• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.81-85
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• 1993

정면밀링은 급속 가공을 매우 효율적으로수행할 수 있기 때문에 널리 사용되고 있다. 그러나 밀링커트는 단속 절삭 공구로서 절삭날의 단속절삭작용에 의한 변동적삭력과 여러날의 동시가공에의한 절삭력의 교란 때문에 절삭성이 기계가공에 문제가 되어 왔다. 이러한 문제점들을 해결하기 위하여 기계설계자들은 절삭 력의 교란에 의하여 일어나는 진동을 줄이기 위하여 기계구조의 강성을 증가시켰으나 이것은 비용이 많이 들게 되므로 공구 형상을 개선하여 안정된 절삭을 시도하였다. 본 연구에서는 절삭력 모델을 이용하여 변위 발생의 원인인 절삭력변동을 최소로 하는 커터의 형상을 3차원으로 최적 설계하였다. 최적 설계 제작된 공 구와 재래식 공구를 사용하여 절삭력, 공구수명, 표면조도를 측정하였다. 최적 설계 제작된 공구와 재래식 공구에 의하여 측정된 결과들을 비교 검토하여개발된 공구의 절삭특성을 규명하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1845-1850
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• 2014

Railway operators have given a lot of efforts to determine the railway route of the minimum cost. In order to determine the optimal alignment, the alignment should be allocated satisfying the design criteria on various geographical condition with the minimum earth works. The determination of the optimal railway alignment is a kind of combination optimization because that must consider various design elements. This study developed a numerical model to determine the optimal railway alignment with the minimum construction cost. The problem was analyzed by the genetic algorithm, and the concept of the optimal alignment was established with the results from the analyses. The methodology was applied to a fictitious rail construction section and the result was evaluated. This methodology is meaningful considering the fact that the cost for energy is greater than that of the construction.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.4
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• pp.280-293
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• 2005

In this study, a model to calculate the expected total construction cost has been developed by combining a model to calculate the sliding distance of a caisson of a vertical breakwater and a model to calculate the rehabilitation cost of a caisson. The optimal cross-section of a caisson of a vertical breakwater is defined as the cross-section that requires a minimum expected total construction cost within the allowable limit of caisson sliding. Two allowable limits are considered: 0.1 m of the expected sliding distance during the lifetime of the breakwater and 0.1 of the probability that the cumulative sliding distance during the lifetime of the breakwater is greater than 0.3 m. A discount rate has also been introduced to convert the future rehabilitation cost to the present value. The introduction of the discount rate reduces the expected total construction cost for the caissons designed for shorter return periods due to frequent rehabilitations. The present design method requires a smaller cross-section than the conventional deterministic method in shallow water depths, enabling us to design a caisson more economically. On the other hand, the above-mentioned allowable limits of caisson sliding show similar results for smaller water depths, while, for larger depths, the former requires a larger cross-section than the latter.

• Journal of Internet of Things and Convergence
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• v.7 no.4
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• pp.9-14
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• 2021

In computing systems that require high reliability, the method of predicting the lifetime of a storage device is one of the important factors for system management because it can maximize usability as well as data protection. The life of a solid state drive (SSD) that has recently been used as a storage device in several storage systems is linked to the life of the NAND flash memory that constitutes it. Therefore, in a storage system configured using an SSD, a method of accurately and efficiently predicting the lifespan of a NAND flash memory is required. In this paper, a method for optimizing the lifetime prediction of a flash memory-based storage device using the frequency of NAND flash memory failure is proposed. For this, we design a cost matrix to collect the frequency of defects that occur when processing data in units of Drive Writes Per Day (DWPD). In addition, a method of predicting the remaining cost to the slope where the life-long finish occurs using the Gradient Descent method is proposed. Finally, we proved the excellence of the proposed idea when any defect occurs with simulation.

• Journal of Korea Water Resources Association
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• v.42 no.9
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• pp.759-771
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• 2009

The electricity cost of pumping system accounts for a large part of the total operating cost for long distance water supply networks. This study presents a method based on dynamic programming for establishing an joint optimal operation of pumps and storages system on a hourly basis. Analysis is taken of the relative efficiencies of the available pumps, the structure of the electricity tariff, the consumer-demand pattern, and the storage characteristics and operational constraints of the pipe. The possible system objectives and constraints are described. An application of the method to the existing Yangju Water Supply System consisted of two pump station and 5 storage pools under the condition of expanding pumping facility in the part of the Capital Area Water Supply System is presented, showing that considerable electricity cost savings are remarkable. The approach was found to be implementable in real system operation and large-scale water supply system design in respect of minimizing life-cycle total cost.

• Journal of the KSME
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• v.34 no.5
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• pp.342-350
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• 1994

본 연구를 통하여 기존에 사용되고 있던 알루미늄 압출재 블레이드를 복합재료로 대치하여 개 발함으로써 이의 타당성을 검토하여 보았다. 풍력발전기의 개발 추세는 점차 메가와트 (megawatt)급 시스템으로 진행되어 터빈 블레이드가 대형화됨에 따른 터빈브레이드의 경량화 및 내구력의 향상이 절실히 요구된다. 이는 복합소재의 사용으로 경량화를 통한 시스템 각요소의 제작비용절감 및 내구력 향상을 통한 시스템의 수명증대의 효과를 확보할 수 있을 것이다. 그 러나 복합재료를 사용한 터빈 블레이드는 기존의 알루미늄을 이용한 재료보다는 가격경쟁에서 다소 떨어지며 제작공정상의 어려움과 정밀한 설계기술의 미개발 등 아직도 많은 난점을 안고 있는 실정이다. 그러나 현재 풍력에너지 이용 선직국의 개발추이로 보아 대용량시스템의 터빈 블레이드는 복합소재의 사용이 필수적이며 보다 효율적인 양산시스템의 구축과 최적설계에 대한 연구가 지속적으로 실시되면 기존의 블레이드와는 충분한 경쟁성을 확보할 것으로 전망된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.12
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• pp.1150-1159
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• 2011

Reliability is defined as a probability that a system will operate properly for a specified period of time under the design operating conditions without failure. Reliability-Redundancy Optimization Problem(RROP) involves selection of components with multiple choices, redundancy levels and redundancy strategy(Active or Standby) for maximizing system reliability with constraints such as cost, weight, etc. Based on the design configuration of Multi-Spectral Camera(MSC) system of KOMPSAT-2, the mathematical programming model for RROP is suggested in this study. Due to the nature of RROP, i.e. NP-hard problem, Parallel Particle Swarm Optimization(PPSO) algorithm is proposed to solve it. The result of the numerical experiment for RROP is presented as instance of recommended design configuration at some mission time.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.20 no.4
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• pp.367-374
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• 2002

Maintainability of highways is an important problem that is considered in the planning steps of a highway development process. A number of asset management systems have been developed to precisely predict maintenance and pavement expenditures for better decision making, But these systems are not helpful in reducing maintenance costs. Optimization of some highway design characteristics in the planning phases may reduce maintenance costs over the life cycle of highway. The formulations for initial and maintenance costs have been developed based on which design variables can be chosen to minimize these costs, focusing on the sideslope in cut and fill sections. Maintenance cost has been represented as a function of sideslope, width of highway cross section, and annual average daily traffic. A real geographic database of between Chung joo and Sang joo city in Choong buk was used and it is presented to investigate the sensitivities of maintenance cost and soil characteristics in selecting alignments. In this study, we present that maintenance cost and soil characteristics are important considerations in alignment optimization.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.2
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• pp.113-127
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• 2007

In this study, a model to calculate the expected total construction cost is developed that simultaneously considers the rehabilitation cost related to the sliding of the caisson, the economic damage cost due to harbor shutdown in the event of excessive caisson sliding, and the economic damage cost due to temporal operational stoppage by excessive wave overtopping. A discount rate is used to convert the damage costs occurred at different times to the present value. The optimal cross-section of a caisson is defined as the cross-section that requires a minimum expected total construction cost within the allowable limit for the expected sliding distance of the caisson during the lifetime of the breakwater. Two values are used for the allowable limit: 0.3 and 0.1 m. It was found that the economic damage cost due to harbor shutdown by excessive caisson sliding is more critical than the rehabilitation cost of the caisson or the economic damage cost by excessive wave overtopping in the decision of the optimal cross-section. In addition, the optimal cross-section of the caisson was shown to be determined by the allowable limit for the expected sliding distance rather than the minimum expected total construction cost as a larger value is used for the threshold sliding distance of the caisson for harbor shutdown.

• Journal of the Korean Institute of Gas
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• v.20 no.1
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• pp.7-12
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• 2016

Natural gas liquefaction process is essential to transport natural gas for long distances. Lots of compressors in this process are needed and the energy for these compressors can be supplied by drivers. Total driver cost can be changed by selecting various drivers. This study focused on the minimization of the driver cost to provide the energy to the compressors. Moreover, scenarios, extracting velocity is changed during whole operating period, are set with considering gas well capacity. The mathematical model was established by considering trade off relationship between the capital cost and the operating cost of the turbines. The model also considers the life time of the driver equipments. As the result, the driver cost of the optimized case was reduced by 6.4% than the base case.