Experimental and Numerical Modelling of a Multiple Oscillating Water Column Structure

The potential exists for ocean energy from waves to meet a large fraction of future global energy needs. Furthermore, synergies between the existing offshore wind industry, and the future offshore wave energy industry, can be exploited. This thesis is concerned with the physical and numerical modelling of an offshore floating platform, as proposed by a commercial developer. It is envisaged that the platform will capture both wave and wind energy, using an array of oscillating water columns (OWC) and conventional wind energy technology. The focus of this thesis is on the wave energy-capturing aspects of the proposed platform. A 1:50, physical scale model of the proposed platform is described, and a tank testing programme for the model, in a variety of configurations, is outlined. A frequency domain, numerical model of the physical scale model is developed. Predictions from the numerical model are compared to the tank testing results. Based on the results of tank testing, and predictions from the numerical model, a number of useful tools for future design work have been created, and some fundamental changes to the design of the platform are proposed. On completion of the tank testing, the platform progressed to Technical Readiness Level 3. Due to the complexities of studying and numerically modelling the hydrodynamic and thermodynamic interactions within the array of OWCs in the model platform, a nonlinear, time domain, numerical model, at a scale of 1:50, of a single OWC from the proposed platform, with control components, is developed. Predictions from the numerical model are compared to the results of testing on a physical model of the single OWC. An investigation to quantify the effect of air compression in the single-OWC model, not captured using Froude scaling, is conducted. The investigation leads to a proposed novel method for measuring the hydrodynamic parameters of a water column. The key conclusions from this thesis are: • A non-linear, time-domain numerical model has been developed for a single-OWC with novel cross section and control components. The numerical model has been extensively validated using the rests obtained from narrow tank testing. • A new method for determining hydrodynamic parameters has been developed and demonstrated numerically. The method has been implemented for an OWC, but requires further validation. • It has been demonstrated through the analysis of data obtained from tank testing that the airflow from the chambers of a V-shaped, 32-OWC wave energy converter (WEC) can absorb power from the wave front with an efficiency of up to 37 % at a wave period of 1.13 s. • A frequency domain model of the multiple degree-of-freedom WEC, predictions from which compare well with results obtained from tank testing, has been developed.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

National University of Ireland Maynooth

Year dc:date.issued

2018

Author dc:creator

• Kelly, Thomas

Language dc:language

en