The Experts below are selected from a list of 378 Experts worldwide ranked by ideXlab platform
Petros Koumoutsakos - One of the best experts on this subject based on the ideXlab platform.
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computing the force distribution on the surface of complex deforming geometries using vortex methods and brinkman penalization
International Journal for Numerical Methods in Fluids, 2017Co-Authors: Siddhartha Verma, Gabriele Abbati, Guido Novati, Petros KoumoutsakosAbstract:Summary The distribution of forces on the surface of complex, deforming geometries is an invaluable output of flow simulations. One particular example of such geometries involves self-propelled swimmers. Surface forces can provide significant information about the flow field sensed by the swimmers, and are difficult to obtain experimentally. At the same time, simulations of flow around complex, deforming shapes can be computationally prohibitive when body-fitted grids are used. Alternatively, such simulations may employ penalization techniques. Penalization methods rely on simple Cartesian grids to discretize the governing equations, which are enhanced by a penalty term to account for the boundary conditions. They have been shown to provide a robust estimation of mean quantities, such as drag and propulsion velocity, but the computation of surface force distribution remains a challenge. We present a method for determining flow-induced forces on the surface of both rigid and deforming bodies, in simulations using re-meshed vortex methods and Brinkman penalization. The pressure field is recovered from the velocity by solving a Poisson's equation using the Green's function approach, augmented with a fast multipole expansion and a tree-code algorithm. The viscous forces are determined by evaluating the strain-rate tensor on the surface of deforming bodies, and on a ‘lifted’ surface in simulations involving rigid objects. We present results for benchmark flows demonstrating that we can obtain an accurate distribution of flow-induced surface-forces. The capabilities of our method are demonstrated using simulations of self-propelled swimmers, where we obtain the pressure and shear distribution on their deforming surfaces. This article is protected by copyright. All rights reserved.
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computing the force distribution on the surface of complex deforming geometries using vortex methods and brinkman penalization
arXiv: Fluid Dynamics, 2016Co-Authors: Siddhartha Verma, Gabriele Abbati, Guido Novati, Petros KoumoutsakosAbstract:The distribution of forces on the surface of complex, deforming geometries is an invaluable output of flow simulations. One particular example of such geometries involves self-propelled swimmers. Surface forces can provide significant information about the flow field sensed by the swimmers, and are difficult to obtain experimentally. At the same time, simulations of flow around complex, deforming shapes can be computationally prohibitive when body-fitted grids are used. Alternatively, such simulations may employ penalization techniques. Penalization methods rely on simple Cartesian grids to discretize the governing equations, which are enhanced by a penalty term to account for the boundary conditions. They have been shown to provide a robust estimation of mean quantities, such as drag and propulsion velocity, but the computation of surface force distribution remains a challenge. We present a method for determining flow- induced forces on the surface of both rigid and deforming bodies, in simulations using re-meshed vortex methods and Brinkman penalization. The pressure field is recovered from the velocity by solving a Poisson's equation using the Green's function approach, augmented with a fast multipole expansion and a tree- code algorithm. The viscous forces are determined by evaluating the strain-rate tensor on the surface of deforming bodies, and on a 'lifted' surface in simulations involving rigid objects. We present results for benchmark flows demonstrating that we can obtain an accurate distribution of flow-induced surface-forces. The capabilities of our method are demonstrated using simulations of self-propelled swimmers, where we obtain the pressure and shear distribution on their deforming surfaces.
Gregory Randall - One of the best experts on this subject based on the ideXlab platform.
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Morphing active contours
IEEE Transactions on Pattern Analysis and Machine Intelligence, 2000Co-Authors: Marcelo Bertalmío, Guillermo Sapiro, Gregory RandallAbstract:A method for deforming curves in a given image to a desired position in a second image is introduced. The algorithm is based on deforming the first image toward the second one via a partial differential equation (PDE), while tracking the deformation of the curves of interest in the first image with an additional, coupled PDE; both the images and the curves on the frame/slices of interest are used for tracking. The technique can be applied to object tracking and sequential segmentation. The topology of the deforming curve can change without any special topology handling procedures added to the scheme. This permits, for example, the automatic tracking of scenes where, due to occlusions, the topology of the objects of interest changes from frame to frame. In addition, this work introduces the concept of projecting velocities to obtain systems of coupled PDEs for image analysis applications. We show examples for object tracking and segmentation of electronic microscopy
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morphing active contours
Lecture Notes in Computer Science, 1999Co-Authors: Marcelo Bertalmío, Guillermo Sapiro, Gregory RandallAbstract:A method for deforming curves in a given image to a desired position in a second image is introduced in this paper. The algorithm is based on deforming the first image toward the second one via a partial Differential equation, while tracking the deformation of the curves of interest in the first image with an additional, coupled, partial Differential equation. The tracking is performed by projecting the velocities of the first equation into the second one. In contrast with previous PDE based approaches, both the images and the curves on the frames/slices of interest are used for tracking. The technique can be applied to object tracking and sequential segmentation. The topology of the deforming curve can change, without any special topology handling procedures added to the scheme. This permits for example the automatic tracking of scenes where, due to occlusions, the topology of the objects of interest changes from frame to frame. In addition, this work introduces the concept of projecting velocities to obtain systems of coupled partial Differential equations for image analysis applications. We show examples for object tracking and segmentation of electronic microscopy. We also briefly discuss possible uses of this framework iifor three dimensional morphing.
Robert J. Pugh - One of the best experts on this subject based on the ideXlab platform.
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Foaming, foam films, antifoaming and Defoaming
Advances in Colloid and Interface Science, 1996Co-Authors: Robert J. PughAbstract:Abstract A general introduction to foams, the initial stages in the production of foams in aqueous solution, foam structures and the classification of bulk foams according to their lifetimes and stability are presented. Fundamental studies on horizontal and vertical isolated foam lamellae with emphasis on drainage and stability are reviewed. For freshly prepared foams containing fairly thick lamellae, the mechanical-dynamical properties of the surface adsorbed layers (surface tension gradients) are decisive for retaining stability. Important parameters to be taken into consideration are the surface elasticity, viscosity (bulk and surface), gravity drainage and capillary suction. Also the film should exhibit low permeability to gases. Providing the stability of a foam film (containing dilute surfactant) is retained during the initial dynamic drainage process, then eventually a static (equilibrium) situation will be reached at film thicknesses c.m.c.) stabilization of films and foams can occur by a micellar laying mechanism (stratification). Antifoaming and Defoaming theories are presented, together with the mechanisms of heterogeneous antifoaming agents (non-polar oil, hydrophobic solid particles or mixtures of both) including recent theories describing the role of the emulsion and pseudo-emulsion film in the stability of foams containing oil droplets. Finally, Defoaming by ultrasonic waves is briefly reviewed.
Rui Li - One of the best experts on this subject based on the ideXlab platform.
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enhancing Defoaming using the foam breaker with perforated plates for promoting the application of foam fractionation
Separation and Purification Technology, 2013Co-Authors: Zhaoliang Wu, Lingling Li, Bin Zhao, Rui LiAbstract:Abstract A novel foam breaker with perforated plates was developed for promoting the application of foam fractionation due to its same advantages as foam fractionation, i.e., low cost, environmental compatibility and simple equipment. Sodium dodecyl sulfate (SDS) was used as a model system for evaluating the performances of the foam breaker. Based on the analysis of Defoaming principle, the effects of the number of perforated plates, SDS concentration and liquid holdup on the Defoaming percentage were researched using perforated plates of different orifice diameters and open area ratios. The results showed that perforated plate could significantly strengthen bubble coalescence or bubble collapse and promote the Defoaming percentage. Compared with the foam breaker without any plates, the Defoaming percentage increased from 19% to 63% using the foam breaker with five perforated plates of orifice diameter 1.0 mm and open area ratio 1.0% under the conditions of SDS concentration 0.5 g/L and liquid holdup 3.0%. As a result, the volume of foam collector decreased by two thirds. Finally, a model was established and it predicted successfully the Defoaming percentage using the foam breaker with perforated plates.
Marcelo Bertalmío - One of the best experts on this subject based on the ideXlab platform.
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Morphing active contours
IEEE Transactions on Pattern Analysis and Machine Intelligence, 2000Co-Authors: Marcelo Bertalmío, Guillermo Sapiro, Gregory RandallAbstract:A method for deforming curves in a given image to a desired position in a second image is introduced. The algorithm is based on deforming the first image toward the second one via a partial differential equation (PDE), while tracking the deformation of the curves of interest in the first image with an additional, coupled PDE; both the images and the curves on the frame/slices of interest are used for tracking. The technique can be applied to object tracking and sequential segmentation. The topology of the deforming curve can change without any special topology handling procedures added to the scheme. This permits, for example, the automatic tracking of scenes where, due to occlusions, the topology of the objects of interest changes from frame to frame. In addition, this work introduces the concept of projecting velocities to obtain systems of coupled PDEs for image analysis applications. We show examples for object tracking and segmentation of electronic microscopy
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morphing active contours
Lecture Notes in Computer Science, 1999Co-Authors: Marcelo Bertalmío, Guillermo Sapiro, Gregory RandallAbstract:A method for deforming curves in a given image to a desired position in a second image is introduced in this paper. The algorithm is based on deforming the first image toward the second one via a partial Differential equation, while tracking the deformation of the curves of interest in the first image with an additional, coupled, partial Differential equation. The tracking is performed by projecting the velocities of the first equation into the second one. In contrast with previous PDE based approaches, both the images and the curves on the frames/slices of interest are used for tracking. The technique can be applied to object tracking and sequential segmentation. The topology of the deforming curve can change, without any special topology handling procedures added to the scheme. This permits for example the automatic tracking of scenes where, due to occlusions, the topology of the objects of interest changes from frame to frame. In addition, this work introduces the concept of projecting velocities to obtain systems of coupled partial Differential equations for image analysis applications. We show examples for object tracking and segmentation of electronic microscopy. We also briefly discuss possible uses of this framework iifor three dimensional morphing.