François Rongère

Inwave : a new flexible design tool dedicated to wave energy converters

This article presents the novel methodology used in the software InWave to address the problem of wave energy converters (WEC) modelling. The originality compared to other recently developed tools lies in a fast semi-recursive multibody dynamic solver which integrates a flexible hydrodynamic solver. The multibody solver works in time domain and is fully nonlinear. It solves the dynamic of systems formed of a fixed or free base articulated with any number of bodies that can be floating or not, with branchy structure ([1]). The integrated hydrodynamic solver is a linear potential flow solver based on boundary elements method. It uses the generalized degrees of freedom approach ([11]). Combined with a relative coordinate parameterization, it allows for a minimization of the number of hydrodynamic boundary value problems that have to be solved, thus allowing a reduction of computational time both for BEM computations and time domain simulations. Time domain reconstruction is performed to link hydrodynamic loads with the multibody dynamic solver. Interaction between bodies through radiation is thus taken into account. InWave is a complete WEC modelling tool including incident wave generation, multibody dynamic solver, hydrodynamic solver, power take-off and mooring models, post-processing and visualization. A successful comparison with the linear potential flow solver Aquaplus ([5]) on a basic cylinder test case is carried out. Finally, a complex test case on a Langlee-like device is presented, comparing InWave results with those from the NumWec project ([2]). A good agreement between both models is found, which increases the confidence in InWave algorithms and implementation.

Systematic Dynamic Modeling and Simulation of Multibody Offshore Structures: Application to Wave Energy Converters

This article presents a framework to model and perform time domain dynamic simulations of offshore structures presenting several interconnected rigid bodies. Both fixed and 6 degree of freedom floating structures are considered. It uses a robotics formalism to parameterize the kinematic chain of the structures and is robust with respect to the number of bodies involved. Direct dynamics algorithms are given, using a consistent notation across offshore engineering and robotics fields. They use efficient recursive techniques based on Newton-Euler equations. The advantage of this framework is that tedious analytical developments are no longer needed. Instead of that, it is sufficient to provide a data parameter table as well as principal inertia parameters of each body to entirely describe the mechanical structure. An example of simulation is given, based on the 7 degree of freedom SEAREV Wave Energy Converter.Copyright

Dynamic modeling and simulation of rowing with a robotics formalism

This paper presents a robotics framework intended to be used for rowing simulation. It provides kinematic and inverse dynamic models for the system composed of boat, rowers and oars. The inverse dynamic model is based on the Recursive Newton-Euler Algorithm with free-floating base dealing with tree-structured systems with kinematic loops. Examples of simulations of a rowing-like model are given along with external force models. It is composed of a total of 6 links for the rower and the oars, the floating boat, and 7 joints. It presents a branched structure with one loop enabling to test the ability of the framework regarding its goals.

Computation of the Diffraction Transfer Matrix and the Radiation Characteristics in the Open-Source BEM Code NEMOH

Until now, widely available boundary element method (BEM) codes did not allow the calculation of two non-conventional hydrodynamic operators, which characterize the way a body diffracts and radiates waves, known as Diffraction Transfer Matrix and Radiation Characteristics respectively. When embedded into the finite-depth interaction theory developed by [1], they drastically speed up the computation of the added mass, damping and excitation force coefficients of a group (“farm”) of floating bodies. This paper presents the implementation of their computation in the open source BEM solver NEMOH using the methodology proposed by [2]. Results for two different geometries, a cylinder and a square box, are presented and compared to an alternative computational approach developed by [3]. A very good agreement between them is found. In addition, the hydrodynamic operators of the cylinder are compared to a semi-analytical solution available in the literature showing a good match. Results obtained using the finite-depth interaction theory are shown for a generic multi-body wave energy converter (WEC) demonstrating how the capabilities added to the BEM software NEMOH can facilitate the numerical modeling of the hydrodynamic interactions in large arrays of bodies.

Dynamic modeling of floating systems: Application to eel-like robot and rowing system

This paper presents the dynamic modeling of floating systems with application for three-dimensional swimming eel-like robot and rowing-like system. To obtain the Cartesian evolution during the design or control of these systems the dynamic models must be used. Owing to the complexity of such systems efficient and simple tools are needed to obtain their model. For this goal we propose an efficient recursive Newton-Euler approach which is easy to implement. It can be programmed either numerically or using efficient customized symbolic techniques.