User-Project : INNWIND.EU Floating Wind Turbine … · INNWIND.EU Floating Wind Turbine ... by the IEA a generic semi-submersible floating platform has been simulated together with

Infrastructure Access Report

Infrastructure: ECN Hydrodynamic and Ocean Engineering Tank

User-Project: INNWIND.EU

Floating Wind Turbine Model Test

INNWIND.EU

Floating Wind Turbine Model Test

(Phase 2, November 2014)

Marine Renewables Infrastructure Network

Status: Draft

Version: 01

Date: 4-December -2014

Infrastructure Access Report: INNWIND.EU

Rev. 01, 08-Oct-2014

Page 2 of 33

ABOUT MARINET MARINET (Marine Renewables Infrastructure Network for emerging Energy Technologies) is an EC-funded network

of research centres and organisations that are working together to accelerate the development of marine renewable

energy - wave, tidal & offshore-wind. The initiative is funded through the EC's Seventh Framework Programme (FP7)

and runs for four years until 2015. The network of 29 partners with 42 specialist marine research facilities is spread

across 11 EU countries and 1 International Cooperation Partner Country (Brazil).

MARINET offers periods of free-of-charge access to test facilities at a range of world-class research centres.

Companies and research groups can avail of this Transnational Access (TA) to test devices at any scale in areas such

as wave energy, tidal energy, offshore-wind energy and environmental data or to conduct tests on cross-cutting

areas such as power take-off systems, grid integration, materials or moorings. In total, over 700 weeks of access is

available to an estimated 300 projects and 800 external users, with at least four calls for access applications over the

4-year initiative.

MARINET partners are also working to implement common standards for testing in order to streamline the

development process, conducting research to improve testing capabilities across the network, providing training at

various facilities in the network in order to enhance personnel expertise and organising industry networking events

in order to facilitate partnerships and knowledge exchange.

The aim of the initiative is to streamline the capabilities of test infrastructures in order to enhance their impact and

accelerate the commercialisation of marine renewable energy. See www.fp7-marinet.eu for more details.

Partners

Ireland

University College Cork, HMRC (UCC_HMRC)

Coordinator

Sustainable Energy Authority of Ireland (SEAI_OEDU)

Denmark

Aalborg Universitet (AAU)

Danmarks Tekniske Universitet (RISOE)

France

Ecole Centrale de Nantes (ECN)

Institut Français de Recherche Pour l'Exploitation de

la Mer (IFREMER)

United Kingdom

National Renewable Energy Centre Ltd. (NAREC)

The University of Exeter (UNEXE)

European Marine Energy Centre Ltd. (EMEC)

University of Strathclyde (UNI_STRATH)

The University of Edinburgh (UEDIN)

Queen’s University Belfast (QUB)

Plymouth University(PU)

Spain

Ente Vasco de la Energía (EVE)

Tecnalia Research & Innovation Foundation

(TECNALIA)

Belgium

1-Tech (1_TECH)

Netherlands

Stichting Tidal Testing Centre (TTC)

Stichting Energieonderzoek Centrum Nederland

(ECNeth)

Germany

Fraunhofer-Gesellschaft Zur Foerderung Der

Angewandten Forschung E.V (Fh_IWES)

Gottfried Wilhelm Leibniz Universität Hannover (LUH)

Universitaet Stuttgart (USTUTT)

Portugal

Wave Energy Centre – Centro de Energia das Ondas

(WavEC)

Italy

Università degli Studi di Firenze (UNIFI-CRIACIV)

Università degli Studi di Firenze (UNIFI-PIN)

Università degli Studi della Tuscia (UNI_TUS)

Consiglio Nazionale delle Ricerche (CNR-INSEAN)

Brazil

Instituto de Pesquisas Tecnológicas do Estado de São

Paulo S.A. (IPT)

Norway

Sintef Energi AS (SINTEF)

Norges Teknisk-Naturvitenskapelige Universitet

(NTNU)


Rev. 01, 08-Oct-2014

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DOCUMENT INFORMATION Title Floating Wind Turbine Model Test

Distribution Public

Document Reference MARINET-TA2-INNWIND.EU

User-Group Leader, Lead

Author

Frank Sandner USTUTT

[Optional: Insert address and contact details]

User-Group Members,

Contributing Authors

Henrik Bredmose DTU

Pierluigi Montinari POLIMI

Ricardo Pereira DNVGL

Carlo Bottasso POLIMI

Florian Amann USTUTT

José Azcona CENER

Faisal Bouchotrouch CENER

Infrastructure Accessed: ECN Hydrodynamic and Ocean Engineering Tank

Infrastructure Manager

(or Main Contact)

Jean-Marc Rousset

REVISION HISTORY Rev. Date Description Prepared by

(Name)

Approved By

Infrastructure

Manager

Status

(Draft/Final)

01


Rev. 01, 08-Oct-2014

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ABOUT THIS REPORT One of the requirements of the EC in enabling a user group to benefit from free-of-charge access to an infrastructure

is that the user group must be entitled to disseminate the foreground (information and results) that they have

generated under the project in order to progress the state-of-the-art of the sector. Notwithstanding this, the EC also

state that dissemination activities shall be compatible with the protection of intellectual property rights,

confidentiality obligations and the legitimate interests of the owner(s) of the foreground.

The aim of this report is therefore to meet the first requirement of publicly disseminating the knowledge generated

through this MARINET infrastructure access project in an accessible format in order to:

• progress the state-of-the-art

• publicise resulting progress made for the technology/industry

• provide evidence of progress made along the Structured Development Plan

• provide due diligence material for potential future investment and financing

• share lessons learned

• avoid potential future replication by others

• provide opportunities for future collaboration

• etc.

In some cases, the user group may wish to protect some of this information which they deem commercially

sensitive, and so may choose to present results in a normalised (non-dimensional) format or withhold certain design

data – this is acceptable and allowed for in the second requirement outlined above.

ACKNOWLEDGEMENT The work described in this publication has received support from MARINET, a European Community - Research

Infrastructure Action under the FP7 “Capacities” Specific Programme.

LEGAL DISCLAIMER The views expressed, and responsibility for the content of this publication, lie solely with the authors. The European

Commission is not liable for any use that may be made of the information contained herein. This work may rely on

data from sources external to the MARINET project Consortium. Members of the Consortium do not accept liability

for loss or damage suffered by any third party as a result of errors or inaccuracies in such data. The information in

this document is provided “as is” and no guarantee or warranty is given that the information is fit for any particular

purpose. The user thereof uses the information at its sole risk and neither the European Commission nor any

member of the MARINET Consortium is liable for any use that may be made of the information.


Rev. 01, 08-Oct-2014

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EXECUTIVE SUMMARY

This report covers the second of two phases of combined wind-and-wave model testing of a generic floating wind

turbine system. The widely studied open concept of the OC4-DeepCwind semi-submersible model has been tested

together with a Froude-scaled rotor with increased chord for low Re-numbers.Two different scaling ratios have been

used in order to represent, first, the 5MW NREL reference wind turbine and, second, the 10MW INNWIND.EU

reference wind turbine. All of rotor speed, wind speed and thrust force are correctly scaled in this approach.In the

second phase of this project the remaining test cases will be finalized (ULS conditions, yawed inflow, error

assessment) and a thrust force generation for both wind turbine models will be tested through a ducted fan in terms

of a hardware-in-the-loop experiment.

It is the explicit goal of this project to make the model and measurement data public to a full extent for the

international research community for model validation of advanced coupled software tools, including aerodynamic

and hydrodynamic CFD.


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CONTENTS

1 INTRODUCTION & BACKGROUND ...................................................................................................................7

1.1 INTRODUCTION .................................................................................................................................................... 7

1.2 DEVELOPMENT SO FAR .......................................................................................................................................... 8

1.2.1 Stage Gate Progress .................................................................................................................................... 9

1.2.2 Plan for this Access .................................................................................................................................... 10

2 OUTLINE OF WORK CARRIED OUT ................................................................................................................. 13

2.1 SETUP ............................................................................................................................................................... 13

2.1.1 Low Reynolds Rotor ................................................................................................................................... 13

2.1.2 Ducted Fan and Software in the Loop ....................................................................................................... 13

2.1.3 Scaled model for the platform ................................................................................................................... 16

2.2 TESTS ............................................................................................................................................................... 19

2.2.1 Test Plan .................................................................................................................................................... 19

2.3 RESULTS ............................................................................................................................................................ 28

2.4 ANALYSIS & CONCLUSIONS................................................................................................................................... 29

3 MAIN LEARNING OUTCOMES ....................................................................................................................... 29

3.1 PROGRESS MADE ............................................................................................................................................... 29

3.1.2 Progress Made: for Marine Renewable Energy Industry ........................................................................... 29

3.2 KEY LESSONS LEARNED ........................................................................................................................................ 30

4 FURTHER INFORMATION .............................................................................................................................. 30

4.1 SCIENTIFIC PUBLICATIONS .................................................................................................................................... 30

5 REFERENCES ................................................................................................................................................ 31

6 APPENDICES ................................................................................................................................................ 31

6.1 STAGE DEVELOPMENT SUMMARY TABLE ................................................................................................................ 31

6.2 ANY OTHER APPENDICES ..................................................................................................................................... 33


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1 INTRODUCTION & BACKGROUND

1.1 INTRODUCTION For floating wind turbine systems various numerical codes and methods are currently available or are still under

development. Here the major developments concern the coupling of advanced aerodynamics and hydrodynamics,

but also non-linear behavior of mooring lines. In addition, these experiments will be useful for the validation of

testing methodologies, in particular for the integration of the aerodynamic rotor thrust during combined wave and

wind tests and the mooring system modelling. The tools and methods validated in this test campaign will be applied

to the design of a floating substructure for a 10MW wind turbine in Task 4.3 of the INNWIND.EU project.

In the international code-comparison project “Offshore Code Comparison Collaboration Continuation (OC4)” funded

by the IEA a generic semi-submersible floating platform has been simulated together with the NREL 5MW reference

wind turbine by numerous institutions worldwide, see [1] and [2]. It is a semi-submersible design with three legs and

20m draft. The hub height is 87.6m. The basic geometry of the floating wind turbine is shown in Figure 1.

Figure 1: Full Scale Semisubmersible [1]

The general mass characteristics of the platform are:

Table 1 General mass parameters of the floating wind turbine in full scale

Magnitude Value Comments

Weight 13473 t Including ballast

Centre of Gravity 13.46 m Below sea water lever (SWL)

Inertia Ixx 6.827E+9 kgm2 About centre of gravity, exclusive added mass

Inertia Iyy 6.827E+9 kgm2 About centre of gravity, exclusive added mass


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Inertia Izz 1.226E+10 kgm2

About centre of gravity, exclusive added mass

An overview of the main parameters that define the tower is provided in Table 2:

Table 2 General parameters of the tower

Magnitude Value Comments

Tower Base Elevation 10 m (Platform Top) Above SWL

Tower Top Elevation 87.6 m (Yaw Bearing) Above SWL

Total Tower Mass 249.718 t -

Tower centre of Gravity Location

43.4m Above SWL. Along Tower Centerline

Inertia Izz 1.226E10 kgm2 About centre of gravity, exclusive added mass

Table 3 shows a summary of the main parameters that define the rotor of the wind turbine model.

Table 3 General parameters of the rotor

Magnitude Value

Total RNA Mass 350 t

Rotor Mass 110 t

Nacelle Mass 240 t

Rotor Diameter 126 m

Rating 5 MW

Hub Height 90 m

Rated Tip Speed 80 m/s

The OC4 mooring lines system is composed by three lines spread symmetrically about the central vertical axis of the

platform. The depth of the location is 200m.

1.2 DEVELOPMENT SO FAR The objective of the project INNWIND.EU is to investigate the development of large offshore wind turbine systems

above 10MW. In workpackage 4 fixed-bottom as well as floating foundations are being analysed. A first goal for the

floating part is to gain valuable knowledge and experience in model testing and a thourough comparison with a wide

range of numerical simulation tools from conceptual models to high-fidelity CFD software. For this end, a generic

floating offshore wind turbine (FOWT) model has been selected.

The model in a scale of 1:45 has been set up by partner USTUTT and preliminary assembled with the wind turbine

model by partner POLIMI. It has been tested in a water tank and the datalogging devices synchronized through a

common trigger signal. In order to reduce the influence of data cables a wireless transmission system has been set

up for the platform inertial measurement unit (IMU) and the fairlead sensors. These waterproof sensors are selected

since no interference with the mooring system dynamics occurs.


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1.2.1 Stage Gate Progress

Previously completed: �

Planned for this project: �

STAGE GATE CRITERIA Orig

app

Curremt

access

Status Next

acces

Stage 1 – Platform only and Froude-scaled rotor tests

• Model building (Platform: USTUTT, wind turbine: POLIMI), sensor application,

data logging system, data transmission.

�

• First test of the assembled FOWT model in water (July 2014 at University of

Stuttgart)

�

• First unmoored free-decay tests in heave with data acquisition (July 2014 at

University of Stuttgart)

�

• System identification (platform only): Static displacement in surge and sway

(mooring ID)

�

• System identification (platform only): Free decay tests (moored) in surge, sway,

heave, pitch

�

• Platform-only tests: Regular waves, irregular waves (set of frequencies for 5 and

10MW scale)

�

• System identification (FOWT, Fr-scaled rotor): Free decay tests (moored) in

surge, sway, heave, pitch

�

• Regular waves and wind (FOWT, Fr-scaled rotor, for RAO) �

• Irregular waves and wind (FOWT, Fr-scaled rotor; Selection of realistic wind-

wave conditions for 5 and 10MW scale)

�

• White noise waves and wind (FOWT, Fr-scaled rotor, for RAO) �

• Comprehensive numerical model validation. �

Stage 2 – Platform with Froude-scaled rotor and HIL rotor tests

• Ultimate limit state conditions, idling rotor (FOWT, Fr-scaled rotor, for RAO).

• Yawed inflow (FOWT, Fr-scaled rotor, for RAO; Rotate tower on platform).

• Assembly of ducted fan tower and platform.

• System identification (FOWT, HIL rotor, for RAO): Free decay tests (moored) in

surge, sway, heave, pitch.

• Regular waves and wind (FOWT, HIL rotor, for RAO).

• Irregular waves and wind (FOWT, HIL rotor, for RAO; Selection of realistic wind-

wave conditions for 5 and 10MW scale).

• Error assessment of shifted ballast for correction of center of gravity . �

• Investigation of inflow conditions and blockage correction, determination of

CFD boundary conditions.

• Forced-displacement tests (platform only, with Hexapod available at ECN). �

• Comprehensive numerical model validation. �

Stage 3 – Blade pitch controller testing

• Blade-pitch control with varying wind speeds.


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STAGE GATE CRITERIA Orig

app

Curremt

access

Status Next

acces

• Individual blade pitch control (IPC).

Stage 4 – Innovative INNWIND.EU floating platform

• Build new platform model for 10MW reference wind turbine in suitable scale.

• Test performance in combined wind-and-wave conditions.

• Compare results with design assumptions and numerical model predictions.

• Finalize structural design of innovative INNWIND.EU platform.

• Preliminary concept of manufacturing and installation.

• Levelized cost of energy analysis.

• Environmental impact analysis.

• Dissemination of results.

1.2.2 Plan for this Access

In a previous access of two weeks the group performed a series of tests of increasing complexity: including free

decays, only regular waves and RAO’s. The plan for this access consists on combined tests of wind and waves. All

possible combinations of steady and turbulent waves and regular and irregular waves are considered. The inclusion

of aerodynamic loads is performed using the ducted fan and software in the loop approach and also using a Reynolds

scaled rotor model.

1.2.2.1 Environmental Conditions Definition

The last part of the test matrix consists of cases representatives of different sea states and also different sea states

in combination with winds. These environmental conditions (irregular sea states, regular sea states and wind

conditions) are presented in Table 4, Table 5 and Table 6. A description of the cases involving these environmental

conditions is provided in the following sections.

Table 4 Irregular Sea Conditions

Irregular Sea States

Sea

State Hs (m) Tp (s)

1 2.75 5.5

2 3.14 6.5

3 4.13 7.3

4 4.88 8.9

5 6 10


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Table 5 Regular Sea Conditions

Regular Sea States

Sea

State Height (m) Period (s)

1 2.75 5.5

2 3.14 6.5

3 4.13 7.3

4 4.88 8.9

5 6 10

Table 6 Wind Conditions

1.2.2.2 Irregular Waves Cases

Irregular wave cases are defined with the Hs and Tp defined in Table 4 with 0º and 45º of heading direction.

1.2.2.3 Wind Loading Characterization

Wind only cases with the platform moored and still water are defined. Constant and turbulent winds with the wind

speeds from Table 6 are reproduced. These cases allow characterizing the wind loading system and verifying that it is

correctly tuned and that the displacements in surge and pitch correspond to the expected values.

In addition, a group of cases consisting in free decay tests in surge and pitch combined with constant winds (see

Table 7) is defined. These cases are useful for the characterization of the damping introduced by the aerodynamic

loading.

Wind Conditions

Wind

State

Steady Wind Speeds

(m/s)

Turbulent Wind

Speeds

(m/s)

1 7 7

2 8.5 8.5

3 11.4 11.4

4 18 18

5 25 25


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Table 7 Free Decay + Constant Wind Conditions

Free Decay + Constant Wind

Initial Displacement

Wind Speed (m/s)

Surge

# 1 6.75m 8.5

# 2 6.75m 11.4

# 3 6.75m 18

Pitch

# 1 5º 8.5

# 2 5º 11.4

# 3 5º 18

1.2.2.4 Combined Wave and Wind Tests

Combination of regular and irregular waves with steady and turbulent winds according to the conditions

described in Table 4, Table 5 and Table 6 are performed.


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2 OUTLINE OF WORK CARRIED OUT

2.1 SETUP

2.1.1 Low Reynolds Rotor

The Setup consists of a wind turbine model with rigid rigid blades and flexible tower, that is mounted on the floating

platform. The nacelle is composed of the following components:

Figure 2: Picture of nacelle

At the bottom of the tower, strain gages are applied for acquiring tower loads. All the signal are then brought away

to the cabinet by water proof cables. The cabinet contains Bachmann control, data acquisition system, motor torque

and and power suppliers. Finally the system communicates throw Ethernet connection with a remote computer

with a user interface.

2.1.2 Ducted Fan and Software in the Loop

An alternative method to the design of a low-Reynolds rotor to achieve representative rotor thrust during the

execution of the tests is the use of a ducted fan to introduce a controlled force at the tower top that represents the

aerodynamic loading. This method has the advantages of being very economical and avoiding an external wind

generation system to introduce the main force impacting the floating system by other means. Several of these

options and the correlated experiments from the literature are outlined in [4]. The use of this method in addition to

the low-Reynolds rotor will allow an assessment of the advantages and shortcomings related to this simplified

testing method.

The basic concept of the method consists of substituting the rotor by a fan driven by an electric motor. The fan

thrust is controlled by the fan rotational speed set by the controller, which again depends on the real time

simulation of the full scale rotor in a turbulent wind field, with the platform motions measured in real time in the

wave tank test. A picture of the ducted fan at the tower top is shown in Figure 2.

• Mechanical components for transmission

• Optical encoder for azimuth

measurement

• 3-Pitch actuators control units with

position control

• Torque actuator housed in tower top for

torque and speed control

• Shaft strain gages and signal conditioning

board

• 36 channels slip ring


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Figure 2 – Ducted fan

The fan and its real-time controller are lighter than the scaled mass and thus, ballast has been added to the nacelle

to match the full scale configuration. The fan is mounted on the same tower as the Froude-scaled rotor.

The model of ducted fan selected to generate the force representing the aerodynamic thrust during the tests is the

DS-30-AXI HDS, manufactured by the German company Schübeler. The fan is powered by a brushless motor HET

2W20 that is controlled by an Electronic Speed Controller (ESC) YGE 90 HV, and works with an industrial AC/DC

power supply. This system configuration produces an approximate force range of 0-18N. The rpm of the motor (and

therefore the force produced by the fan) is controlled by a Pulse Width Modulation (PWM) signal that is generated

with the LabVIEW control software, using servo libraries for Arduino. The demanded force for the fan is provided by

the full scale simulation of the rotor’s aerodynamic thrust.

The software used to compute the aerodynamic loads in real time is the version v6.02c-jmj of the FAST code, with

AeroDyn 12.58. The software has been compiled in Linux and during the test campaign it was ran in a computer with

a 2.54GHz Intel Core Duo CPU and 2GB of RAM.

Figure 4 – Fan Control System Lay Out

The layout of the system is shown in Figure 3. The left side describes the simulation part of the system, which works

in full scale, and the right side represents the wave tank scaled test. The different magnitudes that are interchanged

between both blocks are transformed by the appropriated scaling laws based on the factor scale λ .


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Figure 3 –Software-in-the-Loop Method Diagram

The simulation tool provides the total aerodynamic force on the shaft aeroF from integration of all the aerodynamic

loading at the blade elements. This force in full scale is transformed to the model scale ( aerof ) and the pulse width of

the PWM signal needed to produce the force in the ducted fan is provided by a calibration curve. The control system

regulates the fan speed that introduces the desired force at the model’s hub height. The waves produced by the

wave maker are also acting over the platform and, together with the aerodynamic thrust, inducing motions. The

acquisition system measures the positions and velocities for the 6 degrees of freedom of the platform at a certain

sampling period. These measurements are sent to the simulation tool that is waiting for the data to advance one

time step and calculate the new value of the aerodynamic thrust. For this reason, the sampling period, t∆ , and the

simulation time step, T∆ , have to be set accordingly (with a factor of 0.5λ ).


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2.1.3 Scaled model for the platform

An inertial platform and an accelerometer are housed in the platform, and with three force sensors applied between

the platform connections and mooring lines are managed by arduino system in wireless connection with a second

computer.

Figure 6 Pictures of the model assembled

Figure 7: Picture of the platform model with force sensors


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Figure 8: Picture of the tower load cell

Figure 9: Picture of the cabinet


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Sample ‘Landscape’ section


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2.2 TESTS

2.2.1 Test Plan

Table 8 Wind tests with moored platform and water

Case Description Wind speed (m/s) Wind speed (m/s) (Full scale) Measurements Duration (s)

Comments

Wind tests / moored platform / still water Steady Wind 1,04 7,00 V Wi ML PM 89,4


Wind tests / moored platform / still water

Steady Wind 1,70 11,40 V Wi ML PM 89,4



Wind tests / moored platform / still water Turbulent wind 1,04 7,00 V Wi ML PM 536,7

No turbulent wind


Turbulent wind 1,27 8,50 V Wi ML PM 536,7 No turbulent wind


No turbulent wind


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Turbulent wind 2,68 18,00 V Wi ML PM 536,7 No turbulent wind


No turbulent wind

Table 9 Free decay test with steady wind and moored hull

Case Description Initial Displacement

(m/deg) Initial Displacemen (Full

Scale) (m/deg) Wind speed

(m/s) Wind speed (m/s)

(Full scale) Measurements Duration (s)

Free decay tests + steady wind / moored

hull Surge + Steady wind 0,15 6,75 1,27 8,50 V Wi ML PM 160,8






hull Pitch + Steady wind 5,00 5,00 1,27 8,50 V Wi ML PM 38,1




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Table 10 Regular wave with steady wind

Case Wave Height (m) Period (s) Period (Full Scale)

(s) Wave Direction

(deg) Wind speed (m/s) Measurements Duration (s)

Regular wave + steady wind 0,052 0,820 5,50 0,0 1,043 V Wv Wi ML PM 41,0



Regular wave + steady wind

0,137 1,327 8,90 0,0 2,683 V Wv Wi ML PM 66,3




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Regular wave + steady wind

0,137 1,327 8,90 45,0 2,683 V Wv Wi ML PM 66,3


White Noise / steady wind 0,100 - - 0 1,7 V Wv Wi ML PM 600

Irregular wave + steady wind 0,061 0,820 5,50 0 1,04 V Wv Wi ML PM 536,7

Irregular wave + steady wind

0,070 0,969 6,50 0 1,27 V Wv Wi ML PM 536,7




Irregular wave + steady wind

0,061 0,820 5,50 45 1,04 V Wv Wi ML PM 536,7




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Tests for 10 MW scaled model:

Table 11 Regular/Irregular wave with moored hull

Case Wave Height (m) Period (s) Period (Full Scale) (s)

Wave Direction (deg)

Measurements Duration (s)

Regular waves / moored hull 0,113 0,645 5 0 V Wv ML PM 37,3







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White Noise / moored hull 0,075 - - 0 V Wv ML PM 536,7

White Noise / moored hull 0,150 - - 0 V Wv ML PM 536,7

Irregular waves / moored hull 0,046 0,710 5,5 0 V Wv ML PM 536,7




Irregular waves / moored hull 0,100 1,291 10 0 V Wv ML PM 536,7





Irregular waves / moored hull 0,100 1,291 10 45 V Wv ML PM 536,7


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Table 11 Free decay with steady wind and moored hull

Case Description Initial Displacement (m/deg) Wind speed (m/s) Measurements Duration (s)

Free decay tests + steady wind / moored hull Surge + Steady wind 0,11 1,10 V Wi ML PM 139,3



Free decay tests + steady wind / moored hull Pitch + Steady wind 5,00 1,10 V Wi ML PM 33,0




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Table 12 Free decay with steady wind and moored hull

Case Wave Height (m) Period (s) Wave Direction (deg) Wind speed (m/s) Measurements Duration (s)

Regular wave + steady wind 0,039 0,710 0,0 0,9 V Wv Wi ML PM 35,5









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White Noise / steady wind 0,077 0 1,47 V Wv Wi ML PM 600

Irregular wave + steady wind 0,046 0,710 0 0,90 V Wv Wi ML PM 464,8











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2.3 RESULTS Figure 30 and Figure 31 show selected results for a pitch free-decay test of the platform with the Froude-scaled rotor

mounted on top from week 2. The effect of the cables is assessed through this comparison, where Figure shows the

results for disconnected cables.

Figure 10 – Pitch free decay without cables

(Froude-scaled rotor).

Figure 11 - Pitch free decay with cables (Froude-

scaled rotor).

Figure 32 compares 4 different free decay tests in pitch performed with 4 different wind conditions and using the

coupled fan system to model the wind thrust. In the case with ”no wind” the fan is not connected and, therefore, the

wind loading is zero. The other cases correspond to wind constant velocities of 8.5m/s, 11.4m/s and 18m/s in full

scale (scale factor 1/45). The plot shows that the minimum damping appears in the “No Wind” case, and the

maximum damping corresponds to the case with 11.4m/s of wind that is the rated wind speed, and also the

condition where the aerodynamic thrust is the maximum.


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Figure 12 – Comparison of pitch free decay tests with different constant wind speeds modelled by

the coupled fan system.

2.4 ANALYSIS & CONCLUSIONS

The combined tests of wave and wind have shown a good behaviour of the platform tested with moderate motions

of the concept. One important outcome has been the verification of the two approaches to integrate the

aerodynamic loading in the combined wave and wind tests. The measurements of thrust provided by the scaled low

Reynolds number rotor were in the range of the objective defined by the full scale rotor. In addition, the ducted fan

was also successfully integrated in the tests and the capability to model the aerodynamic damping has been showed

by the execution of pitch free decay tests under steady wind loading at different wind speeds.

3 MAIN LEARNING OUTCOMES

3.1 PROGRESS MADE

The validation of the methodology for the integration of aerodynamic loads on the test using a low-Reynolds, pitch

controlled rotor is a very innovative alternative to the other existing technologies as the use of a drag actuator disk

that can provide a very good performance, including the effect of the control actions. The detailed description of the

built model, the sensors and data loggers used and the test description and data which will be published allow for a

thorough improvement of the testing procedure of floating wind turbines and contribute to the establishment of

“best practices” for future model tests. In addition, the validation of the ducted fan and Software-in-the-Loop

approach is an important outcome of the project. During the implementation of the system, we gain important

experience on how to solve the communication problems between the computers and the acquisition system. Some

of the software in the loop simulations failed due to the use of a blade discretization with excessive number of

elements that slowed the simulation. This was an important lesson learnt.

3.1.1.1 Next Steps for Research or Staged Development Plan – Exit/Change & Retest/Proceed?

Once validated our methodologies for the testing of combined wave and wind cases, we plan to perform a validation

campaign with an innovative platform concept currently under development. It is a hybrid concept between spar

and semisubmersible in concrete.

3.1.2 Progress Made: for Marine Renewable Energy Industry

The validation of the methodology for the integration of aerodynamic loads on the test using a low-Reynolds, pitch-

controlled rotor is a very innovative alternative to the other existing technologies as the use of a drag actuator disk,

that can provide a very good performance, including the effect of the control actions. The ducted fan and software in

the loop method is also an innovative approach with very low cost that can be applied in facilities where no wind

generator exists.


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3.2 KEY LESSONS LEARNED

� The installation of the scaled full mooring system has to be performed with precision. Due to the

dimensions of the basin and the lines this is not an easy task. The platform motion can be very sensitive to

small discrepancies on the mooring system setup.

� The aerodynamic loading has a high impact on the dynamic of the platform, in particular in the pitch motion

that has a high impact on the loading level of the wind turbine. The correct scaling of the thrust is critical for

the validation of a floating wind turbine conceptual design.

� Wireless acquisition systems have shown a very good performance in this test campaign and have the

advantage of not requiring wires that can affect the dynamics of the test and introduce disturbance in the

results

� The low Reynolds rotor designed by our group performed very well and it is an innovative and effective way

of incorporating the aerodynamic loading to the scaled model rotor

� The ducted fan and Software-in-the-Loop approach has showed the capability of modelling the

aerodynamic damping during the tests.

� Parameters as the height and period of the waves generated, wind velocity, force at the rotor,

measurements of the sensors, should be continuously checked during the tests execution to assure they

match the requirements and to prevent the generation of invalid test cases.

4 FURTHER INFORMATION

4.1 SCIENTIFIC PUBLICATIONS

• Sandner, F., Amann, F., Azcona, J., Munduate, X., Bottasso, C. L., Campagnolo, F., Bredmose H, Manjock, A.,

Pereira, R., Robertson, A. (2015). Model Building and Scaled Testing of 5MW and 10MW Semi-Submersible

Floating Wind Turbines. Abstract submitted to EERA Deepwind. Trondheim/NO.

• Müller, K., Sandner, F., Bredmose, H., Azcona, J., Manjock, A., & Pereira, R. (2014). Improved Tank Test

Procedures For Scaled Floating Offshore Wind Turbines. In International Wind Engineering Conference IWEC.

Bremerhaven.

• Azcona, J., Bekiropoulos, D., Bredmose, H., Fischer, A., Heilskov, N. F., Krieger, A., … Voutsinas, S. (2012).

INNWIND.EU D4.2.1: State-of-the-art and implementation of design tools for floating structures.

• Azcona, J., Sander, F., Bredmose, H., Manjock, A., Pereira, R., & Campagnolo, F. (n.d.). INNWIND.EU D4.2.2:

Methods for performing scale-tests for method and model validation.


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5 REFERENCES

[1] A. Robertson, J. Jonkman, M. Masciola, H. Song, A. Goupee, A. Coulling and C. Luan, "Definition of the

Semisubmersible Floating System for Phase II of OC4".

[2] J. Jonkman, S. Butterfield, W. Musial and G. Scott, "Definition of a 5-MW Reference Wind Turbine for Offshore

System Development Definition," no. February, 2009.

6 APPENDICES

6.1 STAGE DEVELOPMENT SUMMARY TABLE The table following offers an overview of the test programmes recommended by IEA-OES for each Technology

Readiness Level. This is only offered as a guide and is in no way extensive of the full test programme that should be

committed to at each TRL.


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6.2 ANY OTHER APPENDICES

Documents

User-Project : INNWIND.EU Floating Wind Turbine … · INNWIND.EU Floating Wind Turbine ... by the IEA a generic semi-submersible floating platform has been simulated together with