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.

DSMC Simulations of Squeeze Film Between a Micro Beam Undergoing Large Amplitude Oscillations and a Substrate

2012 ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Rarefied Gas ◽  
Numerical Study ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Rf Switch ◽  
Dsmc Method ◽  
Flow Parameters ◽  
Fluid Behavior ◽  
Simulation Monte Carlo ◽  
The Impact

This paper investigates the behavior of a gas film in a micro RF switch. A Two-dimensional numerical study of the flow field is performed as the micro-beam oscillates harmonically 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 RF switch (force exerted by gas on the beam’s front and back faces) are 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 non-continuum regime and, as such, the Direct Simulation Monte Carlo (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, velocity amplitudes, and for different film gases, corresponding to ranges of dimensionless flow parameters such as the Reynolds (Re), Strouhal (St) and Mach (Ma) numbers on the gas film behavior.

scholarly journals Simulation of Rarefied Gas Flow in a Rectangular Enclosure

2019 ◽  
Author(s):  
Sumit Chamling Rai ◽  
Jayesh Sanwal ◽  
K Ram Chandra Murthy
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Stochastic Modelling ◽  
Dsmc Method ◽  
Driven Cavity ◽  
Simulation Monte Carlo ◽  
Computationally Intensive ◽  
Velocity Pressure ◽  
Good Agreement

The present work investigates the effects of rarefaction on gas flow patterns in a lid-driven cavity using the simulation package dsmcFoam, on the OpenFOAM platform. Direct Simulation Monte Carlo (DSMC) method is a simulation technique which caters to the regime in between the computationally intensive molecular dynamics solvers, as well as the often inaccurate NS based solvers (applied to the rarefied gas simulations). It was proposed by G.A. Bird which employs the stochastic modelling of particle motion.Simulations are performed and results are verified for the flow of a rarefied gas Argon) for different lid velocities within the domain. The results are presented as streamlines, contours of velocity, pressure and temperature, along with velocities in X and Y directions. They have been found to be in good agreement with the previous experimental and numerical observations. Our simulations show that these eddies are much harder to observe in the rarefied domain, and cannot be observed upto velocities as high as 200m/s in a cavity with aspect ratio 1.

Statistical Modeling of Rarefied Gas Channel Flows

2009 ◽  
Author(s):  
Seckin Gokaltun ◽  
Michael C. Sukop ◽  
George S. Dulikravich
Keyword(s):  
Lattice Boltzmann ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Direct Simulation ◽  
Channel Axis ◽  
Dsmc Method ◽  
Gas Channel ◽  
Simulation Monte Carlo ◽  
Boltzmann Method ◽  
Linear Pressure Distribution

Lattice Boltzmann method (LBM) and direct simulation Monte Carlo (DSMC) method are used for analysis of moderate Knudsen number phenomena. Simulation results are presented for pressure-driven isothermal rarefied channel flow at various pressure ratios. Analytical equations for non-linear pressure distribution and velocity profiles along the channel axis are used to verify the present LBM and DSMC results. We conclude that the LBM method can be used as an alternative model to DSMC simulations.

scholarly journals Application of DSMC method to astrophysical flows

2003 ◽  
Vol 208 ◽  
pp. 425-426
Author(s):  
Takuya Matsuda ◽  
Hiromi Mizutani ◽  
Henri. M. J. Boffin
Keyword(s):  
Thermal Conduction ◽  
Rarefied Gas ◽  
Turbulent Viscosity ◽  
Direct Simulation Monte Carlo ◽  
Close Binary System ◽  
Close Binary ◽  
Direct Simulation ◽  
Dsmc Method ◽  
Simulation Monte Carlo ◽  
Astrophysical Flows

The Direct Simulation Monte Carlo (DSMC) method, developed originally to calculate rarefied gas dynamical problems, is applied to continuous flow including shocks assuming that the Knudsen number is sufficiently small. In particular, we study the formation of spiral shocks in the accretion disc of a close binary system. The method involves viscosity and thermal conduction automatically, and can thus simulate turbulent viscosity.

Modeling Squeeze Films in the Vicinity of High Inertia Oscillating Microstructures

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Nadim A. Diab ◽  
Issam Lakkis
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Direct Simulation ◽  
Micro Structure ◽  
Dsmc Method ◽  
High Frequencies ◽  
Lubrication Equation ◽  
Simulation Monte Carlo ◽  
Stiffness And Damping

This work investigates the effect of various assumptions proposed by the classical Reynolds lubrication equation. In particular, a microplate oscillating at high frequencies (beyond cutoff) and high velocities leading to appreciable displacement within the film gap is studied. An analytical model is derived with special emphasis on the fluid's inertia effect on the fluid/solid interface. By implementing the direct simulation Monte Carlo (DSMC) method, a numerical method for modeling rarefied gas flow, the analytically based model is adjusted for the force exerted by the gas on the oscillating micro-structure to capture various significant effects related to the fluid's inertia, compressibility, stiffness, and damping.

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.

DSMC Simulations of Squeeze Film Under a Harmonically Oscillating Micro RF Switch With Large Tip Displacements

2012 ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Gas Flow ◽  
Rarefied Gas ◽  
Numerical Technique ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Rf Switch ◽  
Fluid Forces ◽  
Field Velocity ◽  
Micro Cantilever ◽  
Beam Reflection

The two-dimensional unsteady behavior of a rarefied gas film under an oscillating micro-cantilever RF switch is presented. The microbeam, undergoing a parabolic deflection profile, is allowed to oscillate harmonically between its equilibrium position and the fixed substrate underneath for large beam-tip displacements. The gas film dynamics in terms of the flow field velocity and fluid forces exerted on the oscillating microbeam are discussed. The numerical technique used to model the rarefied gas flow is the Direct Simulation Monte Carlo (DSMC) method where the Knudsen (Kn) number is greater than 0.01 (ie. non-continuum regime). Unlike previous work in literature, the beam undergoes large deflections, which requires implementation, in DSMC, of a more realistic molecule-beam reflection behavior based on the instantaneous beam’s position and velocity. The effects of inertia, both local acceleration (St) and convection term (Re), and compressibility (Ma) on the gas film dynamics are examined over ranges of oscillating frequencies, velocity amplitudes, and microbeam’s lengths.

scholarly journals Experimental Validation of a Squeeze-Film Damping Model Based on the Direct Simulation Monte Carlo Method

2007 ◽  
Author(s):  
Hartono Sumali ◽  
David S. Epp ◽  
John R. Torczynski ◽  
Michael A. Gallis
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Experimental Validation ◽  
Tangential Velocity ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Direct Simulation ◽  
Parallel Plates ◽  
Squeeze Film Damping ◽  
Simulation Monte Carlo

A model for computing the force from a gas film squeezed between parallel plates was recently developed using Direct Simulation Monte Carlo simulations in conjunction with the classical Reynolds equation. This paper compares predictions from that model with experimental data. The experimental validation used an almost rectangular MEMS oscillating plate with piezoelectric base excitation. The velocities of the suspended plate and of the substrate were measured with a laser Doppler vibrometer and a microscope. Experimental modal analysis yielded the damping ratio of twelve test structures for several different gas pressures. Small perforation holes in the plates did not alter the squeeze-film damping substantially. These experimental data suggest that the model predicts squeeze-film damping forces accurately. From this comparison, it is seen that these structures have a tangential-velocity accommodation coefficient close to unity.

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