Scoping the Ocean’s Energy Resources
Garret Duffy, Colin Brown, Michael Hartnett, Klaus Leurer, Ivor Marsh, Christian Mohn, Stephen Nash, Nathan Quinlan and Martin White
Renewable Energy Group, NUI Galway
SEABED GEOTECHNICAL ASSESSMENT
G
iven that ocean energy
devices are located in highly
dynamic areas, they are likely
to be subjected to hazards arising from the
interaction of waves and currents with the
seabed. Hazards, such as scour and
migrating bedforms, can significantly affect
the performance and lifetime of an ocean
energy device and need to be adequately
understood before installation commences.
EG can identify areas of a proposed
deployment site that are potentially
hazardous for cabling and device
installation. An example of field
measurements of sediment transport, where
dynamic bedforms were re-surveyed every
month for 6 months, is shown on the right.
Such features place loading on seabed
installations and may expose cables.
R
A
new technique,
patented in Leurer
and Brown (2008) uses
seismograms to predict and measure
important geotechnical quantities such
as porosity, permeability, density, shear
strength and sediment composition.
These quantities must be known in
order to determine the type of seabed
installation and how it will be erected
on the seafloor.
SEDIMENT TRANSPORT HAZARDS
COMPUTATIONAL FLUID DYNAMICS
fficient
extraction of
energy from
waves requires accurate
knowledge of the shape of the
waves. This is done using both
tank experiments and
mathematical models. A
mathematical model of a
breaking wave that has a
good fit with a tank
experiment is shown on the
right.
E
Dune Speed, [m/tide]
Dune Height, [m]
time
T
he Renewable Energy Group (REG) is a team of research scientists and
engineers focussed on developing techniques and strategies vital to successful
implementation of ocean energy extraction in Ireland. The Group is envisioned as
being the first point of contact for ocean energy developers looking to install power
generation devices in Ireland’s offshore. REG will utilise existing skills to locate optimum sites
for wave- and tidal current-driven devices and suggest optimum routes for seafloor cabling.
The group has, and will develop further, links with the Coastal and Marine Resources Centre
and Hydraulics and Maritime Research Centre at University College Cork, Mobile and
Marine Robotics Research Centre (University of Limerick), Marine Institute, Geological Survey
of Ireland and private companies involved in ocean energy.
Detail of 1-metre DEM of sand bank in Bay
of Fundy, Canada surveyed every month
for 6 months in 2002.
Figure below shows sediment transport rate
estimated from the repeat observations.
Sediment Transport Rate,
[kg/m/tide]
Geology classified from seabed acoustic remote sensing
data using a neural network.
Porosity
0.9
0
0.8
0.7
0.6
0.5
0.4
Predicted
1
¼ scale prototype
Wavebob™ device
deployed in
Galway Bay
Time
Depth
2
Automated
inversion
modelling
3
4
5
Observed
Renewable Energy Group
6
7
8
Geology
A
WAVE MODELLING
46°0'N
BATHYMETRIC AND SITE SURVEY
D
etailed
and accurate
knowledge on
Ireland’s wave climate,
supposedly one of the world’s
most energetic, is required to
exploit this resource to the
fullest. REG possesses
established expertise in
predictive wave
modelling.
CURRENT MODELLING AND MEASUREMENT
45°0'N
NOAA
launch
Auk, similar
to the
Keary
0 10 20
40
60
80
Km
44°0'N
66°0'W
65°0'W
64°0'W
R
he critical
importance of
mathematical modelling
to assessing the nature of Ireland’s
ocean energy resource has already
been recognised by Sustainable Energy
Ireland (SEI, 2004); the latter report
modelled Ireland’s tidal current
resource, albeit with coarse and
outdated bathymetry. Further, more
localised models must now be designed
and REG has already proven skills in
this area.
easurement of tidal currents,
preferably over a spring-neap
cycle, is a necessary step to
confirm model predictions of currents
or waves. REG possesses the necessary
equipment, e.g. ADCPs (pictured, at
right), to provide these data.
M
Example application of high-resolution multibeam bathymetry to the problem
of siting ocean energy devices in Minas Channel, Bay of Fundy, Canada.
SPRING CONDITION
T
Celtic Voyager and Celtic
Explorer
NEAP CONDITION
ccurate
bathymetry is vital for
locating offshore power
generation devices for: (1) Accurate
delimitation of potential deployment
regions, defined by the minimum
allowable depth of the device and the
maximum allowable depth of the
marine crane and (2) accurate
computer modelling of currents and
waves. The latter is important for the
accurate assessment of the energy
resource.
EG has access to all the highresolution bathymetry currently
being collected by INFOMAR’s
vessels, Celtic Explorer and Celtic
Voyager and soon to be collected by
the new inshore survey launch Keary.
Data will be processed in a Geographic
Information System to identify
potential deployment regions and
cable routes.
OpenHydro™ test structure installation, European Marine Energy Centre, Orkney
Isles
degrees C
degrees C
Sample model outputs for oceanic circulation on the Irish continental shelf for neap and spring
conditions. Such model outputs will be used to drive hydrodynamic and sediment transport models of
areas identified for potential tidal stream resource extraction.
Cartoon showing
the 4 beams of a
ship-mounted
ADCP simlar to
those owned by
REG
Wave
Height,
[m]
Model Predicted
6
Significant
Wave Height, [m]
Seismic Section
Observed porosity and porosity
predicted from new model
Observed
5
4
3
2
1
1
2
3
4
5
6
7
8
Time (Days)
9
10
11
12
13
14
15