• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2003년도 춘계학술대회 논문집
• /
• pp.214-214
• /
• 2003

During a model test of Hutton TLP, a "ringing" response was first observed about 20 years ago. This phenomenon is a resonant build up over the time of wave period and this burst-like motion can cause the extreme load on the TLP tether. It is often detected in the large and steep irregular waves but the generation mechanism leading to the "ringing" is not yet well understood. According to the research since then, the higher order harmonic components may account for the "ringing" on the floating offshore structures. The main purpose of the present research is, thus, to measure the higher harmonic forces exerted on a vertical truncated circular column and to compare them with available data. A vertical truncated cylinder with a diameter of 3.5inch and a draft of 10.5inch is used as a test structure, which is a scaled model of ISSC TLP column. The cylinder is installed at a distance of 45ft from the wave maker in order to avoid parasitic waves created in the wave flap. Attached to the upper part of the cylinder are two force gages to measure the horizontal (surge) and vertical (heave) forces on the cylinder. The incoming waves are Stokes waves with a slope ranging from 0.06 to 0.24. The forces and waves are measured for 60 seconds with a sampling rate of 50 Hz. Among the recorded data, the first 10 waves are excluded because of transient behavior of the waves and the next The horizontal and vertical forces are analyzed up to 5th order harmonics. The horizontal forces are then compared to the values from the theoretical model called "FNV model". In addition, force transfer functions are also investigated. Major findings in this research are below. 1) The first order forces measured are slightly larger than the theoretical values of "FNV model" 2) The "FNV model" considerably overpredicts the second order forces. 3) The larger the amplitude and more extreme the wave slope, the smaller the predictions are compared to the experimental. 4) The higher harmonic forces are significantly smaller than the first harmonic force for all wave parameters. 5) The normalized forces vs. waves slopes are almost constant in the lower harmonics but vary a lot in the higher harmonics. 6) The trend of forces is more nonlinear in the horizontal forces than in the vertical forces as the wave slope increases. 7) The part of the results above is also observed by other researchers and confirmed again through the present work.

• 설비공학논문집
• /
• 제3권1호
• /
• pp.26-33
• /
• 1991

An experimental study has been performed on the heat transfer by the natural convection from a conducting tube with two axial fins to a surrounding cylinder. In case of vertical fins, the maximum local Nusselt number of conducting tube appears at ${\theta}{\fallingdotseq}145^{\circ}$ and that of outer cylinder appears at ${\theta}=0^{\circ}$, for $l_F=0.3$. In case of horizontal fins, the maximum local Nusselt number of conducting tube appears at ${\theta}=180^{\circ}$ and that of outer cylinder appears at ${\theta}=0^{\circ}$. The local Nusselt number of the upper fin and the downward fin shows negative values for $l_F=1.0$. The local Nusselt number of the lower fin and the downward fin shows higher values than that of the upper fin and the upward fin. The mean Nusselt number of conducting tube in case of vertical fins are increased in order of $l_F=0.6$, 0.3, 1.0 and 0.0, but in case of horizontal fins, in order of $l_F=1.0$, 0.6, 0.3, and 0.0. The mean Nusselt number of outer cylinder in case of vertical fins are increased in order of $l_F=1.0$, 0.0, 0.3 and 0.6, but in case of horizontal fins, in order of $l_F=0.6$, 1.0, 0.3, and 0.0.

• 대한기계학회논문집B
• /
• 제37권12호
• /
• pp.1113-1120
• /
• 2013

본 연구에서는 $45^{\circ}$기울어진 저온의 사각형 밀폐계 내부에 존재하는 고온의 원형 실린더의 위치 변화에 따른 밀폐계 내부 자연대류 현상에 대한 수치해석을 수행하였다. Rayleigh 수는 $10^3$부터 $10^5$까지 변화하였으며 내부 실린더의 위치는 $-0.4{\leq}{\delta}{\leq}0.4$ 범위에서 0.1 간격으로 변화시켰다. 원형 실린더의 위치 변화에 따른 밀폐계 내부의 자연대류 현상은 실린더 표면과 밀폐계 표면의 Nu 수, 밀폐계 내부의 등온선 및 유선을 바탕으로 분석하였다. 본 연구에서 고려한 Rayleigh 수의 범위와 원형 실린더의 위치 범위에서는 밀폐계 내부의 열유동은 정상상태의 특성을 보였다. 그리고 내부 원형 실린더가 벽면에 가까워 질수록 실린더벽면과 밀폐계 벽면의 평균 Nu 수가 증가하였다.

• 대한기계학회논문집B
• /
• 제31권3호
• /
• pp.273-282
• /
• 2007

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model an inner circular cylinder based on finite volume method, for different Rayleigh numbers varying over the range of $10^4\;to\;10^6$. The study goes further to investigate the effect of an inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder is changed vertically along the center-line of square enclosure. The number, size and formation of cell strongly depend on Rayleigh number and the position of inner circular cylinder. The changes in heat transfer quantities have been presented.

• 대한기계학회논문집
• /
• 제13권1호
• /
• pp.153-160
• /
• 1989

본 연구는 수평전도관과 수평원통 사이의 환상공간에 수직격판이 부착된 경우와 수평직판이 부착된 경우에 Rayleigh수와 무차원 관열전도율을 변수로하여 수직해석과 Mach-Mehnder 간섭계를 이용한 실험으로 자연대류 열전달특성을 연구 하였다.

• 설비공학논문집
• /
• 제8권3호
• /
• pp.338-350
• /
• 1996

A numerical analysis is carried out to study the two-dimensional steady state natural convection from vertical wires immersed in cold pure water. The surface of the wire is $0^{\circ}C$ unifrom temperature. Results of the analysis are presented for free stream temperature from $0^{\circ}C$ to $25^{\circ}C$ and the aspect ratio N from $5.26{\times}10^{-3}$ to $1.0{\times}10^{-3}$. The effects of the density extremum and aspect ratio on the flow pattern and the heat transfer characteristics are discussed As the aspect ratio N becomes larger, in the range of $1.0^{\circ}C{\leq}T_{\infty}{\leq}4.4^{\circ}C$ and $6{^{\circ}C}{\leq}T_{\infty}{\leq}17^{\circ}C$, the effect of Pr number on the heat transfer is shown to be more significant than the aspect ratio. Investigating into the effect of the density extremum on the heat transfer from wires, the new heat transfer correlations are suggested with the relation of average Nu mumber vs. modified Ra number. Here, the coefficient values C of correlations are presented as the function of density extremum parameter $R^*$. The effects of the density extremum parameter are also discussed.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2002년도 추계 학술대회논문집
• /
• pp.150-155
• /
• 2002

A commercial CFD code is applied to analyze the 3-D viscous flow field within vertical multi-stage centrifugal pump including impeller with 6 blades and guide vane with 11 blades and is performed by changing flow rate from 10 to $26m^3/h$ at the constant 3500rpm. The purpose of this 3-D numerical simulation is not only to confirm how much the effect of three kinds of blade inlet breadth (11mm, 11.5mm, 12mm) of impeller has influence on the performance of vertical multi-stage pump but also to make clear the cause about performance difference at the exit side of impeller and guide vane. The vertical multi-stage pump consisit of the impeller, guide, vane and cylinder. The grid of numerical analysis used to the vertical multi-stage pump is 18,000, 45,000, and 100000 cells in case of the impeller, guide vane, cylinder and total grid is 730,000 cells. The characteristics such as total pressure coefficient, total head, shaft horse power, power efficiency at the exit side of impeller and guide vane, discharge coefficient are represented according to flow rage changing.

• Journal of applied mathematics & informatics
• /
• 제23권1_2호
• /
• pp.127-140
• /
• 2007

We present the boundary value problem (BVP) for the heave motion due to a vertical circular cylinder in water of finite depth. The BVP is presented in terms of velocity potential function. The velocity potential is obtained by considering two regions, namely, interior region and exterior region. The solutions for these two regions are obtained by the method of separation of variables. The analytical expressions for the hydrodynamic coefficients are derived. Computational results are presented for various depth to radius and draft to radius ratios.

• 대한기계학회논문집
• /
• 제18권5호
• /
• pp.1322-1329
• /
• 1994

The effect of thermal stratification on the stratified flow past a circular cylinder was examined in a wind tunnel. Turbulent intensities, the rms values of temperature and turbulent convective heat flux as well as the velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured by using a hot-wire and cold-wire combination probe. It is found that the temperature field affects as an active contaminant, so that the vertical growth of vortical structure is suppressed and the strouhal number decreases with increasing the extent of stratification. And also, the wake structure can not sustain their symmetricity about the wake centerline and vertical turbulent motion dissipates faster than that of the neutral case when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower of the wake in a stably stratified flow because the turbulent intensities and convective heat flux in the upper half section are larger than those of the lower half of the wake.

• 대한기관식도과학회지
• /
• 제16권2호
• /
• pp.131-137
• /
• 2010

Background: Montgomery T-tube is widely used to maintain airway in many cases. Market-available tubes are not always fit to the trachea of each patient and need some modification such as trimming. Complications do happen in prolonged use like tracheostomy tubes. To overcome above limitations, we designed custom-made T-tube using CT data with the aid of 3D reconstruction software. Material and Method: Boundaries were extracted from neck CT data of normal person and processed by surface rendering methods. Real laryngotracheal model and tracheal inner surface-mimicking tube model were made with plaster and rubber. The main tube was designed by accumulation of circles or simple closed curves made from boundaries. Stomal tube was made by accumulation of squares due to limitation of software. Measurement data of tracheal lumen were used to custom-made T-tubes. Tracheal lumen residing portion (vertical limb) was made like circular cylinder or simple closed curved cylinder. Stomal portion (horizontal limb) was designed like square cylinder. Results: Custom made T-tube with cylindric vertical limb and horizontal limb of square cylinder was designed. Conclusion: CT data was helpful in making custom made T-tube with 3D reconstruction technique. If suitable materials are available, commercial T-tube can be printed out from 3D printers.