Monte Carlo Particle Simulation Research Articles

Test Particle Monte Carlo Simulation of Return Flux on Various Geometric Surfaces due to Ambient Scatter of Outgassing Molecules

The test particle Monte Carlo (TPMC) method is delineated by taking the molecular return flux problem for the flow past a complete sphere as an example and the return flux on a variety of geometric surfaces, including a complete sphere, a circle flat plate, a convex and concave hemisphere, due to ambient scatter of outgassing molecules is simulated by this method. The return flux ratio (RFR) obtained here for the flow past a sphere is in good agreement with previous results. Then, effects of various outgassing and freestream conditions on RFR for flows past three geometric bodies, including a circle flat plate, a convex and concave hemisphere, have been investigated and compared. Moreover, heuristic arguments about geometric, outgassing and freestream governing parameters provide theoretical references for the evaluation and control of return flux contamination.

Test Particle Monte Carlo Simulation of the Interaction of Two Parallel Flat Plates in Free Molecular Flow Regime

A free-molecular flow past two parallel circular flat plates is analyzed by the test particle Monte Carlo (TPMC) method, and flow shadowing and multiple reflections between the two plates is discussed with heuristic arguments based on the kinetic theory of gases. Flow shadowing and multiple reflections have a significant influence on aerodynamic coefficients of the two plates. Lift coefficients of the two plates do not equal to zero at the pitch angle of 0° and drag coefficients of the shading plate are larger than those of the shaded plate. The area ratio and distance of the two plates have an evident effect on flow shadowing and multiple reflections.

Test Particle Monte Carlo Simulation of Return Flux on Various geometric surfaces due to Ambient Scatter of Outgassing Molecules

The test particle Monte Carlo (TPMC) method is delineated by taking the molecular return flux problem for the flow past a complete sphere as an example and the return flux on a variety of geometric surfaces, including a complete sphere, a circle flat plate, a convex and concave hemisphere, due to ambient scatter of outgassing molecules is simulated by this method. The return flux ratio (RFR) obtained here for the flow past a sphere is in good agreement with previous results. Then, effects of various outgassing and freestream conditions on RFR for flows past three geometric bodies, including a circle flat plate, a convex and concave hemisphere, have been investigated and compared. Moreover, heuristic arguments about geometric, outgassing and freestream governing parameters provide theoretical references for the evaluation and control of return flux contamination.

Self-assembly in Nafion membranes upon hydration: water mobility and adsorption isotherms.

By means of dissipative particle dynamics (DPD) and Monte Carlo (MC) simulations, we explored geometrical, transport, and sorption properties of hydrated Nafion-type polyelectrolyte membranes. Composed of a perfluorinated backbone with sulfonate side chains, Nafion self-assembles upon hydration and segregates into interpenetrating hydrophilic and hydrophobic subphases. This segregated morphology determines the transport properties of Nafion membranes that are widely used as compartment separators in fuel cells and other electrochemical devices, as well as permselective diffusion barriers in protective fabrics. We introduced a coarse-grained model of Nafion, which accounts explicitly for polymer rigidity and electrostatic interactions between anionic side chains and hydrated metal cations. In a series of DPD simulations with increasing content of water, a classical percolation transition from a system of isolated water clusters to a 3D network of hydrophilic channels was observed. The hydrophilic subphase connectivity and water diffusion were studied by constructing digitized replicas of self-assembled morphologies and performing random walk simulations. A non-monotonic dependence of the tracer diffusivity on the water content was found. This unexpected behavior was explained by the formation of large and mostly isolated water domains detected at high water content and high equivalent polymer weight. Using MC simulations, we calculated the chemical potential of water in the hydrated polymer and constructed the water sorption isotherms, which extended to the oversaturated conditions. We determined that the maximum diffusivity and the onset of formation of large water domains corresponded to the saturation conditions at 100% humidity. The oversaturated membrane morphologies generated in the canonical ensemble DPD simulations correspond to the metastable and unstable states of Nafion membrane that are not realized in the experiments.

A Conjoined Electron and Thermal Transport Study of Thermal Degradation Induced During Normal Operation of Multigate Transistors

A 3-D full-band particle Monte Carlo (MC) simulator, with full electron and phonon dispersion and a 2-D quantum correction is self-consistently coupled to a phonon MC simulator. The coupling entails feeding the phonon data obtained from the 3-D electrical MC to the phonon MC. The phonon MC reciprocates by providing the resulting spatial temperature map, which is used in the electron MC, with temperature-dependent scattering table, in a self-consistent manner. A key feature of our model is its ability to delineate the influence of the various phonon modes on the electronic transport through the application of anharmonic phonon decay and full phonon dispersion. The electrothermal simulator developed is utilized to assess the performance of silicon-on-insulator (SoI) multigate (MG) MOSFET with nanoscale cross sections. This paper shows that the hotspot in inversion mode SoI MG MOSFET with 20-nm gate length permeates into the channel as the cross section is reduced (covering ~ 50% of the channel for the 5 nm × 5 nm cross section). Furthermore, cross-sectional scaling, a key design rule to mitigate short-channel effects, degenerates device performance well beyond the ideal current gain limits of MG MOSFET architecture of double-gate, trigate, and gate-all-around MOSFET. Consequently, at the sub-20-nm scale adding more gate does not necessarily improve performance.

Depth dependency of neutron density produced by cosmic rays in the lunar subsurface

Depth dependency of neutrons produced by cosmic rays (CRs) in the lunar subsurface was estimated using the three-dimensional Monte Carlo particle and heavy ion transport simulation code, PHITS, incorporating the latest high energy nuclear data, JENDL/HE-2007. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with the measurement by Apollo 17 Lunar Neutron Probe Experiment (LNPE). Our calculations reproduced the LNPE data except for the 350–400mg/cm2 region under the improved condition using the CR spectra model based on the latest observations, well-tested nuclear interaction models with systematic cross section data, and JENDL/HE-2007.

Numerical simulation of multipactor phenomenon on the surface of cylinder window disk

A particle model that is based on Monte Carlo particle simulation arithmetic is built up to investigate the multipactor behavior on the surface of cylinder window disk in pill-box window. The regime of multipactor in the inhomogeneous electric field is obtained. The simulation results prove that the interaction between secondary electrons and window disk is sustained by magnetic field force on the upstream side. The multipactor phenomenon acts intensively in the area with a great electric field. The ponderomotive force does not devote any effort to multipactor on the upstream side. On the downstream side, the multipactor cannot be excited without strong enough surface electrostatic field because of the positive magnetic field force. With the increase of transmitting power, secondary electrons can obtain more energies. Due to the effect of ponderomotive force, the multipactor region transfers from the area with powerful electric field to the weak one on the downstream side. Besides, the resistance effect of electrostatic isolation on multipactor is also confirmed in the input port of cylinder waveguide.

Optimal recloser and autosectionalizer allocation in distribution networks using IPSO–Monte Carlo approach

Determination of optimal location of automatic devices such as reclosers and autosectionalizers (R&AS’s) for reliability improvement of distribution systems is a combinational and complex problem. In this paper, a methodology based on cost/benefit analysis for optimal R&AS’s allocation in distribution systems is proposed. The objective function is considered minimizing the costs of reliability of the distribution systems. Besides, the effect of load types is considered in the optimal R&AS’s allocation. A hybrid method based on Improved Particle Swarm Optimization (IPSO) algorithm and Monte Carlo simulation is proposed for solving the problem. The proposed algorithm is applied to the actual 50-bus distribution system in Qazvin-Iran. Numerical studies are representing of the effectiveness of the proposed method.

Drag coefficient modeling for grace using Direct Simulation Monte Carlo

Drag coefficient is a major source of uncertainty in predicting the orbit of a satellite in low Earth orbit (LEO). Computational methods like the Test Particle Monte Carlo (TPMC) and Direct Simulation Monte Carlo (DSMC) are important tools in accurately computing physical drag coefficients. However, the methods are computationally expensive and cannot be employed real time. Therefore, modeling of the physical drag coefficient is required. This work presents a technique of developing parameterized drag coefficients models using the DSMC method. The technique is validated by developing a model for the Gravity Recovery and Climate Experiment (GRACE) satellite. Results show that drag coefficients computed using the developed model for GRACE agree to within 1% with those computed using DSMC.

Hybrid Monte-Carlo method for simulating neutron and photon radiography

We present a Hybrid Monte-Carlo method (HMCM) for simulating neutron and photon radiographs. HMCM utilizes the combination of a Monte-Carlo particle simulation for calculating incident film radiation and a statistical post-processing routine to simulate film noise. Since the method relies on MCNP for transport calculations, it is easily generalized to most non-destructive evaluation (NDE) simulations. We verify the method's accuracy through ASTM International's E592-99 publication, Standard Guide to Obtainable Equivalent Penetrameter Sensitivity for Radiography of Steel Plates [1]. Potential uses for the method include characterizing alternative radiological sources and simulating NDE radiographs.

Obtaining identical results with double precision global accuracy on different numbers of processors in parallel particle Monte Carlo simulations

We describe and compare different approaches for achieving numerical reproducibility in photon Monte Carlo simulations. Reproducibility is desirable for code verification, testing, and debugging. Parallelism creates a unique problem for achieving reproducibility in Monte Carlo simulations because it changes the order in which values are summed. This is a numerical problem because double precision arithmetic is not associative.Parallel Monte Carlo, both domain replicated and decomposed simulations, will run their particles in a different order during different runs of the same simulation because the non-reproducibility of communication between processors. In addition, runs of the same simulation using different domain decompositions will also result in particles being simulated in a different order.In [1], a way of eliminating non-associative accumulations using integer tallies was described. This approach successfully achieves reproducibility at the cost of lost accuracy by rounding double precision numbers to fewer significant digits. This integer approach, and other extended and reduced precision reproducibility techniques, are described and compared in this work.Increased precision alone is not enough to ensure reproducibility of photon Monte Carlo simulations. Non-arbitrary precision approaches require a varying degree of rounding to achieve reproducibility. For the problems investigated in this work double precision global accuracy was achievable by using 100 bits of precision or greater on all unordered sums which where subsequently rounded to double precision at the end of every time-step.

Uncertain Time Series in Weather Prediction

Abstract The paper reviews about methods have been implemented on uncertain time series data in weather prediction. The aim of uncertain time series analysis is to formulate uncertain data in order to gain knowledge, fit low dimensional models, and do prediction. Euclidean distance, particle swarm optimization, data mining, and Monte Carlo simulation are methods that have been compared to investigate the best ways of predicting. These methods have been implemented since early 1900s. This paper discusses on the performance of every methods.

Stochastic order-based optimal design of a surface reservoir–irrigation district system

This paper explores the effects of streamflow uncertainty and the type of stochastic order, which is used for comparing stochastic variables, on optimal design of a reservoir multi-crop irrigation district system. Four nonlinear mathematical programs with an economic objective function including deterministic, stochastic-EXP with expected value order, stochastic-SD with stochastic dominance (SD) order, and stochastic-EGCL with expected gain-confidence limit (EGCL) order were developed. Afterwards, the approaches of successive linear programming (SLP) and PSO–MC, which combines particle swarm optimization (PSO) algorithm and Monte Carlo simulation (MC), to solve the programs were selected. Hajiarab Irrigation District located in Ghazvin Province of Iran was used as a case study and the results obtained from using different programs and solution approaches were analyzed and compared. Among the solution approaches, SLP could not solve the programs other than the deterministic one while PSO–MC could find at least good solutions, if not the global optima, for all the programs. Among the main decision variables, the stochastic programs resulted in a reduced size of irrigation district compared with that obtained by the deterministic program. Moreover, the programs using stochastic orders other than a simple expected value converged at solutions different from the solution reached by the expected value-based program.

Application of IPSO-Monte Carlo for optimal distributed generation allocation and sizing

Determination of optimal location and size of Distributed Generations (DGs) is one of the major problems of distribution utilities. In this paper, a multi-objective methodology for optimal distributed generation allocation and sizing in distribution systems is proposed. The objective function is considered willing to minimize the costs of active and reactive losses, and to improve the voltage profile and reliability of the distribution systems. Besides, the effect of load models is considered in the optimal DG allocation. A hybrid method based on improved particle swarm optimization (IPSO) algorithm and Monte Carlo simulation is proposed for solving the problem. The proposed algorithm is applied to the practical 33-bus distribution system and results are compared with other versions of PSO and artificial bee colony (ABC) algorithm. Numerical studies are representing of the effectiveness and out-performance of the proposed method.

The simulation results of signal fluctuation for micromegas-like gaseous detector

In the present paper, the mean signal value and its fluctuations were investigated for the well known Micro-Mesh Gaseous Structure (Micromegas) filled with argon-based gas mixtures. The number of primary electrons and ions in the conversion gap were calculated using the FLUKA code for incoming electrons. The signal resolution is a function of the energy loss or the number of produced primary electrons and its fluctuation in the detector volume. The signal generations were made with a Single Particle Monte Carlo simulation technique in the amplification gap region. We assumed a homogeneous electric field inside both the conversion and the amplification gap because the electric field shows only a small change near the openings of the microgrid. Based on the simulation, we discuss the signal fluctuations that affect the work performance of the Micromegas for different argon-based gas mixtures.

Particle Monte Carlo simulation of string-like colloidal assembly in two and three dimensions

We simulate structural phase behavior of polymer-grafted colloidal particles by molecular Monte Carlo technique. The interparticle potential, which has a finite repulsive square-step outside a rigid core of the colloid, was previously confirmed via numerical self-consistent field calculation. This model potential is purely repulsive. We simulate these model colloids in the canonical ensemble in two and three dimensions and find that these particles containing no interparticle attraction self-assemble and align in a string-like assembly, at low temperature and high density. This string-like colloidal assembly is related to percolation phenomena. Analyzing the cluster size distribution and the average string length, we build phase diagrams and discover that the average string length diverges around the region where the melting transition line and the percolation transition line cross. This result is similar to Ising spin systems, in which the percolation transition line and the order-disorder line meet at a critical point.

Monte Carlo simulation of electron transport in a graphene diode with a linear energy band dispersion

Electron transport and energy relaxation in a 100-nm channel n+-n-n+ monolayer graphene diode were studied by using semiclassical Monte Carlo particle simulations. A diode with a conventional parabolic band and an identical geometry and scattering process was also analyzed in an attempt to confirm that the characteristic transport properties originated from the linear energy band structure. We took into account two scattering mechanisms: isotropic elastic scattering and inelastic phonon emission. The carrier velocity distributions in the two diodes show remarkable differences reflecting their band dispersions. Electron velocity in the monolayer graphene diode is high in the channel region and remains almost constant until the energy relaxation begins. Inelastic scattering does not reduce electron velocity so severely, whereas elastic scattering significantly decreases it through backscattering of hot electrons with high kinetic energy. Elastic scattering also degrades the ballisticity and the drain current; however, increasing the inelastic scattering offsets these effects. We found that elastic scattering should be suppressed to improve the performance of graphene devices.

Experimental results and numerical modeling of a high-performance large-scale cryopump. I. Test particle Monte Carlo simulation

For the torus of the nuclear fusion project ITER (originally the International Thermonuclear Experimental Reactor, but also Latin: the way), eight high-performance large-scale customized cryopumps must be designed and manufactured to accommodate the very high pumping speeds and throughputs of the fusion exhaust gas needed to maintain the plasma under stable vacuum conditions and comply with other criteria which cannot be met by standard commercial vacuum pumps. Under an earlier research and development program, a model pump of reduced scale based on active cryosorption on charcoal-coated panels at 4.5 K was manufactured and tested systematically. The present article focuses on the simulation of the true three-dimensional complex geometry of the model pump by the newly developed ProVac3D Monte Carlo code. It is shown for gas throughputs of up to 1000 sccm (∼1.69 Pa m3/s at T = 0° C) in the free molecular regime that the numerical simulation results are in good agreement with the pumping speeds measured. Meanwhile, the capture coefficient associated with the virtual region around the cryogenic panels and shields which holds for higher throughputs is calculated using this generic approach. This means that the test particle Monte Carlo simulations in free molecular flow can be used not only for the optimization of the pumping system but also for the supply of the input parameters necessary for the future direct simulation Monte Carlo in the full flow regime.

Monte Carlo Simulation of Noise and THz Generation in InP FET at Excess of Electrons in Channel

Electron transport and drain current noise in field effect transistor with nnn InP channel have been studied by Monte Carlo particle simulation which simultaneously solves the Boltzmann transport and pseudo-2D Poisson equations. It is shown that at gate voltages giving excess electron concentration in n-region of channel the drain current self-oscillations in THz frequency range are possible. The self-oscillations are driven by electron plasma instability.

Electron transport properties in high-purity Ge down to cryogenic temperatures

Electron transport in Ge at various temperatures down to 20 mK has been investigated using particle Monte Carlo simulation taking into account ionized impurity and inelastic phonon scattering. The simulations account for the essential features of electron transport at cryogenic temperature: Ohmic regime, anisotropy of the drift velocity relative to the direction of the electric field, as well as a negative differential mobility phenomenon along the ⟨111⟩ field orientation. Experimental data for the electron velocities are reproduced with a satisfactory accuracy. Examples of electron position in the real space during the simulations are given and evidence separated clouds of electrons propagating along different directions depending on the valley they belong to.