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292 Fundamentals of Ocean Renewable Energy

TABLE 10.2 Implementation of WEC Module in SNL-SWAN: Description
of Obstacle Cases
Obcase Description
0 Baseline SWAN formulations using constant K t , specified by user
1 WEC power matrix used to calculate K t , applied as a constant value across
all frequencies
2 WEC RCW used to calculate K t , applied as a constant value across all
frequencies
3 WEC power matrix used to calculate K t , applied as a unique value at each
binned frequency
4 WEC RCW used to calculate K t , applied as a unique value at each binned
frequency

is in the range 0.51–0.81, with a mean value across a range of experiments
of K t = 0.74. Abanades et al. [44] used these values to parameterize an
array of 11 WaveCat devices in the SWAN model, simulating changes in the
wave conditions between the array and the coastline. However, the problem
with applying a constant transmission coefficient is that the reduction in wave
energy is applied across all wave frequencies. In reality, a WEC will extract
wave energy as a function of wave frequency. To address this, Smith et al.
[45] developed a frequency-dependent transmission coefficient in SWAN, which
6
has now been formalized in a version of SWAN known as SNL -SWAN
[46]. This version of SWAN incorporates a WEC module with five different
options (referred to as OBCASE) that modify the baseline SWAN OBSTACLE
formulation (Table 10.2). Power matrices for Wave Energy Converters are a
familiar concept from Chapter 5 (Fig. 5.17), and relative capture width (RCW)
is a dimensionless performance parameter that is used extensively in the WEC
industry—it can be thought of as the proportion of incident wave energy (for
a crest length equal to the nominal WEC dimension) captured by the device
[47]. An illustrative comparison between Obcase 2 (RCW applied as a constant
across all frequencies) and Obcase 4 (RCW applied as a unique value at each
binned frequency) is provided in Fig. 10.11.

10.3 OCEAN ENERGY PROJECT DEVELOPMENT
Whilst some renewable energy sources such as wind and solar are cost-
competitive and operate at commercial scales, the ocean renewable energy
sector is generally at the research and development (R&D) stage. Nevertheless,

6. Sandia National Laboratories.