• 한국기계연구소 소보
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• 통권13호
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• pp.87-98
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• 1984

An experimental study carried out to predict the performance characteristics of a high speed planing boat at the two displacements whose hull form shows hard chines form transom to bow. In the resistance test the planing hull model was porpoising at and above 30 knots for both displacements of 30 tons and 24 tons. A small stern wedge was newly designed and attached across hull bottom. The planing hull model with the stern sedge did not show any porpoising up to the speed of 45 knots for both displacements and it analysed results shows the improvement of resistance performance and planing performance comparing with those of original hull form; i.e. for displacement of 30 tons the effective power and trim angle were reduced by 18.9% and 5.71 degrees at the speed of 28 knots, and for the displacement of 24 tons the effective power and trim angle were reduced by 23.63% and 4.37 degrees at the speed of 28 knots, respectively.

• Educational Technology International
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• 제24권2호
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• pp.295-329
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• 2023

The recent development of metaverse-related technology has led to efforts to overcome the limitations of time and space in education by creating a virtual educational environment. To make use of this platform efficiently, applying learning analytics has been proposed as an optimal instructional and learning decision support approach to address these issues by identifying specific rules and patterns generated from learning data, and providing a systematic framework as a guideline to instructors. To achieve this, we employed an inductive, bottom-up approach for framework modeling. During the modeling process, based on the activity system model, we specifically derived the fundamental components of the learning analytics framework centered on learning activities and their contexts. We developed a prototype of the framework through deduplication, categorization, and proceduralization from the components, and refined the learning analytics framework into a 7-stage framework suitable for application in the metaverse through 3 steps of Delphi surveys. Lastly, through a framework model evaluation consisting of seven items, we validated the metaverse learning analytics framework, ensuring its validity.

• 한국분말재료학회지
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• 제15권5호
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• pp.365-370
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• 2008

In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

• 수산해양기술연구
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• 제48권1호
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• pp.40-50
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• 2012

This study aims to analyze the performance of a submersible fish cage which was designed for developing an economical cage system can be applied in korean aquaculture environment easily. To analyze the performance of the designed cage a model test was carried out. In the test, inclination changes of the upper frame and mooring tensions of model cage were measured during the submerging and surfacing motion in still water and wave condition (period: 2s, wave height: 0.1, 0.2, 0.3m). As a result, in the still water condition the model cage kept horizontal balance and inclination degree of the upper frame was about $1^{\circ}$. In the wave condition, the model cage showed bilateral symmetric up-and-down motion but the average inclination degree of the upper frame was about $0^{\circ}$. When the model cage reached at a depth of 1m, the up-and-down motion of the cage was decreased by 12% compared with that of at the surface (period 2s, height 0.3m). In the same wave condition, the maximum and average line tension under the bottom position were about 8% and 11% respectively compared with that of at surface.

• 한국대기환경학회지
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• 제23권4호
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• pp.478-486
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• 2007

Numerical analysis had been performed to understand flow characteristics of the flue gas and slurry in the absorber of a flue gas desulphurization (FGD) system using computational fluid dynamics (CFD) technique. Two-fluid(Euler-Lagrangian) model had been employed to simulate physical phenomenon, which slurry particles injected through slurry spray nozzles fall down and bump into the flue gas inflowing through inlet duct. It was not necessary to adopt pre-defined pressure drop inside the absorber because interaction between flue gas and slurry particles was considered. Hundreds of slurry spray nozzles were considered with the spray velocity at the nozzles, swirl velocity and spreading angle. The results note that the flow disturbance of flue gas is found at the bottom of the absorber, and the current rising with high speed stream is observed in the opposite region of the inflow duct. The high speed stream is reduced as the flue gas goes up, because the high speed stream of flue gas dumps falling slurry particles due to momentum exchange between flue gas and slurry particles. In spite of some disproportion in slurry distribution inside the absorber, escape of slurry particles from the absorber facility is not observed. The pressure drop inside the absorber is mainly occurred at the bottom section.

• Computers and Concrete
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• 제13권1호
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• pp.17-30
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• 2014

This research presents the effect of various ground pozzolanic materials in blended cement concrete on the strength and chloride penetration resistance. An experimental investigation dealing with concrete incorporating ground fly ash (GFA), ground bottom ash (GBA) and ground rice husk ash (GRHA). The concretes were mixed by replacing each pozzolan to Ordinary Portland cement at levels of 0%, 10%, 20% and 40% by weight of binder. Three different water to cement ratios (0.35, 0.48 and 0.62) were used and type F superplasticizer was added to keep the required slump. Compressive strength and chloride permeability were determined at the ages of 28, 60, and 90 days. Furthermore, using this experimental database, linear and nonlinear multiple regression techniques were developed to construct a mathematical model of chloride permeability in concretes. Experimental results indicated that the incorporation of GFA, GBA and GRHA as a partial cement replacement significantly improved compressive strength and chloride penetration resistance. The chloride penetration of blended concrete continuously decreases with an increase in pozzolan content up to 40% of cement replacement and yields the highest reduction in the chloride permeability. Compressive strength of concretes incorporating with these pozzolans was obviously higher than those of the control concretes at all ages. In addition, the nonlinear technique gives a higher degree of accuracy than the linear regression based on statistical parameters and provides fairly reasonable absolute fraction of variance ($R^2$) of 0.974 and 0.960 for the charge passed and chloride penetration depth, respectively.

• 한국음향학회지
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• 제34권3호
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• pp.184-191
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• 2015

본 논문에서는 천해의 거리 독립환경에서 저주파수 대역의 잔향음 준위를 계산하는 정상모드 잔향음 모델 개발을 제안하였다. 정상모드를 이용하여 음원에서 산란체, 산란체에서 수신기까지의 음파 전달을 계산하였다. 산란 면적에서 상하로 전달되는 음파는 각 모드를 이용하여 고려하였다. 산란함수는 기존에 제시된 해저면 조건을 고려한 람베르트 공식(Lambert's law)과 반사각 부근에서는 Kirchhoff 근사법에 의한 가우시안 형태를 조합하였다. 제안 모델을 검증하기 위해 미국 ONR(Office of Naval Research)이 지원한 제 I회 잔향음 모델링 워크샵(Reverberation Modeling Workshop I, RMW I)의 XI, XV번 문제를 기준으로 상대비교를 수행하였다.

• 한국농촌생활과학회지
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• 제4권2호
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• pp.155-162
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• 1993

BIDANI는 활동-연구계획으로서 지역주민이 상부기관의 계획 입안자와 밀접한 관계를 유지하면서 자신의 활동과 포부를 프로그램에 반영토록 하는데 그 목표를 두고 있다. BIDANI는 지역차원의 종합개발 접근이며, 주민의 참여서비스로 지역종합개발계획(BIDP)을 수립한다. 지역의 상황분석, 문제점 우선순위 및 잠재자원의 확인은 주민에 의해 수행된다. 상향식 접근으로 참여 계획을 수립하고 BIDP를 공식화한다. 적절한 유인과 지원으로 지역주민의 참여를 촉진한다. 정부와 사립기관의 사업과 자원활용의 접근성과 효율성을 높힌다. 고위험영양불량 가족집단을 개발프로그램 활동에 참여케 하여 영양의 중요성을 인식케 한다. 정치 및 사회경제적 배려를 최하위 수준에 통합 시키토록 운영한다. 군/시장을 사업소장으로 임명하는 제도화를 통해 프로그램 수행과 지속성을 촉진한다. 따라서 시/군 종합개발프로그램 (C/MIDP)의 “하향식” 계획은 지역의 “상향식” 계획과 연계된다. 시/군지역개발훈련원을 설립하여 지역주재 요원과 주민의 계속 교육을 도모하는 것이 성공과 활력으로 유인하는 개발촉진 요소이다. 비정치적 부문, 즉 학술기관과 사립기관과의 기능적 연계를 강화한다.

• 한국산림과학회지
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• 제88권1호
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• pp.38-46
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• 1999

독일 중부(Solling Hills)의 가문비림 임관의 구조적인 수분증산 통도특성은 LE와 H의 유동량으로 측정되고, 1996년 6월중 재배열된 Penman-Monteith 식을 이용하여 SVAT 모형을 설계하여 도출하였다. 또한 SLODSVAT 모형을 통한 전체 임관 내 각 침엽의 연속적인 수분통도성을 평가하여 임관기공의 통도성을 비교하였다. 이와 같은 결과에서 나온 임관 표면 통도성과 유동량을 설계하고, SLODSVAT 모형에 의해 설계된 기공 통도성 사이에서 중요한 차이점을 알 수 있었다. 이 차이점은 산림 임관의 범위내에 빗물리적인 요소에 의해 영향을 받았음을 알 수 있으며, 일반적으로 임관 표변의 통도성은 전체 측정 기간 동안 임관 기공 전도력보다 크게 나타났다. 또한 산림의 전체 증발산량에 대한 하층부의 공헌도는 작았고, 임관의 복사에너지 균형에 의존하지는 않는 것으로 나타났다. 하층부 증발산량의 기각은 독일 가문비림에 대한 임관 표면 전도력의 과대 평가로서 나타난 결과이다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권10호
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• pp.1062-1067
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• 2015

Floating architecture is a type of building that is geographically located on a sea or a river. It floats under the influence of buoyancy, and does not have an engine for moving it. Korea is a peninsula surrounded by sea except on the north side, so floating architectures have been mainly focused on two points: solving the issue of small territory and providing various leisure & cultural spaces. Floating architectures are expected to save energy effectively, if they use sea water heat, which is known to be clean energy with infinite reserves. To use sea water heat as the heat source and/or heat sink, this study proposes a model in which a sea water heat exchanger is embedded in the concrete structure in the lower part of the floating architecture that is submerged under the sea. Based on the results of performance evaluations of the sea water heat exchanger using CFD (computational fluid dynamics) analysis and mock-up experiments under various conditions, it is found out that the temperature difference between the inlet and outlet of the heat exchanger is in the range of $3.06{\sim}9.57^{\circ}C$, and that the quantity of heat transfer measured is in the range of 3,812~7,180 W. The CFD evaluation results shows a difference of 5% with respect to the results of mock-up experiment.