1,720,995 research outputs found
Supershear Rayleigh Waves at a Soft Interface
Get PDFWe report on the experimental observation of waves at a liquid foam surface propagating faster than the bulk shear waves. The existence of such waves has long been debated, but the recent observation of supershear events in a geophysical context has inspired us to search for their existence in a model viscoelastic system. An optimized fast profilometry technique allows us to observe on a liquid foam surface the waves triggered by the impact of a projectile. At high impact velocity, we show that the expected subshear Rayleigh waves are accompanied by faster surface waves that can be identified as supershear Rayleigh waves.Fil: Le Goff, Anne. Microfluidique, MEMs et Nanostructures. UMR; Francia;Fil: Cobelli, Pablo Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisica; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires; Argentina;Fil: Lagubeau, Guillaume. Universidad de Santiago de Chile; Chile
Clustering of lagrangian particles in 2D turbulence
Get PDFEn este trabajo se diseña y construye un experimento para generar y estudiar turbulencia bidimensional. Se calcularonlos campos de velocidad y vorticidad, el espectro de energía y el parámetro de Bondarenko del sistema en decaimientoy en encendido; resultando en valores dados porαD= (−0.400±0.012)s−1yαE= (0.404±0.005)s−1, respectiva-mente. Además, se estudió la distribución de las partículas en el flujo a través de teselados de Voronoi.In this paper we design and construct an experiment to generate and study 2D turbulence. We calculate velocity and vorticity fields, the energy spectrum and Bondarenko’s parameter for the system both in decay and onset; those values result in αD = (−0.400±0.012) s −1 and αE = (0.404±0.005) s −1 , respectively. Additionally, we study the distribution of particles in the flux through the use of Voronoi tesselations.Fil: Martinovich, Carolina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Zalduendo, Inaki. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Cobelli, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Empirical mode decomposition profilometry: small-scale capabilities and comparison to Fourier transform profilometry
Get PDFWe present the empirical mode decomposition profilometry (EMDP) for the analysis of fringe projection profilometry (FPP) images. It is based on an iterative filter, using empirical mode decomposition, which is free of spatial filtering and adapted for surfaces characterized by a broadband spectrum of deformation. Its performances are compared to Fourier transform profilometry, the benchmark of FPP. We show both numerically and experimentally that using EMDP improves strongly the profilometry small-scale capabilities. Moreover, the height reconstruction distortion is much lower: the reconstructed height field is now both spectrally and statistically accurate. EMDP is thus particularly suited to quantitative experiments.Fil: Lagubeau, Guillaume. Universidad de Santiago de Chile; ChileFil: Cobelli, Pablo Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Bobinski, Tomas. Centre National de la Recherche Scientifique. Laboratoire Pmmh-umr 7636; FranciaFil: Maurel, Agnes. Institut Langevin, Umr Cnrs; FranciaFil: Pagneux, Vincent. Laboratoire D'acoustique, Univ. Maine Umr Cnrs 6613; FranciaFil: Petitjeans, Philippe. Centre National de la Recherche Scientifique. Laboratoire Pmmh-umr 7636; Franci
Design, construction and validation of an instrumented particle for the Lagrangian characterization of flows: Application to gravity wave turbulence
No full textThe design and application of an instrumented particle for the Lagrangian characterization of turbulent free-surface flows is presented in this study. This instrumented particle constitutes a local measurement device capable of measuring both its instantaneous 3D translational acceleration and angular velocity components, as well as recording them on an embarked removable memory card. A lithium-ion-polymer battery provides the instrumented particle with up to 8 h of autonomous operation. Entirely composed of commercial off-the-shelf electronic components, it features accelerometer and gyroscope sensors with a resolution of 16 bits for each individual axis, and maximum data acquisition rates of 1 and 8 kHz, respectively, as well as several user-programmable dynamic ranges. Its ABS 3D-printed body takes the form of a 36 mm diameter hollow sphere, and has a total mass of (19.6 ± 0.5) g, resulting in an effective mass density of 819 kg/m3, which can be adjusted by incorporating ballasts inside its body. Controlled experiments, carried out to calibrate and validate its performance showed good agreement when compared to reference techniques. To assess the practicality of the instrumented particle, we apply it to the statistical characterization of floater dynamics in experiments of surface wave turbulence. In this feasibility study, we focused our attention on the distribution of acceleration and angular velocity fluctuations as a function of the forcing intensity. The IP’s motion is also simultaneously registered by a 3D particle tracking velocimetry (PTV) system, for the purposes of comparison. Our results show, among other findings, that the IP is able to register the gradual departure from Gaussianity and the emergence of strongly non-Gaussian distributions for the translational acceleration fluctuations as the forcing amplitude is progressively increased. Beyond the results particular to this study case, the quality of their agreement with their PTV counterparts and with previous works reported in the literature, constitute a proof of both the feasibility and potentiality of the IP as a tool for the experimental characterization of particle dynamics in such flows.Fil: Cabrera, Facundo. Universidad de Lyon 3; FranciaFil: Cobelli, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Velocity and acceleration statistics in particle-laden turbulent swirling flows
Get PDFWe present a comparison of different particles' velocity and acceleration statistics in two paradigmatic turbulent swirling flows: the von Kármán flow in a laboratory experiment and the Taylor-Green flow in direct numerical simulations. Tracers, as well as inertial particles, are considered. Results indicate that, in spite of the differences in boundary conditions and forcing mechanisms, scaling properties and statistical quantities reveal similarities between both flows, pointing to new methods to calibrate and compare models for particles dynamics in numerical simulations, as well as to characterize the dynamics of particles in simulations and experiments. The comparison also allows us to identify contributions of the mean flow to the inertial-range scaling of the particles' velocity structure functions.Fil: Angriman, Sofia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Cobelli, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Determination of the bottom deformation from space- and time-resolved water wave measurements
Get PDFIn this paper we study both theoretically and experimentally the inverse problem of indirectly measuring the shape of a localized bottom deformation with a non-instantaneous time evolution, from either an instantaneous global state (space-based inversion) or a local time-history record (time-based inversion) of the free-surface evolution. Firstly, the mathematical inversion problem is explicitly defined and uniqueness of its solution is established. We then show that this problem is ill-posed in the sense of Hadamard, rendering its solution unstable. In order to overcome this difficulty, we introduce a regularization scheme as well as a strategy for choosing the optimal value of the associated regularization parameter. We then conduct a series of laboratory experiments in which an axisymmetric three-dimensional bottom deformation of controlled shape and time evolution is imposed on a layer of water of constant depth, initially at rest. The detailed evolution of the air–liquid interface is measured by means of a free-surface profilometry technique providing space- and time-resolved data. Based on these experimental data and employing our regularization scheme, we are able to show that it is indeed possible to reconstruct the seabed profile responsible for the linear free-surface dynamics either by space- or time-based inversions. Furthermore, we discuss the different relative advantages of each type of reconstruction, their associated errors and the limitations of the inverse determination.Fil: Cobelli, Pablo Javier. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Petitjeans, Philippe. Paristech; FranciaFil: Maurel, Agnès. Institut Langevin Ondes Et Images; FranciaFil: Pagneux, Vincent. Laboratoire D'acoustique de L'universite Du Maine; Franci
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Wave turbulence in shallow water models
Get PDFWe study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to 20482 points. In all simulations, the Froude number varies between 0.015 and 0.05, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, nonlinear waves are nondispersive and the spectrum of potential energy is compatible with ∼k−2 scaling. For deeper (Boussinesq) flows, the nonlinear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, ∼k−4/3. In this latter case, the nonlinear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution.Fil: Clark Di Leoni, Patricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Cobelli, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Development of a particle tracking velocimetry system for the lagrangian characterization of fluid flows
Get PDFEn este trabajo se presenta el desarrollo y la caracterización de un sistema de velocimetría por seguimiento de partículas para la medición lagrangiana de flujos. El sistema está basado en el uso conjunto de dos cámaras rápidas que observan sincronizadamente una región común del flujo a estudiar. Se describen en detalle el procedimiento de calibración conjunta del sistema de cámaras, la evaluación de los errores de medición y el procesado de las imágenes individuales para el cálculo de trayectorias de partículas en el espacio 3D. En último lugar, se discuten los resultados de la aplicación de este sistema al estudio de la dinámica de clústeres de partículas flotantes sobre la superficie libre de un campo de ondas turbulento.In this paper we present the development and characterization of a velocimetry system based on individual particle tracking, specially designed for the lagrangian description of fluid flows. This system is based on the joint use of two high-speed cameras which synchronically observe a common region on the flow under study. We describe in detail the joint calibration procedure of the system, as well as the processing of individual images for calculating particle trajectories in three-dimensional space. Lastly, results are shown concerning the application of this measuring system to the dynamics of buoyant particle clustering on the free surface of a turbulent wave field.Fil: Cappelletti, Lucía María. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: del Grosso, Nicolas Francisco. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Cobelli, Pablo Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
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