Session: 09-05-05 Wave Energy: Oscillating Water Columns

Submission Number: 176463

Fundamental Study on Power Conversion Performance of an Oscillating Water Column Surrounded by Artificial Wave-Dissipating Blocks 

Oscillating Water Column (OWC) wave energy converters are among the most mature and reliable wave power technologies, with successful long-term sea trials conducted in several countries. However, their widespread adoption remains limited due to extremely high capital costs, primarily arising from the heavy structural requirements necessary to withstand large wave loads. A promising concept for reducing these costs is to place OWC chambers inside breakwaters surrounded by artificial wave-dissipating blocks, which attenuate incoming waves and thereby reduce structural loads. While such an arrangement can lower the cost of construction, wave attenuation may also suppress internal water column oscillations and degrade power conversion performance. The trade-off between these effects has not yet been systematically quantified.

This study aims to provide fundamental insight into how artificial wave-dissipating blocks affect OWC performance by conducting controlled laboratory experiments in two stages using the same OWC model. The model consisted of a square acrylic chamber (10 cm × 10 cm × 30 cm) mounted against a vertical wall in a 30 cm-deep wave flume. Water level fluctuations and internal air pressures were measured using wave gauges and pressure sensors under controlled wave conditions.

In the first stage, experiments with regular waves were performed to investigate the fundamental hydrodynamic response of the system. The results clearly demonstrated that the presence of artificial wave-dissipating blocks significantly alters the spectral characteristics of the incident waves before they reach the OWC chamber. Specifically, the blocks act as a low-pass filter, strongly attenuating high-frequency components while selectively transmitting long-period components. As a result, the oscillation amplitude of the internal water column decreased compared to the no-block condition, but the response at low frequencies remained evident.

In the second stage, irregular wave experiments based on a modified Bretschneider–Mitsuyasu spectrum were conducted on the same OWC model to evaluate power conversion performance under more realistic sea-state conditions. Despite the reduced oscillation amplitude observed in the first stage, the results showed that power conversion performance did not decrease significantly under long-period wave conditions. Measurable chamber pressure fluctuations were maintained, indicating that energy conversion remained feasible even in the spectrally filtered wave environment created by the wave-dissipating blocks.

These findings demonstrate two key points. First, artificial wave-dissipating blocks function as a low-pass filter that transforms the incident wave spectrum before it interacts with the OWC. Second, even under such filtered wave conditions, the power conversion capability of the OWC remains largely preserved for long-period wave components. Together, these results provide fundamental insights into the hydrodynamic and performance characteristics of OWCs surrounded by artificial wave-dissipating blocks and form a critical basis for future work on optimizing device geometry and balancing structural load reduction with power output efficiency. Ultimately, this study contributes to the advancement of cost-effective OWC systems and supports their potential deployment as viable renewable energy technologies.

Presenting Author: Mitsumasa Iino Ashikaga University

Presenting Author Biography: Mitsumasa Iino, Ph.D. in Engineering, is an Associate Professor in the Natural Energy Course, Mechanical Field at Ashikaga University. He researches wave and wind power, focusing on real sea and tank experiments for Oscillating Water Column wave power generation and dynamic system modeling.

Authors:

Mitsumasa Iino Ashikaga University
Hiroshi Matsushita Nishinippon Institute of Technology