• Nuclear Engineering and Technology
• /
• 제32권4호
• /
• pp.328-341
• /
• 2000

Investigated in this study are the modal characteristics of the coaxial cylindrical shells with fluid-filled annulus. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier series expansion, and their results are compared with those of finite element method to verify the validation of the method developed. The effect of the fluid-filled annulus and the boundary conditions on the modal characteristics of the coaxial shells is investigated using a finite element modeling.

• 대한기계학회논문집B
• /
• 제21권4호
• /
• pp.551-561
• /
• 1997

Mixed convection of air in a horizontal concentric cylindrical annulus is investigated numerically. Isothermal boundary conditions are prescribed at the inner and outer cylinders, with the inner cylinder being warmer. The forced flow is induced by the outer cylinder which is rotating slowly with constant angular velocity with its axis at the center of the annulus. The effect of the forced flow on the flow pattern and heat transfer of natural convection is investigated for the annulus of (inner-cylinder radius/gap width) = 1. There appear two eddies, one eddy or no eddy according to the Rayleigh and Reynolds numbers. Map of the three flow regimes is constructed on the Ra-Re plane. (author). 28 refs., 9 figs., 2 tabs.

• 대한기계학회논문집B
• /
• 제22권12호
• /
• pp.1784-1795
• /
• 1998

Natural convection of low Prandtl number fluids with $Pr{\leq}0.2$ in a narrow horizontal annulus is numerically investigated. For $Pr{\leq}0.2$, hydrodynamic instability induces oscillatory multicellular flows consisting of multiple like-rotating cells. For a fluid with $Pr{\approx}0$, the region in which instability of conduction regime first forms is near the vertical section of annulus, and the multiple cells are distributed uniformly in the lower and upper regions of annulus. As Pr increases, however, the cells are shifted upwards. The like-rotating cells drift downward, as time goes on, and the speed of travel increases with increase of Pr. For a fluid with Pr=0.1, a flow with period-4 solution is observed between chaotic states.

• Nuclear Engineering and Technology
• /
• 제41권10호
• /
• pp.1333-1346
• /
• 2009

To assure the reliability of cylinders or shells with fluid-filled annulus, it is necessary to investigate the modal characteristics considering fluid-structure interaction effect. In this study, theoretical background and several finite element models are developed for cylindrical shells with fluid-filled annulus considering fluid-structure interaction. The effect of the inclusion of the fluid-filled annulus on the natural frequencies is investigated, which frequencies are used for typical dynamic analyses such as responses spectrum, power spectral density and unit load excitation. Their response characteristics are addressed with respect to the various representations of the fluid-structure interaction effect.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2759-2764
• /
• 2008

Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.

• 설비공학논문집
• /
• 제12권8호
• /
• pp.755-762
• /
• 2000

Natural convection of air in a horizontal annulus with the inner cylinder cooled by the application of a constant heat flux and the isothermally heated outer cylinder is considered. The bifurcation phenomenon of flow patterns and the heat transfer characteristics are numerically investigated. The zero initial condition induces a unicellular flow in a half annulus. A bicellular flow consisting of two counter-rotating eddies in a half annulus can be obtained above a certain critical Rayleigh number. A transition from the bicellular to the unicellular flow occurs with a decrease in Rayleigh number. Hysteresis phenomena have not been observed. In the regime of dual flows, the overall Nusselt number of the bicellular flow is greater than that of the unicellular flow.

• Journal of Chest Surgery
• /
• 제22권3호
• /
• pp.463-467
• /
• 1989

The presence of a small aortic annulus creates a difficult technical problem. Whenever possible, the smaller prosthesis of any type should be avoided. A case of aortic stenoinsufficiency with fibrous small aortic annulus [17 mm] in 26 years old adult woman patient was successful operated upon with aortic valve replacement [21 mm St. Jude Medical valve] and enlargement of aortic annulus with Gore-Tex patch. The postoperative course was uneventful.

• 대한설비공학회지:설비저널
• /
• 제8권1호
• /
• pp.1-9
• /
• 1979

Heat transfer characteristics of an annular heat pipe is investigated theoretically and experimentally. An annular heat pipe transports maximum heat which is found to be a cubic polynomial function of the thickness of annulus when the annulus becomes large, maximum heat transfer rate Is limited by boiling criterion. The limit decreases inversely proportional to the thickuess of annulus. Theoretical formula for thermal resistance of annular heat pipe Is proposed. Experimental results on the maximum heat transfer rate satisfactorily agree with theory. Measured thermal resistance is found to be lower than the predicted results as the thickness of annulus becomes large.

• 한국수학사학회지
• /
• 제14권2호
• /
• pp.149-154
• /
• 2001

In this paper we represent the Ahlfors function on the multiply connected planar domain, especially on an annulus and apply it to the Caratheodory metric.

• Clinical and Experimental Pediatrics
• /
• 제46권5호
• /
• pp.484-489
• /
• 2003

목 적 : PA/IVS의 형태학적 및 혈역학적 다양성을 이해하고 최적의 치료방침을 결정하기 위하여 PA/IVS 신생아 환아들에서 심초음파기를 이용하여 우심실의 용적 및 유입부, 유출부의 크기를 측정하여 정상 신생아와 비교해 보았다. 방 법 : 2001년 1월부터 12월까지 청색증 및 심잡음으로 경북대학교병원 신생아실로 전원된 신생아 중 심초음파 검사로 PA/IVS로 진단받은 환아 8명을 대상으로 하였다. 심초음파 검사 당시의 대상환아의 나이는 평균 6.9일(생후 1-34일), 체중은 3,343 gm(2,970-4,000 gm)이고, 이중 남아가 5례, 여아는 3례였다. 대조군으로는 만삭아이면서 심질환이 없이 패혈증 의증이나 황달로 신생아실에 입원한 환아 10명을 대상으로 하였다. 심초음파 검사는 Acuson사의 Aspen 기기(7 Mh 탐촉자 장착)로 시행하여 super-VHS 비디오테이프에 녹화하였고, 기기안에 내장된 프로그램을 이용하여 우심실과 좌심실 용적, 대동맥판, 폐동맥판, 승모판, 삼첨판륜의 직경을 측정하고 대조군과 비교하였다. 결 과 : PA/IVS 환아들의 삼첨판륜의 Z-value는 $-3.69{\pm}2.80$(-8.4--0.45), 삼첨판륜/승모판륜의 직경의 비는 $0.69{\pm}0.15$(0.43-0.84)로 측정되었다. 삼첨판/승모판륜의 직경의 비와 삼첨판 Zvalue의 관계에서는 삼첨판/승모판륜의 크기의 비가 클수록 삼첨판륜의 Z-value가 컸다(r=0.885, P=0.003). 또한 판막성형술만 시행한 환아들 에서는 다른 치료를 시행한 환아들에 비해 우심실 용적과 삼첨판, 폐동맥판의 Z-value가 높았고, 삼첨판륜/승모판륜 직경의 비가 높았으나 통계학적 유의성은 없었다. 결 론 : PA/IVS 환아의 심초음파 평가에서 우심실 용적을 계측하는 것보다 삼첨판의 Z-value 및 삼첨판륜/승모판륜 직경의 비를 구하는 것이 계측방법도 간편하고, 환아의 치료방침 및 예후를 판정하는데 더 좋은 지표로 생각된다.