Potential time domain model with viscous correction and CFD analysis of a generic surging floating wave energy converter

Abstract

a b s t r a c tThe state of the art tools to assess the efficiency of the wave energy converters comprise the boundary element method (BEM) codes which are based on the potential linear approach whereas computational fluid dynamics (CFD) is still considered to be relatively computationally expensive. An attempt to enlarge the scope of the state of the art computational tools for wave energy converter applications is made in order to account for the viscous effects. This is achieved via the viscous damping term of the Morison equation which relies on a coefficient C d -to be estimated prior force calculation.The state of the art wave to wire model together with additional viscous term is termed as potential time domain viscous model and is employed for evaluation of the power efficiency of a generic surging type wave energy conversion system. Finally a comparison of CFD and the viscous time domain model is conducted which concludes that the Morison equations' drag term does offer an improvement.

Assessment of Scale Effects, Viscous Forces and Induced Drag on a Point-Absorbing Wave Energy Converter by CFD Simulations

“…Drag forces are also commonly included in parametrised form as in the Morison equation [15], but this requires calibration of drag coefficients. Such calibration is then made via experiments (see e.g., Rodriguez and Spinnekens work on a heaving box [16,17]) or via CFD simulations (as in the viscous correction method of Bhinder et al [18]). The work of Stansby et al [19] and Gu et al [20] present RANS simulations of different cylinder bottom geometries in surge and heave decay.…”

Evaluation of the Viscous Drag for a Domed Cylindrical Moored Wave Energy Converter

“…In relation to the viscous drag, the power output for a heaving wave energy converter was analysed in Reference [6], where it was reported that the viscous drag force caused a 4% reduction in the annual power production of such a point absorber device. A similar study for a generic surging type wave energy converter reported that the numerical power prediction can result in significant overestimation (more than 100%) if viscous effects are not taken into account [2]. CFD simulations can provide drag values (coefficient) that can be used in the time domain dynamic numerical model, as reported by References [6,7,11].…”

“…Inviscid potential flow solvers provide robust solution of the wave-structure interaction response for a wave energy device and in order to account for the viscous effects, the use of the Morison equation has been reported by a number of studies [2][3][4]. However, identification of the drag coefficient used in this approach is quite challenging.…”

“…The viscous drag's impact on the power production of a generic surging type wave energy converter was studied using a nonlinear time domain model with viscous correction [2,7]. In relation to the viscous drag, the power output for a heaving wave energy converter was analysed in Reference [6], where it was reported that the viscous drag force caused a 4% reduction in the annual power production of such a point absorber device.…”

“…Following NEMOH's results, a time domain model with viscous correction ([2]) was then implemented. In Reference [2] such a model was referred to as a potential time domain viscous (PTDV) model, and a comparison of the viscous correction was presented against CFD computations. It was shown that for a floating wave energy converter, viscous contributions show a significant impact on the power output of the surging wave energy device.…”