Jean-Christophe Gilloteaux

Optimal Damping Profiles For a Heaving Buoy Wave Energy Converter

This paper discusses optimal damping profiles for a heaving buoy Wave Energy Converter (WEC) with a single degree of freedom. The goal is to examine how the device can be controlled to harvest maximum energy from incident waves. Both latching and declutching strategies are allowed via a general parametrization of the damping force. Ultimately, the research attempts to determine the best control strategy to apply considering the relative resonant frequency of the device and the monochromatic wave frequency set.

A Nonlinear Extension for Linear Boundary Element Methods in Wave Energy Device Modelling

To date, mathematical models for wave energy devices typically follow Cummins equation, with hydrodynamic parameters determined using boundary element methods. The resulting models are, for the vast majority of cases, linear, which has advantages for ease of computation and a basis for control design to maximise energy capture. While these linear models have attractive properties, the assumptions under which linearity is valid are restrictive. In particular, the assumption of small movements about an equilibrium point, so that higher order terms are not significant, needs some scrutiny. While this assumption is reasonable in many applications, in wave energy the main objective is to exaggerate the movement of the device through resonance, so that energy capture can be maximised. This paper examines the value of adding specific nonlinear terms to hydrodynamic models for wave energy devices, to improve the validity of such models across the full operational spectrum.

Control-informed geometric optimisation of wave energy converters

Abstract This paper concerns the interplay between the physical geometry of a wave energy converter (WEC) and the control strategy adopted for the converter, with the ultimate aim of optimising the energy output of the device. An energy-based performance function is employed and we attempt to perform numerical optimisation of a heaving buoy employing a latching control strategy. We allow both draught and radius of the axisymmetric buoy to be adjusted using a numerical optimisation. A linear time-domain hydrodynamic program is used in order to simulate the device motion, while the optimization problem is solved by means of a simplex method. Results show the difference in the frequency response of an optimal buoy for a particular sea-state designed with and without knowledge of the control system.

A Study on Prediction Requirements in Time-Domain Control of Wave Energy Converters

Abstract Wave energy converters (WECs) based on oscillating bodies or oscillating water columns would earn huge benefits from a time-domain control on a wave by wave basis. Such a control would allow efficient energy extraction over a wider range of frequencies than what could possibly be achieved when no real-time control is adopted, thus increasing the economical attractiveness of the WECs. Almost every control strategy that showed some potential, however, suffers from the problem that future knowledge of the incident wave elevation, or wave excitation force, is required. In this paper a general control framework for oscillating WECs is presented and a methodology to understand and quantify the wave excitation force prediction requirements, along with the achievable prediction accuracy, is discussed. The two features are compared against each other and linked to the dynamic characteristics of a device. Along with the qualitative discussion, the methodology is applied to some heaving cylinders when reactive control and linear passive control are applied, under different sea conditions.

Fully Coupled Floating Wind Turbine Simulator Based on Nonlinear Finite Element Method: Part I — Methodology

In the present paper, a new fully coupled simulator based on DeepLines™ software is described in order to address floating wind turbines dynamic simulation. It allows its user to take into account either separately or together the hydrodynamic and aerodynamic effects on one or several floating wind turbines. This simulator includes a non linear beam finite elements formulation to model the structural components — blades, tower, drivetrain, mooring lines and umbilicals — for both HAWT and VAWT layouts and advanced hydrodynamic capabilities to define all kinds of floating units and complex environmental loadings. The floating supports are defined with complete hydrodynamic databases computed with a seakeeping program. The aerodynamic loads acting on the turbine rotor are dynamically computed by an external aerodynamic library, which first release includes BEM (blade element moment for HAWTs) and SSM (single streamtube method for VAWTs) methods. The integration in time is performed with an implicit Newmark integration scheme.Copyright

Fully Coupled Floating Wind Turbine Simulator Based on Nonlinear Finite Element Method: Part II — Validation Results

The present paper describes the validation and the modeling capabilities of a new fully coupled floating wind turbine simulator based on DeepLines™ software. A first validation, based on code comparison with NREL-FAST software, is presented and shows very good correlation on a rigidly founded 5MW wind turbine in various wind conditions despite the different modeling techniques and assumptions of the two softwares. This benchmark, in addition to the extensive validation on various offshore projects, makes us confident on DeepLines capabilities to assess founded and floating wind turbine behaviour in a complex offshore environment. Furthermore, some simulation results on jacket and floating founded wind turbines, defined in the frame of IEA OC4 project, are presented and highlight the versatility of our simulator to perform offshore and floating wind turbine optimal design.© 2013 ASME