Experimental test and numerical shape optimization of a point pivoted absorber for wave energy conversion

This paper presents a numerical study on an innovative system for converting energy from waves. It consists of a point pivoted body which oscillates in presence of waves. The system uses a linear electrical generator which converts floating movements of the buoyant body into electrical power. The buoyant body floats, describing an arc, by means of two hinges. A suitable Power Take-off Device (PTO) is placed between buoy support arms and the fixed structure and has the function to convert the mechanical power of the linear oscillating motion of the connecting piston into electrical power. A design assumption is made on the PTO control system: PTO reaction force is assumed to be linearly dependent on piston oscillation velocity with a given force-speed gain. This coefficient is strictly connected to electrical generator characteristics and its value has an effect on power conversion efficiency . A scaled model of this system has also been tested in the wave/towing tank facility of Department of industrial Engineering (DII) of University of Naples “Federico II”. A variety of numerical analyses, such as potential flow simulations and Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations, have been performed to predict the system performances. Numerical and experimental analyses have included the performances of the baseline geometry, both in free response and under wave excitation, in order to characterize the response of the system, and results have been used to understand which parameters affect more the power production. Finally a numerical optimization procedure has been carried out to optimize the shape of the converter with the final objective of increasing the generated power, eventually imposing a constraint on the amount of immersed volume. In this way, a modified configuration has been predicted with higher power output and the same value of submerged volume, but with different shape

Experimental test and numerical shape optimization of a point pivoted absorber for wave energy conversion

This paper presents a numerical study on an innovative system for converting energy from waves. It consists of a point pivoted body which oscillates in presence of waves. The system uses a linear electrical generator which converts floating movements of the buoyant body into electrical power. The buoyant body floats, describing an arc, by means of two hinges. A suitable Power Take-off Device (PTO) is placed between buoy support arms and the fixed structure and has the function to convert the mechanical power of the linear oscillating motion of the connecting piston into electrical power. A design assumption is made on the PTO control system: PTO reaction force is assumed to be linearly dependent on piston oscillation velocity with a given force-speed gain. This coefficient is strictly connected to electrical generator characteristics and its value has an effect on power conversion efficiency . A scaled model of this system has also been tested in the wave/towing tank facility of Department of industrial Engineering (DII) of University of Naples "Federico II". A variety of numerical analyses, such as potential flow simulations and Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations, have been performed to predict the system performances. Numerical and experimental analyses have included the performances of the baseline geometry, both in free response and under wave excitation, in order to characterize the response of the system, and results have been used to understand which parameters affect more the power production. Finally a numerical optimization procedure has been carried out to optimize the shape of the converter with the final objective of increasing the generated power, eventually imposing a constraint on the amount of immersed volume. In this way, a modified configuration has been predicted with higher power output and the same value of submerged volume, but with different shape

Numerical and Experimental Test on an Innovative Device Based on Multiple Rotors in Line to Tap Clean Energy from Tidal and River Current

The main object of this paper is to present the design and the results of an experimental test campaign on an innovative device for the exploitation of marine and river currents. The basic idea is to lay together one or more series of horizontal axis turbines in rows, each one connected to a generator placed on board a ship or a float. The whole system is sustained by a series of buoys, in this way is possible to avoid expensive submarine installations. All the work has been carried out at the Department of Industrial Engineering of the University of Naples "Federico II" and the test campaign has been first performed in the naval towing tank belonging to the same Department and then in real conditions in Messina Strait between Sicily island and mainland. This location is the only one in Italy suitable as test site thanks to a highly regular tidal current reaching a maximum speed of 3 m/s. The turbine's blade was first carefully designed with particular care for the cavitation problems. Two different series of experimental tests on a reduced scale model in the naval tank aimed to optimize the general layout of the device and the tests performed in Messina Strait mainly aimed to confirm the feasibility of the system and to evaluate its response in real operating conditions. The tests have confirmed the good dynamic behavior of the whole system and its feasibility to be scaled up to real scale

Designing a safety structure for an onshore pivoted wave energy converter: Numerical and experimental investigation

The present work concerns the development of a protection system for an onshore WEC device. The considered WEC system has been developed within a publicly funded research project, named GENERA, and is composed by a pivoting floating body which transfer wave energy to an electromechanical PTO. The energy conversion system, developed by Umbra Cuscinetti Spa, is composed by an electrical generator integrated in a ball-screw mechanism. The floating body, which operates the transformation of wave energy into mechanical energy, was developed by Seapower together with its support structure. In order to prevent possible damages due to extreme waves, the device is provided with a safety system. The principal loading conditions expected under extreme waves are investigated by means of numerical and experimental analyses

Design of GEMSTAR tidal current fixed pitch rotor controlled through a Permanent Magnet Generator (PMG) de-fluxing technique

This work reports a study on a tidal current system named GEMSTAR, composed of two hydrokinetic turbines supported by a floating submerged structure. A flexible mooring cable links the floating support to the seabed allowing the free rotation of the system and its alignment to changing current direction. The work is mainly focused on the design of the turbine blade with two objectives: keeping a constant power output above the rated power condition and limiting the thrust increase between rated and maximum operating speed. A fixed pitch blade was considered, in order to reduce the costs associated to a complex pitch control mechanism. An analytical procedure for blade design is proposed and validated by comparison to other numerical methods. Above the rated current speed, the power is held constant while the rotational speed of the turbine and of the generator increases, assuming an over-speeding control strategy. The adopted design configuration relies on the possibility of the generator to operate in de-fluxing working conditions. As reported in the last part of this study, a numerical model of the generator has also been developed and applied to a test case in order to analyse the electric behaviour of the system