Design validation of the BlueTEC tidal turbineUser-Project: BlueTEC Feasibility
Bluewater Energy Services BV
Marine Renewables Infrastructure Network
Research Infrastructure Action
Rev. 1, 04-Aug-2015
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
Coordinator
Denmark Aalborg Universitet (AAU)
Danmarks Tekniske Universitet (RISOE)
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)
Plymouth University(PU)
Tecnalia Research & Innovation Foundation (TECNALIA)
Belgium 1-Tech (1_TECH)
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)
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DOCUMENT INFORMATION Title Design validation of the BlueTEC tidal turbine
Distribution Public
Taurusavenue 46 | 2132 LS Hoofddorp
P.O. Box 3102 | 2130 KC Hoofddorp
The Netherlands
Moritz Palm Solutions Development Engineer
JanKenkhuis Principal Engineer
Matthew Finn
REVISION HISTORY
Approved By Infrastructure
Infrastructure Access Report: BlueTEC Feasibility
Rev 1, 04-Aug-2015
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
provide evidence of progress made along the Structured Development Plan
provide due diligence material for potential future investment and financing
share lessons learned
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.
Infrastructure Access Report: BlueTEC Feasibility
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EXECUTIVE SUMMARY
Based on three decades of offshore marine engineering know-how and experience, Bluewater has developed a state of the art solution for tidal energy conversion. The BlueTEC Tidal Energy Convertor (TEC) is a floating system for the production of electricity from tidal currents. The next stage of development for this technology will be the design, build and test of a small array of these systems. MaRINET funding provided access to a test berth at EMEC so that the site could be carefully studied to validate that the location is suitable for the deployment of the Bluewater technology up to array level.
CONTENTS
1.2.2 Plan for this access ................................................................................................................... 3
1.3 SITE LOCATION .............................................................................................................................. 4
2.1 TEST PLAN..................................................................................................................................... 5
2.1.4 Supply chain assessment ........................................................................................................ 19
2.1.5 Anchor bag trials ..................................................................................................................... 20
2.2 RESULTS ..................................................................................................................................... 21
2.2.3 Project licencing ...................................................................................................................... 26
3.1 PROGRESS MADE ......................................................................................................................... 27
4 REFERENCES .................................................................................................................................... 28
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1 INTRODUCTION & BACKGROUND
1.1 INTRODUCTION Since its foundation in 1978, Bluewater has built a technological lead specialising in design, development, lease and operation of tanker-based production and storage systems and has become a leading global provider of innovative single point mooring systems. In total Bluewater produced more than 100 of these systems, which are installed, operated and maintained in coastal waters, often in harsh conditions.
Based on these three decades of offshore marine engineering know-how and experience, Bluewater has developed a state of the art solution for tidal energy conversion. The BlueTEC Tidal Energy Convertor (TEC) is a floating system for the production of electricity from tidal currents. It offers significant advantages compared to competing designs by accommodating most of the critical equipment above the waterline. Dry and protected components allow for easy access for inspection and repair, resulting in low operation and maintenance costs. The system is designed for cheap manufacturing, enabling transportation in standardized containers to any location in the world. The units will then be assembled and installed locally, without the necessity for sophisticated equipment. A general plan of the Bluewater system is shown in Figure 1 below.
Figure 1: Bluewater platform
The next stage of development for this technology will be the design, build and test of a small array of these systems at the EMEC tidal energy test site which will be a multi-million Euro project. The MaRINET funding provided access to a test berth at EMEC so that the site could be carefully studied to validate that the location is suitable for the deployment of the Bluewater technology.
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Planned for this project:
STAGE GATE CRITERIA Status
Stage 1 – Concept Validation
Hull(s) sea worthiness in real seas (scaled duration at 3 hours)
Restricted degrees of freedom (DofF) if required by the early mathematical models


Initially 2-D (flume) test programme
Evidence of the device seaworthiness
Initial indication of the full system load regimes
Stage 2 – Design Validation
Mooring arrangements and effects on motion
Engineering Design (Prototype), feasibility and costing
Site Review for Stage 3 and Stage 4 deployments
Stage 3 – Sub-Systems Validation

Stage 4 – Solo Device Validation
Accepted EIA
1.2.2 Plan for this access
The objectives for this MaRINET funded site access were as follows:
1. Collect and analyse data for Berth 6 at the EMEC tidal energy test site for use in design of the BlueTEC system for a future array deployment.
2. Collect and analyse data for Berth 9 at the EMEC tidal energy test site to undertake proprietary non- grid connected testing of the Bluewater umbilical and mooring systems.
3. Work with EMEC to establish the necessary licencing requirements to undertake longer term non-grid connected trials of the system.
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1.3 SITE LOCATION The EMEC grid-connected tidal energy test site is located at the Fall of Warness, just west of the island of Eday in the Orkney Islands. The site sits in a narrow channel between the Westray Firth and Stronsay Firth where tidal flow accelerates as water flows through the inter-island constriction on its way from the North Atlantic Ocean to the North Sea. The site was chosen by Bluewater for its high velocity marine currents which can reach almost 4m/sec (7.8 knots) at spring tides. The site occupies an area of approximately 4km x 2km and consists of 7+21 individually cabled test berths. Each berth occupies a circular area of approx. 200m radius from the cable end, within which developers can install their device(s) and undertake testing activities.
Energy generated by devices at each test berth is transmitted via heavily armoured sub-sea cables back to an onshore electricity sub-station for onward transmission to the National Grid. Each test berth can accommodate single devices or small arrays, as well as components or mooring structures.
For this site access, two berth options were considered:
1. Berth 6 – future operational berth 2. Berth 9 – new berth to be utilised for non-grid-connected testing
A sketch of the EMEC tidal energy test site showing the present cabling arrangements together with the position of Berth 9 is provided in Figure 2 below.
Figure 2: Site location sketch showing the position of Berth 9 (blue circle)
1 Seven of the berths are serviced by EMEC-installed/owned cables. The cable servicing the eighth berth is currently owned by a developer. Berth 9 is a new testing berth which has been established to support the Bluewater ancillary tests.
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2 OUTLINE OF WORK CARRIED OUT
2.1 TEST PLAN MaRINET access allowed Bluewater to undertake surveys on the berths at the site and interrogate the data sets which informed design elements of the system. The test plan was split into the following activities:
1. Data gathering: a) Resource assessment (measured and modelled) b) Bathymetry to review foundation options c) Shipping activity to inform berth location selection for a floating TEC
2. Site survey commissioning Remotely Operated Vehicle (ROV) seabed studies to review suitable locations for the novel Bluewater foundations to be deployed
3. Access to EMEC infrastructure to review systems (primarily electrical) 4. Complete marine licencing requirements to allow future development options 5. Supply chain assessment to cost up array scale development 6. Preparation of anchor bags for future sea trials 7. Compilation of results to inform device design
2.1.1 Data Gathering
2.1.1.1 Resource assessment (Measured)
Prior to commissioning an additional resource assessment campaign, the team decided to review the existing data sets available from the EMEC site which were closest to the proposed deployment location for the Bluewater device. From the 25 surveys undertaken to date an RDI Workhorse Sentinel 600kHz Seabed Mounted Acoustic Doppler Current Profiler (ADCP) was deployed for 31 days between 23/12/2009 and 23/01/2010 in around 35m depth chart datum and within 100 meters of Berth 6. The instrument head was situated 1m above the seabed with the first bin centre occurring 2.1m above the transducer head. Subsequent bins were spaced at 1m intervals.
When analysing this data all heights were calculated from the instrument head and water depth assumed to be the total depth from the sea bed to the sea surface. Currents were saved as single ping ensembles every second. On analysis of the data, considerable noise and a number of data spikes were observed in the current data, therefore maximum raw values were treated with caution. A low-pass digital filter (a specific form of weighted averaging) was constructed using the MATLAB filter design toolbox with a 10 minute filter period. Passing the data through this filter yielded a smoothed flow signal.
Figure 3 below shows a plot of a small section of the velocity data for bin 15 plotted against water depth, which gives a good indication of the stage of the tide. A clear pattern of flood and ebb tides can be seen, with a rapid velocity change on the flood tide and a smoother change through the ebb. Good consistency is shown in the filtered data. The relative magnitudes of the mean tidal flow and the turbulent/wave perturbations is clearly apparent.
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Figure 3: Detail of a sample of elevation against velocity for bin 15
Figure 4 to F6 shows the raw flow velocity for 3 bin depths for the duration of the deployment.
Figure 4: Bin 5 flow velocity
Figure 5: Bin 15 flow velocity
Figure 6: Bin 25 flow velocity
Figure 7 below shows the raw and filtered tidal ellipse for bin 15, showing a north to south south-east ebb and flood pattern.
30/12 31/12 31/12 01/01 01/01 -6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
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Figure 7: Raw and filtered tidal ellipse for bin 15
The velocity signals have been analysed with the T_TIDE MATLAB toolbox [Pawlowicz et al, 2002] to determine tidal constituents in a similar manner to those shown in table 2.
Figure 8 below shows the phase of the tidal signals. There is a shift in the timing of peak flow between the upper and lower layers, within the order of 1.7 minutes between bin 1 and bin 22.
Figure 8: Tidal phase through the water column for M2 component
Table 1 below shows the maximum recorded velocity values for 3 depth bins at different points in the water column showing a maximum filtered flow in bin 20 at around 23m depth of 3.962m/s, with lower velocities in the lower and upper bins, down to 3.399m/s maximum velocity in bin 5 around 8m from the seabed. This depth profile relationship is similar to the constituent profile seen in table 2 below. Again, the difference between the filtered and raw velocities gives an indication of the magnitude of flow perturbations experienced at the berth.
63 64 65 66
M2 Phase
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Raw Velocity (m/s) 8.140 8.393 8.013 6.891
Filtered Velocity (m/s) 3.399 3.654 3.777 3.962
Table 1: Absolute maximum raw and filtered velocity values for flow at selected bins
2.1.1.2 Resource assessment (Modelled)
DHI developed a high-resolution depth-integrated hydrodynamic model covering the entire Orkney Islands using the unstructured mesh version of their MIKE 21 hydrodynamic modelling software. Through EMEC (model owner) Bluewater investigated spatial variability of the tidal flow field relating to the Berth 6 location.
Like the other modules included in the flexible mesh series of MIKE by DHI, the model is based on an unstructured cell-centred finite volume method and uses an unstructured mesh in geographical space. The established tidal flow model was executed for the 10-year period 1996 – 2005 (both included).
Figure 9 below shows a time series of the flow speed and surface elevation for 2005 for a point around 100m north of Berth 6. This figure shows the highest modelled flow speed of 2005 was just over 3.25m/s.
Figure 9: Time series of surface elevation and current speed for 2005
Table 2 shows the tidal constituents found by analysis of the time series. The M2 tide dominates the tidal conditions, with the S2 tide being the second principal component.
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Z0 0.1102 0 0.137 0 31.5 180
Q1 0.0319 312.34 0.017 0 114.9 318.3
O1 0.0996 14.26 0.07 0.001 122.5 103.9
P1 0.032 147.54 0.036 -0.003 119.3 280.8
K1 0.1163 161.21 0.125 -0.003 121.1 276.2
N2 0.1699 257.37 0.453 -0.046 120.1 30.4
M2 0.836 279.96 2.254 -0.293 121.4 62.5
S2 0.3013 315.78 0.763 -0.078 120.4 93.6
K2 0.0865 312.41 0.207 -0.023 120.2 90.5
Table 2: Major tidal constituents and tidal ellipse parameters resulting from the tidal harmonic decomposition of the surface elevation and flow at Berth 6 during 2005
The close alignment of the inclinations of the stronger tidal constituents indicates the uniformity of flow direction in the channel. Further details of the model may be may be found in [DHI 2011].
In addition, the model was used to investigate wave heights at the test berth location. This would support design aspects such as fatigue analysis, extreme wave analysis, along with operation and maintenance issues.
The wave model used was MIKE 21 SW Spectral Waves FM and, like the other modules included in the flexible mesh series of MIKE by DHI, this wave model is based on an unstructured cell-centred finite volume method and uses an unstructured mesh in geographical space. The spectral wave model includes two different formulations: a fully spectral formulation and a directionally decoupled parameterised formulation of the wave action balance equation. The fully spectral formulation can in principle be used in wave studies involving wave growth, decay and transformation of wind-generated waves and swell in offshore and coastal areas. However, the computationally less demanding directionally decoupled parametric formulation is sufficient in a number of situations.
For this project, the full spectral model in stationary mode was used for the establishment of the required wave data. In the fully spectral formulation, the source functions are based on the WAM Cycle 4 formulations with significant improvement of the shallow water physics and particularly the numerics. The spectral wave model is parallelised using OpenMP and MPI techniques. The calculation points and model grid at the Fall of Warness site are shown in Figure 10 below; point B is around 2.6km south south-east of the Berth 6 cable end.
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Figure 10: Calculation points and model grid
First, a 20 year model run of the wave propagation into the Fall of Warness site was undertaken, this model run did not utilise any wave-current interaction, which is believed to be significant at the Fall of Warness site. An occurrence plot of the results of the 20 year run at point B is shown in Figure 11 below, with blue dots showing individual occurrences and the red line showing the fitted relationship between significant wave height and period for the 500 highest waves.
Figure 11: Occurrence plot of significant wave height against wave period for 1986-2005
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A 10 year model run of the wave-current interaction at the Fall of Warness site was undertaken for the period of 1996-2005. The shorter time period used was due to the large computational effort required to run the model. Figure 12: shows a wave field plot of an example of a tide flowing towards the south east interacting with a wave field coming from the south east.
Figure 12: Wave current interaction example
Figure 13: below shows an occurrence plot of significant wave height against peak period for each wave in the 10 year run. The red line plots the fitted relationship of the highest 1% of the waves that occurred. Here it can be seen that waves of around 5m significant wave height were modelled at the Fall of Warness site at point FOW 7, around 1.4km south south-east from Berth 6.
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Figure 13: Occurrence plot of significant wave height against peak period
Figure 14: shows the percentage of occurrences per significant wave height and direction for the Fall of Warness site across the 10 year simulation period. It is clear from this plot that the majority of waves occur in the north westerly and south easterly sectors, with a high percentage of occurrences under 1.5m.
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Figure 14: Wave rose plot for percentage occurrence with Hm0 and direction
An extreme wave analysis was carried out for the Fall of Warness site for both extreme significant wave height annually and for extreme significant wave height during the summer months from 15 May to 15 August. Extreme events from the simulated data were selected and fitted to a Weibull distribution before extrapolating to find the maximum significant wave heights for return periods from 1 to 50 years. The nearest calculation point is FoW 7, around 1.4km south south-east of Berth 6. The modelled time series of wave heights is shown in Figure 15:
Figure 15: Time series of significant wave height with major events highlighted
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For consideration at Berth 9, the tidal flow was re-assessed using further data from the numerical model data set [DHI 2009]. The general pattern of the data was similar to that found at Berth 6. The data was subjected to further analysis as shown in figure 16: (below).
Figure 16: Scatter plot of the current velocity as function of the current direction (each dot is one data point)
This analysis clearly shows the directions of peak flood and peak ebb in the data. This agrees with the findings shown in table 2 for Berth 6.
An additional analysis has been done to estimate the occurrence of the current direction in relation of the velocity. Figure 17 below shows the scatter plot of the current velocity and the probability of occurrence as a function of the current direction. The results confirm that the main current direction has also the highest occurrence and that the bandwidth in current direction is quite narrow. In other words the current is most of the time in line with the main direction.
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Figure 17: Probability of occurrence of the current direction in relation to the current velocity is plotted as a function of the direction. The blue dots show the scatter plot of the current velocity and the red line is the probability of occurrence. On the x-axis the current heading is shown, on the left hand y-axis the current velocity in [m/s] and on the right hand axis the probability of occurrence of the current direction.
The conclusions from this data analysis are reported in the following section, however it was decided that the findings from the existing data sets at EMEC are sufficient to inform device design at this stage and no further deployments of ADCPs would be required.
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Bathymetry
A bathymetry survey was conducted by Osiris [Osiris 2005] for the Fall of Warness and reported the following:
Bathymetry
Seabed features
Isopachyte chart
Figure 18: below shows a shaded relief drawing with contours for the bathymetry at Berth 6 (marked with a red cross). The drawing suggests that Berth 6 lies in a relatively flat area in around 34m of water.
Figure 18: Shaded relief bathymetry for Berth 6
Figure 19: shows a greyscale relief bathymetry with seabed features at Berth 6. The image suggests that Berth 6 is situated in an area of exposed, relatively flat bedrock. At the time of the survey there was a bank of course sand and gravel to the east of the cable end.
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Figure 19: Seabed features at Berth 6
The same bathymetry survey [Osiris 2005] was available for Berth 9. Berth 9 is located in similar depth water further to the east. The general location is indicated in figure 20: Although the survey indicated “coarse sand and gravel with cobbles and occasional boulders” at the location, recent ROV footage indicates mostly bedrock with occasional cobbles, with slight sedimentation against prominent features.
Figure 20: Shaded relief bathymetry for Berth 9
Following this a detailed ROV survey was commissioned for the test locations. This was undertaken by Triscom Marine on the 14 of February 2015. The associated report for this is contained in a separate file which is available on request.
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2.1.2 Shipping For the purpose of this development a device-specific navigational risk assessment (NRA) was completed to evaluate the ship collision risk associated with the development. The assessment was conducted internally within Bluewater using the ship traffic analysis provided by EMEC in the form of a site navigation risk assessment (Anatec, 2010) and the ship collision frequency methodology stated in the DNV Recommended Practice F107 (Det Norske Veritas, 2010). From the ship traffic analysis, average sizes and speeds of the vessels, the collision frequencies and the impact energy of each type of vessel passing and attending the test location have been calculated (see Table 3 below).
Type of vessel Number of vessel [per year]
Collision Frequency [per year]
Impact Energy [MJ]
NW-SE Passing vessels
Fishing vessels 95 1.12 x 10-4 8,929 9.11
Recreation Vessels 13 1.45 x 10-5 69,160 3.91
Hook-up/decom. 6 2.27 x 10-7 negligible negligible
Attendant Vessels 2 7.56 x 10-8 negligible negligible
Total 5.57 x 10-4 1796
Table 3: Summary of collision risk assessment results for BlueTEC device
From this risk assessment it is concluded that the total annual collision frequency between the BlueTEC device and the marine traffic is 5.57 x 10-4 collisions per year, corresponding to an average collision return period of 1796 years. The potential impact of a ship collision is dependent on the size and the speed of the ship colliding with the device. The highest impact energy, 76.28 MJ, is found to be the result of NW-SE passing vessels due to the large sizes and high speed of the vessels.
The collision risk with the highest probability (once in 3200 years) is the collision with inter-island ferries. The impact energy of such an event is calculated to be approximately 5.2MJ. Furthermore, for impacts with relatively low impact energy (0 – 15MJ), installation of collision avoidance provision will reduce the probability of such events. To reduce the collision risk various measure are taken. These include a navigation buoy, marking on the device itself, surveillance cameras etc. Based on the collision frequency found for each event and the related impact energy, the risk to the device and marine traffic is considered to be low and acceptable.
2.1.3 Marine licencing and environmental review Although EMEC has been granted the licences/consents necessary for establishing the test site infrastructure, individual developers wishing to test devices or other components/systems at the site are required to apply for and obtain all licences/consents necessary to carry out their project-specific testing activities. For this site access, Bluewater were required to obtain a Marine Licence under Section 25 of the Marine (Scotland) Act 2010 to carry out Marine Scientific Survey works. This required Bluewater to provide appropriate supporting information to assess the potential impact of deploying, operating and decommissioning a long term project on key natural heritage features and navigational safety.
Previous surveys undertaken at the Fall of Warness have identified no benthic species or habitats of conservation importance. However a number of seabird species and marine mammals do use the site, and basking sharks are occasionally sighted. Some of these species may be displaced or attracted to the device, or disturbed during construction. Furthermore, there is a risk of collision with rotating turbine blades, although
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there is as yet no evidence of this occurring with any tidal device. Monitoring will be carried out to assess the potential impacts of the development.
During deployment of a single turbine of similar design for testing in the Strait of Messina, Italy, environmental impacts (noise, collision risk) were assessed and found to be negligible, with no discernible impact on marine life. The environmental impacts of testing the BlueTEC device at the Fall of Warness (see Table 4 below) are assessed to be minor or negligible, with monitoring aiming to provide more information where there is currently uncertainty.
Table 4: Summary table of impacts and receptors for the Bluewater project
2.1.4 Supply chain assessment A supply chain visit was undertaken to pull together supporting data which would address the following issues for a longer term system deployment:
1. Where to fill the individual bags of 16 MT
2. How to transport to the quayside
3. Where to assemble the 7* 16MT bags in the lifting net
4.How to lift the assembled anchor of 112 MT
A tm
o sp
h er
Presence of personnel X X
Vessel presence/operations X X X X X X X X X X X X X X
Construction noise X X X X X X X
Placement of device moorings X X X X
Device Operation
Mooring presence X X X X X X X
Platform presence X X X X X X X X X X X
Turbine rotation X X X X X
Turbine noise X X X X
Energy extraction X X X X
Electricity production/Export X
Maintenance activities X X X X X X X X X X X X X X
Decommissioning
Vessel presence/operations X X X X X X X X X X X X X X
Removal of platform X
Disposal of device components X
Incident risks
Fluid leak/spillage X X X X X X X X X X X X
Component failure/loss X X X X X X
Mooring failure (partial) X X X
Mooring failure (total) X X X
Platform failure X X X X X X X X X X X
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5. What is the maximum lifting capacity of the 220 MT crane related to its reach?
6. Will the multicat be able to lift the bag from seabed in 8 meters of water?
7. If a bag anchor gets lifted in the water with a land crane, can the multicat crane reach and lift it out on the stern roller?
8. Is the multicat capable of carrying the 56 MT submerged weight to final location?
9. Is the Multicat capable of positioning the bag anchor within tolerances as discussed?
10. Interfaces on the rigging
11. Interfaces on the Bluewater provided midwater buoy and mooring line
12. Survey equipment requirement – common practice in renewable energy projects.
13. Sailing duration from Kirkwall to Eday site
14. Duration of the position of the bag anchor on the seabed
15. Daily rate of the Voe Viking
16. Daily rate of a rental ROV suitable to observe the subsea work
2.1.5 Anchor bag trials Seventy-two large bags were filled with local crushed stone aggregate at Cursiter Quarry, Grimbister, Orkney, in readiness for assembly into purpose-built containment nets to form the large bag anchors required for mooring the Bluewater test buoy at the EMEC test site. An initial trial filling of 2 anchor bags was carried out on 22 September 2014 to test the filling arrangement and bag behaviour. Based on this success, the production bags were manufactured and delivered to the quarry for filling.
Filling of the 70 production anchor bags took place on 3-4 November 2014 and was carried out by Heddle Construction Ltd. Each bag was filled with 8 tonnes of crushed stone aggregate. The filled bags were stock- piled in a group at the quarry awaiting the next phase of the project (see Figure 21 below).
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Figure 21: Filling of the anchor bags at Cursiter Quarry, Orkney
The anchor bag project activity was conducted within the MaRINET access period, however the funding for this activity was delivered under a separate project funded by the Marine Renewables Commercialisation Fund (MRCF).
2.2 RESULTS
2.2.1 Site Selection After an initial review of measurement surveys the current direction on the exact location for testing on Berth 9 was still uncertain. Therefore EMEC provided further flow predictions from DHI hydraulic model. This data contains time series of the current velocity and angles for 2015 in 15 minute intervals. The time series are extracted for the cells around the centre point of the berth, see Figure 22 below.
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Figure 22: Grid of the DHI hydraulic model. The black dot indicated the centre points of the berth with numbers of the surrounding cells. The cell size is approximately 70 meters
The angle of the peak current of each cell was determined for ebb and flood to find the main current direction. Table 5 below lists the results; the current is mainly bi-directional, however the change in current direction on average is 175 degrees. The directional change (difference between ebb and flood angle) shows some spreading for the different cells. This is probably caused by inaccuracy of the flow model which was explained by EMEC.
Table 5: Direction of peak ebb and flood current
The water depth at the test berth varies from 32 to 36 metres. This is found to be acceptable by the Bluewater installation team.
Following the review of the data sets gathered for Berth nine, three potential deployment locations were identified (green boxes in Figure 23 below). After a detailed review with the EMEC operations team it was decided that the central box would be chosen as the long term deployment location.
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Figure 23: Proposed location for Berth 9
Based on this analysis the platform orientation was selected to be 150° - 330°. This gave a maximum variation of the peak current direction of 4 degrees with respect to the platform orientation based on the current data set. The footprint with the new orientation was plotted into the bathymetry chart in Figure 24 below. It shows that the anchor points fit between the two power cables.
Figure 24: Mooring footprint plotted at the proposed location (mooring footprint in green, existing power cables in red)
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The mooring system design was progressed based on the data gathered in the access period. Details of the mooring system are referred to in [EFT-L-800-RP-6001-901-A] (mooring analysis) and [EFT-L-800-PH-6007- 901-A] (installation guideline). These documents are available on request.
2.2.2.2 O&M Strategy
An O&M strategy was developed based on a review of the operational conditions at the site and discussions with local supply chain companies. This was used to devise the following table which outlines the vessel requirements for the longer term project.
Activity description Indicative vessel type Indicative number of days
Anchors (2 – 4) and mooring lines DP vessel + 2 Tugs/MultiCat 4 - 8 days
Power cable
1 – 2 days
Device hook-up 3 standard tug-boats 2 - 4 days
Inspection, Operation & maintenance - minor Small Zodiac type or RIB boat 1 day per intervention
Operations & maintenance - major 3 standard tug-boats 1 day per intervention
Decommissioning – device 3 standard tug-boats 2 days
Decommissioning – power cable
1– 2 days
Decommissioning – mooring lines
2 – 4 days
Table 6 Vessel requirements for Berth 6 (non-grid connected) testing
EMEC Berth 6 faces relatively harsh weather conditions and high tidal currents. Consequently, the overall
plan may require adjustment. Furthermore, certain periods are considered sensitive for marine mammals and
seabirds. It is intended to avoid carrying out the more disruptive operations within these periods as far as
possible. Finally, to reduce the overall costs of installation and maintenance and minimise the disturbances
caused by the vessels, the partners wish to co-operate where possible with other developers for the sharing
of offshore vessels. This may result in adjustment of the plan where necessary.
2.2.2.3 Device Marking and Coatings
The device marking options were informed by the Navigational Risk Assessment study and the BlueTEC unit will be outfitted with an automatic identification system (AIS) and accompanied by an NLB approved dedicated navigational buoy. The coatings described in Table 7 below will be applied to the BlueTEC system.
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Part description Type of paint (indicative)
All external surfaces in the submerged and splash zone: platform, equipment and piping
Two layers of solvent free epoxy coating (500 μm), followed by fluoro-polymer
based non toxic anti-fouling (foul release) paint
All external surfaces above the submerged and splash zone: platform, equipment and piping
Two layers of solvent free epoxy coating (500 μm), followed by isocyanate free
finish coating
Handrails, ladders and small construction parts Two layers of HB epoxy anticorrosive coating followed by isocyanate free finish
coating
Two layers of solvent free anticorrosive epoxy coating
Turbine blades and shaft Silicone elastomer non toxic foul release coating
Table 7 Device coating options
2.2.2.4 Cable Connections
The resource data gathered at various depths informed the choices for the bendlimiter and cable termination. Details of the design and cable properties is specified internally at Bluewater and available on request.
2.2.2.5 Test Support Buoy Design
Based on the data collection and analysis studies at the EMEC site Bluewater designed a Test Support Buoy that could be used to accompany the non-grid connected testing activity. It should be noted that Bluewater has yet to fix this design and they are open to any for changes or alternative constructions to the design presented to optimize the fabrication process or reduces fabrication costs.
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Figure 25 BlueTEC device location with temporary buoys only, top view
The body of the buoy will be fabricated from standard size tubular steel. The two tubular floating bodies (1.75 x 8 m) will be connected by two transfers tubular cross beams forming the base of the buoy. Four mooring tubes will be fitted into the floating bodies. The mooring tubes run through the floating body. A general purpose support frame is fitted to mount solar panels and navigational aids on. A simple boat landing will be fitted suitable for small workboats and RIBS. For assembly polymer liners will be bolted into the mooring trumpet at the final assembly of the buoy. All grating should be GRP material and positioning of the grating on drawings is indicative. A safety net should be fitted over the opening between the two floating bodies. Several sensors and instruments will be fitted on the buoy all connected to a central data acquisition system. The sensor position and cabling has not been designed yet.
2.2.3 Project Licencing EMEC provided advice and assistance to Bluewater in preparing the Marine Licence application and supporting documentation, which was submitted to the Regulator (Marine Scotland) in July 2014. The Marine Licence for this project was awarded in September 2014 (copy available on request). No other licences/consents were required at this stage.
2.2.4 Anchor Bag Trials Within the parallel MRCF funded project a number of tests were carried out on the anchor bags at a quayside location to inform future offshore deployment. Whilst this did not involve the EMEC test facilities, the quayside trials led to the following results:
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1. Anchor Bag a) No discernible impact on lifting points during test. b) Minor distortion of base noticed during recovery from immersion. c) No visible damage to bag material after test complete.
2. Ballast
a) Air bubbles seen rising from top of bag for approx. five minutes as it was fully immersed. b) Very minor discolouration of water observed for less than 30 minutes during immersion. c) Discolouration of water not visible immediately, began within first 20 minutes. d) Significant discolouration of water observed during recovery of bag. e) Settlement during immersion produced lower angle of repose in ballast at top of bag. f) Drainage onto pier/into truck suggested minimal loss of ballast material occurring.
Based on the outcomes from these trials, Bluewater have decided to include this cost efficient anchor bag solution within the future design of their system.
3 MAIN LEARNING OUTCOMES
3.1 PROGRESS MADE The access period provided by MaRINET allowed Bluewater to progress a number of critical design options for the BlueTEC system and establish a route for longer term larger scale array level demonstration.
The company now has a detailed understanding of the resource characteristics at the EMEC full scale tidal test site and has built up key relationships with the local supply chain. Based on this, Bluewater has been able to undertake financial modelling of their system to review the Levalised Cost of Energy (LCOE) for their system (see Figure 30). Whilst these results need to be validated by full scale demonstration, they provide a valuable insight into how the BlueTEC technology can become cost competitive with other forms of renewable energy generation.
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Figure 26: Cost reduction potential for the tidal Sector according to SI Ocean Project (2014) adding the positioning of BlueTEC technology (red points)
3.2 KEY LESSONS LEARNED
Bluewater utilised MaRINET access to learn the following key lessons:
1. Before commissioning costly field surveys, make full use of the existing data sets gathered for a demonstration location and investigate modelling options to add power to this data
2. Allow adequate time for licencing of marine energy projects in the UK. Whilst this was streamlined at the EMEC location, this could take more than 24 months for a new site.
3. Anchor bags look like they may present a cost effective solution for mooring marine energy devices
4 REFERENCES [DHI 2009] Tidal Flow and Wave Modelling, Orkney REP356-01-01 20120306
[EMEC 2010] Processing and quality control of currents and tides for FoW-SMADCP-18
[OSIRIS 2005] European Marine Energy Centre Eday, Orkney Islands, Tidal test facility, Marine Geophysical survey, Hydro Contracting / Osiris Projects, Report C5022, October 2005. REP002.
[Pawlowicz et al, 2002] Harmonic Analysis Including Error Estimates in MATLAB using T_TIDE, Pawlowicz, R., B. Beardsley, and S. Lentz, Computers and Geosciences, 28, 929-937
[UKHO 2007] Admiralty chart 2592 Ed. 2
[EFT-L-800-RP-6001-901-A] Mooring and Umbilical analysis – Bluewater internal document
[EFT-L-800-PH-6007-901-A] Installation guideline – Bluewater internal document
[Subsea cable specification] Dynamics subsea cable spec – TKF document
~3m/s site