Abstract
The efficiency response of an oscillating water column (OWC) wave energy converter is analysed by adopting a numerical approach and using various stepped bottom configurations for the seabed. A two-dimensional, fully non-linear higher-order boundary element method (HOBEM) model is developed to simulate the hydrodynamic characteristics and fluid structure interaction for a fixed OWC located in a numerical wave flume. A number of model tests are conducted for various regular incident wave conditions by modifying the wave amplitudes and wavelengths. The measured free surface elevation at the chamber centre and the oscillatory air pressure generated by the fluctuating free surface within the chamber are recorded. The hydrodynamic efficiency of the OWC is determined using these parameters. The simulation results are validated by comparing against previously published experimental and numerical data. Good agreement is observed in both cases. The geometric dimensions of the step are modified by altering the step height and step length. Furthermore, by altering the step length, the location of the front face of the step relative to the front wall of the OWC is adjusted. Therefore, the positional significance of the step can also be analysed in terms of its relative location to the OWC chamber and to the flow field development. It is shown that the geometry of the step and the position of the vertical face of the step relative to the OWC influences the hydrodynamic efficiency. The research demonstrates that by optimising the step geometry and position for a given wave condition a higher operational efficiency can be achieved.
Highlights
Due to limited reserves and exploitation difficulty associated with fossil energy resources and the environmental problems that arises during to the hazardous chemical processing of fossil fuels, renewable energy resources have become more appealing to meet increasing global demands (Rezanejad et al, 2013; Veigas et al, 2014)
A two-dimensional fully non-linear numerical model developed using the potential flow theory and the time-domain higher-order boundary element method (HOBEM) developed by Ning et al (2015) is used to investigate the hydrodynamic performance of this stepped bottom oscillating water column (OWC) energy harvester
Using the time-domain HOBEM, a 2D fully non-linear numerical wave flume with an OWC device having a stepped seabed was developed. This model was used to study the effects of the step geometric parameters on the OWC hydrodynamic efficiency, the free-surface development and the air pressure oscillations inside the OWC chamber
Summary
Due to limited reserves and exploitation difficulty associated with fossil energy resources and the environmental problems that arises during to the hazardous chemical processing of fossil fuels, renewable energy resources have become more appealing to meet increasing global demands (Rezanejad et al, 2013; Veigas et al, 2014). Ning et al (2015) developed a two-dimensional (2-D) fully non-linear numerical wave flume (NWF) based on a timedomain higher-order boundary element method (HOBEM) This model used it to investigate the influence of the immergence and width of the front wall and the width of air chamber on the hydrodynamic performance of a fixed OWC wave energy device (Ning et al, 2016). A two-dimensional fully non-linear numerical model developed using the potential flow theory and the time-domain HOBEM developed by Ning et al (2015) is used to investigate the hydrodynamic performance of this stepped bottom OWC energy harvester. It can be observed that the present numerical model is in fair agreement with the experimental data in both the high and low frequency range but has a slight difference in the mid-frequency range, most noticeably between 0.7 ≤ Kh ≤ 1.2
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