• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.5
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• pp.81-90
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• 2016

Due to droughts and water shortages causing severe damage to crops and other vegetations, much attention has been given to efficient irrigation for upland farming. However, little information has been known to measure soil moisture levels in a field scale and apply their spatial variability for proper irrigation scheduling. This study aimed to characterize the spatial variability and temporal stability of soil water contents at depths of 10 cm, 20 cm and 30 cm on flat (loamy soil) and hill-slope fields (silt-loamy soil). Field monitoring of soil moisture contents was used for variogram analysis using GS+ software. Kriging produced from the structural parameters of variogram was applied for the means of spatial prediction. The overall results showed that the surface soil moisture presented a strong spatial dependence at the sampling time and space in the field scale. The coefficient variation (CV) of soil moisture was within 7.0~31.3 % in a flat field and 8.3~39.4 % in a hill-slope field, which was noticeable in the dry season rather than the rainy season. The drought assessment analysis showed that only one day (Dec. 21st) was determined as dry (20.4 % and 24.5 % for flat and hill-slope fields, respectively). In contrary to a hill-slope field where the full irrigation was necessary, the centralized irrigation scheme was appeared to be more effective for a flat field based on the spatial variability of soil moisture contents. The findings of this study clearly showed that the geostatistical analysis of soil moisture contents greatly contributes to proper irrigation scheduling for water-efficient irrigation with maximal crop productivity and environmental benefits.

• Industrial Engineering and Management Systems
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• v.2 no.1
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• pp.9-27
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• 2003

In a wafer fabrication factory, the completion time of an order is affected by many factors related to the specifics of the order and the status of the system, so is difficult to predict precisely. The level of influence of each factor on the order completion time may also depend on the production system characteristics, such as the rules for releasing and dispatching. This paper presents a method to identify those factors that significantly impact upon the order completion time under various combinations of scheduling rules. Computer simulations and statistical analyses were used to develop effective due date assignment models for improving the due date related performances. The first step of this research was to select the releasing and dispatching rules from those that were cited so frequently in related wafer fabrication factory researches. Simulation and statistical analyses were combined to identify the critical factors for predicting order completion time under various combinations of scheduling rules. In each combination of scheduling rules, two efficient due date assignment models were established by using the regression method for accurately predicting the order due date. Two due date assignment models, called the significant factor prediction model (SFM) and the key factor prediction model (KFM), are proposed to empirically compare the due date assignment rules widely used in practice. The simulation results indicate that SFM and KFM are superior to the other due date assignment rules. The releasing rule, dispatching rule and due date assignment rule have significant impacts on the due date related performances, with larger improvements coming from due date assignment and dispatching rules than from releasing rules.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.263-281
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• 2017

Global optimization that considers the processes at integrated steel mills is more important than the local optimization to improve the efficiency of a single process. Research utilizing mathematical models at integrated steel mills predominantly focus on solving problems solely for a specific process or focusing on what techniques are applied to. However, it is important to define the problems that must be solved at the steelworks, identify the objectives and constraints that can be modeled, and selection of methodologies that can be applied to the problems. The purpose of this study is to investigate the problems in improving efficiency at integrated steel mills from the viewpoint of production & operations management. We review the research have been conducted in order to solve those problems. We classified the research into 6 categories and suggested future research direction based on the global optimization. It is expected that research themes for improving the efficiency at integrated steel mills will be derived.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.441-454
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• 2008

Shipyard design and equipments layout problem, which are directly linked with the productivity of ship production, is an important issue serving as reference data of production plan for later massive production of ships. So far in many cases, design of a shipyard has been relying on the experienced engineers in shipbuilding, resulting in sporadic and poorly organized processes. And thus, economic losses as well as trials and errors in that accord have been pointed out as inevitable problems. This paper extracts a checklist of major elements to fine tune the shipbuilding yard designing process and the input/output data based on the simulation based shipbuilding yard layout designing framework and methodology proposed in existing researches, and executed initial architecture to develop software that integrates all the relevant processes and designing tools. In this course, both user request and design data by the steps are arranged and organized in the proposed layout design template form. In addition, simulation is done based on the parent shipbuilding process planning and scheduling data of the ship product, shipbuilding process and work stage facilities that constitute shipbuilding yard, and design items are verified and optimized with the layout and equipment list showing optimal process planning and scheduling effects. All the contents of this paper are based on simulation based shipbuilding yard layout designing methodology, and initial architecture processes are based on object oriented development methodology and system engineering methods.

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.2
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• pp.444-454
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• 2014

The range of optimization problem in aquaculture is very wide, resulting from the range of species, mode of operation. Quite a few studies focus marine net-cages, but studies on land based culture farm are few or no. This paper considers a allocation problem to meet production planning in land based aquaculture system. A water pool allocation model in land based aquaculture system was developed. The solution finds the value of decision variable to minimize yearly production costs that sums up the water pool usage cost and sorting cost. The model inputs were (1) the fish growth rate (2) critical standing corp (3) number of water pool (4) number of fish. The model outputs were (5) number of water pool in growing phase (6) cost of cultivation (6) optimal facility allocation(number of water pool for each growing phase). To solve the problem, an efficient heuristic algorithm based on a greedy manner is developed. Branch and bound and heuristic is evaluated through numerical examples.

• Journal of Korean Society for Quality Management
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• v.32 no.2
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• pp.154-167
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• 2004

The TOC/DBR and Six Sigma are the most attention-getting concepts for managing manufacturing companies in Korea. Using the ideas and methods of the TOC/DBR, companies can achieve a large reduction of work-in-process and finished-good inventories, significant improvement in scheduling performance, and substantial earnings increase. The Six Sigma approach derives the overall process of selecting the right projects based on their potential to improve performance metrics and selecting/training the right people to get the business results. These two concepts have different backgrounds and different viewpoints for production systems. So, if the two concepts collaborate each other, the synergy effects to innovate production systems can be expected. This paper proposes a new approach to implement the TOC/DBR concepts in production systems. This approach uses some concepts of Six Sigma which stresses educations, project approaches (step by step procedure using a Roadmap), and improvement philosophy.

• Journal of the Korea Safety Management & Science
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• v.9 no.3
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• pp.119-125
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• 2007

As competition in manufacturing enterprise is contested, the scope of safely production planning, manufacturing enterprise should ensure, has been reduced. The more upstream of SCM, the more reduction of scope of production planning. As a result, order fluctuation is more sharply contested. Through improving the logistics network, it is best way that the end user's demand information is conveyed to upstream of SCM, but it is difficult in fact. In this paper, it mention the way of robustic adjustment, in the suppliers' point of view, the end user's demand information is dammed up, as they postpone responding the customer's order as a possible. And it will show the result of appling the way, as a case study.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.04a
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• pp.476-486
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• 1995

In this paper, an attempt has been made to revise Raafat' s(1985) results on an inventory model for decaying raw materials and the finished product at a constant rate which was based on Goyal's integrated inventory model for a single product system. This paper is concerned with scheduling the frequencies of order quantity of several different raw materials on a production inventory model. The purpose of this paper is to present a simple method of deciding the frequencies of order quantity of raw materials, in the sense of minimizing the average total cost of the system. We describe on iterative procedure for directly determining near optimal frequencies of order quantity for the raw materials and the associated fundamental cycle time which can be used for constructing the production duration of the finished product. In cases where feasible schedules cannot be constructed using the values from the iterative procedure, the procedure provides a basis for changing the order quantity frequencies and the fundamental cycle time to obtain feasible schedules. An example is given to illustrate the derived results.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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• pp.470-475
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• 2002

An alternative to traditional production planning and control systems such as MRP and JIT is the drum-buffer-rope (DBR). Using the DBR system, companies can achieve a large reduction of work-in-process (WIP) and finished-goods inventories (FGI). significant improvement in scheduling performance, and substantial earnings increase. The purpose of this paper is to analyze the effect of the DBR system in a serial production line. Using Markov process, we modeled a DBR system with three stages. For the model developed we analyze the system characteristics and then present an optimization model for system design. The system performance is also analyzed through sensitivity analysis.

• Journal of Korean Institute of Industrial Engineers
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• v.28 no.4
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• pp.344-350
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• 2002

An alternative to traditional production planning and control systems such as MRP and JIT is the drum-buffer-rope(DBR). Using the DBR system, companies can achieve a large reduction of work-in-process (WIP) and finished-goods inventories (FGI), significant improvement in scheduling performance, and substantial earnings increase. The purpose of this paper is to analyze the effect of the DBR system in a serial production line. Using Markov process, we modeled a DBR system with three stages. For the model developed, we analyze the system characteristics and then present an optimization model for system design. The system performance is also analyzed through sensitivity analysis.