• 대한기계학회논문집A
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• 제39권11호
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• pp.1123-1129
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• 2015

자동차부품 세척장비는 엔진과 변속기 블록 등의 가공과정에서 잔류하는 기름때를 제거하며, 잦은 수류방향 전환과 고압수의 분사를 위해 한 쌍의 2 방향 밸브를 사용한다. 그러나 정교한 밸브제어장치 없이 2 방향 밸브를 사용하는 경우 급격한 수류방향 전환에 따른 맥동현상이 발생하여 사용에 어려움이 따른다. 대안으로 하나의 3 방향 절환밸브를 사용하는 방법은 정교한 제어장치 없이도 정확한 수류방향 절환이 원활히 이루어져 이러한 문제점을 해결할 수 있다. 그러나 복잡한 유로 및 바텀플러그 형상으로 인해 유속변화가 심하게 발생하여 공동현상이 나타날 수 있다. 본 연구에서는 3 방향 절환밸브 내의 유동특성을 해석적으로 평가하였으며, 바텀플러그 하부에서 나타나는 공동현상을 공동화지표와 POC(Percent of cavitation)를 도입하여 정량화하였다. 공동현상의 저감을 위해 바텀플러그 형상을 매개변수화하고, 해석의 수렴성 개선과 해석시간을 단축시킬 수 있는 단순 유한요소모델을 이용하여 유동해석을 통한 형상최적설계를 실시하였다. 완전요인배치법을 통한 실험계획법과 인공신경망 기반 반응표면모델을 적용하여 공동현상이 발생하지 않는 POC 가 30% 미만인 바텀플러그의 형상을 제시하였다. 얻어진 최적해는 POC 27%에 대하여 바텀플러그의 허리길이와 꼬리길이가 각각 6.42mm 및 6.96mm 이다.

• 융합정보논문지
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• 제8권1호
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• pp.89-94
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• 2018

최근 곤충산업에 대한 관심도와 필요성이 증대되고 있다. 제2의 식량으로까지 일컬어지고 있는 곤충은 다양한 분야에 그 쓰임새가 활용되어지고 있다. 이렇게 다양한 분야에서 활용되어지고 있는 곤충의 대량생산에 대한 관심도가 증가되고 있으며, 그를 위한 환경분석에 대한 연구의 필요성도 증대되고 있다. 다른 선진국의 몇몇 나라에서는 IoT를 접목시킨 자동화 사육시스템이 개발되고 있다. 하지만 수많은 종류의 곤충에 적용시키기에는 한정되어 있고, 가격이 너무 비싸 농가에 보급되어 활용되지 못하고 있다. 따라서 본 논문에서는 농가에서 실직적으로 사용될 수 있는 최적의 시스템을 만들어 보급하기 위한 연구를 진행하였다. 약용과 식용으로 많이 사용되는 흰점박이꽃무지의 유충3기인 굼벵이의 사육환경에 가장 큰 영향을 미치는 톱밥배지의 수분를 토양센서를 이용하여 자동으로 체크하고 그 결과를 LED를 통해 알려주는 알림서비스를 사육환경에 적용하여 최적의 사육환경을 만들고자 한다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.551-558
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• 2004

Recently, fuel prices have been continually raised in diesel engine. Such a change in the fuel price influences enormously the development trend of marine diesel engines for slow speed, In other words, the focus was shifted from large diameter and high speed to low fuel consumption. Accordingly, more efforts are being made for engine manufacturing and development to develop highly efficient engines. In this study. a single cylinder 4 stroke cycle DI slow speed diesel engine was designed and manufactured, a 4 stroke cycle was configured and basic performances were evaluated. The results are as follows. The optimal fuel injection timing had the lowest value when specific fuel consumption was in BTDC 8~$10^{\circ}$, a little more delayed compared to high speed diesel engines. Cycle variation of engines showed about 5% difference at full loads. This is a significantly small value compared to the cycle variation in which stable operation is possible, showing the high stability of engine operation is good. The torque and brake thermal efficiency of engine increased with an increase of engine 250-450 rpm. but fuel consumption ratio increased from the 450 rpm zone and thermal efficiency abruptly decreased. Mechanical efficiency was maximally 70% at a 400 rpm that was lower than normal engines according to the increase of mechanical frictional loss for cross head part. The purpose of this study was to get more practical engines by comparing the above results with those of slow speed 2 stroke cycle diesel engines.

• 대한교통학회지
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• 제24권2호
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• pp.31-41
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• 2006

본 논문은 전통적인 경제학적 개념의 수요함수와 비용과의 관계로서 혼잡비용을 추정할 때 어려움을 극복하고 실제 적용 가능한 혼잡비용을 추정하는 것이다. 본 논문에서는 속도-밀도 곡선을 이용한 공학적인 방법론을 이용하여 속도에 대한 탄력성을 통해 도로의 소통상황에 따른 실질적으로 적용 가능한 혼잡통행료를 산출하기 위해서 실질 교통량자료를 이용하여 속도, 밀도 및 교통량 관계에 따른 이론적인 혼잡요금을 추정하였다. 또한, 본 논문은 장래 전자통행료징수시스템의 도입을 전제로 속도에 따른 적정혼잡통행료를 산정 하였다 특히 연구대상 지역(강변북로)의 자료를 이용하여 다양한 분석결과 Drake모형이 가장 적합한 것으로 분석되었으며, 산정된 모형을 이용하여 통행속도의 변화에 따른 적정 혼잡통행료를 추정하였다. 본 논문의 분석결과를 임금율법에 적용하여 혼잡통행료를 부과할 경우 44km/h-68krn/h일 때 최적의 혼잡 통행료는 94원에서 3,255원으로 추정되었다. 한계대체율법을 적용한 경우에는 속도가 44km/h-68km/h일 때 최적의 혼잡 통행료는 107원에서 6,381원으로 추정되었다.

• 한국연초학회지
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• 제29권2호
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• pp.66-73
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• 2007

This study was carried out to investigate the changes of curing condition on microclimate of temperature, relative humidity during curing process of burley tobacco leaves. The developed facility, ridge opening type was designed to open the central top roof. The air-cured variety, (N. tabacum cv KB111) was normally grown at the Eumseong tobacco experimental station in 2007. Mean daily temperature of $3^{\circ}C$ in ridge opening type curing facility was lower than that of conventional, whereas mean daily relative humidity of 12.6 % RH was lower in conventional curing facility for the entire stage of curing. The frequency distribution of optimal air temperature at daytime was higher 37.5 % in ridge opening type curing facility than that of conventional, while that of optimal relative humidity was lower 8.2 %. In the ridge opening type curing facility, the excessive drying leaves were low, however the price per kilogram was high. These results suggest that the new developed curing facility may be applied to improved microclimate inside the curing facility for curing burley.

• 한국IT서비스학회지
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• 제7권2호
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• pp.1-12
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• 2008

The development of IT and explosively growing number of Internet users are rapidly spreading and developing e-commerce, while creating diverse on-line transaction methods such as a negotiation, a reverse auction, and a bid. Among these transaction methods, the transactions by means of a negotiation are being made for goods that have no posted price. In particular, the transactions by means of a negotiation are expected to be widely used in the B2B. In order to determine their transportation costs, shippers usually make negotiations with many transporters and logistics companies. And before long, these negotiations are expected to be made on an on-line automated negotiation system. Because of this, this study has tried to develop an automated negotiation methodology that is absolutely necessary for an on-line automated negotiation. This study has estimated and selected the evaluation functions for multi-lateral negotiators' proposals, thus developing an automated negotiation methodology. As a result of this study, a new direction for an automated negotiation has been suggested. Also we expect that this study will be widely used in the automated negotiation of diverse fields.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5231-5248
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• 2016

As a service-oriented paradigm, web service composition has obtained great attention from both academia and industry, especially in the area of cloud service. Nowadays more and more web services providing the same function but different in QoS are available in cloud, so an important mission of service composition strategy is to select the optimal composition solution according to QoS. Furthermore, the selected composition solution should satisfy the service level agreement (SLA) which defines users' request for the performance of composite service, such as price and response time. A composite service is feasible only if its QoS satisfies user's request. In order to obtain composite service with the optimal QoS and avoid SLA violations simultaneously, in this paper we first propose a QoS evaluation method which takes the SLA satisfaction into account. Then we design a service selection algorithm based on our QoS evaluation method. At last, we put forward a parallel running strategy for the proposed selection algorithm. The simulation results show that our approach outperforms existing approaches in terms of solutions' optimality and feasibility. Through our running strategy, the computation time can be reduced to a large extent.

• Journal of the Korean Data and Information Science Society
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• 제26권6호
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• pp.1479-1494
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• 2015

최적의 포트폴리오를 선택하기 위한 연구는 평균-분산모형을 시작으로 다양하게 진행되어 왔다. 과거에는 위험자산의 확률분포가 정규분포를 따른다고 가정하여, 투자자가 보유한 위험자산의 분산이 최소화되고 기대수익률이 최대가 되도록 포트폴리오를 구성하도록 하였다. 그러나 실제 위험자산의 분포에는 극단적인 사건들이 많이 발생하기 때문에 정규분포보다 훨씬 꼬리부분이 두꺼우며, 또한 왼쪽꼬리와 오른쪽꼬리가 대칭적이지도 않은 것으로 밝혀졌다. 이에 본 논문에서는 위험자산의 확률분포를 극단치 이론에서 널리 사용되는 일반화 파레토분포 (GPD)로 모형화하였고 체계적인 위험의 추정을 위하여 VaR를 이용하는 한편, 최적의 포트폴리오의 탐색을 위해서는 유전자 알고리즘을 사용하였다. 제안 방법의 적정성을 확인하기 위해 국내 증시에서 최적 포트폴리오를 탐색해 보았으며, 그 결과 GPD로 투자자산의 위험을 추정하였을 때 가장 좋은 결과를 얻을 수 있었다.

• KSBB Journal
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• 제24권2호
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• pp.140-148
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• 2009

The microbial biosurfactants can be substituted to the chemical detergents in some industrial processes. In this study we developed a biotechnological processes for the biosurfactants with microorganisms. The biosurfactants have a lot of advantages in comparision with the chemical surfactants. They are proenvironmental even during and after industrial use. But there are not so many kinds of biosurfactants. The production cost and the end price is much higher than the chemical surfactants. But nowdays there are many kinds of microorganisms, which can produce the surfactants in large quantity and fast. We tried to develop a production process for the large scale with some microorganisms. At first Candida bombicola KCTC 7145, Sphingomonas chungbukensis KCTC 2955 and Sphingomonas yanoikuyae KCTC 2818 are cultivated and studied. For the large scale production process we used molasses as a complex medium and tried to optimize the process. Molasses contains 17 to 25% of water, 45 to 50% of sugar and 25% of carbohydrate, it can be fully used as a substrate. The microorganisms have been cultivated in the diluted media with molasses 2, 5, 8 and 10%, respectively, The optimal conditions for the cultivation and the production process have been studied. For the study the optical density, glucose concentration and the surface tension were measured. Candida bombicola KCTC 7145 and the 5% molasses media was selected as an optimal condition for the production process of a biosurfactant. During cultivation of Candida bombicola KCTC 7145 in the 5% molasses medium kerosene and corn oil were added for promoting the biosurfactants.

• Computers and Concrete
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• 제6권3호
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• pp.253-268
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• 2009

This study aims to develop a cost-based high-performance concrete (HPC) mix optimization system based on an integrated approach using artificial neural networks (ANNs) and genetic algorithms (GA). ANNs are used to predict the three main properties of HPC, namely workability, strength and durability, which are used to evaluate fitness and constraint violations in the GA process. Multilayer back-propagation neural networks are trained using the results obtained from experiments and previous research. The correlation between concrete components and its properties is established. GA is employed to arrive at an optimal mix proportion of HPC by minimizing its total cost. A system prototype, called High Performance Concrete Mix-Design System using Genetic Algorithm and Neural Networks (HPCGANN), was developed in MATLAB. The architecture of the proposed system consists of three main parts: 1) User interface; 2) ANNs prediction models software; and 3) GA engine software. The validation of the proposed system is carried out by comparing the results obtained from the system with the trial batches. The results indicate that the proposed system can be used to enable the design of HPC mix which corresponds to its required performance. Furthermore, the proposed system takes into account the influence of the fluctuating unit price of materials in order to achieve the lowest cost of concrete, which cannot be easily obtained by traditional methods or trial-and-error techniques.