AquaBuOY scale 1:10 Test in Nissum Bredning

Project no: 2006-1-6435

Confidential

Rambøll Danmark A/S Bredevej 2 2830 Virum (cvr.nr. 35128417) Energinet.dk Fjordvejen 1-11 7000 Fredericia (cvr. nr. 28980671)

November 2007

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Content: Introduction:.................................................................................................................................... 2 History of the project...................................................................................................................... 2 Scope and Objectives..................................................................................................................... 4 Conclusions .................................................................................................................................... 4

Choice of Scale and test site ........................................................................................................4 Choice of model Fabrication and Material ..................................................................................5 Choice of end-stop solution the by-pass section..........................................................................6 Choice of Instrumentation of the 1:10 scale model .....................................................................7

Methodology used installing of the scale model in Nissum Bredning ...................................... 8 Results and conclusion................................................................................................................ 10 Parallel research projects ............................................................................................................ 11

Testing of the Hose-pump..........................................................................................................11 1:50 Scale Experiment HMRC Cork .........................................................................................12 Prototype testing Oregon USA ..................................................................................................13

Introduction: This R&D project involves building a 1:10 scale model of an AquaBuOY wave energy converter and followed by open sea testing at the test site in Nisum Bredning on 6.5 meter deep water. The experiment has been designed to demonstrate the function and power generation of the AquaBuOY and thus validate the numerical model. In addition the tests provides AquaEnergy and Ramboll with valuable practical experience prior to larger scale testing. The full scale AquaBuOY has a diameter of 7 meter and is projected to generate about 250 kW in sea states of Hs = 5m installed on a water depth of approximately 60 meter. Further optimization is anticipated in later and parallel stages of the product development program.

History of the project During the Swedish wave energy programme in the early 1980th the company Technocean was created to develop wave energy in Sweden. Driving forces behind Technocean was a multidisciplinary team of researchers from Chalmers University such as professor Lasse Bergdahl, Jan Forsberg og Bengt-Olaf Sjöström og Lennart Claeson and others [1]. During the years 1979 to 1981 the Swedish company Interproject Service IPS in cooperation with Technocean developed and tested a wave power converter the “IPS Buoy” outside Götenborg in the open sea. The IPS converter is described in [2] and some of the results in [3]. The research within Technocean lead to another concept called the “Hose pump project” developed in cooperation with the large Swedish company Svenske Varv. The Hose pump project consisting of four floats was also tested outside Götenborg pumping high pressure water to a small pelton turbine placed on shore. The Swedish wave energy programme ended around 1986 and cooperation between IPS and Technocean continued and Gunner Fredrikson CEO of IPS maintained patents. In co-operation with Bengt Olaf they patented in 1999 the incorporation of hose-pumps in the IPS buoy “the AquaBuOY”.

Ocean Tested IPS Buoy Ocean Tested Hose Pump AquaEnergy's AquaBuOY

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During the period 1992 – 1996 I was co-ordinator of the EU project OWEC-1, where both IPS and Technocean was included as project partners along with most of the leading European wave energy experts. During this project I developed in co-operation with ES-Consult numerical models for the two Swedish wave energy projects the IPS and the Hose-pump project, which had many similar features to the point absorbers system developed by Danish Wave Power. Gunnar Fredrikson´s two sons Göran and Hans live in USA. Hans´s introduced his colleague Alla Weinstein to his father to realise the wave energy project in USA. Alla Weinstein got via Gunnar Fredriksen contact with Bengt-Olaf and started the company AquaEnergy in USA to develop the project together with her brother Yuiri. In 2001 Bengt Olaf Sjöström og Yuiry died in a plane crash, as their little airplane crashed while surveying the ocean area of Makaha Bay in the north westerly corner of USA, where they planned to build a wave energy plant. In addition to the tragic personal losses also the project expertise was lost. Only the remains of the laptop from Bengt Olaf was found washed up on the beach some months later. Gunnar Fredriksen from IPS recommended Alla Weinstein to initiate a co-operation between AquaEnergy and Ramboll with the aim to reconstruct the numerical model of the AquaBuOY and further development. This cooperation and development started in 2002 and filled in a void for Ramboll regarding wave energy as the Danish wave energy programme just had terminated due to change of government in 2001. The development has in the five-year period since 2002 evolved through different stages with private as well as public financial support.

o AquaEnergy o Ramboll o Aalborg University o Dunlop o Black&Veatch o EFP, DK o Carbontrust o SEI o UCC o Energinet DK o Finevera Renewables

As a result of AquaEnergy´s search for private investment Finavera Renewables bought AquaEnergy in 2006. Finavera thereby introduced the economical recourses necessary to build the first large prototype of the AquaBuOY that was deployed in Oregon USA September 2007.

Kim Nielsen, November 2007

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Scope and Objectives

o To build a sufficiently large physical model of the AquaBuOY (scale 1:10) suitable to validate and investigate the interaction of the device components.

o To obtain preliminary experience with the principles of operating the model in a sea environment,

regarding installation, mooring, survivability and maintenance.

o To provide a comparison between the measured and the calculated (projected) performance parameters for selected sea states conditions.

o Assess viability of the use of the drag reduction components such as placement of a “bulb” below the

acceleration tube to reduce the fluid friction.

Conclusions The scale 1:10 project has provided valuable learning experience and sufficient confidence in the construction and operating principles of the AquaBuOY to support the design and deployment of a half scale prototype of the AquaBuoy. Incorporating the experience from the scale 1:10 project the company Finevera Renewables have constructed and successfully deployed a prototype of the AquaBuOY of the coast in Oregon USA. The development of the AquaBuOY is a multinational co-operation and valuable interaction has taken place between parallel research projects and the 1:10 scale design process.

Choice of Scale and test site During the Marine Energy Challenge development programme in the UK – AquaBuOY was one among several wave energy converters offered the possibility of UK engineering expertise in assessment of design and to further optimize the performance. Based on the calculated power production in the Orkney wave climate 28kW/m the study showed the optimal dimensions for the AquaBuOY at this site dimensions are as follows: Float diameter: 7 meter Float draught: 4,8 meter Tube lenght: 30 meter Tube diameter: 4,65 meter Rated Absorbed Power: 273 kW (in wave conditions Hs = 5m & Tz = 7,5 sec) A 1:10 scale model means that a converter of identical geometry, but 10 times smaller in all linear dimensions can be tested in waves also ten times smaller in height and 100,5 = 3,2 times smaller in wave periods. The power delivered from the scale model in the scaled rated conditions will be 103,5 times smaller compared to full scale. Thus results from a model can be scaled up using Froudes model law and thus results from a small experiment can be used to predict the performance of a larger geometrical identical system in scaled up sea conditions. The testing in Nissum Bredning was selected as this site previously had been used for scale testing of systems like the Wave Dragon, Wavestar and the other systems. The test site Nissum Bredning with

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significant wave heights up to about 1 meter compares well to a scale test of 1:10 and this ratio was chosen for the test. Physical dimensions: Parameter Model Scale factor

10 Full scale

Float diameter 0,7 meter 10 7 Float height 0,48 meter 10 4,8 Displaced volume 185 litre 103 185 m3 Accelerator tube diameter 0,46 meter 10 4,65 meter Accelerator tube length 3 meter 10 30 meter Rated absorbed Power 86 watt 103,5 273 kW Significant wave height (at rated power) 0,5 meter 10 5 meter Average wave period (at rated power) 2,3 seconds 100,5 7,5 seconds

Choice of model Fabrication and Material The scale model is constructed in PVC and build by Brønnum Plast using as far as possible standard tube dimensions as shown on the photo below. The lower bulb on the tube was designed to reduce the drag resistance of the heave motion.

The PVC model of the AquaBuOY in scale 1:10, Left: the float and the by-pass section,

Right: the lower part of the acceleration tube with the bulb below.

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Choice of end-stop solution the by-pass section The bypass mechanism was invented by IPS to avoid overload on the linear power take-off in case the center piston moved outside its working area. The by-pass solution consisted of a working area for the piston with a slightly smaller diameter compared to the tube diameter. In case the piston moved out the working area water could flow pass the piston and reduce the end-stop loads. The construction parts are shown in the photo below and the assembled section below. The piston is attached to a central guide-rod. This design turned out to take up quite a lot of length in the tube – and a different was developed for the half scale prototype.

The piston (black) in its working area just beneath the by pass area.

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Choice of Instrumentation of the 1:10 scale model Following the 1:50 scale experiments in Cork, Ireland, in the spring 2007 (page 12) it was decided to incorporate a similar mechanical power take-off on the 1:10 scale model as shown oh the picture below. AquaEnergy/Finavera subcontracted the instrumentation and testing of the model to Aalborg University and a separate report describing the instrumentation is enclosed [4].

The power take of based on mechanical components is shown on the photo to the left. The PTO could be mounted on top of the float. At the top is a friction element that combined with the springs provides the damping characteristics close to that of the hose-pumps. Measurements of the piston displacement relative to the float, the load on the rod and the motion of the float. The instrumentation includes

o Load cell o Position sensor o Tri-axial accelerometer

Based on the force measured and the relative velocity of the piston (derived from the relative position measurements) the average power absorbed over a period of time can be calculated as:

dttvtFT

P r

T

mech )()(1

0∫=

F(t) Force in rod connection vr(t) Relative velocity between piston and float T Measurement period The measurements are stored in a data handler box on the float powered by batteries placed in a separate container next to the float.

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Methodology used installing of the scale model in Nissum Bredning The system was tested in Nissum Bredning (Denmark) and a small team from Aalborg University installed the scale model July 22 2007, from Oddesund in the early morning in very calm water. The installation was done within 3 hours.

Transportation at sea

Float moored between three mooring buoys.

In the days to come the forecast was rough windy weather with wind directions from west and south west. The predicted waves at the site based on measured wind data is shown in the report from Aalborg University and within the next few days wave conditions in terms of significant wave height was increasing up to 0,7 meter (highest waves about 1,4 meter).

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The following week on July 28 the Aalborg team observed the model in wave conditions calculated to Hs = 0,7 meter with average wave periods of about 3 seconds. The team estimated that the model had problems as it was observed to be leaning to one side as shown on the photo below.

Observation of the float July 28 2007

The following inspection on July 30 verified the suspicion as the model was stranded on the beach.

Float ashore on July 30 2007

It appeared that a structural failure in the upper flange connecting the float to the tube had taken place. The float had tilted to a horizontal position. The connecting fins had cut the mooring lines and the float stranded on the beach. Weeks later the lower part of the tube was also recovered and removed from the beach.

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Results and conclusion The 1:10 scale project has made it possible to investigate different design solutions with respect to incorporation of power take off system and testing equipment in small scale as well as the design of the end stop by-pass solution for the piston. The practical experience showed that even in the relative small scale the model needed to be handled with great care to avoid damage. The PVC material is fragile and sensitive to impact loads and the bolting flanges between the sections in the acceleration tube appeared to be relatively weak compared to the overall strength of the model when placed horizontal for transportation. The placement of ballast in order to obtain the correct metacenter height also showed some difficulty due to the light weight of the PVC structure. It was finally decided to place the sand ballast in the hull (about 80 kg) to obtain the correct water line. Even though the model was operating vertical in heave when installed – the initial tilting of the model showed that the sand could move resulting in a sloped angel of the centerline. The installation was very easy and could be carried out within a few hours in calm weather. Following the installation the weather changed and for 2 weeks the waves made it impossible with the available transportation means to access the devise. Observations made by AAU after one week showed that the model was not floating vertical but leaning to one side. After two weeks the lower part of the acceleration tube had broken off – the mooring lines had been cut and the model could be picked up on the beach. The data handler box with stored measurements appeared empty and data from the experiment could not be retrieved. Concluding and looking back on the experience of this exercise it appears that a number of further initial tasks could have been incorporated to ensure a better performance.

o In the case of this system initial tests of the structure could probably have revealed if the bolting sections needed further reinforcement – or pretension by wires.

o Dry test of measuring equipment and data collection system combined with a setup to activate the

Power take off on land could probably have provided a better understanding of why no data was obtained.

The main practical experience from the 1:10 scale model tests however has given sufficient confidence in the operation of the device and the experience and knowledge gained has supported the development of the AquaBuOY i.e. shown areas where a redesign was needed, such as a redesign of the bypass system to allow better support for the piston and at the same time provide sufficient length to incorporate the hoses within the length of the acceleration tube.

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Parallel research projects Testing of the Hose-pump Dynamic testing of the hose-pump was realized at a test rig build at AEAT in the UK, with the support from the UK Carbon trust and Dunlop as lead partner. Three different hose constructions were tested. The results demonstrated an efficiency of around 75% in converting mechanical power into hydraulic power. The tests also showed that fatigue was a problem that needed further research in order to construct hoses with sufficient long operating life. The test showed that the construction induced rotation that after a few months caused failure of the hose at its termination. A principle to reduce the rotation by adjusting the applied angles of reinforcement in different layers of the hose was proposed and incorporated in the design.

Hose being tested at the test rig

The theory for the pump regarding flow and pressure for different strokes and periods was verified. And fatigue tests followed.

Dynamic test rig for testing the hose pump – AEAT

Initially for the 1:10 project the PTO was proposed to be composed of similar rubber hoses – produced by Festo Practical considerations and detailed design regarding these small hoses however revealed that even if they in theory could provide the required damping, incorporating two opposing sets within the length of the acceleration tube was not possible. Further the flow resistance through the standard fittings would generate excessive flow losses and make the power measurements difficult without additional measurement equipment. Sea testing of hoses was therefore postponed to larger scale testing.

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1:50 Scale Experiment HMRC Cork To verify the performance and optimize the AquBuOY Finavera/AquaEnergy was funded through the Irish government Sustainable Energy Ireland SEI, to conduct 1:50 scale testing at HMRC, Cork, Ireland. The testing and preparation of result took place in January - March 2007. The model tests helped calibrate and validate the numerical model developed by Ramboll. Further the principles of the PTO for experimental testing was changed from hydraulic to a mechanic system including springs and friction. The combination of springs and friction turned out to provide very similar characteristics as the forces from the hose-pumps. It was agreed to incorporate this PTO system in the 1:10 scale testing also.

The 1:50 scale model ready for testing at HMRC

The main results from the 1:10 scale model experiments were data produced on performance for a wide range of sea states and damping settings. The numerical model was improved by incorporating of more accurate hydrodynamic parameters for the combined float and tube geometry as well as drag resistance measured experimentally. The comparison between measured and calculated energy production showed an overall good agreement. The numerical model was transferred from Ramboll to Finavera as part of this project to be used in further optimization an evaluation. The results are described in a confidential report as part of the SEI project.

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Prototype testing Oregon USA During the spring and summer of 2007 the design and building of the 1:2 scale model took place in Oregon USA by companies hired by Finavera renewable. The speed and efficiency in getting the project up and running was quite remarkable seen with European eyes. Only about one and a half month after the project manager Denis from USA had been witnessing the installation of the 1:10 scale system in Nissum Bredning, he was ready to install the 1:2 scale model on the west coast of the USA September 1 2007.

AquaBuOY 1:2 construction and prototype testing in USA, Oregon September 2007 [5]

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References: [1] Energi från havets vågor, Lennart Claeson mfl, Technocean AB, 1987 [2] First Symposium on Wave Energy Utilization, 30 October –1 November 1979 [3] Proceedings of the 2nd International Symposium on Wave Energy Utilisation, The Norwegian Institute of Technology, Trondheim Norway June 22-24, 1982 [4] AquaBuOY Wave Energy Converter, real sea testing at Nissum Bredning Denmark September 2007, Dep. of Civil engineering, Aalborg University [5] Finaveras webpage www.finavera.com