scholarly journals Ocean Energy Systems Wave Energy Modeling Task 10.4: Numerical Modeling of a Fixed Oscillating Water Column

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1718
Author(s):  
Harry B. Bingham ◽  
Yi-Hsiang Yu ◽  
Kim Nielsen ◽  
Thanh Toan Tran ◽  
Kyong-Hwan Kim ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Free Surface ◽  
Water Column ◽  
Wave Energy ◽  
Potential Flow ◽  
Energy Systems ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Ocean Energy ◽  
Internal Chamber

This paper reports on an ongoing international effort to establish guidelines for numerical modeling of wave energy converters, initiated by the International Energy Agency Technology Collaboration Program for Ocean Energy Systems. Initial results for point absorbers were presented in previous work, and here we present results for a breakwater-mounted Oscillating Water Column (OWC) device. The experimental model is at scale 1:4 relative to a full-scale installation in a water depth of 12.8 m. The power-extracting air turbine is modeled by an orifice plate of 1–2% of the internal chamber surface area. Measurements of chamber surface elevation, air flow through the orifice, and pressure difference across the orifice are compared with numerical calculations using both weakly-nonlinear potential flow theory and computational fluid dynamics. Both compressible- and incompressible-flow models are considered, and the effects of air compressibility are found to have a significant influence on the motion of the internal chamber surface. Recommendations are made for reducing uncertainties in future experimental campaigns, which are critical to enable firm conclusions to be drawn about the relative accuracy of the numerical models. It is well-known that boundary element method solutions of the linear potential flow problem (e.g., WAMIT) are singular at infinite frequency when panels are placed directly on the free surface. This is problematic for time-domain solutions where the value of the added mass matrix at infinite frequency is critical, especially for OWC chambers, which are modeled by zero-mass elements on the free surface. A straightforward rational procedure is described to replace ad-hoc solutions to this problem that have been proposed in the literature.

Scale and Configuration Effects of an Airchamber on PTO of Oscillating Water Column Type Wave Energy Converters

2021 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shota Hirai ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Air Pressure ◽  
Scale Model ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Wave Energy Converters ◽  
Air Chamber ◽  
Energy Converters

Abstract Wave energy converters (WECs) have been extensively researched. The behaviour of the oscillating water column (OWC) in OWC WECs is extremely complex due to the interaction of waves, air, and turbines. Several problems must be overcome before such WECs can be put to practical use. One problem is that the effect of the difference in scale between a small-scale experimental model and a full-scale model is unclear. In this study, several OWC models with different scales and geometries were used in forced oscillation tests. The wave tank was 7.0 m wide, 24.0 m long, and 1.0 m deep. In the static water experiment, we measured the air pressure and water surface fluctuations in an air chamber. For the experiments, models with a box shape with an open bottom, a manifold shape with an open bottom, and a box shape with a front opening, respectively, were fabricated. Furthermore, 1/1, 1/2, and 1/4 scale models were fabricated for each shape to investigate the effects of scale and shape on the air chamber characteristics. Numerical calculations were carried out by applying linear potential theory and the results were compared with the experimental values. The results confirmed that the air chamber shape and scale affect the air pressure fluctuation and water surface fluctuation inside the OWC system.

Modeling of Oscillating Water Column wave energy systems

2016 ◽  
Author(s):  
A.J. Garrido ◽  
I. Garrido ◽  
J. Lekube ◽  
M. de la Sen ◽  
E. Carrascal
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Energy Systems ◽  
Oscillating Water Column

scholarly journals EVALUATION OF STATIC PRESSURE BEHAVIOR IN AN OSCILLATING WATER COLUMN WAVE ENERGY CONVERTER

2019 ◽  
Vol 18 (1) ◽  
pp. 36
Author(s):  
E. A. Pinto Jr ◽  
M. Das N. Gomes ◽  
L. A. O. Rocha ◽  
E. D. dos Santos ◽  
L. A. Isoldi
Keyword(s):  
Free Surface ◽  
Water Column ◽  
Wave Energy ◽  
Static Pressure ◽  
Sea Water ◽  
Renewable Energy Sources ◽  
Oscillating Water Column ◽  
Flow Acceleration ◽  
Pressure Behavior ◽  
Flow Through

The international scenario of non-renewable resources scarcity coupled with increasing energy demand are incentives for the diversification of the world's energy matrix with a focus on renewable energy sources. Among these sources, energy from sea waves is especially attractive because its global resource is estimated around 2 TW, comparable to the average electrical power consumed worldwide each year. There are currently several technologies proposed for the sea wave energy conversion into electricity. Among them it stands out the Oscillating Water Column (OWC) converter, which basically consists of a hydropneumatic chamber and a turbine duct where a turbine is installed. Its chamber is opened below the sea water free surface while the turbine duct outlet is free to atmosphere. Inside the chamber the water free surface oscillating movement produced by the incident waves causes the air to flow through the turbine duct and to activate the turbine, so the OWC principle of operating can be approximated to a cylinder-piston system. Therefore, one of the methodologies used in the computational modeling to simulate the operating principle of this device is the Piston Methodology, which simplifies the problem analysis considering only the air flow through the OWC converter. Among the phenomena that occur within the OWC device, the static pressure behavior is arguably one of the most important because it is through it that it is possible to estimate the hydropneumatic power and the converter efficiency. Thus, the objective of this work is to evaluate the static pressure behavior within the OWC, using the Piston Methodology, by imposing a monochromatic wave boundary condition in an axisymmetric domain. Among the obtained results it was inferred that the static pressure, in this case, depends directly on the flow acceleration and it is strongly influenced by the vorticity generated in domains with a change of area.

scholarly journals TURBINE−CHAMBER COUPLING IN AN OWC WAVE ENERGY CONVERTER

2012 ◽  
Vol 1 (33) ◽  
pp. 2 ◽  
Author(s):  
Ivan Lopez ◽  
Gregorio Iglesias ◽  
Mario Lopez ◽  
Francisco Castro ◽  
Miguel Ángel Rodríguez
Keyword(s):  
Numerical Modeling ◽  
Water Column ◽  
Wave Energy ◽  
Wave Power ◽  
Optimum Level ◽  
Oscillating Water Column ◽  
Wave Energy Conversion ◽  
Energy Converter ◽  
Air Turbine ◽  
Pneumatic Power

Oscillating Water Column (OWC) systems are one of the most popular technologies for wave energy conversion. Their main elements are the chamber with the water column and the air turbine. When studying the performance of an OWC system both elements should be considered together, for they are effectively coupled: the damping exerted by the air turbine affects the efficiency of the conversion from wave power to pneumatic power in the OWC chamber, which in turn affects the air flow driving the turbine. The optimum level of damping is that which maximizes the efficiency of the conversion from wave to pneumatic power. In this work the turbine-chamber coupling is studied through a combination of physical and numerical modeling.

scholarly journals Ocean Energy Systems Wave Energy Modelling Task: Modelling, Verification and Validation of Wave Energy Converters

2019 ◽  
Vol 7 (11) ◽  
pp. 379 ◽  
Author(s):  
Wendt ◽  
Nielsen ◽  
Yu ◽  
Bingham ◽  
Eskilsson ◽  
...  
Keyword(s):  
Wave Energy ◽  
Potential Flow ◽  
Numerical Models ◽  
Energy Systems ◽  
Verification And Validation ◽  
Ocean Energy ◽  
Fully Nonlinear ◽  
Wave Energy Converters ◽  
Modelling Task ◽  
Energy Converters

The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.

Numerical Studies on Hydrodynamics of a Floating Oscillating Water Column

2011 ◽  
Author(s):  
Wanan Sheng ◽  
Anthony Lewis ◽  
Raymond Alcorn
Keyword(s):  
Free Surface ◽  
Water Column ◽  
Wave Energy ◽  
Energy Extraction ◽  
Oscillating Water Column ◽  
Floating Structure ◽  
Damping Coefficients ◽  
Hydrodynamic Damping ◽  
Internal Water ◽  
First Case

The oscillating water column (OWC) is one of the more successful wave energy converters so far due to its mechanical and structural simplicity; there are no components for power take-off in seawater. Though there are some successful practical developments in bottom-fixed OWCs, floating OWCs are still in different stages of development. A specific oscillating water column, the OE Buoy (i.e. backward-bent duct device, ‘B2D2’), developed by OceanEnergy (Ireland), has recently attracted much attention. A 1:2.5 scale device has finished a sea-trial in Galway Bay (Ireland) for a period over two years during which period the device has gone through a severe storm. Thus its survivability has been confirmed to some extent. In this research, numerical simulations to the floating wave energy device are performed using a boundary element method code WAMIT. To consider the motions of the internal water in the column for energy extraction, a “numerical lid” is placed on the free surface in the column. In WAMIT, the motions of the “numerical lid” can be calculated by introducing relevant generalized modes to the conventional 6-DOF motions of the floating structure. For wave energy extraction, the “piston effect” of the internal water must be considered. To include the effect of the mooring system to the motions of floating structure, the mooring forces have been linearised, and their equivalent spring coefficients have been input to WAMIT for analysis of the moored floating structure. For the numerical simulation, the first case is to tune the damping coefficients based on wave tank results since in WAMIT, only hydrodynamic damping is included in calculation. In reality, larger damping may be needed to limit the large responses in heave of floating structure and the motion of the internal water surface. The tuned damping coefficients are then applied to the modified OWCs of different duct length, in which it is hoping that the corresponding responses of the internal free surface structure are used to assess the performance of the floating OWC. The aim of the research is to explore the relation between the OWC size and its performance so that it may provide a reference for optimizing the design of a floating OWC in the future.

scholarly journals The Potential of Conversion of Sea Wave Energy to Electric Energy: The Performance of Central Sulawesi West Sea using Oscillating Water Column Technology

2021 ◽  
Vol 926 (1) ◽  
pp. 012073
Author(s):  
Y A Rahman ◽  
Setiyawan
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Electric Energy ◽  
Oscillating Water Column ◽  
Ocean Energy ◽  
Door Opening ◽  
Ocean Wave Energy ◽  
Marine Energy ◽  
Column Technology ◽  
Calculation Results

Abstract With seas area of 70% larger than land, Indonesia encourages the potential for marine energy as an alternative to renewable energy. One of the technologies developed to utilize ocean energy is the Oscillating Water Column (OWC). The OWC method can convert ocean wave energy by using an oscillation column directing wave energy through the OWC door opening to generate electricity. This study aims to determine the magnitude of the waves utilized in West Central Sulawesi’s seas region include Alindau beach, Marana beach, and Kaliburu beach. Based on wave forecasting using wind data for five years, the maximum wave height for five years is 0.20 m. Estimated power from the calculation results obtained a rate significant with an efficiency level of 11.97%. Alindau is a potential location to develop wave energy.

Utilization of Wave Dissipating Caissons as an OWC Type Wave Energy Convertor

2015 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hiroaki Eto ◽  
Kazuyoshi Kihara ◽  
Hisaaki Maeda ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Theoretical Calculations ◽  
Low Cost ◽  
Vertical Movement ◽  
Compressed Air ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Column System ◽  
Air Turbine

Wave energy convertors (WEC) of oscillating water column (OWC) types make compressed air due to vertical movement of a part of water column, which are surrounded by some walls in water. As a result, the compressed air works to rotate an air turbine which also works for an electrical generator. If a structural system can make to move water such like a water column, a shape of a structure would not matter. Wave dissipating caissons installed in or on the existing production line can make to transfer a water wave to a flow and to reduce wave energy by making to overflow them. The caissons which can be overflowed by the water would actuate a water region vertically such like an oscillating water column system. This study investigated if we can utilize wave dissipating caissons as a WEC. Wave dissipating caissons also decrease wave energy due to passing through themselves. Even so, when an air turbine can be installed onto the caisson in order to harvest wave energy, it would be possible to produce electricity at low cost. The study conducted model experiments using the model assumed that wave dissipating double-caissons were remodelled to OWC type WECs with side walls and evaluated performance of the primary conversion of them. In addition, effects of how to arrange the number of the WECs on the primary conversion efficiency were investigated with theoretical calculations based on the linear potential theory and the possibility of utilization of wave dissipating caissons as a WEC was examined in the study.

Improvement of Performance of Wave Power Conversion Due to the Projecting Walls for Oscillating Water Column Type Wave Energy Converter

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hikaru Omori ◽  
Hiroyuki Osawa ◽  
Hisaaki Maeda
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Prediction Method ◽  
Past Research ◽  
Wave Energy Converter ◽  
Air Pressure ◽  
Wave Power ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Energy Converter

This paper describes a method to improve the performance of primary conversion of wave power takeoff. The wave energy converter (WEC) used here was of oscillating water column (OWC) type. This method for improvement has been already proposed in past research and its usefulness has been confirmed. It involves projecting walls (PWs) being attached to the front of the inlet–outlet of the OWC. The prediction method of hydrodynamic behaviors for the OWC type WEC with PWs installed is explained in this paper. The boundary element method with the Green's function is applied, and influence of air pressure and free surface within every air-chamber was directly taken into consideration in the prediction method based on linear potential theory. Validity of the prediction method was proved by comparing the results with the results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation, and the efficiency of primary conversion of wave power were investigated. From the calculations, length of the PWs was shown to affect the efficiency of primary conversion. It was possible to equip the PWs so as to enable improvements in oblique waves to beam sea conditions as well as in the head sea conditions. This paper examined not only the PWs but also the application and effects of the end walls (EWs) with the slit. The EWs were very useful to improve the efficiency.

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