• 대한조선학회논문집
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• 제48권1호
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• pp.15-22
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• 2011

In this paper, cavitation patterns of model tests were compared with those of full-scale measurement for a propeller of crude oil carrier which was suffered from erosions on suction side of blade tip region. Cavitation tests were performed at design and ballast draft using model and full scale nominal wakes. A model ship and wire mesh method was used for the simulation of wake patterns of model nominal wakes. For the prediction of full-scale wake patterns, a RANS solver(Fluent 6.3) was used and wire mesh method was used for the simulation of the full scale wakes. Comparison results show that cavitation patterns using predicted full-scale wake patterns are closer to cavitation patterns of full-scale measurement at ballast draft condition. Also, cloud cavitations were observed on the position of eroded area at both full-scale measurement and cavitation tests using simulated full-scale wake patterns.

• 산업공학
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• 제13권4호
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• pp.564-571
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• 2000

Manufacturing companies are implementing a so-called customer-centered supply chain management to have a competitive advantage. In these efforts, collaboration not only within a company but also with suppliers, partners and customers is emphasized. The fast delivery, reducing the total lead-time from development to delivery, is pursued more than ever, though the quality and cost are still importantly regarded. Die manufacturing companies are not exception from these trends, because a die is a necessary tool for almost manufacturing industries. The planning and scheduling system plays an important role in supply chain management. In this study, we address a scheduling problem of a die manufacturing company. The problem is very complex due to many reasons including the uncertainty in environment and the complexity of constraints. Considering the importance of due-date satisfaction and human planners' roles, we designed the solution algorithm and the user interface respectively. In the implementation phase, modeling constructs and basic solution algorithms of ILOG solver and ILOG scheduler are used. In the paper, the problem and the algorithm are described with ILOG constructs, and the experience of use is also addressed.

• 한국산학기술학회논문지
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• 제3권1호
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• pp.10-19
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• 2002

본고는 다종, 소규모 회분식 공정 또는 공장을 수학적 프로그래밍 기법으로 최적 설계하는 방법에 대한 것이다. 제안된 일반 회분식 공장문제는 Papageorgaki와 Reklaitis에 의해 혼합정수비선형식(MINLP)으로 수립된 것인데, 최적해답을 보장하며 공장의 확장 등 불확실성을 고려하여 선형화 한 후(MILP) 푸는 방법론이 제시되었다. Bende식 문제분할 방식을 개조하여 몇가지 예제에 대한 풀이를 제시하였다. IBM의 OSL 최적화 패키지를 이용하였고 MILP를 직접 푸는 경우보다 계산시간을 크게 단축할 수 있었다.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4722-4730
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• 2022

This paper introduces a new point depletion-based source term calculation code named BESNA (Bateman Equation Solver for Nuclear Applications), which is aimed to estimate nuclide inventories and source terms from spent nuclear fuels. The BESNA code employs a new modified CE/CM (Constant Extrapolation - Constant Midpoint) predictor-corrector scheme in depletion calculations for improving computational efficiency. In this modified CE/CM scheme, the decay components leading to the large norm of the depletion matrix are excluded in the corrector, and hence the corrector calculation involves only the reaction components, which can be efficiently solved with the Talyor Expansion Method (TEM). The numerical test shows that the new scheme substantially reduces computing time without loss of accuracy in comparison with the conventional scheme using CRAM (Chebyshev Rational Approximation Method), especially when the substep calculations are applied. The depletion calculation and source term estimation capability of BESNA are verified and validated through several problems, where results from BESNA are compared with those calculated by other codes as well as measured data. The analysis results show the computational efficiency of the new modified scheme and the reliability of BESNA in both isotopic predictions and source term estimations.

• 한국정밀공학회지
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• 제22권5호
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• pp.130-137
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• 2005

Recently, the importance of CAE research is growing with the advances of the automotive and computer industry. In addition, multi-body dynamics and powertrain analysis are the most important factors in improving the vehicle design. Since engine torque with curve-data was used for analyzing full car simulation in the multi-body dynamics system for many years, it is impossible to assess the concurrent analysis of the engine and powertrain element included in a real full car system. In powertrain, since vehicle are usually modeled as a simple mass and a inertia, they can not be seen as real cars. Moreover, it is hard to obtain additional dynamics data other than the longitudinal velocity value in movement. Because of the reason that was previously discussed, it is necessary to consolidate the two parts as one routine program for design and development through the coordinate system connectivity, and presented here is a program named O-DYN. Using an object-oriented language C++, this program has a good structure with the valuable characteristics of objectivity, inheritance, and reusability. The reliability of this multi-body dynamics program is examined by DADS, which is the general dynamics program, using DAE solver and PECE integral function with the common coordinator separation method. As a result, we can obtain a better solution and total dynamics data in either area through this process. This program will be useful for analyzing full car simulation with powertrain.

• 한국수자원학회논문집
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• 제46권6호
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• pp.655-666
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• 2013

최근 이상기후로 인해 홍수 등 자연재해의 강도 및 빈도가 증가하고 있다. 2002년 태풍 루사, 2003년 태풍 매미 등 집중호우에 따른 대규모 홍수로 인해 인명 및 재산피해의 급격한 증가가 나타났으며, 이는 불규칙한 기상변화에 대한 기존의 방재대책과 홍수예측시스템의 한계를 보여주고 있다. 이러한 이상 홍수에 효율적으로 대응하기 위해서는 홍수범람 양상을 정확하게 모의할 수 있는 범람모형을 통해 효과적인 대응방안 마련하는 것이 중요하지만 기존의 홍수범람해석모형은 해석시간의 과다소요 및 해석결과의 정확성 등의 문제가 존재한다. 따라서 본 연구에서는 2002년 8월 집중호우로 인해 붕괴된 낙동강 유역의 백산제를 대상으로 쿼드트리격자를 사용하는 Gerris모형을 이용하여 홍수범람해석을 수행하였으며, 기존의 홍수범람모형 중 비구조격자를 사용하는 FLUMEN모형 및 실제 범람지역과의 비교를 통해 쿼드트리 격자기반 홍수범람모형의 적용성 및 효율성을 판단하였다.

• 한국해안·해양공학회논문집
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• 제20권3호
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• pp.247-254
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• 2008

조 등(2004)에 의하여 연안 조위 발생빈도 분포함수로 제시된 쌍봉형 정규분포는 관측조위의 발생빈도와 매우 잘 일치하고 있으나 Monte-Carlo 모의기법을 이용하는 신뢰성 설계과정에서 수백만개의 조위를 발생하는 경우 비현실적인 조위가 발생되어 과대 또는 과도설계가 발생한다. 따라서 본 연구에서는 비현실적인 조위발생을 원천적으로 차단하기 위하여 경계조위 상한-하한을 설정하여 분포함수의 범위를 제한하는 이중절단 쌍봉형 정규분포 함수를 제안하였으며, 제안된 함수분포에 포함된 매개변수를 비선형최적화기법을 이용하여 추정-제시하였다. 제안된 분포함수는 기존의 쌍봉형 정규분포에 비하여 뚜렷하게 정량적으로 크게 개선되는 모습을 보이지는 않으나, 신뢰성 설계과정에서 비현실적인 조위발생의 가능성을 제거할 수 있으며, 비현실적인 조위발생으로 유발되는 설계인자의 비현실적인 과대 및 과소평가 가능성도 자동적으로 제거되는 효과를 기대할 수 있는 것으로 파악되었다.

• 에너지공학
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• 제20권4호
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• pp.278-285
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• 2011

본 연구에서는 리튬이온 전지의 충 방전 특성에 관한 모델링과 전산모사를 수행하였다. 전지의 시스템 구성은 단순화된 2차원 형태의 단일셀에 대하여 모델링하였고, 공학적 편미분방정식 풀이자인 FEMLAB을 이용하여 288 K와 318 K 범위내에서 충방전 특성에 대한 열적 모델링을 수행하였다. 모델링에 채택한 물성치 변수들에 대하여 온도특성을 고려하였으며, 이를 통하여 전지의 특징적인 충방전의 사이클 변화와 충방전 전하량의 변화를 체계적으로 전산모사하였다. 그 결과 충방전 속도에 상관없이 충방전의 주기가 온도가 낮아질수록 짧아짐을 정량적으로 해석할 수 있었다. 이에 부가하여 전지내에서 리튬이온의 물질전달 현상을 해석하여, 전지의 충방전 특성과의 상관관계를 고찰하였다.

• 한국병원경영학회지
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• 제9권2호
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• pp.128-148
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• 2004

Both undergraduate and graduate programs in health services management(HSM) are recently established in colleges and universities in Korea, and the programs train their students for diverse sectors within the field of healthcare management, including hospitals, nursing facilities, consulting firms, health industries such as pharmaceutical, insurance companies, etc. This study investigates many of the managerial roles expected to graduates from academic curricula in HSM, and required competencies to be successful in their positions. The information of roles and competencies for HSM graduates were collected, and their importances were evaluated by healthcare management experts through a Delphi method. As the result, 11 items for present roles and 13 items for future roles were derived, and 15 and 16 items were derived for present and future competencies respectively. Utilizing the classification of work roles by Timmreck and that of managerial competencies by Robbins, the importance of roles and competencies of healthcare managers was analyzed and interpreted. The major domains of roles at present turned out to be 'organizer', 'planner', 'problem solver', and 'coordinator' in order according to importance. On the other hand, as graduates develop their careers, the domains of future roles would be changed to 'director' and 'planner'. For competencies, the most important domain at present was 'technical skill', but the future important domain was 'interpersonal and emotional intelligence'. The result of this study can be seen as an initial step toward improving the academic curricula of HSM in college and universities and promoting collaborative efforts between academic programs and on-site practices in healthcare industries.

• 한국추진공학회지
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• 제18권4호
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• pp.1-8
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• 2014

과대팽창이 발생하는 축대칭 초음속 노즐에서 노즐압력비가 충격파 구조와 추력성능에 미치는 영향을 규명하기 위해 지상연소시험평가용 추력기 노즐을 대상으로 수치모사를 수행하였다. k-${\omega}$ SST 난류 모델을 적용한 Reynolds-averaged Navier-Stokes 방정식을 상용코드 FLUENT를 사용하여 해석한 결과, 노즐 압력비가 증가함에 따라 추력성능이 단조적으로 증대되고, 노즐 내부에서 생성된 충격파와 유동박리점이 노즐 출구방향으로 밀려나는 사실을 확인하였다. 또, 노즐내부 충격파와 팽창파 위치의 직접적 영향을 받는 노즐 출구면에서의 유동구조가 추력성능에 미치는 영향도 상세히 조사하였다.