Loading...
Search for:
monte-carlo-methods
0.027 seconds
Total 401 records
Numerical simulation of confined nano-impinging jet in microscale cooling application using DSMC method
, Article ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 1 August 2010 through 5 August 2010, Montreal, QC ; Issue PARTS A AND B , 2010 , Pages 359-366 ; 9780791854501 (ISBN) ; Akhlaghi, H ; Karchani, A ; Schneider, G. E ; Sharif University of Technology
2010
Abstract
In this study, we simulate rarefied gas flow through a confined nano-impinging jet using direct simulation Monte Carlo (DSMC) method. The effects of geometrical parameters, pressure ratio, and wall conditions on the heat transfer from a hot surface are examined. Hot surface modeled via diffusive constant wall temperature. Various inlet/confining surface conditions such as specular, adiabatic, and constant temperature are implemented and the effects of them on the wall heat flux rates are studied. The results show that Knudsen number, velocity slip, and temperature jump are main reasons which specify magnitudes of wall heat flux rates. Among all geometrical parameters, H/W ratio has the...
The simulations of flow and heat over microscale sensors in supersonic rarefied gas flows using DSMC
, Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, 4 January 2016 through 6 January 2016 ; Volume 2 , 2016 ; 9780791849668 (ISBN) ; Mosayebi, G ; Sharif University of Technology
American Society of Mechanical Engineers
Abstract
As the use of MEMS-based devices and systems are continuously increasing, the understanding of their correct characteristics becomes so serious for the related researches. In this study, the supersonic rarefied gas flow over microscale hotwires is investigated using the Direct Simulation Monte Carlo (DSMC) method. Indeed, the DSMC has been accepted as a powerful method to study the rarefied gas flow especially in transitional regime. Therefore, it can be considered as a reliable method to investigate the rarefied supersonic flow over microscale objects including the microscale hotwires. In this work, we study the effective parameters, which affect the performance of these sensors at constant...
Direct simulation Monte Carlo solution of subsonic flow through micro/nanoscale channels
, Article Journal of Heat Transfer ; Volume 131, Issue 9 , 2009 , Pages 1-8 ; 00221481 (ISSN) ; Darbandi, M ; Mirjalili, V ; Sharif University of Technology
2009
Abstract
We use a direct simulation Monte Carlo (DSMC) method to simulate gas heating/cooling and choked subsonic flows in micro/nanoscale channels subject to either constant wall temperature or constant/variable heat flux boundary conditions. We show the effects of applying various boundary conditions on the mass flow rate and the flow parameters. We also show that it is necessary to add a buffer zone at the end of the channel if we wish to simulate more realistic conditions at the channel outlet. We also discuss why applying equilibrium-based Maxwellian distribution on molecules coming from the channel outlet, where the flow is nonequilibrium, will not disturb the DSMC solution. The current...
Monte carlo modeling of magnification mode for quantitative assessment of image quality in mammography systems
, Article 2019 IEEE International Symposium on Medical Measurements and Applications, MeMeA 2019, 26 June 2019 through 28 June 2019 ; 2019 ; 9781538684276 (ISBN) ; Khodajou Chokami, H ; Vosoughi, N ; Noorvand, M ; IEEE; IEEE Instrumentation and Measurement Society; Kadir Has University (KHU); UME ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
Scattered radiations are one of the most important factors in the degradation of the image quality of mammography systems. Some techniques have been proposed for the reduction of such rays. Magnification mode can be done by increasing the air gap which determined by the distance of the breast and image intensifier. It is one of the useful techniques to elevate the produced image quality due to the rejection of scattered photons. Monte Carlo N-Particle eXtended transport code (MCNPX) version 2.7.0 is a software package for the simulation of physical processes. In this work, this computer code is used for analyzing the effects of magnification mode on mammographic image quality. To this...
Analytical and numerical studies of sequence dependence of passage times for translocation of heterobiopolymers through nanopores
, Article Journal of Chemical Physics ; Volume 129, Issue 23 , 2008 ; 00219606 (ISSN) ; Roshani, F ; Nourmohammad, A ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
2008
Abstract
We consider chaperone-assisted translocation of biopolymers with two distinct monomers or bases A and B, with the size of the chaperones being λα, where α is a monomer's size. The probability that A and B are neighbors in the biopolymer is PAB. A master equation is used, together with the detailed-balanced condition, in order to derive analytical results for the statistics of the first-passage times of the biopolymer as a function of PAB, λ, and the biopolymer's configuration. Monte Carlo simulations have also been carried out in order to compute the same quantities for biopolymers with 100-900 monomers and several λ. The results indicate nontrivial dependence of the variance of the...
Chiral ising Gross-Neveu criticality of a single Dirac Cone: A quantum Monte Carlo study
, Article Physical Review Letters ; Volume 128, Issue 22 , 2022 ; 00319007 (ISSN) ; Negari, A. R ; Maciejko, J ; Vaezi, A ; Sharif University of Technology
American Physical Society
2022
Abstract
We perform large-scale quantum Monte Carlo simulations of SLAC fermions on a two-dimensional square lattice at half filling with a single Dirac cone with N=2 spinor components and repulsive on-site interactions. Despite the presence of a sign problem, we accurately identify the critical interaction strength Uc=7.28±0.02 in units of the hopping amplitude, for a continuous quantum phase transition between a paramagnetic Dirac semimetal and a ferromagnetic insulator. Using finite-size scaling, we extract the critical exponents for the corresponding N=2 chiral Ising Gross-Neveu universality class: the inverse correlation length exponent ν-1=1.19±0.03, the order parameter anomalous dimension...
Analysis of Single Electron Transistor with Metallic Island and its Application in Logic Circuits
, M.Sc. Thesis Sharif University of Technology ; Faez, Rahim (Supervisor) ; Bagheri Shouraki, Saeed (Supervisor)
Abstract
As the traditional MOSFET is reaching to its scaling limit, it is crucial to find an alternative. Single Electron Devices have shown promising features, such as nano-scale dimensions and extremely low power consumption that can lead to new generation of integrated circuits. In this thesis we have presented an analytical study of metallic single electron devices, particularly single electron transistors (SET). We have illustrated our study with some major logic applications of SET. The main goal of this thesis is to develop simulation software for single electron circuits, comparable with the well-known commercial software “SIMON”, which can provide steady-state and transient analysis of the...
Theoretical Study of Solvent and Substituent Effects on Kinetic and Mechanism of Organic Reactions and Theoretical Study of Enzyme Reactions
, Ph.D. Dissertation Sharif University of Technology ; Gholami, Mohammad Reza (Supervisor)
Abstract
Computational chemistry is used to study solvent and substituent effects on kinetics and mechanism of some organic reactions. It also is used to study enzyme reactions and enzyme structures. Organic reactions were studied by ab initio quantum mechanics and Monte Carlo simulations. The enzyme studies were done by QM/MM and MD methods in Lund University. The studied organic reactions are 1) Reactions of hydroxylamine and aminoxide anion with methyl iodide. 2) Rearrangement of allyl p-tolyl ether. 3) Reactions of 1,4-Benzoquinone with Cyclopentadiene and Cyclohexadiene derivatives and reaction of cyclopentadiene and vinyl acetate. In the enzyme studies the catalytic reaction of Glyoxalase...
Organ Body Dose Simulation Using Monte Carlo Code EGS5 and Human Phantom and Bench-Marking with TL Dosimetry
, M.Sc. Thesis Sharif University of Technology ; Sohrabpour, Mostafa (Supervisor) ; Mahdavi, Rabie (Supervisor)
Abstract
Varian Clinac 2100 accelerator head was simulated using EGS5 Monte Carlo code. Phase space method was applied to this simulation. Two phase space plates were used in these simulations; one was inserted before the moveable jaws and the other one was placed after the jaws. The first plate was simulated for energy. And the second plate was to simulate each field size at the set energy. In the phase space method used in the EGS5 code one extracts the particle parametric information from a file as opposed to following the original particles that start at the source point. It is expected that this file to be a replica of the particles that pass the plate and further it should not add any...
Dose Simulation in Different Body Parts in Radiotherapy Using BEAM Monte Carlo Code on Human Phantom and Bench-Marking with TL Dosimetry
, M.Sc. Thesis Sharif University of Technology ; Sohrabpour, Moustafa (Supervisor) ; Mahdavi, Rabi (Supervisor)
Abstract
In this thesis the calculated dose by corePLAN treatment planning software is compared with the calculated dose from combining BEAMnrc and DOSXYZnrc Monte Carlo codes. First Varian Clinic 2100c/d linear accelerator was simulated and modeling parameters such as electron beam energy and its spatial distribution FWHM were tuned in order for PDD and dose profile curves to have an agreement with less than 2% error with the ion chamber dosimetry. In the second section the derived X-ray beams from the accelerator head simulations were used to calculate dose in different organs of a RANDO phantom. The female RANDO phantom was simulated based on its CT data using DOSXYZnrc code. The CT files of the...
Developing Seismic Fragility Curves for Seismically Isolated Bridges
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor)
Abstract
Purpose of this research is to investigate the effects of different seismic isolation techniques and effect of their location on seismic behavior of assymetric bridges and on mitigating their seismic demand. According to different types of isolators and their possible locations, a research is necessary to help to choose the optimum choice among different possible choices for isolators and their location. In this strudy, Lead-Rubber Beraing (LRB), Friction Pendulum Systme (FPS) and High Damping Rubber (HDR) isolators have been investigated and 3D bridge models are 3-span concrete box girder with 50 meters long each span and each interior piers, 7 or 14 meters long. Isolators also can be...
Investigation of the Solvation of CO2-philic Compounds in the Super Critical CO2 by Monte Carlo Simulations
, Ph.D. Dissertation Sharif University of Technology ; Tafazzoli, Mohsen (Supervisor)
Abstract
Although CO2 is an environmentally benign solvent, many organic solutes are only sparingly soluble in CO2. We use Monte Carlo simulations in the context of statistical perturbation theory, Widom’s particle insertion and expanded ensemble techniques in order to investigate the molecular properties involved in enhancing the solubility of materials in CO2. Our Monte Carlo simulation of diluted methane and its fluorinated forms showed that substitution of H atom with F atom, results in more favorable solvation, but with further increase of F atom (after CH2F2) due to small size of solute it is impossible for all CO2 molecules in the first solvation shell (FSS) to have a good orientation against...
Optimal Locating and Sizing of Distributed Resources for Transmission Congestion Managemet
, M.Sc. Thesis Sharif University of Technology ; Abbaspour-Tehrani Fard, Ali (Supervisor) ; Rashidinejad, Masoud (Supervisor)
Abstract
This thesis presents a variety of methods have been proposed for optimal locating and sizing of Distributed Resource (DR) in restructured power system to reduce congestion and enhance security. Initially three different methodologies, based upon LMP and congestion rent, are presented that form priority list of candidate buses to reduce solution space. For taking into account security, The N−1 contingency criterion is performed and then a priority list of the worst contingencies from congestion rent point of view is organized. Based upon both normal condition and selected contingencies of the network a priority list of buses for optimal placement and for each level of power output of DR is...
Exact Simulation of Varian Clinac 2100C/D with Use of Phase Space file and Representation of Appropriate Source Model for Clinical Applications
, Ph.D. Dissertation Sharif University of Technology ; Sohrabpour, Mostafa (Supervisor) ; Rabi Mahdavi, Saeed (Co-Advisor)
Abstract
MC Simulation is considered to be one of the most accurate methods for transport of radiation in various media. Computational speed is the limiting factor to apply the MC method in clinical settings. One of the methods to increase the speed in MC simulations is the use of phase space file (PSF). PSF is generated by transporting the particles through the linear accelerator head. The characteristics of these particles crossing a reference plane are stored in the PSF file. The PSF can be used in subsequent simulations as a radiation source. The use of PSF is effective but has a drawback of having latent variance. Latent variance is a problem inherent in using phase space files. Latent variance...
Development of the Electron and Photon Transport Code for Dose Calculations on GPU and Benchmarking with EGSnrc Simulation for Radiotherapy
, M.Sc. Thesis Sharif University of Technology ; Sohrabpour, Mostafa (Supervisor)
Abstract
Almost half of all cancer patients receive radiation therapy as main or part of the treatment process. Before performing radiation therapy, first it is necessary to determine the patient’s treatment plan and estimate the outcome of it based on the dose distribution. The quality of treatment is dependent on the accuracy of dosimetry calculations that lies in Monte Carlo algorithms. Unfortunately, most of the computation time is long and not suitable for clinical applications. On the other hand, a real treatment planning will be possible if all aspects of radiation therapy should be considered. The radiation source that is obtained from a medical linear accelerator head is one of these...
Accelerating MCNP using the Adjoint Flux
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Naser (Supervisor) ; Ayyoubzadeh, Mohsen (Co-Advisor)
Abstract
Nuclear engineering simulation requires computer codes which are capable of particle transportation and presenting valid answers. The Monte Carlo method is one of the particle transportation methods and the MCNP code is also a common and efficient code using Monte Carlo method. We usually come across statistical errors in Monte Carlo simulation for reducing which a number of methods have been presented which are called variance reduction methods. In simulating deep penetrating problems, analog Monte Carlo method is weak which leads to considerable error. The chosen variance reduction method for this study is the one which uses adjoint flux. In this study, a 3D deterministic transport code...
Time-variant Reliability Analysis of Offshorre Structure Subject to Multiple Hazards
, M.Sc. Thesis Sharif University of Technology ; Golafshani, Ali Akbar (Supervisor) ; Mahsuli, Mojtaba (Supervisor)
Abstract
The main purpose in this study is the determination of offshore structures reliability index over time by considering the simultaneous effects of natural hazards. Importance of this study stems from the effect of events associated with time which induces high amount of uncertainties on offshore structures performance during their life time. Extreme wave, marine current, earthquake, fatigue, corrosion and marine growth hazards are considered in this paper. The intensity and occurrence time of all hazards are time dependent parameter. In addition some of these hazards have the possibility to coincidence and the interaction effect. Whereas, the previous studies in this field, the effect of each...
Tool Life Prediction Using Bayesian Updating
, M.Sc. Thesis Sharif University of Technology ; Akbari, Javad (Supervisor)
Abstract
Traditional tool life models and wear prediction do not take into account the variation inherent in metal cutting processes. These lead to additional manufacturing costs. This research presents a stochastic method for both tool life and tool wear prediction. In the first part, Bayesian inference is applied to estimate the two model constants of Taylor tool life prediction model using a discrete grid method. Tool wear tests are performed using an uncoated M42 HSS tool and AISI 1018 carbon steel work material. Test results are used to update initial beliefs about the constants and the updated beliefs are then used to predict tool life using a probability density function (pdf). Finally, the...
Tolerance Design of Mechanical Systems based on Reliability Modeling under Bayesian Inference
, M.Sc. Thesis Sharif University of Technology ; Khodaygan, Saeed (Supervisor) ; Assempour, Ahmad (Supervisor)
Abstract
Mechanical production centers are seeking to produce the highest quality products at the lowest cost. Intrinsic processes of manufacturing are not precise processes, and factors such as tool wear, tool vibration and fixation, fixing defects, and other factors that occur during production, make the pieces deviate from the designer's desirable geometry. Usually, due to deviations of parts from their size, their dimensional and geometric characteristics change. Because the components are rarely just a part, often in the majority of parts of the assembly, the operation of the set may be impaired due to the accumulation of changes. Errors that are usually caused during component assembly due to...
Re-entry Vehicle Control Algorithm Design Using Non-linear Dynamic Inversion
, M.Sc. Thesis Sharif University of Technology ; Fathi, Mohsen (Supervisor) ; Assadian, Nima (Supervisor)
Abstract
This thesis is about guiding and controlling the six-degrees of freedom of the reentry vehicle with focus on designing controller by using non-linear dynamic inversion method. Intended reentry vehicle is Apollo which is a reentry capsule without wing and with lifted body and also the proportion of lift to drag is low. Guiding variable instruction, the angle of rolling and constant, are the side slip and attack which reentry vehicle must follow these instructions with the help of controller and with regard to the rotational dynamic of the vehicle. In this thesis more exact six-degrees-freedom model of the vehicle is extracted and the controlling system to
stabilize and to follow guidance...
stabilize and to follow guidance...