An Investigation Into the Non-Linear Effects Resulting From Air Cushions in the Orecon Oscillating Water Column (OWC) Device

2009 ◽  
Author(s):  
Jim L. Lye ◽  
David T. Brown ◽  
Fraser Johnson
Keyword(s):  
Water Column ◽  
Mooring Line ◽  
Oscillating Water Column ◽  
Trapped Air ◽  
Model Scale ◽  
Sea Bed ◽  
Structural Responses ◽  
Linear Effects ◽  
The Waves ◽  
Base Structure

When designing an Oscillating Water Column (OWC) device, the motions and structural responses in waves are of great interest. However, predictions of these motions are complicated by the presence of air chambers above a large proportion of the waterplane area. Modeling the stiffness provided by air cushions at model scale presents a number of problems as air stiffness does not scale according to the laws of Froude scaling. To-date, the closest analogy might be an air-lifted gravity base structure, or crane vessel. However, in an OWC device, the air is not trapped as it is allowed to vent through a turbine. As a result, in still water, none of the mass of the buoy is supported by the air column. However, as the buoy is subjected to waves of increasing height the influence of the air chambers on the motions response becomes more pronounced. Experiments into the behavior of structures with trapped air springs have focused largely on benign sea conditions as the air cushions are generally used in vessels or structures involved with installation operations or similar. In contrast, the behavior of an OWC device must be predicted in all conditions up to, and including, survival conditions. BPP-TECH are providing technical support to the designers of the Orecon MRC wave energy buoy. This buoy uses chambers of varying drafts to generate electricity from the waves. The buoy is tension moored to the sea bed in order to constrain the heave motions to maximize the air pressure within the chambers as waves pass. A series of tank tests were undertaken at the OCEANIDE facility in order to investigate the motions of the buoy while tension moored and also measure the mooring line tensions. This paper will focus on the methods used to represent the air chambers at model scale and will present the results of the tests. A variety of different orifice sizes were used in the test campaign in order to provide a spread of values that would offer an insight into the effect of the air chambers on the motions of the structure in waves.

scholarly journals Experimental Study of a Moored Floating Oscillating Water Column Wave-Energy Converter and of a Moored Cubic Box

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1834 ◽  
Author(s):  
Minghao Wu ◽  
Vasiliki Stratigaki ◽  
Peter Troch ◽  
Corrado Altomare ◽  
Tim Verbrugghe ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Wave Energy Converter ◽  
Surface Elevation ◽  
Mooring Line ◽  
Oscillating Water Column ◽  
Energy Converter ◽  
Large Wave ◽  
Water Surface Elevation

This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has been introduced to cover the existing data scarcity and knowledge gaps regarding response of moored floating OWC WECs. The obtained data will be available in the future for the validation of nonlinear numerical models. The experiment focuses on the assessment of the nonlinear motion and mooring-line response of a 1:25 floating moored OWC WEC model to regular waves. The OWC WEC model motion has 6 degrees of freedom and is limited by a symmetrical 4-point mooring system. The model is composed of a chamber with an orifice on top of it to simulate the power-take-off (PTO) system and the associated damping of the motion of the OWC WEC model. In the first place, the motion response in waves of the moored floating OWC WEC model is investigated and the water surface elevation in the OWC WEC chamber is measured. Secondly, two different mooring-line materials (iron chains and nylon ropes) are tested and the corresponding OWC WEC model motions and mooring-line tensions are measured. The performance of these two materials is similar in small-amplitude waves but different in large wave-amplitude conditions. Thirdly, the influence of different PTO conditions is investigated by varying the diameter of the top orifice of the OWC WEC model. The results show that the PTO damping does not affect the OWC WEC motion but has an impact on the water surface elevation inside the OWC chamber. In addition, an unbalanced mooring configuration is discussed. Finally, the obtained data for a moored cubic model in waves are presented, which is a benchmarking case for future validation purposes.

scholarly journals Optimization of Radial Impulse Turbine for Oscillating Water Column Wave Renewable Energy

2019 ◽  
Vol 8 (12) ◽  
pp. 5699-5703
Keyword(s):  
Water Column ◽  
Oscillating Water Column ◽  
Peak Efficiency ◽  
Impulse Turbine ◽  
Trapped Air ◽  
Turbine Efficiency ◽  
Turbine Performance ◽  
Radial Turbine ◽  
Wide Range ◽  
Computational Fluid Dynamics Cfd

An oscillating water column (OWC) extracts the power of waves by trapping air above a water column. This trapped air is compressed and decompressed by the wave action flow inside a turbine power to the mechanical power during process, and it is important as the turbines are expected to operate in oscillating and reversing flows over a wide range of conditions. The objectives of this study are to determine and analyze the type of radial impulse turbine of OWC and to optimize the performance of a radial impulse turbine for OWC by using Computational Fluid Dynamics (CFD). This requires a comprehensive investigation on turbine configuration, turbine efficiency, OWC integration, and turbine operation with respect to climate condition. The outcome of this study to settle the main drawbacks of radial turbine namely lower peak efficiency and damping on OWC can be considered. Later, these problems will be further study to identify the behavior of the airflow through the machine, sources of energy loss, and impact of different parameters on the turbine performance.

scholarly journals Modelling of the multi-chamber oscillating water column in regular waves at model scale

2017 ◽  
Vol 136 ◽  
pp. 316-322 ◽  
Author(s):  
Mohammad Shalby ◽  
Paul Walker ◽  
David G. Dorrell
Keyword(s):  
Water Column ◽  
Oscillating Water Column ◽  
Regular Waves ◽  
Model Scale

Wave power extraction from an oscillating water column at the tip of a breakwater

2009 ◽  
Vol 626 ◽  
pp. 395-414 ◽  
Author(s):  
HERVÉ MARTINS-RIVAS ◽  
CHIANG C. MEI
Keyword(s):  
Water Column ◽  
Angle Of Incidence ◽  
Oscillating Water Column ◽  
Sea Waves ◽  
Power Extraction ◽  
Grid Connection ◽  
Simple Geometry ◽  
Construction Operation ◽  
The Waves ◽  
Extracted Power

To reduce the costs of construction, operation, maintenance, energy storage and grid connection, some devices for extracting energy from sea waves are likely to be installed on the coast. We study theoretically a single oscillating water column (OWC) installed at the tip of a long and thin breakwater. The linearized problems of radiation and scattering for a hollow cylinder with an open bottom are then solved by the usual method of eigenfunction expansions and integral equations. Since a thin breakwater is the limit of a wedge, an exact solution for the diffraction by a solid cylinder at the tip of a wedge is derived to facilitate the analysis. Following Sarmento & Falcão (J. Fluid Mech., vol. 150, 1985, pp. 467–485), power takeoff by Wells turbines is modelled by including air compressibility in the chamber above the water surface. The effects of air compressibility on the extraction efficiency is studied. It is shown that for this simple geometry the angle of incidence affects the waves outside the structure but not the extracted power.

scholarly journals The Effect of Mooring Line Parameters in Inducing Parametric Resonance on the Spar-Buoy Oscillating Water Column Wave Energy Converter

2020 ◽  
Vol 8 (1) ◽  
pp. 29 ◽  
Author(s):  
Giuseppe Giorgi ◽  
Rui P. F. Gomes ◽  
Giovanni Bracco ◽  
Giuliana Mattiazzo
Keyword(s):  
Water Column ◽  
Parametric Resonance ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Production Efficiency ◽  
Parametric Instability ◽  
Mooring Line ◽  
Nonlinear Phenomenon ◽  
Oscillating Water Column ◽  
Highly Nonlinear

Although it is widely accepted that accurate modeling of wave energy converters is essential for effective and reliable design, it is often challenging to define an accurate model which is also fast enough to investigate the design space or to perform extensive sensitivity analysis. In fact, the required accuracy is usually brought by the inclusion of nonlinearities, which are often time-consuming to compute. This paper provides a computationally efficient meshless nonlinear Froude–Krylov model, including nonlinear kinematics and an integral formulation of drag forces in six degrees of freedom, which computes almost in real-time. Moreover, a mooring system model with three lines is included, with each line comprising of an anchor, a jumper, and a clump weight. The mathematical model is used to investigate the highly-nonlinear phenomenon of parametric resonance, which has particularly detrimental effects on the energy conversion performance of the spar-buoy oscillating water column (OWC) device. Furthermore, the sensitivity on changes to jumper and clump-weight masses are discussed. It is found that mean drift and peak loads increase with decreasing line pre-tension, eventually leading to a reduction of the operational region. On the other hand, the line pre-tension does not affect power production efficiency, nor is it able to avoid or significantly limit the severity of parametric instability.

Floating Moored Oscillating Water Column With Meshless SPH Method

2018 ◽  
Author(s):  
Alejandro J. C. Crespo ◽  
Matthew Hall ◽  
José M. Domínguez ◽  
Corrado Altomare ◽  
Minghao Wu ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Coupled Model ◽  
Physical Modelling ◽  
Numerical Results ◽  
Mooring Line ◽  
Oscillating Water Column ◽  
Mooring Lines ◽  
Wave Energy Converters ◽  
Energy Converters

The meshless method called Smoothed Particle Hydrodynamics (SPH) is here proposed to simulate floating Oscillating Water Column (OWC) Wave Energy Converters (WECs). The SPH-based DualSPHysics code is coupled with MoorDyn, an open-source dynamic mooring line model. The coupled model is first validated using laboratory tests of a floating solid box moored to the wave flume bottom using four mooring lines interacting with regular waves. The numerical free-surface elevation at different locations, the motions of the floating solid box (heave, surge and pitch) and the tensions in the mooring lines are compared with the experimental data. Secondly, the coupled model is employed to simulate a floating OWC WEC moored to the sea bottom, while numerical results are also validated using data from physical modelling. The numerical results are promising to simulate floating OWC WECs. However, some discrepancies are noticed since the simulations presented in this work only consider a single-phase (water) so the full OWC WEC behaviour is only partially reproduced. Nevertheless, considering the aforementioned limitations, DualSPHysics can be used at this stage as complementary tool to physical modelling for a preliminary design of floating wave energy converters.

scholarly journals Oscillating water column plant

2021 ◽  
Vol 44 ◽  
pp. 47-50
Author(s):  
Dan Maimon
Keyword(s):  
Environmental Impact ◽  
Water Column ◽  
Wave Motion ◽  
Electrical Energy ◽  
Oscillating Water Column ◽  
Economical Method ◽  
Column System ◽  
The Waves ◽  
Column Plant ◽  
No Emissions

This article is describing the way of construction and operation of an oscillating water column system in order to recover as much as possible from the waves energy. The oscillating water column plant is used for the production of electrical energy by tidal currents, and it is currently the most widespread and economical method for the conversion of wave motion. The environmental impact of these infrastructures remains very low: no emissions of gas or any waste during their operation. In addition, the swell is a formidable source of energy.

scholarly journals Hydrodynamic performance analysis of a shore fixed oscillating water column wave energy converter in the presence of bottom variations

2019 ◽  
Vol 234 (1) ◽  
pp. 37-47
Author(s):  
Piyush Mohapatra ◽  
Trilochan Sahoo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Column ◽  
Boundary Integral ◽  
Hydrodynamic Performance ◽  
Design Stage ◽  
Pressure Jump ◽  
Front Wall ◽  
Oscillating Water Column ◽  
Sea Bed

In this study, the effect of the stepped sea bed on the hydrodynamic performance of an oscillating water column device is investigated using computational fluid dynamics . This investigation is performed in a numerical wave tank modeled using ANSYS Fluent, which incorporates a transient, multiphase volume of fluid method to track the air–water interface. The power take-off unit is modeled as a porous zone in the flow field to produce the pressure jump versus flow characteristics that of a real air turbine. The efficiency of the chamber with and without the stepped bottom is analyzed and compared with known results in the literature. The flow parameters such as the temporal evolution and distribution of the pressure field, velocity field and free surface are studied to understand the performance of the proposed model. The study reveals that there is an improvement in hydrodynamic efficiency with the inclusion of the stepped bottom beneath the oscillating water column chamber, which is in agreement with the previous studies carried out using analytical and boundary integral equation methods. Moreover, the computational fluid dynamics model helps to understand the flow dynamics inside the oscillating water column chamber in a more intricate manner compared to the potential flow-based studies pursued in the literature. The formation of vortices within the oscillating water column chamber, near the front wall and stepped bottom could be captured, which affects the chamber performance to a certain extent. Overall, the study could be useful in the initial design stage of shore fixed oscillating water column devices.

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