Power estimates of an undulating membrane tidal energy converter

Abstract

An experimental study of an undulating membrane based on the Eel Energy device is presented in this paper. This system uses interaction between a semi-rigid plate and an axial flow to generate undulation. At full scale, the deformation of the structure is then converted into electrical power using linear electromagnetic generators. In order to simulate the power takeoff on a 1/20th scale prototype, hydraulic dampers are located all over the length of the device. The dampers have non-linear behaviour. A representative damping parameter have been introduced to study their impact. Results are presented in function of fluid velocity and damping adjustment. Undulation mode, frequency and forces on the structure are described. Results show that fluid velocity has a destabilizing effect on the membrane, increasing undulation frequency and lowering its amplitude, while damping has the opposite effect. Furthermore, two methods used to evaluate the power conversion are described and evaluated from trajectory and forces data analysis. Power estimation shows an evolution proportional to cubic current speed at low flow speed, as for classical tidal turbines. Power also seems to scale with the square of the product between undulation frequency and amplitude. Highlights ► An experimental model of undulating membrane tidal energy converter at 1/20th scale is presented. ► Power TakeOff simulation using hydraulic dampers is proposed and described. ► Two methods of power conversion estimation have been described and evaluated. ► Membrane motion and forces are measured in function of current speed and damping adjustment ► Power conversion scales with the square product of undulation main frequency and motion amplitude.

Numerical modelling of an undulating membrane tidal energy converter

“…As noticed during previous experiments [1], the membrane undergoes small deformations and large displacements, which generate non-linear behaviours. This explains the use of the co-rotational finite elements method for the computation of the stiffness matrix.…”

“…Results in term of structure behavior and flow properties are then analyzed in section III. The first comparisons with experimental results from [1] enable to validate these numerical developments.…”

“…The 1/20 th scale prototype of an undulating membrane tidal energy converter is described in [1] and summarised here. Its results are used for comparison with the numerical model.…”

“…A fluid-structure interaction numerical model is developed in order to study this device. It follows the development of a 1/20 th scale experimental model [1] and a linear analytical model [2]. The purpose of the numerical model is to represent accurately the membrane motion, the flow around it, and the hydrodynamic forces on the structure.…”

Flutter and resonances of a flag near a free surface

“…In contrast, the present study considers the effect of confinement by a free surface which may deform under the effect of the fluctuating pressure generated by the flapping structure. Such analysis is necessary to understand flag-current-free surface coupling and its relevance for the design of flexible energy harvesters intended for ocean or river purposes [4,26,27], the performance prediction of recent self-powered water-pump devices based on flexible structures [28], or the analysis of the effect of a current on wave energy harvesters [29] and wave breakers [30].…”