Force Reacting Principle Applied to a Heave Point Absorber Wave Energy Converter (original) (raw)
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Buoy Analysis in a Point-Absorber Wave Energy Converter
IEEE Journal of Oceanic Engineering
In this paper, a single-body point absorber system is analyzed to enhance its power absorption performance. The wave energy converter consists of a single floating body coupled to a direct-drive power takeoff system placed on the seabed. The geometry of a cylindrical buoy with large draft is modified, obtaining a particular geometry that is used to enhance the power absorption of the wave converter at a given site and at a finite depth. A numerical analysis tool (NEMOH) is used to obtain the buoy's frequency-dependent hydrostatic parameters; in addition, the buoy's dimensions are parameterized to tune the natural frequency of the oscillating system toward the frequency of dominant incident waves, thus enhancing wave power absorption for a specific wave frequency range. Furthermore, the damping influence of the power takeoff system on the performance of the wave energy converter is also considered.
International Marine Energy Journal, 2021
A single-body point absorber system is analysed to improve its power absorption at a finite water depth. The proposed wave energy converter consists of a single floating body coupled to a direct-drive power take-off system placed on the seabed. The structure of a cylindrical buoy with large draft is changed by a single body composed of three structures rigidly coupled, reducing its volume and improving its frequency-dependent hydrostatic parameters that are obtained through a numerical analysis tool called NEMOH. The undamped natural frequency of the oscillating system is tuned to a specified wave period and the performance of the WEC system is obtained assuming a linear Power Take-Off system. In time domain, the performance of the WEC device is carried-out under a regular (sinusoidal) and irregular incident wave profile. Comparing the performance of the WEC system using the cylindrical and the proposed buoy outcomes that the system with the proposed buoy is able to absorb more ene...
Journal of Offshore Mechanics and Arctic Engineering, 2013
The present paper summarizes analyses of a two-body floating wave energy converter (WEC) to determine the mooring tension and the effect of the mooring system on energy capture. Also, the effect of the power take-off (PTO) is assessed. An axisymmetric Wavebob-type WEC is chosen as the object of investigation. However, the PTO system is modeled in a simplified manner as ideal linear damping and spring terms that couple the motions of the two bodies. The analysis is performed using SIMO, which is a time domain simulation tool that accommodates the simulation of multibody systems with hydrodynamic interactions. In SIMO, docking cone features between the two bodies allow movement as per actual operation, and fenders are applied to represent end stops. Six alternative mooring configurations are applied to investigate the effect of mooring on power capture. Mooring analysis is performed to determine the necessary capacity of mooring lines for each configuration to carry the tension due to the WEC motion in extreme conditions. Hydrodynamic loads are determined using WAMIT. We assumed that the WEC will be operated to capture wave power at the Yeu site in France. The analysis is performed for several regular and irregular wave conditions according to wave data available for that site. Simulations are performed to study the effect of the PTO system, end stops settings and several mooring configurations on power capture.
International Journal of Marine Energy
Compact arrays of small wave absorbers have been proposed as an advantageous solution for the extraction of wave energy when compared to a big isolated point absorber. Numerous challenges are associated with the numerical modeling of such devices, notably the computation of the hydrodynamic interactions among the large number of floats of which they are composed. Efficient calculation of the first-order linear hydrodynamic coefficients requires dedicated numerical tools, as their direct computation using standard boundary element method (BEM) solvers is precluded. In this paper, the Direct Matrix Method interaction theory by Kagemoto and Yue (1986) is used as an acceleration technique to evaluate the performance of a generic wave energy converter (WEC) inspired by the Wavestar SC-concept and to perform layout optimization. We show that there exists an optimum number of floats for a given device footprint. Exceeding this number results in a "saturation" of the power increase, which is undesirable for the economic viability of the device. As in previous studies on multiple absorber WECs, significant differences were observed in energy production among floats, due to hydrodynamic interactions.
Development and Testing of a Point Absorber Wave Energy Conversion
Volume 5: Ocean Space Utilization; Ocean Renewable Energy, 2011
Wave energy conversion as a means for small scale energy production is approaching commercial viability. This paper presents the undergoing development of a wave energy conversion device at the University of Hawaii at Manoa. The device is a three part point absorber with two buoys, one floating and absorbing incoming waves; the other maintaining tension on the third mechanism, the submerged power-takeoff unit. This design is discussed as three concept configurations for WEC construction. The analytical solution is developed, and the buoys response is computed due to a selected and analyzed sea-state.
In this paper, a simple buoy was used for the power generation tests with a DE powered by waves in the two-dimensional wave tank and the experimental results were analyzed. This research result shows that the optimization of equipment shape and buoy based on the characteristics of the wave for power generation is very important. The extension and contraction of the DE are determined by the motion characteristics of the Heave of the simple shaped buoy model. Furthermore, in order to have freedom in tuning the motion characteristics of Heave, we found that a device capable of setting the spring characteristics of the DE to the smallest possible size with respect to the size of the floating body is necessary. By well matching these factors, high power generation with high efficiency can be realized in a real sea area.
Development of a novel point absorber in heave for wave energy conversion
Renewable Energy, 2014
This paper presents an advanced design methodology for electric power generation from the vast ocean wave energy. A novel single-buoy heaving device called wave energy converter (WEC) based on hydrostatic transmission (HST), or can be shortened as HSTWEC, is proposed to convert mechanical energy generated by ocean waves into electric energy. Modeling and simulations with both regular and irregular waves were then carried out to investigate working performances of the designed HSTWEC. The results showed that more than 78% of wave energy can be absorbed. In addition, an adaptive controller was designed to improve the performance of the suggested device. Effectiveness of the overall HSTWEC control system was finally proved by simulations.
This paper presents, assesses, and optimizes a point absorber wave energy converter (WEC) through numerical modeling, simulation, and analysis. Wave energy conversion is a technology uniquely suited for assisting in power generation in the offshore oil and gas platforms. A linear frequency domain model is created to predict the behavior of the heaving point absorber WEC system. The hydrodynamic parameters are obtained with AQWA, a software package based on boundary element methods. A linear external damping coefficient is applied to enable power absorption and an external spring force is introduced to tune the point absorber to the incoming wave conditions. The external damping coefficient and external spring forces are the control parameters, which need to be optimized to maximize the power absorption. Two buoy shapes are tested and a variety of diameters and drafts are compared. Optimal shape, draft, and diameter of the model are then determined to maximize its power absorption capacity. Downloaded From: http://energyresources.asmedigitalcollection.asme.org/ on 05/23/2014 Terms of Use: http://asme.org/terms
An Analysis Of The Performances Of Various Buoys As The Floats Of Wave Energy Converters
2016
The power generated by eight point absorber type wave energy converters each having a different buoy are calculated in order to investigate the performances of buoys in this study. The calculations are carried out by modeling three different sea states observed in two different locations in the Black Sea. The floats analyzed in this study have two basic geometries and four different draft/radius (d/r) ratios. The buoys possess the shapes of a semi-ellipsoid and a semi-elliptic paraboloid. Additionally, the draft/radius ratios range from 0.25 to 1 by an increment of 0.25. The radiation forces acting on the buoys due to the oscillatory motions of these bodies are evaluated by employing a 3D panel method along with a distribution of 3D pulsating sources in frequency domain. On the other hand, the wave forces acting on the buoys which are taken as the sum of Froude-Krylov forces and diffraction forces are calculated by using linear wave theory. Furthermore, the wave energy converters ar...