• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.265-272
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• 2007

The purpose of Vehicle Routing Problem (VRP) is to design the least costly (distance, time) routes for a fleet of identically capacitated vehicles to serve geographically scattered customers. There may be some restrictions such as the maximal capacity for each vehicle, maximal distance for each vehicle, time window to visit the specific customers, and so forth. This paper is concerned with VRP to minimize the sum of elapsed time from departure, where the elapsed time is defined as the time taken in a moving vehicle from the depot to each customer. It is important to control the time taken from departure in the delivery of perishable products or foods, whose freshness may deteriorate during the delivery time. An integer linear programming formulation is suggested and a heuristic for practical use is constructed. The heuristic is based on the set partitioning problem whose performances are compared with those of ILOG dispatcher. It is shown that the suggested heuristic gave good solutions within a short computation time by computational experiments.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2004.05a
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• pp.660-663
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• 2004

The vehicle routing problem with time-varying speed(VRPTVS) is difficult to handle with regular problem solving approaches. An approach by partitioning the service zone into three sub-zones to reduce computing time and vehicle traveling distance is suggested in this paper. To develop a partitioning algorithm for VRPTVS, all customer locations are divided into two sections such as morning zone and evening zone, excluding daytime zone. And then each service zone is calculated to find a possible number of delivery points and chosen by time window having more number of possible delivery points by considering customer location and varying speeds. A temporary complete route that can serve all target points is developed by this procedure and a pairwise exchange method is applied to reduce the traveling time.

• Journal of the Korea Society for Simulation
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• v.16 no.3
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• pp.1-9
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• 2007

Travel time between two points depends upon whether it is a rush hour or not in metropolitan area. It is true that there is big differences on the time required to get through the area whether going in busy morning or near noon. Another issue is that there exist many delivery points which closely located each other; so no need to consider traveling hours among these points. We designed an efficient procedure to reduce the complexity by considering closely located delivery points as one big delivery point. A computer simulation model is constructed for comparison purposes of the developed heuristic with the optimum solution.

• Journal of Korean Institute of Industrial Engineers
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• v.23 no.2
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• pp.275-288
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• 1997

The container transportation problem is a kind of generalized pickup and delivery problem(GPDP), and a typical NP-hard problem of which polynomial algorithm has not yet been developed. In this problem, trucks have to transport containers from origins to destinations, while have to satisfy several restrictions such as request time, cargo closing time, driver's break time. In this paper, we present a straightforward heuristic and a user-interactive truck dispatching system which supports decision makers.

• Industrial Engineering and Management Systems
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• v.9 no.2
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• pp.178-194
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• 2010

To improve the ship operation in automated container terminals, it is important to schedule different types of handling equipment to operate synchronously. For example, a vehicle with container receiving and lifting capabilities is used to transport containers from a storage yard to a vessel and vice versa, while a triple quay crane (QC) can handle up to three 40-ft containers simultaneously. This paper discusses the manner in which vehicles should be assigned to containers to support such multi-lifts of QCs by using information about the locations and times of deliveries. A mixed-integer programming model is introduced to optimally assign delivery tasks to vehicles. This model considers the constraint imposed by the limited buffer space under each QC. A procedure for converting buffer-space constraints into time window constraints and a heuristic algorithmfor overcoming the excessive computational time required for solving the mathematical model are suggested. A numerical experiment is conducted to compare the objective values and computational times of the heuristic algorithm with those of the optimizing method to evaluate the performance of the heuristic algorithm.

• IE interfaces
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• v.12 no.4
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• pp.557-566
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• 1999

This paper considers a door-to-door service system in which pickups or deliveries are performed by a trip of a single vehicle. Each customer request specifies the quantity of the load transported, the location, and the time window within which it is to be picked up or delivered. Since the system is demand responsive, i.e., new or emergent requests become available in real-time, the current vehicle route has to be reconstructed to include these requests. In this case, only continuous vehicle tracking enables control over the requests and ensures that the requests are satisfied on time. This paper suggests a pilot pickup/delivery management system integrating a geographic information system(GIS) and a global position system(GPS) to efficiently deal with such a dynamic environment. The GIS offers a way of displaying the vehicle route on digital maps for the region under concerned. Also displayed is the current location of the vehicle obtained from the GPS. A heuristic algorithm is used to dynamically determine the vehicle route. A practical example is provided to show the feasibility of the system.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.199-204
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• 2008

Sensor nodes have various energy and computational constraints because of their inexpensive nature and ad-hoc method of deployment. Considerable research has been focused at overcoming these deficiencies through faster media accessing, more energy efficient routing, localization algorithms and system design. Our research attempts to provide a method of improvement MAC performance in these issues. We show that traditional carrier-sense multiple access(CSMA) protocols like IEEE 802.11 do not handle the first constraint adequately, and do not take advantage of the second property, leading to degraded latency and throughput as the network scales in size, We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is a randomized CSMA protocol, but unlike previous legacy protocols, does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, it carefully decides a fixed-size contention window, non-uniform probability distribution of transmitting in each slot within the window. We show that it can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely used simulator ns-2. We, finally show that proposed MAC scheme comes close to meeting bounds on the best latency achievable by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to latency.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.4
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• pp.16-22
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• 2019

After Dantzig and Rasmer introduced Vehicle Routing Problem in 1959, this field has been studied with numerous approaches so far. Classical Vehicle Routing Problem can be described as a problem of multiple number of homogeneous vehicles sharing a same starting node and having their own routes to meet the needs of demand nodes. After satisfying all the needs, they go back to the starting node. In order to apply the real world problem, this problem had been developed with additional constraints and pick up & delivery model is one of them. To enhance the effectiveness of pick up & delivery, hub became a popular concept, which often helps reducing the overall cost and improving the quality of service. Lots of studies have suggested heuristic methods to realize this problem because it often becomes a NP-hard problem. However, because of this characteristic, there are not many studies solving this problem optimally. If the problem can be solved in polynomial time, optimal solution is the best option. Therefore, this study proposes a new mathematical model to solve this problem optimally, verified by a real world problem. The main improvements of this study compared to real world case are firstly, make drivers visit every nodes once except hub, secondly, make drivers visit every nodes at the right time, and thirdly, make drivers start and end their journey at their own homes.

• Proceedings of the Safety Management and Science Conference
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• 2000.11a
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• pp.91-94
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• 2000

본 연구에서는 차량용량이 같지 않은 복수의 다른 종류의 차량을 고려하여, 차량이 이동하면서 배달과 수거를 동시에 수행하고 수거지점으로부터 화물을 수거하여 차고지로 운송하는 귀로 화물(Backhauls)을 갖는 PDP(Pickup and Delivery Problem)문제를 그 연구 대상으로 한다. 동시에 차량을 통해 이동되는 품목이 단일 품목이 아니고, 배달 및 수거시간제약조건을 갖는 다품목 시간제약 수송차량 배차문제를 Time-space network를 이용하여 정수선형계획문제로 정식화한다. 이를 최적화 S/W LINGO를 이용하여 위의 모든 제약조건을 만족하면서 운용되는 차량수와 차량의 이동경로를 최소화하는 해를 구하고, 분석한 내용을 보여주고자 한다. 덧붙여 위 문제의 입·출력자료를 데이터베이스화하여 지리정보시스템(Geographic Information System : GIS)과 통합한 차량운행경로결정 지원시스템을 구축하기 위한 방법을 제시하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8A
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• pp.600-609
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• 2009

The traditional carrier sense multiple access (CSMA) protocol like IEEE 802.11 Distributed Coordination Function (DCF) does not handle the constraints adequately, leading to degraded delay latency and throughput as the network scales are enlarged. We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is like the randomized CSMA protocol, but unlike previous legacy protocols, it does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, we carefully decide to select a fixed-size contention window with non-uniform probability distribution of transmitting in each slot. We show that the proposed method can offer up to severaansimes latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely using network simulation package,caS-2. We finally show that proposed MAC scheme comes close to meet bounds on the best latency being achieved by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to delay latency.