Balancing Power Absorption and Structural Loading for an Asymmetric Heave WaveEnergy Converter in Regular Waves
Abstract
The aim of this paper is to maximize the powertoload ratio of the Berkeley Wedge: a onedegreeoffreedom, asymmetrical, energycapturing, floating breakwater of high performance that is relatively free of viscosity effects. Linear hydrodynamic theory was used to calculate bounds on the expected timeaveraged power (TAP) and corresponding surge restraining force, pitch restraining torque, and power takeoff (PTO) control force when assuming that the heave motion of the wave energy converter remains sinusoidal. This particular device was documented to be an almostperfect absorber if onedegreeoffreedom motion is maintained. The success of such or similar future wave energy converter technologies would require the development of control strategies that can adapt device performance to maximize energy generation in operational conditions while mitigating hydrodynamic loads in extreme waves to reduce the structural mass and overall cost. This paper formulates the optimal control problem to incorporate metrics that provide a measure of the surge restraining force, pitch restraining torque, and PTO control force. The optimizer must now handle an objective function with competing terms in an attempt to maximize power capture while minimizing structural and actuator loads. A penalty weight is placed on the surge restraining force, pitch restraining torque, and PTO actuation force, therebymore »
 Authors:
 Publication Date:
 Research Org.:
 National Renewable Energy Lab. (NREL), Golden, CO (United States)
 Sponsoring Org.:
 USDOE Office of Energy Efficiency and Renewable Energy (EERE), NREL Laboratory Directed Research and Development (LDRD)
 OSTI Identifier:
 1335572
 Report Number(s):
 NREL/CP500067557
 DOE Contract Number:
 AC3608GO28308
 Resource Type:
 Conference
 Resource Relation:
 Conference: Presented at the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2016), 1924 June 2016, Busan, South Korea
 Country of Publication:
 United States
 Language:
 English
 Subject:
 16 TIDAL AND WAVE POWER; asymmetric heave wave energy converter; Berkeley Wedge; wave energy converter
Citation Formats
Tom, Nathan M., Madhi, Farshad, and Yeung, Ronald W. Balancing Power Absorption and Structural Loading for an Asymmetric Heave WaveEnergy Converter in Regular Waves. United States: N. p., 2016.
Web. doi:10.1115/OMAE201655050.
Tom, Nathan M., Madhi, Farshad, & Yeung, Ronald W. Balancing Power Absorption and Structural Loading for an Asymmetric Heave WaveEnergy Converter in Regular Waves. United States. doi:10.1115/OMAE201655050.
Tom, Nathan M., Madhi, Farshad, and Yeung, Ronald W. 2016.
"Balancing Power Absorption and Structural Loading for an Asymmetric Heave WaveEnergy Converter in Regular Waves". United States.
doi:10.1115/OMAE201655050.
@article{osti_1335572,
title = {Balancing Power Absorption and Structural Loading for an Asymmetric Heave WaveEnergy Converter in Regular Waves},
author = {Tom, Nathan M. and Madhi, Farshad and Yeung, Ronald W.},
abstractNote = {The aim of this paper is to maximize the powertoload ratio of the Berkeley Wedge: a onedegreeoffreedom, asymmetrical, energycapturing, floating breakwater of high performance that is relatively free of viscosity effects. Linear hydrodynamic theory was used to calculate bounds on the expected timeaveraged power (TAP) and corresponding surge restraining force, pitch restraining torque, and power takeoff (PTO) control force when assuming that the heave motion of the wave energy converter remains sinusoidal. This particular device was documented to be an almostperfect absorber if onedegreeoffreedom motion is maintained. The success of such or similar future wave energy converter technologies would require the development of control strategies that can adapt device performance to maximize energy generation in operational conditions while mitigating hydrodynamic loads in extreme waves to reduce the structural mass and overall cost. This paper formulates the optimal control problem to incorporate metrics that provide a measure of the surge restraining force, pitch restraining torque, and PTO control force. The optimizer must now handle an objective function with competing terms in an attempt to maximize power capture while minimizing structural and actuator loads. A penalty weight is placed on the surge restraining force, pitch restraining torque, and PTO actuation force, thereby allowing the control focus to be placed either on power absorption or load mitigation. Thus, in achieving these goals, a perunit gain in TAP would not lead to a greater perunit demand in structural strength, hence yielding a favorable benefittocost ratio. Demonstrative results in the form of TAP, reactive TAP, and the amplitudes of the surge restraining force, pitch restraining torque, and PTO control force are shown for the Berkeley Wedge example.},
doi = {10.1115/OMAE201655050},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 6
}

The aim of this paper is to maximize the powertoload ratio of the Berkeley Wedge: a onedegreeoffreedom, asymmetrical, energycapturing, floating breakwater of high performance that is relatively free of viscosity effects. Linear hydrodynamic theory was used to calculate bounds on the expected timeaveraged power (TAP) and corresponding surge restraining force, pitch restraining torque, and power takeoff (PTO) control force when assuming that the heave motion of the wave energy converter remains sinusoidal. This particular device was documented to be an almostperfect absorber if onedegreeoffreedom motion is maintained. The success of such or similar future wave energy converter technologies would requiremore »

Balancing Power Absorption and Structural Loading for a Novel FixedBottom Wave Energy Converter with Nonideal Power TakeOff in Regular Waves: Preprint
In this work, the net power delivered to the grid from a nonideal power takeoff (PTO) is introduced followed by a review of the pseudospectral control theory. A powertoload ratio, used to evaluate the pseudospectral controller performance, is discussed, and the results obtained from optimizing a multiterm objective function are compared against results obtained from maximizing the net output power to the grid. Simulation results are then presented for four different oscillating wave energy converter geometries to highlight the potential of combing both geometry and PTO control to maximize power while minimizing loads. 
Balancing the PowertoLoad Ratio for a Novel Variable Geometry Wave Energy Converter with Nonideal Power TakeOff in Regular Waves: Preprint
This work attempts to balance power absorption against structural loading for a novel variable geometry wave energy converter. The variable geometry consists of four identical flaps that will be opened in ascending order starting with the flap closest to the seafloor and moving to the free surface. The influence of a pitch motion constraint on power absorption when utilizing a nonideal power takeoff (PTO) is examined and found to reduce the losses associated with bidirectional energy flow. The powertoload ratio is evaluated using pseudospectral control to determine the optimum PTO torque based on a multiterm objective function. The pseudospectral optimalmore » 
Balancing Power Absorption and Fatigue Loads in Irregular Waves for an Oscillating Surge Wave Energy Converter: Preprint
The aim of this paper is to describe how to control the powertoload ratio of a novel wave energy converter (WEC) in irregular waves. The novel WEC that is being developed at the National Renewable Energy Laboratory combines an oscillating surge wave energy converter (OSWEC) with control surfaces as part of the structure; however, this work only considers one fixed geometric configuration. This work extends the optimal control problem so as to not solely maximize the timeaveraged power, but to also consider the powertakeoff (PTO) torque and foundation forces that arise because of WEC motion. The objective function of themore » 
Balancing Power Absorption and Fatigue Loads in Irregular Waves for an Oscillating Surge Wave Energy Converter
The aim of this paper is to describe how to control the powertoload ratio of a novel wave energy converter (WEC) in irregular waves. The novel WEC that is being developed at the National Renewable Energy Laboratory combines an oscillating surge wave energy converter (OSWEC) with control surfaces as part of the structure; however, this work only considers one fixed geometric configuration. This work extends the optimal control problem so as to not solely maximize the timeaveraged power, but to also consider the powertakeoff (PTO) torque and foundation forces that arise because of WEC motion. The objective function of themore »