Theoretical and experimental analysis of a dual chamber OWC device

Abstract

Numerous studies on floating Oscillating Water Column (OWC) devices underscore their widespread adoption as a preferred methodology for wave energy conversion, primarily due to their simplicity of operation, structural robustness, ease of maintenance, and versatility. The earliest hydrodynamic analysis of a floating OWC was conducted by McCormick [1], laying the foundation for a wealth of subsequent research aimed at enhancing the wave power absorption efficiency of such systems. Since that time, numerous studies have concentrated on enhancing energy capture and conversion through the development and optimization of various types of OWC converters.

The dual chamber OWC configuration is particularly efficient due to its ability to harness resonance between chambers, facilitating optimal interaction with a wide range of wave frequencies. This design enables enhanced energy capture by amplifying water column oscillations, thereby improving the pneumatic efficiency of the system. Furthermore, the dual chamber setup ensures smoother and more consistent airflow to the turbines, which significantly enhances the overall energy conversion process. Such a configuration also demonstrates superior adaptability to varying wave conditions, further underlining its utility in diverse marine environments [2]-[3].

This study presents the development of a dual chamber Oscillating Water Column concept designed to maximize offshore wave energy exploitation. The proposed device features two coaxial free-surface piercing toroidal cylinders with vertical symmetry axes, moored using tensioned tethers in the manner of a Tension Leg Platform (TLP). Detailed modeling of the system is provided, encompassing the hydrodynamic interactions between the floating structure, the mooring system, and the air turbine at the top of the oscillating chambers.

Theoretical findings were validated through experimental investigations on a scaled-down prototype conducted at the Laboratory of Ship and Marine Hydrodynamics, National Technical University of Athens. This experimental campaign was carried out under the Basic Research Financing (Horizontal support for all Sciences) initiative, supported by the National Recovery and Resilience Plan (Greece 2.0), Project Number: 015681, ETHOS: Novel Type Offshore Floating Wave Energy Converter for Efficient Power Absorption.

The analysis revealed distinctive hydrodynamic phenomena within the dual chamber system, including pumping and sloshing behaviors that arise at specific wave numbers. These phenomena were observed to significantly enhance the energy capture efficiency of the device. A comparison between the theoretical predictions and the experimental results demonstrated an excellent correlation, affirming the robustness of the proposed model.

Overall, the findings underscore the advantages of dual chamber OWCs over their single chamber counterparts, particularly in terms of hydrodynamic performance at specific wave numbers. The dual chamber configuration amplifies energy capture while ensuring smoother airflow dynamics, making it a promising solution for efficient wave energy conversion in offshore environments.

• [1] McCormick, M.E., 1976. A modified linear analysis of a wave-energy conversion buoy. Ocean Eng. 3 (3), 133–144.
• [2] Ning, D.Z., Zhou, Y., Zhang, C., 2018. Hydrodynamic modeling of a novel dual-chamber OWC wave energy converter. Appl. Ocean Res. 78, 180–191.
• [3] Ning, D.Z., Wang, R.Q., Chen, L.F., Sun, K., 2019. Experimental investigation of a land based dual-chamber owc wave energy converter. Renew. Sustain. Energy Rev. 105, 48–60
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