Numerical and Experimental Identification of the Aerodynamic Power Losses of the ISWEC

Abstract

The wave energy sector is experiencing lively years of conceptual innovation and technological advances. Among the great variety of candidates, only a few are going to be able to reach maturity and, eventually, industrial feasibility and competitiveness. The essential requisite for success is the continuous innovation in response to the incremental experience gained during the design and prototyping stages. In particular, the ability to generate detailed mathematical models, representative of every phenomenon involved in the system, is crucial for informing the design and control stages, allowing to maximize productivity while minimizing costs, and inspiring technological breakthrough and innovation. This papers considers the case of the ISWEC (Inertial Sea Wave Energy Converter), where a technological leap is tightly linked with the modelling of aerodynamic losses around its spinning flywheel, the core of the energy conversion chain. Two mathematical models of increasing complexity are considered, one semi-empiric and one based on computational fluid dynamics, which are successfully validated against experimental data. Such models are used to quantify the benefits of a technological innovation consisting of enclosing the flywheel in a sealed container, allowing pressure regulation to reduce aerodynamic friction. Compared to the free configuration, power losses with the enclosed configuration are about half already at atmospheric pressure, and about one third at half the atmospheric pressure.

Review of Wave Energy Converter and Design of Mooring System

“…Numerical Modeling [139][140][141][142][143] Numerical and Experimental [144][145][146][147][148] Physical Experiment [149][150][151][152][153] Consequently, the simulations of the floating WECs still need to rely on the linear potential theory. Time-domain simulations were performed to integrate nonlinear adverse effects with the aid of the methods of convolution like van Oortmerssen [154] or Cummins [155].…”

Experimental Investigation of the Mooring System of a Wave Energy Converter in Operating and Extreme Wave Conditions

“…ISWEC is a floating wave energy converter designed to exploit wave energy through the gyroscopic effect of a flywheel [33]. The gyroscopic power take-off (PTO) system is enclosed in a sealed hull [34], retained by slack mooring lines anchored on the seabed. A schematic representation of the device concept is shown in Figure 2.…”

Nonlinear Dynamic and Kinematic Model of a Spar-Buoy: Parametric Resonance and Yaw Numerical Instability

“…If φ is not exactly zero, Equation (10) shows that a velocity in roll can cause an acceleration in yaw. For the case of 3-DoF excitation (linear FK model or nonlinear FK model away from the parametric instability region), φ is not excited and simply decays from a small initial value φ 0 ; consequently,ψ ≈ 0.…”

“…Let us consider the two hydrodynamic excitation conditions: Table 1 summarizes all possible conditions that can arise in the absence of restoring and damping terms in yaw. In the ideal case (I x = I y ), there is no forcing term in yaw, so that the yaw response will follow roll and pitch angles, according to Equation (10). In particular, in the 3-DoF excitation condition, yaw will follow the decay of roll; in the 5-DoF excitation condition, the oscillatory part of yaw will follow the pitch sustained response, modulated by the frequency of the roll response.…”

“…The fidelity of mathematical models is crucial for a reliable estimation of the cost of electricity and for the effectiveness of model-based control strategy [6,7], which are essential for achieving economic viability [8,9]. As the wave energy field grows in experience and maturity, the necessity of nonlinear models, for a comprehensive design of most WEC types, becomes increasingly apparent [10][11][12].…”