• 한국시뮬레이션학회논문지
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• 제13권2호
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• pp.23-34
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• 2004

Regenerative simulation (RS) is a method of stochastic steady-state simulation in which output data are collected and analysed within regenerative cycles (RCs). Since data collected during consecutive RCs are independent and identically distributed, there is no problem with the initial transient period in simulated processes, which is a perennial issue of concern in all other types of steady-state simulation. In this paper, we address the issue of experimental analysis of the quality of sequential regenerative simulation in the sense of the coverage of the final confidence intervals of mean values. The ultimate purpose of this study is to determine the best version of RS to be implemented in Akaroa2 [1], a fully automated controller of distributed stochastic simulation in LAN environments.

• 정보처리학회논문지D
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• 제10D권6호
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• pp.1025-1032
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• 2003

백분위수는 시뮬레이션 결과의 전체적인 성향을 파악하는데 아주 유용한 측정 기법 중의 하나이다. 그러나, 시뮬레이션으로 수집된 데이터들에 대한 평균이나 표준편차와는 달리 백분위수를 추정하기 위해서는 모든 관측된 데이터들을 저장해야 만 한다, 왜냐하면 백분위수의 추정을 위해서는 관측된 모든 데이를 분류하여 오른차순으로 정렬하는 등 여러 단계의 처리과정이 필요하기 때문이다. 따라서, 백분위수 추정을 위해서는 관측된 모든 데이터를 저장하기 위한 대용량의 저장장치와 정렬을 위한 계산시간 (O($nlog_{2}n$))이 요구된다. 이러한 문제점을 해결하기 위한 여러 백분위수 추정 기법들이 제안되었으나 고정된 샘플 크기의 시뮬레이선(fixed sample size simulation) 을 수행할 경우에만 적용 가능하다. [11, 12, 21]. 본 논문에서는 3가지 백분위수 추정 기법(linear PE, batching PE, spectral $P^2$ PE) 을 순차적인 안정상태 시뮬레이션(sequential steady-state simulation) 에 적용하여 연구하였다. 또한, 3가지의 백분위수 추정 기법들에 대해 coverage 분석을 수행한 결과를 제시하였다.

• 정보처리학회논문지A
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• 제9A권4호
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• pp.519-524
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• 2002

본 논문에서는 분산 시뮬레이션 기법 중에 하나인 MRIP(Multiple Replications In Parallel) 시나리오에서 각종 순차적인 시뮬레이션 분석 방법들의 성능을 측정할 수 있는 포함범위(Coverage)에 대한 신뢰구간(confidence intervals) 및 속도향상(Speedup)에 대해 살펴보았다. F-분포를 기반으로 한 신뢰구간에 대한 추정기(estimator)를 단일 프로세서와 다중 프로세서 상에서 참조모델(reference model)로 $M/M/1/{\infty},\;M/D/I/{\infty}과\;M/H_{2}/1/{\infty}$큐잉 시스템을 활용하여 정상상태(steady-state)에서의 평균치를 추정하는 시뮬레이션에 적용하였다. 순차적인 포함범위 분석을 위해서는 수많은 시뮬레이션 실행(Run)들이 요구되는데, MRIP 분산 시뮬레이션 시나리오에서 다중 프로세서를 이용하여 시뮬레이션을 수행하여 최종 시뮬레이션 결과를 얻는데 걸리는 신간을 감소시켰다. 또한, LNA으로 연결된 분산 컴퓨팅 시스템에 시뮬레이션을 동시에 수행시킴으로써 쉽게 필요한 수의 시뮬레이션 실행결과(Run)를 수집할 수 있다. 이는 샘플의 수가 증가됨으로써 좀더 신뢰도가 높은 최종 신뢰구간을 시뮬레이션 수행자가 얻을 수 있게 해준다.

• 대한산업공학회지
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• 제22권1호
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• pp.65-82
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• 1996

This paper proposes a sequential procedure which can be used to determine a truncation point and run length to reduce or remove bias owing to artificial startup conditions in simulations aimed at estimating steady-state behavior. It is based on the idea of Lyapunov exponent in chaos theory. The performance measures considered are relative bias, coverage, estimated relative half-width of the confidence interval, and mean amount of deleted data.

• 정보처리학회논문지D
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• 제11D권1호
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• pp.219-228
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• 2004

지금까지 비율(proportion)에 대한 신뢰구간의 근사적 추정량(approximate estimator)에 대한 여러 기법들이 제안되었으나, 시뮬레이션 결과에 대한 coverage 분석을 수행할 경우에는 정규분포에 기반 한 신뢰구간 추정량이 주로 이용되었다. 그 이유는 정규분포에 대한 근사법이 다른 근사법들 보다 실제 구현하는데 쉽게 여겨졌기 때문이다. 하지만, 최근에 arcsin 변환에 기반한 coverage 분석을 위한 근사법이 [12]에서 시뮬레이션 수행 시에 최종결과에 요구되는 정확도의 조절과 비율을 추정하기 위해서 사용되었다. 본 논문에서는 세 개의 신뢰구간 추정량 근사법(정규분포 기반 근사법, arcsin 변환 기반 근사법, 그리고 F-분포 기반 근사법)을 비교 분석하였다. 세 신뢰구간에 대한 추정량을 단일 프로세서와 다중 프로세서 상에서 참조모델(reference model)로 M/M/1/$\infty$와 W/D/l/$\infty$ 큐잉 시스템을 활용하여 정상상태(steady-state)에서의 평균치를 추정하는 시뮬레이션에 적용하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.87-92
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• 1991

A naphtha reforming process treats the feed naphtha for the production of BTX and high octane gasoline. In this paper, the development of NAFOS (Naphtha Reformer Steady-State Simulator), which is the efficient tool for the wide range of reforming process studies, is presented. NAFOS system is based on the sequential modular approach and composed of unit computation routines, physical properties data base, numerical routines, flowsheet convergence routine and user interfaces for input-output control. The developed NAFOS system has been tested by computation of the UOP Platforrming process. Simulation results of NAFOS corresponded with that of established general purpose simulator (ASPEN PLUS), and faster for the same simulation case.

• Environmental Engineering Research
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• 제19권2호
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• pp.165-174
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• 2014

A model combining multi-dimensional discretized population balance equations with a computational fluid dynamics simulation (CFD-DPBE model) was developed and applied to simulate turbulent flocculation and sedimentation processes in sediment retention basins. Computation fluid dynamics and the discretized population balance equations were solved to generate steady state flow field data and simulate flocculation and sedimentation processes in a sequential manner. Up-to-date numerical algorithms, such as operator splitting and LeVeque flux-corrected upwind schemes, were applied to cope with the computational demands caused by complexity and nonlinearity of the population balance equations and the instability caused by advection-dominated transport. In a modeling and simulation study with a two-dimensional simplified pond system, applicability of the CFD-DPBE model was demonstrated by tracking mass balances and floc size evolutions and by examining particle/floc size and solid concentration distributions. Thus, the CFD-DPBE model may be used as a valuable simulation tool for natural and engineered flocculation and sedimentation systems as well as for flocculant-aided sediment retention ponds.

• 대한기계학회논문집B
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• 제30권10호
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• pp.966-972
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• 2006

A numerical simulation is performed fur developing turbulent flow in a strongly curved 180 deg pipe and its downstream tangent by a new solution code(PowerCFD) which adopts an unstructured cell-centered method. The governing equations are discretized as the full elliptic from of the equations of motion. Three typical two-equation turbulence models of low-Reynolds-number form are used to approximate the turbulent stress field. Solutions fur both streamwise and circumferential velocity components are compared with the experimental data by Azzola et at.(1986). The ${\kappa}-{\omega}$ model by Wilcox(1988) is found to give better prediction performance than the other two. Predicted secondary velocities and streamwise velocity component contours at sequential longitudinal stations are also presented in order to enable a detailed description of the complete flow. It is also found that, in the bend both mean streamwise and secondary velocities never achieve a fully-developed state and the code is capable of producing very well the complex nature of steady flow in a strongly curved pipe.

• Journal of Biosystems Engineering
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• 제35권4호
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• pp.224-230
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• 2010

The purpose of this study was to develop position control system of an electric actuator for automatic shuttle shifting of a tractor. The electric actuator was installed at the link of the forward-reverse gearshift of the tractor transmission, and controlled in the ranges of forward, neutral, and reverse positions. The position control system of the electric actuator was developed based on PID (Proportional Integral Derivative) controller and transfer function of the electric actuator. The coefficients of the PID controller were determined by Ziegler-Nichols (Z-N) method and optimized using simulation program. The prototype AMT (Automated Manual Transmission) test unit of the tractor was installed and used to evaluate the performance of the position control. The evaluation system for the control performance consisted of forward-reverse actuator, motor driver, and controller. The tests were conducted as the controlled positions of the actuator were changed from neutral position to forward, neutral, and reverse positions in sequence. The sequential tests were repeated 20 times. The operations of changing the gearshift were considered as the step response of the control system. Maximum overshoot, settling time, and steady-state error were analyzed. The results showed that performance of the position control system was reasonable and qualified. The maximum overshoots, the steady-state errors, and the settling times of the position control system were 10~20%, 1~5%, and 0.92~1.49 sec, respectively. The modifications of the electric actuator will be required to enhance the performance of position control during field operation.