Performance analysis of dual sphere wave energy converter integrated with a chambered breakwater system

Abstract

The integration of a dual sphere wave energy converter with a chambered breakwater system is found to enhance the performance of both structures. Such an integrated system is well suited for regions that receive medium wave energy potential at an estimated annual mean wave power less than 30 kW/m. The hydrodynamic efficiency of the integrated system is investigated through experiments. The dual sphere wave energy converter was installed near to the porous and impermeable wall of the chambered breakwater system in the integrated system. The power generation capability of the dual sphere wave energy converter exposed to the wave elevations measured inside the chamber is numerically investigated in the present study. The average power generation capability of the dual sphere wave energy converter is found to be enhanced by 63% after integration with the chambered breakwater. The significance of the position of installing the wave energy converter inside the chamber has been highlighted. The economic competitiveness of the wave energy converter is found to be improved after its integration with the chambered breakwater system.

Introduction

In a recent report by Renewables global status report (2019), the estimated global electricity production from renewable sources is found to be 26.2% with a major contribution of 15.8% from hydropower [1]. Ocean energy, on the other hand, has contributed to 0.4% towards electricity production. Amongst various renewable energy resources, ocean wave energy has a huge potential due to its abundance covering over 71% of the earth. Falcão reviewed the development of wave energy converters, their hydrodynamics, and how the control system for wave energy absorption has evolved since the 1970s [2]. Among the WECs classified based on their operating principle, location, and size of the converter [3], a point absorber was found to be the cost-efficient technology [4]. Though there have been advancements in the area of development of different wave energy converter (WEC) designs the high cost of construction limits its commercialization. Integrating the WEC with other marine facilities is found to improve the power generation performance of the WECs and thereby promote cost-sharing [5, 6]. Oscillating water column [[7], [8], [9]] and overtopping breakwater [[10], [11], [12], [13]] are the two types of WEC successfully integrated with existing coastal defense structures. Introducing a WEC in front of the seawalls is found to improve the efficiency of WEC [14, 15]. The performance of a single WEC in front of an infinite vertical wall has been investigated through the analytical method [[16], [17], [18]]. A numerical study also analyzed the performance of a heaving point absorber near a vertical wall and found that the performance of the device was significantly improved [19]. The integration of WEC with other marine facilities for the medium wave energy potential regions was reported to be beneficial [20]. In India, the approximated wave power potential across the coastline of 7500 km is estimated to be about 41 GW [21]. Also, 23% of the Indian coastline is reported to be affected by erosion [22]. Integrating a WEC with the chambered breakwater (CBW), a concept presented by Jarlan [23] is found to improve the performance of the WEC and CBW [24]. The wave attenuation characteristics of single and multiple CBW were investigated in past studies [[25], [26], [27], [28], [29]]. The reflection and wave attenuation characteristics of the CBW are found to depend primarily on the porosity of the front wall and relative chamber width. The wave absorbing ability of the Jarlan type perforated breakwater was improved after installing a horizontal porous plate inside the chamber [30]. Various configurations of Jarlan-type perforated wall caissons considering the wave reflection, transmission, and wave forces from different cases of perforated/slotted coastal structures were classified [31]. The past studies revealed that the studies attempting to investigate the utilization of the wave energy inside the chambered breakwater using a WEC are scarce. Krishnendu and Balaji [24] investigated an idea of integrating the CBW with the single heaving type WEC system; this offered a dual functioning performance in which, one can absorb the wave energy and another can partially convert the trapped wave energy to usable power. In the integrated system, the incident waves are allowed to pass through the seaside porous wall of the CBW, and by varying the chamber width to wavelength (B/L) ratio, these waves are trapped inside the chamber. The trapped oscillating wave energy can then be extracted using a suitable WEC without compromising the primary purpose of the CBW to absorb the energy. The performance of single S-WEC integrated with the CBW was studied by varying the distance of its installation and examined for its adopted range of wave conditions in the previous study. In one case the S-WEC was installed at a position 0.50 m away from the center of the chamber towards the porous wall and in the other case, the S-WEC was installed at the same distance from the center towards the impermeable wall [24].

The present study investigates the performance of dual S-WEC, installed at two different positions working concurrently inside the chamber. In this system, the first S-WEC is installed near to the porous wall and the second S-WEC is installed near to the impermeable wall, at a distance of 0.20 m from the respective walls. The performance of the single and dual S-WEC integrated with the CBW is compared and the significance of the position of the S-WEC inside the chamber in improving its performance is highlighted. The paper is structured as follows. Section 2 describes the experimental and numerical details. The validation of the numerical model is presented under Section 3 (Results and Discussion) followed by the outcomes from this study described in Section 4 (Conclusions).