Floating Vertical Axis Wind Turbines...Seventh Framework Programme – H2OCEAN project (). As part...

Infrastructure Access Report

Infrastructure: UCC-HMRC Ocean Wave Basin

User-Project: FloVAWT

Floating Vertical Axis Wind Turbines

Floating Power Plant, Cranfield University

Marine Renewables Infrastructure Network

Status: Final Version: 02 Date: 29-Nov-2013

EC FP7 “Capacities” Specific Programme Research Infrastructure Action

Infrastructure Access Report: FloVAWT

Rev. 02, 29-Nov-2013 of 18

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 Vertical Axis Wind Turbines

Distribution Public

Document Reference MARINET-TA1-FloVAWT

User-Group Leader, Lead Author

Michael Borg Cranfield University

User-Group Members, Contributing Authors

Sarah Bellew Floating Power Plant Miguel Fernandez Floating Power Plant

Infrastructure Accessed: UCC-HMRC Ocean Wave Basin

Infrastructure Manager (or Main Contact)

Florent Thiebaut

REVISION HISTORY Rev. Date Description Prepared by

(Name) Approved By Infrastructure

Manager

Status (Draft/Final)

02 29.11.2013 Access Report Michael Borg Final


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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 describes a series of experimental tests carried out at UCC HMRC on a hybrid floating wind-wave energy converter and the lessons learnt during this experimental campaign. After having to modify the original proposal due to a change in infrastructure granted, a test plan was set out to optimise the design of Floating Power Plant’s P80 wave energy converter device. A physical model was designed and constructed to of a modular nature to allow fast and efficient design changes during the access time. Geometry modifications such as leg draft, heave plate size and wave absorbers position were possible with this model design. A two-tier test plan was implemented were first the P80 design space was investigated and after obtaining an optimal design configuration, this configuration underwent intensive testing in a wide range of sea states. During this stage a number of different mooring lines were also examined to assess their effect on platform performance. The results obtained in this access funded by the European Community have greatly furthered the development of the P80 hybrid floating wind-wave energy converter, as well as aided in the validation of a coupled dynamics model for marine energy converters, FloVAWT.


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CONTENTS

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

1.1 INTRODUCTION .................................................................................................................................................... 7 1.2 DEVELOPMENT SO FAR .......................................................................................................................................... 7 1.2.1 Stage Gate Progress .................................................................................................................................... 8 1.2.2 Plan for This Access ..................................................................................................................................... 9

2 OUTLINE OF WORK CARRIED OUT ...................................................................................................................9

2.1 SETUP ................................................................................................................................................................. 9 2.1.1 Physical Model............................................................................................................................................. 9 2.1.2 Instrumentation ......................................................................................................................................... 10 2.1.3 Model Setup & Facility Calibration ............................................................................................................ 10

2.2 TESTS ............................................................................................................................................................... 11 2.2.1 Test Plan .................................................................................................................................................... 11

2.3 RESULTS ............................................................................................................................................................ 14 2.4 ANALYSIS & CONCLUSIONS................................................................................................................................... 15

3 MAIN LEARNING OUTCOMES ....................................................................................................................... 16

3.1 PROGRESS MADE ............................................................................................................................................... 16 3.1.1 Progress Made: For This User-Group or Technology ................................................................................. 16

3.2 KEY LESSONS LEARNED ........................................................................................................................................ 16

4 FURTHER INFORMATION .............................................................................................................................. 16

4.1 WEBSITE & SOCIAL MEDIA ................................................................................................................................... 16

5 APPENDICES ................................................................................................................................................ 16

5.1 STAGE DEVELOPMENT SUMMARY TABLE ................................................................................................................ 16


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1 INTRODUCTION & BACKGROUND

1.1 INTRODUCTION Cranfield University and Floating Power Plant (FPP) are currently in co-operation through the European Union Seventh Framework Programme – H2OCEAN project (www.h2ocean-project.eu). As part of this project, a numerical aero-hydro-elastic model (called FloVAWT) is being developed to investigate the behaviour of a combined vertical axis wind turbine (VAWT) and floating wave energy converter (WEC) device. The initial FloVAWT proposal to MARINET consisted of carrying out wind-wave tests on a generic floating VAWT at Ecole Centrale Nantes (ECN) or Consiglio Nazionale delle Ricerche (CNR-INSEAN) for validation of the FloVAWT numerical model, but this proposal was offered the use of the UCC-HMRC wave basin by the Selection Committee. Following this decision, the original proposal was modified to allow for novel tests to be carried out at the wave-only HMRC basin since there currently are no wind-generation facilities. This new proposal entailed the preliminary testing of a 1:50 scale model of the P80 WEC device currently being developed by FPP that is being utilised in the H2OCEAN project. As the P80 device has a very novel geometry the tests carried out at HMRC focused on concept validation and design changes, as well as obtaining data to validate and tune the numerical model FloVAWT.

1.2 DEVELOPMENT SO FAR Floating Power Plant are the developers of a novel, floating, wave- and wind-energy hybrid device. Since the initial conception of the invention, Floating Power Plant have performed hydrodynamic tests on their device at 1:16 and 1:14,5 scale in wave flumes and 1:33 and 1:9,5 scale in wave basins, with the purpose of design development and optimisation. Further to this, P37, a 37 m wide test platform (see Figure 1) has been undergoing offshore testing for three complete test phases (totally more than 2 years) and is currently in its fourth test phase. The test platform is provides electricity to the grid from both wind and wave energy, however its purpose is purely for research and development. The PTO for the WECs has undergone rigorous testing as well as regular optimisation through both dry and offshore testing. Floating Power plant’s first commercial platform will be the P80, which is 80 m in width (see Figure 2). This platform is likely to be deployed in a more energetic and deeper test site than the P37 platform. For this reason modifications to the current design have been made within the company which prior to this MARINET testing period at UCC-HMRC had not been tested using physical tests.

Figure 1: P37 Offshore Test Platform

Figure 2: P80 Conceptual Design

http://www.h2ocean-project.eu/


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The numerical model currently being developed consists of a number of interconnected modules that model:

the aerodynamics of the VAWT

the hydrodynamics of the floating WEC

the mooring lines anchoring the floating structure

the elastic behaviour of the superstructure (i.e. the VAWT) With regards to the FloVAWT numerical model validation, the tests carried out at HMRC shall be used in the validation of the hydrodynamics and mooring lines modules. Furthermore tuning of the hydrodynamics module based on these tests is carried out to better account for nonlinear viscous forcing. Further details about the background theory and implementation of FloVAWT are available by contacting the User Group Leader.

1.2.1 Stage Gate Progress Previously completed: Planned for this project:

STAGE GATE CRITERIA Status

Stage 1 – Concept Validation

Linear monochromatic waves to validate or calibrate numerical models of the system (25 – 100 waves)

Finite monochromatic waves to include higher order effects (25 –100 waves)

Hull(s) sea worthiness in real seas (scaled duration at 3 hours)

Restricted degrees of freedom (DoF) if required by the early mathematical models

Provide the empirical hydrodynamic co-efficient associated with the device (for mathematical modelling tuning)

Investigate physical process governing device response. May not be well defined theoretically or numerically solvable

Real seaway productivity (scaled duration at 20-30 minutes)

Initially 2-D (flume) test programme

Short crested seas need only be run at this early stage if the devices anticipated performance would be significantly affected by them

Evidence of the device seaworthiness

Initial indication of the full system load regimes

Stage 2 – Design Validation

Accurately simulated PTO characteristics

Performance in real seaways (long and short crested)

Survival loading and extreme motion behaviour.

Active damping control (may be deferred to Stage 3)

Device design changes and modifications

Mooring arrangements and effects on motion

Data for proposed PTO design and bench testing (Stage 3)

Engineering Design (Prototype), feasibility and costing

Site Review for Stage 3 and Stage 4 deployments

Over topping rates

Stage 3 – Sub-Systems Validation

To investigate physical properties not well scaled & validate performance figures

To employ a realistic/actual PTO and generating system & develop control strategies


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STAGE GATE CRITERIA Status

To qualify environmental factors (i.e. the device on the environment and vice versa) e.g. marine growth, corrosion, windage and current drag

To validate electrical supply quality and power electronic requirements.

To quantify survival conditions, mooring behaviour and hull seaworthiness

Manufacturing, deployment, recovery and O&M (component reliability)

Project planning and management, including licensing, certification, insurance etc.

Stage 4 – Solo Device Validation

Hull seaworthiness and survival strategies

Mooring and cable connection issues, including failure modes

PTO performance and reliability

Component and assembly longevity

Electricity supply quality (absorbed/pneumatic power-converted/electrical power)

Application in local wave climate conditions

Project management, manufacturing, deployment, recovery, etc

Service, maintenance and operational experience [O&M]

Accepted EIA

Stage 5 – Multi-Device Demonstration

Economic Feasibility/Profitability

Multiple units performance

Device array interactions

Power supply interaction & quality

Environmental impact issues

Full technical and economic due diligence

Compliance of all operations with existing legal requirements

1.2.2 Plan for This Access The plan for this access was to assess different design configurations of the P80 device, and once a provisionally optimal configuration was identified, to perform a series of intensive tests to thoroughly assess the device performance. The implementation of this aim was to design and manufacture a modular physical scale model where the geometrical and inertial configurations were easily adjusted. The intensive tests involved a variety of sea states and survival conditions, as well as assessing the vaning behaviour of the device in long- and short-crested waves. Different types of mooring lines were also used to investigate their relative impact on the motion of the device, particularly in extreme conditions. Throughout the access period, the experimental data obtained was continually analysed to assess the different design configurations by understanding the loading regimes on the device and the motion performance of the device.

2 OUTLINE OF WORK CARRIED OUT

2.1 SETUP

2.1.1 Physical Model The model was built predominantly out of wood (coated in a waterproof resin) and aluminium. The model allowed for several alternative designs to be tested. The model consisted of a cross shaped platform, comprising a hull


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(containing the mooring turret at one end) and a bridge (containing the wave energy devices, also known as floaters). The bridge could be moved along the hull during the experiments in order to modify the overall geometry. Two front legs were attached to the bridge, and one rear leg to the hull. The legs consisted of different blocks of wood, which could be added or removed during the experiments in order to test the effect of varying the drafts of the legs. Heave plates can be attached to the bottom of the legs, with their main aim being to reduce the platform motions. A weighted wooden pole was used to represent the wind turbine. During certain tests, a force was applied to the top of the wooden pole in order to represent a wind that is misaligned to the waves. This was carried out using a mass and pulley system. Power was not extracted from the wave energy devices, however a damping system was implemented in order to achieve motions of the floaters that were representative of when a Power Take-Off (PTO) system was applied on the full-scale device. This damping system was implemented using pistons which were located above the floaters. A computer model of the scaled model is shown in Figure 3 and the resulting physical model at HMRC is shown in the photo in Figure 4.

Figure 3 - Conceptual model of the physical scale model

Figure 4 - Actual physical scale model

2.1.2 Instrumentation For measuring the six degrees of freedom motion of the physical model, a Qualysis ProReflex non-contact motion capture measurement system that is installed at the HMRC test facility was used. This system enables non-contact, accurate motion measurement using a set of reflective markers attached to the device and a camera system which uses infrared LEDs mounted around each lens to track the markers. To record the motion of the platform, 4 reflective markers were attached to the platform, three in the same plane as each other and one in a different plane. Further to this, a marker was placed on each of the floaters to monitor their individual motions. Furthermore, the forces in the mooring lines were measured by using strain gauges that were connected to the individual mooring lines at the fairlead connection points.

2.1.3 Model Setup & Facility Calibration

2.1.3.1 Wave Height Measurement Gauges

Throughout the test period, the relationship between the voltage in the gauges and the location of the free surface on the gauge were regularly determined. These calibration tests consisted of recording the voltage from each gauge


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at two different known heights in still water (so that the free surface is located at two different places on the gauges). This data was used to determine the translation of the recorded voltage to wave height throughout the experiments for the rest of the day.

2.1.3.2 Mooring Line Strain Gauges

The strain gauges used to measure the forces in the mooring lines were calibrated in a similar manner as the wave gauges. Known masses were used to load the strain gauge vertically and the corresponding strain was recorded. From this, the relation between the strain produced in the gauge and the applied load was obtained.

2.1.3.3 Model Setup/Calibration

Floaters Damping Systems

The damping system was constructed from pistons located above each floater. This damping was dynamically representative of a PTO system, even though power was not being extracted. The pistons each contained two valves (one for the upwards stroke, and one for downwards stroke) which could be opened and closed (by varying amounts) to vary the damping for each floater. The desired damping was achieved by mounting the damping system vertically, applying a known mass to the actuator and recording the time taken for the actuator to fully extend. By matching this time to a specific value, the desired damping was obtained.

Platform Ballasting

The platform hull and bridge was required to be at the same draft when at rest (i.e. zero platform trim) throughout the access period. During the early part of the access period, the geometry of the platform was varied by applying ballasting weights to compartments in the hull and the side hulls. The desired location of the free surface was marked at various places on the platform. Each time a modification was made to the geometry, the ballast weights were added or subtracted to match the free surface to these markers.

2.2 TESTS

2.2.1 Test Plan The access time was organised to comprise of a three stage test plan. The first was setup and calibration (as outlined in the previous section), the second was optimisation of the device configuration, and the third stage was intensive testing of the ‘quasi’-optimal device configuration. The first stage was allotted three days, the second stage was allotted five days and the third stage was allotted six days, with one final day allotted to dismantle the model and ensure the testing facilities are in their original state. The work carried out in the first stage dealing with the setup and calibration of the model and facility is described in the previous sections. For the second and third stages, both regular and irregular waves were realised during tests, and are described in the following sections.

2.2.1.1 Regular Waves

The regular waves implemented had 2% and 8% steepness and are shown in Table 1. These were all within the capabilities of the test facility.

Table 1 - Description of regular wave tests

Test Number Model wave height (m)

Model wave period (s)

Full-scale wave height (m)

Full-scale wave period (s)

Steepness

R1 0,137 2,09 6,85 14,81 2 %

R2 0,101 1,80 5,03 12,69 2 %

R3 0,077 1,57 3,85 11,11 2 %

R4 0,061 1,40 3,04 9,87 2 %

R5 0,049 1,26 2,47 8,89 2 %

R6 0,041 1,14 2,04 8,08 2 %

R7 0,029 0,97 1,46 6,84 2 %


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R8 0,022 0,84 1,10 5,92 2 %

R9 0,017 0,74 0,85 5,23 2 %

R10 0,014 0,66 0,68 4,68 2 %

R11 0,244 1,40 12,18 9,87 8 %

R12 0,197 1,26 9,86 8,89 8 %

R13 0,163 1,14 8,15 8,08 8 %

R14 0,117 0,97 5,84 6,84 8 %

R15 0,088 0,84 4,38 5,92 8 %

R16 0,068 0,74 3,41 5,23 8 %

R17 0,055 0,66 2,73 4,68 8 %

2.2.1.2 Irregular Waves

To maximise the use of the access time, irregular wave spectra were selected from a database of 21 wave spectra that HMRC already had calibrated for the wave basin, which are described in Figure 5. Five spectra (indicated by the red ovals in Figure ) were used during stage 2 and all 21 irregular sea spectra were utilised during stage 3.

Figure 5 - Irregular sea spectra description

2.2.1.3 Stage Two Description

The main purpose of this stage was to determine the optimum configuration of the P80 device. The device was formed of a main hull and a cross-bridge that contains 4 side hulls, each of which contains the rotation point for a floater. The point where the cross-bridge is attached to the main hull shall be referred to as the cross-point. Three different locations of the cross-point were tested. Beneath the two outer side-hulls, fore-legs could be located, and beneath the hull an aft-leg could be included, with heave plates located beneath these legs. Different drafts of fore- and aft-legs are tested. Figure 6 graphically summarises the various geometry configurations that are tested.


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Figure 6 - P80 device geometry configurations

Optimisation I – Vaning Tests

The P37 platform has proven its ability to passively orientate itself to face the incoming waves, even when the wind is misaligned to the waves. To test this in the wave basin, a force that is representative of thrust, was applied to the top of the wind-turbine pole using a mass and pulley system. The ability of the platform to realign itself (i.e. vane) under the simulated wind-wave conditions was tested in irregular waves The time that the platform took to realign itself was measured, as well as the extent to which it was able to realign itself (i.e. the angle that the platform holds to the predominant wave direction once it had reached steady state). Three locations of cross-sections were tested in the vaning tests. The middle draft of the fore and aft legs were implemented. To maximize the moment arm for the thrust force, the wind-turbine pole was located at the aft end of the hull during the vaning tests. The results can later be extrapolated to different locations of wind-turbine pole on the hull using moments. The vaning tests were repeated with the floaters attached and detached in order to gauge the influence of the floater motion on the vaning capabilities of the platform.

Optimisation II – Stability Tests

For increased platform stability the pitch motions of the platform must be kept minimal. The two extreme locations of cross-points that were tested in the vaning tests were again tested here to analyse their stability in various wave conditions. For the stability tests, the medium draft of the fore- and aft- legs were used. Two different locations of the wind-turbine on the hull were tested. The tests were performed both with the floaters attached (on) and detached (off).

Optimisation III – Effects of Leg Drafts

In this set of tests, the effect of the length of the fore- and aft-legs was investigated in regular and irregular waves. From these set of tests, the most promising leg lengths were obtained for use in stage 3. Figure 6 outlines the geometry selections for these tests.

2.2.1.4 Stage Three Description

Once the optimal configuration was identified from all the tests carried out in stage two, a series of intensive tests were carried out on this configuration. Firstly different mooring line configurations were investigated as described in the following sections.


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Mooring Line Weight Variation

The mooring line was made for thin, low stiffness line with distributed weights. Froude scaling could not appropriately be used to represent the mooring lines hydrodynamic properties. Thin lines were therefore used to limit the hydrodynamic loads and keep the stiffness to a minimum, better representing the heavy chain behaviour (which has a low structural stiffness, but a restoring force due to weight lifting when the platform moves). As the weight is responsible of the mooring stiffness, it is appropriate to scale the line weight with Froude scaling. At full scale, in 50 m water depth, three groups of three mooring lines are expected to be used. Each group of three (nearly parallel) lines have a combined submerged weight per metre of 120 kg/m. In the model, each group of 3 (nearly parallel) lines was replaced by a single line. By Froude scaling, the weight per meter of each line was be 120 x (1/50)^3 = 0,048 kg/m. Fishing lead shot weights were attached to the line at regular intervals to obtain the desired average weight per meter. • Mooring 1 (æ) = light mooring: 0,025 kg/m • Mooring 2 (ø) = standard mooring: 0,05 kg/m • Mooring 3 (å) = heavy mooring: 0,075 kg/m Mooring 2 was used for the first portion of the access period. After comparing mooring weights 1, 2 and 3, however, the remainder of the tests were carried out using Mooring 3, which was found to have more appropriate properties. Regular waves were applied to each of the three moorings, so that the resulting RAOs can be used.

Free-Decay Tests

Repeated free decay tests were carried out to assess the natural frequency of the physical model and better understand the hydrodynamic damping forces acting on the submerged structure. These tests are very important for tuning the numerical model being developed to assist in more accurate numerical predictions.

Wave Tests

As mentioned earlier in this stage the P80 device was tests for all regular and irregular waves outlined above. Additionally, a number of short-crested (three-dimensional) wave spectra were also tested to assess the impact of the floaters moving out of phase relative to one another. The motion of the individual wave absorbing floaters was also of interest in these tests. Table outlines the characteristics of the 3D Bretschneider sea spectra. The wake effect of the floating platform was also measured in these series of tests.

Table 2 - Three-dimensional Bretschneider sea spectra characteristics

Test number Model scale significant wave height, Hs (mm) Model scale peak wave period, Tp (s)

1 24 1.20

2 114 1.23

3 114 1.76

4 23 1.76

2.3 RESULTS Some preliminary results concerning the platform motion and flow regime shall be presented in this section. Note that due to the commercially sensitive nature of this project, only limited data can be presented. Figure 7 presents the mean pitch angle of the ‘optimised’ platform configuration as a function of incident regular wave height at full scale for two wave steepness values, 2% (blue) and 8% (green).


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Figure 8 presents a sample heave free decay test for the ‘optimised’ platform configuration. This data allows for tuning of the numerical model, as well as assessing the natural frequency of the platform.

2.4 ANALYSIS & CONCLUSIONS The P80 device has shown to be a very stable platform even in adverse sea conditions throughout the experimental campaign. From Figure 7 one can see that the mean pitch angle is small, even when operating in large waves. This has also been observed in heave and roll. The coupled motion of the floaters on the main hull appeared to dampen the system motion, which contributed to the system stability even in adverse environmental conditions. Another aspect analysed was the ability of the device to vane when misaligned to the wave direction, with promising results. The free decay tests performed provided the necessary data to further tune the numerical model. An example was given in Figure 8, whereby a curve was fitted to the heave free decay response and the subsequent additional damping required in the model was obtained, augmenting the motion predictions of the numerical model. In this report, the modifications to the original proposal to allow testing of a hybrid wind and wave energy convertor as part of the development of a combine VAWT-WEC floating system were presented. Details of the physical scale model and experiment set up were discussed in Section 2.1 and the aims of this experimental campaign to perform concept validation and assessment were achieved through a large range of tests outlined in Section 2.2. Some limited results were presented in Section 2.3 due to the commercial sensitivity of the device and these where briefly discussed above. The tests have shown that the device is very stable in a variety of sea conditions. The free decay tests have allowed further development of the numerical model to more accurately capture the relatively complex dynamics of the combined wind-wave device. To conclude, this experimental campaign made possible by MARINET has given strong indications for the further development of the model.

Figure 7 - P80 mean pitch angle for a range of 2% (blue) and 8% (green) regular waves

Figure 8 – Non-dimensionalised heave free decay response


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3 MAIN LEARNING OUTCOMES

3.1 PROGRESS MADE

3.1.1 Progress Made: For This User-Group or Technology This experimental campaign led to a much deeper understanding of how the P80 device interacts with the sea, leading to the identification of an optimised design configuration of the device. The investigations into the vaning performance are very important in the continual design of the device, in particular the mooring system design and placement of the wind turbine on the device. Understanding the influence of the length of the fore and aft legs has allowed for the device design to be more cost-effective through the reduction of material costs. The platform was found to very stable in a variety of sea states, making it a promising design for further development. The significant amounts of data generated from this experimental campaign is of great use for the validation and further development of the numerical model being used to investigate this floating system. The tuning of the numerical model to better represent viscous forces allows for more accurate predictions of the motion performance of the device. The knowledge gained on the practical aspects of carrying out experimental tests in a wave basin has been of great importance to the further development of experimental campaigns. The next step to further develop the design is to perform another set of experiments with the inclusion of a scale model wind turbine to better assess the interaction between the wind and wave energy converters. With reference to the stage development table in the Appendix, the progress of Floating Power Plant’s device has not followed such a linear progression plan. Floating Power Plant have already completed many wave basin and wave flume scaled tests as well as over 2 years of offshore tests at a benign site (TRL 6). The tests discussed in this report follow on from TRL 6, however are testing some design modifications which, at 1:50 scale in panchromatic waves, are back in stages TRL 2 or 3. Floating Power Plant will continue to follow a more circular development plan, as a lot is learnt at each test stage, resulting in potential design optimisations which must be tested in controlled environments before being implemented at full scale.

3.2 KEY LESSONS LEARNED Optimal geometry configuration deduced from a series of experimental tests, allowing for a deep

understanding of the effects of individual components.

Effect of heave plates and leg draft may be substantial in certain conditions.

Use of free decay tests enables more reliable numerical predictions

The inclusion of the patented wave energy floaters within the platform design substantially improve the ability of the platform to ‘vane’ (i.e. redirect itself to face the waves once misaligned, for example by the wind)

The modification of the platform geometry in-between tests during the access period took a significant amount of time. Model modifications should ideally be kept to a minimum during experimental tests.

4 FURTHER INFORMATION

4.1 WEBSITE & SOCIAL MEDIA Website: www.floatingpowerplant.com LinkedIn/Twitter/Facebook Links:

5 APPENDICES

5.1 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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Floating Vertical Axis Wind Turbines...Seventh Framework Programme – H2OCEAN project (). As part...

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