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 Wave power extraction from a bottom-mounted oscillating water column converter with a V-shaped channel

2014 ◽  
Vol 470 (2167) ◽  
pp. 20140074 ◽  
Author(s):  
Zhengzhi Deng ◽  
Zhenhua Huang ◽  
Adrian W. K. Law
Keyword(s):  
Water Column ◽  
Water Depth ◽  
Wave Energy ◽  
High Efficiency ◽  
Expansion Method ◽  
Opening Angle ◽  
Energy Extraction ◽  
Oscillating Water Column ◽  
Wave Direction ◽  
Power Extraction

An analytical theory is developed for an oscillating water column (OWC) with a V-shaped channel to improve the pneumatic efficiency of wave energy extraction. An eigenfunction expansion method is used in a cylindrical coordinate system to investigate wave interaction with the OWC converter system. Auxiliary functions are introduced to capture the singular behaviours in the velocity field near the salient corners and cusped edges. Effects of the OWC dimensions, the opening angle and length of the V-shaped channel, as well as the incident wave direction, on the pneumatic efficiency of wave energy extraction are examined. Compared with a system without the V-shaped channel, our results show that the V-shaped channel can significantly increase the conversion efficiency and widen the range of wave frequency over which the OWC system can operate at a high efficiency. For typical coastal water depths, the OWC converter system can perform efficiently when the diameter of the OWC chamber is in the range of 1 5 – 1 2 times the water depth, the opening angle of the V-shaped channel is in the range of [ π /2, 3 π /4] and the length of the V-shaped channel is in the range of 1–1.5 times the water depth.

System Identification of a Floating Oscillating Water Column Wave Energy Converter

2011 ◽  
Author(s):  
Brad Stappenbelt ◽  
Massimo Fiorentini ◽  
Paul Cooper ◽  
Song-Ping Zhu ◽  
Jean-Roch Nader
Keyword(s):  
System Identification ◽  
Water Column ◽  
Wave Energy ◽  
Forced Vibration ◽  
Lumped Parameter Model ◽  
Oscillating Water Column ◽  
Floating Structure ◽  
Novel Approach ◽  
Heave Motion ◽  
Energy Conversion Devices

One of the objectives of studies regarding the performance of floating oscillating water column (OWC) wave energy conversion devices is the prediction of the heave motion of the chamber and the water column. This paper presents a method to evaluate the parameters involved in the dynamics of partially submerged bodies in order to predict the coupled movement of the chamber and the water column in the frequency domain. System identification was performed and a lumped parameter model of the heave motions of a floating OWC was proposed. A novel approach utilising the reverse SISO method was employed to allow frequency dependent parameters for both the floating structure and the oscillating water column to be determined from several forced vibration experiments. Experimental results under forced vibration and wave excitation agree reasonably well with the dynamic model established.

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 WAVE CONTROL AND WAVE-ENERGY EXTRACTION BY USE OF CYLINDRICAL OSCILLATING WATER COLUMN DEVICE

2016 ◽  
Vol 72 (2) ◽  
pp. I_883-I_888
Author(s):  
Wataru KIOKA ◽  
Shintaro YAMAUCHI ◽  
Shinichiro FUJISAWA ◽  
Toshikazu KITANO
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Energy Extraction ◽  
Oscillating Water Column ◽  
Wave Control

scholarly journals Numerical Evaluation of the Hydropneumatic Power of the Oscillating Water Column Wave Energy Converter Submitted to Regular and Irregular Waves

2021 ◽  
pp. 32-43
Author(s):  
Augusto Hack da Silva Koch ◽  
Maycon da Silveira Paiva ◽  
Caroline Barbosa Monteiro ◽  
Phelype Haron Oleinik ◽  
Liércio André Isoldi ◽  
...  
Keyword(s):  
Free Surface ◽  
Water Column ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Oscillating Water Column ◽  
Regular Waves ◽  
Energy Converter ◽  
Sea State ◽  
Electric Generator

The purpose of this study is to computationally analyze the hydropneumatic power available in the air duct of an Oscillating Water Column (OWC) Wave Energy Converter (WEC) device when subject to realistic sea state data (irregular waves) and when submitted to the regular waves representative of this sea state. The OWC WEC is mainly composed of a hydropneumatic chamber and an air duct where a turbine and electric generator are coupled. The chamber is open below the free surface while the duct is open to the atmosphere. The oscillating movement of the water-free surface inside the chamber causes the air to flow, moving the turbine and generating electricity. To execute this study, a bi-dimensional computational model was considered and numerical simulations of wave generation were carried out using ANSYS Fluent, which is a Computational Fluid Dynamics (CFD) software based on the Finite Volume Method (FVM). The Volume of Fluid (VOF) multi-phase model was applied in the treatment of the water-air interaction. To evaluate the average hydropneumatic power available in the duct, the static pressure, velocity, and air mass flow rate were monitored. The results were analyzed, showing that the available power is 250% greater when the device is subject to realistic irregular waves rather than subject to representative regular waves.

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.

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