Numerical study of fluid-structure interaction with macro-scale particle methods

The problems of fluid-structure interaction (FSI) are often encountered in different industries as well as the nature. The macro-scale particle methods are advantageous in the FSI simulations, which include smoothed particle hydrodynamics (SPH), macro-scale pseudo- particle modelling (MaPPM), and so forth. Compared with the grid-based numerical techniques, particle methods could provide the flow and/or deformation details without complex tracking of interfaces. The progress of FSI simulation of multiphase flows with rigid particles is presented, and some major findings about heterogeneous structures are stressed. Meanwhile, weakly compressible outflow from elastic tube is investigated, and some preliminary results of flow details are presented. The possible development of macro-scale particle methods in the FSI simulation is prospected finally

Thermal-Diffusional Instability in White Dwarf Flames: Regimes of Flame Pulsation

Thermal-diffusional pulsation behaviors in planar as well as outwardly and inwardly propagating white dwarf carbon flames are systematically studied. In the 1D numerical simulation, the asymptotic degenerate equation of state and simplified one-step reaction rates for nuclear reactions are used to study the flame propagation and pulsation in white dwarfs. The numerical critical Zel'dovich numbers of planar flames at different densities ($\rho=2$, 3 and 4$\times 10^7$~g/cm$^3$) and of spherical flames (with curvature $c=$-0.01, 0, 0.01 and 0.05) at a particular density ($\rho=2\times 10^7$~g/cm$^3$) are presented. Flame front pulsation in different environmental densities and temperatures are obtained to form the regime diagram of pulsation, showing that carbon flames pulsate in the typical density of $2\times10^7~{\rm g/cm^3}$ and temperature of $0.6\times 10^9~{\rm K}$. While being stable at higher temperatures, at relatively lower temperatures the amplitude of the flame pulsation becomes larger. In outwardly propagating spherical flames the pulsation instability is enhanced and flames are also easier to quench due to pulsation at small radius, while the inwardly propagating flames are more stable.Comment: ApJ, 841, 21 (2017), 25 pages in arxiv versio

Schottky-Contact Formation between Metal Electrodes and Molecularly Doped Disordered Organic Semiconductors

We study using three-dimensional kinetic Monte Carlo (KMC) simulations to what extent the formation of Schottky contacts between a metal electrode and a molecularly doped disordered organic semiconductor can be understood from the theory for crystalline inorganic semiconductors, adapted to include the effects of the localized nature of the states in which the charge carriers reside and the hopping transport in between these states. The thickness of the Schottky-contact depletion region is found to be significantly smaller than as expected when the energetical disorder is neglected. The presence of energetic disorder is also found to influence the voltage dependence of the width of the depletion regions near the contacts of single-layer double-Schottky-contact devices. The voltage drop over the two depletion regions and the remaining charge-neutral bulk layer is shown to be described successfully by a semianalytical model, based on an accurately parameterized bulk mobility function of the dopant concentration, energetic disorder, and the electric field. We furthermore find that the mobility in the depletion regions is drastically reduced. As a result, the depletion-region formation process can be ultraslow, with a characteristic time scale ranging from microseconds to beyond milliseconds.</p

Numerical study of fluid-structure interaction with macro-scale particle methods

The problems of fluid-structure interaction (FSI) are often encountered in different industries as well as the nature. The macro-scale particle methods are advantageous in the FSI simulations, which include smoothed particle hydrodynamics (SPH), macro-scale pseudo- particle modelling (MaPPM), and so forth. Compared with the grid-based numerical techniques, particle methods could provide the flow and/or deformation details without complex tracking of interfaces. The progress of FSI simulation of multiphase flows with rigid particles is presented, and some major findings about heterogeneous structures are stressed. Meanwhile, weakly compressible outflow from elastic tube is investigated, and some preliminary results of flow details are presented. The possible development of macro-scale particle methods in the FSI simulation is prospected finally

Theoretical analysis on the applicability of traditional SPH method

As a fully Lagrangian, particle-based numerical method, the traditional smoothed particle hydrodynamics (SPH) generally suffers from the accuracy problem. To investigate the physical origins of this numerical error, the elastic effect between SPH particles is specifically identified by analogy with physical entities, and a unique non-dimensional number is proposed to evaluate the relative dominance of viscous to elastic effect. Through the simulation of two-dimensional Couette flow, the velocity profile and arrangement of particles are examined for various ratios of viscous to elastic effect. The effective viscosity of SPH particles decreases as this non-dimensional number increases, while the increase of particle number significantly reduces the effective viscosity only at lower ratio of viscous to elastic effect. The disparity among nominal viscous dissipation, total dissipation, and theoretical dissipation further confirms the presence of unphysical dissipation resulting from the elastic effect. In summary, due to the constraints from the Mach number and the ratio of viscous to elastic effect, there exists a critical Reynolds number below which the Newtonian behavior could be approximately obtained through suitable choice of model parameters

Powder Technol.

A simple treatment for surface tension in immiscible fluids is proposed for macro-scale particle methods such as smoothed particle hydrodynamics (SPH) and macro-scale pseudo-particle modeling (MaPPM). By introducing a repulsion between the neighboring particles of different fluids, surface tension arises automatically, while simple equations of state are still possible for each phase. This treatment is validated by comparative simulations on the deformation of a square liquid drop in suspension using the volume of fluid (VOF) method. The relationship between surface tension and the repulsion intensity parameter in our model is obtained by the sessile drop method. (C) 2007 Elsevier B.V. All rights reserved.A simple treatment for surface tension in immiscible fluids is proposed for macro-scale particle methods such as smoothed particle hydrodynamics (SPH) and macro-scale pseudo-particle modeling (MaPPM). By introducing a repulsion between the neighboring particles of different fluids, surface tension arises automatically, while simple equations of state are still possible for each phase. This treatment is validated by comparative simulations on the deformation of a square liquid drop in suspension using the volume of fluid (VOF) method. The relationship between surface tension and the repulsion intensity parameter in our model is obtained by the sessile drop method. (C) 2007 Elsevier B.V. All rights reserved

Theoretical analysis on the applicability of traditional SPH method

As a fully Lagrangian, particle-based numerical method, the traditional smoothed particle hydrodynamics (SPH) generally suffers from the accuracy problem. To investigate the physical origins of this numerical error, the elastic effect between SPH particles is specifically identified by analogy with physical entities, and a unique non-dimensional number is proposed to evaluate the relative dominance of viscous to elastic effect. Through the simulation of two-dimensional Couette flow, the velocity profile and arrangement of particles are examined for various ratios of viscous to elastic effect. The effective viscosity of SPH particles decreases as this non-dimensional number increases, while the increase of particle number significantly reduces the effective viscosity only at lower ratio of viscous to elastic effect. The disparity among nominal viscous dissipation, total dissipation, and theoretical dissipation further confirms the presence of unphysical dissipation resulting from the elastic effect. In summary, due to the constraints from the Mach number and the ratio of viscous to elastic effect, there exists a critical Reynolds number below which the Newtonian behavior could be approximately obtained through suitable choice of model parameters

Smoothed particles as a non-Newtonian fluid: A case study in Couette flow

The rheological behavior in a two-dimensional Couette flow simulated using smoothed particle hydrodynamics (SPH) is studied. Newtonian behavior is found to be conditional and shear thinning is significant, leading to a non-linear relationship between apparent viscosity and shear rate, which can be well described by the Sisko model. The transient layered structure of particles with corresponding distortion in velocity profile is observed. The possibility of utilizing this inherent property of SPH for the simulation of non-Newtonian fluids is prospected finally. (C) 2009 Elsevier Ltd. All rights reserved

Tribological analysis of oxide scales during cooling process of rolled microalloyed steel

The composition and phase transformation of oxide scale in cooling process (after hot rolling) of rolled microalloyed steels affect tribological features of rolled strip and downstream process, and the produced steel surface quality. In this study, physical simulation of surface roughness transfer during cooling process with consideration of ultra fast cooling (UFC) was carried out in Hille 100 experimental rolling mill, the obtained oxide scale was examined with SEM to show its surface and phase features. The results indicate that the surface roughness of the oxide scale increases as the final cooling (coiling) temperature increases, and the flow rate of the introduced air decreases. The cracking of the surface oxide scale can be improved when the cooling rate is 20 °C/s, the strip reduction is less than 12%, and the thickness of oxide scale is less than 15 μm, independent of the surface roughness. A cooling rate of more than 70 °C/s can increase the formation of retained wustite and primary magnetite precipitates other than the precipitation of α-iron. This study is helpful in optimising the cooling process after hot rolling of microalloyed steels to obtain quality surface products

Enhanced axial mixing of rotating drums with alternately arranged baffles

Traditional rotating drums are a popular type of tumbling mixer; however, they generally suffer from poor axial mixing with granular materials. To overcome this weakness, a system of alternately arranged baffles is presented, and its effect on particle mixing is numerically assessed using a GPU-based discrete element method. It is found that this arrangement of baffles displays better axial mixing performance than drums with (or without) traditional baffles, and that maximum mixing efficiency can be obtained through a suitable choice of baffle dimension and number. Essentially, this novel arrangement promotes the bulk movement of particles in the axial direction because of the combined radial scattering and axial guiding effects of the baffles. Together with the enhanced dispersive mixing, axial convective mixing serves to increase the axial mixing efficiency. Moreover, it is found that alternately arranged baffles produce good performance in various granular systems of rotating drums. Thus, the proposed system is a promising approach for industrial applications in more complicated mixers. (C) 2015 Elsevier B.V. All rights reserved