scholarly journals Using Plücker Coordinates for Pumping Speed Evaluation of Molecular Pump in the DSMC Method

2001 ◽  
Vol 7 (1) ◽  
pp. 11-20 ◽  
Author(s):  
Fong-Zhi Chen ◽  
Ming-June Tsai ◽  
Yu-Wen Chang ◽  
Rong-Yuan Jou ◽  
Hong-Ping Cheng
Keyword(s):  
Three Dimensional ◽  
Direct Simulation Monte Carlo ◽  
Flow Simulation ◽  
Vacuum Pump ◽  
Ruled Surface ◽  
Molecular Flow ◽  
Dsmc Method ◽  
Plücker Coordinates ◽  
Straight Line ◽  
Speed Performance

In this study, the Plücker coordinates representation is used to formulate the ruled surface and the molecular path for pumping speed performance evaluation of a molecular vacuum pump. The ruled surface represented by the Pliicker coordinates is used to develop a criterion for when gas molecules hit the pump surface wall. The criterion is applied to analyze the flow rate of a new developed vacuum pump in transition regimes by using the DSMC (Direct Simulation Monte Carlo) method. When a molecule flies in a neutral electrical field its path is a straight line. If the molecular path and the generators of a ruled surface are both represented by the Pliicker coordinates, the position of the molecular hit on the wall can be verified by the reciprocal condition of the lines. The Plücker coordinates representation is quite convenient in the DSMC method for this three-dimensional molecular flow simulation.

A Geometrical treatment of the Correspondence between Lines in Threefold Space and Points of a Quadric in Fivefold space

1925 ◽  
Vol 22 (5) ◽  
pp. 694-699 ◽  
Author(s):  
H. W. Turnbull
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Quadratic Relation ◽  
Four Dimensions ◽  
Homogeneous Coordinates ◽  
Plücker Coordinates ◽  
Straight Line ◽  
Set Up ◽  
Image Position ◽  
Three Dimensional Space

§ 1. The six Plücker coordinates of a straight line in three dimensional space satisfy an identical quadratic relationwhich immediately shows that a one-one correspondence may be set up between lines in three dimensional space, λ, and points on a quadric manifold of four dimensions in five dimensional space, S5. For these six numbers pij may be considered to be six homogeneous coordinates of such a point.

Coupled FVM-DSMC Simulation of Micro-Nozzle With Unstructured-Grid

2008 ◽  
Author(s):  
Zhixin Sun ◽  
Zengyao Li ◽  
Yaling He ◽  
Wenquan Tao
Keyword(s):  
Flow Field ◽  
Unstructured Grid ◽  
Direct Simulation Monte Carlo ◽  
Flow Simulation ◽  
Dsmc Method ◽  
Structured Grid ◽  
Micro Nozzle ◽  
Dsmc Simulation ◽  
Volume Method ◽  
Solid Area

The flow field and temperature distributions of free molecular micro-electro-thermal resist jet (FMMR) were studied resorting to DSMC-FVM coupled method. Direct Simulation Monte Carlo (DSMC) method is the most useful tool to simulate the flow field of FMMR and unstructured grid is suitable for the flow simulation in a complicated region with tilted wall surface. DSMC code based on unstructured grid system was developed and then the result was compared with that of structured grid and analytical solution to validate the reliability of the developed code. The DSMC method was then used to simulate the fluid flow in the micro-nozzle (Kn>0.01) and the temperature distribution in the nozzle wall was obtained by the Finite Volume Method (FVM). The Dirichlet-Neumann method was used to couple the wall heat flux and temperature between flow field and solid area. The effect of different income pressure was studied in detail and the results showed that the temperature of solid area changed drastically at different income pressure, so the commonly-adopted method of pre-setting boundary temperature before simulation was unreasonable. The results showed that the influence of boundary layer decreased as the pressure increased.

scholarly journals Numerical simulation of 3-D flow around sounding rocket in the lower thermosphere

2006 ◽  
Vol 24 (1) ◽  
pp. 89-95 ◽  
Author(s):  
J. Kurihara ◽  
K.-I. Oyama ◽  
N. Iwagami ◽  
T. Takahashi
Keyword(s):  
Lower Thermosphere ◽  
Three Dimensional ◽  
Density Measurement ◽  
Direct Simulation Monte Carlo ◽  
Sounding Rocket ◽  
Atmospheric Conditions ◽  
Axially Symmetric ◽  
Asymmetric Flow ◽  
Dsmc Method ◽  
Spin Modulation

Abstract. Numerical simulations using the Direct Simulation Monte Carlo (DSMC) method are known to be useful for analyses of aerodynamic effects on in-situ rocket measurements in the lower thermosphere, but the DSMC analysis of a spin modulation caused by an asymmetric flow around the rocket spin axis has been restricted to the two-dimensional and axially symmetric simulations in actual sounding rocket experiments. This study provides a quantitative analysis of the spin modulation using a three-dimensional (3-D) simulation of the asymmetric flow with the DSMC method. Clear spin modulations in the lower thermospheric N2 density measurement by a rocket-borne instrument are simulated using the rocket attitude and velocity, the simplified payload structure, and the approximated atmospheric conditions. Comparison between the observed and simulated spin modulations show a very good agreement within 5% at around 100km. The results of the simulation are used to correct the spin modulations and derive the absolute densities in the background atmosphere.

Aerothermodynamic modelling of meteor entry flows

2019 ◽  
Vol 492 (2) ◽  
pp. 2308-2325 ◽  
Author(s):  
Federico Bariselli ◽  
Aldo Frezzotti ◽  
Annick Hubin ◽  
Thierry E Magin
Keyword(s):  
Cross Sections ◽  
Impact Ionization ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Vapour Phase ◽  
Molecular Flow ◽  
Material Transport ◽  
Dsmc Method ◽  
Detailed Chemistry ◽  
Ionization Coefficients

ABSTRACT Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes above 80 km, where the atmosphere is rarefied. Ground radio stations allow us to detect the concentration of electrons in the meteoroid trail, which are produced by hyperthermal collisions of ablated species with the freestream. The interpretation of these data currently relies on phenomenological methods, derived under the assumption of free molecular flow, that poorly accounts for the detailed chemistry, diffusion in the vapour phase, and rarefied gas effects. In this work, we employ the direct simulation Monte Carlo (DSMC) method to analyse the detailed flowfield structure in the surroundings of a 1 mm meteoroid at different conditions, spanning a broad spectrum of Knudsen and Mach numbers, and we extract resulting ionization efficiencies. For this purpose, we couple the DSMC method with a kinetic boundary condition which models evaporation and condensation processes in a silicate material. Transport properties of the ablated vapour are computed following the Chapman–Enskog theory starting from Lennard–Jones potentials. Semi-empirical inelastic cross-sections for heavy- and electron-impact ionization of metals are computed analytically to obtain steric factors. The ionization of sodium is dominant in the production of free electrons, and hyperthermal air–vapour collisions play the most important role in this process. The ionization of air, classically disregarded, contributes to the electron production as significantly as ionization of magnesium and iron. Finally, we propose that DSMC could be employed as a numerical experiment providing ionization coefficients to be used in synthetic models.

Comparison of DSMC and CFD Models of Heat Transfer in a Rarefied Two-Dimensional Geometry

2018 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner ◽  
Stefan K. Stefanov
Keyword(s):  
Heat Transfer ◽  
Rarefied Gas ◽  
Complex Geometry ◽  
Direct Simulation Monte Carlo ◽  
Accurate Method ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Two Dimensional ◽  
Dsmc Method ◽  
Cfd Simulations

During vacuum drying of used nuclear fuel (UNF) canisters, helium pressure is reduced to as low as 67 Pa to promote evaporation and removal of remaining water after draining process. At such low pressure, and considering the dimensions of the system, helium is mildly rarefied, which induces a thermal-resistance temperature-jump at gas–solid interfaces that contributes to the increase of cladding temperature. It is important to maintain the temperature of the cladding below roughly 400 °C to avoid radial hydride formation, which may cause cladding embrittlement during transportation and long-term storage. Direct Simulation Monte Carlo (DSMC) method is an accurate method to predict heat transfer and temperature under rarefied condition. However, it is not convenient for complex geometry like a UNF canister. Computational Fluid Dynamics (CFD) simulations are more convenient to apply but their accuracy for rarefied condition are not well established. This work seeks to validate the use of CFD simulations to model heat transfer through rarefied gas in simple two-dimensional geometry by comparing the results to the more accurate DSMC method. The geometry consists of a circular fuel rod centered inside a square cross-section enclosure filled with rarefied helium. The validated CFD model will be used later to accurately estimate the temperature of an UNF canister subjected to vacuum drying condition.

Investigation of the Squeeze Film Dynamics Underneath a Microstructure With Large Oscillation Amplitudes and Inertia Effects

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Dsmc Method ◽  
Inertia Effects ◽  
Flow Parameters ◽  
Fluid Behavior ◽  
Dimensionless Groups ◽  
Simulation Monte Carlo ◽  
The Impact

This paper presents direct simulation Monte Carlo (DSMC) numerical investigation of the dynamic behavior of a gas film in a microbeam. The microbeam undergoes large amplitude harmonic motion between its equilibrium position and the fixed substrate underneath. Unlike previous work in literature, the beam undergoes large displacements throughout the film gap thickness and the behavior of the gas film along with its impact on the moving microstructure (force exerted by gas on the beam's front and back faces) is discussed. Since the gas film thickness is of the order of few microns (i.e., 0.01 < Kn < 1), the rarefied gas exists in the noncontinuum regime and, as such, the DSMC method is used to simulate the fluid behavior. The impact of the squeeze film on the beam is investigated over a range of frequencies and velocity amplitudes, corresponding to ranges of dimensionless flow parameters such as the Reynolds, Strouhal, and Mach numbers on the gas film behavior. Moreover, the behavior of compressibility pressure waves as a function of these dimensionless groups is discussed for different simulation case studies.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

Coarse-To-Fine 3D Randomized Hough Transform for Dim Target Detection

2014 ◽  
Vol 519-520 ◽  
pp. 1040-1045
Author(s):  
Ling Fan
Keyword(s):  
Target Detection ◽  
Hough Transform ◽  
Constant Velocity ◽  
Three Dimensional ◽  
Randomized Hough Transform ◽  
Straight Line ◽  
Memory Complexity ◽  
Coarse To Fine

This paper makes some improvements on Roberts representation for straight line in space and proposes a coarse-to-fine three-dimensional (3D) Randomized Hough Transform (RHT) for the detection of dim targets. Using range, bearing and elevation information of the received echoes, 3D RHT can detect constant velocity target in space. In addition, this paper applies a coarse-to-fine strategy to the 3D RHT, which aims to solve both the computational and memory complexity problems. The validity of the coarse-to-fine 3D RHT is verified by simulations. In comparison with the 2D case, which only uses the range-bearing information, the coarse-to-fine 3D RHT has a better practical value in dim target detection.

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