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.

This paper presents an analytical linear model developed to study the behaviour of a buckled membrane tidal energy converter. The Euler beam theory and the elongated body theory are used for the fluid structure interaction formulation. The effect of electromechanical converters used to convert the undulating motion into electrical energy is reproduced by adding a term equivalent to viscous material damping. The influence of compression force, flaps and hanging conditions is studied, as well as the effects of simulated power takeoff through internal damping. The system's behaviour is characterized by undulating mode, critical flow velocity, motion frequency and amplitude. Highlights ► The behaviour of an undulating membrane tidal energy convertor has been modelized. ► The model is linearized to enable light computation. ► Results of frequency, trajectory and hydrodynamic forces fit the experiments. ► Optimization of the tidal energy collected is discussed.

Most of the research done on tidal energy focuses on marine current turbines. Therefore, tidal turbine's wake is well-documented. The tidal energy converter studied here is based on the fluid-structure interactions that occur between a flexible membrane and an axial flow, resulting in an undulating motion that can be used to harvest energy. This device's performance had been studied but it is the first time its wake is experimentally characterized from two-dimensional Particle Image Velocimetry (PIV) measurements. PIV is synchronized with a motion tracking system that gives information on trajectory and power conversion. Wake measurement gives access to velocity deficit, turbulence intensity and vorticity. Three configurations are tested in order to identify the influence of the main adjustment parameters. Pre-stress increases the membrane vertical speed, leading to a more important vertical expansion of the wake. The power extraction slows down the membrane's motion, thus limiting the wake's length and intensity. The flume tank measurements suggest that the best location for a downstream device in a tidal farm would be in the same horizontal position, at 5 membrane's length. In the open sea, the membrane interaction effects should not predominant. Highlights► Undulating membrane first wake characterization from PIV measurements, ► Phase-averaged velocity deficit and vorticity are measured and presented, ► Vorticity dissipation rate result can be used to calibrate numerical model.

The dynamic behaviour of an undulating tidal energy converter under wave and current loadings is studied. Therefore, a small scale prototype of a damped pre-stressed undulating membrane is tested in a wave and current recirculatory tank. The membrane's dynamic profile and hydrodynamic forces are measured synchronously with the surface elevation for both regular and irregular waves in current direction. Spectrum analysis reveals that the response to wave loading depends on the wave frequency and is reduced by damping-type power take-off. Coupling between the wave frequency and the main undulation frequency or its harmonics is also observed. An increase of 30% of the forces must be foreseen in case of wave condition in the tested range. Highlights► Undulating membrane tidal energy converter's response under wave and current. ► Waves increase hydrodynamic loading fluctuations on the membrane. ► Power Take-Off reduces the influence of wave loading on the membrane. ► Synchronization occurs when wave frequency is close to the system's fundamental.

The undulating membrane tidal energy converter is a device that uses the flutter instabilities occurring from the interaction between a slender body and a fluid flow. A new numerical model has been developed using a 2D corotational finite element method to represent the structure and the unsteady point-vortex method to compute the flow. These methods as well as the interaction process are presented. Trajectory and frequency of the undulating motion, hydrodynamic forces on the structure and velocity field in the wake are presented. Comparison shows a good agreement with experimental results obtained from a 1/20th scale prototype without power take off tested in flume tank.