R. V. Chaplin

A JOINT NUMERICAL AND EXPERIMENTAL STUDY OF A SURGING POINT ABSORBING WAVE ENERGY CONVERTER (WRASPA)

This paper presents the findings from using several commercial computational fluid dynamics codes in a joint numerical and experimental project to simulate WRASPA, a new wave energy converter (WEC) device. A series of fully 3D non-linear simulations of WRASPA are presented. Three commercial codes STAR-CCM, CFX and FLOW-3D are considered for simulating the WRASPA device and final results are presented based on the use of Flow-3D. Results are validated by comparison to experimental data obtained from small scale tank tests undertaken at Lancaster University (LU). The primary aim of the project is to use numerical simulation to optimize the collector geometry for power production over a range of likely wave climates. A secondary aim is to evaluate the ability of commercial codes to simulate rigid body motion in linear and non-linear wave climates in order to choose the optimal code with respect to compute speed and ease of problem setup. Issues relating to the ability of a code in terms of numerical dissipation of waves, wave absorption, wave breaking, grid generation and moving bodies will all be discussed. The findings of this paper serve as a basis for an informed choice of commercial package for such simulations. However the capability of these commercial codes is increasing with every new release.Copyright

Control systems for Wraspa

The paper discusses the need for a wave energy converter (WEC) to sense and respond to its environment in order to survive and to produce its maximum useful output. Such systems are described for Wraspa, a WEC being developed at Lancaster University and first reported at ICCEP in 2007. The main control system that continually monitors and optimises the power-take-off is termed “Stepwise Control” and seeks to continually adjust the damping force applied to the collector to suit the wave force that drives it. The complete instrumentation and control system that will be needed is considered briefly, including the above PTO control system; direction sensing and heading control; tide level compensation; condition monitoring and provisions for access and maintenance.

Optimum Power Capture of a New Wave Energy Converter in Irregular Waves

This paper presents the optimum power capture of a new point-absorber wave energy converter, in irregular waves. A stepwise control system for the wave energy converter (WEC) is developed. The control system is used to efficiently extract power from irregular waves where amplitudes vary from wave to wave. The Bretschneider spectrum is used in the experiment and the device is ‘tuned’ to the peak period of the sea state. It is shown that this WEC has a reasonable capture width in irregular waves. However, the optimum mean power depends on the wave spectrum, the shape of the collector body, its freeboard and the device pivot depth.Copyright

Numerical and experimental study of a point absorbing wave energy converter in regular waves

This paper describes recent numerical modelling of a new wave energy converter WRASPA (Wave-driven, Resonant, Arcuate action, Surging Power-Absorber). The presented results are based on a range of regular incident waves. Also the experimental setup is outlined to illustrate the brief design principles of the device. A comparison of experimental and numerical results is performed as part of the validation process. The interaction of waves with WRASPA device has been simulated using a commercial code Flow-3D as one of the primary objectives of this project. The ability of the method to compute a range of linear waves and coupled motion of the device is discussed. The codes ability to deal with wave propagation and interaction with rigid moving structures is evaluated.

Investigating a Power-Obsorber Wave Energy Converter

This paper presents the assessment of the optimum performance of a wave energy converter. In this device which is hinged at the seabed, wave forces act on the face of a collector body, carried on an arm that rotates about a fixed horizontal axis. The collector body oscillates at about the frequency of the ocean swell generating high power from this relatively small and economical device. The performance of the device is investigated using numerical hydrodynamic analysis and the wave tank experiment for a model at a nominal scale of 1/100. Also the optimum mean power output of the device in irregular wave climates is assessed. A first-order method is used to calculate the mean power spectrum of the device in waves of dissimilar spectra. It is shown that the choice of tuning period has a major effect on the power absorbed, hence on the power output.Copyright