Wake effect assessment in long- and short-crested seas of heaving-point absorber and oscillating wave surge WEC arrays

Gael Verao Fernandez, Vasiliki Stratigaki, Panagiotis Vasarmidis, Philip Balitsky, Peter A Troch

Research output: Contribution to journalArticle

Abstract

In the recent years, the potential impact of wave energy converter (WEC) arrays on the surrounding wave field has been studied using both phase-averaging and phase-resolving wave propagation models. Obtaining understanding of this impact is important because it may affect other users in the sea or on the coastline. However, in these models a parametrization of the WEC power absorption is often adopted. This may lead to an overestimation or underestimation of the overall WEC array power absorption, and thus to an unrealistic estimation of the potential WEC array impact. WEC array power absorption is a result of energy extraction from the incoming waves, and thus wave height decrease is generally observed downwave at large distances (the so-called "wake" or "far-field" effects). Moreover, the power absorption depends on the mutual interactions between the WECs of an array (the so-called "near field" effects). To deal with the limitations posed by wave propagation models, coupled models of recent years, which are nesting wave-structure interaction solvers into wave propagation models, have been used. Wave-structure interaction solvers can generally provide detailed hydrodynamic information around the WECs and a more realistic representation of wave power absorption. Coupled models have shown a lower WEC array impact in terms of wake effects compared to wave propagation models. However, all studies to date in which coupled models are employed have been performed using idealized long-crested waves. Ocean waves propagate with a certain directional spreading that affects the redistribution of wave energy in the lee of WEC arrays, and thus gaining insight wake effect for irregular short-crested sea states is crucial. In our research, a new methodology is introduced for the assessment of WEC array wake effects for realistic sea states. A coupled model is developed between the wave-structure interaction solver NEMOH and the wave propagation model MILDwave. A parametric study is performed showing a comparison between WEC array wake effects for regular, long-crested irregular, and short-crested irregular waves. For this investigation, a nine heaving-point absorber array is used for which the wave height reduction is found to be up to 8% lower at 1.0 km downwave theWEC array when changing fromlong-crested to short-crested irregularwaves. Also, an oscillatingwave surgeWEC array is simulated and the overestimation of the wake effects in this case is up to 5%. These differences in wake effects between different wave types indicates the need to consider short-crested irregular waves to avoid overestimating theWEC array potential impacts. TheMILDwave-NEMOH coupled model has proven to be a reliable numerical tool, with an efficient computational effort for simulating the wake effects of two differentWEC arrays under the action of a range of different sea states.

Original languageEnglish (US)
Article number1126
JournalWater (Switzerland)
Volume11
Issue number6
DOIs
StatePublished - Jun 1 2019

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energy conversion
wave energy
Oceans and Seas
energy
wave-structure interaction
wave propagation
sea state
Wave propagation
Hydrodynamics
interaction
wave height
sea
effect
Research
wave power
redistribution
hydrodynamics
ocean wave
wave field
potential energy

Keywords

  • MILDwave
  • Numerical coupling
  • Periodic lateral boundaries
  • WEC array impacts
  • WEC array interactions

ASJC Scopus subject areas

  • Biochemistry
  • Geography, Planning and Development
  • Aquatic Science
  • Water Science and Technology

Cite this

Wake effect assessment in long- and short-crested seas of heaving-point absorber and oscillating wave surge WEC arrays. / Fernandez, Gael Verao; Stratigaki, Vasiliki; Vasarmidis, Panagiotis; Balitsky, Philip; Troch, Peter A.

In: Water (Switzerland), Vol. 11, No. 6, 1126, 01.06.2019.

Research output: Contribution to journalArticle

Fernandez, Gael Verao ; Stratigaki, Vasiliki ; Vasarmidis, Panagiotis ; Balitsky, Philip ; Troch, Peter A. / Wake effect assessment in long- and short-crested seas of heaving-point absorber and oscillating wave surge WEC arrays. In: Water (Switzerland). 2019 ; Vol. 11, No. 6.
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