Elie Rivoalen

Numerical and experimental study of the interaction between two marine current turbines

Abstract The understanding of interaction effects between marine energy converters represents the next step in the research process that should eventually lead to the deployment of such devices. Although some a priori considerations have been suggested recently, very few real condition studies have been carried out concerning this issue. Trials were run on 1/30th scale models of three-bladed marine current turbine prototypes in a flume tank. The present work focuses on the case where a turbine is placed at different locations in the wake of a first one. The interaction effects in terms of performance and wake of the second turbine are examined and compared to the results obtained on the case of one single turbine. Besides, a three-dimensional software, based on a vortex method is currently being developed, and will be used in the near future to model more complex layouts. The experimental study shows that the second turbine is deeply affected by the presence of an upstream device and that a compromise between individual device performance and inter-device spacing is necessary. Numerical results show good agreement with the experiment and are promising for the future modelling of turbine farms.

JOSEPHINE: A parallel SPH code for free-surface flows ☆

Abstract JOSEPHINE is a parallel Smoothed Particle Hydrodynamics program, designed to solve unsteady free-surface flows. The adopted numerical scheme is efficient and has been validated on a first case, where a liquid drop is stretched over the time. Boundary conditions can also be modelled, as it is demonstrated in a second case: the collapse of a water column. Results show good agreement with both reference numerical solutions and experiments. The use of parallelism allows significant reduction of the computational time, even more with large number of particles. JOSEPHINE has been written so that any untrained developers can handle it easily and implement new features. Program summary Program title: JOSEPHINE Catalogue identifier: AELV_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AELV_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5139 No. of bytes in distributed program, including test data, etc.: 22 833 Distribution format: tar.gz Programming language: Fortran 90 and OpenMPI Computer: All shared or distributed memory parallel processors, tested on a Xeon W3520, 2.67 GHz. Operating system: Any system with a Fortran 90 compiler and MPI, tested on Debian Linux. Has the code been vectorised or parallelised?: The code has been parallelised but has not been explicitly vectorised. RAM: Dependent upon the number of particles. Classification: 4.12 Nature of problem: JOSEPHINE is designed to solve unsteady incompressible flows with a free-surface and large deformations. Solution method: JOSEPHINE is an implementation of Smoothed Particle Hydrodynamics. SPH is a Lagrangian mesh free particle method, thus, no explicit tracking procedure is required to catch the free surface. Incompressibility is satisfied using a weakly compressible model. Boundary conditions at walls are enforced by means of the ghost particles technique. The free-surface dynamic and kinematic conditions are applied implicitly. Running time: 15 mn on 4 processors for the dam-break case with 5000 particles, dependent upon the real duration (2 s here).

From Navier-Stokes to Stokes by means of particle methods

The viscous flow around a circular cylinder was investigated by means of a particle method over a wide Reynolds number range, from 0.0001 to 1000. A special care was devoted to the satisfaction of the no-slip condition which was expressed through a fourth order partial differential equation for the stream function according to the method initially proposed by Achdou and Pironneau. This equation was solved by a boundary integral method which simultaneously satisfied a Dirichlet and a Neumann condition. The algorithm was immersed within a particle method framework and results in a versatile method which can deal with relatively high Reynolds numbers as well as Stokes flows. The numerical results were analysed and compared to those obtained by others numerically, experimentally and even theoretically for the low Reynolds number limit. The behaviour of the method for the two extreme cases was specially investigated.