• International Journal of Air-Conditioning and Refrigeration
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• 제11권4호
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• pp.178-187
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• 2003

In this study, ventilation flow rate and pressure rise through a tunnel are simulated numerically using computational fluid dynamics (CFD) for various conditions such as roughness height of the surface of tunnel, swirl angle and hub/tip ratio of jet fan, and entrance and exit effects. By using a modified wall function, friction factor can be predicted with respect to the Moody chart within 10% of error for the circular pipe flow and 15% for the present tunnel. For more accurate design, the effect of the swirl angle and hub/tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan needs to be considered.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.240-247
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• 1998

Leakage vortices formed near blade tip causes an increase of total pressure loss near casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the less distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and aprroximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• 한국분무공학회지
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• 제13권4호
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• pp.180-186
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• 2008

The aim of this work is to investigate the effect of ambient conditions on the spray behavior of biodiesel-ethanol blended fuels. In order to analyze the spray behavior, spray tip penetration and spray cone angle were obtained from the visualization system and the effects of ethanol blending are compared macroscopic characteristics with the numerical results. It was reveled that the ethanol contents in biodiesel-ethanol blended fuels affect the spray tip penetration a little and increased the spray cone angle. Increased ambient pressure induced the decrease of the spray tip penetration, and the increased ambient temperature lead to the increase of the spray tip penetration. In addition, the increased ambient temperature promoted the vaporization and atomization of spray with the effect of increasing ethanol fuel.

• 한국유체기계학회 논문집
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• 제2권1호
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• pp.73-80
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• 1999

Leakage vortices formed new blade tip causes an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of the tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated by varying the tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the loss distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• International Journal of Aeronautical and Space Sciences
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• 제1권1호
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• pp.1-12
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• 2000

The wake geometries of a two-bladed rotor in axial flights using a time-marching free-wake method without a non-physical model of the far wake are calculated. The computed free-wake geometries of AH-1G model rotor in climb flight are compared with the experimental visualization results. The time-marching free-wake method can predict the behavior of the tip vortex and the wake roil-up phenomena with remarkable agreements. Tip vortices shed from the two-bladed rotor can interact with each other significantly. The interaction consists of a turn of the tip vortex from one blade rolling around the tip vortex from the other. Wake expansion of wake geometries in radial direction after the contraction is a result of adjacent tip vortices begging to pair together and spiral about each other. Detailed numerical results show regular pairing phenomenon in the climb flights, the hover at high angle of attack and slow descent flight too. On the contrary, unstable motions of wake are observed numerically in the hover at low angle of attack and fast descent flight. It is because of the inherent wake instability and blade-vortex-interaction rather then the effect of recirculation due to the experimental equipment.

• 대한기계학회논문집
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• 제19권2호
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• pp.451-462
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• 1995

Single overload tests performed to examine the crack retardation behavior for the specimen thickness and overload ratios. Delayed crack length was tend to increase in small thickness and big overload ratio but was difference between delayed crack length and plastic zone size that expected in specimen thickness. So retardation behavior that estimated in plastic zone size, was not sufficient. Crack tip branching and striation distribution, secondary mechanisms that effected in retardation behavior, was examined by experiment and finite element analysis. Crack tip branching was affected by micro structure, and appeared the more complicatedly according to increasing damage by overload and decreasing crack driving force in base line stress level. And crack tip branching the branching angle decreased crack driving force in the crack tip. And a characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.59-62
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• 1999

Inception and propagation of electrical tree and properties of Partial discharge(PD) pulses accompanying with tree as a function of needle tip radius in low density polyethylene were discussed. To study on these characteristics in different tip radius, we used specimens with needle-plane electrode system made of LDPE, observed inception and propagation of electrical tree by optical microscope with computer and investigated the characteristics of the phase resolved PD pulses accompanying with propagation of electrical tree. The PD quantities detected and analysed were PD magnitude, mean phase angle, average discharge, and the statistical characteristics of the PD pulses. As the tip radius ${\gamma}$ increases, tree inception stress E$\sub$i/ converges to constance value. This result suggests that tree inception stress E$\sub$i/ increases due to stress relaxation when the tip radius is small. Branch-type electrical tree was formed When E$\sub$i/ is 640-750[kV/mm]. bush-type electrical tree when E$\sub$i/ is 370∼400[kV/mm], branch-like electrical tree when E$\sub$i/ is 370-400[kV/mm].

• 대한기계학회논문집A
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• 제30권3호
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• pp.269-278
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• 2006

This paper proposes slip line fields for bending of unequally notched specimens in plane strain that have a sharp crack in one side and a sharp V-notch in the other side. Depending on the back angle, two slip line fields are proposed, from which the limit moment and crack tip stress fields are obtained as a function of the back angle. Excellent agreement between slip line field solutions with those from detailed finite element limit analysis based on non-hardening plasticity provides confidence in the proposed slip line fields. One interesting point is that, for the unequally notched specimen, the difference between the crack tip triaxial stress for tension and that for bending increases significantly with increasing the back angle. This suggests that such a specimen could be potentially useful to investigate the crack tip constraint effect on fracture toughness of materials. In this respect, the possibility of designing a new toughness testing specimen with varying crack tip constraint is discussed.

• 한국주조공학회지
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• 제31권4호
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• pp.191-197
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• 2011

Transparent organic materials have been frequently used as an analog of the solidifying metallic materials, because their transparency permits an in-situ observation of the microstructural development during solidification through optical microscopy. Pivalic acid (PVA)-ethanol system showing an anisotropic property in solid-liquid interfacial energy and interface kinetics was adopted in the present experiment, and the detailed experiments performed are as follows: (1) variation of dendrite tip temperature with growth velocity, (2) correlation between primary dendrite arm spacing (${\lambda}_1$) and the growth orientation away from the heat flow direction (tilt angle: ${\theta}$), (3) variation of dendrite tip radius (R) with growth velocity (V), (4) dendrite tip stability parameter (${\sigma}^*$) and its dependence on the concentration. Concerning the correlation between the dendrite tip temperature and growth velocity the present result is well suited to Hunt-Lu equation. As the tilt angle increases, the average primary dendrite spacing tends to increase.

• Archives of Plastic Surgery
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• 제32권2호
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• pp.205-213
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• 2005

There are several characteristics of the nose of orientals. The dorsum of nose is flat and low, the skin is thick with severe tension, the nasal tip is bulbous, the nostril is wide, and the projection of the nose is limited due to a poorly developed alar cartilage with a short columella. In order to improve these untoward characteristics of the nose of Orientals aesthetically, plain augmentation of the dorsum and tip-plasty with conventional methods has been performed by many plastic surgeons. However these conventional rhinoplasty is not enough to obtain satisfactory results when transforming into a more beautiful and aesthetically charming appearance. In order to produce the optimal nasal shape and profile, it is extremely important to consider the aesthetic surgical factors, which are; the position of the nasion, the optimal nasolabial angle(95-100 degree in Orientals), the natural exposure of infra-tip lobule with and columella, the position of the tip defining point in harmony with the dorsal profile and the smooth and natural silhouette of the lateral nasal profile as it descends into the inferior portion of the nose. From April, 2003 to August, 2004, a total of 52 patients underwent open rhinoplasty, adhering to the strict aesthetic principles considered and described priorly. Surgical approach was done through a transcolumella incision and an alar rim incision. The nasal dorsum was augmented with a silicone implant and the shape of the columella and the nasolabial angle were finessed with a silicone strut implant which was placed in between the medial crurae in a manner of a non-visible graft. The nasal tip was corrected by alar cartilage suture technique and onlay graft of shield shaped Alloderm and Gore-Tex. Author obtained the optimal nasal shape and profile aesthetically, and the results, considered satisfactory in all patients without any complications, are as follows; 1. the average increase in nasal length was 2.5 mm, 2. the average decrease in nasal width was 2.1 mm, 3. the average increase in nasal tip projection was 3.2 mm, 4. the changes of nasolabial angles were from 85.5 degree to 94.7 degree, 5. the changes of the angle between the long axis of the external naris was from 101.3 degree to 89.5 degree. In conclusion, this surgical procedure is an effective, reliable and a valuable method in improving the nasal shape, tip projection, nasolabial angle and especially, the lateral facial profile of Orientals aesthetically.