• 대한기계학회논문집B
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• 제26권7호
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• pp.951-958
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• 2002

Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

• 대한기계학회논문집B
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• 제23권6호
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• pp.795-801
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• 1999

An experimental investigation has been conducted with the objective of studying the mixing mechanism near the nozzle exit in a tone-excited jet diffusion flame. The fuel jet was pulsed by means of a loudspeaker-driven cavity. The excitation frequencies were chosen for the two cases of the non-resonant and resonant frequency identified as a fuel tube resonance due to acoustic excitation. The effect of tone-excitations on mixing pattern near the nozzle exit and flame was visualized using various techniques, including schlieren photograph and laser light scattering photograph from $TiO_2$ seed particles. In order to clarify the details of the flame feature observed by visualization methods, hotwire measurements have been made. Excitation at the resonant frequency makes strong mixing near the nozzle. In this case, the fuel jet flow in the vicinity of nozzle exit breaks up into disturbed fuel parcels. This phenomena affects greatly the combustion characteristics of the tone excited jet and presumably occurs by flow separation from the wall inside the fuel nozzle. As a result, in the resonant frequency the flame length reduces greatly.

• 한국CDE학회논문집
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• 제15권5호
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• pp.354-361
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• 2010

The paper presents an efficient computation of optimal tool length for 5-axis mold & die machining. The implemented procedure processes an NC file as an initial input, where the NC data is generated by another commercial CAM system. A commercial CAM system generates 5-axis machining NC data which, in its own way, is optimal based on pre-defined machining condition such as tool-path pattern, tool-axis control via inclination angles, etc. The proper tool-length should also be provided. The tool-length should be as small as possible in order to enhance machinability as well as surface finish. A feasible tool-length at each NC block can be obtained by checking interference between workpiece and tool components, usually when the tool-axis is not modified at this stage for most CAM systems. Then the minimum feasible tool-length for an NC file consisting of N blocks is the maximum of N tool-length values. However, it can be noted that slight modification of tool-axis at each block may reduce the minimum feasible tool-length in mold & die machining. This approach can effectively be applied in machining feature regions such as steep wall or deep cavity. It has been implemented and is used at a molding die manufacturing company in Korea.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제14권4호
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• pp.322-326
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• 1992

Epiphora is overflow of tears due to obstruction of lacrimal duct. Dacryocystorhinostomy is the most common procedure to eliminate the epiphora secondary to complete or partial obstruction of the nasolacrimal duct. The procedure is to artificially create passage between lacrimal sac and nasal cavity. Especially, epiphora would be accompany often by nasolacrimal duct obstruction when trauma of oromaxillofacial area lead to nasal fracture, medial wall fracture of orbit. Therefore in this case there are many case to perform dacryocystorhinostomy because probing and tubing is difficult to resolve the epiphora. We performed 4 cases of dacryocystorhinostomy for adult nasolacrimal duct obstruction from May 1991 to October 1991. The results were very satisfactory in all the case. Epipora disappeared in all case.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.407-418
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• 2004

Prandtl-Meyer expansion flow with homogeneous condensation is investigated experimentally and by numerical computations. The steady and unsteady periodic behaviors of the diabatic shock wave due to the latent heat released by condensation are considered with a view of technical application to the condensing flow through steam turbine blade passages. A passive control method using a porous wall and cavity underneath is applied to control the diabatic shock wave. Two-dimensional, compressible Navier-Stokes with the nucleation rate equation are numerically solved using a third-order TVD (Total Variation Diminishing) finite difference scheme. The computational results reproduce the measured static pressure distributions in passive and no passive Prandtl-Meyer expansion flows with condensation. From both the experimental and computational results, it is found that the magnitude of steady diabatic shock wave can be considerably reduced by the present passive control method. For no passive control, it is found that the diabatic shock wave due to the heat released by condensation oscillates periodically with a frequency of 2.40㎑. This unsteady periodic motion of the diabatic shock wave can be completely suppressed using the present passive control method.

• Restorative Dentistry and Endodontics
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• 제14권1호
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• pp.205-210
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• 1989

The purpose of this study was to observe the minim pins of Link plus (which has buttress thread and shoulder stop design) inserted into dentin and the dentin surrounding pin. The gingival walls of class II cavity were prepared with high speed handpiece in molar teeth not elapsed time after teeth were extracted, and pinhole of 2mm in depth was positioned about 1 mm to the dentinoenamel junction and minim pin was inserted with wrench. After initial examination of the specimens, the specimens were sectioned longitudinally and horizontally to the pins with carborundum disc and low speed diamond saw (Isomet Buehler Ltd) All specimens were coated Au of 250-300${\AA}$ in thickness with Ion Sputter JFC 100 and observed under Scanning Electron Microscope (JSM-35) The following results were obtained. 1. The shoulder stop was seated on the enterance of pinhole in gingival wall, and there were the irregular space between the pin and dentin at the enterance to the pin hole and flakes of dentin lifting from the dentin floor. 2. In case of section to pin horizontally or longitudinally, the dentin debris were observed in gap between pin and dentin, and small cracks were often seen in the dentin surrounding minim pins.

• 한국추진공학회지
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• 제12권1호
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• pp.7-15
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• 2008

Pressure Sensitive Paint(PSP)는 압력에 반응하는 도료를 뜻한다. PSP를 이용하여 압력을 측정하기 위해서는 Paint Calibration과 PSP를 도포한 모델의 풍동실험이 필요하다. PSP는 이 두 가지의 결과를 이용한 이미지의 후처리과정을 통하여 압력정보를 포함한 이미지를 얻을 수 있는 신기술이다. 본 연구에서는 PSP에 필요한 장치 및 설비들을 구성하고 PSP를 이용하여 초음속 유동장 내의 압력측정 실험을 실시하였다. 압력측정 실험은 초음속 유동장의 노즐 벽면의 압력을 측정하였으며, 측정 압력에 대해서는 압력공(Pressure Tap)에 의한 결과값과 전산해석의 결과값을 통하여 비교하였고, 그 실험 결과를 바탕으로 PSP는 표면압력을 측정함에 있어서 압력공을 이용한 기존의 방식을 대체할 수 있는 기술임을 확인하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.253-259
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• 2002

Micro cell structures with high aspect ratio were fabricated by injection molding method. The mold inserts had dimension $1.9cm\times8.3cm$ composed of a lot of micro posts and were fabricated by LIGA process. The size of the micro posts was $157{\mu}m\times157{\mu}m\times500{\mu}m$ and the gaps between two adjacent posts were $50{\mu}m$. Using Polymethylmethacrylate (PMMA) injection molding was performed. The key experimental variables were temperature, pressure, and time. By controlling these, good shaped mim cell structures with $50{\mu}m$ in wall thickness and $500{\mu}m$ in depth were obtained. In order to understand micro molding mechanism, shape changes of molded PMMA were studied with experimental variables. And the durability of mold insert was investigated, too. The results show that the most important factor in molding processes was the mold temperature that is closely related to the filling of the melt into the micro cavity. And the holding time before cooling showed a great effect on the quality of molded PMMA.

• Journal of Chest Surgery
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• 제48권3호
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• pp.202-205
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• 2015

Formation of an aneurysm in the sinus of Valsalva of the aortic root is usually due to an area of congenital weakness in its wall. This aneurysm may progressively dilate and rupture into any of the cardiac chambers or into the pericardial cavity. Though this is conventionally treated by surgery, interventional therapy using various closure devices is becoming more common. Embolization of these closure devices may occur. We report a case of embolization of such a device into the left pulmonary artery which during surgical retrieval, unmasked the hidden ventricular septal defect (VSD). Therefore one has to be cautious while making a diagnosis of rupture of the sinus of Valsalva of right coronary sinus without VSD.

• International Journal of Automotive Technology
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• 제3권1호
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• pp.9-16
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• 2002

In plasma jet ignition, combustion enhancement effects occur toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of a cylindrically shaped combustion chamber, plasma jet should issue toward the round combustion chamber wall. The plasma jet igniter that had an annular circular orifice has been developed. The purpose of this study is to elucidate the relationship between the newly developed plasma Jet igniter configuration and combustion enhancement effects. In this newly developed plasma Jet igniter, flame front wrinkle appears on the flame front and flame propagates rapidly. Plasma Jet influences on the flame propagation far long period when the plasma jet igniter has issuing angle 90 degrees and large cavity volume, because the plasma jet only lasts several ms. However, in the early stage of combustion, flame front area of issuing angle 45 degrees is larger than that of 90 degrees, because the initial flame kernel is formed by the plasma jet.