Oscillating-water-column wave energy converters and air turbines: A review

https://hal.archives-ouvertes.fr/hal-01145072/document

A database of capture width ratio of wave energy converters

Wave energy development continues to advance in order to capture the immense ocean energy available globally. A large number of wave energy conversion concepts have been developed and researched to date but we are still not able to see a convergence of technologies. This provides the requirement and additional opportunity for further research. This paper provides a review and discusses the development of the OWC concept of wave energy converters in general and the evolved variation of the M-OWC more specifically. The review outlines the increased potential of the M-OWC concept and its current state through its advancement in recent years. Although still under development the M-OWCs have the potential to provide promising results, through the various innovative concepts under consideration, and support the progression and further development of wave energy as another serious contender in the renewables energy mix.

/pdf/development-of-multi-oscillating-water-columns-as-wave-3ckm1k1z9b.pdf

Development of multi-oscillating water columns as wave energy converters

Numerical study of fixed Oscillating Water Column with RANS-type two-phase CFD model

Experimental and numerical study of the response of the offshore combined wind/wave energy concept SFC in extreme environmental conditions

Despite the well-known limitations of linear potential flow theory, hydrodynamic coefficients obtained from boundary element methods (BEM) are commonly used to estimate the hydrodynamic parameters of wave energy converters (WECs).These parameters may then be used to simulate the behavior of WECs in response to incident waves. In this work, the usefulness to the wave energy community of the open-source BEM solver, NEMOH, developed by the Ecole Centrale de Nantes, is independently considered by comparison with the commercially-available BEM solver, WAMIT. The pre-processing, processing and post-processing stages of analysing four typical wave energy converting concepts are considered. Results for both solvers are presented in both the frequency and time domains. Other issues considered include computational time taken by both solvers, mesh generation, user-friendliness and the availability of supporting documentation.

Using NEMOH for Modelling Wave Energy Converters: A Comparative Study with WAMIT

Combining offshore wind and wave energy converting apparatuses presents a number of potentially advantageous synergies. To facilitate the development of a proposed floating platform combining these two technologies, proof of concept scale model testing on the wave energy converting component of this platform has been conducted. The wave energy component is based on the well-established concept of the oscillating water column. A numerical model of this component has been developed in the frequency domain, and the work presented here concerns the results of this modelling and testing. The results of both are compared to assess the validity and usefulness of the numerical model.

Comparison of the Experimental and Numerical Results of Modelling a 32-Oscillating Water Column (OWC), V-Shaped Floating Wave Energy Converter

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.

https://www.mdpi.com/1996-1073/14/6/1718/pdf

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

As part of an investigation into the feasibility of
an offshore combined wind/wave energy converting platform,
comprising one or more wind turbines mounted on a floating
structure in which a number of oscillating water columns (OWCs)
are embedded, testing was carried out on a 1:50 scale model of the
wave energy converting component of the platform. The model
comprises two legs joined at one end at an angle of 90 degrees. A
form of soft latching is implemented through the use of high and
low-pressure plenums to which the OWC chambers communicate
via air admittance valves. The model was tested in a number of
configurations, subject to varying amounts of simulated power
take-off damping and over a range of incident regular-wave
periods. Platform motions, OWC chamber and plenum pressure
and water column motions were recorded for each test. This
paper discusses some considerations in the design, construction,
instrumentation and testing of the model. Thermodynamic theory
describing the flow of air throughout the system, based on the
conservation of mass, is developed and related to the motion of
the water columns. Representative results from the model testing
in the time domain are presented. Finally, some conclusions are
drawn from these results.

Modelling and results for an array of 32oscillating water columns

System identification (SI) techniques represent an alternative strategy to provide the hydrodynamic model of oscillating water column (OWC) devices, compared to more traditional physics-based methods, such as linear potential theory (LPT) and computational fluid dynamics (CFD). With SI, the parameters of the model are obtained, by minimizing a model-related cost function, from input-output data. The main advantage of SI is its simplicity, as well as its potential validity range, where the dynamic model is valid over the full range for which the identification data was recorded. The paper clearly shows the value of a global nonlinear model, both in terms of accuracy and computational simplicity, over an equivalent multi-linear modelling solution. To this end, the validation performance of the nonlinear model is compared to the results provided by a range of linear models. Furthermore, in order to provide a more comprehensive comparative analysis, some practical aspects related to real-time implementation of multi-linear and nonlinear SI models are discussed. For the experimental campaign, real wave tank (RWT) data of a scaled OWC model are gathered from the narrow tank experimental facility at Dundalk Institute of Technology (DkIT). Particular attention is paid to the selection of suitable input signals for the experimental campaign, in order to ensure that the model is subjected to the entire range of equivalent frequencies, and amplitudes, over which model validity is required.

Thomas Kelly

Papers

Using NEMOH for Modelling Wave Energy Converters: A Comparative Study with WAMIT

Comparison of the Experimental and Numerical Results of Modelling a 32-Oscillating Water Column (OWC), V-Shaped Floating Wave Energy Converter

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

Modelling and results for an array of 32oscillating water columns

Nonlinear Data-Based Hydrodynamic Modeling of a Fixed Oscillating Water Column Wave Energy Device