# Balancing Power Absorption and Structural Loading for an Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint

## Abstract

The aim of this paper is to maximize the power-to-load ratio of the Berkeley Wedge: a one-degree-of-freedom, asymmetrical, energy-capturing, floating breakwater of high performance that is relatively free of viscosity effects. Linear hydrodynamic theory was used to calculate bounds on the expected time-averaged power (TAP) and corresponding surge restraining force, pitch restraining torque, and power take-off (PTO) control force when assuming that the heave motion of the wave energy converter remains sinusoidal. This particular device was documented to be an almost-perfect absorber if one-degree-of-freedom 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.:
- NREL Laboratory Directed Research and Development (LDRD)

- OSTI Identifier:
- 1270787

- Report Number(s):
- NREL/CP-5000-65656

- DOE Contract Number:
- AC36-08GO28308

- Resource Type:
- Conference

- Resource Relation:
- Conference: Presented at the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2016), 19-24 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 Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint*. United States: N. p., 2016.
Web.

```
Tom, Nathan M., Madhi, Farshad, & Yeung, Ronald W.
```*Balancing Power Absorption and Structural Loading for an Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint*. United States.

```
Tom, Nathan M., Madhi, Farshad, and Yeung, Ronald W. Fri .
"Balancing Power Absorption and Structural Loading for an Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint". United States. https://www.osti.gov/servlets/purl/1270787.
```

```
@article{osti_1270787,
```

title = {Balancing Power Absorption and Structural Loading for an Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint},

author = {Tom, Nathan M. and Madhi, Farshad and Yeung, Ronald W.},

abstractNote = {The aim of this paper is to maximize the power-to-load ratio of the Berkeley Wedge: a one-degree-of-freedom, asymmetrical, energy-capturing, floating breakwater of high performance that is relatively free of viscosity effects. Linear hydrodynamic theory was used to calculate bounds on the expected time-averaged power (TAP) and corresponding surge restraining force, pitch restraining torque, and power take-off (PTO) control force when assuming that the heave motion of the wave energy converter remains sinusoidal. This particular device was documented to be an almost-perfect absorber if one-degree-of-freedom 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 per-unit gain in TAP would not lead to a greater per-unit demand in structural strength, hence yielding a favorable benefit-to-cost 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 = {},

journal = {},

number = ,

volume = ,

place = {United States},

year = {2016},

month = {7}

}