreme Wind and Wave Load Effects, an extended version.	71
4.4 Load Combination in a Storm Event	38
4.5 Storm Profiles for Wind Loads	89
4.6 Structural reliability methods applicable for offshore wind turbines, a short review	73
4.7 Examples of Fatigue Lifetime and Reliability Evaluation of Larger Wind Turbine Components (2003)	25
4.8 The accuracy of wind turbine design codes derived from VEWTDC results	17

5 Structural integrity

  

Title	No.
5.1 Corrosion Protection for Offshore Wind Turbines	34
5.2 Comparison of international regulations with regard to the achieved bearing capacity of structural members.	24
5.3 Review of existing design methods using analytical and numerical tools for integrated design procedures for offshore turbines	23
5.4 Probable inconsistency load case 6.1	30
5.5 On the calculation of combined wind and wave loads (example DLC 6.1)	33
5.6 Combined Characteristic Extreme Loads	86
5.7 Memo on The Algorithm Behind DLC 6.1	54
5.8 Memo Concerning DLC 6.1	57
5.9 Transformation of Climate Data Between Different Reference Time Periods	55
5.10 Calculation methods for DLC6.x, discussion note	65
5.11 Design of Concrete Structures for Offshore Wind Turbines, a paper	50

6 Operation and maintenance

  

Title	No.
6.1 Labour Safety and Health and Safety	28
6.2 Optimisation of the O&M costs to lower the energy costs	74
6.3 Proposal for standardisation/interface for data-collection	75

7 Presentations and Miscellaneous

  

Title	No.
7.1 Offshore certification (2001)	5
7.2 “Load Analysis and Certification of Offshore Wind Turbines” K. Argyriadis, S. Schwartz, EWEC 2003.	31
7.3 An offshore wind turbine model, Proc. of EWEC 2001, Copenhagen, Denmark July 2001	2
7.4 Wind conditions for offshore wind turbine design, RECOFF, comparison of Standards and Regulations, 3rd IEA experts meeting on wind conditions for turbine design	32
7.5 Response Extrapolation for Offshore Wind Turbines, Poster at EWEC 2003	43
7.6 Response Extrapolation for Offshore Wind Turbines, The poster corresponding to document no. 43	66
7.7 Safety Factors and Model Uncertainty, IEA Annex 11, 2002	44
7.8 Calibration of Partial Safety Factors for Extreme Loads on Wind Turbines, Oral Presentation at EWEC 2003	41
7.9 Udvikling indenfor offshore standardisering og relateret udviklingsarbejde , PowerPoint presentation at Dansk Vindenergi's konference, 2003, in Danish	45
7.10 Fatigue and extreme loads in wind farm clusters - and need for measurements, PowerPoint presentation at ENDOW workshop, Risø March 7-8 2002	46
7.11 Background for ”effective” turbulence model	47
7.12 Extrapolation of extreme wind loads during normal operation, poster at EWEC 2003	48
7.13 Vindlaster på offshorevindmøller, presented at Dansk Vandteknisk Selskabs Møde i Nysted, 2003, in Danish	49
7.14 Wave Spectrums and Forces For the Design Load Cases 1.2 & 6.1a,b,c of the 61400-3 IEC Standard	51
7.15 Partial Safety Factors and Characteristic Values for Combined Extreme Wind and Wave Load Effects, Special Topic Conference, TU Delft 2004	37
7.16 Partial Safety Factors and Characteristic Values for Combined Extreme Wind and Wave Load Effects, power point presentation at EAWE Special Topic Conference, TU Delft, 19-21 April. 2004	52
7.17 Partial Safety Factors and Characteristic Values for Combined Extreme Wind and Wave Load Effects, an extention of document no. 52	53
7.18 Extreme structural loads at non-extreme mean wind speeds	80
7.19 Extreme structural loads at non-extreme mean wind speeds, Poster	83

Risø National Laboratory (Denmark) (Project Coordninator): 

Sten Frandsen, sten.frandsen@risoe.dk phone: +45 4677 5072
Niels Jacob Tarp-Johansen, niels.jacob.tarp-johansen@risoe.dk

Garrad Hassan & Partners Ldt (United Kingdom): 

David Quarton, quarton@garradhassan.co.uk

Tim Camp, camp@garradhassan.co.uk

Ed Norton, norton@garradhassan.co.uk

Germanischer Lloyd Certification GmbH (Germany): 

Kimon Argyriadis, as@gl-group.com

Christian Nath, na@gl-group.com

Netherlands Energy Research Foundation (Holland): 

Bernard H. Boulder, bulder@ecn.nl

Centre for Renewable Energy Sources, CRES (Greece): 

Kyriakos Rossis, kros@cres.gr

Pantelis Vionis, pvioni@cres.gr

Webmaster
Jan 24 2007