Diffuse-interface theory provides a foundation for the modeling and simulation of microstructure evolution in a very wide range of materials, and for the tracking and capturing of dynamic interfaces between different ...
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Diffuse-interface theory provides a foundation for the modeling and simulation of microstructure evolution in a very wide range of materials, and for the tracking and capturing of dynamic interfaces between different materials on larger scales. Smoothed particle hydrodynamics (SPH) is also widely used to simulate fluids and solids that are subjected to large deformations and have complex dynamic boundaries and/or interfaces, but no explicit interface tracking or capturing is required, even when topological changes such as fragmentation and coalescence occur, because of its Lagrangian particle nature. Here we developed a SPH model for single-component two-phase fluids that is based on diffuse-interface theory. In the model, the interface has a finite thickness and a surface tension that depend on the coefficient k of the gradient contribution to the Helmholtz free energy functional and the density-dependent homogeneous free energy. In this model, there is no need to locate the surface (or interface) or to compute the curvature at and near the interface. One- and two-dimensional SPH simulations were used to validate the model.
In this paper we consider mixed finite element methods for second order elliptic problems. In the case of the lowest order Brezzi-Douglas-Marini elements （if d = 2） or Brezzi- Douglas-Duran-Fortin elements （if d = ...
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In this paper we consider mixed finite element methods for second order elliptic problems. In the case of the lowest order Brezzi-Douglas-Marini elements （if d = 2） or Brezzi- Douglas-Duran-Fortin elements （if d = 3） on rectangular parallelepipeds, we show that the mixed method system, by incorporating certain quadrature rules, can be written as a simple, cell-centered finite difference method. This leads to the solution of a sparse, positive semidefinite linear system for the scalar unknown. For a diagonal tensor coefficient, the sparsity pattern for the scalar unknown is a five point stencil if d = 2, and seven if d = 3. For a general tensor coefficient, it is a nine point stencil, and nineteen, respectively. Applications of the mixed method implementation as finite differences to nonisothermal multiphase, multicomponent flow in porous media are presented.
Numerical simulations are used to model the boundary layer disturbance field due to a spanwise periodic array of circular disks at the surface. Our earlier computations (Fischer and Choudhari 2004) reproduced some of ...
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ISBN:
(纸本)9781624100598
Numerical simulations are used to model the boundary layer disturbance field due to a spanwise periodic array of circular disks at the surface. Our earlier computations (Fischer and Choudhari 2004) reproduced some of the major trends associated with roughness induced transient growth as measured by White and Ergin (2003), confirming the accuracy of their data reduction technique. The present paper explores the effects of roughness height, shape, and size on the transient growth along the wake of the roughness array. Results indicate the range of roughness heights over which the energy levels of the dominant stationary disturbance are consistent with the empirically determined Rek2 scaling of White and Ergin. Computations further reveal the intricate effects of disturbance nonlinearity on transient growth characteristics. At sufficiently large roughness heights, simulations indicate spontaneous vortex shedding behind the roughness array, which has been identified in previous experiments as a precursor to premature transition (i.e., tripping) of the laminar boundary layer. The effect of stationary, suboptimal transient growth disturbances on the amplification of Tollmien-Schlichting instability waves in the boundary layer is also assessed in the light of the recent findings concerning the stabilizing influence of optimal growth streaks (Cossu and Brandt 2002).
The turbulent flow fields associated with the incompressible flow over a 6:1 prolate spheroid at high angle of attack, and the supersonic flow over an ogive cylinder are studied. Both these flows are characterized by ...
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ISBN:
(纸本)9781624100925
The turbulent flow fields associated with the incompressible flow over a 6:1 prolate spheroid at high angle of attack, and the supersonic flow over an ogive cylinder are studied. Both these flows are characterized by large separation and vortical flow regions and therefore provide a challenging database for comparison of turbulent closure models. Of interest is the ability to predict the effects of separation and associated vortical motion common to both flows. Two turbulent models are investigated that each represent the class of linear eddy-viscosity models (LEVMs) and explicit algebraic stress models (EASMs). Since the EASM accounts for anisotropic effects, the influence of these effects on flow field predictions can be assessed. The EASM model is shown to both improve the separation location prediction and pressure trough under the secondary vortex on the 6:1 prolate spheroid at high angle of attack and high Reynolds number, and improve the prediction of the separation location on a supersonic ogive cylinder.
The computation of the two-electron four-center integrals over gaussian basis functions is a significant component of the overall work of many ab initio methods used today, Improvements in the computational efficiency...
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The computation of the two-electron four-center integrals over gaussian basis functions is a significant component of the overall work of many ab initio methods used today, Improvements in the computational efficiency of the base algorithms have provided significant impact, Somewhat overlooked are methods that provide approximations to these integrals and their implementation in application software. A partial review of approximate integral techniques focused on the resolution of the identity (RI) four-center, two-electron integral approximation is given. The past and current uses of the RI algorithms are presented along with possibilities for further exploitation of the technology.
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