IEC TS 62600-3:2020

Marine energy - Wave, tidal and other water current converters - Part 3: Measurement of mechanical loads

IEC TS 62600-3:2020 describes the measurement of mechanical loads on hydrodynamic marine energy converters such as wave, tidal and other water current converters (including river current converters) for the purpose of load simulation model validation and certification. This document contains the requirements and recommendations for the measurement of mechanical loads for such activities as site selection, measurand selection, data acquisition, calibration, data verification, measurement load cases, capture matrix, post-processing, uncertainty determination and reporting.
This document also defines the requirements for full-scale structural testing of subsystems or parts with a special focus on full-scale structural testing of marine energy converter rotor blades and for the interpretation and evaluation of achieved test results. This document focuses on aspects of testing related to an evaluation of the structural integrity of the blade. The purpose of the tests is to confirm to an acceptable level of probability that the whole installed production of a blade type fulfils the design assumptions.

General Information

• Status: Published
• Publication Date: 13-May-2020
• ICS: 27.140 - Hydraulic energy engineering
• Technical Committee: TC 114 - Marine energy - Wave, tidal and other water current converters
• Drafting Committee: ahG 15 - TC 114/ahG 15
• Current Stage: PPUB - Publication issued
• Start Date: 14-May-2020
• Completion Date: 07-May-2020

Standards Content (Sample)

IEC TS 62600-3 ®
Edition 1.0 2020-05
TECHNICAL
SPECIFICATION
Marine energy – Wave, tidal and other water current converters –
Part 3: Measurement of mechanical loads
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IEC TS 62600-3 ®
Edition 1.0 2020-05
TECHNICAL
SPECIFICATION
Marine energy – Wave, tidal and other water current converters –

Part 3: Measurement of mechanical loads

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.140 ISBN 978-2-8322-8105-5

– 2 – IEC TS 62600-3:2020 © IEC 2020
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
1.1 General . 11
1.2 Subdivision of marine energy converter types . 11
2 Normative references . 14
3 Terms and definitions . 15
4 Symbols, units and abbreviated terms . 15
4.1 Symbols . 15
4.2 Greek symbols . 16
4.3 Subscripts . 17
4.4 Abbreviated terms . 17
5 General . 17
5.1 Document structure . 17
5.2 Safety during testing . 18
5.3 Technology qualification . 18
5.4 Load measurement . 18
6 Test requirements . 18
6.1 General . 18
6.2 Test site requirements all WEC and CEC . 19
6.3 Subsystem or structural component laboratory load testing . 19
6.4 Measurement load cases all WEC and CEC . 19
6.4.1 General . 19
6.4.2 MLCs during steady-state operation . 20
6.4.3 MLCs during transient events . 21
6.4.4 MLCs for dynamic characterization . 21
6.4.5 MLC for abnormal operating condition . 22
6.4.6 Capture matrices . 22
6.5 Measurement load cases for MECs with blades connected to a rotor shaft . 23
6.5.1 General . 23
6.5.2 MLCs for dynamic characterization . 23
6.5.3 Capture matrices . 24
6.6 Quantities to be measured for all WEC and CEC . 25
6.6.1 General . 25
6.6.2 Load quantities . 25
6.6.3 Meteorological and oceanographic quantities . 26
6.6.4 MEC operation quantities . 26
6.7 Quantities to be measured for MECs with blades connected to a rotor shaft. 27
6.7.1 General . 27
6.7.2 Load quantities . 28
6.7.3 Oceanographic and meteorological quantities . 28
6.7.4 MEC operation quantities . 28
6.8 MEC configuration changes . 29
7 Instrumentation . 29
7.1 Load quantities for all WEC and CEC . 29
7.1.1 General . 29

7.1.2 Types of sensors . 30
7.1.3 Choice of sensor location . 30
7.1.4 The connection between prime mover and PTO . 30
7.1.5 The connection between PTO and substructure and/or foundation . 31
7.1.6 The connection between PTO and floating device . 31
7.1.7 Measurement of station keeping loads . 31
7.1.8 Prime mover absolute and relative position . 31
7.1.9 PTO absolute and relative position . 32
7.1.10 Substructure or floating device absolute and relative position . 32
7.1.11 Water pressure measurements . 32
7.2 Operation quantities for all WEC and CEC . 32
7.2.1 General . 32
7.2.2 Electrical power . 32
7.2.3 Hydraulic power . 33
7.2.4 Generator speed . 33
7.2.5 Brake moment or force . 33
7.2.6 MEC status . 33
7.2.7 Brake status . 33
7.2.8 Draft or freeboard measurement . 33
7.3 Load quantities for MECs with blades connected to a rotor shaft . 33
7.3.1 General . 33
7.3.2 Blade root bending moments . 33
7.3.3 Blade bending moment distribution . 34
7.3.4 Blade torsion frequency/damping . 34
7.3.5 Rotor yaw and tilt moment . 34
7.3.6 Rotor torque . 34
7.3.7 Tubular column bending . 34
7.3.8 Darrieus style rotor bending . 35
7.3.9 PTO and blade absolute and relative position . 35
7.4 Operation quantities for MECs with blades connected to a rotor shaft . 35
7.4.1 General . 35
7.4.2 Rotor speed or generator speed . 35
7.4.3 Yaw misalignment . 35
7.4.4 Rotor azimuth angle. 35
7.4.5 Pitch position . 35
7.4.6 Pitch speed . 36
7.4.7 Brake moment . 36
7.5 Oceanographic and meteorological quantities . 36
7.5.1 General . 36
7.5.2 Measurement and installation requirements . 36
7.5.3 Sea or river ice loads and ice accretion . 36
7.6 Data acquisition system (DAS) . 36
7.6.1 General . 36
7.6.2 Resolution and sampling frequency . 36
7.6.3 Anti-aliasing. 37
8 Determination of calibration factors . 37
8.1 Overview. 37
8.2 General . 37

– 4 – IEC TS 62600-3:2020 © IEC 2020
8.3 Calibration of load channels for all WEC and CEC . 38
8.4 Calibration of non-load channels for all WEC and CEC . 38
8.5 Calibration of load channels for MECs with blades connected to a rotor shaft . 38
8.5.1 General . 38
8.5.2 Blade bending moments . 39
8.5.3 Main shaft moments . 40
8.5.4 Tubular column bending moments . 40
8.6 Calibration of non-load channels for MECs with blades connected to a rotor
shaft . 41
8.6.1 Pitch angle . 41
8.6.2 Rotor azimuth angle. 41
8.6.3 Yaw angle. 41
8.6.4 Oceanographic and meteorological . 41
8.6.5 Brake moment or force . 41
9 Data verification . 42
9.1 Overview. 42
9.2 General . 42
9.3 Verification checks for all WEC and CEC . 42
9.4 Verification checks for MECs with blades connected to a rotor shaft . 43
9.4.1 General . 43
9.4.2 Blade moments . 43
9.4.3 Main rotor shaft . 44
9.4.4 Tubular column . 44
10 Processing of measured data . 45
10.1 Overview. 45
10.2 General . 45
10.3 Load quantities . 45
10.4 Current speed and/or sea state trend detection . 45
10.5 Statistics . 46
10.6 Rainflow counting . 46
10.7 Cumulative rainflow spectrum . 46
10.8 Damage equivalent load (DEL) . 46
10.9 Current speed or wave energy flux binning . 47
10.10 Power spectral density (PSD) . 48
11 Uncertainty estimation . 48
12 Reporting. 48
Annex A (normative) Full-scale structural laboratory testing of rotor blades . 52
A.1 General . 52
A.2 Coordinate systems . 52
A.3 General principles . 54
A.3.1 Purpose of tests . 54
A.3.2 Limit states . 55
A.3.3 Practical constraints . 55
A.3.4 Results of test . 55
A.4 Documentation and procedures for test blade . 56
A.5 Blade test program. 56
A.5.1 Areas to be tested . 56
A.5.2 Test program . 57

A.6 Test plans . 58
A.6.1 General . 58
A.6.2 Blade description . 58
A.6.3 Loads and conditions . 58
A.6.4 Instrumentation . 58
A.6.5 Expected test results . 58
A.7 Load factors for testing . 59
A.7.1 General . 59
A.7.2 Partial safety factors used in the design . 59
A.7.3 Factors on materials . 59
A.7.4 Partial factors on loads . 59
A.7.5 Application of load factors to obtain the target load . 60
A.8 Test loading and test load evaluation . 61
A.8.1 General . 61
A.8.2 Influence of load introduction . 62
A.8.3 Static load testing . 62
A.8.4 Fatigue load testing . 63
A.9 Test requirements . 64
A.9.1 Test records . 64
A.9.2 Instrumentation calibration . 64
A.9.3 Measurement uncertainties . 64
A.9.4 Root fixture and test stand requirements . 64
A.9.5 Environmental conditions monitoring . 65
A.9.6 Deterministic corrections . 65
A.9.7 Static test . 65
A.9.8 Fatigue test . 66
A.9.9 Other blade property tests . 66
A.10 Test results evaluation . 67
A.10.1 General . 67
A.10.2 Catastrophic failure . 67
A.10.3 Permanent deformation, loss of stiffness or change in other blade
properties . 67
A.10.4 Superficial damage . 68
A.10.5 Failure evaluation . 68
A.11 Renewed testing . 68
A.12 Reporting . 69
A.12.1 General . 69
A.12.2 Test report content . 69
A.12.3 Evaluation of test in relation to design requirements . 70
Annex B (informative) Example coordinate systems for MECs with blades connected
to a rotor shaft . 71
B.1 General . 71
B.2 Blade coordinate system . 71
B.3 Hub coordinate system . 71
B.4 Nacelle coordinate system . 72
B.5 Tubular column coordinate system . 73
B.6 Yaw misalignment . 74
B.7 Cone angle and tilt angle . 74
B.8 Rotor azimuth angle . 75

– 6 – IEC TS 62600-3:2020 © IEC 2020
B.9 Blade pitch angle . 75
Annex C (informative) Recommendations for design and testing of MECs with respect
to ice loading and ice accretion . 76
Annex D (informative) Offshore load measurements . 77
D.1 General . 77
D.2 Fibre optic strain sensors . 77
D.3 Published experience . 78
D.4 Operational sound. 79
Annex E (informative) Uncertainty analysis . 80
Annex F (informative) Load model validation . 82
F.1 General . 82
F.2 Methods for loads comparison . 82
F.2.1 Statistical binning . 82
F.2.2 Spectral functions . 83
F.2.3 Fatigue spectra . 83
F.2.4 Data point by data point . 83
Annex G (informative) Formulation of test load for rotor blade testing . 84
G.1 Static target load . 84
G.2 Fatigue target load . 84
Annex H (informative) Difference between design and test load condition for rotor
blade testing . 85
H.1 General . 85
H.2 Load introduction . 85
H.3 Bending moments and shear . 85
H.4 Radial loads . 87
H.5 Torsion loads . 87
H.6 Environmental conditions . 87
Annex I (informative) Influence of the number of load cycles on fatigue tests of rotor
blades . 88
I.1 General . 88
I.2 Background. 88
I.3 The approach used . 88
Bibliography . 92

Figure 1 – General scheme of marine energy converters fixed to the seabed or shore . 12
Figure 2 – General scheme of floating marine energy converters moored to the
seabed or shore . 13
Figure 3 – Marine energy converter with blades connected to a rotor shaft supported
by a fixed substructure . 13
Figure 4 – Marine energy converter with blades connected to a rotor shaft supported
by a floating device . 14
Figure 5 – Turbine loads: rotor, blade and base of tubular column loads . 28
Figure A.1 – Chordwise (flatwise, edgewise) coordinate system . 53
Figure A.2 – Rotor (flapwise, lead-lag) coordinate system . 54
Figure B.1 – Blade coordinate system . 71
Figure B.2 – Hub coordinate system . 72
Figure B.3 – Nacelle coordinate system . 73

Figure B.4 – Tubular column coordinate system . 73
Figure B.5 – Yaw misalignment . 74
Figure B.6 – Cone angle and tilt angle . 74
Figure H.1 – Difference of moment distribution for target and actual test load . 85
Figure H.2 – Distribution of the shear force as a function of the spanwise location for
different numbers of load application point . 86
Figure H.3 – Distribution of the bending moment as a function of the spanwise location
for different numbers of load application points . 86
Figure I.1 – Simplified Goodman diagram . 88
Figure I.2 – Test load factor γ as a function of the reduction factor H . 91
ef r
Table 1 – MLCs during steady-state operation . 21
Table 2 – Measurement of transient load cases . 21
Table 3 – MLCs for dynamic characterization . 22
Table 4 – Capture matrix for parked condition . 23
Table 5 – Capture matrix for normal transient events . 23
Table 6 – Capture matrix for other than normal transient events . 23
Table 7 – MLCs for dynamic characterization . 24
Table 8 – Capture matrix for parked condition . 24
Table 9 – All WEC and CEC load quantities . 26
Table 10 – Oceanographic and meteorological quantities . 26
Table 11 – MEC operation quantities . 27
Table 12 – MECs with blades connected to a rotor shaft load quantities . 28
Table 13 – MEC with blades connected to a rotor shaft operation quantities . 29
Table 14 – Summary of suitable calibration methods . 39
Table A.1 – Blade test program . 57
Table A.2 – Recommended values for γ as a function of the reduction factor H . 60
ef r
Table A.3 – Examples of situations typically requiring or not requiring renewed testing . 69
Table E.1 – List of uncertainty components . 81
Table I.1 – Recommended values for γ as a function of the reduction factor H . 91
ef r
– 8 – IEC TS 62600-3:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MARINE ENERGY – WAVE, TIDAL AND
OTHER WATER CURRENT CONVERTERS –

Part 3: Measurement of mechanical loads

FOREWORD
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• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide whether
they can be transformed into International Standards.
IEC TS 62600-3, which is a Technical Specification, has been prepared by IEC technical
committee 114: Marine energy – Wave, tidal and other water current converters.

The text of this Technical Specification is based on the following documents:
Enquiry draft Report on voting
114/326/DTS 114/336A/RVDTS
Full information on the voting for the approval of this technical specification can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62600 series, published under the general title Marine energy –
Wave, tidal and other water current converters, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 10 – IEC TS 62600-3:2020 © IEC 2020
INTRODUCTION
This part of IEC 62600 outlines specifications for the full-scale mechanical loads measurement
on hydrodynamic marine energy converters (MECs). It is directed at a technology readiness
level (TRL) of 7 to 9, meaning the last prototype or the first production device. This document
also outlines the demands for full-scale structural testing of rotor blades as well as the
interpretation and evaluation of test results.
In the process of structural design of marine energy converters, thorough understanding and
accurate quantification of the loading is of utmost importance. In the design stage, loads can
be predicted with simulation models and codes. However, such models have their modelling
restrictions and uncertainties, and they always need to be validated by measurement.
Mechanical load measurements can be used both as the basis for design and as the basis for
certification. The design of marine energy converters is covered by IEC 62600-2: Marine Energy
– Wave, tidal and other water current converters – Part 2: Design requirements for marine
energy systems.
This document is aimed at the test institute, the marine energy converter manufacturer and the
certifying body and defines the requirements for mechanical loads tests resulting in consistent
and reproducible test results.
There exists a large variety of marine energy converter working principles. This document aims
to cover most hydrodynamic marine energy converter working principles. Therefore,
generalised tests are presented at the level of the common subsystems. For Tidal Energy
Converters (TECs) and for other water current converters, the most common working principle
is a turbine comprising blades connected to a rotor shaft. Therefore, detailed tests are specified
for this working principle. For marine energy converter working principles that do not fit partly
or completely in the scope of this document, the technology qualification process is introduced.
Through the technology qualification process, the user can adapt the test programme to their
specific marine energy converter.
This document is comparable to the international wind standards IEC 61400-13: Wind turbines
– Part 13: Measurement of mechanical loads and IEC 61400-23: Wind turbines – Part 23: Full-
scale structural testing of rotor blades. Since testing laboratories and certification bodies
already have experience with these wind standards, it is convenient to adapt the same methods
where possible.
There is not much published experience with offshore mechanical load measurement on marine
energy converters. This document is a first step towards a future International Standard which
can be used as part of a type certification process of marine energy converters. First,
experience should be gained with offshore mechanical load measurement and with the
application of this document.
Compliance with this document does not relieve any person, organization, or corporation from
the responsibility of observing other applicable regulations.

MARINE ENERGY – WAVE, TIDAL AND
OTHER WATER CURRENT CONVERTERS –

Part 3: Measurement of mechanical loads

1 Scope
1.1 General
This part of IEC 62600 describes the measurement of mechanical loads on hydrodynamic
marine energy converters such as wave, tidal and other water current converters (including
river current converters) for the purpose of load simulation model validation and certification.
This document contains the requirements and recommendations for the measurement of
mechanical loads for such activities as site selection, measurand selection, data acquisition,
calibration, data verification, measurement load cases, capture matrix, post-processing,
uncertainty determination and reporting.
Informative annexes are also provided to improve understanding of testing methods. The
methods described in this document can also be used for mechanical loads measurements for
other purposes such as obtaining a measured statistical representation of loads, direct
measurements of the design loads, safety and function testing, or measurement of subsystem
or component structural loads.
Through a technology qualification process, the test requirements can be adapted to the specific
marine energy converter.
This document also defines the requirements for full-scale structural testing of subs
...