Solving the Boltzmann equation on GPU’s

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.We present algorithms specifically tailored for solving kinetic equations onto graphics processing units. Unlike particle methods, the proposed methods of solution are ideally suited for solving the unsteady low speed flows which typically occur inMEMS containing oscillating components. The efficiency of the algorithms is demonstrated by solving the two-dimensional low Mach number driven cavity flow of a monatomic gas. Computational results show that it is possible to cut down the computing time of the sequential codes up to two order of magnitudes. The algorithms can easily be extended to three-dimensional flows and to non-equilibrium flows of mixtures

A kinetic theory description of liquid menisci at the microscale

A kinetic model for the study of capillary flows in devices with microscale geometry is presented. The model is based on the Enskog-Vlasov kinetic equation and provides a reasonable description of both fluid-fluid and fluid-wall interactions. Numerical solutions are obtained by an extension of the classical Direct Simulation Monte Carlo (DSMC) to dense fluids. The equilibrium properties of liquid menisci between two hydrophilic walls are investigated and the validity of the Laplace-Kelvin equation at the microscale is assessed. The dynamical process which leads to the meniscus breakage is clarified

Direct simulation Monte Carlo applications to liquid-vapor flows

The paper aims at presenting Direct Simulation Monte Carlo (DSMC) extensions and applications to dense fluids. A succinct review of past and current research topics is presented, followed by a more detailed description of DSMC simulations for the numerical solution of the Enskog-Vlasov equation, applied to the study of liquid-vapor flows. Results about simulations of evaporation of a simple liquid in contact with a dense vapor are presented as an example

3D surface acquisition systems and their applications to facial anatomy : let’s make a point

In the last decades 3D optical devices have gained a primary role in facial anthropometry, where they find several applications from the anatomical research to clinics and surgery. With time the number of articles focusing on 3D surface analysis has raised, as well as validation studies which aim at verifying the reliability of different devices and methods of acquisition in comparison with other methods or direct anthropometry. This review aims at making a point in the field of 3D surface acquisition systems, describing the most used types of available devices and comparing the relevant outcomes in acquiring 3D facial models. Results show that currently stereophotogrammetric devices represent the gold standard, further improved by the diffusion of portable models. Caution should be given to the use of low-cost devices, more and more frequently described by literature, as often they do not meet the basic criteria for being applied to the anatomical study of face

Velocity distribution function of spontaneously evaporating atoms

Numerical solutions of the Enskog-Vlasov (EV) equation are used to determine the velocity distribution function of atoms spontaneously evaporating into near-vacuum conditions. It is found that an accurate approximation is provided by a half-Maxwellian including a drift velocity combined with different characteristic temperatures for the velocity components normal and parallel to the liquid-vapor interface. The drift velocity and the temperature anisotropy reduce as the liquid bulk temperature decreases but persist for relatively low temperatures corresponding to a vapor behaviour which is only slightly non-ideal. Deviations from the undrifted isotropic half-Maxwellian are shown to be consequences of collisions in the liquid-vapor interface which preferentially backscatter atoms with lower normal-velocity component

Solving the Boltzmann Equation on GPU

We show how to accelerate the direct solution of the Boltzmann equation using Graphics Processing Units (GPUs). In order to fully exploit the computational power of the GPU, we choose a method of solution which combines a finite difference discretization of the free-streaming term with a Monte Carlo evaluation of the collision integral. The efficiency of the code is demonstrated by solving the two-dimensional driven cavity flow. Computational results show that it is possible to cut down the computing time of the sequential code of two order of magnitudes. This makes the proposed method of solution a viable alternative to particle simulations for studying unsteady low Mach number flows.Comment: 18 pages, 3 pseudo-codes, 6 figures, 1 tabl