We have worked at tidal stream sites around the UK, including
the
Pentland Firth, Fall of Warness, the English Channel, Irish Sea
and Kintyre/North Channel. Resource modelling usually involves running
a regional 2d model of the site with a horizontal resolution of 50m or
better, driven by a calibrated shelf model.
Experience in modelling surge tides has highlighted the importance of
proper specification of boundary conditions for such models:
over-simplification of tidal boundaries can significantly affect
resource estimates. We use a balance of directly modelled and inferred tidal
constituents in our shelf model and adjust the boundary conditions of
the regional model using local data. This leads to
significantly improved model performance in calibration/validation.
Proper consideration of nodal variations, and identification and
quantification of non tidal signals at tidal sites is also of prime
importance.
Resource is expressed in terms of the standard metrics, e.g.
kinetic energy flux in kW/m^2. Means of speed, speed^2 and speed^3 are
useful.
Considering tidal sites as a whole, head loss and flow spwwd are important, as shown by Garrett and Cummins.
This figure shows the Taylor flux (work done) in the Pentland Firth on
a flood tide (bottom right) calculated from a 2d model. High Taylor
flux to the W and low Taylor flux to the E is reflected in an
increase in the kinetic energy of the water column (top right shows the
flux of kinetic energy). Frictional dissipation is shown at the bottom
left.
3d modelling
For more detailed work, 3d modelling may be undertaken. Vertical
shear impacts on resource and the stress experienced by devices, and
wakes are limited in the vertical.Care is needed in choosing vertical turbulent parameters for 3d models.
Tidal
devices (either single or arrays) may be incuded in the model using a
range of techniques:
-Modification of the friction coefficient in a 2d
model,
-Actuator disk approach (2d/3d models)
-Blade momentum approach (high resolution 3d models)
Velocity deficit, blade momentum description of 2 blade tidal device
Tidal barrage
We have the capacity to model the energy and impact of tidal barrage schemes of any geometry,
Wave models
We can run regional and local wave models for sites of interest, coupled or uncoupled with appropriate tidal models.
Inclusion of wave devices in the model has been done using a simple absorbtion radiation model.
For tidal sites, waves can have a significant effect on the flow
regime, however conventional wave models may struggle to cope with the
fast flow speeds at such sites. To cope with this problem, the
dissipation parameterisation in the Tomawac model has been modified in
accordance with recent research; this allows wave modelling of tidal sites.
Wave model of Kintyre area, NW gale, showing strong
wave current interaction to the SW of the Mull of Kintyre. Wave direction shown by arrows.
Possible work:
-2D & 3D tidal models (telemac, POM, ADCIRC)
-Device models: Actuator disk, blade.
-Wave models (Tomawac, Swan) coupled/uncoupled with tidal models
-Sediment model (Sisyphe)
-Data analysis
-adcp, turbulence, tide gauge, tidal prediction, non tidal estimation.
