Session: 09-02-03 WEC performance analysis

Paper Number: 80110

80110 - The Influence of Different Configurations and Spacings on the Performance of Oscillating Wave Surge Converters When Operating in Wave Farms 

The energy that can be generated by sea waves is significant and permanent. However, as an unpredictable resource, to successfully capture its energy and design, deploy, operate and maintain wave energy conversion technologies is extremely demanding. Thus, research on these technologies and the response of such devices to different sea conditions is an ongoing challenge. Due to this large energy available, the efforts to develop marine energy devices with higher technology readiness and performance levels (TRL and TPL, respectively) are continuously pursued. A possible solution to increase the TPL across successful wave energy technologies is to enhance the power capture against the cost by extending the current installations of existing Wave Energy Converters (WEC) to include neighbouring devices. It is expected that this practice will not only allow to increase energy production but also to reduce the operating and maintenance costs by using the installations and resources already available.

Among these technologies, Oscillating Wave Surge Converters (OWSC) have proved to be a promising solution for the wave energy conversion industry. These devices are composed by a rotating surface-piercing buoyant flap hinged to a base on the sea bed. In particular, research done for this type of devices includes its response to incident wave fields operating in isolation as well as in wave farms. To deploy wave farms is not as straightforward as to extend the hydrodynamic response of one device. When the incident wave field interacts with a single energy device, it will be disturbed/modified by wave effects, such as reflection, diffraction and radiation. This perturbed wave field will interact with neighbouring devices and its influence can be constructive or destructive in the hydrodynamic performance of each of them.

To measure the efficiency of the array, the power capture of a wave farm is compared to that of the sum of the same number of devices performing in isolation; this ratio, commonly referred as q factor, should be higher than 1 for the configuration to be successful. However, there is no particular configuration system that can achieve a constructive interference under every sea wave condition, hence, the design stage should ensure that the system will have a constructive interaction in the most common sea states of its location. Thus, to find a set of configurations that comply a positive interaction has become important in the study of wave farms.

In this work, the q factor of configurations of three-OWSC, varying the spacing and arrangement, is predicted using Computational Fluid Dynamics method, specifically the open-source package OpenFOAM. The efficiency of the power capture of a single unit is calculated using the Maximum Capture Width Ratio (MCWR), which is defined as the ratio of the total mean power absorbed by one device to the mean power per unit wave width of the incident wave, to the characteristic length of the device. In this system the Power Take-Off mechanism of the unit device is calculated for a specific wave frequency.

It is shown that if the spacing between the devices is large enough, the modified wave fields will not interact with the adjacent devices. Conversely, when this space is too large, the cost benefits associated to deploying an array decrease. Thus, in a compact scenario, this study recommends a specific layout for a specific set of sea wave conditions bringing positive interaction for different wave frequencies.

Presenting Author: Daniela Benites Munoz University College London

Authors:

Daniela Benites Munoz University College London
Luofeng Huang Cranfield University
Giles Thomas University College London