Embed Size (px)
Citation preview
Towards an Australian capability inarrays of ocean wave-power machines
Project overview and summary of final report
ARENA Emerging Renewables Program Funding Agreement number A00575
June 2018
Contributing authors
Richard Manasseh1
Swapnadip De Chowdhury1
Md. Kamrul Hasan1
Irene Penesis2
Alan Fleming2
Gregor Macfarlane2
Jean-Roch Nader2
Contributing institutions
1: Swinburne University of Technology(primary contractor to ARENA)
2: Australian Maritime College,University of Tasmania(under subcontract)
Contributing partners
Carnegie Clean Energy LtdBiopower Systems Pty LtdCSIRO Oceans & Atmospheres
Citation
Manasseh, R., De Chowdhury, S., Hasan, M.,Penesis, I., Fleming, A., MacFarlane, G., Nader,J.-R., 2018, Towards an Australian capability inarrays of ocean wave-power machines: Projectoverview and summary of final report, SwinburneUniversity of Technology, Melbourne, Australia.22pp.
Copyright
Copyright in this report is held by the authors,with the exception of copyright in the imagesfrom CSIRO acknowledged in figure captionswhich is retained by CSIRO.
Acknowledgements
We are grateful to many individuals who havecontributed to aspects of this research. Theyinclude Suhith Illesinghe, Alexander Babanin,Alessandro Toffoli, Brian Winship and JustinLeontini. The permission of CSIRO to reproducescreenshots from the Australian Renewable En-ergy Mapping Infrastructure (AREMI) website isgratefully acknowledged.
Disclaimer
The contents of this report, of the detailed re-ports submitted to ARENA, and of the publica-tions referenced in this report represent scientificand engineering research that is generic and ex-ploratory in nature. This research should notbe used for decision-making or design, activitiesthat must be preceded by investigations specificto each case. The Contributing Institutions andContributing Partners accept no liability whatso-ever for any loss or damage directly or indirectlyoccurring from this research.
Contact
Prof Richard ManassehSwinburne University of TechnologyPO Box 218, Hawthorn, VIC 3122Melbourne, [email protected]
i
Contents
Executive Summary 1
1 Wave-energy converters and wave-energy-converter arrays 21.1 Wave-energy conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 WEC arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Method 32.1 Re-capitulation of theoretical models . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 All resonating WECs divided into just two types . . . . . . . . . . . . . . . . . . . . 42.3 Comparison with data from the model basin at AMC . . . . . . . . . . . . . . . . . 4
3 Results - Geographical performance of wave-energy arrays 73.1 Input wave-climate datasets used for the Measure and their locations . . . . . . . . 73.2 WEC array configurations to be evaluated . . . . . . . . . . . . . . . . . . . . . . . 73.3 Results generated from inputs on array performance in the various locations . . . . . 73.4 Optimal array type, size and configuration at each location . . . . . . . . . . . . . . 103.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4 Results - currents around a single wave-energy converter 174.1 Experiment at Garden Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.2 Laboratory experiments on a single WEC . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Knowledge-sharing activities 185.1 Referred journal papers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.2 Referred full conference papers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.3 Conference presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.4 General talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.5 Closed-audience talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.6 Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.6.1 Newspaper articles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.6.2 Television items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.6.3 Radio items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ii
Executive Summary
• Aims. This ARENA Measure was devised to understand the performance of ocean wave-energy arrays in Australia. The primary objective was to deliver a software tool enabling arrayperformance to be estimated. A secondary objective was to determine the pattern of localcurrents created by a wave-energy converter, one of the possible environmental impacts ofwave-energy converters.
• Arrays or ‘farms’ of the ocean Wave Energy Converters (WECs) are multiples of the individualWECs already developed or under development, organised into groups in relatively close prox-imity to enable regionally-significant electricity generation. It is recognised internationally thatowing to the peculiarities of wave physics, an array of such machines can effectively behaveas one complex machine, rendering wave-energy ‘farms’ completely different to farms of windturbines. Inappropriate siting of the machines relative to each other could result in much lesspower than the same number of isolated individual machines, while appropriate siting coulddeliver much more power than the same number of isolated individuals.
• Methods. Analytic (purely mathematical) techniques previously published in the internationalliterature were adapted into a semi-analytic model (mathematical formulae requiring evaluationby specialised software). The core of the model, subject to the most severe approximations,was a set of coefficients found to be comparable with the equivalents extracted from laboratoryexperiments.
• Key Deliverable. A software tool modelling this performance, the Array Power from OceansGeneric Estimator for Australia (APOGEA) was delivered to ARENA.
• Key Results. The power extractable by arrays of interacting wave-energy machines, as opposedto the power extractable by isolated machines, appeared very significantly higher in certaingeographical locations, while appearing very similar in other locations. It was speculated thatthis was due to the wave direction being much more uniform in those certain locations, allowingappropriately-configured arrays (which are sensitive to wave direction as well as wave power)to take full advantage of that location. Regions that might hitherto have been neglectedas wave-energy prospects appeared to have potential. It was also found that wave-energy converters may generate currents in their immediate vicinity; further work to study thisphenomenon and its potential environmental impacts was recommended.
• Key Conclusion. A wave energy development needs to be planned as an array from the outset.Meteorological and oceanographic data need to be processed by engineering calculations suchas those of the present Measure. When considering a given location for a development, notonly the height of the waves matters; the variability in wave direction must also be considered.
1
1 Wave-energy converters and wave-energy-converter arrays
1.1 Wave-energy conversion
This subsection is is extracted from the Project Plan for the present ARENA Measure, edited toupdate references.
Unlike for wind energy, there is no single established wave-energy conversion concept. This is dueto fundamental mechanical principles. The wind turbine, and its water equivalents the hydroelectricor tidal-flow turbines, require in essence only a single moving part to extract power from the motivefluid, be that fluid air or water. That is because the inherent motion of wind (or of water exiting adam, or driven by an ebb or flood tide) is uni-directional.
However, the inherently reciprocating (to-and-fro) nature of waves, in which the speed of thewater is never steady and constantly reverses, demands a more complex mechanism. And up to now,no perfect mechanism for this task has been invented. This fundamental issue has led to a plethoraof alternative inventions. Thus there are many, totally varied WEC inventions, most championed bya separate wave-power company, and they have been growing rapidly in recent years [1, 2].
There are wave-energy technologies at almost all positions in the technology-development life-cycle, ranging from purely conceptual to grid-connected pilot plants. Although most of the conceptshave been theoretically modelled and experimentally tested in laboratories, most wave-energy tech-nologies are still in the development stage [1, 2].
1.2 WEC arrays
This subsection is is extracted from the report on Measure Deliverable 3.1 submitted to ARENA,edited to update references.
Given this diversity of designs, the true test of the benefits of any given WEC technology is likelyto become apparent only once that technology is deployed in reasonably large numbers, in arrays or‘farms’. When the number of machines is significant, economies of scale in construction, operationand maintenance will become apparent. Moreover, the capital required to develop a farm shifts theentire scale of operation to one in which the developer would be large enough to have some resilienceto inevitable setbacks. It is for this reason that it is important to understand the array operation ofWECs. However, as noted below, predicting the output of a farm of WECs and hence its economicviability is much more difficult than simply multiplying the output of one machines by the numberof machines.
Unlike wind turbines, wave-power machines have an exceptional ability to affect each other. Thishas been recognised since wave-power arrays were first proposed in the 1970s, and continues to beof concern in the present day (see literature cited in [3]). It was recognised by Budal in 1977 (see [3]for reference) that an inappropriate spacing (positioning) of machines relative to each other couldresult in only half the power predicted if one simply multiplied the output of a single machine bythe number of machines: a detrimental outcome. Conversely, the optimal arrangement could deliverabout 50% more power than one would naıvely predict: a beneficial outcome. While there are manytheoretical analyses, there is no significant experimental validation, and some of the theories are verycomplex, with no clear guidance on how to extract results of practical relevance. Budal introducedwhat he called the q factor (not to be confused with the Q or quality factor more widely used in
2
many branches of engineering). Budal’s q factor is the ratio defined by
q =power delivered by array of N interacting WECs
N × (power delivered by a single WEC).
Much of the technical work of the present Measure could be summarised as ‘estimating the q factoraround Australia’. If q is less than one, the configuration of the array (i.e. the number of machines,and their relative spacing and orientations) is detrimental. If q is greater than one, the configurationof the array is beneficial. The q factor, multiplied by the nominal power output (in MW) of a givenmake and model of individual machine, gives the actual power per machine in MW that an array ofsuch machines can deliver. Effectively, this is a map of the q factor around Australia; examples arein section 3 below.
2 Method
This section is extracted from the report on Measure Deliverable 5.2 submitted to ARENA.
2.1 Re-capitulation of theoretical models
The full set of theoretical assumptions was presented in Deliverable 2.2. Here, a brief re-capitulationis given, with equation (17) from D2.2 reproduced. The use of potential flow is critical to the theory.Potential flow arises automatically on making the following four assumptions:
• The water is incompressible;
• The behaviour is linear, so that the wave amplitude is very small compared with the wavelength;
• The water is inviscid, so that friction is negligible;
• The behaviour is sinusoidal in time.
Equivalently, one can assume potential flow from the outset, and then assume incompressibility.These assumptions, whichever the sequence in which they are made, imply that the velocity fieldsof the devices can be linearly superposed. This concept of superposition is the basis of the entireMeasure, in which the technology types are separated into generic monopolar and dipolar machines.To illustrate, imagine there are only two machines. The interaction of these two machines at aparticular spacing is given by
x1 + γ12x2(t− τ) + 2ζω0x1 + ω20x1 = F eiωt,
x2 + γ21x1(t− τ) + 2ζω0x2 + ω20x2 = F eiωt, (17)
in which xi is the displacement of the ith machine, γ12 and γ21 represent the strength of the couplingthat depends on the inter-machine spacing, and τ is the time delay owing to propagation from onedevice to another. In practice, γ and τ together are derived from the real and imaginary componentsof the ‘hydrodynamic coefficient’ commonly referred to in maritime engineering, where it representsthe influence of one body (such as a ship) on another, owing to waves sent from one body to the
3
other. The ocean waves exert a force per unit mass on the machine of amplitude F and radianfrequency ω.
Thus, it is the estimation of the numbers γij and τij , ∀i, j ∈ N for various configurations ofWECs around Australia that formed the technically demanding contribution of the present Measure.Once those numbers can be estimated, the maps of power extractable from the ocean by WEC arraysaround Australia can be plotted.
2.2 All resonating WECs divided into just two types
The key theoretical approach used in the present ARENA Measure is to greatly simplify the operationof all resonating WECs insofar as their interaction physics is concerned. The assumption is that anytype of resonating WEC technology can be represented by a superposition of the interactions oftwo generic devices: a generic monopolar device and generic dipolar device. Monopolar machines,effectively moving vertically only, create a circular pattern of waves in the sea around them, rather likethe pattern seen on dropping a rock into a pond. Dipolar machines, effectively moving horizontallyonly, create a pattern similar to that seen in the high-school science class when iron filings are puton a sheet of paper above a bar magnet. This assumption is in turn predicated on the assumptionof potential flow that has been adopted for WEC analyses since the 1970s.
2.3 Comparison with data from the model basin at AMC
The experiments at AMC utilised the novel concept of having a sphere that was able to oscillateboth vertically, synthesising monopolar behaviour, and horizontally, synthesising dipolar behaviour(figure 1). This meant that a complex mechanism had to be created to execute both motions, buthad the advantage that no artefacts due to the formation of vortices would particularly affect themonopolar versus the dipolar motion. Had a cylinder been used, vortices would have formed at itssharp edges, and vortices do not occur under the linear potential flow assumptions used in the theory.Initial trials at AMC, reported at the time of Deliverable 1, had suggested different technologiesfor the monopolar and dipolar devices could certainly have been used, but would inevitably haveproduced vortices adversely affecting one type of technology more than the other. Moreover, theentire purpose of the Measure is to calculate the array interactions without being biased by thespecifics of individual developers’ technologies. Details such as vortex formation matter for thedamping on individual developers’ designs, but not insofar as the coupling between machines in anarray is concerned. In order to measure the hydrodynamic co-efficient, one sphere was driven, andthe other spheres were fixed. However, the fixed spheres were able to sense forces applied to themvia precision-calibrated force transducers. Since the hydrodynamic co-efficient is effectively the forceapplied by one machine to another, this method was thought the most effective for measuring theco-efficients.
The spheres were 250 mm in diameter and the experiments are described fully in published papers[4, 5].
Figure 2 shows the comparison. Two theoretical approaches (both, in practice, evaluated nu-merically), the multiple-scattering semi-analytic approach, and a numerical potential-flow simulation(using the open-source solver NEMOH, produced by Ecole Centrale de Nantes), are compared withthe experimental data measured in the AMC model test basin. It can be seen that the analytic model
4
Figure 1: The driven spherical model. Top: elevation drawing. Bottom: as installed, with the drivingmechanism enclosed in a specially-excavated chamber in the concrete floor of the AMC Model Basin.
compares well with the experimental data. Both the peak and the general shape of the function arereproduced. The analytic result is remarkably close to the experimental data over much of the curve,with the exception of a band of frequencies between about 0.50 and 0.75 Hz, where the experi-
5
mental data exhibit a small ‘bump’. This may be due to a nonlinear subharmonic or ultraharmonic,which would not be reproduced by the linear theory or simulation; both use potential flow, thus pre-supposing linear behaviour. Interestingly, the analytic theory is actually closer to the experimentaldata than the numerical simulation. This may be because the analytic theory has obtained a highereffective resolution, since its functions are exactly matched to the geometry.
Figure 2: Comparison of the coupling constant (real part of the hydrodynamic co-efficient) withmeasured data from the model test basin at AMC, for two spheres separated by 1500 mm. Shownis the vertical (heave) component of the coupling constant due to machine 1 acting on machine 2,as a function of the frequency applied to machine 1. The code to compute the multiple scatteringproblem for a sphere was provided by Natalia Sergienko of the University of Adelaide.
Finally, the point-absorber assumption was rigorously tested by comparison with the multiple-scattering approach for various spacings between machines, as detailed in [4]. It was found thatfor inter-machine spacings of 5 radii (measured from the centreline of one machine to another) thepoint-absorber approximation was good, and for a spacing of 10 radii, it was very good. Hence, aspacing of 10 radii was used for the results presented in Deliverable 5.1.
It must be noted that while the point-absorber assumption holds, the shape of the WEC - orthe shape of any model representing a WEC - is irrelevant. It is only the pattern with which itmoves (monopolar versus dipolar) that matters. In practice, for analytic and numerical convenience,the results reported in D5.1 were for cylindrical floating bodies. However, as noted above, in theAMC laboratory, any shape other than a sphere would have generated vortices artificially biasingthe results for monopolar versus dipolar, by introducing factors irrelevant to the coupling betweenmachines. The entire premise of the Measure is to have generic technologies. Hence, figure 2 showsa comparison validating the multiple-scattering approach taken, and the comparisons are necessarilymade for a sphere.
6
3 Results - Geographical performance of wave-energy arrays
This section is extracted from the report on Measure Deliverable 5.1 submitted to ARENA.
3.1 Input wave-climate datasets used for the Measure and their locations
The datasets used were downloaded from the Australian Wave Energy Atlas (AWavEA), producedby CSIRO under an ARENA Measure that overlapped in timing with the present Measure and wascompleted about six months prior to the present Measure. Owing to prior projects involving regionsoutside Australia, the CSIRO’s mapping codes used to generate the AWavEA also include the islandof Timor, the eastern parts of New Guinea, and some islands of Melanesia including New Caledoniaand Vanuatu.
As well as being displayed in graphical form on the Australian Renewable Energy Mapping In-frastructure (AREMI), the AWavEA datasets are available for general public download, and wereimported into the present Measure’s software tool called Array Power from Oceans Generic Estima-tor for Australia (APOGEA) produced as Deliverable 4.2 and described in Deliverable 4.1.
3.2 WEC array configurations to be evaluated
As proposed in the Measure Project Plan and detailed in Deliverable D5.3, the two technology typesexamined in the present Measure were defined to be monopolar and dipolar machines.
Precise definitions of the term ‘Configuration’ should be established. In the Measure ProjectPlan, the term ‘Configuration’ was used fairly loosely to mean any combination of the numberof machines, their geometric layout relative to each other, the spacing between machines and theorientation of the array relative to the prevailing wave direction. The definitions were originally looseowing to uncertainty as to what would prove most valuable to investigate; now that the project iscomplete, precision is possible. The APOGEA software provides for three cases we can call BaseConfigurations: two machines in a line, three machines in a line and three machines in an equilateraltriangle. These Base Configurations can be oriented at any angle relative to the cardinal directions(due east is defined as zero degrees).
Furthermore, for dipolar machines, there is a further angle that could be varied, which is the lineof action of the machines. Thus, the resulting Configuration is precisely defined by three values:(Base Configuration, Orientation Angle, Line-of-Action Angle). For monopolar machines, recall thatthe ‘Line of Action’ has no meaning, since monopolar machines radiate waves in a perfectly circularpattern and thus have no preferred horizontal direction.
Six configurations will be studied for illustrative purposes; they are shown in figure 3.
3.3 Results generated from inputs on array performance in the various locations
The APOGEA software was run on AWavEA datasets for each month and for the entire Australiancontinental shelf, for each Base Configuration and for each of 0, 45, 90 and 135 degrees orientationrelative to due east. A virtually infinite number of maps could be generated by APOGEA for variouspermutations of WEC technology type, Base Configuration and array orientation angle (and fordipolar machines, in addition to the array orientation angle, the machine’s line-of-action angle).Furthermore, input data could be chosen for any of the 12 months of the year. Thus, it was decided
7
Monopolar WECs
Dipolar WECs
Base Config. 1 Base Config. 2 Base Config. 3
Figure 3: Base Configurations examined for illustrative purposes in the present report. Arrowson the dipolar machines illustrate an east-west line-of-action of the machines. Using the notation(Base Configuration, Orientation Angle, Line-of-Action Angle), the three configurations in this figureillustrate (1, 0◦, -), (2, 90◦, -), (3, 90◦, -) for the monopolar machines and (1, 0◦, 0◦), (2, 90◦,0◦), (3, 90◦, 0◦) for the dipolar machines. It must be emphasised that any Line-of-Action Angle ispossible in APOGEA.
that only cases demonstrating the most interesting differences, which effectively inform the userabout the points noted below, were worth uploading to AREMI. If other cases were of interest, theycould always be generated from APOGEA on demand.
Each machine was given a nominal maximum power output of 2 MW. The only reason for thislimit is graphical; the AREMI system requires all maps to have the same colour scale, so a fixedupper limit is required. The machines were assumed to be tuned to the peak wave frequency at eachlocation, so they are always resonating.
The cases uploaded were configurations as shown in figure 3; for the two technology types,monopolar and dipolar, for Base Configuration 1 oriented on an east-west line, Base Configuration 2oriented on a north-south line, and Base Configuration 3 oriented such that one side of the trianglewas on a north-south line (three Base Configurations). For the dipolar machines, an east-west line ofaction was selected. The months of August, December and January were selected (three months).The result was 2 × 3 × 3 = 18 images. These were delivered to CSIRO in the standard Mercatorprojection, quality-checked and transformed onto the mapping projection used by AREMI (a global-perspective projection). CSIRO intends to transfer these data to AREMI on the next AREMI update,and has made them publically available in the interim by visiting the page
http://oa-gis.csiro.au/geoserver/web/?wicket:bookmarkablePage=:org.geoserver.
web.demo.MapPreviewPage
8
then navigating to ‘Layer Preview’ on the left-hand of the page, and searching for ‘Swinburne’.An example result is shown in figure 4, in which three machines are arranged in an equilateral
triangle with one side of the triangle, i.e. configuration (3, 90◦, -). It must be emphasised thatone would never contemplate a development in which the array were oriented in the same directionirrespective of its geographical location; the machines would of course be deployed in the optimumorientation for that location. An optimum orientation will shortly be demonstrated. However, byforcing the array to be in the same orientation irrespective of location, some interesting, stark andinformative contrasts become clear. The data in figure 4 essentially echo the input wave energy mapfrom AREMI: there is high to very high power on the southern and western coasts of the continent,low power on the south-eastern coast, and very low power in the tropical north.
Figure 4: Monopolar Configuration (3, 90◦, - ): three monopolar machines in an equilateral triangle,with one side of the triangle on an north-south line, for the month of August. The colour scaleshows the power extracted per machine in the array, so that in regions where 1 MW power is shown(greenish coloured regions), the array of N = 3 machines produces N × 1 = 3 MW.
9
3.4 Optimal array type, size and configuration at each location
In figure 5, the results are shown for a triangular array of dipolar machines that is optimally orientedat each point on the map, with the lines of action of the dipolar machines also optimally oriented.
The optimal orientation was achieved by running APOGEA for different array angles with respectto the monthly means of the peak wave direction, and then choosing that configuration which yieldsmaximum array power.
The configuration shown in figure 5 offered the highest overall power overall, as evidenced bymany bright-yellow zones (power per machine exceeding 1.6 MW). In some locations, particularlyoff SW Tasmania, power exceeded the nominal 2 MW maximum power per machine imposed byAREMI’s need to have a uniform colour scale. Most notable, however, is what might be called ahigh level of ‘contrast’ in this map, compared to non-optimal maps such as figure 4. It is not simplya case of the power being uniformly higher everywhere. Rather, bright-yellow zones indicating highpower are close to green or blue zones representing moderate or low power. Large variations in arraypower occur over a few tens of kilometres.
Figure 5: Dipolar Configuration (3, optimal-orientation-angle, optimal line-of-action angle):equilateral-triangular configuration of three machines custom-rotated at each point on the mapsuch that maximum power is obtained, for the month of August.
10
To explore and to understand these interesting variations, it is instructive to examine in detailsome specific regions, beginning with the southern coast of Victoria and the northern coast ofTasmania shown in figure 6. This region probably exhibits the most interesting contrasts found inthe present Measure. To emphasise the effect of the array, in the left-hand panel, the raw input wavepower from the AWavEA is shown. In the right-hand panel, the array power for same region is shown,extracted from figure 5. A comparison is highlighted between two stretches of coast of approximatelyequal length: the coast of Victoria between Portland and Cape Otway, which is sometimes calledthe ‘Shipwreck Coast’; and the coast between San Remo and Wilson’s Promontory, called for thepurposes of this report the ‘West Gippsland’ coast. The Shipwreck Coast includes stretches of coast(from west to east) in Glenelg Shire, Moyne Shire, the City of Warrnambool, Corangamite Shire andColac-Otway Shire (the red line on the map stretches from approximately Warrnambool to CapeOtway). The West Gippsland coast includes stretches of coast (from west to east) in Bass CoastShire and South Gippsland Shire.
The Shipwreck Coast has high to very high incident raw wave energy, owing to the combinationof two factors. Firstly, it faces almost directly into the Southern Ocean swell generated by theRoaring Forties (the powerful westerly winds that encircle the globe, peaking at roughly 45◦ S) aswell as being completely exposed to those same winds - travelling due west of Cape Otway, there isno land mass blocking the westerly wind before one reaches the eastern coast of Patagonia roughly12,000 km away1. Secondly, the continental shelf is fairly narrow off this coast, being roughly 50 kmwide. As swell propagates from the deep ocean onto a continental shelf, it gradually loses energyowing to friction from the sea bed; in the deep ocean 50 km off the Shipwreck Coast, the incidentpower is roughly 60 MW per kilometre of wave crest, but at the coast the power has dropped toroughly 40 MW/km. Therefore, the narrower the shelf, the more wave energy is delivered to thecoast. Consequently, this coast was identified by developers as a one of the nation’s peak wave-energyresource regions. Two ARENA-funded wave-energy projects were proposed for this coast.
In contrast, by the time the Southern Ocean swell reaches the West Gippsland coast, it hastravelled over roughly 250 km of continental shelf, five times more distance over a shelf than at theShipwreck Coast. The West Gippsland coast also lies in a ‘shadow’ cast by King Island. The powerof the swell has consequently been reduced to roughly 20 MW/km at Cape Liptrap, half the powerat the Shipwreck Coast, and to only about 10 MW/km at Venus Bay.
However, the power available from the dipolar configuration shown in figure 6 is actually greateron the West Gippsland Coast than on the Shipwreck Coast, reaching 1.6 MW per machine (4.8 MWfor the array) at Cape Liptrap, versus roughly 1.2 MW per machine (3.6 MW for the array) over theShipwreck Coast. Thus, despite the input power being half, the output power is a third greater.
A possible reason for this apparent paradox may lie in the second factor mentioned above - thecontinental shelf. The continental shelf may reduce the raw wave power available at the coast, butit also reduces the variability in wave direction. This is due to the phenomenon of refraction, whichturns waves travelling across the continental shelf so that they always tend to travel at right anglesto the coast. This is the same phenomenon that causes waves to always head onto a beach, so thatthe crests are always parallel to the beach. According to the AWavEA data, the monthly variabilityof the input wave power (the monthly variability of the maximum directionally resolved wave power)
1This coincidence of coastal orientation and prevailing winds and swell also created danger for 19th century sailingships attempting to reach Melbourne on the fastest route from Europe, thus giving the coast its name.
11
Figure 6: Configuration 3, Dipolar, optimal-orientation, August: Comparison of input wave power(AWavEA; Source: Bureau of Meteorology and CSIRO, c© 2013) and array power (close-up offigure 5) for the southern coast of Victoria. Different aspect ratios for the input and array-powermaps are due to different geographical projections. Colour scale for the array-power map is the sameas in figure 5.
on the Shipwreck Coast is roughly twice that on the West Gippsland Coast. This may be becausethe much narrower continental shelf on the Shipwreck Coast has much less opportunity to re-orientthe swell.
An individual monopolar machine on the Shipwreck Coast would always outperform an individualdipolar machine of equivalent efficiency on the West Gippsland coast, since monopolar machinesare not sensitive to wave direction and there is more power on the Shipwreck Coast. However,dipolar machines, unlike monopolar machines, are sensitive to the wave direction, and thus arraysof dipolar machines are extremely sensitive to the wave direction. Dipolar arrays achieve stronginter-machine coupling and thus strong constructive interference when both the array angle as welland the machine line-of-action angle are optimally oriented. Following this reasoning, a much moreuniform direction of waves on the West Gippsland coast would allow an optimally-oriented dipolararray of machines to couple together very effectively, and thus extract power much more efficiently.Without a detailed analysis of local wave-direction climate and its effects on dipolar machine anddipolar array performance, this explanation remains a speculation.
This result (irrespective of the explanation for it) should not be interpreted to mean that WestGippsland is necessarily an ideal wave-energy prospect. All WECs operate with a combination ofmonopolarity and dipolarity, and when a particular developer’s technology is considered, the mapswill have to be recalculated for the specific combination of monopolarity and dipolarity represented bythat specific technology. Rather, this result merely states that it may be misleading to consider onlythe raw wave power when planning a wave energy development; knowledge of the wave direction, andof the variability in direction, may lead to reversals in opinion on what might be the best location,or, equivalently, on what might be the best technology for a given location.
12
A possibly-related phenomenon can be observed on the coast of Western Australia, betweenPerth and Bunbury, as shown in figure 7. Here, the continent forms a large peninsula, the Leeuwin-Naturaliste Ridge, which projects westwards, somewhat shielding the coast between Bunbury andPerth from direct exposure to Southern Ocean swell coming from the south-southwest. Unlike thesituation in Victoria, the effect seems not to be due to greatly differing distances travelled overcontinental shelf, but may be due to the effect of Cape Naturaliste. This point has the effect ofrotating the swell through the phenomenon of wave diffraction, so that almost irrespective of inputwave direction, the swell is rotated so that it travels in a uniform direction towards the Perth-Bunburycoast. The satellite image of Cape Naturaliste on Google Maps (https://www.google.com/maps/@-33.5308173,115.0055903,1744m/data=!3m1!1e3) illustrates a diffraction effect. This may beconsistent with the observation from AWavEA that the variability along the Perth-Bunbury coastis roughly half that near Albany, which is at the southernmost tip of Western Australia and fullyexposed to Southern Ocean swell. Thus, despite the raw wave power being less off the Perth-Bunburycoast than an equivalent distance off Albany, an optimally-oriented dipolar array could potentiallyextract more power if located between Perth and Bunbury, approximately along the coasts of theCity of Rockingham, the City of Mandurah, the Shire of Waroona, the Shire of Harvey and the Cityof Bunbury. Meanwhile, it is clear from figure 4 that a monopolar array would perform just as wellnear Albany than between Perth and Bunbury, and would probably perform better near Albany if itwere far enough from the coast.
Figure 7: Configuration 3, Dipolar, optimal-orientation, August: Comparison of input wave power(AWavEA; Source: Bureau of Meteorology and CSIRO, c© 2013) and array power (close-up offigure 5) for the coast between Perth and Bunbury in Western Australia. Different aspect ratios forthe input and array-power maps are due to different geographical projections. Colour scale for thearray-power map is the same as in figure 5.
A further comparison is made in figure 8 of the South Australian coast centred roughly onAdelaide. Here, differences, less remarkable than in the cases in Victoria and Western Australia, arenotable on the tip of the Yorke Peninsula and the NW tip of Kangaroo Island. Nonetheless, these
13
are coasts some tens of kilometres in length where optimally-oriented dipolar arrays could extractmore power than might be supposed based simply on the raw wave climate. A similar prospect isapparent just north of Cape Jaffa. In these locations as in the example of the Perth-Bunbury coast,wave diffraction may account for these observations.
Figure 8: Configuration 3, Dipolar, optimal-orientation, August: Comparison of input wave power(AWavEA; Source: Bureau of Meteorology and CSIRO, c© 2013) and array power (close-up offigure 5) for the South Australian coast around Adelaide. Different aspect ratios for the input andarray-power maps are due to different geographical projections. Colour scale for the array-power mapis the same as in figure 5.
A final comparison is presented in figure 9 for a zone in the Coral Sea north of Lizard Island,Queensland. This is interesting, since, unlike the previous examples, the entire region is completelyshielded from Southern Ocean swell by the bulk of the Australian continent. Rather, waves in thisregion come predominantly from the east-south-east direction. It is typical of tropical seas thatthere is little variation in the wave direction, since the regular progression of high- and low-pressuresystems that characterise the mid-latitudes, changing the wind direction on a regular basis, is absent.The zone that stands out (greenish-coloured) on the array-power panel of figure 9 has only slightlyless wave-direction variability from the zones immediately to the north or south. This zone ofcomparatively high array power lies just outside the Great Barrier Reef, more than 20 km from thecoast and over the deep ocean. Here, therefore, the continental-shelf factors referred to previouslydo not improve the array power output; in contrast, the wave direction is already uniform over thedeep ocean, permitting an optimally-oriented array to extract up to 1.2 MW per machine. However,once inside the Barrier Reef, and hence over the continental shelf, this advantage disappears. Asimilar situation can be seen along the entire New South Wales coast; optimally-oriented dipolararrays could extract up to 1.2 MW per machine, benefiting from the uniformity of South Pacificswell, but only over the deep ocean and not on the continental shelf.
It is worth noting that more sophisticated dipolar-device concepts, as well as many monopolardevices with some dipolar component, allow for the device’s line-of-action to swing in response to
14
Figure 9: Configuration 3, Dipolar, optimal-orientation, August: Comparison of input wave power(AWavEA; Source: Bureau of Meteorology and CSIRO, c© 2013) and array power (close-up offigure 5) for the Coral Sea. Different aspect ratios for the input and array-power maps are due todifferent geographical projections. Colour scale for the array-power map is the same as in figure 5.
changes in wave direction. If this occurred, the strong coupling of dipolar devices in an array wouldbe reduced; for the three-machine equilateral-triangle array of figure 5, such ‘decoupling’ would occurif the swing is not close to some multiple of 60◦. Meanwhile, many more than three machines, ifarranged on an equilateral lattice, would still achieve coupling if the swings in direction were multiplesof 30◦, and strong coupling for multiples of 60◦. In any case, since the dipolar-array advantage onlyseems present where the local wave-direction climate has low variation, devices in those locationswould not swing much.
3.5 Summary
The present report demonstrates an interaction of three ARENA Measures; the input raw wave datacame from the AWavEA Measure, the present Measure processed those data to generate maps ofarray power, and the output of the present Measure was delivered to the AREMI web server, itselfthe product of a separate ARENA Measure.
Generic WEC arrays were modelled around the entire Australian continental shelf (and adjacentregions such as Timor, eastern Papua New Guinea, New Caledonia and Vanuatu). Generic monopolarand dipolar arrays were considered. It was found that the sensitivity of dipolar devices to input wavedirection means that when dipolar devices were placed in arrays, very significant differences frommonopolar arrays emerged. It appears that dipolar arrays can generate considerably more power thanmonopolar arrays with nominally the same power-per-machine, provided the input wave direction doesnot vary much and the dipolar array is appropriately oriented. It must be recalled that no WEC ispurely dipolar or monopolar but is rather some combination of these two modes of operation in aproportion that depends on each developer’s design; the present results represent idealised extremes
15
of ‘pure monopolar’ and ‘pure dipolar’.Consequently, some geographical locations previously thought unlikely prospects for wave energy
emerged as zones of potentially high WEC-array power output. It was speculated that this maybe due to some fortuitous local combinations of the continental shelf width and orientation, andthe input wave-direction climate. Examples or unexpectedly-high potential power extractability thatwere discovered and featured in this report were the West Gippsland Coast of Victoria, the WesternAustralian Coast between Perth and Bunbury, the Southern Yorke Peninsula Coast in South Australia,and a zone in the Coral Sea north of Lizard Is., Queensland. Unexpectedly-high potential power wasalso noted off parts of New Caledonia and Vanuatu.
The overall conclusion is that the raw input wave climate data represented by the Wave EnergyAtlas needs to be filtered through array algorithms such as those developed in the present Measure.Significant benefits would only be realised when the whole array is installed, rather than incrementalbenefits accruing as successive machines are installed.
When considering WEC proposals based on a specific technology, filtering the wave climate databy array algorithms would help to ensure sites appropriate to that specific technology are selected.This may suit an entrepreneur-led philosophy.
Equivalently, if a particular region is interested in developing a wave energy industry, the questioncould be posed of which, if any, array configuration and generic WEC technology could delivereconomically-significant power to the interested region. Array algorithms could address this question,permitting a targeted tendering process. This may suit a government- or community-led philosophy.
Finally, it must be understood that the present Measure necessarily takes a synoptic look at thewhole Australian continental shelf based on generic technologies. It is possible that the potentialadvantages revealed for the coastal regions featured in this report could turn out to be less significantonce a detailed analysis is performed for a specific technology. Of course, regional factors specificto each developer’s technology, such as distance to deep-water ports, closeness to high-voltagetransmission infrastructure, water depth and seabed type would need to be considered. Furthermore,any concomitant need for coastal protection from waves, which may greatly reduce the effectivelevelised cost of electricity [1], would need to be considered. Moreover, less tangible but still vitallyimportant costs and benefits such as any alteration to the coastal environment, access to skilledlabour and local employment generation [6] would have to be factored into consideration of anyproposal.
16
4 Results - currents around a single wave-energy converter
This section is extracted from the report on Measure Deliverable 5.4 submitted to ARENA.
4.1 Experiment at Garden Island
This experiment is fully described by the reporting under the CSIRO AWavEA ARENA Measure; theAWavEA team was instructed by ARENA to undertake this work. Prior to awarding of the presentMeasure, it was thought such data would be very difficult to measure in the ocean. As detailedin the Introduction to the paper published on this topic [7], the currents would be weak relativeto the velocities created by the waves themselves, but their effect could be considerable in movingsediments, etc., over a long period of time. Moreover, the currents would only be noticeable in theimmediate vicinity of the WECs.
Analysis of the data collected over the course of 2015 was undertaken in collaboration with stafffrom Carnegie Clean Energy Ltd. (then Carnegie Wave Energy Ltd.). The location of the sea-bedmounted acoustic Doppler current meters, for operational safety reasons, was further away from theWEC mooring points than one would expect currents to be measurable. Consistently, no currentswere observed in the data.
4.2 Laboratory experiments on a single WEC
The laboratory experiments are described by a paper published in the proceedings of the 12th Euro-pean Wave and Tidal Energy Conference 27th Aug -1st Sept 2017, Cork, Ireland [7].
The experiments clearly demonstrated the presence of currents generated by the WEC model.As expected, these currents were localised to the immediate vicinity of the machine.
17
5 Knowledge-sharing activities
This section is extracted from the report on Measure Deliverable 5.7 submitted to ARENA.
5.1 Referred journal papers
These are full papers subjected to an editorial process for an academic journal, in which the editorsends the papers for detailed anonymous peer review. The editor may reject the paper immediately orafter receipt of the anonymous reviews. If found acceptable by the editor on receipt of the anonymousreviews, papers usually require revision and re-submission to satisfy reviewers’ concerns. Multiplerounds of revision and re-submission are possible, with the editor able to reject the paper entirely atany time.
Paper [8] was prepared for journal submission but remains on a publically-accessible preprintserver since a recently-published book rendered this paper out of date by the time prepared.
Papers accepted by journals were [1], [6], [3], [9]A contribution was also made to [2] which was lead by the AWavEA ARENA Measure.
5.2 Referred full conference papers
These are full papers submitted to a technical conference and subjected to an editorial processmanaged by the conference organisers. The organisers send the papers for brief anonymous peerreview, most often by reviewers also submitting papers to the same conference. Rejection is possibleby the organisers with or without reviews, if the topic is thought irrelevant or the standard poor.Papers usually require some revision and re-submission to satisfy reviewers’ concerns. The papermust be presented in person at the conference by one of the authors.
Refereed full conference papers were [4], [10], [11], [12], [13], [7],
5.3 Conference presentations
These are presentations at technical conferences backed only by a written abstract that is usuallyonly a few paragraphs, sometimes with a figure and some references. The abstracts are reviewed,but often the reviewing is only by the conference organisers. The paper must be presented in personat the conference by one of the authors.
Technical conference presentations were [14], [15], [16] [17], [18], [19], [20], [21], [22], [23] and[24]
5.4 General talks
These presentations are usually identified only by a title, and a paragraph at most of written intro-duction. They may be invited, or unsolicited; invited talks are indicated. They may be at an eventrequiring a nominal cover-charge to enter but are otherwise open to the general public.
Public talks given were [25], [26], [27] and talk [28] is upcoming.
18
5.5 Closed-audience talks
These presentations are usually identified only by a title, and are made to a closed audience, forexample in industry or government. These were [29], [30] and [31]. In addition, more informalpresentations were given to the Measure partners, Carnegie Clean Energy Ltd. and Biopower SystemsPty. Ltd.
5.6 Media
A contribution was made to [32] which was lead by the AWavEA ARENA Measure.Media items generated by activities of the present Measure, not including items on the university
and ARENA websites specifically promoting the project, are listed below. Active links in this file areto media items that are still accessible; some media outlets remove old items.
5.6.1 Newspaper articles
The Examiner, 15 March 2016: AMC trialling world-first wave-energy research
5.6.2 Television items
• ABC News, 15 March 2016: Study helping to make wave energy more viable
• http://www.sctvnews.com.au/news/ (15th March bulletin, 3:15 mark)
• Scope, 3 September 2017: Wave Machines
5.6.3 Radio items
ABC News, 16 March 2016: Wave energy research demonstration at the Australian Maritime College
19
References
[1] R Manasseh, K McInnes, and M Hemer. Pioneering developments of marine renewable energyin Australia. Int. J. Ocean & Climate Systems, 8(1):50–67, 2017.
[2] M. A. Hemer, R. Manasseh, K. L. McInnes, I. Penesis, and T. Pitman. Perspectives on a wayforward for ocean renewable energy in Australia. Renewable Energy, (accepted), 2018.
[3] S. De Chowdhury and R Manasseh. Behaviour of eigenmodes of an array of oscillating watercolumn devices. Wave Motion, 74:56–72, 2017.
[4] I. Penesis, R. Manasseh, J.-R. Nader, S. De Chowdhury, A. Fleming, G. Macfarlane, and Md K.Hasan. Performance of ocean wave-energy arrays in australia. pages 246–253. 3rd Asian Waveand Tidal Energy Conference, Marina Bay Sands Hotel, Singapore, 24–28 October 2016,ISBN978-981-11-0782-5., 2016.
[5] J.-R. Nader, A. Fleming, G. Macfarlane, I. Penesis, and R. Manasseh. Novel experimentalmodelling of the hydrodynamic interactions of arrays of wave energy converters. Int. J. MarineEnergy, 20:109–124, 2017.
[6] R. Manasseh, S. A. Sannasiraj, K. L. McInnes, V. Sundar, and P. Jalihal. Integration of marinerenewable energy with the needs of coastal societies. Int. J. Ocean & Climate Systems, 8(1):19–36, 2017.
[7] Fleming A. and Manasseh R. Preliminary experimental observation of surface currents producedby simulating WEC radiation and diffraction wave fields. pages 1–7. Proceedings of the 12thEuropean Wave and Tidal Energy Conference (EWTEC 2017), 27 August - 1 September 2017,Cork, Ireland, 2017.
[8] S De Chowdhury, J-R Nader, A Madrigal Sanchez, A Fleming, B Winship, S Illesinghe, A Toffoli,A Babanin, I Penesis, and R Manasseh. A review of hydrodynamic investigations into arrays ofocean wave energy converters. arXiv preprint arXiv:1508.00866, 2015.
[9] A. Fleming, G. Macfarlane, and B. Winship. Application of photogrammetry for spatial freesurface elevation and velocity measurement in wave flumes. Part M: Journal of Engineering forthe Maritime Environment (Under Review, submitted 7th March 2018), 2018.
[10] R. Manasseh, M. K. Hasan, and S. De Chowdhury. Nonlinear behaviour of interacting oscillatingwater columns. Proceedings, 20th Australasian Fluid Mechanics Conference, Perth, Australia,5–8 December, 2016.
[11] R. Manasseh, M. K. Hasan, J. S. Leontini, L. Puticiu, and S. De Chowdhury. Effects ofmachine nonlinearity on the performance of idealised wave-energy converters. Proceedings,12th European Wave and Tidal Energy Conference, Cork, Ireland, 27–31 August, 2017.
[12] S. De Chowdhury, R. De La Cruz, V. T. Hyunh, B. Winship, and R. Manasseh. Computation ofpower from an array of wave energy converters using a boundary element method. Proceedings,20th Australasian Fluid Mechanics Conference, Perth, Australia, 5–8 December, 2016.
20
[13] Bennet M., Penesis I., Fleming A., MacFarlane G., and Nader J-R. Experimental study intothe diffracted wave field downstream of an array of wave energy converters in irregular waves.pages 1–10. Proceedings of the 12th European Wave and Tidal Energy Conference (EWTEC2017), 27 August - 1 September 2017, Cork, Ireland, 2017.
[14] R. Manasseh. Predicting performance of WEC arrays. Australian Wave Energy Atlas StakeholderWorkshop 2014, Vibe Savoy Hotel, Melbourne, Australia, 3–4 December 2014, 2014.
[15] R. Manasseh and S. De Chowdhury. Issues of wave energy converter operation in arrays (Invited).2nd Australasian Conference on Wave Science, School of Mathematical Sciences, University ofAdelaide, 6–9 December, 2015.
[16] R Manasseh. Developments of ocean renewable energy in Australia. Indo-Australian MarineRenewable Energy Workshop, Chennai, India, 4–6 April, 2016.
[17] R Manasseh and De Chowdhury, S. Development of analytical models for exact calculations ofinteractions in an array of wave energy converters. Indo-Australian Marine Renewable EnergyWorkshop, Chennai, India, 4–6 April, 2016.
[18] A. Fleming, J.-R. Nader, G. Macfarlane, I. Penesis, and R. Manasseh. Experimental investigationof WEC array interactions. page A20. Proc. Australian Ocean Renewable Energy Symposium,18-20 October 2016, Melbourne, Australia, 2016.
[19] R. Manasseh and S. De Chowdhury. Generic monopolar and dipolar interactions between waveenergy converters. Proceedings, Australian Ocean Renewable Energy Symposium, 18–20 Octo-ber, Melbourne, Australia, 2016.
[20] S. De Chowdhury and R. Manasseh. Behaviour of eigenmodes of an array of oscillating wave en-ergy converters. Proceedings, Australian Ocean Renewable Energy Symposium, 18–20 October,Melbourne, Australia, 2016.
[21] S. Narasimhon, S. A. Sannasiraj, S. De Chowdhury, and R. Manasseh. Interaction between twofloating bodies in surface waves using SPH. Australian Ocean Renewable Energy Symposium,Vibe Savoy Hotel, Melbourne, Australia, 18-20 October 2016.
[22] R. Manasseh. Protecting coasts with structures that generate power (invited). Coast and MarineStructures 2017, Royal on the Park, Brisbane, Australia, 21-22 March, 2017.
[23] R. Manasseh, De Chowdhury, S., J.-R. Nader, A. Fleming, G. MacFarlane, and I. Penesis.Principles of modelling array interactions of generic wave-energy converters for a predictivesoftware tool. Second Indo-Australian Marine Renewable Energy Workshop, Chennai, India, 19February, 2018.
[24] De Chowdhury, S. and R. Manasseh. Assessment of WEC array power in Australia via asoftware tool based on a semi-analytical model. Second Indo-Australian Marine RenewableEnergy Workshop, Chennai, India, 19 February, 2018.
[25] R. Manasseh. Benefits of wave energy converter operations in arrays. All-Energy Australia 2014,Melbourne Convention & Exhibition Centre, 15–16 October, 2014, Melbourne, Australia, 2014.
21
[26] R. Manasseh. Farms of wave energy converters. All-Energy Australia 2016, Melbourne Conven-tion & Exhibition Centre, 4–5 October, 2016, Melbourne, Australia, 2016.
[27] R. Manasseh. Ocean power opportunities for Australia (invited). Institution of Engineers, Energyfor the Future event, 22 May, 2017.
[28] R. Manasseh. What if we could use the ocean for power? City of Boroodara, What If talkseries, 26 June, 2018.
[29] R. Manasseh and S. Illesinghe. Wave power and the renewable energy mix. Victorian Govern-ment Department of Department of Economic Development, Jobs, Transport and Resources,Melbourne, 8 May, 2015.
[30] R. Manasseh and S. Illesinghe. Wave power in Victoria. State Government of Victoria, advisorsto Ministries of Energy, Water and the Office of the Premier, Melbourne, 13 November, 2015.
[31] R. Manasseh and J. Sanjayan. Wave energy conversion for coastal protection. Presentation toWestkon Precast Pty. Ltd., 23 November, 2016.
[32] Hemer M., Penesis I., McInnes K., Manasseh R., and Pitman T. Catching the waves: it’s timefor Australia to embrace ocean renewable energy. The Conversation, page 18 October, 2016.
22
