• Geomechanics and Engineering
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• 제21권2호
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• pp.123-132
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• 2020

Due to the various restrictions and problems related to the construction of new roads in urban areas, underground road construction has been receiving a great deal of attention in the field of tunnel engineering. In this study, a double-deck road tunnel with a diverging section was analyzed for the evaluation of its stability. Both numerical analysis and scale model tests were performed, the results were used to develop a stability evaluation method for double-deck tunnels with diverging sections constructed in rocks by NATM. From regression analyses conducted on the results of the numerical analysis, an equation and a chart were derived, these tools allow us to obtain the strength/stress ratio (SSR) for double-deck road tunnels with a diverging tunnel in various diverging conditions quickly and accurately. These tools have great potential to help engineers evaluate the stability of double-deck tunnels in the preliminary design stage.

• International Journal of Aeronautical and Space Sciences
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• 제6권1호
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• pp.1-7
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• 2005

The inlet boundary condition of computations about the supersonic turbine flow is commonly applied as far-field inlet boundary condition with specified velocity. However, the inflow condition of supersonic turbine is sometimes affected by the shocks or expansion waves propagated from leading edges of blade. These shocks and expansion waves alter the inlet boundary condition. In this case, the inlet boundary condition can not be specified Therefore, in this paper, numerical analyses for three different inlet conditions - fa-field inlet boundary condition, inlet boundary condition with a linear nozzle and inlet boundary condition with a converging-diverging nozzle - have been performed and compared with experimental results to solve the problem. It is found that the inlet condition with a linear nozzle or a converging-diverging nozzle can prevent changing of inlet boundary condition, and thus predict more accurately the supersonic flow within turbine cascade than a far-field inlet boundary condition does.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.85-91
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• 2003

The lift-off characteristics of the triple flame within a diverging duct have been studied experimentally using a multi-slot burner, which can control the concentration gradient and the mean velocity independently. In this experiment the triple flame was stabilized successfully in lift-off condition and flame stabilization with a duct or without a duct, lift-off heights, and some other characteristics were examined for propane flame. It was examined that the effects with various concentration gradient and mean velocity on the triple flame. It was found that minimum value of the lift-off heights exist at a certain concentration gradient for constant mean velocity and flame with a duct is more stable than that without. Moreover the propagation velocity of the flame becomes maximum at a certain concentration gradient regardless of mean velocity.

• Geomechanics and Engineering
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• 제15권3호
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• pp.869-877
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• 2018

The continually growing demand for underground space in dense urban cities is also driving the demand for underground highways. Building the underground highway tunnel, however, can involve complex design and construction considerations, particularly when there exists divergence or convergence in the tunnel. In this study, interaction between two asymmetric noncircular tunnels-that is, a larger main tunnel and a smaller tunnel diverging from the main tunnel, was investigated by examining the distributions of the principal stresses and the strength/stress ratio for varying geometric conditions between the two tunnels depending on diverging conditions using both numerical analysis and scale model test. The results of numerical analysis indicated that for the $0^{\circ}$, $30^{\circ}$, $60^{\circ}$ diverging directions, the major principal stress showed an initial gradual decrease and then a little steeper increase with the increased distance from the left main tunnel, except for $90^{\circ}$ where a continuous drop occurred, whereas the minor principal stress exhibited an opposite trend with the major principal stresses. The strength/stress ratio showed generally a bell-shaped but little skewed to left distribution over the distance increased from the left larger tunnel, similarly to the variation of the minor principal stress. For the inter-tunnel distance less than 0.5D, the lowest strength/stress ratio values were shown to be below 1.0 for all diverging directions ($0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$). The failure patterns observed from the model test were found to be reasonably consistent with the results of numerical analysis.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.99-103
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• 2003

캐스케이드 내 유동 해석은 터보 펌프의 설계 제작에 필수적인 요소이다. 그러나 기존의 무한 입구 경계 조건에서는 입구 유동의 초기 설정 경계치와 계산 후 입구 유동 경계치의 차이가 발생하여 원하는 입구 경계 조건에서의 유동 해석을 하지 못한다. 이에 본 연구에서는 Fine Turbo를 이용하여 입구 경계 조건으로 무한 경계 조건을 적용하였을 때 발생하는 문제점을 분석하였다. 그리고 무한 입구 경계 조건 대신 캐스케이드 앞에 수축·확산 노즐이나 직선 노즐을 위치시켜 전산 해석을 실시하여 그 특성을 비교, 검토하였다.

• 한국추진공학회지
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• 제9권2호
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• pp.70-77
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• 2005

축소-팽창 디퓨저가 장착된 초음속 이젝터를 제작하여, 다양한 위치에서의 측정된 압력으로 부유동의 초음속 시동조건을 찾아내었다. 우선 부유동 흡입구의 크기의 영향을 알아내기 위하여 다양한 흡입구 직경으로 실험하였으며, 부유동의 초음속 시동은 흡입구 직경과 축소-팽창 디퓨저 직경의 비, d/D가 0.306 미만인 경우에만 일어났다. 이보다 큰 d/D에서는, 아음속 시동이 먼저 시작되고, 흡입구를 막으면서 주유동의 유입이 전 유동장을 채우게 되어 수직 충격파를 축소-팽창 디퓨저의 하류로 내려보내게 된다 이러한 상황에서 다시 흡입구를 열어도 히스테리시스의 영향으로 초음속 시동이 유지된다.

• 대한기계학회논문집B
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• 제38권4호
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• pp.321-328
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• 2014

고고도 모사를 위한 축소형 디퓨저의 비연소장 조건에서의 성능특성을 수치적으로 파악하였다. 디퓨저 입구길이를 노즐 출구직경과 비교해 0, 50, 100%로 변화 시켰고, 디퓨저 목의 길이는 2차목의 직경과 비교해 3, 5, 6, 7, 8, 12로 다양화하여 해석하고 실제 모사실험 값과 비교하였다. 그 결과 디퓨저의 입구길이가 짧아질수록 plume의 형상은 수축되었다. 또한, 디퓨저의 2차목 길이가 디퓨저 지름의 최소 8배보다 짧으면 내부에 마하디스크가 형성되어 압력의 급격한 상승을 일으킨다. 아음속 디퓨저의 길이는 설계치의 0, 50, 75, 100%로 변화시켜 유동의 변화를 관찰하였고, 길이가 짧아질수록 2차목 내부에 갑작스런 압력 상승을 야기함을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.839-847
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• 2004

In this study, the flow characteristics within supersonic cascades are numerically investigated by using Fine Turbo, a commercial CFD code. Cascade flows are computed for three different inlet conditions. : a uniform supersonic inlet condition, a linear nozzle and a converging-diverging nozzle located in front of cascades. The effect of inlet conditions is compared and flow characteristics including shock patterns and shock-boundary layer interaction are analyzed. Also the effect of design parameters such as pitch-chord ratio, blade angle and blade surface curvature on the flow within supersonic cascades are studied.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.156-160
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• 2007

Ejector system is a device to transport a low-pressure secondary flow by using a high-pressure primary flow. Ejector system is, in general, composed of a primary nozzle, a mixing section, a casing part for suction of secondary flow and a diffuser. It can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejector system is simple in construction and has no moving parts, so it can not only compress and transport a massive capacity of fluid without trouble, but also has little need for maintenance. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an applicable model and operating conditions for an ejector in the condition of sonic and subsonic, which can be extended to the hydrogen fuel cell vehicle. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Optimization technique and numerical simulation was adopted for an optimal geometry design and satisfying the required performance at design point of ejector for hydrogen recirculation. Also, some sonic and subsonic ejectors with the function of changing nozzle position were manufactured precisely and tested for the comparison with the calculation results.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.256-259
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• 2008

Ejector system is a device to transport a low-pressure secondary flow by using a high-pressure primary flow. Ejector system is, in general, composed of a primary nozzle, a mixing section, a casing part for suction of secondary flow and a diffuser. It can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejector system is simple in construction and has no moving parts, so it can not only compress and transport a massive capacity of fluid without trouble, but also has little need for maintenance. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an applicable model and operating conditions for an ejector in the condition of sonic and subsonic, which can be extended to the hydrogen fuel cell vehicle. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Optimization technique and numerical simulation was adopted for an optimal geometry design and satisfying the required performance at design point of ejector for hydrogen recirculation. Also, some ejectors with a various of nozzle throat and mixing chamber diameter were manufactured precisely and tested for the comparison with the calculation results.