skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Development of a nearshore oscillating surge wave energy converter with variable geometry

Abstract

This paper presents an analysis of a novel wave energy converter concept that combines an oscillating surge wave energy converter (OSWEC) with control surfaces. The control surfaces allow for a variable device geometry that enables the hydrodynamic properties to be adapted with respect to structural loading, absorption range and power-take-off capability. The device geometry is adjusted on a sea state-to-sea state time scale and combined with wave-to-wave manipulation of the power take-off (PTO) to provide greater control over the capture efficiency, capacity factor, and design loads. This work begins with a sensitivity study of the hydrodynamic coefficients with respect to device width, support structure thickness, and geometry. A linear frequency domain analysis is used to evaluate device performance in terms of absorbed power, foundation loads, and PTO torque. Previous OSWEC studies included nonlinear hydrodynamics, in response a nonlinear model that includes a quadratic viscous damping torque that was linearized via the Lorentz linearization. Inclusion of the quadratic viscous torque led to construction of an optimization problem that incorporated motion and PTO constraints. Results from this study found that, when transitioning from moderate-to-large sea states the novel OSWEC was capable of reducing structural loads while providing a near constant power output.

Authors:
 [1];  [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1254107
Report Number(s):
NREL/JA-5000-64377
Journal ID: ISSN 0960-1481
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Renewable Energy; Journal Volume: 96; Journal Issue: PA; Related Information: Renewable Energy
Country of Publication:
United States
Language:
English
Subject:
16 TIDAL AND WAVE POWER; oscillating surge wave energy converter; variable structures; structural load control; linearization

Citation Formats

Tom, N. M., Lawson, M. J., Yu, Y. H., and Wright, A. D. Development of a nearshore oscillating surge wave energy converter with variable geometry. United States: N. p., 2016. Web. doi:10.1016/j.renene.2016.04.016.
Tom, N. M., Lawson, M. J., Yu, Y. H., & Wright, A. D. Development of a nearshore oscillating surge wave energy converter with variable geometry. United States. doi:10.1016/j.renene.2016.04.016.
Tom, N. M., Lawson, M. J., Yu, Y. H., and Wright, A. D. 2016. "Development of a nearshore oscillating surge wave energy converter with variable geometry". United States. doi:10.1016/j.renene.2016.04.016.
@article{osti_1254107,
title = {Development of a nearshore oscillating surge wave energy converter with variable geometry},
author = {Tom, N. M. and Lawson, M. J. and Yu, Y. H. and Wright, A. D.},
abstractNote = {This paper presents an analysis of a novel wave energy converter concept that combines an oscillating surge wave energy converter (OSWEC) with control surfaces. The control surfaces allow for a variable device geometry that enables the hydrodynamic properties to be adapted with respect to structural loading, absorption range and power-take-off capability. The device geometry is adjusted on a sea state-to-sea state time scale and combined with wave-to-wave manipulation of the power take-off (PTO) to provide greater control over the capture efficiency, capacity factor, and design loads. This work begins with a sensitivity study of the hydrodynamic coefficients with respect to device width, support structure thickness, and geometry. A linear frequency domain analysis is used to evaluate device performance in terms of absorbed power, foundation loads, and PTO torque. Previous OSWEC studies included nonlinear hydrodynamics, in response a nonlinear model that includes a quadratic viscous damping torque that was linearized via the Lorentz linearization. Inclusion of the quadratic viscous torque led to construction of an optimization problem that incorporated motion and PTO constraints. Results from this study found that, when transitioning from moderate-to-large sea states the novel OSWEC was capable of reducing structural loads while providing a near constant power output.},
doi = {10.1016/j.renene.2016.04.016},
journal = {Renewable Energy},
number = PA,
volume = 96,
place = {United States},
year = 2016,
month =
}
  • This study investigates the effect of design changes on the hydrodynamics of a novel oscillating surge wave energy converter being developed at the National Renewable Energy Laboratory. The design utilizes controllable geometry features to shed structural loads while maintaining a rated power over a greater number of sea states. The second-generation design will seek to provide a more refined control of performance because the first-generation design demonstrated performance reductions considered too large for smooth power output. Performance is evaluated using frequency domain analysis with consideration of a nonideal power-take-off system, with respect to power absorption, foundation loads, and power-take-off torque.
  • This study investigates the effect of design changes on the hydrodynamics of a novel oscillating surge wave energy converter being developed at the National Renewable Energy Laboratory. The design utilizes controllable geometry features to shed structural loads while maintaining a rated power over a greater number of sea states. The second-generation design will seek to provide a more refined control of performance because the first-generation design demonstrated performance reductions considered too large for smooth power output. Performance is evaluated using frequency domain analysis with consideration of a nonideal power-take-off system, with respect to power absorption, foundation loads, and power-take-off torque.
  • The aim of this study is to describe a procedure to maximize the power-to-load ratio of a novel wave energy converter (WEC) that combines an oscillating surge wave energy converter with variable structural components. The control of the power-take-off torque will be on a wave-to-wave timescale, whereas the structure will be controlled statically such that the geometry remains the same throughout the wave period. Linear hydrodynamic theory is used to calculate the upper and lower bounds for the time-averaged absorbed power and surge foundation loads while assuming that the WEC motion remains sinusoidal. Previous work using pseudo-spectral techniques to solvemore » the optimal control problem focused solely on maximizing absorbed energy. This work extends the optimal control problem to include a measure of the surge foundation force in the optimization. The objective function includes two competing terms that force the optimizer to maximize power capture while minimizing structural loads. A penalty weight was included with the surge foundation force that allows control of the optimizer performance based on whether emphasis should be placed on power absorption or load shedding. Results from pseudo-spectral optimal control indicate that a unit reduction in time-averaged power can be accompanied by a greater reduction in surge-foundation force.« less