• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.460-465
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• 2000

In this study, a durability estimation system of turning centers is developed to systematically evaluate the effects of structural specification and testing condition on the durability. All loads such as weights, inertia forces, cutting force and so on, are automatically transferred from the upper elements to the lower elements by the force flow which can be derived from the structural code of turning center. And the external loads applying to the moving and rolling elements are determined by using the equilibrium conditions of force and moment. Especially, the durability of turning center is estimated based on the lifes of moving and rolling elements under the required testing condition.

• 한국추진공학회지
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• 제5권1호
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• pp.26-33
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• 2001

제트베인 추력편향장치는 노즐 뒤에 장착되어 노즐에서 분사되는 초음속 제트의 유동방향을 편향시킴으로써 하나의 노즐로 피치, 요, 롤 방향의 제어를 할 수 있는 장치이다. 제어력을 얻기 위해 초음속 유동중에 노출되어 있는 제트베인에는 열 및 공기역학적 하중이 작용하게 되며, 제트베인의 형상 및 편향각에 따라 나타나는 충격파 및 제트베인 상호 유동간섭으로 인해 비행 추력 손실 및 측력의 크기에 영향을 미치게 된다. 본 연구에서는 마하 2.88 노즐 중에 놓인 제트베인의 피치 및 요, 롤 방향의 특성을 규명하기 위해 6 종의 제트베인을 선정하고, 각 방향에 따른 제트베인 편향각 $0^{\cire}$~$25^{\cire}$ 범위에서 $5^{\cire}$ 간격으로 유동시험을 각각 수행하였다. 또한, 유동해석을 병행하여 제트베인간의 유동 간섭 특성을 분석하였다. 연구 결과 제트베인간의 상호간섭은 나타나지 않으며, 제트베인의 공기역학적 특성은 현과 리드의 길이 비에 크게 좌우되고, 최대 추력손실은 롤 제어시 축추력의 17%로 나타났다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 제6회 단조 심포지엄
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• pp.29-37
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• 2001

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1347-1357
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• 2005

Effects of combustor-level high free-stream turbulence on the blade-surface heat/mass transfer have been investigated in the three-dimensional flow region near the endwall within a high-turning turbine rotor cascade passage. Free-stream turbulence intensity and integral length scale in the high turbulence case are 14.7 percents and 80 mm, respectively. The result shows that there is no considerable discrepancy in the blade heat/mass transfer near the endwall between the low and high turbulence cases. As departing from the endwall, however, the deviation between the two cases becomes larger, particularly in the region where flow separation and re-attachment occur. Under the high turbulence, flow disturbances such as boundary-layer separation and re-attachment seem to be suppressed, which makes the blade heat/mass transfer more uniform. Moreover, there are some evidences that endwall vortices tend to be weakened under the high turbulence.

• 한국도로학회논문집
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• 제18권5호
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• pp.95-103
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• 2016

PURPOSES : Permitted left turn is a turning maneuver in which a vehicle turns left using a gap between oncoming vehicles, called gap acceptance, and it enables for more efficient traffic operation at intersections. In Korea, the permitted left turn has not been a common maneuver at signalized or un-signalized intersections. However, many experts and the Police Agency tried to apply this effective turning maneuver at intersections in Korea since 2010. Though the investigation of gap acceptance is significantly important in understanding a driver's behavior at intersections, there have not been many studies about this topic, specifically a study to develop probability models of gap acceptance behavior. METHODS : In this study, the probability model of gap acceptance behavior for a permitted left turn was developed based on observational field studies. To develop the model, seven variables were analyzed including gap, waiting time, traffic volume, conflict-flow vehicle type, left-turning vehicle type, the number of lane, and time. RESULTS : In the final model, gap and left-turning vehicle type were found to be significant influencing factors. CONCLUSIONS : Through this model development, it was concluded that as the gap size increased, the probability of gap acceptance was higher. Moreover, when a left-turning vehicle was a passenger car, the probability of gap acceptance was higher than compared to large size buses or freight cars.

• Advances in aircraft and spacecraft science
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• 제7권5호
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• pp.441-458
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• 2020

Rectangular-to-Ellipse Shape Transition (REST) inlets are a class of inward turning inlets designed for hypersonic flight. The aerodynamic design of REST inlets involves very complex flows and shock-wave patterns. These inlets are used in highly integrated propulsive systems. Often the design of these inlets may require many geometrical constraints at different cross-section. In present work a design approach for hypersonic inward-turning inlets, adapted for REST inlets, is coupled with a multi-objective optimization procedure. The automated procedure iterates on the parametric representation and on the numerical solution of a base flow from which the REST inlet is generated by using streamline tracing and shape transition algorithms. The typical design problem of optimizing the total pressure recovery and mass flow capture of the inlet is solved by the proposed procedure. The accuracy of the optimal solutions found is discussed and the performances of the designed REST inlets are investigated by means of fully 3-D Euler and 3-D RANS analyses.

• 대한기계학회논문집B
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• 제32권3호
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• pp.207-215
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• 2008

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. At the Reynolds number of $2.09{\times}10^5$, heat/mass transfer coefficients are measured for the tip gap height-to-chord ratio, h/c, of 2.0% at turbulence levels of Tu = 0.3 and 14.7%. A tip-surface flow visualization is also performed for h/c = 2.0% at Tu = 0.3%. The results show that there exists a strong flow separation/re-attachment process, which results in severe local thermal load along the pressure-side corner, and a pair of vortices named "tip gap vortices" in this study is identified along the pressure and suction-side tip corners near the leading edge. The loci and subsequent development of the pressure- and suction-side tip gap vortices are discussed in detail. The combustor-level high inlet turbulence, which increases the tip-surface heat/mass transfer, provides more uniform thermal-load distribution.

• 한국지반환경공학회 논문집
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• 제8권4호
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• pp.27-39
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• 2007

본 논문은 유효수직응력과 간극분포의 공간적 상관길이에 따른 거친 단일 균열 내에서의 유체흐름에 대한 특성을 수치적으로 분석한 것이다. 균열 내의 공간적으로 상관된 변화하는 간극분포는 지구통계학적 방법(i.e. Turning Bands algorithm)을 이용하여 발생시켰으며, 유효수직응력에 따른 간극분포의 변화를 묘사하기 위해 유효수직응력과 역학적 간극 사이의 단순한 비선형 관계식를 이용하였으며, 이를 흐름 모형에 결합하였다. 모의분석결과 균열 내의 유체흐름은 적용된 유효수직응력과 간극분포의 공간적 상관길이에 따라 변화하는 간극분포의 기하학적 특성에 크게 영향을 받은 것으로 나타났다. 그밖에 본 연구에서 모의된 유체흐름의 결과를 이용하여 유효수직응력과 균열의 유효투수성 사이의 관계를 나타내는 수정 Louis 식을 제안하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.422-427
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• 2000

The design of low-solidity vaned diffusers and the effect on the performance of a turbocharger compressor is discussed. The effect of vane number and turning angle was investigated while maintaining a basic design with a leading edge angle of $70^{\circ}$, leading and trailing edge radius ratios of 1.1 and 1.3. All results are compared with those obtained with the standard vaneless diffuser configuration and it was shown that all designs increased and shifted the pressure ratio to reduced flowrates. Despite the low-solidity configuration none of the vane designs provided a broad operating range, and the vane leading edge angle was not main factor that system went into the surge condition. The diffuser of higher trailing edge angle improved the flow range for the compressor to operate at lower flow region.

• 대한기계학회논문집B
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• 제20권12호
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• pp.3917-3925
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• 1996

A numerical analysis on three dimensional turbulent incompressible flows through linear cascades of turbine rotor blades with high turning angles has been performed by using a generalized k-.epsilon. model which is a high Reynolds number form and derived by RNG(renormalized group) method to account for the variation of the rate of strain. A second order upwind scheme is used to suppress numerical diffusion in approximating the convective terms. Body-fitted coordinates are adopted to represent the complex blade geometry accurately. For the case without tip clearance, velocity vectors and static pressure contours are shown to be in good agreement with previous experimental results. For the case with tip clearance, the effects of the passage vortex and tip clearance flow on the total pressure loss as well as their interactions are discussed.