Power Enhancement of WEC Array via Wave Runup in Channel

When waves pass through a channel, wave elevation is observed to increase, a phenomenon known as wave runup. Attempts are made to utilize the wave runup along a channel supported on a floating platform to enhance the energy generation from the array of point absorber WECs. Such floating platforms could be integrated into the floating breakwater, floating pier or other floating platforms utilized as floating cities for efficient ocean space utilization. The channel is created by modelling two vertical walls supported on a floating platform with WECs deployed in the channel. The performance of the wave farm in terms of energy generation and interaction factor are assessed. The paper investigates the effect of channel widths and depths on the power absorption of the arrays. A three-stepped floating platform with varying depths along the channel is then studied to obtain optimal depths along the channel where the highest energy is harvested. Thereafter, three arrays of WECs deployed in a larger three-stepped channel floating platform are considered and the effectiveness of such configuration in harvesting energy is assessed. The wave elevation surrounding the wave farm is presented to show the effect the wave runup has on energy generation. The results show that the energy generation of wave energy converters when the arrays are placed in a three-stepped channel floating platform could be increased significantly. A q-factor above 1.0 could be achieved for wave periods greater than 6s and the array can generate greater energy for omnidirectional waves.

The Performance of a Spectral Wave Model at Predicting Wave Farm Impacts

For renewable ocean wave energy to support global energy demands, wave energy converters (WECs) will likely be deployed in large numbers (farms), which will necessarily change the nearshore environment. Wave farm induced changes can be both helpful (e.g., beneficial habitat and coastal protection) and potentially harmful (e.g., degraded habitat, recreational, and commercial use) to existing users of the coastal environment. It is essential to estimate this impact through modeling prior to the development of a farm, and to that end, many researchers have used spectral wave models, such as Simulating WAves Nearshore (SWAN), to assess wave farm impacts. However, the validity of the approaches used within SWAN have not been thoroughly verified or validated. Herein, a version of SWAN, called Sandia National Laboratories (SNL)-SWAN, which has a specialized WEC implementation, is verified by comparing its wave field outputs to those of linear wave interaction theory (LWIT), where LWIT is theoretically more appropriate for modeling wave-body interactions and wave field effects. The focus is on medium-sized arrays of 27 WECs, wave periods, and directional spreading representative of likely conditions, as well as the impact on the nearshore. A quantitative metric, the Mean Squared Skill Score, is used. Results show that the performance of SNL-SWAN as compared to LWIT is “Good” to “Excellent”.

Investigation of Ocean-Wave-Focusing Characteristics Induced by a Submerged Crescent-Shaped Plate for Long-Crested Waves

The need for renewable energy has gained importance with growing concerns about climate change. Wave energy has attracted considerable attention owing to its sustainability potential. Reflection, refraction, diffraction, and shoaling of waves occur when waves propagate through a submerged structure. These mechanics, when properly utilized, can be employed to focus waves to a specific location and also to increase wave heights, by which wave energy is usually represented, for planning and designing wave farms. Wave focusing induced by a submerged crescent-shaped plate for different wave conditions, incident wave directions, and submerged depths mainly considering the potential applications of absorber wave-energy converters within the wave farm was investigated experimentally and numerically. All experimental regular wave conditions were controlled to be nonbreaking, and the numerical results were obtained by a 3D model, implemented through the boundary element method based on Airy wave theory. The results show that wave focusing appears behind the plate along the direction of the incident waves, and the locations of focused waves tend to be farther away from the plate for shorter-period waves. The maximum measured wave height can be 3.44 times higher than the incident wave height.