Numerical Modelling of Fixed Oscillating Water Column Wave Energy Conversion Devices: Toward Geometry Hydraulic Optimization

Abstract

The Oscillating Water Column (OWC) is one of the simplest and most studied concepts for wave energy conversion. The commercial scale diffusion of the OWC technology is, however, strongly dependent upon the device optimization. Research at a fundamental level is therefore still required. Analytical, numerical and experimental models are necessary tools for advancing in the knowledge of the system and thus promoting its passage at the commercial level. In this work, a simplified frequency domain rigid piston model has been applied to preliminary select expected ranges of air pressures and air velocities for the instrumental set up of laboratory experiments. The set up of a Computational Fluid Dynamic (CFD) model implemented in the open source OpenFOAM®1 environment is then presented. The multiphase model solves incompressible 3D Navier-Stokes equations, using Large Eddy Simulation (LES) for turbulence modelling, and adopts a Volume of Fluid method (VOF) to track the air-water interface. A preliminary validation of the model with physical tests data is conducted. The numerical approach seems to be promising for an accurate simulation of the OWC device energy conversion process. Hence, the validated model can be a useful research tool for different problems, particularly for systematic parameter studies to extend the range of conditions tested in the laboratory.

Numerical study of fixed Oscillating Water Column with RANS-type two-phase CFD model

“…In recent work with OpenFOAM and IHFOAM, it was also observed that the pressure in the numerical model was slightly over-predicted [22] when RANS equations were solved. On the other hand, when a LES model was used, the numerically predicted pressure was closer to the experimentally measured pressure [35]. In other studies, the correlation between the experimental and the numerical results is similar to the present study, however the pressure fluctuations were 80 Pa [22], 180 Pa [18], 200 Pa [35] and 900 Pa [19], which are significantly smaller in comparison to 1400 Pa which is observed here.…”

“…On the other hand, when a LES model was used, the numerically predicted pressure was closer to the experimentally measured pressure [35]. In other studies, the correlation between the experimental and the numerical results is similar to the present study, however the pressure fluctuations were 80 Pa [22], 180 Pa [18], 200 Pa [35] and 900 Pa [19], which are significantly smaller in comparison to 1400 Pa which is observed here. The reason for the high pressure is the high damping induced from the small orifice in combination with the high waves.…”

“…This method is commonly used for floating bodies [43], but rarely for fixed OWC. A similar approach to the present one for performing a decay test with a fixed OWC was presented recently [35], where the FFT of the time series was used to determine the resonant frequency of the device. Here, the theory of mechanical vibrations with viscous damping is employed.…”

Blue Growth Development in the Mediterranean Sea: Quantifying the Benefits of an Integrated Wave Energy Converter at Genoa Harbour

“…Given through use of long-term metocean condition, response of the turbines can be tuned to H m0 ≤ 3.5 m. Even with this small configuration change, it is expected that the performance can be increased to 40-50% by adapting the turbine operation to the local conditions [47], usually done by CFD modeling that has shown the improvements that an OWC can attain [56,57]. However, such an effort is outside of the scope for this paper, whose primary focus is to quantify the resource, energy and economic potential.…”

“…Through the coupling of multi-model nesting, energy analysis and utilising a non-optimised WEC solution, ratios are proposed for which an investment would be feasible. Past studies indicated the possibility of tuning the converter behaviour to local condition, hence scaling its performance is expected to increase the energy production by at least 50% [47,56,59]. An integrated breakwater OWC operates at shallow water areas where surge and depth breaking will be more dominated, and thus simple Froude scaling is not possible.…”