Littérature scientifique sur le sujet « VLFS equipped with OWC devices »

Abstract Oscillating Water Column systems (OWC) have been in the spotlight in the last 20 years since these devices are considered one of the most promising devices among wave energy technology. These systems produce electricity by means a generator driven by a turbine, which takes advantage of the bidirectional flow created by the OWC itself. Among these turbines suitable for bidirectional flows, it is possible to find radial impulse turbines, which are the focus of this work. Traditionally, the radial impulse turbines have shown lower efficiencies than their competitors. However, the radial turbines present interesting mechanical features and, recently, some research show that the difference has been reduced. Following this thread, this work deals with another modification in the radial impulse turbine looking for a further improvement. By using a validated CFD model, it has been analysed the influence of the lean angle of the blade. Until now, all the turbines present in the literature are leaned zero degrees, leading to a strong interaction between the guide vanes and the blades. This work shows results of the same turbine, equipped with blades leaning from -5deg to 25deg, in order to determine the influence such a modification on the maximum total-to-static efficiency. Results have revealed a slight improvement in the maximum efficiency for positive leaning angles, whereas negative angles drive the turbine to worse performance.

The increasing population density and the industrial expansion significantly affect the availability of land. In this context, the high modularity of Very Large Floating Structures (VLFSs) may indeed represent a promising alternative for multipurpose use. Furthermore, the interest for the sea as a source of renewable marine energy, particularly for wave energy, has tremendously increased in the last decade and years. Among the large diversity of Wave Energy Converters (WECs), the Oscillating Water Column (OWC) is one of the most promising concept. Moreover, when an OWC is incorporated in a VLFS, its efficiency in terms of wave energy absorption is not only increased, but also it has additionally the benefit of attenuating the heave motion of the floating structure. Hence, there is a growing interest in the development of an innovative VLFS equipped with OWC devices. In this scope, the mitigating effect of the OWC on the heave motion of the VLFS can be combined with an increased efficiency of the OWC, thus better contributing to supply energy for the facilities located on the floating system. The main goal of this PhD research is the investigation of a VLFS-OWC System conceived for a hypothetical installation in a Mediterranean area, characterized by a moderate wave climate. For this purpose, small-scale experiments have been carried out in the wave-current flume of the Maritime Engineering Laboratory (LABIMA) of Florence University. The laboratory tests focused on the effect of: (i) the OWC design parameters (i.e., OWC geometry); (ii) the incident wave conditions (i.e., regular and irregular wave trains); (iii) the damping induced by a non-linear air turbine (i.e., a self-rectifying impulse turbine) idealised by vents with different diameters in the OWC chamber roof; (iv) the length and the heave motion of the VLFS on the performance of the OWC, including the attenuating effect of the incorporated OWC on the heave motion of the VLFS-OWC system. The design of the fixed OWC, VLFS and VLFS-OWC models as well as the testing programme and laboratory procedures, are based on an extensive literature review of the available numerical and physical models on OWC devices and VLFS technologies. The main findings of this study may be summarized as follows: - the most dominant parameters affecting the performance of a fixed OWC are the chamber width (in wave propagation direction), the front wall draught and the damping induced by the air turbine; - the additional parameters affecting the efficiency of an OWC integrated in a VLFS are the length of the structure and the heave motion; - formulae are developed for predicting the heave motion of the VLFS-OWC system respectively, for regular waves and irregular waves; - formulae are developed for improving the prediction of the performance of a fixed OWC for a floating OWC (integrated in a VLFS) respectively, for regular irregular waves. These findings have contributed to improve the understanding of the functioning of the OWC device and the relative importance of the aforementioned parameters affecting the device under moderate wave climate.

This paper describes potential of PTO (Power Take-Off) and the damper effect of motion in a large scale pontoon type floating structure on which lots of oscillating water column (OWC) type wave energy convertors (WEC) are installed. It is enable to use upper space for utilizing marine renewable energy such as wind power, tidal power, wave power generation farm using large pontoon structure. Due to the concept, it should reduce cost of maintenance as well. For investigation of PTO and elastic motion behaviours of large floating structures, we calculated three types of models on which OWC devices were installed differently. We examined how much reduction was possible when including elastic motion effects and the fixed type which radiation wave was not taken into account. In this paper, a boundary condition in order to give effect of a free water surface with air pressure is theoretically modeled. We can directly consider influence of wave energy absorption to hydrodynamic forces and wave exciting forces on the floating structure with the Green’s function method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and vertical displacement within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. As a result, performance of PTO and hydroelastic motion of the floating structure increased when including elastic motion effect. In addition, expected value of annual PTO was about 4.4MW with 146 OWCs.

Abstract Oscillating water column (OWC) type wave energy converters (WECs) have been researched and developed. OWC WECs are relatively friendly to maintain them in operation because all of mechanical units are set above a sea water surface. In addition, a feature of an OWC device is similar to an air dumper system. Thus, it should be possible not only to harvest wave energy but also to reduce motion of a floating system at the same time. As well as WEC system should be used with other ocean renewable energies as a combined system. This paper describes hydrodynamic characteristics of OWC devices and wave fields around them of multi-OWC devices equipped large floating structures. For this research, the linear potential theory based in-house programme code was applied to calculate hydrodynamic performance of OWC regions and elastic motion behaviours of the structures. Besides, calculation results were compared with some experimental results of characteristics of OWC devices on reference papers published. Then we proved validity of the calculation method. We have quantitatively summarized how much the reduction effect can be seen according to the aircushion placement and the number of aircushions on the floating body. the paper investigated arrangement of OWC devices on the floating structure with several variations. Using the prediction method, effects of arrangement of OWC devices on the performances are investigated.

Very Large Floating Structures, so-called Mega-Floats, are the kind of social infrastructures. They are generally expected to keep their integrity for a long period, for example, more than 100 years. So, it is necessary to develop Long-Term Integrity Prediction and Diagnosis System to diagnose the soundness of Mega-Floats. In the present study, we paid our attention to dolphin-fender type mooring devices that pontoon type VLFS are equipped with. As a part of Long-Term Integrity Prediction and Diagnosis System, we developed a long-term integrity prediction code (Cumulative Fatigue Damage Prediction Code) to predict damage of these dolphins. We made an at-sea experiment with pontoon type VLFS model of 201.5 [m] length, 100 [m] breadth, and 3 [m] depth (We call this “At-Sea Experiment for Verifying Functions of Mega-Float Information Data Center”). The model had two dolphin-fender type mooring devices and we applied Cumulative Fatigue Damage Prediction Code to these devices.