Parametric Evaluation of the Performance Characteristics of Tight Moored Wave Energy Converters

2005 ◽  
Author(s):  
Spyridon A. Mavrakos ◽  
Georgios M. Katsaounis
Keyword(s):  
Wave Energy ◽  
Wave Climate ◽  
The Body ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Diffraction Radiation ◽  
Climate Conditions ◽  
Wave Energy Converters ◽  
Energy Converters

The paper aims at presenting a numerical model to predict performance characteristics of tight moored vertical axisymmetric wave energy converters that are allowed to move in heave, pitch and sway modes of motion. The hydrodynamic characteristics (exciting wave forces, hydrodynamic parameters) of the floats are evaluated using a linearized diffraction–radiation method of analysis that is suited for the type of bodies under consideration. According to this method matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain. Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account. The floating WEC is connected to an underwater piston that feeds a hydraulic system with pressurized fluid. Numerical results showing parametrically the performance characteristics in terms of the expected power production for several types of floats that are exposed to the wave climate conditions commonly encountered in the Mediterranean area are presented and discussed.

Effect of Floaters’ Geometry on the Performance Characteristics of Tightly Moored Wave Energy Converters

2009 ◽  
Author(s):  
Spyros A. Mavrakos ◽  
Georgios M. Katsaounis ◽  
Michalis S. Apostolidis
Keyword(s):  
Wave Energy ◽  
Cylindrical Body ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Diffraction Radiation ◽  
Wave Energy Converters ◽  
Internal Cone ◽  
Constant Displacement ◽  
Energy Converters

The paper deals with the investigation of the effect that floaters’ hydrodynamics has on the performance characteristics of tightly moored vertical axisymmetric wave energy converters. Several geometries of WEC’s floaters have been examined by assuming that they have constant displacement. Specifically, a cylindrical body with and without vertical and horizontal skirts at its bottom, a cone and a two–body, piston–like arrangement, which consists of an internal cone and an exterior torus, have been investigated and comparatively assessed. The WEC’s first-order hydrodynamic characteristics, i.e. their exciting wave forces and the correspondent hydrodynamic parameters, are evaluated using a linearized diffraction–radiation semi-analytical method. A dynamical model for evaluating of the floaters’ performance in time domain is developed that properly accounts for the floaters hydrodynamic behavior, the modeling of the hydraulic system and of the power take–off mechanism. The effect of the floaters geometry on the efficiency of the converter is analyzed through the results for the power absorption, under the excitation of several sea states.

scholarly journals Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1985 ◽  
Author(s):  
Dimitrios N. Konispoliatis ◽  
Spyridon A. Mavrakos
Keyword(s):  
Wave Energy ◽  
Cylindrical Wave ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Theoretical Evaluation ◽  
Power Absorption ◽  
Array Configuration ◽  
Wave Energy Converters ◽  
Vertical Breakwater ◽  
Energy Converters

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave.

scholarly journals Wave Energy Assessment at Valencia Gulf and Comparison of Energy Production of Most Suitable Wave Energy Converters

2020 ◽  
Vol 17 (22) ◽  
pp. 8473
Author(s):  
Raúl Cascajo ◽  
Emilio García ◽  
Eduardo Quiles ◽  
Francisco Morant ◽  
Antonio Correcher
Keyword(s):  
Renewable Energy ◽  
Wave Energy ◽  
Energy Demand ◽  
Alternative Energy ◽  
Average Energy ◽  
Wave Climate ◽  
Energy Output ◽  
Renewable Sources ◽  
Wave Energy Converters ◽  
Energy Converters

Seaports’ energy strategy should rely on the use of renewable energy. Presently, the share of renewable energy used by many of the ports worldwide is negligible. Some initiatives are in the process of implementation to produce some of the energy used by the Port of Valencia, one the largest ports in the Mediterranean Basin. Among these initiatives, a photovoltaic plant with an installed capacity of 5.5 MW is under a tendering process and the assessment studies for the deployment of three to five windmills are close to being finished. However, this is not enough to make it a “zero emissions port” as some of the energy demand would still be covered by fossil fuels. Therefore, we should consider clean alternative energy sources. This article analyses the wave energy resources in the surroundings of the Port of Valencia using a 7-year series of data obtained from numerical modelling (forecast). The spatial distribution of wave power is analysed using data from 3 SIMAR points at Valencia Bay and is compared to the data obtained by the Valencia Buoy I (removed in 2005). The obtained results are used to estimate the power matrices and the average energy output of two wave energy converters suitable to be integrated into the port’s infrastructure. Finally, the wave energy converters’ production is compared to the average amount of energy that is forecast to be obtained from other renewable sources such as solar and wind. Due to the nature of the Gulf’s wave climate (mostly low waves), the main conclusion is that the energy obtainable from the waves in the Valencia Gulf will be in correlation with such climate. However, when dealing with great energy consumers every source of production is worthwhile and further research is needed to optimize the production of energy from renewable sources and its use in an industrial environment such as ports.

Performance Characteristics of a Tightly Moored Piston-Like Wave Energy Converter Under First- and Second-Order Wave Loads

2008 ◽  
Author(s):  
Spyros A. Mavrakos ◽  
George M. Katsaounis ◽  
Ioannis K. Chatjigeorgiou
Keyword(s):  
Wave Energy ◽  
Second Order ◽  
Wave Energy Converter ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Diffraction Radiation ◽  
Wave Loads ◽  
Energy Converter ◽  
Eigenfunction Expansions ◽  
First Order

The paper deals with the presentation of a model to predict performance characteristics of a tightly moored piston-like wave energy converter which is allowed to move in heave, pitch and sway modes of motion. The WEC’s piston-like arrangement consists of two floating concentric cylinders, the geometry of which allow the existence of a cylindrical moonpool between the external cylinder, the ‘torus’ and the inner cylinder, the ‘piston’. The first-order hydrodynamic characteristics of the floating device, i.e. exciting wave forces and hydrodynamic parameters, are evaluated using a linearized diffraction-radiation semi-analytical method of analysis that is suited for the type of bodies under consideration. According to the analysis method used, matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain (Mavrakos et al. 2004, 2005). Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account (Cummins, 1962; Faltinsen, 1990). The floating WEC is connected to an underwater hydraulic cylinder that feeds a hydraulic system with pressurized oil. The performance of the system under the combined excitation of both first- and second order wave loads is here analyzed. To this end, the diffraction forces originated from the second order wave potentials are computed using a semi-analytical formulation which, by extension of the associated first-order solution, is based on matched axisymmetric eigenfunction expansions.

The effect of arrays of wave energy converters on the nearshore wave climate

2019 ◽  
Vol 172 ◽  
pp. 373-384 ◽  
Author(s):  
Reduan Atan ◽  
William Finnegan ◽  
Stephen Nash ◽  
Jamie Goggins
Keyword(s):  
Wave Energy ◽  
Wave Climate ◽  
Wave Energy Converters ◽  
Energy Converters

scholarly journals Validation of CFD for the Determination of Damping Coefficients for the Use of Wave Energy Converters Modelling

2013 ◽  
Author(s):  
Olivia Thilleul ◽  
Aurélien Babarit ◽  
Aurélien Drouet ◽  
Sébastien Le Floch
Keyword(s):  
Wave Energy ◽  
Turbulence Models ◽  
Computational Time ◽  
Diffraction Radiation ◽  
Viscous Effects ◽  
Drag Coefficients ◽  
Damping Coefficients ◽  
Wave Energy Converters ◽  
Convergence Study ◽  
Energy Converters

Diffraction-radiation codes enable to model the behaviour of Wave Energy Converters (WEC) and seakeeping of ships on many sea-states with very little computational time. However, the viscous effects are neglected and therefore the simulations lead to relatively inaccurate values. The inaccuracy mainly occurs at the resonance frequency, especially in roll motions for which viscous effects are of major importance. Classically, the viscous effects are represented by adding viscous damping coefficients obtained either from experimental data or analytical approaches based on numerous approximations. In order to improve the accuracy of the diffraction-radiation solvers, the damping coefficients can also be calculated from Computational Fluid Dynamics (CFD) simulations. The first part of this paper presents the three CFD solvers and turbulence models used in this validation study: ICARE and ISIS-CFD are developed by Ecole Centrale de Nantes and Star-CCM+ is a general purpose solver developed by CD-adapco. For each case, a preferred solver is chosen and a second solver is used for verification in most cases. The second part briefly presents the theory that obtains drag coefficients in oscillatory flows, which are closely related to damping coefficients in waves. Each of the three following parts introduces the experimental test cases to which numerical results are compared to. The numerical parameter convergence study leads to a choice of around 200 timesteps per period with an adapted mesh enabling to obtain drag coefficients with errors lower than 5%. A mesh convergence study in the wake area leads to a mesh refinement of around 2 to 2.5 % of the body characteristic length. In order to reduce the computational time, the total number of cells can be decreased by mainly refining locations where specific flow detachment occurs, such as body corners or sharp edges. Turbulence models are also varied. Validation results are finally presented in terms of single or coupled damping coefficients and added mass coefficients. They are presented for various non-dimensional numbers such as Keulegan-Carpenters and Reynolds number.

scholarly journals Frequency-Based Performance Analysis of an Array of Wave Energy Converters around a Hybrid Wind–Wave Monopile Support Structure

2020 ◽  
Vol 9 (1) ◽  
pp. 2
Author(s):  
Sofia Gkaraklova ◽  
Pavlos Chotzoglou ◽  
Eva Loukogeorgaki
Keyword(s):  
Wave Energy ◽  
Wind Wave ◽  
Radial Distance ◽  
Boundary Integral ◽  
Irregular Waves ◽  
Diffraction Radiation ◽  
Power Absorption ◽  
Wave Energy Converters ◽  
Oblate Spheroidal ◽  
Energy Converters

In this paper, we investigate, in the frequency domain, the performance (hydrodynamic behavior and power absorption) of a circular array of four semi-immersed heaving Wave Energy Converters (WECs) around a hybrid wind–wave monopile (circular cylinder). The diffraction/radiation problem is solved by deploying the conventional boundary integral equation method. Oblate-spheroidal and hemispherical-shaped WECs are considered. For each geometry, we assess the effect of the array’s net radial distance from the monopile and of the incident wave direction on the array’s performance under regular waves. The results illustrate that by placing the oblate spheroidal WECs close to the monopile, the array’s power absorption ability is enhanced in the low frequency range, while the opposite occurs for higher wave frequencies. For hemispherical-shaped WECs, the array’s power absorption ability is improved when the devices are situated close to the monopile. The action of oblique waves, with respect to the WECs’ arrangement, increases the absorbed power in the case of oblate spheroidal WECs, while these WECs show the best power absorption ability among the two examined geometries. Finally, for the most efficient array configuration, consisting of oblate spheroidal WECs situated close to the monopile, we utilize an “active” Power Take-Off (PTO) mechanism, facilitating the consideration of a variable with frequency PTO damping coefficient. By deploying this mechanism, the power absorption ability of the array is significantly enhanced under both regular and irregular waves.

Hydrodynamic Behavior of Overtopping Wave Energy Converters Built in Sea Defense Structures

2010 ◽  
Author(s):  
Lander Victor ◽  
Jens Peter Kofoed ◽  
Peter Troch
Keyword(s):  
Wave Energy ◽  
Sea Water ◽  
Wave Climate ◽  
Wave Flume ◽  
Wave Energy Converters ◽  
Physical Model Tests ◽  
Vertical Walls ◽  
Linear Slope ◽  
Energy Converters

Many sea defense structures need to be adapted to the rising sea water level and changing wave climate due to global warming. The accordingly required investments open perspectives for wave energy converters (WECs) — that are built as part of the sea defense structures — to become economically viable. In this paper the average overtopping discharges q of overtopping wave energy converters built in sea defense structures are studied. Physical model tests with this type of devices have been carried out in a wave flume leading to experimentally determined values for the average overtopping discharge q. These experimental data are compared with predicted average overtopping discharges using existing empirical formulae from literature — derived mainly for sea defense structures. Overtopping WECs have small relative crest freeboard heights and smooth slopes to maximize overtopping, which is contradictive to the basic role of sea defense structures. As a consequence, the experimentally achieved average overtopping discharges are situated in a range that is not well covered by the existing traditional prediction formulae. The presented results for linear-slope overtopping WECs fill the gap between those for smooth dikes and those for plain vertical walls. The overtopping behavior in that particular range is discussed in this paper.

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