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Lagrangian Framework (lagrangian + framework)

Distribution by Scientific Domains
Engineering100%

Selected Abstracts

Effect of Heterogeneity on Radionuclide Retardation in the Alluvial Aquifer Near Yucca Mountain, Nevada

GROUND WATER, Issue 3 2001
S. Painter
The U.S. Department of Energy is currently studying Yucca Mountain, Nevada, as a potential site for a geological high-level waste repository. In the current conceptual models of radionuclide transport at Yucca Mountain, part of the transport path to pumping locations would be through an alluvial aquifer. Interactions with minerals in the alluvium are expected to retard the downstream migration of radionuclides, thereby delaying arrival times and reducing ground water concentrations. We evaluate the effectiveness of the alluvial aquifer as a transport barrier using the stochastic Lagrangian framework. A transport model is developed to account for physical and chemical heterogeneities and rate-limited mass transfer between mobile and immobile zones. The latter process is caused by small-scale heterogeneity and is thought to control the macroscopic-scale retardation in some field experiments. A geostatistical model for the spatially varying sorption parameters is developed from a site-specific database created from hydrochemical measurements and a calibrated modeling approach (Turner and Pabalan 1999). Transport of neptunium is considered as an example. The results are sensitive to the rate of transfer between mobile and immobile zones, and to spatial variability in the hydraulic conductivity. Chemical heterogeneity has only a small effect, as does correlation between hydraulic conductivity and the neptunium distribution coefficient. These results illustrate how general sensitivities can be explored with modest effort within the Lagrangian framework. Such studies complement and guide the application of more detailed numerical simulations. [source]

Interface tracking finite volume method for complex solid,fluid interactions on fixed meshes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2002
H. S. Udaykumar
Abstract We present a numerical technique for computing flowfields around moving solid boundaries immersed in fixed meshes. The mixed Eulerian,Lagrangian framework treats the immersed boundaries as sharp solid,fluid interfaces and a conservative finite volume formulation allows boundary conditions at the moving surfaces to be exactly applied. A semi-implicit second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We present applications of the method to two types of problems: (a) solidification in the presence of flows and particles, (b) fluid,structure interactions in flow control. In both these problems, the sharp interface method presents advantages by being able to track arbitrary interface motions, while capturing the full viscous, unsteady dynamics. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Numerical analysis of a new Eulerian,Lagrangian finite element method applied to steady-state hot rolling processes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2005
Josef Synka
Abstract A finite element code for steady-state hot rolling processes of rigid,visco-plastic materials under plane,strain conditions was developed in a mixed Eulerian,Lagrangian framework. This special set up allows for a direct calculation of the local deformations occurring at the free surfaces outside the contact region between the strip and the work roll. It further simplifies the implementation of displacement boundary conditions, such as the impenetrability condition. When applied to different practical hot rolling situations, ranging from thick slab to ultra-thin strip rolling, the velocity,displacement based model (briefly denoted as vu-model) in this mixed Eulerian,Lagrangian reference system proves to be a robust and efficient method. The vu-model is validated against a solely velocity-based model (vv-model) and against elementary methods based on the Kármán,Siebel and Orowan differential equations. The latter methods, when calibrated, are known to be in line with experimental results for homogeneous deformation cases. For a massive deformation it is further validated against the commercial finite-element software package Abaqus/Explicit. It is shown that the results obtained with the vu-model are in excellent agreement with the predictions of the vv-model and that the vu-model is even more robust than its vv-counterpart. Throughout the study we assumed a rigid cylindrical work roll; only for the homogeneous test case, we also investigated the effect of an elastically deformable work roll within the frame of the Jortner Green's function method. The new modelling approach combines the advantages of conventional Eulerian and Lagrangian modelling concepts and can be extended to three dimensions in a straightforward manner. Copyright © 2004 John Wiley & Sons, Ltd. [source]