floating wind turbine model test...5mw reference wind turbine by numerous institutions worldwide,...

Infrastructure Access Report

Infrastructure: ECN Hydrodynamic and Ocean Engineering Tank

User-Project: INNWIND.EU

Floating Wind Turbine Model Test (Phase 1, Sept 22-Oct, 3 2014)

INNWIND.EU

Marine Renewables Infrastructure Network

Status: Draft Version: 01 Date: 08-Oct-2014

EC FP7 “Capacities” Specific Programme Research Infrastructure Action

Infrastructure Access Report: INNWIND.EU

Rev. 01, 08-Oct-2014 of 40

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)

http://www.fp7-marinet.eu/


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DOCUMENT INFORMATION Title Floating Wind Turbine Model Test (Phase 1, Sept 22-Oct, 3 2014)

Distribution Public

Document Reference MARINET-TA1-INNWIND.EU

User-Group Leader, Lead Author

José Azcona CENER (Group Leader) Frank Sandner USTUTT (Lead Author)

User-Group Members, Contributing Authors

Henrik Bredmose DTU Pierluigi Montinari POLIMI Filippo Campagnolo POLIMI Ricardo Pereira DNVGL Florian Amann USTUTT Christof Wehmeyer Ramboll

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


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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.


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EXECUTIVE SUMMARY This report covers the first 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. The common practice for combined wind-and-wave model testing of floating wind turbines shall be improved through a better understanding of the error sources in this kind of model testing. Therefore various different configurations are tested in this series in order to be compared and analysed.


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CONTENTS

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

1.1 INTRODUCTION .................................................................................................................................................... 7 1.2 DEVELOPMENT SO FAR .......................................................................................................................................... 9 1.2.1 Stage Gate Progress .................................................................................................................................... 9 1.2.2 Plan For This Access ................................................................................................................................... 10

2 OUTLINE OF WORK CARRIED OUT ................................................................................................................. 11

2.1 SETUP ............................................................................................................................................................... 11 2.2 TESTS ............................................................................................................................................................... 16 2.3 RESULTS ............................................................................................................................................................ 21 2.4 ANALYSIS & CONCLUSIONS................................................................................................................................... 24

3 MAIN LEARNING OUTCOMES ....................................................................................................................... 25

3.1 PROGRESS MADE ............................................................................................................................................... 25 3.1.1 Progress Made: For This User-Group or Technology ................................................................................. 25 3.1.2 Progress Made: For Marine Renewable Energy Industry .......................................................................... 27

3.2 KEY LESSONS LEARNED ........................................................................................................................................ 28

4 FURTHER INFORMATION .............................................................................................................................. 29

4.1 SCIENTIFIC PUBLICATIONS .................................................................................................................................... 29 4.2 WEBSITE & SOCIAL MEDIA ................................................................................................................................... 29

5 REFERENCES ................................................................................................................................................ 29

6 APPENDICES ................................................................................................................................................ 30

6.1 DETAILED TEST MATRIX ....................................................................................................................................... 31 6.1.1 Tests for 5 MW scaled model: ................................................................................................................... 33 6.1.2 Tests for 10 MW scaled model: ................................................................................................................. 39


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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. Combined wind-wave experiments are 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]


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The general mass characteristics of the model are:

Table 1 - General model parameters.

Magnitude Value Comments

Total mass 152.167kg Including ballast

Platform mass 142.647kg

Wind turbine mass 9.52kg Without cable

Centre of Gravity 0.2198 m Below sea water lever (SWL)

Distance between

columns 1.11 m

Hub height 2m

Rotor diameter (Fr-

scaled rotor) 1.4m

Rotor diameter

(ducted fan) 0.15m

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. The OC4-DeepCwind semi-submersible is the platform model used in this test. Although at least two test campaigns with this model have already been completed, see [1], it was still selected to be used here. The vast understanding of this platform, the availability of results, see [2] and [3], allow for a comprehensive scientific study of the general effects coming through the wind-, wave-, and mooring-line induced coupled dynamics. The results from this campaign, which will be published for the international scientific community can then be compared with the other tests in order to assess the effects of the wind and wave generator or the different model uncertainties. For the modeling of the rotor-induced forces various methodologies exist, which have been summarized in [4]. Here, a Froude-scaled rotor will be used as described in [5] but also a ducted fan, which works without an external wind generator. It is a hardware-in-the-loop approach, which produced a thrust force, determined through a model-based real-time control algorithm, see [6]. For the assessment of the effects of higher turbine ratings the scaling ratio was adjusted in order to model also a 10MW wind turbine. As a reference the INNWIND.EU 10MW reference wind turbine is used, see [7]. The scaling ratio was selected to 60. With this choice, the thrust force on the rotor, the rotor speed, the wind speed and the tip speed ratio are scaled correctly. Thus, the 10MW case can be studied with correctly scaled aerodynamic forces in the experiment. The platform behaves adequately also in this case, since the thrust force is comparable to the 5MW case. However, the platform geometry is not anymore a scaled version of the OC4-DeepCwind semi-submersible since the scaling ratio has been increased. In the following the previous developments in Task 4.2 of INNWIND.EU will be described and the completed tests outlined. With the summary and conclusions it will be shown that a second test phase is necessary to finalize the planned test matrix and complete the scientific outcomes of this test series.


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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 thorough comparison with a wide range of numerical simulation tools from conceptual models to high-fidelity CFD software. The models used by the partners have been described in [9]. For this end, a generic floating offshore wind turbine (FOWT) model has been selected with the scaling procedures reported in [10]. 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.

1.2.1 Stage Gate Progress The process planned in Task 4.2 of INNWIND.EU is roughly outlined in the stage gate table below. The stage gates which were initially planned for a four-weeks access are denoted in the left column. These plans have been changed in order to fit into the granted slot (22.9.-3.10.2014) and the currently installed infrastructure (e.g. Hexapod for determined platform motion). The next access to the ECN facility is already planned with the stages indicated in the right column. The test cases corresponding to the ones planned for the next test are described in section 3.1.1.1.

Previously completed: Planned for this project:

STAGE GATE CRITERIA Orig app

Current 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.


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STAGE GATE CRITERIA Orig app

Current access

Status Next acces

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

Regular waves with fixed hull

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.

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 Stage1: This part contains the platform and the Froude-scaled rotor. Most of it could be completed in the first phase at ECN. Mainly the system identification tests could be completed, except for the forced oscillation tests and the fixed platform tests, due to constraints of the ECN facilities. Thus, they have been shifted to the next phase, end of October 2014. Stage 2: It is the focus of the next test (end of October 2014) to finalize the tests with the Froude-scaled rotor (see 2.1 below) and to mount the ducted fan, see 3.1.1.1. The forced-oscillation and fixed platform tests are planned for this application, which are essential for the determination of hydrodynamic coefficients of the platform model.


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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

Stage 3: The assessment of different pitch-controller concepts, including individual pitch control (IPC) is especially of interest, since the Froude-scaled rotor has these features, which have not been applied before. It is planned for further tests. Stage 4: Here, a new platform model will be built based on the experience and validated model from the generic-WT tests. A new platform concept will be designed in detail.

2 OUTLINE OF WORK CARRIED OUT An overview of the 1:45 platform model, built at USTUTT and the Froude-scaled rotor with individual pitch control, built at POLIMI will be described below. The ducted fan configuration which will be used in the next test is described in section 3.1.1.1.

2.1 SETUP The setup consists of a wind turbine model with rigid blades and flexible tower that is mounted on the floating platform. The nacelle, see Figure 2, is composed of the following components:


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Figure 2 - Picture of the nacelle.

At the bottom of the tower, strain gages are applied for acquiring tower loads, see Figure 5. All the signals are then brought away to the cabinet, see Figure 6 by water proof cables. The cabinet contains Bachmann control, data acquisition system, motor torque and power suppliers. Finally, the system communicates throw Ethernet connection with a remote computer with a user interface, see Figure 7. 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.


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Figure 3 - Pictures of the model assembled.

Figure 4 - Picture of the platform model with force sensors.


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Figure 5 - Picture of the tower load cell.

Figure 6 - Picture of the cabinet.


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Figure 7 - Real-time monitoring and data acquisition.

Figure 8 – INNWIND.EU user group.


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2.2 TESTS The detailed tentative test matrix can be found in the appendix, 1.1 with the completed cases marked in green. The test schedule starts with cases where the mooring system is not installed (forced oscillations, regular waves with fixed hull and free decay tests with free hull) and then continues with the cases where the platform is moored. During the first week the platform only is tested, without the wind turbine. In order to match the hydrostatic properties the ballast was shifted to a higher level to keep the center of mass constant. The cases including wind are presented in the last part of the test matrix, first with simple cases for the characterization of the wind loading, and then in combined wave and wind cases. For every case, its importance has been indicated with a number between 1 and 3 (1: high priority; 3: low priority). This will help to decide which cases could be skipped in case of delays on the time schedule during the test execution. All the magnitudes defining the test cases in this document are presented in full scale, but in the test matrix datasheet they are provided also in the scaled model. The first sheet of the excel file attached is called “Parameters” and collects all the parameters that define the test campaign: scale, sea state conditions, winds, initial displacements for the free decay tests, frequencies and amplitudes of the forced oscillations cases, etc. The sheet called “Platform Test Matrix” details all the test cases of the campaign, based on these parameters. Therefore, if any of the data in “Parameters” is changed, all the affected cases in the test matrix will automatically update. In the following subsections, the different groups of cases of the test matrix are described and commented.

2.2.1 Free Decay Tests Free decay tests are performed for system identification. These cases include free decay experiments with the platform free (heave, roll and pitch) and moored (surge, sway, heave, roll, pitch and yaw). Therefore, the platform, unmoored for the first part of the test campaign will be moored during the execution of this group of cases for the free decay tests with “moored hull”. Then, it will stay moored for the rest of the campaign. All the free decay tests are performed twice, with two different initial displacements.

Table 2 - Initial Displacements for the Free Decay Tests.

Free Decay Tests: Initial Displacement

Test

Repetition Free Hull Moored Hull

Surge #1 13.5m

#2 6.75m

Sway #1 13.5m

#2 6.75m

Heave #1 4.5m 4.5m

#2 2.25m 2.25m

Roll #1 10º 10º

#2 5º 5º

Pitch #1 10º 10º

#2 5º 5º

Yaw #1 10º

#2 5º


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2.2.1.1 Moored Platform Static Displacement

In this test, a static displacement on the moored platform in surge and sway is introduced with the objective of verifying the stiffness of the mooring system installed in the wave tank. The forces and moments on the 6 degrees of freedom of the platform will be measured. The relationships between restoring forces and moments with respect to the surge and sway displacements are provided in [1]:

Figure 9: Restoring Force/Moment vs Surge [1] and restoring Force/Moment vs Sway [1]

Based on Figure 9, the following static displacements to be introduced to the platform in surge and sway have been chosen:

Table 1. Surge Displacements

Static Displacement

Surge (m)

-20

-10

10

20

25

30

Table 2. Sway Displacements

Static Displacement

Sway (m)

-10

-5

10

5


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2.2.1.2 Regular Waves with Moored Hull

The motion RAO’s of the platform are sought to be obtained from these experiments. The periods of the regular waves for the execution of these tests match the ones of the forced-oscillation tests. They are shown in Table 18:

Table 1. Periods for the Regular Waves with Moored Hull Tests

2.2.1.3 Environmental Conditions Definition for Wind-Wave Tests

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 3, Table 4 and Table 5. A description of the cases involving these environmental conditions is provided in Section 2.2.1.6.

Table 3 - 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

Regular Waves

Moored Hull

Amplitude (m) 6.75

Pe

rio

ds

(s)

5

6

7

8

9

10

11

15

20

25


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Table 4 - 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 5 - Wind Conditions.

2.2.1.4 Irregular Waves Cases

This group of cases consists of irregular waves with the Hs and Tp defined in Table 5 with 0º and 45º of heading direction.

2.2.1.5 Wind Loading Characterization

The group of wind only cases assume a moored platform in still water. Constant and turbulent winds with the wind speeds from Table 5 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. The free decay tests in surge and pitch are here combined with constant winds (see Table 6). 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 6 - 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

2.2.1.6 Combined Wave and Wind Tests

The combined wind and wave cases are combinations of regular and irregular waves with steady and turbulent winds according to the conditions described in Table 3, Table 4 and Table 5.


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2.3 RESULTS Only preliminary results are shown here due to the fact that this report has been produced shortly after the first test session and a second session is expected after which this report will be extended. For the purpose of publishing all model information and results after the completion of this test series a code has been set up to read in a central excel table with information on the sensors used (calibration factors, location, reference frame, corresponding data file entry etc.) and the test runs (time, corresponding data files, etc.). Consequently, all three data files are read in and the data stored in binary matlab format including all information from the central excel sheet in structure format. Here, results are shown for irregular waves and wind for all sensors comparing the 5MW case with the 10 MW case. The conditions are listed in Table 7. The results are discussed in Section 2.4

Table 7 - Irregular Wave Comparison: Environmental Conditions

5MW 10MW

Significant wave height [m] 0.061 0.069

Peak spectral period [s] 0.82 0.94

Wind speed [m/s] 1.04 1.47

Figure 10 – Irregular Wave Comparison, time series #1, see Table 7.


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2.4 ANALYSIS & CONCLUSIONS It can be seen in Figure 10 how the higher wind speed for the 10MW case increases the tension in the upwind line (fairlead #2) and reduces the tension in the downwind lines (fairleads #1 and #3). This is because the higher thrust force yields a larger displacement in surge (PtfmTDx). Also the platform pitch angle (PtfmRDy) is increased, see also Figure 10. The IMU data in Figure 11 will be integrated and compared to the camera motion measurements from Figure 10. The blade pitch angles at the bottom of Figure 11 and the top of Figure 12 show that in order to produce the higher thrust force in the 10MW case a smaller pitch angle was necessary and also the rotor speed is higher, see Figure 12. The wind and wave conditions were selected to be comparable for these figures, see Figure 13. In summary, it can be said that the sensors and logging systems worked for this first phase and that they can be used without major changes for the next phase in order to produce relevant data for comparisons between the test runs (e.g. 5 vs. 10MW, w/ and w/o power cables, w/ and w/o adjusted ballast) and numerical model validation of the international research community.


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3 MAIN LEARNING OUTCOMES

3.1 PROGRESS MADE During the first test phase the main system identification tests with and without platform could be completed, except for the forced displacement and fixed hull tests. Also most of the tests with the Froude-scaled rotor could in general be covered and thus, most parts of stage 1 (see Section 1.2.1) could be finalized. It is sought to complete the remaining tests, especially with 45 deg wave heading and the irregular seas with the remaining frequencies in the next test. Also, some findings on the fairleads sensors and the aerodynamic properties of the rotor, which are described in Section 3.2, will be further investigated.

3.1.1 Progress Made: For This User-Group or Technology For INNWIND.EU very useful results are obtained which allow a comparison with previous tests of the same model for error quantification and detailed numerical model validation. The improvement of a Froude-scaled rotor as opposed to a geometrically scaled rotor will be investigated through comparison with previous results. Also, essential experience in testing of floating wind turbines is gained throughout the user group. The built model has been confirmed together with the sensors and data transmission devices and, especially, the common trigger signal for all of the three systems (wind turbine, platform and wave basin).

3.1.1.1 Next Steps for Research or Staged Development Plan (Plan for 2nd phase)

As a new step in our research, we plan to implement in the same platform model a different approach to include a realistic scaled thrust dynamic force during the wave tank test. The basic concept of this method consists on substituting on the scaled model the rotor driven by wind by a fan driven by an electrical motor that produces an airstream. This fan can introduce a variable force dependent on the revolutions per second (rpm) that is equivalent to the total aerodynamic thrust over the rotor. A controller varies the fan rotational speed to modify the variable force. The thrust over the rotor is calculated through a simulation in full scale of the wind turbine and provided to the fan controller. In order to couple the computed aerodynamic force with the platform motions during the tests, the simulation includes into the computation of the thrust the positions and velocities of the 6 degrees of freedom of the scaled platform at every instant during the execution of the wave tank tests. These positions and velocities are provided by the acquisition system in real time. For this reason, the simulation and the test have to be synchronized and the real time of the system has to be guaranteed. We also refer to the method as Software-in-the-Loop (SIL).

Figure 3.1 Photograph of the fan used in the SIL method

In the following the remaining system identification tests which could not yet be completed are described.

3.1.1.2 Forced Oscillations

The group of cases A consists of prescribed forced oscillations of the platform on the 6 rigid body degrees of freedom at different frequencies. The frequencies have been chosen based on computations using the WAMIT software [1]. Figure 2 to Figure 4 show the computed added mass and potential damping for the different degrees


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of freedom of the platform. The added mass and damping values at the chosen frequencies for the forced oscillations experiments are shown in the figures as black dots.

Figure 2: Surge & Sway Added Mass and Damping Figure 16: Heave Added Mass and Damping

Figure 4: Roll & Pitch Added Mass and Damping Figure 18: Yaw Added Mass and Damping

Table 13 collects all the periods selected for the forced oscillation tests in each degree of freedom. Amplitude 1 for the oscillations will be tested with all the periods. Only the periods shown in Table 8 in red font will be tested again with the amplitude 2 for verification purposes.


Rev. 01, 08-Oct-2014 of 40

Table 8 - Periods for the Forced Oscillation Tests.

Forced Oscillations

Surge Sway Heave Roll Pitch Yaw

Amplitude #1 1.125m 1.125m 1.125m 5º 5º 5º

Amplitude #2 2.25m 2.25m 2.25m 10º 10º 10º

Pe

rio

ds

(s)

5 5 5 5 5 4

6 6 6 5.5 5.5 4.5

6.4 6.4 7 6 6 5

7 7 8 6.5 6.5 6

8 8 8.4 7 7 6.5

9 9 9 8 8 7

10 10 10.5 10 10 8

12 12 11.5 11.5 11.5 10

15 15 13 15 15 15

20 20 20 20 20 20

3.1.1.3 Regular Waves with Fixed Hull

Here the platform is fixed and the forces induced by incoming regular waves with different periods are measured. This will allow obtaining the force RAO’s of the platform. The periods of the regular waves are shown in Table 9. These tests have been chosen based on WAMIT computations of the Exciting Force Coefficients (X1, X2, X3, X4, X5, and X6 correspond to the coefficients in surge, sway, heave, roll, pitch and yaw). The force RAO’s can be obtained also by testing the fixed platform under a White Noise wave spectrum. This has already been done in the first phase with two different significant wave heights (4.5m and 9m).

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 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.


Rev. 01, 08-Oct-2014 of 40

Table 9 - Regular Wave Periods in Fixed Hull Tests.

Regular Waves

Fixed Hull

Amplitude (m) 6.75

Pe

rio

ds

(s)

5

6

7

8

9

10

11

15

20

25

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 dynamics 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. Here, the determination of a valid

location in the open wind generator for the reference wind speed u∞ is essential and needs further research.

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.

The fairlead sensors should be able to sustain a by far higher force than the maximum force during the tests

in order to prevent damage during installation. The mounting technique of the fairleads sensors will have to be improved in the next test since towards the end of the first test, one of the sensors was removed from its initial position.


Rev. 01, 08-Oct-2014 of 40

4 FURTHER INFORMATION

4.1 SCIENTIFIC PUBLICATIONS List of any scientific publications made (already or planned) as a result of this work:

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.

4.2 WEBSITE & SOCIAL MEDIA Website: www.innwind.eu

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] A. Robertson, A. Goupee, J. Jonkman, I. Prowell, P. Molta, A. Coulling and M. Masciola, "Summary Of Conclusions And Recommendations Drawn From The Deepcwind Scaled Floating Offshore Wind System Test Campaign," in Proceedings of the ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering, 2013.

[3] A. Robertson, J. Jonkman, W. Musial, F. Vorpahl and W. Popko, "Offshore Code Comparison Collaboration , Continuation : Phase II Results of a Floating Semisubmersible Wind System," in Proceedings of the EWEA Offshore, 2013.

[4] A. Robertson, J. Jonkman, F. Vorpahl, W. Popko, J. Qvist, L. Froyd, X. Chen, J. Aycona, E. Uzunoglu, C. Guedes Soares, C. Luan, H. Yutong, F. Pencheng and A. Heege, "Offshore Code Comparison Collaboration Continuation Within Iea Wind Task 30: Phase Ii Results Regarding A Floating Semisubmersible Wind System," in Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering, San Francisco, USA, 2014.

[5] K. Müller, F. Sandner, H. Bredmose, J. Azcona, A. Manjock and R. Pereira, "Improved Tank Test Procedures For Scaled Floating Offshore Wind Turbines," in International Wind Engineering Conference IWEC, Bremerhaven, 2014.

[6] C. Bottasso, F. Campagnolo and V. Petrovic, "Wind tunnel testing of scaled wind turbine models: Beyond aerodynamics," Journal of Wind Engineering and Industrial Aerodynamics, vol. 127, pp. 11-28, #apr# 2014.

[7] J. Azcona, F. Bouchotrouch, M. González, J. Garciandía, X. Munduate, F. Kelberlau and T. a. Nygaard, "Aerodynamic Thrust Modelling in Wave Tank Tests of Offshore Floating Wind Turbines Using a Ducted Fan," Journal of Physics: Conference Series, vol. 524, p. 012089, #jun# 2014.

[8] C. Bak, F. Zahle, R. Bitsche, T. Kim, A. Yde, L. Henriksen, A. Natarajan and M. Hansen, "InnWind 10MW Reference Wind Turbine".

[9] J. Azcona, D. Bekiropoulos, H. Bredmose, A. Fischer, N. F. Heilskov, A. Krieger, T. Lutz, A. Manjock, D. Manolas,


Rev. 01, 08-Oct-2014 of 40

D. Matha, K. Meister, R. Pereira, J. Ronby, F. Sandner and S. Voutsinas, "INNWIND.EU D4.2.1: State-of-the-art and implementation of design tools for floating structures," 2012.

[10] J. Azcona, F. Sander, H. Bredmose, A. Manjock, R. Pereira and F. Campagnolo, "INNWIND.EU D4.2.2: Methods for performing scale-tests for method and model validation".

[11] Wamit, "Wamit User Manual 6.4".

[12] S. Voutsinas, D. Manolas, F. Sandner and A. Manjock, "INNWIND.EU D4.2.3: Integrated design methods and controls for floating offshore wind turbines".

6 APPENDICES


Rev. 01, 08-Oct-2014 of 40

6.1 DETAILED TEST MATRIX Common test’s (the same for 10 MW scaled model/5 MW scaled model):

Table 1. Free Decays

Case Description Initial Displacemen (Full Scale) (m/deg)

Measurements Duration (Full

scale) (s) Comments

Free Decay / free hull Heave #1 4,5 V PM 200 No mooring system

Free Decay / free hull Heave #2 2,25 V PM 200 No mooring system

Free Decay / free hull Roll #1 10 V PM 200 No mooring system

Free Decay / free hull Roll #2 5 V PM 250 No mooring system

Free Decay / free hull Pitch #1 10 V PM 250 No mooring system

Free Decay / free hull Pitch #2 5 V PM 250 No mooring system

MOORING LINES CONECTION 2h

Free Decay / free hull Surge #1 13,5 V ML PM 1100 No mooring system

Free Decay / free hull Surge #2 6,75 V ML PM 1100 No mooring system

Free Decay / free hull Sway #1 13,5 V ML PM 1100 No mooring system

Free Decay / free hull Sway #2 6,75 V ML PM 1100 No mooring system

Free Decay / free hull Heave #1 4,5 V ML PM 200 No mooring system

Free Decay / free hull Heave #2 2,25 V ML PM 200 No mooring system


Rev. 01, 08-Oct-2014 of 40

Table 2. Static displecement surge

Case Displacement (m) Displacement Full Scale (m)

Measurements Comments

Static displacement surge -0,444 -20 V PF Mooring stiffness verification

Static displacement surge -0,222 -10 V PF Mooring stiffness verification

Static displacement surge 0,222 10 V PF Mooring stiffness verification




Static displacement sway -0,222 -10 V PF Mooring stiffness verification

Static displacement sway -0,111 -5 V PF Mooring stiffness verification

Static displacement sway 0,222 10 V PF Mooring stiffness verification

Static displacement sway 0,111 5 V PF Mooring stiffness verification

Free Decay / free hull Roll #1 10 V ML PM 250 No mooring system

Free Decay / free hull Roll #2 5 V ML PM 250 No mooring system

Free Decay / free hull Pitch #1 10 V ML PM 250 No mooring system

Free Decay / free hull Pitch #2 5 V ML PM 250 No mooring system

Free Decay / free hull Yaw #1 10 V ML PM 800 No mooring system

Free Decay / free hull Yaw #2 5 V ML PM 800 No mooring system


Rev. 01, 08-Oct-2014 of 40

6.1.1 Tests for 5 MW scaled model:

Table 3. Regular waves with moored hull

Case Wave Height (m) Period (s) Wave Direction

(deg) Measurements Duration (s)

Regular waves / moored hull 0,043 0,75 0 V Wv ML PM 37,3











Rev. 01, 08-Oct-2014 of 40

White Noise / moored hull 0,1 - 0 V Wv ML PM 536,7

White Noise / moored hull 0,2 - 0 V Wv ML PM 536,7

Irregular waves / moored hull 0,061 0,820 0 V Wv ML PM 536,7











Rev. 01, 08-Oct-2014 of 40

Table 4. 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










Turbulent wind 1,04 7,00 V Wi ML PM 536,7

No turbulent wind



No turbulent wind



No turbulent wind



No turbulent wind



No turbulent wind


Rev. 01, 08-Oct-2014 of 40

Table 5. 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






Rev. 01, 08-Oct-2014 of 40

Table 6. 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


0,073 0,969 6,50 0,0 1,267 V Wv Wi ML PM 48,4


0,092 1,088 7,30 0,0 1,699 V Wv Wi ML PM 54,4


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


0,140 1,491 10,00 0,0 3,727 V Wv Wi ML PM 74,5


0,052 0,820 5,50 45,0 1,043 V Wv Wi ML PM 41,0


0,073 0,969 6,50 45,0 1,267 V Wv Wi ML PM 48,4


0,092 1,088 7,30 45,0 1,699 V Wv Wi ML PM 54,4


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


Rev. 01, 08-Oct-2014 of 40


0,133 1,491 10,00 45,0 3,727 V Wv Wi ML PM 74,5

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


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


0,092 1,088 7,30 0 1,70 V Wv Wi ML PM 536,7


0,108 1,327 8,90 0 2,68 V Wv Wi ML PM 536,7


0,133 1,491 10,00 0 3,73 V Wv Wi ML PM 536,7


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


0,070 0,969 6,50 45 1,27 V Wv Wi ML PM 536,7


0,092 1,088 7,30 45 1,70 V Wv Wi ML PM 536,7


0,108 1,327 8,90 45 2,68 V Wv Wi ML PM 536,7


0,133 1,491 10,00 45 3,73 V Wv Wi ML PM 536,7


Rev. 01, 08-Oct-2014 of 40

6.1.2 Tests for 10 MW scaled model:

Table 7. 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










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


Rev. 01, 08-Oct-2014 of 40

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


Rev. 01, 08-Oct-2014 of 40

Table 8. Wind tests with moored platform and water

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


Steady Wind 0,9 V Wi ML PM 77,5










Turbulent wind 0,9 V Wi ML PM 464,8










Rev. 01, 08-Oct-2014 of 40

Table 9. Free decaywith 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






Pitch + Steady wind 5,00 1,10 V Wi ML PM 33,0






Rev. 01, 08-Oct-2014 of 40

Table 10. Free decaywith 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










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




Rev. 01, 08-Oct-2014 of 40








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