• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.321-326
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• 2008

The engineering use of CFD is recently extending to the prediction of maneuvering characteristics, response to waves, propeller performance, and so on. The focus of the research is shifting to simulation of more complex processes. Typical examples of such processes are bow or stern slamming, green water problem, propeller cavitation, hull-propeller interaction, or drag reduction by bubble injection. Those processes are characterized by keywords such as high nonlinearity, unsteadiness, multiphase flow. In this paper, two new attempts which have been recently made by the author's research group are presented. One is the prediction of propeller cavitation and its effect to the ship hull. The other is the application to the drag reduction by use of air bubbles.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.185-188
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• 1999

수중에서 기포의 강한 비선형성을 이용하여 기포막상의 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 확인과 두 입사 음파의 전파방향으로 차주파수 음파가 분포하고 있음을 관측하였다 본 논문에서는 기포막을 이용하여 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 지향특성을 예측할 수 있음을 제시하였다.

• 천문학회지
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• 제29권2호
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• pp.83-91
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• 1996

We present a model that rotating primordial blackholes(PBHs) produced at the end of inflation generate the random, non-oriented primordial magnetic field. PBHs are copiously produced as the Universe completes the cosmic phase transition via bubble nucleation and tunneling processes in the extended inflation hypothesis. The PBHs produced acquire angular momentum through the mutual tidal gravitational interaction. For PBHs of mass less than 1013g, one can show that the evaporation (photon) luminosity of PBHs exceeds the Eddington limit. Thus throughout the lifetime of the rotating PBH, radiation flow from the central blackhole along the Kerr-geodesic exerts torque to ambient plasma. In the process similar to the Bierman's battery mechanism electron current reaching up to the horizon scale is induced. For PBHs of Grand Unified Theories extended inflation with the symmetry breaking temperature of $T_{GUT}\;\~\;10^{10}$ GeV, which evaporate near decoupling, we find that they generate random, non-oriented magnetic fields of $\~10^{-11}G$ on the last-scattering surface on (the present comoving) scales of $\~O(10)Mpc$.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권2호
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• pp.346-363
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• 2015

We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We integrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and validate the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavitating systems.

• Tribology and Lubricants
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• 제38권3호
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• pp.109-114
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• 2022

This paper reports the development of an oil flushing system combined with a microbubble generator. Oil flushing plays a crucial role in regulating the lubricant's performance during the lubricant replacement process. Moreover, harmful contaminants, such as sludge, wear particles, and rust, from piping systems or lubrication system can be removed by oil flushing. Oil flushing aims to increase the system's efficiency using a dedicated flushing oil, increasing of the supply pressure and generating a vortex. In addition, it helps the mechanical system or equipment achieve peak performance and reduces the potential for premature failure. However, the contaminant-removal applications of existing oil flushing system are limited. In this research, we aim to improve the performance of oil flushing system by incorporating a microbubble generator, which uses the venture effect to generate microbubbles and mixes them with lubricant. The microbubbles in the blended lubricant remove contaminants from the lubrication system more effectively. Structural mechanics and fluid dynamics are analyzed through fluid-structure interaction (FSI) analysis, and the numerical analysis results are used for the designing the system. The magnitude of the maximum stress is investigated based on the pressure results obtained by the CFD analysis; through the CFD analysis, the mixing ratio of air (bubble) and lubricant is evaluated using the volume of fluid (VOF) model according to the working conditions.

• Spatial Information Research
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• 제22권6호
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• pp.55-65
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• 2014

본 논문은 조경설계를 위한 창의적 개념화를 지향하는 공간 의사 결정 시스템 모델에 대한 연구이다. (1)정보의 폭발 및 무시 (2)원칙성과 융통성의 딜레마 (3)비구조화된 성격의 계획 및 설계라는 세가지 특징 때문에, 현재 정보중심의 GIS는 큰 역할을 못하고 있다. 이에 현재의 정보중심의 GIS에 대한 대안으로 공간 개념화를 지향하는 SDSS(공간의 사결정지원시스템)모델을 제시하고자 한다. 미래의 공간 개념화 지향의 SDSS는 인지적 관점을 기반으로 한 공간개념화를 현재의 GIS기술과 연계시킴으로써 조경설계의 비구조적인 문제를 효율적이고, 창조적으로 해결할 수 있다. 공간개념화 지향의 SDSS 모델은 (1)인간정보처리 (2)도구 및 이론의 상호작용 (3)인지과학 및 실천인식론 (4)의사결정지원 시스템 (5)인간과 컴퓨터의 상호작용 (6)창조적인 사고라는 핵심이론 및 기술을 반영한다. 향후 구현될 공간 개념화 지향의 SDSS는 설계자가 공간계획 및 설계상에서 "숨겨진 조직"을 파악할 수 있게 하고, 생성 및 개념화 능력을 통해 새로운 아이디어를 개발하고 이를 다른 설계자와 공유할 수 있게 한다. 공간개념화는 (1)버블다이어그램 지향의 설계지원 시스템 (2)어의적 기억의 확장으로서의 프로토타입 (3)삽화적 기억의 확장으로서 스크립트라는 세 가지 핵심 아이디어를 통해 공간 설계의 개념화를 보다 용이하게 할 수 있다. 앞으로 이 세 가지 아이디어는 계획 및 설계를 위한 GIS기술의 미래 방향을 제시할 수 있을 것이다.

• Nuclear Engineering and Technology
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• 제44권3호
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• pp.261-272
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• 2012

Molten Core Concrete Interaction (MCCI) is a complex process characterized by concrete ablation and volatile generation; Thermal and solutal convection in a bubble-agitated melt; Physico-chemical evolution of the corium pool with a wide solidification range (of the order of 1000 K). Twelve experiments have been carried out in the VULCANO facility with prototypic corium and sustained heating. The dry oxidic corium tests have contributed to show that silica-rich concrete experience an anisotropic ablation. This unexpected ablation pattern is quite reproducible and can be recalculated, provided an empirical anisotropy factor is assumed. Dry tests with oxide and metal liquid phases have also yielded unexpected results: a larger than expected steel oxidation and unexpected topology of the metallic phase (at the bottom of the cavity and also on the vertical concrete walls). Finally, VULCANO has proved its interest for the study of mitigation solutions such as the COMET bottom flooding core catcher.

• 한국가구학회지
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• 제23권2호
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• pp.185-194
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• 2012

Contemporary society maintains mass-product system that keeps endless cycle of making and consuming. In this vein, everyday life becomes to be under the control of function and efficiency. On the contrary, the people are getting to have a desire of escaping from this everydayness, that is, the desire for non-everydayness. British architect, Nigel Coates understood the potentiality of contemporary metropolis which produce new experiences through their heterogeneities. During 1980s, Japanese economic bubble provided rich nourishment to the desire for non-everydayness based on consumers' tastes. Nigel Coates snatched this phenomena and designed commercial spaces aligned to the non-everydayness. He shows very eloquent version of escaping sense. We can find the exquisite quality of non-everydayness through design vocabulary of object's form and arrangement. In the viewpoint of object form, Coates adopted classical statues of Greek, that is antique, and modern gadgets such as airplane wings and seats. Also, we can find abundant gestures of curvilineal contours throughout the objects he designed. As for the objects' arrangement, he introduced repetition and curved composition that can stimulate human interaction with interior scape.

• 한국항공우주학회지
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• 제33권6호
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• pp.1-7
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• 2005

비압축성 평균 Navier-Stokes 방정식에 $\varepsilon{-SST}$ 난류 모델을 적용하여 정사각주 주위 유동과 지면의 간극 유동을 해석하였다. 지면이 운동할 경우에는 지면의 박리 전단층의 강도가 약화되어 사각주 상/하부의 박리 전단층 상호 작용을 촉진시키므로 고정 지면에 비하여 더 낮은 간극에서도 와류 배출이 발생한다. 지면 효과를 고려할 경우 고정 지면의 경우와는 달리 지면의 박리 거품이 존재하지 않게 되고, 이로 인하여 2차 박리 주파수는 나타나지 않는다. 이와 더불어 지면이 운동할 경우 고정 지면에 비해 더 높은 와류 배출 주파수와 공력 계수가 나타남을 확인하였다.

• Nuclear Engineering and Technology
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• 제28권3호
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• pp.229-246
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• 1996

A mechanistic model has been developed to predict the release behavior of fission gas during steady-state irradiation of LWR UO$_2$ fuel. Under the assumption that UO$_2$ grain surface is composed of fourteen identical circular faces and grain edge bubble can be represented by a triangulated tube around the circumference of three circular grain faces, it introduces the concept of continuous formation of open grain edges tunnels that is proportional to grain edge swelling. In addition, it takes into account the interaction between the gas release from matrix to grain boundary and the reintroduction of gas atoms into the matrix by the irradiation-induced re-solution of grain face bubbles. It also treats analytically the behavior of intragranular, intergranular, and grain edge bubbles under the assumption that both intragranular and intergranular bubbles are uniform in both radius and number density. Comparison of the present model with experimental data shows that the model's prediction produces reasonable agreement for fuel with centerline temperatures of 1000 to 140$0^{\circ}C$, wide scatter band for fuel with centerline temperatures lower than 100$0^{\circ}C$, and underprediction for fuel with centerline temperatures higher than 140$0^{\circ}C$.