Simple Interface Model Research Articles

Flow Dynamics Measured and Simulated Inside a Single Levitated Droplet

The flow dynamics inside a single liquid droplet of toluene levitated by a countercurrent of deuterated water (D2O) is investigated noninvasively and quantitatively by nuclear magnetic resonance (NMR) imaging techniques for the first time and compared with computational fluid-dynamics (CFD) calculations. For this purpose, a unique device is developed meeting the requirements for long period measurements (namely, a permanently stable droplet position and shape) and for measurements on series of droplets (namely, a high reproducibility of generation and position of droplets). The measurement cell of this device is manufactured with low tolerances regarding axial symmetry and positioned vertical and central in the NMR magnet with high precision enabling axially symmetric flow dynamics. The measured flow field shows good agreement with 2D axially symmetric CFD calculations with the finite element (FEM) code SEPRAN. A simple interface model with one free parameter accounts for the rigid cap encountered in the ...

A simple approach toward quantitative phase field simulation for dilute-alloy solidification

We present a simple approach that could help quantitative phase field simulation for dilute-alloy solidification. The proposed approach mends the solute trapping problem by using a simple interface model (SIM), which requires only one free parameter. To test the feasibility of this model, a free dendritic growth from a small nucleus is simulated, and a good agreement with the anti-trapping current (ATC) model [Karma, Phys. Rev. Lett. 87 (2001) 115701] is obtained. By further studying the solute trapping effect during directional solidification, we find that the results give, with this model, a good thermodynamic consistence without solute trapping over two-order increment of the solidification speed and the interface thickness. Good agreement with the classical theory is obtained as well.

Quantitative phase field simulation of deep cells in directional solidification of an alloy

The formation of deep cells after the onset of Mullins–Sekerka instability during the thin-film directional solidification of a succinonitrile/acetone alloy has been simulated quantitatively by phase field modeling. The solute trapping introduced by the diffusive interface is corrected by a simple interface model, so that at the interface the equilibrium segregation is restored and the Gibbs–Thompson relation is satisfied. With the increasing pulling speed, the transitions from planar to λ c/2 shallow cells, smaller wavelength finite-depth cells, and deep cells are clearly illustrated. The formation of deep cells with change of overall morphologies is performed, and its wavelength transition is consistent with the reported experiments. Furthermore, during the development of a cellular pattern starting from a planar interface, the crossover wavelength under different solidification speeds, where the deformation is comparable to the wavelength, agrees reasonably well with the Warren–Langer theory.

Born integral, stationary phase and linearized reflection coefficients in weak anisotropic media

SUMMARY We show that the linearized reflection coefficients for arbitrary anisotropic media embedded in an isotropic background can be derived directly from a Born formalism. Due to rapidly varying phases of the scattered waves from first-order perturbations in density and elastic parameters, the major contributions to the observed wavefield for any source–receiver pair far from the volume of scatterers arise from the stationary points of a scattering integral, called the Born integral. For simple interface models, such integrals can be evaluated analytically using the method of stationary phase. The resulting scattering function relates linearly to the approximate (linearized) reflection coefficient through a scaling factor determined by the angle of incidence and the properties of the background medium. We consider a homogeneous isotropic background to express the approximate reflection coefficients as a sum of an isotropic and an anisotropic reflection coefficient. The isotropic coefficient is a weighted sum of density and isotropic perturbations about the background, whereas the anisotropic coefficient is a weighted sum of anisotropic perturbations where the weights depend on the angles of incidence, the properties of the background medium as well as the azimuth of the plane of reflection with respect to some symmetry plane of the weakly anisotropic medium. We derived expressions for approximate PP and PS reflection coefficients of a weakly isotropic medium, a weakly orthorhombic medium and a weak but arbitrarily anisotropic medium underlying an isotropic medium. Our expressions for PP reflection coefficients are exactly the same as those obtained from first-order perturbation theory which were previously derived by linearization of the exact reflection coefficients. For converted PS waves, our expressions are valid only for small angles of incidence, but have much simpler forms than those obtained by linearization of exact reflection coefficients. We also derive the approximate PP reflection coefficient of a transversely isotropic medium with a tilted axis of symmetry in an explicit form and investigate the effects of dip of the symmetry axis on these reflection coefficients. Numerical results demonstrate that neglecting the dip of a moderately dipping (30°–60°) symmetry axis of a transversely isotropic medium yields significant errors in determining the weakly anisotropic parameters through an analysis of variations of amplitude with azimuth.

Calculation of electronic structure at bonding interface between vanadium and oxide ceramics for insulator coating applications

Fundamental understanding of metal and ceramics bonding will provide useful guideline to develop a robust coating material for fusion reactor application. We have studied the bonding interface using the model that had three layers of CaO slab adhered to both sides of three layers of V slabs by means of the electronic structure calculation. The simple interface model of vanadium and CaO facing each other at the (0 0 1) plane was employed. Total energy and adhesive energy were evaluated. We found that the relation of adhesive energy and separation distance of the interface is described well by the Rydberg function. The ideal strength of the interface was calculated to be 6.4 GPa. It is proposed that these methods could be applied to systematic development of robust coating materials for fusion applications.

Chemical structure of the ultrathinSiO2/Si(100)interface: An angle-resolved Si2pphotoemission study

The ultrathin ${\mathrm{SiO}}_{2}/\mathrm{S}\mathrm{i}(100)$ interface has been investigated by extensive high-resolution angle-resolved photoemission measurements of the Si $2p$ core levels. The polar angle dependence of the Si $2p$ intensities are measured in detail for the different suboxide $({\mathrm{Si}}^{1+},$ ${\mathrm{Si}}^{2+},$ and ${\mathrm{Si}}^{3+})$ components originating from transition layers at the interface. The depth distribution of the different suboxide species is quantitatively analyzed by a simple electron attenuation scheme. It is unambiguously shown that the ${\mathrm{Si}}^{3+}$ species is distributed over a significantly wider region from the interface, while the ${\mathrm{Si}}^{1+}$ and ${\mathrm{Si}}^{2+}$ species exist mostly within the first interfacial layer. A chemically nonabrupt interface is thus clearly supported, and a simple interface model is introduced which is composed of three transition layers.

Flow/damage surfaces for fiber-reinforced metals having different periodic microstructures

Flow/damage surfaces can be defined in terms of stress, inelastic strain rate, and internal variables using a thermodynamics framework. A macroscale definition relevant to thermodynamics and usable in an experimental program is employed to map out surfaces of constant inelastic power in various stress planes. The inelastic flow of a model silicon carbide/ titanium composite system having rectangular, hexagonal, and square diagonal fiber packing arrays subjected to biaxial stresses is quantified by flow/damage surfaces that are determined numerically from micromechanics, using both finite element analysis and the generalized method of cells. Residual stresses from processing are explicitly included and damage in the form of fiber-matrix debonding under transverse tensile and/or shear loading is represented by a simple interface model. The influence of microstructural architecture is largest whenever fiber-matrix debonding is not an issue; for example in the presence of transverse compressive stresses. Additionally, as the fiber volume fraction increases, so does the effect of microstructural architecture. With regard to the micromechanics analysis, the overall inelastic flow predicted by the generalized method of cells is in excellent agreement with that predicted using a large number of displacement-based finite elements.

An interface model for the prediction of Young's modulus of layered silicate‐elastomer nanocomposites

AbstractRecent experiments on layered silicate‐elastomer nancomposites by Burnside and Giannelis have shown that there is a discrepancy between theoretical modulus predictions and experimental modulus measurements. A theory is proposed to explain this discrepancy. We hypothesize that the discrepancy is due to imperfect bonding between the matrix/inclusion interface which effectively reduces the aspect ratio and the volume fraction of the inclusion. We use a simple interface model to quantify the imperfect interfacial bonding. From this model, we introduce the concept of the effective aspect ratio and effective volume fraction of the inclusions. These effective quantities depends on a single material parameter, namely, the constant interfacial shear stress, τ. The interfacial shear stress for the elastomer‐silicate nanocomposites is found by fitting the theory to the experimentally measured modulus of Burnside and Giannelis. The interfacial shear stress is in the range of thousands of Pascals. For the elastomer‐silicate nanocomposite systems considered here, the interfacial shear stress can be decomposed into two parts; intrinsic shear stress τi and frictional shear stress τf. The intrinsic interfacial shear stress τi depends only on the volume fraction of inclusions and decreases with increasing volume fraction of inclusions. On the other hand, the frictional shear stress τf is found to increase linearly with the applied strain. Since the mean stress is also proportional to the applied strain, this gives rise to an effective coefficient of friction, which is found to be 0.0932 for the nanocomposite system considered here.

Effect of structural non-uniformity on the temperature dependence of the crystal-melt interfacial tension

The temperature dependence of the crystal-melt interfacial tension is calculated for three simple interface models, two uniform ones and one consisting of a bilayer. The differences are appreciable, and it is found that the analysis shows that the adjusting the interface width to a non-integer interface value is a better approximation to the more realistic bilayer than adjusting the thermodynamic parameters to a uniform interface of the full bilayer width.

Local Simulation of Two-Phase Flows Including Interface Tracking with Mass Transfer

This paper presents a moving mesh, two-dimensional finite volume method suitable for tracking interfaces across which there is mass transfer. We consider liquid and vapor phases of single component fluids separated by a phase interface in an evolving flow field. Metastable bulk states are allowed (as are superheated vapor and subcooled liquid bulk states) while the interface is assumed to exist in thermal and chemical equilibrium. Mass transfer occurs at the interface, driven by the local flow conditions. The interface is tracked by nodes representing the liquid and vapor sides at the same spatial location. The interface motion is found from the solution of the coupled interfacial conditions and bulk fluid equations. The bulk fluids are considered as viscous, conducting, and compressible fluids necessitating the use of the continuity, momentum and energy equations in the bulk regions. The control volume continuity, momentum and energy equations are modified in the presence of a phase interface to include surface properties using a simple interface model with surface tension and surface energy. Simple simulations are presented illustrating the method.

The binding of alkali atoms to the surfaces of liquid helium and hydrogen

Alkali atoms have been shown previously to have only unstable binding states inside liquid4He. We calculate the equilibrium configurations and binding energies of single alkali atoms near the liquid-vapor interface of4He and3He. A simple interface model is used to predict the surface deformation due to the presence of the atoms. A more realistic density functional model yields somewhat higher energies in the case of4He. For all alkali atoms, we find the surface binding energies to be around 10 to 20 K. A similar analysis with atom-H2 interactions finds that alkali atoms tend to submerge into liquid H2, with the exception of Li.

Soil-structure interface effects on dynamic interaction analysis of reinforced concrete lifelines

A simple interface model for the analysis of the soil-structure interaction for reinforced concrete lifelines subjected to seismic loading is proposed. This study was aimed to obtain a better understanding of the behaviour of such structures by considering the effects of various interface materials and burial conditions. The proposed model takes into account the soil, and interface properties as well as accurate free-field conditions. The interface model is represented by the relationships between shear and bulk moduli and volumetric strains which can be obtained from soil triaxial tests. Three typical burial conditions of structures were studied, and for each condition three different sand-type soils were considered. The numerical results were compared with similar results without the introduction of the interface model, and they indicated that the interface material had a significant effect on the behaviour of the structures.

Experiments on natural convection in complex enclosed spaces containing either two fluids or a single fluid

Heat transfer coefficients were determined experimentally for natural convection in the enclosed space between two concentrically positioned vertical cylinders having different finite heights. The space was filled with a pair of fluid layers, one atop the other. The investigated two-fluid systems included air and water, air and hexadecane, and hexadecane and water. Experiments were also performed for the case in which the intercylinder space was filled with a single fluid—air, water, or hexadecane. Parametric variations were carried out for the height of the fluid-fluid interface and for the Rayleigh number. Comparisons were made between the experimental results and predictions obtained from numerical solutions of the problem. Very good agreement prevailed for the single-fluid cases and also for the two-fluid cases where meniscus and interfacial tension effects were either negligible or small. When these effects were more significant, as for the hexadecane-water system (the only liquid-liquid system investigated), it was found possible to achieve satisfactory agreement by making use of a relatively simple interface model. For the single-fluid results, the effect of the Prandtl number variation (between 0.71 and 40) was highlighted.