• 한국음향학회지
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• 제2권1호
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• pp.1-10
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• 1983

The presence of the sound tube and resonance cavity is unique in Korea Brahman Bells which is no examples in other country bells in the world. The sound tube erected in the crown is effective to emit the fundamental tone of the bell when the condition of resonant transmissibility is satisfied. The results of our analysis shows that the optimum length of the sound tube in the Bell Emile is 96cm but is not the present length, 77cm. The resonance cavity erected underneath the lip of the Bell Emile is found to be for the resonance of standing waves in the space including both bell cavity and resonance cavity and resonance cavity to the fundamental tone of the bell itself, in order that the strongest vibration can last long by least energy and lengthen the reverberation of the bell. Some historical remarks are also made on the magic flute, MANPASIKJUK, which was in existence in Shilla that can lull all evil waves, such as plagues, storms, droughts, famines and even enemies. The sound tube erected in the crown of the bell was originated in this magic flute. Finally, a strong proposal is advanced on the new national symbol of Korean traditional cultural assets. Indeed, it should be highly recommended that the Great King's Bell Emile would be the only real symbol of our national cultural assets by its own right of excellency and richness in every aspect of arts and sciences.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.45-50
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• 2004

Two phenomena often encountered in liquid flow, which were completely absent in gas or vapor flow, were cavitation and flashing. These phenomena were of significant interest in any comprehensive discussion of control valves or contracted devices since their occurrence would affect the device sizing procedures, might introduce noise and vibration, and also may limit the life expectancy of device components and the immediate downstream piping. Thus, this study aimed to find the reduction method of occurred cavitation in system by the computer simulation. A derivative six model with different dimensions of cavity were adopted. From the results, it was found that the length of the cavity was mote important factor to reduce the pressure drop over the control valves or contracted devices than the depth of the cavity. And the pressures along the centerline of the contracted devices were dropped two times in the case of haying the large length (Lc=1.5D) of cavity.

• 대한조선학회논문집
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• 제51권5호
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• pp.435-449
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• 2014

The effects of the gravity field and the free surface on the cavity shape and the drag are investigated through a numerical analysis for the steady supercavitating flow past a simple two-dimensional body underneath the free surface. The continuity and the RANS equations are numerically solved for an incompressible fluid using a $k-{\epsilon}$ turbulence model and a mixture fluid model has been applied for calculating the multiphase flow of air, water and vapor using the method of volume of fluid and the Schnerr-Sauer cavitation model. Numerical solutions have been obtained for the supercavitating flow about a two-dimensional $30^{\circ}$ wedge in wide range of depths of submergence and inflow velocities. The results are presented for the cavity shape, especially the length and the width, and the drag of the wedge in comparison with those of the case for the infinite fluid flow neglecting the gravity and the free surface. The influences of the gravity field and the free surface on the aforementioned quantities are discussed. The length and the width of the supercavity are reduced and the centerline of the cavity rises toward the free surface due to the effects of the gravity field and the free surface. The drag coefficient of the wedge, however, is about the same except for shallow depths of submergence. As the supercavitating wedge is approaching very close to the free surface, it is found the length and the width of a cavity are shorten even though the cavitation number is reduced. Also the present result suggests that, under the influence of the gravity field and the free surface, the length of the supercavity for a certain cavitation number varies and moreover is proportional to the inverse of the submergence depth Froude number.

• 한국추진공학회지
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• 제12권1호
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• pp.57-63
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• 2008

공기흡입식 추진 기관인 스크램제트 엔진은 연소기 내부 유동이 초음속으로 유동장의 연소기 내부 체류 시간이 수 ms로 매우 짧다. 이 짧은 시간동안 연소과정이 모두 이루어져야 하므로 초음속 연소기술에 대한 연구는 매우 중요하다. 본 논문은 초음속 연소 기술 중 연료-공기의 혼합을 증대시키는 방법에 관심을 두고 Cavity를 이용한 방법을 선택하여 높이를 10mm로 고정시키고 길이를 변화시켰으며, Cavity 후류에서 지름 1mm의 분사구를 통해 음속 let을 분사시키는 유동장을 형성하여 3차원 Navier-Stokes 방정식을 통해 점성 유동장을 해석하였다. 해석 결과 Cavity 길이/높이비(L/H)가 클수록 Vorticity가 값이 증가하였고 Vorticity의 증가 영역이 유동장의 위, 옆 방향으로 확장되는 것을 볼 수 있었다. 하지만 Vorticity가 증가하는 만큼 추력특성을 떨어뜨리는 정체압력 손실이 증가하므로 연소기 설계 시 최대의 혼합과 최소의 정체압력 손실을 고려한 최적 형상 설계가 필요하다는 것을 확인하였다.

• 치과방사선
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• 제2권1호
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• pp.53-57
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• 1972

The author measured the length of crown, root and tooth on the films which was taken by intraoral bisecting technic with mesh plate on the films. The films were taken from the dry skulls, dentiform and patients who had to be removed their upper incisors and the other patients who adimitted for dental care. From this serial experiment the results was made as follows: 1. By using the film and mesh plate in the oral cavity, the real tooth length can be measured easily on the film surfaces. 2. It can be avoided the film distortion in the oral cavity when taking the film using the mesh plate and film together. 3. When measuring the film, length of crown was elongated and length of root was shortened. 4. When using the well-trained bisecting technic, the real tooth length can be measured directly on the intraoral film.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.743-746
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• 2002

Experimental investigation of the flow field of supersonic cavity is described. In this research, supersonic cavity is used in chemical laser system. For efficient laser, downstream flow after cavity need to be uniform and clear for pressure recovery system. In previous research, it's known that there's oscillation In cavity and is due to Mach number and L/D ratio. A strong recompression occurs at the after wall and the flow is visibly unsteady. Cavity flow in this research is of the open type, that is, length-to-depth ratio $L/D<10\;at\;M\;=\;3$. Experiment is done with pressure measurement by piezo-type sensor and visualization by Schlirern method. The time-dependent experimental result is compared with computation.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• 한국태양에너지학회 논문집
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• 제24권2호
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• pp.33-38
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• 2004

Outside wall systems we lost much energy from the dew of thermal bridge and unsuitable adiabatic construction. The air vent wall system can make reduce cooling loads from the outside wall in summer. The basic concept is connected with buoyant force by the difference of density. An external surface of a wall absorbs solar radiation, and transfers it to the air in the cavity. The warmed air gets buoyant force. So the warmed air is released through the top opening and cooler outside air replaces the space in the cavity. So because of the cavity and the openings, the cooling load reduction by natural ventilation is believed to be considerable. The purpose of this study is finding optimal length of air cavity by numerical analyses.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.255-260
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• 2005

To achieve efficient combustion within a manageable length, a successful fuel injection scheme must provide rapid mixing between the fuel and airstreams. The aim of the present numerical research is to investigate the flame holding and combustion enhancement. Additional fuel into the cavity prevents shear flow impingement on the trailing edge of the cavity. The high temperature freestream flow mixes with the cold hydrogen fuel that is injected into the cavity and raises the fuel temperature remarkably and become to start combustion. The high pressure in the cavity due to the cavity structure and combustion leads the hydrogen fuel to upstream. The shock in the cavity to be generated by the fuel injection joins together and reflects off the ceiling wall. This makes high pressure and low mach number region and makes a small recirculation in this region. This high stagnation temperature is nearly recovered in the shear layer in front of the cavity and leads to start combustion. In the downstream of the cavity, the wall pressure drops significantly. This means that the combustion phenomenon is diminished. Because fuel lumps at the trailing edge of the cavity then it spreads after the cavity so, in this region there is a strong expansion.

• 한국지반환경공학회 논문집
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• 제14권12호
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• pp.61-69
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• 2013

도로 및 철도의 터널 공사가 증가함에 따라 공사 시에 다양한 지반조건에서 터널 공사 단계를 진행하고 있다. 특히, 석회암 지역에서 터널 공사를 진행하게 되는 경우에는 대부분의 공동이 터널 계획구간에 존재하고 있는 실정이다. 하나 또는 그 이상의 공동은 터널의 안정성을 저하하는 것으로 예상된다. 따라서, 본 연구에서는 터널과 공동과의 상호 영향을 알아보고자 실내 모형 축소실험과 수치해석을 시행하였다. 실내모형실험은 터널과 공동 간의 거리에 따른 모형지반의 파괴하중을 확인하였고, 공동의 형상에 따른 파괴하중을 확인하였다. 실내모형실험결과 파괴하중은 공동과 터널 간의 거리가 0.5D 이내로 감소함에 따라서 파괴하중 역시 감소하는 것으로 나타났다. 수치해석은 모형실험의 검증을 위해 시행하였으며, 실내모형실험과 동일하게 터널과 공동 간의 거리가 0.5D 이내로 근접하는 경우 터널의 안정성이 저하되는 것으로 확인되었다.