Assessment of primary energy conversions of oscillating water columns. I. Hydrodynamic analysis

Abstract

This is an investigation on the development of a numerical assessment method for the hydrodynamic performance of an oscillating water column (OWC) wave energy converter. In the research work, a systematic study has been carried out on how the hydrodynamic problem can be solved and represented reliably, focusing on the phenomena of the interactions of the wave-structure and the wave-internal water surface. These phenomena are extensively examined numerically to show how the hydrodynamic parameters can be reliably obtained and used for the OWC performance assessment. In studying the dynamic system, a two-body system is used for the OWC wave energy converter. The first body is the device itself, and the second body is an imaginary “piston,” which replaces part of the water at the internal water surface in the water column. One advantage of the two-body system for an OWC wave energy converter is its physical representations, and therefore, the relevant mathematical expressions and the numerical simulation can be straightforward. That is, the main hydrodynamic parameters can be assessed using the boundary element method of the potential flow in frequency domain, and the relevant parameters are transformed directly from frequency domain to time domain for the two-body system. However, as it is shown in the research, an appropriate representation of the “imaginary” piston is very important, especially when the relevant parameters have to be transformed from frequency-domain to time domain for a further analysis. The examples given in the research have shown that the correct parameters transformed from frequency domain to time domain can be a vital factor for a successful numerical simulation

A Review of Wave-to-Wire Models for Wave Energy Converters

“…In the case of floating OWC devices, the converter needs to be considered as a multi-body system comprised of the floating structure (floater) and the imaginary piston. If both bodies are constrained to oscillate in heave only, the floating OWC becomes a two-body system [49,57] and the configuration matrix shown in Equation (3) can be used.…”

“…It is important to note that, although the different aspects (hydrodynamics, thermodynamics and air-turbines) are very often described and modelled individually and independently, they are actually interdependent [7,[48][49][50][51].…”

Wave energy conversion of oscillating water column devices including air compressibility

“…14 This allows a low torque acting on the PTOs and thus a high reliability of the OWC PTO for a long-term wave energy production. 15,16 The good examples are those practical wave power plants which have been developed and generated power to the grid, and these practices have proven that the OWC plants have very high reliability in long-term wave power generation. It is reported that the LIMPET OWC plant has generated electricity to the grid for more than 60 000 h in a period of about 10 years, 7 whilst a more recent development is the Mutriku OWC wave energy plant in Spain.…”

“…This equation has been widely accepted and used by other researchers. 28,30 Recently, Sheng et al 15,16,27 have developed the dynamic equations for fully coupling the thermodynamics for accommodating air compressibility and the hydrodynamics of the OWC devices. However, the effects of air compressibility have not been systematically studied on how the device performance and power conversion capacity can be modified.…”

“…are more popular for any complexity of the geometries of the OWC devices. 15,[21][22][23][24] For air compressibility in the OWC devices, some investigations have been carried out. 15,16,23,[25][26][27][28][29] Sarmento et al 26 first put forward a formula for air compressibility under the assumption of a large volume of the air chamber (compare to the air volume changes).…”