On the use of computational models for wave climate assessment in support of the wave energy industry
Date
2011-11-02
Authors
Hiles, Clayton E.
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Abstract
Effective, economic extraction of ocean wave energy requires an intimate under-
standing of the ocean wave environment. Unfortunately, wave data is typically un-
available in the near-shore (<150m depth) areas where most wave energy conversion
devices will be deployed. This thesis identities, and where necessary develops, ap-
propriate methods and procedures for using near-shore wave modelling software to
provide critical wave climate data to the wave energy industry. The geographic focus
is on the West Coast of Vancouver Island, an area internationally renowned for its
wave energy development potential.
The near-shore computational wave modelling packages SWAN and REF/DIF
were employed to estimate wave conditions near-shore. These models calculate wave
conditions based on the off-shore wave boundary conditions, local bathymetry and
optionally, other physical input parameters. Wave boundary condition were sourced
from theWaveWatchIII off-shore computational wave model operated by the National
Oceanographic and Atmospheric Administration. SWAN has difficulty simulating
diffraction (which can be important close to shore), but is formulated such that it
is applicable over a wide range of spatial scales. REF/DIF contains a more exact
handling of diffraction but is limited by computational expense to areas less than a
few hundred square kilometres. For this reason SWAN and REF/DIF may be used
in a complementary fashion, where SWAN is used at an intermediary between the
global-scale off-shore models and the detailed, small scale computations of REF/DIF.
When operating SWAN at this medium scale a number of other environmental factors
become important.
Using SWAN to model most of Vancouver Island's West Coast (out to the edge of
the continental shelf), the sensitivity of wave estimates to various modelling param-
eters was explored. Computations were made on an unstructured grid which allowed
the grid resolution to vary throughout the domain. A study of grid resolution showed
that a resolution close to that of the source bathymetry was the most appropriate.
Further studies found that wave estimates were very sensitive to the local wind condi-
tions and wave boundary conditions, but not very sensitive to currents or water level
variations. Non-stationary computations were shown to be as accurate and more
computationally efficient than stationary computations. Based on these findings it is
recommended this SWAN model use an unstructured grid, operate in non-stationary
mode and include wind forcing. The results from this model may be used directly to
select promising wave energy development sites, or as boundary conditions to a more
detailed model.
A case study of the wave climate of Hesquiaht Sound, British Columbia, Canada
(a small sub-region of the medium scale SWAN model) was performed using a high
resolution REF/DIF model. REF/DIF was used for this study because presence
of a Hesquiaht Peninsula which has several headlands around which diffraction was
thought to be important. This study estimates the most probable conditions at a
number of near-shore sites on a monthly basis. It was found that throughout the
year the off-shore wave power ranges from 7 to 46kW/m. The near-shore typically
has 69% of the off-shore power and ranges from 5 to 39kW/m. At the near-shore site
located closest to Hot Springs Cove there is on average 13.1kW/m of wave power, a
significant amount likely sufficient for wave power development.
The methods implemented in this thesis may be used by groups or individuals to
assess the wave climate in near-shore regions of the West Coast of Vancouver Island
or other regions of the world where wave energy extraction may be promising. It
is only with detailed knowledge of the wave climate that we can expect commercial
extraction of wave energy to commence.
Description
Keywords
ocean wave power, Vancouver Island (B.C.), SWAN model, Hesquiaht