• 대한산업공학회지
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• 제12권1호
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• pp.19-30
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• 1986

This paper provides an evaluation of static flowshop scheduling heuristics for minimizing makespan as an objective function in the dynamic flowshop model, in which new jobs with stochastic processing times arrive at the shop randomly over time and are added into the waiting jobs for processing. A total of sixteen scheduling heuristics, including several revisions and combinations of previously reported me-sixteen scheduling heuristics, including several revisions and combinations of previously reported methods, are surmmarized. These scheduling rules are evaluated via computer using a SLAM discrete event simulation model. The results for the simulation are analyzed using both statistical and nonstatistical methods. The results from the study suggest which of the popular scheduling rules hold promise for application to practical dynamic flowshop problems.

• 한국컴퓨터정보학회논문지
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• 제15권8호
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• pp.181-192
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• 2010

본 논문에서는 연속제조 생산방식을 취하는 제조업에서 기계고장이 발생하여 생산 일정이 실시간으로 변경되어 야 하는 환경에서도 적용 가능한 dispatching 방법을 개발한다. 개발된 dispatching 방법은 생산지연으로 인한 재료의 재가열 비용과 설치비용, 잔여납기일을 고려하여 지표를 개발하고, 지표의 값이 가장 작은 재료에 우선순위를 부여하여 기계에 할당하는 방식을 취하고 있다. 개발된 dispatching방법의 우수성 입증하기 위해 SPT와 선입선출 방법을 비교대상으로 선출하고, 이들 방법을 통계적 시뮬레이션을 통해 도출된 손실비용을 비교분석한다. 통계적으로 유효성을 입증하기 위해 각 방법별로 200개의 데이터와 20번의 반복을 통해 실험을 실시하며, 실험결과 본 연구에서 제시한 방법이 비교대상 방법에 비해 유효한 손실비용의 감소효과를 보였다. 또한 본 논문에서 개발된 통계적 시뮬레이터는 대기시간에 발생 가능한 비용을 추가하거나 변경이 용이하여 불확실성을 고려한 생산일정계획부문에 유용하게 사용될 것으로 기대한다.

• 한국CDE학회논문집
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• 제13권1호
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• pp.36-44
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• 2008

This paper proposes a modeling and simulation process of a panel production line (PPL) in a shipyard. The panel production line is an assembly process to produce a main panel of a flat block and a curved block. In this paper, its activity analysis is carried out using expression of IDEF0, and its process is qualitatively and quantitatively analyzed and modeled by Petri Nets. A commercial discrete event simulation tool, $QUEST^{TM}$, is used for virtual PPL and simulation. The modeling results by Petri Net are mapped to elements of the simulation tool. Finally, an integrated simulation environment of PPL is implemented in order to efficiently utilize the virtual PPL model. With the help of IDEF0 and Petri Nets, we could systematically analyze and describe the PPL process that are characterized as being concurrent, asynchronous, distributed, parallel, nondeterministic, and/or stochastic. Also, the dynamic and concurrent activities of a PPL system were able to be simulated. A timing concept can be included into the Petri nets model to evaluate performance and dependability issues of the system.

• Smart Structures and Systems
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• 제14권1호
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• pp.39-54
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• 2014

Node layout optimization of structural wireless systems is investigated as a means to prolong the network lifetime without, if possible, compromising information quality of the measurement data. The trade-off between these antagonistic objectives is studied within a multi-objective layout optimization framework. A Genetic Algorithm is adopted to obtain a set of Pareto-optimal solutions from which the end user can select the final layout. The information quality of the measurement data collected from a heterogeneous WSN is quantified from the placement quality indicators of strain and acceleration sensors. The network lifetime or equivalently the network energy consumption is estimated through WSN simulation that provides realistic results by capturing the dynamics of the wireless communication protocols. A layout optimization study of a monitoring system on the Great Belt Bridge is conducted to evaluate the proposed approach. The placement quality of strain gauges and accelerometers is obtained as a ratio of the Modal Clarity Index and Mode Shape Expansion values that are computed from a Finite Element model of the monitored bridge. To estimate the energy consumption of the WSN platform in a realistic scenario, we use a discrete-event simulator with stochastic communication models. Finally, we compare the optimization results with those obtained in a previous work where the network energy consumption is obtained via deterministic communication models.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권2호
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• pp.579-603
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• 2018

In this paper we propose a QoS-enhanced intelligent stochastic optimal fair real-time packet scheduler, QUEST, for 4G LTE traffic in routers. The objective of this research is to maximize the system QoS subject to the constraint that the processor utilization is kept nearly at 100 percent. The QUEST has following unique advantages. First, it solves the challenging problem of starvation for low priority process - buffered streaming video and TCP based; second, it solves the major bottleneck of the scheduler Earliest Deadline First's failure at heavy loads. Finally, QUEST offers the benefit of arbitrarily pre-programming the process utilization ratio.Three classes of multimedia 4G LTE QCI traffic, conversational voice, live streaming video, buffered streaming video and TCP based applications have been considered. We analyse two most important QoS metrics, packet loss rate (PLR) and mean waiting time. All claims are supported by discrete event and Monte Carlo simulations. The simulation results show that the QUEST scheduler outperforms current state-of-the-art benchmark schedulers. The proposed scheduler offers 37 percent improvement in PLR and 23 percent improvement in mean waiting time over the best competing current scheduler Accuracy-aware EDF.

• 산업경영시스템학회지
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• 제40권4호
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• pp.211-220
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• 2017

The application of the theoretical model to real assembly lines has been one of the biggest challenges for researchers and industrial engineers. There should be some realistic approach to achieve the conflicting objectives on real systems. Therefore, in this paper, a model is developed to synchronize a real system (A discrete event simulation model) with a theoretical model (An optimization model). This synchronization will enable the realistic optimization of systems. A job assignment model of the assembly line is formulated for the evaluation of proposed realistic optimization to achieve multiple conflicting objectives. The objectives, fluctuation in cycle time, throughput, labor cost, energy cost, teamwork and deviation in the skill level of operators have been modeled mathematically. To solve the formulated mathematical model, a multi-objective simulation integrated hybrid genetic algorithm (MO-SHGA) is proposed. In MO-SHGA each individual in each population acts as an input scenario of simulation. Also, it is very difficult to assign weights to the objective function in the traditional multi-objective GA because of pareto fronts. Therefore, we have proposed a probabilistic based linearization and multi-objective to single objective conversion method at population evolution phase. The performance of MO-SHGA is evaluated with the standard multi-objective genetic algorithm (MO-GA) with both deterministic and stochastic data settings. A case study of the goalkeeping gloves assembly line is also presented as a numerical example which is solved using MO-SHGA and MO-GA. The proposed research is useful for the development of synchronized human based assembly lines for real time monitoring, optimization, and control.