The Experts below are selected from a list of 17922 Experts worldwide ranked by ideXlab platform
Tomy Varghese - One of the best experts on this subject based on the ideXlab platform.
-
we e 134 11 ultrasound cardiac strain imaging of left ventricle using Lagrangian tracking
Medical Physics, 2013Co-Authors: Tomy VargheseAbstract:Purpose: Lagrangian Description of myocardial tissue deformation is essential for accurate regional strain estimation of left ventricular wall over time. Failure to couple the estimated displacement and strain information with the correct myocardial tissue structure will lead to erroneous displacement and strain estimation. Methods: In this study, a method to obtain Lagrangian based deformation tracking is presented. Myocardial tissue is divided into a fixed number of pixels whose deformation is tracked over the cardiac cycle. An algorithm that utilizes a polar‐grid generated between the estimated endocardial and epicardial contours for the left ventricle in cardiac short axis images is proposed to ensure Lagrangian Description. Displacement estimations from consecutive radiofrequency frames were then mapped onto the polar grid to obtain a distribution of the cumulated displacement that is mapped to the polar grid over time. Results: This method was validated against a finite element analysis (FEA) based canine heart model coupled to an ultrasound simulation program. Segmental analysis of the accumulated displacement and strain over cardiac cycles show excellent agreement between the ideal Results obtained directly from the FEA model and our Lagrangian approach for deformation mapping. Eulerian based estimation results on the other hand, show significant deviation from the ideal Results. A comparison of the displacement and strain estimated on parasternal short axis view on a healthy volunteer is also presented. Conclusion: Lagrangian deformation tracking using a polar grid demonstrates accurate results when validated against finite element cardiac model. In addition to the cardiac application, this approach can also be applied to transverse scans of arteries.
-
Lagrangian displacement tracking using a polar grid between endocardial and epicardial contours for cardiac strain imaging
Medical Physics, 2012Co-Authors: Tomy VargheseAbstract:Purpose: Accurate cardiac deformation analysis for cardiac displacement and strain imaging over time requires Lagrangian Description of deformation of myocardial tissue structures. Failure to couple the estimated displacement and strain information with the correct myocardial tissue structures will lead to erroneous result in the displacement and strain distribution over time. Methods: Lagrangian based tracking in this paper divides the tissue structure into a fixed number of pixels whose deformation is tracked over the cardiac cycle. An algorithm that utilizes a polar-grid generated between the estimated endocardial and epicardial contours for cardiac short axis images is proposed to ensure Lagrangian Description of the pixels. Displacement estimates from consecutive radiofrequency frames were then mapped onto the polar grid to obtain a distribution of the actual displacement that is mapped to the polar grid over time. Results: A finite element based canine heart model coupled with an ultrasound simulation program was used to verify this approach. Segmental analysis of the accumulated displacement and strain over a cardiac cycle demonstrate excellent agreement between the ideal result obtained directly from the finite element model and our Lagrangian approach to strain estimation. Traditional Eulerian based estimation results, on the other hand, show significant deviation from the ideal result. Anin vivo comparison of the displacement and strain estimated using parasternal short axis views is also presented. Conclusions: Lagrangian displacement tracking using a polar grid provides accurate tracking of myocardial deformation demonstrated using both finite element andin vivo radiofrequency data acquired on a volunteer. In addition to the cardiac application, this approach can also be utilized for transverse scans of arteries, where a polar grid can be generated between the contours delineating the outer and inner wall of the vessels from the blood flowing though the vessel.
Mario J Juha - One of the best experts on this subject based on the ideXlab platform.
-
total Lagrangian finite element formulation of the flory rehner free energy function
Revista Facultad De Ingenieria-universidad De Antioquia, 2013Co-Authors: Mario J JuhaAbstract:The total Lagrangian finite element implementation of the Flory-Rehner free-energy function in the framework of a hyperelastic material model is addressed. It is explicitly given all the equations required to implement this material model in an implicit nonlinear finite element analysis, particularly, it is shown how to derive the so-called algorithmic or consistent linearized tangent moduli in the Lagrangian Description. Some analytical and numerical results for different boundary-value problems are presented to validate the implementation.
-
total Lagrangian finite element formulation of the flory rehner free energy function formulacion de elemento finito total Lagrangiano de la funcion de energia libre de flory rehner
2013Co-Authors: Mario J JuhaAbstract:The total Lagrangian finite element implementation of the Flory-Rehner free-energy function in the framework of a hyperelastic material model is addressed. It is explicitly given all the equations required to implement this material model in an implicit nonlinear finite element analysis, particularly, it is shown how to derive the so-called algorithmic or consistent linearized tangent moduli in the Lagrangian Description. Some analytical and numerical results for different boundary-value problems are presented to validate the implementation.
-
total Lagrangian finite element formulation of the flory rehner free energy function
arXiv: Numerical Analysis, 2012Co-Authors: Mario J JuhaAbstract:We address the total Lagrangian finite element implementation of the Flory-Rehner free-energy function in the framework of a hyperelastic material model. We explicitly give all the equations required to implement this material model in an implicit nonlinear finite element analysis, particularly, we show how to derive the so-called algorithmic or consistent linearized tangent modulus in the Lagrangian Description. Some analytical and numerical results for different boundary-value problems are presented to validate the implementation.
Javier Bonet - One of the best experts on this subject based on the ideXlab platform.
-
A parameter-free total Lagrangian smooth particle hydrodynamics algorithm applied to problems with free surfaces
Computational Particle Mechanics, 2021Co-Authors: Kenny W. Q. Low, Antonio J Gil, Chun Hean Lee, Jibran Haider, Javier BonetAbstract:This paper presents a new Smooth Particle Hydrodynamics computational framework for the solution of inviscid free surface flow problems. The formulation is based on the Total Lagrangian Description of a system of first-order conservation laws written in terms of the linear momentum and the Jacobian of the deformation. One of the aims of this paper is to explore the use of Total Lagrangian Description in the case of large deformations but without topological changes. In this case, the evaluation of spatial integrals is carried out with respect to the initial undeformed configuration, yielding an extremely efficient formulation where the need for continuous particle neighbouring search is completely circumvented. To guarantee stability from the SPH discretisation point of view, consistently derived Riemann-based numerical dissipation is suitably introduced where global numerical entropy production is demonstrated via a novel technique in terms of the time rate of the Hamiltonian of the system. Since the kernel derivatives presented in this work are fixed in the reference configuration, the non-physical clumping mechanism is completely removed. To fulfil conservation of the global angular momentum, a posteriori (least-squares) projection procedure is introduced. Finally, a wide spectrum of dedicated prototype problems is thoroughly examined. Through these tests, the SPH methodology overcomes by construction a number of persistent numerical drawbacks (e.g. hour-glassing, pressure instability, global conservation and/or completeness issues) commonly found in SPH literature, without resorting to the use of any ad-hoc user-defined artificial stabilisation parameters. Crucially, the overall SPH algorithm yields equal second order of convergence for both velocities and pressure.
Marc Brachet - One of the best experts on this subject based on the ideXlab platform.
-
capturing reconnection phenomena using generalized eulerian Lagrangian Description in navier stokes and resistive mhd
Fluid Dynamics Research, 2009Co-Authors: Carlos Cartes, Miguel D Bustamante, Marc Brachet, A PouquetAbstract:New generalized equations of motion for the Weber‐Clebsch potentials that describe both the Navier‐Stokes and magnetohydrodynamics (MHD) dynamics are derived. These depend on a new parameter, which has dimensions of time for Navier‐Stokes and inverse velocity for MHD. Direct numerical simulations (DNSs) are performed. For Navier‐Stokes, the generalized formalism captures the intense reconnection of vortices of the Boratav, Pelz and Zabusky (BPZ) flow, in agreement with the previous study by Ohkitani and Constantin. For MHD, the new formalism is used to detect magnetic reconnection in several flows: the three-dimensional (3D) Arnold, Beltrami and Childress (ABC) flow and the (2D and 3D) Orszag‐Tang (OT) vortex. It is concluded that periods of intense activity in the magnetic enstrophy are correlated with periods of increasingly frequent resettings. Finally, the positive correlation between the sharpness of the increase in resetting frequency and the spatial localization of the reconnection region is discussed.
-
generalized eulerian Lagrangian Description of navier stokes and resistive mhd dynamics
arXiv: Fluid Dynamics, 2008Co-Authors: Carlos Cartes, Miguel D Bustamante, A Pouquet, Marc BrachetAbstract:New generalized equations of motion for the Weber-Clebsch potentials that describe both the Navier-Stokes and MHD dynamics are derived. These depend on a new parameter, which has dimensions of time for Navier-Stokes and inverse velocity for MHD. Direct numerical simulations are performed. For Navier-Stokes, the generalized formalism captures the intense reconnection of vortices of the Boratav, Pelz and Zabusky flow, in agreement with the previous study by Ohkitani and Constantin. For MHD, the new formalism is used to detect magnetic reconnection in several flows: the 3D Arnold, Beltrami and Childress (ABC) flow and the (2D and 3D) Orszag-Tang vortex. It is concluded that periods of intense activity in the magnetic enstrophy are correlated with periods of increasingly frequent resettings. Finally, the positive correlation between the sharpness of the increase in resetting frequency and the spatial localization of the reconnection region is discussed.
-
generalized eulerian Lagrangian Description of navier stokes dynamics
Physics of Fluids, 2007Co-Authors: Carlos Cartes, Miguel D Bustamante, Marc BrachetAbstract:Generalized equations of motion for the Weber-Clebsch potentials that reproduce Navier-Stokes dynamics are derived. These depend on a new parameter, with the dimension of time, and reduce to the Ohkitani and Constantin equations in the singular special case where the new parameter vanishes. Let us recall that Ohkitani and Constantin found that the diffusive Lagrangian map became noninvertible under time evolution and required resetting for its calculation. They proposed that high frequency of resetting was a diagnostic for vortex reconnection. Direct numerical simulations are performed. The Navier-Stokes dynamics is well reproduced at small enough Reynolds number without resetting. Computation at higher Reynolds numbers is achieved by performing resettings. The interval between successive resettings is found to abruptly increase when the new parameter is varied from 0 to a value much smaller than the resetting interval.
Eugenio Oñate - One of the best experts on this subject based on the ideXlab platform.
-
particle finite element method in fluid mechanics including thermal convection diffusion
Computers & Structures, 2005Co-Authors: Romain Aubry, Sergio Idelsohn, Eugenio OñateAbstract:A method is presented for the solution of an incompressible viscous fluid flow with heat transfer using a fully Lagrangian Description of the motion. Due to the severe element distortion, a frequent remeshing is performed in an efficient manner. An implicit time integration through a classical fractional step is presented. The non-linearities of the formulation are taken into account and solved with the fixed-point iteration method. The displacement and temperature solutions are coupled through the Boussinesq approximation. The Lagrangian formulation provides an elegant way of solving free-surface problems with thermal convection as the particles are followed during their motion. To illustrate the method, the Rayleigh-Benard instability with and without free surface in two dimensions has been computed.
-
non linear explicit dynamic analysis of shells using the bst rotation free triangle
Engineering Computations, 2002Co-Authors: Eugenio Oñate, Patricio Cendoya, J MiquelAbstract:The paper describes the application of the simple rotation‐free basic shell triangle (BST) to the non‐linear analysis of shell structures using an explicit dynamic formulation. The derivation of the BST element involving translational degrees of freedom only using a combined finite element–finite volume formulation is briefly presented. Details of the treatment of geometrical and material non linearities for the dynamic solution using an updated Lagrangian Description and an hypoelastic constitutive law are given. The efficiency of the BST element for the non linear transient analysis of shells using an explicit dynamic integration scheme is shown in a number of examples of application including problems with frictional contact situations.
