FluidFFT: common API (C++ and Python) for Fast Fourier Transform HPC libraries

The Python package fluidfft provides a common Python API for performing Fast Fourier Transforms (FFT) in sequential, in parallel and on GPU with different FFT libraries (FFTW, P3DFFT, PFFT, cuFFT). fluidfft is a comprehensive FFT framework which allows Python users to easily and efficiently perform FFT and the associated tasks, such as as computing linear operators and energy spectra. We describe the architecture of the package composed of C++ and Cython FFT classes, Python "operator" classes and Pythran functions. The package supplies utilities to easily test itself and benchmark the different FFT solutions for a particular case and on a particular machine. We present a performance scaling analysis on three different computing clusters and a microbenchmark showing that fluidfft is an interesting solution to write efficient Python applications using FFT

Structured-light-based surface measuring for application in fluid–structure interaction

International audienceThe study implements a method based on the analysis of a sinusoidal fringe pattern. This method allows the retrieval of a three dimensional surface shape from a two dimensional video recording of the deformation of fringes projected on the surface. A detailed description of the method and the implementation is provided which will facilitate its adaption to and utilization in custom FSI applications (the code is published under open-source license). An application example is presented in the form of an experiment. A hyperflexible hydrofoil is set under forced rotational oscillation in a closed water tunnel to mimic the characteristics of a vertical-axis hydrokinetic cross-flow turbine. The flexible structures encounter large deformations which are linked to corresponding hydrodynamic forces. To capture this interdependence, the deformations were recorded in sync with forces registered with a six-axis load cell. A validation of the method is presented and shows good accuracy in the deformation measurements of a hyperflexible hydrofoil. A benefit compared to other common techniques like Laser-interferometer measurements is the simplicity and modest hardware requirements of the method with the possibility to acquire height fields with good spatial and temporal resolution, which allows a spectral analysis of the surface deformation. The hydrodynamic forces are presented together with the corresponding deformation of the structure, and spectral analyses are performed which demonstrates the possibilities of the proposed method. In summary, the presented method allows the analysis of fluid-structure interactions using a simple assembly consisting of a projector and a high-speed camera. Graphic abstract frequency [Hz] oscillation base frequency flicker fluid-structure interaction imposed motion frequency [Hz] inlet outlet projection high-speed camer

FluidDyn: a Python open-source framework for research and teaching in fluid dynamics

FluidDyn is a project to foster open-science and open-source in the fluid dynamics community. It is thought of as a research project to channel open-source dynamics, methods and tools to do science. We propose a set of Python packages forming a framework to study fluid dynamics with different methods, in particular laboratory experiments (package fluidlab), simulations (packages fluidfft, fluidsim and fluidfoam) and data processing (package fluidimage). In the present article, we give an overview of the specialized packages of the project and then focus on the base package called fluiddyn, which contains common code used in the specialized packages. Packages fluidfft and fluidsim are described with greater detail in two companion papers, Mohanan et al. (2018a,b). With the project FluidDyn, we demonstrate that specialized scientific code can be written with methods and good practices of the open-source community. The Mercurial repositories are available in Bitbucket (https://bitbucket.org/fluiddyn/). All codes are documented using Sphinx and Read the Docs, and tested with continuous integration run on Bitbucket, Pipelines and Travis. To improve the reuse potential, the codes are as modular as possible, leveraging the simple object-oriented programming model of Python. All codes are also written to be highly efficient, using C++, Cython and Pythran to speedup the performance of critical functions

FluidImage, a libre framework for scientific treatments of large sets of images

National audienceFluidImage A software for the fluid dynamic community, by the fluid dynamic communityA libre framework for scientific treatments of large sets of imagesEasy, safe and efficient for all users, nice for the developer

Numerical investigation of mode failures in submerged granular columns

In submerged sandy slopes, soil is frequently eroded as a combination of two main mechanisms: breaching, which refers to the retrogressive failure of a steep slope forming a turbidity current, and, instantaneous sliding wedges, known as shear failure, that also contribute to shape the morphology of the soil deposit. Although there are several modes of failures, in this paper we investigate breaching and shear failures of granular columns using the two-fluid approach. The numerical model is first applied to simulate small scale granular column collapses with different initial volume fractions to study the role of the initial conditions on the main flow dynamics. For loosely packed granular columns, the porous medium initially contracts and the resulting positive pore pressure leads to a rapid collapse. Whereas in initially dense-packing columns, the porous medium initially dilates and negative pore pressure is generated stabilizing the granular column, which results in a slow collapse. The proposed numerical approach shows good agreement with the experimental data in terms of morphology and excess of pore pressure. Numerical results are extended to a large-scale application known as the breaching process. This phenomenon may occur naturally at coasts or on dykes and levees in rivers but it can also be triggered by humans during dredging operations. The results indicate that the two-phase flow model correctly predicts the dilative behavior and, the subsequent turbidity currents, associated to the breaching process

French Roadmap for complex Systems 2008-2009

This second issue of the French Complex Systems Roadmap is the outcome of the Entretiens de Cargese 2008, an interdisciplinary brainstorming session organized over one week in 2008, jointly by RNSC, ISC-PIF and IXXI. It capitalizes on the first roadmap and gathers contributions of more than 70 scientists from major French institutions. The aim of this roadmap is to foster the coordination of the complex systems community on focused topics and questions, as well as to present contributions and challenges in the complex systems sciences and complexity science to the public, political and industrial spheres

Analyse expérimentale de l'aérodynamique proche paroi et modélisation du bruit de bord de fuite d'un profil d'aile en écoulement subsonique

This work is devoted to the experimental study of the trailing edge noise mechanisms, especially broad band, resulting of the hydrodynamic waves diffraction on the sharp edge of a foil in flow, in view of its modelisation. In that way, a detailed examination of the dynamic behaviour of the characteristic aerodynamic quantities of the phenomenon (wall pressure and velocity fluctuations) has been made on a Naca 0012 airfoil. It has then been possible to obtain experimentally the statistic of the wall pressure field, and more particularly the wall pressure fluctuation wave number spectrum representative of the boundary layer turbulence dynamic, a fundamental quantity for the acoustic field estimation. Models of the literature of the wall pressure statistic (Corcos, Chase) have been fixed and validated, and finally used for the modelisation of the noise from the trailing edge of the airfoil.Finally, measurements of the acoustic pressure radiated have been made in an anechoic wind tunnel, allowing to show the potentialities and the limitations of the implemented aeroacoustic model. The approach proposed by Chase in terms of wall pressure statistic modelisation appears to be able to represent correctly the influence of the main parameters of the problem (Reynolds number, airfoil incidence), while it has clearly been shown the necessity to take correctly account for the Kutta condition for the estimation of the noise radiated.Ce travail porte sur l'étude expérimentale des mécanismes de génération de bruit de bord de fuite, notamment large bande, résultant de la diffraction des ondes hydrodynamiques sur le bord effilé d'un profil en écoulement en vue de leur modélisation. A cet effet, l'examen détaillé de la dynamique des grandeurs aérodynamiques caractéristiques du phénomène (fluctuations de la pression pariétale et de la vitesse) a été mené au voisinage proche d'un profil d'aile de type Naca 0012. Il a ainsi été possible de déterminer expérimentalement la statistique du champ de pression pariétale, et notamment le spectre en nombres d'ondes des fluctuations de pression pariétale représentatif de la dynamique de la turbulence dans la couche limite, donnée essentielle à l'évaluation du champ acoustique rayonné. Des modèles de la statistique du champ de pression pariétale tirés de la littérature (Corcos, Chase) ont ensuite pu être calés et validés, et finalement utilisés pour la modélisation du bruit de bord de fuite du profil.Enfin, des mesures de la pression acoustique rayonnée réalisées en soufflerie anéchoïque ont permis de préciser les potentialités et limitations du modèle aéroacoustique développé. Le modèle statistique de pression pariétale proposé par Chase s'est avéré à même de représenter correctement l'influence des principaux paramètres du problème (nombre de Reynolds, incidence du profil), de même qu'il a clairement été mis en évidence la nécessité de prendre correctement en compte la condition de Kutta

Analyse expérimentale de l'aérodynamique proche paroi et modélisation du bruit de bord de fuite d'un profil d'aile en écoulement subsonique

Ce travail porte sur l étude expérimentale des mécanismes de génération de bruit de bord de fuite, notamment large bande, résultant de la diffraction des ondes hydrodynamiques sur le bord effilé d un profil en écoulement en vue de leur modélisation. A cet effet, l examen détaillé de la dynamique des grandeurs aérodynamiques caractéristiques du phénomène (fluctuations de la pression pariétale et de la vitesse) a été mené au voisinage proche d un profil d aile de type Naca 0012. Il a ainsi été possible de déterminer expérimentalement la statistique du champ de pression pariétale, et notamment le spectre en nombres d ondes des fluctuations de pression pariétale représentatif de la dynamique de la turbulence dans la couche limite, donnée essentielle à l évaluation du champ acoustique rayonné. Des modèles de la statistique du champ de pression pariétale tirés de la littérature (Corcos, Chase) ont ensuite pu être calés et validés, et finalement utilisés pour la modélisation du bruit de bord de fuite du profil. Enfin, des mesures de la pression acoustique rayonnée réalisées en soufflerie anéchoïque ont permis de préciser les potentialités et limitations du modèle aéroacoustique développé. Le modèle statistique de pression pariétale proposé par Chase s est avéré à même de représenter correctement l influence des principaux paramètres du problème (nombre de Reynolds, incidence du profil), de même qu il a clairement été mis en évidence la nécessité de prendre correctement en compte la condition de Kutta.This work is devoted to the experimental study of the trailing edge noise mechanisms, especially broad band, resulting of the hydrodynamic waves diffraction on the sharp edge of a foil in flow, in view of its modelisation. In that way, a detailed examination of the dynamic behaviour of the characteristic aerodynamic quantities of the phenomenon (wall pressure and velocity fluctuations) has been made on a Naca 0012 airfoil. It has then been possible to obtain experimentally the statistic of the wall pressure field, and more particularly the wall pressure fluctuation wave number spectrum representative of the boundary layer turbulence dynamic, a fundamental quantity for the acoustic field estimation. Models of the literature of the wall pressure statistic (Corcos, Chase) have been fixed and validated, and finally used for the modelisation of the noise from the trailing edge of the airfoil. Finally, measurements of the acoustic pressure radiated have been made in an anechoic wind tunnel, allowing to show the potentialities and the limitations of the implemented aeroacoustic model. The approach proposed by Chase in terms of wall pressure statistic modelisation appears to be able to represent correctly the influence of the main parameters of the problem (Reynolds number, airfoil incidence), while it has clearly been shown the necessity to take correctly account for the Kutta condition for the estimation of the noise radiated.POITIERS-BU Sciences (861942102) / SudocSudocFranceF