• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2017년도 학술발표회
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• pp.271-271
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• 2017

상수관망 수리해석 기법은 절점의 사용량 및 누수량을 기지의 값으로 고려하여 총 수요량이 모두 공급될 수 있다고 가정하여 해석하는 수요기반해석(Demand Driven Analysis, DDA)과 사용량과 누수량은 절점 압력수두에 의해 달라질 수 있어, 공급가능량 및 누수량과 절점의 압력수두 모두를 미지수로 고려하여 해석하는 수압기반해석(Pressure Driven Analysis, PDA)으로 구분될 수 있다. 본 연구에서는 수압기반사용량 모의(Pressure Dependent Demand, PDD)와 수압기반누수량 모의(Pressure Dependent Leakage, PDL)기능이 모두 구현되고, 다양한 시나리오 분석이 가능한 소프트웨어(SW)인 K-NRisk를 개발하였다. K-NRisk는 2016년 7월에 공개된 상수관망 해석범용모형인 EPANET3 소스코드 기반으로 개량 개발되었으며, 기존 EPANET2와 비교하였을 경우 사용자 편의성 증대를 위한 입출력 기능 및 SW 활용도 제고를 위한 대표업무분석 기능이 신규 개발, 강화되었다. 개발된 SW를 관망정비 및 공급안정성 확보 목적을 위한 수리해석 시 적용하여 그 결과를 분석하였다. 적용결과 기존 수요기반해석이 가지고 있는 한계점을 보완하고, 실제업무 시 활용가능함을 확인하였다.

• Korea Trade Review
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• 제47권1호
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• pp.13-24
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• 2022

This study was conducted because the global economic downturn caused by COVID-19 caused a surge in logistics costs and it was no longer possible to predict logistics costs using existing methods. For this study, we made the assumption that economic indicators affect logistics cost. Chapter 2 examines the current status of the liner market and factors affecting logistics costs. Based on this, Chapter 3 collects independent and dependent variables to determine the analysis model. As the independent variable, economic indicators of major countries constituting the SCFI were selected, and the dependent variables were the SCFI Europe Index and the SCFI USA Index. In Chapter 4, a panel analysis was conducted based on this, and it was confirmed that major economic indicators had a negative (-) effect on SCFI. This is contrary to the existing research results, which can be attributed to the special situation caused by COVID-19 and the imbalance of demand and supply by region. The results of this study are meaningful in that they can predict long-term logistics cost volatility without analyzing supply and demand, and can be applied to other studies as well.

• Journal of Korean Society of Transportation
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• 제26권3호
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• pp.155-167
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• 2008

This paper studies a multiple user class variable demand user equilibrium and system optimal condition, and then establishes solution algorithms for them. The traffic network equilibrium is accomplished with basis on following assumptions. For considering heterogeneous road user, several user classes have discrete set of VOTs and the travel demand of each user classes varies according to generalized travel cost. this paper specifically investigates following question on multi-class variable demand: Are user equilibrium flows pattern dependent on the unit (time or money) perceived by road user classes? What is system optimal condition according to the unit used in measuring the travel cost or disutility? Finally, using this network equilibrium condition, The traffic assignment algorithm of each equilibrium condition are established.

• Journal of Digital Convergence
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• 제16권5호
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• pp.137-143
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• 2018

Korea's air passenger traffic has been growing steadily. In this paper, we propose a forecasting model of air passenger demand to ascertain the growth trend of air passenger transportation performance in Korea. We conducted a simulation based on System Dynamics with the demand as a dependent variable, and international oil prices, GDP and exchange rates as exogenous variables. The accuracy of the model was verified using MAPE and $R^2$, and the proposed prediction model was verified as an accurate prediction model. As a result of the demand forecast, it is predicted that the air passenger demand in Korea will continue to grow, and the share of low cost carriers will increase sharply. The addition of the Korean transportation performance of foreign carriers in Korea and the transportation performance of Korean passengers due to the alliance of airlines will provide a more accurate forecast of passenger demand.

• Journal of Korean Institute of Industrial Engineers
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• 제27권3호
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• pp.233-238
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• 2001

This paper deals with demand forecasting of parts in an automobile model which has been extinct. It is important to estimate how much inventory of each part in the extinct model should be stocked because production lines of some parts may be replaced by new ones although there is still demands for the model. Furthermore, in some countries, there is a strong regulation that the automobile manufacturing company should provide customers with auto parts for several years whenever they are requested. The major characteristic of automobile parts demand forecasting is that there exists a close correlation between the number of running cars and the demand of each part. In this sense, the total demand of each part in a year is determined by two factors, the total number of running cars in that year and the failure rate of the part. The total number of running cars in year k can be estimated sequentially by the amount of shipped cars and proportion of discarded cars in years 1, 2,$\cdots$, i. However, it is very difficult to estimate the failure rate of each part because available inter-failure time data is not complete. The failure rate is, therefore, determined so as to minimize the mean squared error between the estimated demand and the observed demand of a part in years 1, 2,$\cdots$, i. In this paper, data obtained from a Korean automobile manufacturing company are used to illustrate our model.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.1021-1038
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• 2016

Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (${\mu}$), and period (T) parameters ($R-{\mu}-T$) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of $R-{\mu}-T$ based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both $R-{\mu}-T$ and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

• Journal of the Architectural Institute of Korea Planning & Design
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• 제36권1호
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• pp.125-136
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• 2020

This study aims to seek a proper policy direction in response to the demand for apartment remodeling. As the research methods, we diagnosed the current status of the remodeling policy and analyzed the demand for apartment remodeling nationwide. According to the result of analysis, we suggested the fundamental direction and tasks for remodeling policies to be pursued at the government level. The results of the study are summarized as follows. First, the result of analysis showed that the demand for environmental improvement(performance improvement) remodeling project was much higher than other types of remodeling projects. The percentage of unit increased-type remodeling that can secure business feasibility is about 10% and only 30% when it comes to reducing project costs. The remaining 70-90% need to be promoted in environmental improvement remodeling projects which dependent on the residents' payment. Second, in order to prepare a policy action plan in response to the demand for apartment remodeling, it is necessary to set up clear policy goals and strategies for apartment remodeling in advance at the national level. Along with proactive goals and strategies, graded policy support should be accompanied per type of remodeling and business demand. We also suggest to simplify administrative procedures and support the R&D research to develop technologies. It would help to utilize the unit increased-type remodeling. On the other hand, for utilizing the environmental improvement remodeling which takes up a relatively high proportion, the policy should take care of as follows: offering housing performance information, rationalizing long term repair reserve, fostering small companies and experts. Finally, apartment management system should be advanced from the perspectives of managing old apartments and institutional foundations such as new construction and customized regulations for differentiated remodeling should be accompanied.

• Korean Management Science Review
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• 제25권2호
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• pp.57-71
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• 2008

We study factors that affect consumers' switching behaviors among service providers in Korean mobile telecommunications service market. For empirical analysis, quarterly time series data from the first quarter of 2004 through the second quarter of 2007 were used. We chose the number of switchers to each mobile service provider in each quarter as dependent variables. Independent variables include acquisition costs per subscriber, which play the role of subsidy to mobile handset, switching costs, time trend, structural change effect, and waiting demand effects. Through the empirical analysis, we found that each provider's churn-in customers are affected by different factors. Specifically, the number of churn-in customers into SK Telecom is explained mainly by SK Telecom's customer acquisition costs and waiting demand from KTF, while the number of customers switching into KTF is better explained by switching costs from the previous service provider and waiting demand from SK Telecom. Those who chose LG Telecom as their new provider, on the other hand, were mainly attracted by LG Telecom's high subscriber acquisition cost.

• Journal of Korean Institute of Industrial Engineers
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• 제40권4호
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• pp.435-441
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• 2014

This paper considers a single-product problem for inbound lot-sizing and outbound dispatching at a third-party warehouse, where the demand is dynamic over the discrete time horizon. Each demand must be delivered into the corresponding delivery time window which is the time interval characterized by the earliest and latest delivery dates of the demand. Ordered products are shipped by heterogeneous container types. Each container type has type-dependent carrying capacity and the unit freight cost depends on each container type. Total freight cost is proportional to the number of each container type used. Also it is assumed that related cost functions are concave and backlogging is not allowed. The objective of the paper is to simultaneously determine the optimal inbound lot-sizing and outbound dispatching plans that minimize total costs which include ordering, shipping, and inventory holding costs. The optimal solution properties are characterized for the problem and then a dynamic programming algorithm is presented to find the optimal solution.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 한국경영과학회/대한산업공학회 2005년도 춘계공동학술대회 발표논문
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• pp.904-913
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• 2005

This paper deals with an integrated problem of inventory control and dynamic pricing strategies for a commodity with price and sales-period dependent demand pattern, where a seller and customers have complete information of each other. The problem consists of two parts; one is each buyer's benefit problem which makes the best decision on price and time for buyer to purchase items, and the other one is a seller's profit problem which decides an optimal sales strategy concerned with inventory control and discount schedule. The seller's profit function consists of sales revenue and inventory holding cost functions. The two parts are closely related into each other with some related variables, so that any existing general solution methods can not be applied. Therefore, a simplified model with single seller and two customers in considered first, where demand for multiple units is allowed to each customer within a time limit. Therewith, the model is generalized for a n-customer-classes problem. To solve the proposed n-customer-set problem, a dynamic programming algorithm is derived. In the proposed dynamic programming algorithm, an intermediate profit function is used, which is computed in case of a fixed initial inventory level and then adjusted in searching for an optimal inventory level. This leads to an optimal sales strategy for a seller, which can derive an optimal decision on both an initial inventory level and a discount schedule, in $O(n^2)$ time. This result can be used for some extended problems with a small customer set and a short selling period, including sales strategy for department stores, Dutch auction for items with heavy holding cost, open tender of materials, quantity-limited sales, and cooperative buying in the on/off markets.