• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.235-240
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• 1995

The paper describes hypersonic rarefied flow of helium and nitrogen over a flat plate by the direct simulation Monte Carlo (DSMC) method. The effect of incomplete accommodation and plate thickness are analyzed and the computational results are compared with wind tunnel test data. Also computational aspects of the method are outlined.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.643-648
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• 2001

The direct simulation Monte Carlo(DSMC) method is applied to investigate steady and unsteady flow fields of a single-stage disk-type drag pump. Two different kinds of pumps are considered: the first one is a rotor-rotor combination, and the second one is a rotor-stator combination. The pumping channels are cut on a rotor and stator. The rotor and stator have 10 Archimedes' spiral blades, respectively. In the present DSMC method, the variable hard sphere model is used as a molecular model, and the no time counter method is employed as a collision sampling technique. For simulation of diatomic gas flows, the Borgnakke-Larsen phenomenological model is adopted to redistribute the translational and internal energies. The DSMC results are in good agreement with the experimental data.

• 한국농공학회지
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• 제36권1호
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• pp.54-62
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• 1994

The expanding technique of the Stochastic Finite Element Method(SFEM) is proposed in this paper for adapting direct integration methods in stochastical dynamic analysis of structures. Grafting the direct integration methods and the SFEM together, one can deal with nonlinear structures and nonstationary process problems without any restriction. The stochastical central diffrence and stochastic Houbolt methods are introduced to show the expanding technique, and their adaptabilities are discussed. Results computed by the proposed method (the Stochastic Finite Element Method in Dynamics: SFEMD) for two degree-of-free- dom system are compared with those obtained by Monte Carlo Simulation.

• Wind and Structures
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• 제31권1호
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• pp.59-73
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• 2020

Wind fragility analysis (WFA) of concrete chimney is often executed disregarding temperature effects. But combined wind and temperature effect is the most critical limit state to define the safety of a chimney. Hence, in this study, WFA of a 70 m tall RC chimney for combined wind and temperature effects is explored. The wind force time-history is generated by spectral representation method. The safety of chimney is assessed considering limit states of stress failure in concrete and steel. A moving-least-squares method based dual response surface method (DRSM) procedure is proposed in WFA to alleviate huge computational time requirement by the conventional direct Monte Carlo simulation (MCS) approach. The DRSM captures the record-to-record variation of wind force time-histories and uncertainty in system parameters. The proposed DRSM approach yields fragility curves which are in close conformity with the most accurate direct MCS approach within substantially less computational time. In this regard, the error by the single-level RSM and least-squares method based DRSM can be easily noted. The WFA results indicate that over temperature difference of 150℃, the temperature stress is so pronounced that the probability of failure is very high even at 30 m/s wind speed. However, below 100℃, wind governs the design.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2009년도 정보통신설비 학술대회
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• pp.242-247
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• 2009

In this paper, we investigate interference between short-range radiocommunication devices (SRDs) with frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS) methods when they are in the same frequency bands. In order to analyze interference from unwanted emission of SRD with DSSS to that of FHSS, Monte-Carlo (MC) simulation method is employed and interference probabilities are calculated. We simulate interference scenarios in accordance with several duty cycles and bandwidths. It is also assumed that the propagation model is free space The effect of distance between interfering transmitter and victim receiver is analyzed and bit error rate (BER) is simulated. From the interference analysis results, it is shown that duty cycle affects compatibility more than bandwidth does. Also, we can make sure of the separation distance which satisfies BER criterion when there are only one interfering transmitter and multiple interfering transmitters.

• 대한기계학회논문집B
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• 제28권12호
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• pp.1501-1510
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• 2004

The pumping characteristics of a single-stage disk-type drag pump (DTDP) are calculated for the variation of the vertical clearance between a rotor and stator by the three-dimensional direct simulation Monte Carlo (DSMC) method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on the both the upper and lower sides of a rotating disk, but a stationary disk is planar. The interaction between molecules is described by the variable hard-sphere model. The no time counter method is used as a collision sampling technique. The vertical clearance has a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4∼533 Pa. When the numerical results are compared with the experimental data, the numerical results agree well quantitatively

• 대한기계학회논문집B
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• 제26권10호
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• pp.1394-1405
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• 2002

The performance of micro-actuators utilizing radiometric forces are studied numerically. The Knudsen number based on gas density and characteristic dimension is varied from near-continuum to highly rarefied conditions. Direct simulation Monte Carlo(DSMC) calculations have been performed to estimate the performance of the micro-actuators. In the present DSMC method, the variable hard sphere molecular model and no time counter technique are used to simulate the molecular collision kinetics. For simulation of diatomic gas flows, the Borgnakke-Larsen phenomenological model is adopted to redistribute the translational and internal energies.

• ETRI Journal
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• 제14권4호
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• pp.19-27
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• 1992

Since. as is well known, direct computation of the reliability for a large-scaled and complex net work generally requires exponential time, a variety of alternative methods to estimate the network reliability using simulation have been proposed. Monte Carlo sampling is the major approach to estimate the network reliability using simulation. In the paper, a dynamic Monte Carlo sampling method, called conditional minimal cut set (CMCS) algorithm, is suggested. The CMCS algorithm simulates a minimal cut set composed of arcs originated from the (conditional) source node until s-t connectedness is confirmed, then reduces the network on the basis of the states of simulated arcs. We develop the importance sampling estimator and the total hazard estimator and compare the performance of these simulation estimators. It is found that the CMCS algorithm is useful in reducing variance of network reliability estimator.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3317-3323
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• 2022

Half Value Layer calculations theoretically need prior specification of linear attenuation calculations, since the HVL value is derived by dividing ln(2) by the linear attenuation coefficient. The purpose of this study was to establish a direct computational model for determining HVL, a vital parameter in nuclear radiation safety studies and shielding material design. Accordingly, a typical gamma-ray transmission setup has been modeled using MCNPX (version 2.4.0) general-purpose Monte Carlo code. The MCNPX code's INPUT file was designed with two detection locations for primary and secondary gamma-rays, as well as attenuator material between those detectors. Next, Half Value Layer values of some well-known gamma-ray shielding materials such as lead and ordinary concrete have been calculated throughout a broad gamma-ray energy range. The outcomes were then compared to data from the National Institute of Standards and Technology. The Half Value Layer values obtained from MCNPX were reported to be highly compatible with the HVL values obtained from the NIST standard database. Our results indicate that the developed INPUT file may be utilized for direct computations of Half Value Layer values for nuclear safety assessments as well as medical radiation applications. In conclusion, advanced simulation methods such as the Monte Carlo code are very powerful and useful instruments that should be considered for daily radiation safety measures. The modeled MCNPX input file will be provided to the scientific community upon reasonable request.

• 한국전산유체공학회지
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• 제19권2호
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• pp.40-48
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• 2014

For rarefied gas flow regimes, physical phenomena such as velocity slip and temperature jump occur on the solid body surface. To predict these phenomena accurately, either the Navier-Stokes solver with a slip boundary condition or the direct simulation Monte Carlo method should be used. In the present study, flow simulations of a wedge were conducted in Mach-10 flow of argon gas for several different flow regimes using a two-dimensional Navier-Stokes solver with the Maxwell slip boundary condition. The results of the simulations were compared with those of the direct simulation Monte Carlo method to assess the present method. It was found that the values of the velocity slip and the temperature jump predicted increase as the Knudsen number increases. Also, the results are comparatively reasonable up to the Knudsen number of 0.05.