• Advances in aircraft and spacecraft science
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• 제2권4호
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• pp.427-443
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• 2015

The present paper is the follow-on of a former work in which the influence of the gas-surface interaction models was evaluated on the aerodynamic coefficients of an aero-space-plane and on a section of its wing. The models by Maxwell and by Cercignani-Lampis-Lord were compared by means of Direct Simulation Monte Carlo (DSMC) codes. In that paper the diffusive, fully accommodated, semi-specular and specular accommodation coefficients were considered. The results pointed out that the influence of the interaction models, considering the above mentioned accommodation coefficients, is pretty strong while the Cercignani-Lampis-Lord and the Maxwell models are practically equivalent. In the present paper, the comparison of the same models is carried out considering the dependence of the accommodation coefficients on the angle of incidence (or partial accommodation coefficients). More specifically, the normal and the tangential momentum partial accommodation coefficients, obtained experimentally by Knetchel and Pitts, have been implemented. Computer tests on a NACA-0012 airfoil have been carried out by the DSMC code DS2V-64 bits. The airfoil, of 2 m chord, has been tested both in clean and flapped configurations. The simulated conditions were those at an altitude of 100 km where the airfoil is in transitional regime. The results confirmed that the two interaction models are practically equivalent and verified that the use of the Knetchel and Pitts coefficients involves results very close to those computed considering a diffusive, fully accommodated interaction both in clean and flapped configurations.

• Advances in Computational Design
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• 제2권3호
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• pp.165-194
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• 2017

The present work proposes the thermo mechanically induced statistics of nonlinear transverse central deflection of elastically supported functionally graded (FG) plate subjected to static loadings with random system properties. The FG plate is supported on two parameters Pasternak foundation with Winkler cubic nonlinearity. The random system properties such as material properties of FG material, external loading and foundation parameters are assumed as uncorrelated random variables. The material properties are assumed as non-uniform temperature distribution with temperature dependent (TD) material properties. The basic formulation for static is based on higher order shear deformation theory (HSDT) with von-Karman nonlinear strain kinematics through Newton-Raphson method. A second order perturbation technique (SOPT) and direct Monte Carlo simulation (MCS) are used to compute the nonlinear governing equation. The effects of load parameters, plate thickness ratios, aspect ratios, volume fraction, exponent, foundation parameters, and boundary conditions with random system properties are examined through parametric studies. The results of present approaches are compared with those results available in the literature and by employing direct Monte Carlo simulation (MCS).

• Advances in aircraft and spacecraft science
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• 제8권1호
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• pp.53-67
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• 2021

The increasing interest in the exploration of Mars stimulated the authors to study aerodynamic problems linked to space vehicles. The aim of this paper is to evaluate the aerodynamic effects of a flapped wing in collaborating with parachutes and retro-rockets to reduce velocity and with thrusters to control the spacecraft attitude. 3-D computations on a preliminary configuration of a blunt-cylinder, provided with flapped fins, quantified the beneficial influence of the fins. The present paper is focused on Aerodynamics of a wing section (NACA-0010) provided with a trailing edge flap. The influence of the flap deflection was evaluated by the increments of aerodynamic force and leading edge pitching moment coefficients with respect to the coefficients in clean configuration. The study was carried out by means of two Direct Simulation Monte Carlo (DSMC) codes (DS2V/3V solving 2-D/3-D flow fields, respectively). A DSMC code is indispensable to simulate complex flow fields on a wing generated by Shock Wave-Shock Wave Interaction (SWSWI) due to the flap deflection. The flap angle has to be a compromise between the aerodynamic effectiveness and the increases of aerodynamic load and heat flux on the wing section lower surface.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 1995년도 추계학술발표회논문집
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• pp.53-59
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• 1995

The accurcy and the application limits of the Three-Curve Method(TCM) and Zonal Cavity Method(ZCM) are evaluated. Average illuminance values are calculated by TCM and ZCM for various lighting conditions using general Diffusing Luminaires and Direct Luminaires. These values are compared with the values from Monte-Carlo Simulation(MCS) for the same lighting conditions. Accuracy of MCS was proved by Moon's Analytical Method.

• 한국지반공학회논문집
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• 제32권11호
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• pp.31-42
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• 2016

지진에 대한 사면안정 해석은 지진에 의한 관성력을 정적하중으로 고려하는 유사정적해석을 널리 사용하고 있다. 사면과 같은 지반 구조물은 지반정수의 불확실성이 포함되어 있어 확률론적 해석을 이용하여 지반정수의 불확실성을 고려해야 한다. 본 연구에서는 지반의 불확실성을 고려한 확률론적 사면안정해석을 수행하였으며, 구조물이 임의 수준의 지반 운동을 받을 때 파괴상태에 도달하는 확률을 그래프로 나타낸 취약도 곡선을 작성하였다. 유사정적해석으로 확률론적 사면안정해석을 수행하기 위해 Monte Carlo Simulation(MCS)을 시행하였다. MCS의 소요 시간을 단축하기 위하여 인공신경망 기반의 응답면 기법을 이용해 파괴확률을 산출하여 수평지진계수별 취약도 곡선을 작성하는 방법을 제시하였다. 인공신경망을 이용하여 작성한 취약도 곡선을 MCS의 결과와 비교해 본 결과 상당한 시간 절약에 비해 유사한 결과를 얻을 수 있었다.

• 폴리머
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• 제24권2호
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• pp.182-193
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• 2000

폴리알킬렌테레프탈레이트 (PAT)의 고리 올리고머의 몰 고리화 정수(molar cyclization equilibrium constants)를 회전 이성 상태 (rotational isomeric state) (RIS) 모델에 의해Monte Carlo 모사로부터 얻었다. Jacobson-Stockmayer 이론과 이를 보완한 Flory, Suter, 그리고 Mutter의 방법으로는 각 PAT의 고리 올리고머의 함량과 분포를 잘 설명할 수 없었다. RIS모델을 이용한 직접 계산법으로는 반응거리를 ${\gamma}$=0.5 < ${\gamma}^{2}$> $^{1/2}$로 잡아준 경우에 모든 PAT에 대해서 실험치에 가까운 고리 올리고머의 분포를 얻었다. 또한 각 PAT의 입체형태의 변화에 따른 몰고리화 정수의 변화를 고찰하기 위하여 PAT 반복단위 중의 통계적 가중치 rl과 필를 변화시키면서 각 PAT의 몰 고리화 정수를 구하였다. 여러 반응거리와 ${\gamma}$=0.5 < ${\gamma}^{2}$> $^{1/2}$로 설정한 경우에 ${\sigma}_{1}$과 ${\sigma}_{2}$의 변화에 모든 PAT의 평형 고리 올리고머의 함량이 약간 변하기는 하나 그 분포는 그대로유지되었다. 각 PAT의 몰 고리화 정수는 주어진 입체배열에 의해서 일차적으로 결정이 되며 입체형태의 변화에 의해서도 다소 영향을 받는다는 것을 알았다.

• 지구물리와물리탐사
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• 제12권4호
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• pp.281-288
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• 2009

한반도의 감쇠상수에 대한 고유 및 산란감쇠 분리가 최근 해석적인 방법으로 수행되었으나, 깊이에 따라 변하는 산란구조를 고려하기 위해서는 해석적인 방법보다는 수치적인 방법을 써야한다. 그런데, 수치적인 방법의 일종인 Direct Simulation Monte Carlo(DSMC)법은 1차원부터 3차원에 이르기까지 확장성이 좋은 방법이나, 이를 이용한 조사는 잘 이루어지지 않고 있는 상황이다. 븐 연구에서는 해석적인 방법과 DSMC법을 소개하고, 균일한(isotropic)산란 모델에 대하여 두 방법의 결과 값을 비교하였다. 그 결과, 산란감쇠계수$\eta_s$는 동일하나 고유감쇠계수($\eta_i$)의 경우 해석적인 방법이 DSMC 방법보다 값과 그 오차 범위가 더 컸다. 더욱이 DSMC법으로 구한 $Q^{-1}_t$값이 한반도의 기존 연구결과에 가까운 것으로 보아, DSMC법이 한반도의 감쇠상수 분리에 보다 신뢰도 높은 결과를 도출할 수 있는 것으로 보인다.

• 한국정보통신학회논문지
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• 제3권4호
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• pp.839-847
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• 1999

본 논문에서는 MC 시뮬레이션 기법과 QA 시뮬레이션 기법을 이용하여 인접채널간섭, 동위상간섭, 가우시안 잡음이 존재하는 직접위성방송 채널을 성능 평가하였다. 시뮬레이션을 하기 위한 시스템 파라미터들은 현재 무궁화호 위성에서 사용하고 있는 파라미터 및 링크 설계를 기초로 하여 설정하였으며, 두 가지 기법 모두 성능이 수학적 이론 성능에 근접함을 알 수 있었다.

• Environmental Analysis Health and Toxicology
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• 제10권1_2호
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• pp.21-35
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• 1995

Risk assessment processes, which include processes for the estimation of human cancer potency using animal bioassay data and calculation of human exposure, entail uncertainties. In the exposure assessment process, exposure scenarios with various assumptions could affect the exposure amount and excess cancer risk. We compared risk estimates among various exposure scenarios of vinyl chloride, trichloroethylene and tetrachloroethylene in tap water. The contaminant concentrations were analyzed from tap water samples in Seoul from 1993 to 1994. The oral and inhalation cancer potencies of the contaminants were estimated using multistage, Weibull, lognormal, and Mantel-Bryan model in TOX-RISK computer software. In the first case, human excess cancer risk was estimated by the US EPA method used to set the MCL(maximum contaminant level). In the second and third case, the risk was estimated for multi-route exposure with and without adopting Monte-Carlo simulation, respectively. In the second case, exposure input parameters and cancer potencies used probability distributions, and in the third case, those values used point estimates(mean, and maximum or 95% upper-bound value). As a result, while the excess cancer risk estimated by US EPA method considering only direct ingestion tended to be underestimated, the risk which was estimated by considering multi-route exposure without Monte-Carlo simulation and then using the maximum or 95% upper-bound value as input parameters tended to be overestimated. In risk assessment for volatile organic compounds, considering multi-route exposure with adopting Monte-Carlo analysis seems to provide the most reasonable estimations.

• 농촌계획
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• 제19권4호
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• pp.125-135
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• 2013

Analysis and evaluation of uncertainty is adopting the advanced methodology among the methods for greenhouse gas emission assessment that was defined in GPS2000 (Good practice guideline 2000) and GPG-LULUCF (GPG Land Use, Land-Use Change and Forestry). In 2006 IPCC guideline, two approaches are suggested to explain the uncertainty for each section with a national net emission and a prediction value on uncertainty as follows; 1) Spread sheet calculation based on the error propagation algorithm that was simplified with some assumptions, and 2) Monte carlo simulation that can be utilized in general purposes. There are few researches on the agricultural field including greenhouse gas emission that is generated from livestock and cultivation lands due to lack of information for statistic data, emission coefficient, and complicated emission formula. The main objective of this study is to suggest an evaluation method for the uncertainty of greenhouse gas emission in agricultural field by means of intercomparison of the prediction value on uncertainties which were estimated by spread sheet calculation and monte carlo simulation. A statistic analysis for probability density function for uncertainty of emission rate was carried out by targeting livestock intestinal fermentation, excrements treatment, and direct/indirect emission from agricultural lands and rice cultivation. It was suggested to minimize uncertainty by means of extraction of emission coefficient according to each targeting section.