Study of U-shaped sloshing tanks to tune Wave Energy Converters through high-fidelity CFD simulations as geometry changes

This paper investigates the dynamics of aU-shaped sloshing tank varying its geometrical properties. The U - tank is designed to be coupled and integrated within a floating Wave Energy Converter, generating a second peak in its dynamic and allowing a bandwidth widening or a response amplification. The geometrical and liquid-filling properties directly affect the dynamics according to analytic models until second-order effects arise, such as secondary sloshing in the free-surface place, for in-stance, due to broader reservoirs or the elbows becoming sharper for manufacturing purposes. In light of the above considerations, a high-fidelity simulation is performed to overcome all those effects that are not considered in the simplified models. The results show a performance decrease when the reservoirs become more extensive and the elbow sharper

A submerged point absorber wave energy converter for the Mediterranean Sea

Regarding the serious environmental and energy problem existing in the world, renewable technology has taken the global attention. The unexploited huge potential of wave energy challenges the world scientific community, to achieve a sustainable wave energy absorption. Mediterranean is a closed sea with lower energy potential compared to the oceans. However, an efficient WEC that maximizes the power output not with respect to the available power but to its characteristics and cost, could be a feasible solution. A preliminary assessment has been carried out of a submerged point absorber installed in the coast of the Pantelleria island. For the design and selection of the technical characteristics of the WEC a method proposed by Falnes is followed. In order to control and test the performance of the device in different situations, a mathematical model has been constructed in Matlab Simulink based on the Cummins Equation

Non-linear simulation of a wave energy converter with multiple degrees of freedom using a harmonic balance method

Computationally efficient simulation methods for wave energy converters (WECs) are useful in a variety of applications. The simulation task is particularly challenging when nonlinearities are present in the WEC model. Using a Fourier projection of the system inputs and variables, harmonic balance (HB) is a computationally-efficient method to solve for the steady-state motion of a non-linear system, preserving an accurate representation of the non-linear effects. In previous work, HB has been used for the simulation of WECs with one degree of freedom (DoF). Here, HB is presented for WEC systems with an arbitrary number of DoFs. A non-linear, 2-DoF model of the ISWEC wave energy device is used as an example of application. The HB implementation of the ISWEC model is described in detail. Through numerical applications, chosen in both regular and irregular waves, general features of the HB method are exemplified, in particular the exponential convergence rate to the actual mathematical solution, and the sensitivity, in some cases, to the starting point of the HB algorit

ISWEC Design Tool

ISWEC (Inertial Sea Wave Energy Converter) is a gyroscopic effect based wave power extraction device. The aim of this paper is to present a tool developed for the design process of this WEC. The main purpose of the software is to allow to the system engineer to compute the annual electrical productivity using a simplified model, taking into account several considerations such as system geometrical and electrical configurations, the hull properties or the installation site. To obtain this result, an automatic optimization of control parameters is implemented. A cost function is minimized under various system constraints (e.g. PTO torque and power, flywheel speed) and the absorbed power of the system is evaluated. Output of the software is the device productivity, along with considerations about structural loads, PTO utilization, floater and mass properties. The software will help the system engineer to take preliminary decisions and to verify the adaptability of this WEC to the considered sea site. The methodology here proposed can be easily generalised to other applications, especially in wave energy field, where severe constraints and time consuming simulations are common, and the use of a tool like this can reduce develop time, giving different information from the very start of the project

Application of a Passive Control Technique to the ISWEC: Experimental Tests on a 1:8 Test Rig

In this work, we address the use of Hardware In the Loop test rig for renewable energy application. Such test rig is designed to evaluate the performances of the wave harvesting system called ISWEC. The ISWEC is a floating, slack-moored, gyroscopic Wave Energy Converter. The full-scale prototype has an electric-mechanical Power take-off (PTO) composed by a gearbox and a brushless torque motor. The system is torque controlled to keep the gyroscope in the desired position range and to obtain maximum productivity. In order to obtain this, two different control methods are under study: a proportional-derivative (PD) law and a passive control method. The PD control law regulates the torque on the PTO providing a stiffness term to recall the gyroscope in the vertical position and a damping term to extract power. In this configuration, the PTO performs the recall effect, resulting in an increase of the torque load. To overcome such problems, the use of an eccentric mass to provide the stiffness term is analyzed. The experimental tests demonstrate the reduction of the PTO torque, justifying the gap in the system productivity provided by the passive control as assessed with the numerical model

PeWEC: Preliminary Design of a Full-Scale Plant for the Mediterranean Sea

Nowadays, atmospheric pollution and climate change have encouraged Governments to invest in renewable technologies for clean energy production. Wave Power constitutes an interesting option in the panorama of renewables and starting from the first results achieved in the ’70s, in the last and present decade the major efforts have been concentrated to makeWave Energy Converters (WECs) more profitable and predictable. The research activities described in this work concern the development of a pendulum converter (PeWEC: Pendulum Wave Energy Converter), designed for the Mediterranean Sea scenario. In the first part of the paper, the mathematical model describing the floater and pendulum dynamics is presented. The equations previously described are then used to implement a modelbased design and optimization methodology. The latter is constituted by three different tools connected in cascade and characterized by an increasing degree of complexity and fidelity. The combination of these tools, together with the evaluation of the plant Levelized Cost of Energy (LCOE), allow to determine an optimal device configuration for the installation site chosen. The methodology is here used to design a preliminary layout of the full-scale PeWEC device, considering the Pantelleria Island (Italy) wave climate as reference