• 물과 미래
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• 제21권3호
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• pp.291-291
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• 1988

2차원 흐름이 원주주위를 지날 때 발생하는 흐름의 변화가 기본방정식인 연속방정식과 운동량방정식에 의하여 수치적으로 해석된다. 수치해석 과정은 기본방정식에 유함수, 와도 및 흐름의 특성을 나타내는 무차원 매개변수를 도입하여 무차원 유함수-와소수송식을 유도한 후, successive over relaxation scheme과 alternating direct implicit scheme으로 수행된다. 수치실험은 레이놀즈수 125-275를 기존의 수치해석에서는 주로 수치실험 결과와 비교한다. 원주표면의 압력을 구하는 방법에 있어서 기존의 수치해석에서는 주로 방사 운동량방정식만을 사용하였으나, 본 논문에서는 기존의 방법외에 방사 운동량방정식 및 접선 운동량방정식에 의해 압력을 계한하고, 두 값을 비교하여 레이놀즈수에 따른 압력을 구하는 방법을 제시한다. 또한 와도의 분포를 도시하여 원주에 의한 후류의 영향을 받지 않는 외부경계의 한계를 새로이 설정한다.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.768-773
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• 2011

The prediction method of future events using the time histories of velocity or pressure, etc., is a useful way for controlling various air vehicles. For example, the sensors of velocity or pressure can be used to extract the time mode coefficients of eigenmode of flow field, and then the result is applied to suppress wake or drag. The velocity information is mapped to the entire flow field, so this mapping function can be used to predict the future events based on the current information. The mapping function is composed of the huge amount of weight parameters, so the efficient way of finding these parameters is needed. Here, the neural network algorithm is studied to draw a mapping function using the number and location of velocity sensors.

• 대한기계학회논문집
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• 제17권12호
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• pp.3135-3147
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• 1993

A numerical method is presented which can solve the steady flow and heat transfer from a rotating and heated circular cylinder in a uniform flow for a range of Reynolds number form 5 to 100. The steady response of the flow and heat transfer is simulated for various spin parameter. The effects on the flow field and heat transfer characteristics known as lift, drag and heat transfer coefficient are analyzed and the streamlines, velocity vectors, vorticity, temperature distributions around it were scrutinized numerically. As spin parameter increases the region of separation vortex becomes smaller than upper one and the lower region will vanish. The lift force, a large part is due to the pressure force, increases as the Reynolds number and it increases linearly as spin parameter increases. The pressure coefficient changes rapidly with spin parameter on the lower surface of the cylinder and the vorticity is sensitive to the spin parameter near separation region. As spin parameter increases the maximum heat coefficient and the thin thermal layer on front region are moved to direction of rotation. However, with balance between the local increase and decrease, the overal heat transfer coefficient is almost unaffected by rotation.

• 물과 미래
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• 제31권4호
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• pp.291-297
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• 1998

2차원 흐름이 원주주위를 지날 때 발생하는 흐름의 변화가 기본방정식인 연속방정식과 운동량방정식에 의하여 수치적으로 해석된다. 수채해석 과정은 기본방정식에 유함수, 와도 및 흐름의 특성을 나타내는 무차원 매개변수를 도입하여 무차원 유함수-와소수송식을 유도한후, successive over relaxation scheme과 alternating direct implicit scheme으로 수행된다. 수치실험은 레이놀즈수 125-275를 갖는 흐름에 대하여 수행되었으며, 시간에 따른 유선, 와도, 원주표면의 압력을 구하는 방법에 있어서 기존의 수치해석에서는 주로 방사 운동량방정식만을 사용하였으나, 본 논문에서는 기존의 방법외에 방사 운동량방정식 및 접선 운동량방정식에 의해 압력을 계한하고, 두값을 비교하여 레이놀즈수에 따른 압력을 구하는 방법을 제시한다. 또한 와도의 분포를 도시하여 원주에 의한 후류의 영향을 받지 않는 외부경계의한계를 새로이 설정한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.294-298
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• 2003

The complex, unsteady, self-sustained pressure oscillations induced by supersonic flow past a rectangular cavity is investigated using numerical simulations. The present numerical study is performed using a parallel, multiblock solver for the two-dimensional, compressible Navier­Stokes equations. Open cavities with length-to-depth (L / D) ratio in the range 0.5 - 3.3 are considered. This paper sheds light on the cavity physics, cavity oscillatory mechanism, and the organisation of vortical structures inside the cavity. The vortex shedding phenomenon, the shear layer impingement event at the aft wall and the movement of the acoustic/compression wave within the cavity are well predicted. The vortical structures· and the source of the acoustic disturbances are found to be located near the aft wall of the cavity. With the increase in the cavity length, strong recompression of the flow near the aft wall leading to a sudden jump in the cavity form drag is observed. The estimated cavity tones are in good agreement with the available semi­empirical relation. Multiple peaks are noticed in deep and long cavities. For the present free­stream Mach number 1.71, it is observed that around L/D=2.0, the cavity oscillatory mechanism changes from the transverse to longitudinal oscillatory mode. The effects of this transition on various fluid dynamics and acoustic properties are also discussed.

• 대한조선학회논문집
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• 제45권5호
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• pp.477-486
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• 2008

Numerical analysis for slamming impact phenomena has been carried out when 2-dimensional wedge shaped structure with finite deadrise angles enter the free surface by using a commertial CFD code, FLUENT. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct scheme (or PLIC-VOF scheme) is used for the tracking of the deforming free surface. User defined function of 6 degrees of freedom motion and moving dynamic mesh option are used for the expression of the downward motion of the structure and deforming of unstructured meshes adjacent to the structure. The magnitude and the location of impact pressure and the total drag force which is the summation of pressures distributed at the bottom of the structure are analyzed. Results of the analysis show good agreement with the results of similarity solution, asymptotic solution and the solution of BEM.

• 천문학회보
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• 제35권2호
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• pp.54-54
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• 2010

Interplanetary space is filled with dust particles originating mainly from comets and asteroids. Such interplanetary dust particles lose their angular momentum by olar radiation pressure, causing the dust grains to slowly spiral inward Poynting-Robertson effect). As dust particles move into the Sun under the influence of Poynting-Robertson drag force, they may encounter regions of resonance just outside planetary orbits, and be trapped by their gravities, forming the density enhancements in the dust cloud (circumsolar resonance ring). The circumsolar resonance ring near the Earth orbit was detected in the zodiacal cloud through observations of infrared space telescopes. So far, there is no observational evidence other than Earth because of the detection difficulty from Earth bounded orbit. A Venus Climate Orbiter, AKATSUKI, will provide a unique opportunity to study the Venusian resonance ring. It equips a near-infrared camera for the observations of the zodiacal light during the cruising phase. Here we consider whether Venus gravity produces the circumsolar resonance ring around the orbit. We thus perform the dynamical simulation of micron-sized dust particles released outside the Earth orbit. We consider solar radiation pressure, solar gravity, and planetary perturbations. It is found that about 40 % of the dust particles passing through the Venus orbit are trapped by the gravity. Based on the simulation, we estimate the brightness of the Venusian resonance ring from AKATSUKI's locations.

• Wind and Structures
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• 제26권2호
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• pp.89-98
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• 2018

For most full-scale tall buildings the Reynolds number of a flow field around a circular cylinder under strong wind is usually greater than $2{\times}10^7$, which is difficult to achieve in most wind tunnel tests. To explore the wind characteristics of tall cylindrical buildings with equidirectional grooves from subcritical to transcritical flow ($6.6{\times}10^4{\leq}Re{\leq}3.3{\times}10^5$ and $9.9{\times}10^6{\leq}Re{\leq}7.2{\times}10^7$), wind tunnel tests and full-scale large eddy simulations were carried out. The results showed that the rectangular-grooves narrow the wake width due to the downstream movement of the separation point and the deeper grooves cause smaller mean and fluctuating pressure while the peak pressure is little affected. Furthermore, the grooves lead to lower frequency of vortex shedding but the Strouhal number remains at the range from 0.15 to 0.35. The drag coefficient of the cylinders with grooves was found to be 2~3 times as large as that of smooth cylinders.

• Journal of Advanced Marine Engineering and Technology
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• 제34권8호
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• pp.1094-1099
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• 2010

수중에 있는 구 주위의 3차원 층류유동을 수치 해석하였다. 유한체적법을 기반으로 나비에 스톡스 방정식을 비구조격자로 풀어 물체주위의 동역학 현상을 규명하였다. 보티시티, 속도, 동압, 레지듀얼, 항력계수 등의 데이터를 가지고 분석하였다. 레이놀드 수는 425, 300, 250, 100 이다. 구 사이의 거리가 작은 경우가 구 한 개의 후류 유동보다 안정됨을 보였고 구 사이의 간격이 커짐에 따라 유동현상은 불안정하게 나타났다. 후방의 구는 정체압력의 감소를 보였고 이로 인해 저항이 줄어들게 됨을 알 수 있었다. 항력계수의 비교는 본 수치계산이 타당함을 입증하였다.

• 한국전산유체공학회지
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• 제18권4호
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• pp.9-16
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• 2013

Cavitation on an axi-symmetric hemispherical head-form body was studied using an Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To consider compressibility effects on the vapor phase and cavity interface, a pressure-based compressible flow CFD code was developed. To validate the developed CFD code, cavitating flow around the hemispherical head-form body was simulated using pressure-based incompressible and compressible CFD codes and validated against existing experimental data in the three-way comparison. The cavity shedding behavior, length of re-entrant jet, drag history, and Strouhal number of the hemispherical head-form body were compared between two CFD codes. The results, in this paper, suggested that the computations of cavitating flow with compressibility effects improve the description of cavity dynamics.