The Experts below are selected from a list of 19152 Experts worldwide ranked by ideXlab platform
Robert E. Wyatt - One of the best experts on this subject based on the ideXlab platform.
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an arbitrary lagrangian Eulerian Approach to solving the quantum hydrodynamic equations of motion equidistribution with smart springs
Journal of Chemical Physics, 2003Co-Authors: Corey J Trahan, Robert E. WyattAbstract:Recently, the quantum trajectory method (QTM) has been utilized in solving several quantum mechanical wave packet scattering problems including barrier transmission and electronic nonadiabatic dynamics. By propagating the real-valued action and amplitude functions in the Lagrangian frame, only a fraction of the grid points needed for Eulerian fixed-grid methods are used while still obtaining accurate solutions. Difficulties arise, however, near wave function nodes and in regions of sharp oscillatory features, and because of this many quantum mechanical problems have not yet been amenable to solution with the QTM. This study proposes a hybrid of both the Lagrangian and Eulerian techniques in what is termed the arbitrary Lagrangian–Eulerian method (ALE). In the ALE method, an additional equation of motion governing the momentum of the grid points is coupled into the quantum hydrodynamic equations. These new “quasi-” Bohmian trajectories can be dynamically adapted to the emergent features of the time evolvin...
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an arbitrary lagrangian Eulerian Approach to solving the quantum hydrodynamic equations of motion equidistribution with smart springs
Journal of Chemical Physics, 2003Co-Authors: Corey J Trahan, Robert E. WyattAbstract:Recently, the quantum trajectory method (QTM) has been utilized in solving several quantum mechanical wave packet scattering problems including barrier transmission and electronic nonadiabatic dynamics. By propagating the real-valued action and amplitude functions in the Lagrangian frame, only a fraction of the grid points needed for Eulerian fixed-grid methods are used while still obtaining accurate solutions. Difficulties arise, however, near wave function nodes and in regions of sharp oscillatory features, and because of this many quantum mechanical problems have not yet been amenable to solution with the QTM. This study proposes a hybrid of both the Lagrangian and Eulerian techniques in what is termed the arbitrary Lagrangian–Eulerian method (ALE). In the ALE method, an additional equation of motion governing the momentum of the grid points is coupled into the quantum hydrodynamic equations. These new “quasi-” Bohmian trajectories can be dynamically adapted to the emergent features of the time evolvin...
Zhao Feng Tian - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of turbulent gas particle flow in a 90 bend Eulerian Eulerian Approach
Computers & Chemical Engineering, 2008Co-Authors: Krishna Mohanarangam, Zhao Feng TianAbstract:Abstract A numerical investigation into the physical characteristics of dilute gas–particle flows over a square-sectioned 90° bend is reported. The modified Eulerian two-fluid model is employed to predict the gas–particle flows. The computational results using both the methods are compared with the LDV results of Kliafas and Holt, wherein particles with corresponding diameter of 50 μm are simulated with a flow Reynolds number of 3.47 × 10 5 . RNG-based κ – ɛ model is used as the turbulent closure, wherein additional transport equations are solved to account for the combined gas–particle interactions and turbulence kinetic energy of the particle phase turbulence. Moreover, using the current turbulence modelling formulation, a better understanding of the particle and the combined gas–particle turbulent interaction has been shown. The Eulerian–Eulerian model used in the current study was found to yield good agreement with the measured values.
S Balachandar - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the equilibrium Eulerian Approach for the evolution of particle concentration in isotropic turbulence
International Journal of Multiphase Flow, 2003Co-Authors: Sarma L Rani, S BalachandarAbstract:Abstract In the current work, the accuracy of the equilibrium Eulerian Approach in evolving the particulate concentration field is evaluated by comparing it against the Lagrangian Approach, for varying particle response time and terminal velocity. In particular, we compare the statistics of preferential accumulation and gravitational settling of particles in a cubic box of isotropic turbulence. Twelve simulations corresponding to four values of nondimensional particle response time, τp=0.05, 0.1, 0.2, 0.4, and three values of nondimensional terminal velocity, | V s |=0.5,2,4 are considered. The equilibrium Eulerian Approach obviates the need to solve additional governing equations for the particle velocity field. It, however, involves evolution of the particle concentration field using the equilibrium Eulerian velocity field. A spectral diffusion term is included in the particle concentration equation to provide an essentially non-oscillatory behavior to the solution. There is good agreement between the equilibrium Eulerian and Lagrangian statistics for small particles. With increasing particle size, the equilibrium Eulerian Approach tends to somewhat overestimate particle preferential concentration in regions of excess strain-rate over rotation-rate compared to the Lagrangian Approach. Over the entire range of parameters considered, the equilibrium Approach provides a good approximation to the actual mean and rms fluctuating settling velocities of the particle.
Corey J Trahan - One of the best experts on this subject based on the ideXlab platform.
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an arbitrary lagrangian Eulerian Approach to solving the quantum hydrodynamic equations of motion equidistribution with smart springs
Journal of Chemical Physics, 2003Co-Authors: Corey J Trahan, Robert E. WyattAbstract:Recently, the quantum trajectory method (QTM) has been utilized in solving several quantum mechanical wave packet scattering problems including barrier transmission and electronic nonadiabatic dynamics. By propagating the real-valued action and amplitude functions in the Lagrangian frame, only a fraction of the grid points needed for Eulerian fixed-grid methods are used while still obtaining accurate solutions. Difficulties arise, however, near wave function nodes and in regions of sharp oscillatory features, and because of this many quantum mechanical problems have not yet been amenable to solution with the QTM. This study proposes a hybrid of both the Lagrangian and Eulerian techniques in what is termed the arbitrary Lagrangian–Eulerian method (ALE). In the ALE method, an additional equation of motion governing the momentum of the grid points is coupled into the quantum hydrodynamic equations. These new “quasi-” Bohmian trajectories can be dynamically adapted to the emergent features of the time evolvin...
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an arbitrary lagrangian Eulerian Approach to solving the quantum hydrodynamic equations of motion equidistribution with smart springs
Journal of Chemical Physics, 2003Co-Authors: Corey J Trahan, Robert E. WyattAbstract:Recently, the quantum trajectory method (QTM) has been utilized in solving several quantum mechanical wave packet scattering problems including barrier transmission and electronic nonadiabatic dynamics. By propagating the real-valued action and amplitude functions in the Lagrangian frame, only a fraction of the grid points needed for Eulerian fixed-grid methods are used while still obtaining accurate solutions. Difficulties arise, however, near wave function nodes and in regions of sharp oscillatory features, and because of this many quantum mechanical problems have not yet been amenable to solution with the QTM. This study proposes a hybrid of both the Lagrangian and Eulerian techniques in what is termed the arbitrary Lagrangian–Eulerian method (ALE). In the ALE method, an additional equation of motion governing the momentum of the grid points is coupled into the quantum hydrodynamic equations. These new “quasi-” Bohmian trajectories can be dynamically adapted to the emergent features of the time evolvin...
Stanley Osher - One of the best experts on this subject based on the ideXlab platform.
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a level set based Eulerian Approach for anisotropic wave propagation
Wave Motion, 2003Co-Authors: Jianliang Qian, Litien Cheng, Stanley OsherAbstract:The geometric optics approximation to high frequency anisotropic wave propagation reduces the anisotropic wave equation to a static Hamilton–Jacobi equation. This equation is known as the anisotropic eikonal equation and has three different coupled wave modes as solutions. We introduce here a level set-based Eulerian Approach that captures all three of these wave propagations. In particular, our method is able to accurately reproduce the quasi-transverse, or quasi-S, waves with cusps, which form a class of multi-valued solutions. The level set formulation we use is borrowed from one for moving curves in three spatial dimensions, with the velocity fields for evolution following from the method of characteristics on the anisotropic eikonal equation. We present here our derivation of the algorithm and numerical results to illustrate its accuracy in different cases of anisotropic wave propagations related to seismic imaging. © 2002 Elsevier Science B.V. All rights reserved.
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a non oscillatory Eulerian Approach to interfaces in multimaterial flows the ghost fluid method
Journal of Computational Physics, 1999Co-Authors: Ronald Fedkiw, Tariq D Aslam, Barry Merriman, Stanley OsherAbstract:While Eulerian schemes work well for most gas flows, they have been shown to admit nonphysical oscillations near some material interfaces. In contrast, Lagrangian schemes work well at multimaterial interfaces, but suffer from their own difficulties in problems with large deformations and vorticity characteristic of most gas flows. We believe that the most robust schemes will combine the best properties of Eulerian and Lagrangian schemes. In this paper, we propose a new numerical method for treating interfaces in Eulerian schemes that maintains a Heaviside profile of the density with no numerical smearing along the lines of earlier work and most Lagrangian schemes. We use a level set function to track the motion of a multimaterial interface in an Eulerian framework. In addition, the use of ghost cells (actually ghost nodes in our finite difference framework) and a new isobaric fix technique allows us to keep the density profile from smearing out, while still keeping the scheme robust and easy to program with simple extensions to multidimensions and multilevel time integration, e.g., Runge?Kutta methods. In contrast, previous methods used ill-advised dimensional splitting for multidimensional problems and suffered from great complexity when used in conjunction with multilevel time integrators.
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an Eulerian Approach for vortex motion using a level set regularization procedure
Journal of Computational Physics, 1996Co-Authors: Eduard Harabetian, Stanley Osher, Chiwang ShuAbstract:We present an Eulerian, fixed grid, Approach to solve the motion of an incompressible fluid, in two and three dimensions, in which the vorticity is concentrated on a lower dimensional set. Our Approach uses a decomposition of the vorticity of the form ? =P(?)?, in which both ? (the level set function) and ? (the vorticity strength vector) are smooth. We derive coupled equations for ? and ? which give a regularization of the problem. The regularization is topological and is automatically accomplished through the use of numerical schemes whose viscosity shrinks to zero with grid size. There is no need for explicit filtering, even when singularities appear in the front. The method also has the advantage of automatically allowing topological changes such as merging of surfaces. Numerical examples, including two and three dimensional vortex sheets, two-dimensional vortex dipole sheets, and point vortices, are given. To our knowledge, this is the first three-dimensional vortex sheet calculation in which the sheet evolution feeds back to the calculation of the fluid velocity. Vortex in cell calculations for three-dimensional vortex sheets were done earlier by Trygvassonet al.
