• Journal of the Korea Society of Computer and Information
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• v.23 no.3
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• pp.85-92
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• 2018

We consider a project scheduling problem in which the jobs can be compressed by using additional resource to meet the corresponding due dates, referred to as a time-cost tradeoff problem. The project consists of two independent subprojects of which precedence graph is a chain. The due dates of jobs constituting the project can be interpreted as the multiple assessments in the life of project. The penalty cost occurs from the tardiness of the job, while it may be avoided through the compression of some jobs which requires an additional cost. The objective is to find the amount of compression that minimizes the total tardy penalty and compression costs. Firstly, we show that the problem can be decomposed into several subproblems whose number is bounded by the polynomial function in n, where n is the total number of jobs. Then, we prove that the problem can be solved in polynomial time by developing the efficient approach to obtain an optimal schedule for each subproblem.

• Journal of the Korean Operations Research and Management Science Society
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• v.20 no.2
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• pp.23-38
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• 1995

In manfacturing systems, to overcome the inherent complexities and uncertainties, due-dates are usually decided by some simple rules. This study proposes a computational procedure for estimating production lead time for computerized manufacturing systems. Based on the current system status stored in the computers, the procedure estimates production lead time for an incoming order. The result is more accurate than the ones produced by old rules, and yet the procedure is fast in computation speed enough to use in real time. Simulations are used to prove these.

• Journal of the Korean Association of Geographic Information Studies
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• v.26 no.4
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• pp.40-55
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• 2023

Arbor Day is a day that encourages people to plant trees and symbolizes the timing of planting. Arbor Day has been honored on April 5th in Korea, but it often does not agree to actual planting time due to global warming. This study confirmed the discrepancy between Arbor Day and regional soil-thawing times and reviewed alternative dates for tree planting using satellite-based soil-thaw data (FT-ESDR) from 1991 to 2020. Study results showed that the start time of planting on the Korean Peninsula, which was indicated by soil-thaw dates, was March 24 during 1991-2000, and it progressively changed to March 17 during 2011-2020. Should Arbor Day be changed based on soil-thaw periods, mid-March would be the most comprehensive, suitable alternative period considering the number of governmental administration units (cities and counties) and the land area of soil-thaw. Tree-Planting Day (March 14) and International Day of Forests (March 21) were found suitable for alternative dates to Arbor Day because they were close to the average soil-thaw time of Korean Peninsula (March 19) and land area whose soil-thaw time was within 10 days from those two dates ranged from 52.5% to 58.8% centered geographically on the mid-section of the peninsula. Since the periods of soil-thaw will continue to change due to climate change, it is necessary to reflect the trend of advancing planting periods in the future if Arbor Day is changed to an earlier date.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.10a
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• pp.435-439
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• 2001

In many make-to-order production systems customers ask due date confirmed and kept. Unexpected urgent orders from valuable customers often requires short lead times, which causes existing orders in the production schedule to be delayed so that their confirmed due dates cannot be met. This Imposes significant uncertainty on the production schedule in a supply chain. In this paper, we propose a new concept of capacity reservation as a viable tool for due date promising and suggest its operational alternatives. Simulation results show that the reserved capacity scheme appears to outperform simple FCFS scheduling policy in terms of the number of valuable urgent orders accepted and total profit attained.

• IE interfaces
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• v.14 no.4
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• pp.341-347
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• 2001

This paper describes a real-time manufacturing scheduling system on Internet using DBR(Drum-Buffer-Rope) scheduling method. We intend to change company-oriented manufacturing scheduling, which has been used at most manufacturing companies, to customer-oriented manufacturing scheduling. Customers can not only choose product kinds, quantities and order due dates, but also evaluate optimum order due date by themselves in real-time through internet and then the results will be converted into practical manufacturing scheduling. If the company cannot meet the customer order due date, it will offer reliable and accurate information to the customers by suggesting the earliest order due date. To evaluate the customer order due date in real time, companies should be able to estimate their accurate production capacity. This research uses Goldratt's DBR scheduling method to realize that function. The DBR scheduling does not recognize the production capacity of the whole company, but only of the constraint resources which have a great effect on the company throughput. Thus, it can improve the customer service level as well as the profit by performing more dynamic and reliable scheduling through Internet.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.27 no.2
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• pp.141-146
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• 1982

In the vine training methods, main vine training yield was 36% higher than the non-training. Main vine training date was studied for increasing cone yield in hops. Training was done four different dates from May 14 to May 29 including non-training as a check. Earlier training increased cone yield from 12 to 43% due to more beared branches per plant, longer branch length caused by accelerating the branch growth, and an increased of number of cone per beared branch and total cone number.

• Proceedings of the Safety Management and Science Conference
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• 2001.05a
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• pp.185-188
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• 2001

Many production management systems for increasing productivity, minimizing inventory, keeping due dates and maximizing use of resources have been proposed, and GT, MRP and JIT are frequently used among these systems. The three systems have merits and demerits through comparing with each other. Because each system has mutual dependence, a hybrid production system is necessary for using their merits maximally. In this study, a hybrid production system is designed by combining GT, MRP and JIT, which is suitable in the domestic production system.

• IE interfaces
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• v.9 no.2
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• pp.75-82
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• 1996

A scheduling system is developed for a parallel machine flow shop which reflects the situations of the manufacturing processes in the tire industry. The schedule is generated via simulation using heuristic rules to get satisfaction on such constraints as due dates, demands, work-in-process, process capacity, set-up times and scheduling speed. This system, constructed with relational DB, SQL and C language, consumes less than 10 minutes of PC simulation to handle real size problems.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1998.10a
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• pp.214-214
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• 1998

• Korean Management Science Review
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• v.13 no.1
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• pp.1-12
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• 1996

This paper deals with production scheduling of block assembly shop in shipbuilding company. The Objectives of the schedule are leveling of daily total workload and fair assignment of workload to each department of the shop. Optimizing the objectives, we consider some restrictions which consisit of block due dates, workability of each department, and space restriction. We formulate the problem in mathematical form. But the model is too complex to find the optimal solution (the problem is NP-complete) and we use the genetic algorithm to find a good solution.