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Laurent David

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Papers by Laurent David

Conclusions and Outlook

Springer eBooks, 2022

The FIThydro project not only compiled, assessed and analyzed published knowledge on the effects ... more The FIThydro project not only compiled, assessed and analyzed published knowledge on the effects of hydropower to fish and the environment, but also generated new knowledge and recognized still existing knowledge and research gaps. These gaps concern diverse aspects and challenges that planning, construction and operation of hydropower plants pose in terms of mitigating and lowering environmental impacts. The aspects relate to the following fields of action: P. Rutschmann (B)

Head loss modelling of flexible structures bundles placed in a turbulent free surface flow

HAL (Le Centre pour la Communication Scientifique Directe), Nov 22, 2022

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Bayesian inference applied to spatio-temporal reconstruction of flows around a NACA0012 airfoil

Experiments in Fluids, 2014

In this paper, we shall investigate sequential data assimilation techniques to improve the stabil... more In this paper, we shall investigate sequential data assimilation techniques to improve the stability of reducedorder models for fluid flows. The reduced-order model used relies on a Galerkin projection of Navier-Stokes equations on proper orthogonal decomposition (POD) basis vectors estimated from snapshots of the flow fields obtained with timeresolved particle image velocimetry (TR-PIV) measurements. The coefficients of the dynamical system are given through a least-squares regression technique applied to the experimental data and lead to a low-order model which is known to diverge, or damp, rapidly in time if left uncontrolled. In this context, a sequential data assimilation method based on a Bayesian approach is proposed. In this formalism, reduced-order models (ROMs) are modeled with discrete time from the hidden Markov processes. Given the whole trajectories of the POD temporal modes, the state of ROM coefficients initially provided by noisy PIV measurements are re-estimated from a Kalman filtering of the sequential data. Results are obtained for the flow around a NACA0012 airfoil at Reynolds numbers of 1000 and 2000 and angles of attack of 10 ; 15 ; 20 and 30 .

Analyse du comportement des poissons dans les bassins de la passe à fentes verticales de Vichy pour deux configurations de bassins

Optimization of the volume reconstruction for classical Tomo-PIV algorithms (MART, BIMART and SMART): synthetic and experimental studies

Measurement Science and Technology, 2014

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Numerical Comparison Of Rans, Urans And Les Simulations Of Turbulent Flow In Vertical Double Slot Fishways

Proceedings of the 39th IAHR World Congress

Numerous actions have been undertook to achieve a good ecological status or potential of the Euro... more Numerous actions have been undertook to achieve a good ecological status or potential of the European Union members water bodies. Vertical Double Slot Fishways (VDSF) have been implemented to bypass obstacles on rivers, however few studies have been made on their design or efficiency. This paper proposes a numerical comparison of three methods: RANS, URANS and LES simulations to model the turbulent flow occurring in VDSFs. All three methods present a coherent average global dynamic of the system. The velocities displayed are of the same order of magnitude as the ones recorded experimentally. The LES simulation additionally presented instantaneous data. The jets coming from the slots are wavering, one taking dominance at one point in time, only to be over-taken by the other later on. The flow inside the pools is thus much more chaotic than average trajectories implied. The access to this instantaneous information is useful since it is the flow faced by the fish, unlike the average flow. If fish reactions to a given unsteady flow were recorded, fish behaviour towards unfamiliar unsteady flows could be predicted. From these predictions, future fish structures could be designed with the theoretical reaction from the fish inside it.

Tomographic Reconstruction of 3D Objects Using Marked Point Process Framework

Journal of Mathematical Imaging and Vision, 2018

For reconstructing sparse volumes of 3D objects from projection images taken from different viewi... more For reconstructing sparse volumes of 3D objects from projection images taken from different viewing directions, several volumetric reconstruction techniques are available. Most popular volume reconstruction methods are algebraic algorithms (e.g. the multiplicative algebraic reconstruction technique, MART). These methods which belong to voxel-oriented class, allows volume to be reconstructed by computing each voxel intensity. A new class of tomographic reconstruction methods, called "object-oriented" approach, has recently emerged and was used in the Tomographic Particle Image Velocimetry technique (Tomo-PIV). In this paper, we propose an object-oriented approach, called IOD-OVRMPP (Iterative Object Detection-Object Volume Reconstruction based on Marked Point Process), to reconstruct the volume of 3D objects from projection images of 2D objects. Our approach allows the

Implementation of vibration correction schemes to the evaluation of a turbulent flow in an open channel by tomographic particle image velocimetry

Measurement Science and Technology, 2014

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires 1

Spanwise gradients in flow speed and leading edge vortex attachment on low Reynolds number wings

It is now accepted that the aerodynamic performance of low aspect ratio revolving wings, such as ... more It is now accepted that the aerodynamic performance of low aspect ratio revolving wings, such as insect wings or maple seed membranes, largely relies on sustained leading edge vortex attachment. However, the mechanisms responsible for this sustained attachment are still poorly understood. Here, we compute the Navier-Stokes solution of the flow around a finite wing (i) subjected to a uniform oncoming flow, (ii) subjected to a spanwise varying oncoming flow and (iii) revolving about its root. Therefore, we are able to isolate the mechanisms associated with the spanwise gradient of the local wing speed from those associated with centrifugal and Coriolis effects. We show that over flapping amplitudes typical of insect flight the spanwise gradient of the local wing speed may suffice in maintaining leading edge vortex attachment. We correlate this result with the development of spanwise flow and we evaluate the sensitivity of such a mechanism to the Reynolds number. It is noted, however, that leading edge vortex attachment through the spanwise gradient of the local wing speed does not promote large lift, which ultimately arises from centrifugal and Coriolis effects.

Velocity and pressure field correlation analysis for low-order modeling of elbow flow

The highly turbulent flow of liquids in piping systems can constitute a steady-state source of dy... more The highly turbulent flow of liquids in piping systems can constitute a steady-state source of dynamic loading of the structure, which might in turn lead to fatigue failure. As part of an effort to build a reduced-order model of the flow-induced excitation, the present study analyzes the correlation found between pressure and velocity in the elbow flow. A previously validated incompressible Large-eddy simulation (LES) of water flowing at Reynolds number 5.6 x 10 through a 90° elbow was used to provide a series of realizations of the local velocity and pressure fields. The correlation between pressure and the velocity fields is evaluated. Proper Orthogonal Decomposition (POD) of the velocity field is applied under the form of Snapshot-POD, giving coherent flow motion information. The pressure field is finally projected onto the flow modes (extended POD) and a discussion regarding the construction of a loworder model of the excitation based on the extended modes is proposed.

Experimental study of fish-friendly angled bar racks with horizontal bars

Journal of Hydraulic Research, 2021

This paper presents an experimental study of angled fish-friendly bar racks with horizontal bars,... more This paper presents an experimental study of angled fish-friendly bar racks with horizontal bars, using a physical model in an open channel. Head losses are investigated for two bar shapes, three ratios between bar spacing and bar thickness and four angles of orientation of the racks. The Froude and bar-Reynolds numbers were respectively 0.275 and 3600. The head loss coefficients decrease as the blockage ratio and the angle of orientation of the rack decrease. They are well predicted by a formula produced previously for an inclined rack, with some adaptations. Velocity fields are characterized upstream and downstream of the racks, showing no effect of the angle of orientation and no heterogeneity over channel width. Consequently, the normal and tangential components of the velocity along the rack are in agreement with the theoretical values given by angular decomposition. These results serve to assess the compliance with biological criteria to avoid impingement risks and guide fish towards a bypass.

Mesure de grandeurs cinématiques tridimensionnelles par tomographie optique à balayage et tomographie par reconstruction algébrique

International audienc

Particle Image Velocimetry

Encyclopedia of Aerospace Engineering, 2010

Particle Image Velocimetry (PIV) is a laser-based technique to measure the instantaneous velocity... more Particle Image Velocimetry (PIV) is a laser-based technique to measure the instantaneous velocity distribution within a planar domain. The present chapter introduces the working principle of PIV and discusses its relevance for aerodynamic testing of aerospace vehicles and propulsion systems. The main components of an experiment performed by PIV are the seeding particles, the illumination system, the digital image recording and the algorithms used to analyze the motion of recorded particle images. The chapter closes with a discussion on the accuracy and spatial resolution of PIV measurements and on the data reduction procedures typically applied to post-process PIV data. Keywords: LASER; tracers; digital imaging; cross-correlation; vortices; vorticity

Time-resolved image analysis for turbulent flows

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt età la diffusion de documents scientifiques de niveau recherche, publiés ou non, emanant desétablissements d'enseignement et de recherche français ouétrangers, des laboratoires publics ou privés.

3D particle volume tomographic reconstruction based on marked point process: Application to Tomo-PIV in fluid mechanics

2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2014

In recent years, marked point processes have received a great deal of attention. They were applie... more In recent years, marked point processes have received a great deal of attention. They were applied with success to extract objects in large data sets as those obtained in remote sensing frameworks or biological studies. We propose in this paper a method based on marked point processes to reconstruct volumes of 3D particles from images of 2D particles provided by the Tomographic Particle Image Velocimetry (Tomo-PIV) technique. Unlike other reconstruction methods, our approach allows us to solve the problem in a parsimonious way. It facilitates the introduction of prior knowledge and naturally solves the memory problem which is inherent to pixel based approach used by classical tomographic reconstruction methods. The best reconstruction is found by minimizing an energy function which defines the marked point process. In order to avoid local minima, we use a simulated annealing algorithm. Results are presented on simulated data.

Full 3D displacement field measurement by Optical Scanning Tomography and PIV Tomography

EPJ Web of Conferences, 2010

This work is about the development of new techniques for the measurement of the three components ... more This work is about the development of new techniques for the measurement of the three components of the velocity inside a volume. A comparison of two techniques, optical scanning tomography and algebraic reconstruction tomography method, is performed with 3D displacement tests of transparent solid blocks. 1 3D measurement fields This work is about the development of new techniques to study 3D mechanical problems involved inside a volume, in particular in the framework of fluid mechanics. For that, Tomographic Particle Image Velocimetry (Tomo-PIV) has been developed to measure the three components of the velocity in a whole volume [1]. This technique consists in recording some projections from different orientations and in using an algebraic reconstruction method to generate a volume image of particles. Optical scanning tomography is another method to generate volumes images and is also an alternative to record the volume particles. In this paper, reconstructions of particle volumes by MART algebraic tomography [2-4] and by optical scanning tomography [5,6] are compared on rigid body motion tests. For that, resin blocks have been manufactured with different particle diameters and particle rates and are moved in a tank filled with a fluid resin to suppress the effect of refraction index. For the same position, blocks are recorded by four cameras for the multi sensor tomography and by one camera perpendicular to the laser beam for multi-plane tomography. Particle volumes reconstructed by both techniques are compared. Accuracy of the reconstruction, drawbacks and limitations are presented and discussed. For the different positions of the blocks, Digital Volume Correlation (DVC), the 3D extension of Digital Image Correlation (DIC), is used to measure displacement uncertainty and evaluate the influence of each tomography method. 2 Multi-sensor tomography Currently the main techniques used in tomography for the volumic reconstruction in fluid mechanics fluids are ART algebraic reconstruction (Algebraic Reconstruction Technic) and MART (Multiplicative ART). Indeed, these methods are well adapted to reconstruct a volume starting from a very limited number of views (2 to 6). The problem of reconstruction can be written like a linear

Hydrodynamic angles, orientation and velocity of the hand in front crawl swimming

The hydrodynamic parameters of the hand (Angle of attack, sweepback, velocity and orientation) pl... more The hydrodynamic parameters of the hand (Angle of attack, sweepback, velocity and orientation) play an important role in the generation of the resultant forces. These parameters were measured throughout an aquatic stroke to study the possible modifications caused by a variation of the swimming pace. Seventeen competitive swimmers swam at the long distance, middle distance and sprint paces. Parameters were calculated from the trajectory of seven markers on the hand measured with an optoelectronic system. Results showed that sweepback and angle of attack, and orientation of the hand do not vary significantly depending to the pace. Only the velocity of the hand increases when the pace increases, but only during the less propulsive phases. The increase of pace is then explained by the swimmer's capacity to maintain propulsive phases rather than increasing the force generation within each cycle.

Nouvelle méthode de reconstruction de volumes de particules 3D basée sur les processus ponctuels marques: Application à la TOMO-PIV en mécanique de fluide

Mesure volumique par tomo-PIV d'un écoulement dans un canal turbulent de surface libre derrière une grille

La mesure directe de la dissipation dans les écoulements n'est pas possible mais les nouvelles te... more La mesure directe de la dissipation dans les écoulements n'est pas possible mais les nouvelles techniques de mesure volumique comme la tomo-PIV permettre de calculer le tenseur des gradients de vitesse et par la même la dissipation instantanée. Cet article présente des mesures de vitesse par tomo-PIV d'un écoulement à surface libre pour un nombre de Reynolds de 36000 dans un canal incliné à l'aval d'un assemblage de grilles. La faisabilité des mesures est réalisée et deux configurations de grilles sont comparées. On montre notamment que la dissipation n'est pas homogène et isotrope dans la région de l'écoulement mesurée.

Stereoscopic measurement of free surface flows

EPJ Web of Conferences, 2010

The present paper adresses the problem of combined three-dimensionnal measurements of shape and v... more The present paper adresses the problem of combined three-dimensionnal measurements of shape and velocity of moving free surfaces. A measurement method based on the cross-correlation of image pairs obtained from a calibrated stereoscopic vision system is presented. The underlying concept of the method consists in the generation of parametric shape and displacement forms which are directly projected on the camera models. This procedure is then integrated in an iterative optimization process so that elevation, orientation, curvature and displacement of each surface subset are accurately estimated. Application is made on inclined plane flows of complex non-Newtonian fluids as an alternative to conventionnal rheometric devices.