• 한국수자원학회논문집
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• 제56권7호
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• pp.439-449
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• 2023

최근 계측 기술의 발전으로 압력계와 유량계 등 다양한 센서를 설치하여 상수도관망의 상태를 효과적으로 파악할 수 있게 되었으나, 도시가 광범위하게 개발됨에 따라 계측 신뢰도에 영향을 미치는 변수는 다양해지고 있다. 특히 상수도관망 분석에 중요한 영향력을 가지는 수요 데이터의 경우 직접 계측의 난이도가 높고 결측이 발생하기 쉬운 것으로 알려져 데이터 생성의 중요도가 증가하고 있다. 본 논문에서는 상수도관망에서 누락된 데이터를 정확하게 생성하기 위해 생성적 딥러닝 모델에 기반한 적대적 학습 기반 오토인코더(ATAE) 모델을 제안한다. 제안된 모델은 판별 신경망과 생성 신경망의 두 가지 신경망의 적대적 학습을 사용하여 압력 데이터로부터 수요 데이터를 생성한다. 학습이 완료된 ATAE 모델의 생성 신경망은 관망의 계측되는 압력 데이터가 존재하는 경우, 그로부터 추정된 관망 수요 데이터를 제공할 수 있다. ATAE 모델은 미국 텍사스주 오스틴의 실제 상수도망에 적용되어 성능이 검증되었다. 수요 및 압력 시계열 데이터의 불확실성 정도에 따른 ATAE 예측 결과의 정확도를 비교하여 데이터 불확실성의 영향을 분석하였으며, 또한 수요 수준에 따른 데이터 수집 기간별 생성 결과를 비교하여 이에 따른 데이터 생성 성능을 검토하였다.

• 한국경영공학회지
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• 제23권4호
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• pp.87-103
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• 2018

This paper introduces the method to develop two main types of the fuzzy OEE (Overall Equipment Effectiveness) models via triangular membership function for measuring uncertainty. The fuzzy OEE includes model type 1 and model type 2. The model type 1 is used when the theoretical machine speed only reflects the time loss whereas model type 2 is used when the actual machine speed reflects both time and speed loss. Model type 2 has shown to perform a lower availability rate and a higher performance rate compared to model type 1. In addition, the fuzzy UPH (Unit Per Hour) which is derived from using the fuzzy OEE is presented to satisfy demand uncertainty. The fuzzy UPH can easily measure the fuzzy tact time and cycle time by reciprocating itself. Finally, this study demonstrates the fuzzy OEE models using IVIFS (Interval-Valued Intuitionistic Fuzzy Set) based on the characterization via membership function, non-membership function and hesitant function. For the purpose of analyzing the fuzzy system OEE, the OEE for each machine of plant structure is considered triangular interval-valued intuitionistic fuzzy number. Regardless of plant structure, the validity degree of fuzzy membership function of system OEE decreases when the number of machine with worst value of the validity degree increases. Corresponding examples are presented in this paper for practitioner to understand the applicability and practicability of the proposed fuzzy OEE methods.

• Earthquakes and Structures
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• 제23권4호
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• pp.385-401
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• 2022

Uncertainty quantification is the most important challenge in seismic fragility assessment of structures. The precision increment of the quantification method leads to reliable results but at the same time increases the computational costs and the latter will be so undesirable in cases such as reliability-based design optimization which includes numerous probabilistic seismic analyses. Accordingly, the authors' effort has been put on the development and validation of an approach that has reduced computational cost in seismic fragility assessment. In this regard, it is necessary to apply the appropriate methods for consideration of two categories of uncertainties consisting of uncertainties related to the ground motions and structural characteristics, separately. Also, cable-stayed bridges have been specifically selected because as a result of their complexity and the according time-consuming seismic analyses, reducing the computations corresponding to their fragility analyses is worthy of studying. To achieve this, the fragility assessment of three case studies is performed based on existing and proposed approaches, and a comparative study on the efficiency in the estimation of seismic responses. For this purpose, statistical validation is conducted on the seismic demand and fragility resulting from the mentioned approaches, and through a comprehensive interpretation, sufficient arguments for the acceptable errors of the proposed approach are presented. Finally, this study concludes that the combination of the Capacity Spectrum Method (CSM) and Uniform Design Sampling (UDS) in advanced proposed forms can provide adequate accuracy in seismic fragility estimation at a significantly reduced computational cost.

• 한국항만경제학회지
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• 제36권4호
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• pp.93-106
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• 2020

무역은 국가 경제에 중요한 경제활동이다. 특히, WTO 출범 이후 2001년 중국의 WTO 가입, 다자간 무역체계의 확립, 자유무역협정(FTA) 등으로 무역의 범위가 확대되고, 국가 간 무역장벽의 완화 및 통합화로 인해 무역시장의 규모가 확대되고 있다. 그러나 무역시장 규모가 확대됨에도 불구하고, 2008년 글로벌 금융위기, 2016년 브렉시트, 2018년 미·중 무역전쟁과 같은 극단적인 사건 발생하여 무역시장이 직접적으로 타격받고 있다. 이에 본 연구는 무역활동을 대변하는 변수인 국제 해운 운임지수와 미국, 중국 무역 불확실성 사이의 의존구조를 분석 하였다. 분석 결과를 요약하면 다음과 같다. 첫째, 미국, 중국 무역 불확실성과 국제 해운 운임지수 조합의 결합분포가 각각 Frank copula, rotated Clayton copula 270°으로 나타나, 미국, 중국 국가별로 동일한 분포 구조를 보이는 것으로 나타났다. 둘째, Kendall's tau 상관관계를 살펴보면, 국제 해운 운임지수와 미국, 중국 무역 불확실성 사이에 음(-)의 의존성을 갖지만, 의존성 정도는 중국 무역 불확실성과 국제 해운 운임지수의 조합에서 더 크게 나타났다. 즉, 전 세계 수요와 무역 불확실성의 의존성은 미국보다 중국이 더 강하다는 것을 확인하였다. 마지막으로, 꼬리 의존성 결과를 살펴보면, 미국, 중국 무역 불확실성과 국제 해운 운임지수가 서로 독립적인 관계로 나타났다. 이는 무역 불확실성의 극단적인 사건 혹은 국제 해운 운임지수의 극단적인 사건이 발생해도 서로 영향을 받지 않는 것으로 의미한다.

• 한국경영과학회지
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• 제18권3호
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• pp.151-157
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• 1993

In this paper, we investigate the effects of yield randomness for lot-sizing in a multi-stage production system. The practical importance of incorporating yield randomness into production models has been emphasized by many researchers. Yield randomness, especially in semiconductor manufacturing, poses a mojor challenge for production planning and control. The task becomes even more difficult if the demand for final product is uncertain. An attempt to meet the demand with a higher level of confidence forces one to release more input in the fabrication line. This leads to excessive work-in-process (WIP) inventories which cause jobs to spend unpredictably longer time waiting for the machines. The result is that it is more difficult to meet demand with exceptionally long cycle time and puts further pressure to increase the safety stocks. Due to this spiral effect, it is common to find that the capital tied in inventory is the msot significant factor undermining profitability. We propose a policy to determine the quantity to be processed at each stage of a multi-stage production system in which the yield at each stage may be random and may need rework.

• 상하수도학회지
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• 제25권3호
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• pp.293-305
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• 2011

A special concern is paid to the risks with which small-sized water resources systems are confronted in supplying water in the far future. Taking the Gwangdong dam reservoir as a case study, the authors seek to understand demand-side and supply-side disturbances of a reservoir, which, respectively, corresponds to effects of water demand changes on the intake amount and those of climate changes on the inflow amount. In result, it is demonstrated that both disturbances in the next 50 years are almost unpredictable. Yet the projection ranges, thought of as relatively reliable information that models offer, reveal that severity and period of water shortage is very likely to change. It is therefore concluded that water resources management requires more rigorous approaches to overcoming high uncertainties. The methods and models for projecting those disturbances are selected, based on practicality and applicability. Nevertheless, they show a large usefulness, especially in dealing with data shortage and reducing the needs for expensive modeling resources.

• Industrial Engineering and Management Systems
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• 제14권3호
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• pp.248-274
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• 2015

This study discusses a contract to promote collection and recycling of used products in a green supply chain (GSC). A collection incentive contract is combined with a reward-penalty contract. The collection incentive contract for used products is made between a retailer and a manufacturer. The reward-penalty contract for recycling used products is made between a manufacturer and an external institution. A retailer pays an incentive for collecting used products from customers and delivers them to a manufacturer with a product order quantity under uncertainty in product demand. A manufacturer remanufactures products using recyclable parts with acceptable quality levels and covers a part of the retailer's incentive from the recycled parts by sharing the reward from an external institution. Product demand information is assumed as (i) the distribution is known (ii) mean and variance are known. Besides, the optimal decisions for product quantity, collection incentive of used products and lower limit of quality level for recyclable parts under decentralized integrated GSCs. The analysis numerically investigates how (1) contract for recycling activity, (ii) product demand information and (iii) quality of recyclable parts affect the optimal operation for each GSC. Supply chain coordination to shift IGSC is discussed by adopting Nash Bargaining solution.

• 대한산업공학회지
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• 제31권2호
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• pp.106-119
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• 2005

Uncertainties inherent in customer demand patterns make it difficult for supply chains to achieve just-in-time inventory replenishment, resulting in loosing sales opportunity or keeping excessive chain wide inventories. In this paper, we propose two intelligent adaptive inventory control models for a supply chain consisting of one supplier and multiple retailers, with the assumption of information sharing. The inventory control parameters of the supplier and retailers are order placement time to an outside source and reorder points in terms of inventory position, respectively. Unlike most extant inventory control approaches, modeling the uncertainty of customer demand as a stationary statistical distribution is not necessary in these models. Instead, using a reinforcement learning technique, the control parameters are designed to adaptively change as customer demand patterns change. A simulation based experiment was performed to compare the performance of the inventory control models.

• 품질경영학회지
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• 제33권1호
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• pp.64-72
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• 2005

The ever increasing demand for enhanced competitiveness of engineered products requires "designing-in-quality" strategies that can effectively and efficiently incorporate concepts of uncertainty and quality into design. Multi-attribute utility function is commonly used to represent the decision-maker's preference on multiple design attributes under conditions of uncertainty and risk. One of the major issues in implementing this approach concerns the generation of appropriate utility function, especially in a complex engineering design environment. Typically, the decision maker's preference is revealed through lottery questions rather than being structured on the deductive reasoning to reflect the nonlinear tradeoffs among the attributes. The use of such intuitive procedures can lead to inexact preference information that may result in inaccuracy and rank reversal problems. This paper presents an alternative procedure based on the pair-wise comparisons between design alternatives towards a consistent preference presentation in assessing multiplicative utility function. The effectiveness of the overall procedures is tested with the aid of an injection-molding process design for a capacitor can and the results are discussed.

• 한국시스템다이내믹스연구
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• 제11권3호
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• pp.61-86
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• 2010

This research analyzed on the future energy society of Korea in 2030 using system thinking approach. Key uncertainty factors determining the future energy society were analyzed in a multi disciplinary view point such as politics, economy, society, ecology and technology. Three causal loop diagrams for the future energy system in Korea and related policy leverages were shown as well. 'Global economic trends', 'change of industrial structure' and 'energy price' were identified as key uncertainty factors determining the Korean energy future. Three causal loop diagrams named as 'rate of energy self－sufficiency and alternative energy production', 'economic activity and energy demand' and 'Excavation of new growth engines' were developed. We integrated those causal loop diagrams into one to understand the entire energy system of the future, proposed three strategic scenarios(optimistic, pessimistic and most likely) and discussed implications and limits of this research.