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#### Ballistic and collisional flow contributions to anti-fourier heat transfer in rarefied cavity flow

, Article Scientific Reports ; Volume 8, Issue 1 , 2018 ; 20452322 (ISSN) ; Roohi, E ; Stefanov, S ; Sharif University of Technology
Abstract

This paper investigates anti-Fourier heat transfer phenomenon in a rarefied gas confined within a lid-driven cavity using a novel flow decomposition technique in the direct simulation Monte Carlo (DSMC) method proposed by Stefanov and co-workers. An isothermal cavity with different degrees of flow rarefaction from near continuum to mid transition regimes was considered to investigate cold-to-hot heat transfer from ballistic/collision flow decomposition viewpoint. A new cold-to-hot heat transfer indicator in the form of a scalar product of normalized heat flow vector and normalized temperature gradient vector has been introduced for the overall, ballistic and collision parts of these vectors....

#### Simulation, design optimization, and experimental validation of a silver SPND for neutron flux mapping in the Tehran MTR

, Article Nuclear Engineering and Technology ; Volume 52, Issue 12 , 2020 , Pages 2852-2859 ; Ayyoubzadeh, S. M ; Terman, M. S ; Sharif University of Technology
Korean Nuclear Society
2020

Abstract

This paper deals with the simulation-based design optimization and experimental validation of the characteristics of an in-core silver Self-Powered Neutron Detector (SPND). Optimized dimensions of the SPND are determined by combining Monte Carlo simulations and analytical methods. As a first step, the Monte Carlo transport code MCNPX is used to follow the trajectory and fate of the neutrons emitted from an external source. This simulation is able to seamlessly integrate various phenomena, including neutron slowing-down and shielding effects. Then, the expected number of beta particles and their energy spectrum following a neutron capture reaction in the silver emitter are fetched from the...

#### , M.Sc. Thesis Sharif University of Technology ; Behnia, Fereidoon (Supervisor)

Abstract

In this thesis, Particle Filter Methods are investigated in the context of moving targets tracking and the associated performance analysis. The application scope of this algorithm which is a particular case of Sequential Monte Carlo Method is far broader than tracking of moving targets. This algorithm can be used for mathematical calculations such as estimation of mathematical expectations, integrals, surface area of curves and many other mathematical calculations. In addition, it has applications in other branches of science like genetics. This algorithm is based on random sampling of a probability density function and resampling from the extracted samples. We change this algorithm in...

#### Development of a 3D multigroup program for dancoff factor calculation in pebble bed reactors

, Article Annals of Nuclear Energy ; Vol. 72, issue , 2014 , pp. 311-319 ; ISSN: 03064549 ; Vosoughi, N ; Sharif University of Technology
Abstract

The evaluation of multigroup constants in reactor calculations depends on several parameters. One of these parameters is the Dancoff factor which is used for calculating the resonance integral and flux depression in the resonance region in heterogeneous systems. In the current paper, a computer program (MCDAN-3D) is developed for calculating three dimensional black and gray Dancoff coefficients, based on Monte Carlo, escape probability and neutron free flight methods. The developed program is capable to calculate the Dancoff factor for an arbitrary arrangement of fuel and moderator pebbles. Moreover this program can simulate fuels with homogeneous and heterogeneous compositions. It might...

#### Numerical study of species separation in rarefied gas mixture flow through micronozzles using DSMC

, Article Physics of Fluids ; Volume 31, Issue 4 , 2019 ; 10706631 (ISSN) ; Darbandi, M ; Sharif University of Technology
American Institute of Physics Inc
2019

Abstract

This work investigates the species separation in the rarefied flow of the argon-helium mixture through convergent-divergent micronozzles. Imposing a molecular mass ratio in the order of 10, the flow of this mixture can lead to the formation of serious nonhomogeneous phenomena such as the species separation. This study is performed in the ranges of 2.0-4.0 for the geometrical expansion ratio, 200-400 K for the wall temperature, and 0.003-1.454 for the inlet Knudsen number. The effects of these parameters are examined on the separative performances of micronozzle. The direct simulation Monte Carlo method is selected as the solution method because it can provide reliable solutions in the...

#### Study of Light Propagation in Biological Tissues by Means of the Monte Carlo Simulation and Diffusion Method

, M.Sc. Thesis Sharif University of Technology ; Amjadi, Ahmad (Supervisor) ; Ansari, Mohammad Ali (Supervisor)
Abstract

The tissue characteristics are important for all kinds of medical laser applications in order to understand the interaction mechanisms between light and tissue. Knowledge about light transport in tissue is essential for cancer treatment and cancer diagnostic techniques. By having the diffused reflectance of a tissue we can determine its optical characteristics. In this thesis we have solved the inverse process. That is, we compute the diffused reflectance of a turbid media with pre-determined optical parameters. This problem can be solved using two methods: Monte Carlo simulation and diffusion method. Since Monte Carlo simulation is computationally very expensive, it is not used in medical...

#### The Prediction Branching Polypropylene Monte Carlo Method

, M.Sc. Thesis Sharif University of Technology ; Mousavi, Ali (Supervisor)
Abstract

Linear structure of polypropylene, which is a direct result of Ziegler-Natta catalysts, led to the melt strength of the polymer is low and it does not show hardness strain. This defect is cause to the use of polypropylene in some processes, such as thermoforming, making foam etc. are limited. A main methods to solve this defect are branching structure of the polymer. There are three general methods for this purpose, which are modified by chemical, electron beam irradiation and polymerization in the presence of metallocene catalyst. The first two methods that past processing, polypropylene branching using linear type is produced, while the third method branching occurs during polymerization....

#### Developing a Parallel DSMC Algorithm for Simulating Flow in Micro-Nano Propulsion Systems

, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract

With the rapid development of mico-nano propulsion systems in micro-spacecrafts and micro-sattelites, precise investigation of flow field in these devices has become necessary. Micro propulsion systems usually have a thrust in order of mili Newton, and they can be used for maneuvers of spacecrafts with mass of less than 10 kg. Micro propulsion systems are usually classified according to their thrust generation mechanism to different classes like cold gas, and chemical propulsion systems. Cold gas micro propulsion systems obtain their energy from thermodynamic expansion of gas and not by combustion. If the flow fiel dimensionare comparable to mean free path, rarefaction effects are observed...

#### Second virial coefficients of Exp-6 chains: A Monte Carlo simulation

, Article Chemical Physics ; Volume 397, Issue 1 , March , 2012 , Pages 26-33 ; 03010104 (ISSN) ; Ramazani Saadatabadi, A ; Khanpour, M ; Sharif University of Technology
2012

Abstract

The second virial coefficients of Exp-6 chains are calculated using the Monte Carlo method. The results are presented as the scaled second virial coefficient B 2/(m 2σ 3) for various chain lengths m and repulsive-wall steepness parameters α at different scaled temperatures T *. The scaled coefficient reduces and converges to a constant value as m → ∞. Interestingly, the scaled coefficient scales as B 2/(m 2σ 3) ∝ -α -1, where the dependence reduces for larger m. The gyration radius increases with α, and in good solvent regime, scales like a self-avoiding chain when m → ∞. The interaction energy between two chains depends on m, T *, and α. With increasing m, the interaction becomes less...

#### An effective optimization algorithm for locally nonconvex lipschitz functions based on mollifier subgradients

, Article Bulletin of the Iranian Mathematical Society ; Volume 37, Issue 1 , 2011 , Pages 171-198 ; 10186301 (ISSN) ; Yousefpour, R ; Sharif University of Technology
Abstract

We present an effective algorithm for minimization of locally nonconvex Lipschitz functions based on mollifier functions approximating the Clarke generalized gradient. To this aim, first we approximate the Clarke generalized gradient by mollifier subgradients. To construct this approximation, we use a set of averaged functions gradients. Then, we show that the convex hull of this set serves as a good approximation for the Clarke generalized gradient. Using this approximation of the Clarke generalized gradient, we establish an algorithm for minimization of locally Lipschitz functions. Based on mollifier subgradient approximation, we propose a dynamic algorithm for finding a direction...

#### Monte Carlo simulation of recrystallization with hardness input of cold worked metal

, Article Materials Science and Engineering A ; Volume 496, Issue 1-2 , 2008 , Pages 389-392 ; 09215093 (ISSN) ; Sharif University of Technology
2008

Abstract

A Monte Carlo model on the basis of hardness input is developed to predict the annealing microstructure of deformed specimens in tensile, compression, and tensile + compression tests. From experimental value of hardness, the stored energy of the deformed specimens is calculated and entered into the Monte Carlo model. The consistency between the simulation results and experimental data shows that the developed model based on hardness input can be more practical since the effect of different deformation states is considered for estimating of stored energy. © 2008 Elsevier B.V. All rights reserved

#### An analytical and experimental investigation on the normal grain growth in metals using the Monte Carlo method

, Article Materials and Design ; Volume 28, Issue 9 , 2007 , Pages 2533-2539 ; 02613069 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
Elsevier Ltd
2007

Abstract

The prediction of material microstructure is of great interest to the material designers since the property and performance of materials depend strongly on their microstructures. In this work, a Monte Carlo approach is used to investigate the normal grain growth of aluminum and pure copper. The grain growth was calculated at certain temperatures using the grain growth law and compared with the simulation results by varying the Q as a parameter of simulation lattice orientation for pure aluminum. Also the results predicted by the Monte Carlo method showed a good agreement with the experimental results of grain growth of pure cooper. It was found that increase in Q increases the accuracy of...

#### Using the direct simulation Monte Carlo method to study the effect of wall temperature variation on gas mixing evolution through micro T-mixers

, Article 11th International Energy Conversion Engineering Conference ; 2013 ; Sabouri, M ; Lekzian, E ; Schneider, G. E ; Sharif University of Technology
2013

Abstract

In this work, we study the gas mixing behavior in a micro T-mixer using the direct simulation Monte Carlo (DSMC) method. The gas mixing process is monitored through a T-mixer, which is fed by two different CO and N2 gases; flowing into the T-mixer through the upper and lower inlets. We investigate the effects of axial and lateral wall temperature gradients on the mixing evolution at different rarefaction levels. The achieved results show that any temperature difference between the channel walls would result in an increase in mixing length for the chosen wall temperature gradient ranges and the studies pressure cases. Our observations show that a positive temperature gradient toward the...

#### Development of a 3D program for calculation of multigroup Dancoff factor based on Monte Carlo method in cylindrical geometry

, Article Annals of Nuclear Energy ; Volume 78 , 2015 , Pages 49-59 ; 03064549 (ISSN) ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2015

Abstract

Evaluation of multigroup constants in reactor calculations depends on several parameters, the Dancoff factor amid them is used for calculation of the resonance integral as well as flux depression in the resonance region in the heterogeneous systems. This paper focuses on the computer program (MCDAN-3D) developed for calculation of the multigroup black and gray Dancoff factor in three dimensional geometry based on Monte Carlo and escape probability methods. The developed program is capable to calculate the Dancoff factor for an arbitrary arrangement of fuel rods with different cylindrical fuel dimensions and control rods with various lengths inserted in the reactor core. The initiative...

#### Detection of ammonia gas by knudsen thermal force in micro gas actuator

, Article Case Studies in Thermal Engineering ; Volume 12 , 2018 , Pages 276-284 ; 2214157X (ISSN) ; Barzegar Gerdroodbary, M ; Mosavat, M ; Ganji, D. D ; Sharif University of Technology
Abstract

Direct Simulation Monte Carlo (DSMC) method is applied to evaluate the performance of a new micro gas sensor (MIKRA) for mass analysis of ammonia in the rarefied gas. In order to simulate a rarefied gas inside the micro gas detector, Boltzmann equation is applied to obtain high precision results. This study performed comprehensive studies to reveal the main mechanism of force generation and applied this for the analysis of the gas mixture. Our findings show that value of generated Knudsen force significantly varies when the percentage of the NH3 varies in the mixture. According to obtained results, the maximum Knudsen force increases when the fraction of the ammonia decreases. Our findings...

#### A new approach for solution of time dependent neutron transport equation based on nodal discretization using MCNPX code with feedback

, Article Annals of Nuclear Energy ; Volume 133 , 2019 , Pages 519-526 ; 03064549 (ISSN) ; Salehi, A. A ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2019

Abstract

This paper proposes a new method for solving the time-dependent neutron transport equation based on nodal discretization using the MCNPX code. Most valid nodal codes are based on the diffusion theory with differences in approximating the leakage term until now. However, the Monte Carlo (MC) method is able to estimate transport parameters without approximations usual in diffusion method. Therefore, improving the nodal approach via the MC techniques can substantially reduce the errors caused by diffusion approximations. In the proposed method, the reactor core is divided into nodes of arbitrary dimensions, and all terms of the transport equation e.g. interaction rates and leakage ratio are...

#### A time dependent Monte Carlo approach for nuclear reactor analysis in a 3-D arbitrary geometry

, Article Progress in Nuclear Energy ; Volume 115 , 2019 , Pages 80-90 ; 01491970 (ISSN) ; Salehi, A. A ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2019

Abstract

A highly reliable tool for transient simulation is vital in the safety analysis of a nuclear reactor. Despite this fact most tools still use diffusion theory and point-kinetics that involve many approximation such as discretization in space, energy, angle and time. However, Monte Carlo method inherently overcomes these restrictions and provides an appropriate foundation to accurately calculate the parameters of a reactor. In this paper fundamental parameters like multiplication factor (K eff ) and mean generation time (t G ) are calculated using Monte Carlo method and then employed in transient analysis for computing the neutron population, proportional to K eff , during a generation time...

#### Implementation of a dynamic Monte Carlo method for transients analysis with thermal-hydraulic feedbacks using MCNPX code

, Article Annals of Nuclear Energy ; Volume 130 , 2019 , Pages 240-249 ; 03064549 (ISSN) ; Salehi, A. A ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2019

Abstract

Transient analysis which is vital in safety analysis requires a reliable calculation method. Most valid tools use diffusion theory with many approximations by now. However, the Monte Carlo method inherently overcomes these approximations and accurately calculates the parameters of a reactor. In this paper, a new time-dependent transport approach is described to simulate the nuclear reactor dynamic correctly using the MCNPX code. In this approach the fundamental parameters of a nuclear reactor like multiplication factor (K eff ) and mean generation time (t G ) are calculated using MCNPX code. They are then employed in the formulas to compute neutron population, proportional to K eff , during...

#### A new Monte Carlo approach for solution of the time dependent neutron transport equation based on nodal discretization to simulate the xenon oscillation with feedback

, Article Annals of Nuclear Energy ; Volume 141 , 2020 ; Salehi, A. A ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2020

Abstract

In this paper a probabilistic methodology based on core nodalization is proposed to estimate the core power in the presence of xenon oscillation. A time-dependent Monte Carlo neutron transport code named MCSP-NOD is developed for dynamic analysis in arbitrary 3D geometries to simulate xenon oscillations as well as sub-critical condition with feedbacks. The new code is based on the approach adopted in MCNP-NOD which was previously introduced as a tool for core transient analysis using the MCNPX platform. As before, the core is divided into nodes of arbitrary dimensions, and all terms of the transport equation e.g. interaction rates, leakage ratio are estimated using the MC techniques....

#### Study of Net Current of Particles in 2D Pulsated Potential Landscape

, M.Sc. Thesis Sharif University of Technology ; Ejtehadi, Mohammad Reza (Supervisor)
Abstract

In systems possessing spatial or dynamical symmetry breaking, Brownian motion combined with unbiased external input signals, deterministic and random alike, can assist directed motion of particles at nanoscale. “Brownian motors” are devices by whi thermally or extrinsically activated processes are controlled and used to generate directed motion in space. Rectification devices involving asymmetric substrates are termed ratets and if the potential priodically turns on and off in time, it is called “Pulsated Ratet.“ In this resear net current of particles in 2D pulsated asymmetric potential landscapes is surveyed theoretically and by

Monte Carlo method simulation

Monte Carlo method simulation