• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.2
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• pp.256-263
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• 2009

KORAIL carries out an improvement project of railway signaling system for the conventional line from the existing method which permits a train to move within limited speed the ground signal of ATS(Automatic Train Stop) system. The proposed system makes possible that a train can be driven using a speed profile created by onboard signaling system(ATP) with the movement authority from ground balise. A driving test over 100,000km is being executed by developing a tilting train for the speed elevation on the conventional line. And, the introduction of the tilting train by ATP system to the Jung-ang line is expected. However, a speed elevation on a curved line section has a restriction. Therefore, research on safety braking model and train separation control technology for the localization of ATP system is required preferentially. In this paper, we presented a safety braking model of ATP system and a train separation control method that use ground balise as variable information provider, and executed a performance simulation.

• The Journal of Pediatrics of Korean Medicine
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• v.18 no.2
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• pp.107-117
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• 2004

Objective : Atopic dermatitis has a close relationship with degranulation of mast cell and separation of Histamine. As there's no experiment with herb, using Arctii Fructus, we investigated experimental influence of Arctii Fructus on degranulation of mast cell and separation of histamine in SD rat. Methods : The SD rats are classified into three groups. One group is normal one treated by normal saline before medical treatment. The other is control group prescribed to Compound 48/80 before normal saline treatment. And the third is experimental group prescribed to compound 48/80 after medical treatment of Arctii Fructus. Then, I investigated the experimental results by measuring the degree of degranulation and separation of histamine. The results of investigation on SD rat group showing the degree of inhibitory effect of degranulation of a mast cell are as follow, the normal group treated by normal saline reflecting the degree of degranulation is $6.10{\pm}0.20\;%$, the control group treated by only compound 48/80 is $87.56{\pm}11.00\;%$, the experimental group which treated by compound 48/80 and Arctii Fructus's medical treatment is $16.26{\pm}4.67\;%$. Results : The normal group treated by only normal saline reflecting the degree of degranulation is $6.10{\pm}0.20\;%$, the control group treated by only compound 48/80 is 87.56=11.00 %, the experimental group treated by compound 48/80 and Arctii Fructus's medical treatment is $16.26{\pm}4.67\;%$. This result indicates that the degree of degranulation of mast cell is obviously inhibited (p<0.0l) in the experimental group in comparison with control one. The analysis of data obtained from plasma, which collected from the experimented SDrats' hearts before their death, and the measurement of quantity of histamine secretion show the following results. The quantity of normal group and control one is $25.34{\pm}4.58$ nM, $348.59{\pm}30.77$ nM respectively, and experimental one prescribed to compound 48/80 after medical treatment of Arctii Fructus is $263.56{\pm}21.34$ nM. This result indicates that separation of histamine isobviously inhibited in the experimental group in comparison with control one (p<0.05). Conclusions : Arctii Fructus does obviously inhibit the degree of degranulation of mast cell (p<0.0l) and separation of histamine in the plasma (p<0.05).

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.97-103
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• 2011

With the aim to increase blade loadings and stable operating range in highly loaded compressors, this article has been conducted to explore, through a numerical parametric study, the potential of passive control using slotted bladings in cascade configurations. The objective of this numerical investigation is to analyze the influence of location, width and slope of the slots and therefore identify the optimal configuration. The approach is based on two dimensional cascade geometry, low speed regime, steady state and turbulent RANS model. The results show the efficiency of this passive technique to delay separation and enhance aerodynamic performances of the compressor cascade. A maximum of 28.3% reduction in loss coefficient have been reached, the flow turning is increased with approximately $5^0$ and high loading over a wide range of angle of attack have been obtained for the optimized control parameter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.479-491
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• 1994

Discrete vortex method was applied for simulating an active control of turbulent leading- edge separation bubble. The leading-edge separation zone was perturbed by a time-dependent sinusoidal perturbation of different frequencies and levels. In order to describe the local sinusoidal perturbation at the separation point, a source pulsation vortex technique was proposed. The present two-dimensional vortex simulations were qualitatively compared with the experimental results for a blunt circular cylinder, where perturbation was introduced along the square-cut leading edge of the cylinder $(Kiya et al.^{(6,7)}).$ It was found that the reattachment length attained a minimum point at low levels of perturbation and two minima at a moderate higher perturbation frequency. The effects of local perturbation on the evolution of leading-edge separation bubble were scrutinized by comparing the perturbed flow with the natural flow. These comparisons were made for the distributions of mean velocity and its velocity fluctuations, intermittency and wall velocity. The motions of instantaneous reattachment in the space-time domain were demonstrated, which were also compared with the experimental findings. In order to investigate the reduction mehanism of reattachment length in the separation bubble, various cross-correlations for velocity and pressure and the relevant convection velocities were evaluated. It was observed that the convection velocity was closely associated with its corresponding pulsationg frequency.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.541-548
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• 2003

The design and performance of HTMD(hybrid tuned mass dampers) are evaluated for the response control of a md excited 76-story benchmark building. When a HTMD utilizes active control forces, the optimally designed TMD (Tuned Mass Damper) generates the modal separation at the first natural frequency resulting in difficulties for applying active control forces additionally. Whereas, the modal separation does no occur if the un is designed with the non-optimally designed TMD is used. Therefore, the response control performance of the HTMD with a non-optimally designed TMD is better that one with an optimally designed TMD. Further, the non-optimally designed TMD has an advantage of smaller stroke than the optimally designed TMD relieving the difficulty of limited strokes.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.191-194
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• 2006

In this paper, we present a detailed mechanism of drag reduction by dimples and roughness on a sphere by measuring the streamwise velocity above the dimpled and roughened surfaces, respectively. Dimples cause local flow separation and trigger the shear layer instability along the separating shear layer, resulting in generation of large turbulence intensity. With this increased turbulence, the flow reattaches to the sphere surface with high momentum near the wall and overcomes strong adverse pressure gradient formed in the rear sphere surface. As a result, dimples delay main separation and reduce drag significantly. The present study suggests that generation of a separation bubble, i.e. a closed-loop streamline consisting of separation and reattachment, on a body surface is an important flow-control strategy for drag reduction on a bluff body such as the sphere and cylinder. In the case of roughened sphere, the boundary layer flow is directly triggered by roughness and changes to a turbulent flow. Due to this change, the drag significantly decreases. As the Reynolds number further increases, transition to turbulence occurs earlier on the sphere surface. Because of faster growth of turbulent boundary layer by roughness, earlier transition thickens the boundary layer, resulting in earlier separation and drag increase with increasing Reynolds number

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.675-678
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• 2017

In the present, various methods have been employed to obtain the lesser thrust loss. Numerical simulations have been carried out for optimizing the thrust vector control system. Thrust vector control based on coflowing shear layer is an effective method to control the primary jet direction in the absence of moving parts. Thrust vector in symmetric nozzles is acquired by secondary flow injections that result to boundary layer separation. The pressure in secondary flow inlet was varied to check the deflection angle of jet flow.

• Journal of Mechanical Science and Technology
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• v.18 no.9
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• pp.1493-1499
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• 2004

This paper describes the speckle shearing interferometry, a non-destructive optical method, for quantitative estimation of void defect and monitoring separation defect inside of a pneumatic tire. Previous shearing interferometry has not supplied quantitative result of inside defect, due to effective factors. In the study, factors related to the details of an inside defect are classified and optimized with pipeline simulator. The size and the shape of defect can be estimated accurately to find a critical point and also is closely related with shearing direction. The technique is applied for quantitative estimation of defects inside of a pneumatic tire. The actual traveling tire is monitored to reveal the cause of separation and the starting points. And also unknown void defects on tread are inspected and the size and shape of defects are estimated which has good agreement with the result of visual inspection.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.57-64
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• 2005

Aerodynamic characteristics of three-dimensional wings in ground effect for Aero-levitation Electric Vehicle(AEV) are numerically investigated for various fairing shapes at the junctions of 3D Wings. Numerical results show that a sizeable three-dimensional comer flow separation occurs with formation of an arch vortex at the junction of main and vertical wings, and also that this is predicted the main cause of the high lift-to-drag(L/D) reduction rate of the main wing. To avoid the comer flow separation, the main idea of this study is to reduce the cross section gradient of the comer flow tube near the trailing edge for various fairing shapes. Improvements on L/D ratios of the wings are pursued by breaking the coherence of superimposed adverse pressure gradients at the wing junction when the cross section gradient is changed slowly at the trailing edge.

• Bulletin of the Korean Chemical Society
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• v.23 no.12
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• pp.1819-1822
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• 2002