3. 3
• Research Background
• Rathlin Sound
• Numerical Methodology
• Domain Spatial Discretization
• Calibration of Numerical Model
• Natural State at Rathlin Sound
• Rathlin Sound Resource Assessment
• Conclusions
Content
4. 4
Characterization of tidal resource of idealised coastal site in the vicinity of
an island near a landmass
Validity assessed of outcomes from idealised study by Pérez-Ortiz et al. [1]
when applied to an actual coastal site
The Rathlin Sound is a very good example of an island near a landmass
Rathlin Island
Northern Ireland
Research Background
6. 6
Numerical model based on Fluidity [2] solver of shallow water equations
Site bathymetry data from HydroSpatial One Gridded Bathymetry [3]
Sea surface elevation at open boundary conditions derived from the
Oregon State University European shelf solution [4]
Power extraction by tidal turbines modelled through additional absorption
term kf in the momentum equations applied at footprint of tidal farm
Power extraction methodology neglects turbine and farm scale mixing
losses, thus representing an upper limit to power extraction
Numerical Methodology
7. 7
Domain Spatial Discretization
Domain divided into four mesh
regions with mesh resolution
specified in each region
Model forced solely with M2
tidal signal at open boundaries
Solution convergence assessed
at transects at entrance and
exit of Rathlin Sound, and 10
km downstream from entrance
and exit of Rathlin Sound
8. 8
Calibration of Numerical Model
Two measured field datasets: 3 ADPs deployed
south-east of Rathlin Sound [5] and 3 UK tidal
gauge stations [6]: Portrush, Bangor and Portpatrick
Model forced by 8 constituents at open boundaries,
and 15 days’ data used for calibration process
Calibration performed by altering seabed friction
coefficient Cd between 0.001 and 0.005
Measured free surface and velocity data best
approximated with Cd = 0.0025 M2 Tidal Amplitude
9. 9
Natural State at Rathlin Sound
Mean and maximum speeds at the site are ~2 and 3 m/s respectively
when model is forced with M2 tidal signal
Speed Vorticity
10. 0 0.5 1 1.5 2 2.5 3 3.5
100
200
300
400
kf
7P(MW)
10
Kinetic Power Undisturbed Conditions
Power Extracted
Power Dissipated Naturally at Seabed
Kinetic Power with Farm
Rathlin Sound Resource Assessment (1/2)
Upper limit to power extraction east of Rathlin Sound: 298 MW
Power figures agree with outcomes of island-landmass idealised study
Analytical channel model [7] underpredicts by 51 % the numerical results
11. 11
Rathlin Sound Resource Assessment (2/2)
Mean Speed Vorticity
Substantial reduction in mean speed flows in Rathlin Sound and offshore
east and south-east at maximum power extraction
Mean difference in sea surface elevation of 10 % and 1 % in the near and
far-field respectively
12. 12
Conclusions
Calibrated model captures main flow features in vicinity of Rathlin Sound
Upper limit to power extraction at Rathlin Sound: ~298 MW
Comparison with results from idealised strait between island and landmass
Analytical channel model underpredicts by 51 % the numerical results
At maximum power extracted, substantial reduction occurs in mean speed
flows in the Rathlin Sound, offshore east and south-east of Rathlin Sound
14. 14
[1] A. Pérez-Ortiz, A. G. L. Borthwick, H. Smith, P. Vigars, and Q. Xiao, “Tidal Resource in Strait
between Island and Landmass,” in Proceedings of the 11th European Wave and Tidal Energy
Conference, 2015, pp. 1–10.
[2] C. J. Cotter, D. A. Ham, and C. C. Pain, “A mixed discontinuous/continuous finite element pair for
shallow-water ocean modelling,” Ocean Model., vol. 26, no. 1–2, pp. 86–90, Jan. 2009.
[3] “Edina Digimap Service. Hydrospatial one, gridded bathymetry. 2014.,” 2015. [Online]. Available:
http://edina.ac.uk/digimap/. [Accessed: 07-Jul-2015].
[4] G. D. Egbert and L. Erofeeva, “OSU Tidal Data Inversion.” [Online]. Available:
http://volkov.oce.orst.edu/tides/. [Accessed: 05-Feb-2013].
[5] Dp Marine Energy Ltd, “Fairhead Tidal ADCP Campaign.” Personal communication, 2014.
[6] British Oceanographic Data Centre, “UK Tidal Gauge Network,” 2015. [Online]. Available:
https://www.bodc.ac.uk/data/online_delivery/ntslf/. [Accessed: 10-Jul-2015].
[7] C. Garrett and P. Cummins, “The power potential of tidal currents in channels,” Proc. R. Soc. A
Math. Phys. Eng. Sci., vol. 461, no. 2060, pp. 2563–2572, Aug. 2005.
References
