• Korean Journal of Computational Design and Engineering
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• v.19 no.1
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• pp.12-18
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• 2014

Shot-peening is frequently used on various mechanical parts because it can improve the fatigue life of components by generating compressive residual stresses on the surface. This can be done by repeatedly hitting the work-piece surface with small balls and making indentations on it. In fact, finding optimal peening time among various peening parameters is the most important. Under-peening can not improve the fatigue life sufficiently while over-peening causes cracks and reduces fatigue life in contrast. In general, optimal peening time is experimentally determined by measuring arc-height using Almen-strip in accordance with SAE J442 standard. To save the time and efforts spent in carrying out experiments to find optimal peening time, this paper presents a computer simulation algorithm for the estimation of surface coverage made by impeller type shot-peening machines (PMI-0608). Surface coverage is defined as the proportion of the work-piece surface that has been indented in a given time of shot-peening. An example (standard tensile test specimen) is presented to validate the proposed method.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.14 no.24
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• pp.149-154
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• 1991

The one of the important problems in the design of queueing systems is the decision of the order of service stations. The object of this problem is the decision of the order that minimizes the expected sojourn time per customer in the given arrival process and service time distributions. In this paper, the tandem queueing system in series is studied with the emphasis on the optimal order of the tandem queueing system which has three stations with single servers. In one system, customers arrive at the first station with Poisson process. This system is composed of service stations with a constant, a general distribution and a Exponential distribution is studied. To select the optimal order after the orders of each pair of two stations is decided, it is compared the two orders of system. With this results, total expected delay of the systems which has three stations is compared. The result is the best that service station with constant time is on the first place, then the service station with general distribution and the service station with Exponential distribution is followed. And the other system is consist of service stations with a constant and two probabilistic distributions. In this case, two probabilistic distributions has a non-overlapping feature. It is the optimal order that the service station with constant time is on the first place then the service station with longer service time and the service station with shorter service time is followed.

• Food Science and Preservation
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• v.8 no.2
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• pp.157-163
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• 2001

Optimal conditions for hot water extraction of Liriope spicata tuber were investigated with changes in solvent ratio(2∼6 fold) and heating time(1∼5 hr) by response surface methodology. The content of extractable solids increased with an increased in solvent ratio, and the highest content showed at heating time of 3 hr. The content of total steroid saponin increased with a decrease in solvent ratio, and increased with an increase in heating time at increasing the solvent ratio. The content of non-reducing sugar containing oligosaccharides at a lower solvent ratio didn’t show changes depending on heating time, while that at a higher ration decreased with an increase in heating time. Optimal extraction conditions using hot water as the limited conditions of 15∼18% extractable solids, 1.5∼2.0% total steroid saponin, 6∼8% reducing sugar, 6∼7% non-reducing sugar and 13∼15 brix were 3 hrs of heating time and 4 fold of solvent ratio.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.310-313
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• 1996

Mathematical programming method for finding optimal solution of job shop scheduling is inadequate to real situation because fo too much computation time. In contrast, dispatching rule is helpful for reducing compuation time but is not guaranted to find optimal solution. The purpose of this paper is to develop a new dispatching rule and procedure to minimize mean flow time whose result is near the optimal solution for job shop scheduling. First step is to select machine which have shortest finishing operation time among the schedulable operations. Second step is to select operation with regard to estimated remaining operation time. The suggested rule is compared with nondelay and MWKR rule for three examples, and is confirmed to be most effective to minimize mean flow time.

• The Journal of Information Systems
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• v.28 no.4
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• pp.175-197
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• 2019

Purpose This study develops a heuristic algorithm to solve the time-resource tradeoffs in project scheduling problems with a real basis. Design/methodology/approach Resource constrained project scheduling problem with time-resource tradeoff is well-known as one of the NP-hard problems. Previous researchers have proposed heuristic that minimize Makespan of project scheduling by deriving optimal combinations from finite combinations of time and resource. We studied to solve project scheduling problems by deriving optimal values from infinite combinations. Findings We developed heuristic algorithm named Push Algorithm that derives optimal combinations from infinite combinations of time and resources. Developed heuristic algorithm based on simulated annealing shows better improved results than genetic algorithm and further research suggestion was discussed as a project scheduling problem with multiple resources of real numbers.

• Proceedings of the Korean Reliability Society Conference
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• 2000.11a
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• pp.329-333
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• 2000

Delay time analysis is a pragmatic mathematical concept readily embraced by engineers which has been developed as a means to model maintenance decision problem. This paper considers an inspection period using delay time analysis for fishing vessel equipment. We assume that delay time distribution is Weibull and inspections are perfect. In this paper, we determine the optimal inspection period which minimize the expected downtime per unit time.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.875-880
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• 2008

In this paper, a novel method to determine the optimal checkpoint interval for real-time control task is proposed considering its performance degradation according to tasks's execution time. The control task in this paper has a specific sampling period shorter than its deadline. Control performance is degraded as the control task execution time is prolonged across the sampling period and eventually zero when reached to the deadline. A new performance index is defined to represent the performance variation due to the extension of task execution time accompanying rollback fault recovery. The procedure to find the optimal checkpoint interval is addressed and several simulation examples are presented.

• Journal of the military operations research society of Korea
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• v.18 no.1
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• pp.61-73
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• 1992

Up to the present, the operating time has been studied on only a single aircraft attacking a single target or multiple targets under enemy threats. This study is to determine optimal operating time and appropriate size of aircrafts attacking multiple targets. Measures of mission effectiveness is defined through derivation of the probability of the various events associated with operating. By using these measures, the expected benefit of operating and the expected cost of operating are generated as a function of time. To formulate operating time determination model, the expected gain of operating is defined as the difference between the expected benefit of operating and the expected cost of operating. The model can be used to determine optimal operating time which maximizes the expected gain of operating, and can be used as the basis for determining the appropriate size of aircrafts.

• International Journal of Reliability and Applications
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• v.2 no.2
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• pp.99-105
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• 2001

Delay time analysis is a pragmatic mathematical concept readily embraced by engineers which has been developed as a means to model maintenance decision problem. This paper considers an inspection period using delay time analysis for fishing vessel equipment. We assume that delay time has a Weibull distribution. In this paper, we determine the optimal inspection period which minimize the expected downtime per unit time. Explicit solutions for the optimal inspection are presented for illustrative purposes.

• Korean Journal of Medicinal Crop Science
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• v.24 no.4
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• pp.263-270
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• 2016

Background: In this study, microwave extraction was used, which is an effective method to extract useful bioactive substances as it requires low quantities of solvent and short time periods. The aim of this study was to determine the optimal extraction conditions for Agrimonia pilosa Ledeb. Methods and Results: The independent variables were ethanol concentration, microwave power, and extraction time, each of which had five levels. The dependent variables were total polyphenol and total flavonoid content, and DPPH radical scavenging activity. To determine the optimal extraction conditions for bioactive compounds, a response surface methodology was employed. Contour maps were generated from polynomial equations. The optimal conditions were then assumed by superimposing these contour maps. Based on the resulting graph, the optimal microwave extraction conditions for Agrimonia pilosa Ledeb were determined as 42 - 48% ethanol concentration, 240 - 280W microwave power, and 13 - 20 min of extraction time. Conclusions: Ethanol concentration had a significant effect on microwave extraction, in terms of total polyphenol and total flavonoid content, as well as DPPH radical scavenging activity. Microwave power and extraction time influenced the total polyphenol content, but not the total flavonoid content or the DPPH radical scavenging activity.