Three-dimensional Monte Carlo Method Research Articles

An investigation of a slider air bearing with a asperity contact by a three-dimensional direct simulation Monte Carlo method

A direct simulation Monte Carlo (DSMC) method is used to solve a slider air bearing problem when isolated contacts occur. A flat slider with a spherical asperity underneath is simulated when the tip of the asperity contacts a plate moving at constant speed. Two-dimensional pressure profiles are obtained by using the ideal gas law. The air bearing force on the slider is obtained by calculating the time-averaged change in the vertical momentum of the simulated particles striking the slider. The results show that the pressure is bounded at the contact point. There exists a vacuum region around the contact point where no molecule is small enough to enter. The results also show that the peak pressure and the resultant force converges as the calculation grid gets denser.

Three-dimensional direct simulation Monte Carlo method for slider air bearings

The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision model. Two-dimensional pressure profiles are obtained across the film thickness direction. The results obtained from the two methods agree well with each other for Knudsen numbers as large as 35 which corresponds to a minimum spacing of 2 nm. The result for contact slider is also obtained by the DSMC simulation and presented in this paper.

Radiative Transfer in Cirrus Clouds. Part IV: On Cloud Geometry, Inhomogeneity, and Absorption

Abstract The effects of cloud geometry and inhomogeneity on the radiative properties of cirrus clouds are investigated by using the successive orders of scattering (SOS) approach for radiative transfer. This approach is an integral solution method that em be directly applied to specific geometry and inhomogeneous structure of a medium without the requirement of solving the basic differential radiative transfer equation. A specific interpolation scheme is developed for the intensity and source function iterations to reduce the computation effort, and its accuracies are checked with existing results from the plane-parallel adding-doubling method, a number of two-dimensional models, and the three-dimensional Monte Carlo method. The SOS approach is shown to be particularly useful for cirrus clouds with optical depths less than about 5. Some demonstrative results show that the importance of the cloud-side scattering is dependent on the cloud horizontal dimension relative to the vertical thickness and that the ...

Description of the thermalization process of the sputtered atoms in a glow discharge using a three-dimensional Monte Carlo method

A three-dimensional Monte Carlo model is developed to simulate the thermalization process of atoms sputtered from the cathode in a glow discharge cell. A comparison is made with a simplified analytical thermalization model and the relative importance of different interaction potentials and scattering assumptions on quantities related to thermalization is investigated. Typical results of the thermalization model are (i) the thermalization profile (which gives the distribution of the thermalized sputtered atoms), (ii) the relative amount of atoms that can reach the backplate of the discharge cell without being thermalized, and (iii) the relative amount of backscattering to the cathode. The influence of gas pressure, kind of gas, and cathode material on the thermalization process is also investigated.

Three-dimensional Monte Carlo calculation of the VUV electroluminescence and other electron transport parameters in xenon

The paper presents a set of electroluminescence and other transport parameters calculated using a detailed three-dimensional Monte Carlo method, which simulates the drift of electrons in gaseous xenon (p=760 Torr, T=293 K) under reduced electric fields E/N in the 3 to 16 Td range (E/P approximately 1 to 5 V cm-1 Torr-1), which is the region for secondary scintillation production in xenon filled gas proportional scintillation counters. Results are compared with available experimental or theoretical data as well as an earlier one-dimensional Monte Carlo simulation. The calculated parameters are the excitation and scintillation efficiencies and the reduced light yield, together with mean time intervals, mean drift distances and mean number of elastic collisions between xenon excitation collisions. The authors also present electron drift velocities, mobilities and characteristic energies, as well as mean electron energy and electron energy distribution functions.

An analytical, aperture, and two-layer carrier diffusion MTF and quantum efficiency model for solid-state image sensors

A two-dimensional analytical model is formulated for calculating the pixel response, modulation transfer function (MTF), and quantum efficiency of front-side illuminated, solid-state image sensors. Included in this unified model are the effects of lateral diffusion of charge carriers within a two-layer substrate and less than full pixel sampling apertures. The results of this model are compared to those of a numerical, three-dimensional Monte Carlo algorithm and to the analytical results reported by Blouke and Robinson. We find good agreement between the quantum efficiency and MTF calculated by the present model and by the three-dimensional Monte Carlo method. However, we find higher quantum efficiency and lower MTF than the previously reported analytical two-layer model. The unified aspect of the present model correctly combines the effects of sampling aperture and lateral diffusion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Three-dimensional rarefied flow simulations for the Aeroassist Flight Experiment vehicle

Hypersonic rarefied flow about the Aeroassist Flight Experiment vehicle has been investigated using a three-dimensional direct simulation Monte Carlo method. Calculations are performed for the transitional flows encountered during the vehicle's atmospheric entry for altitudes of 110 and 100 km with an entry velocity of 9.9 km/s. The simulations are performed using a five-species reacting gas model that account for rotational and vibrational internal energies. The solutions indicate that dissociation is important at altitudes of 110 km and below. Results are presented for surface pressures, convective heating, flowfield structure, and aerodynamic coefficient variations with altitude.

Direct simulation of three-dimensional hypersonic flow about intersecting blunt wedges

The general three-dimensional direct simulation Monte Carlo method is used to study the hypersonic flow around two blunt wedges that intersect at a 90 deg angle. Results are obtained for the transitional flow regimes found at 85 and 100 km altitude with a reentry velocity of 7.5 km/s. The disturbance field in front of the double-wedge body is found to be larger than that produced by a single wedge. Surface pressures and flow densities are higher near the wedge intersection, whereas surface heating and shear streses are greater at locations removed from the corner. Results also show that three-dimensional flow structure occurs only near the wedge corner, and that the flow monotonically approaches the limiting two-dimensional wedge flow case in the spanwise direction.

Monte Carlo Calculations of Source Characteristics of FNS Water Cooled Type Tritium Target

The source neutron characteristics of a water cooled type tritium target at the Fusion Neutronics Source (FNS) facility were calculated using a three-dimensional Monte Carlo method. The angular distribution and the energy spectra of the source neutrons were calculated and compared with the measured results. The comparison showed a reasonable agreement which increased the confidence of both measurement and calculation. The calculated neutron spectra which are free from the detector resolution smearing and which extend to lower neutron energy, will be used as the reference source for the future analyses of the experiments using the present-type water cooled target.

Monte Carlo calculations of source characteristics of FNS water cooled type tritium target.

The source neutron characteristics of a water cooled type tritium target at the Fusion Neutronics Source (FNS) facility were calculated using a three-dimensional Monte Carlo method. The angular distribution and the energy spectra of the source neutrons were calculated and compared with the measured results. The comparison showed a reasonable agreement which increased the confidence of both measurement and calculation. The calculated neutron spectra which are free from the detector resolution smearing and which extend to lower neutron energy, will be used as the reference source for the future analyses of the experiments using the present-type water cooled target.