• Journal of the Korean Society of Safety
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• v.21 no.5 s.77
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• pp.22-27
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• 2006

Even though the interior of urban transit vehicle has been changed as a preventing measure against fire to make it inflammable, there remains a possibility of fire breaking out in case of gasoline etc being brought in the subway. However, there is also the possibility that in case if fire toxic gas is generated and hot air spreads in carriage it will prove very dangerous for people sitting inside. This is a comparative study where we compare simulation results with model examining the time and direction the fire spreads when it breaks out. Also there is vertical distribution of temperature in carriage where the fire spreads out. This study is about demonstrating how to establish smokeless system in urban vehicle, about its necessity, and about vehicle system restructuring. This study also makes an effort to find more advanced method for efficient fire safety in trains. In existing vehicles, in case of fire, the smoke can't go out when doors are closed and hence it spreads in whole train. Even though the method of using ventilation or exhaust established inside the carriage to throw smoke out is much better than the way of opening end doors in each carriage, this study is trying to do research on second way. Through simulation we see that in second case, even though not as good as the first one, smoke can exit through gates. Even though the first method is better, the second can also be uses to let fire out. We can know that in the first case as the smoke can exit out faster, it provides more safety for people. So this system provides better fire safety condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.784-788
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• 2004

A visualization study of shock formation of the supersonic jet nozzle using a Shadowgraph Method (SM) was carried out to investigate the effect of the longitudinal variation of coaxial pipe end tip position inside the supersonic nozzle. The experiment was performed for the Mach number range from 1.1 to 1.2 at nozzle exit. The well known shock cell structure was shown with the pipe end located deep inside the nozzle for the studied Mach number. With the pipe end approaches nozzle exit, it was found that the shock cell structure disappeared and turned into complex formation. In order to understand the mechanism of the shock structural change, computational simulation was carried out using the Navier-Stokes solver, FLUENT. Topological sketch was added with an aid of the visualization and the numerical simulation.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.133-140
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• 1998

A Navier-Stokes code based on a unstructured finite volume method is used to simulate the MIT flapping foil experiment. A low Reynolds number $k-{\varepsilon}$ turbulence model is used to close the Reynolds averaged Navier-Stokes equations. Computations are carried out for a domain involving two flapping foils and a downstream hydrofoil. The computational domain is meshed with unstructured quadrilateral elements, partly structured. Numerical solutions show good agreement with experiment. Unsteadiness inside boundary layer is entrained when a unsteady vortex impinge on the blade surface. It shoves that local peak value inside the boundary layer and also local minimum near the edge of boundary layer as it developes along the blade surface. The unsteadiness inside the boundary layer is almost isolated from the free stream unsteadiness and being convected at local boundary layer speed, less than the free stream value.

• The Pure and Applied Mathematics
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• v.15 no.1
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• pp.47-55
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• 2008

Local convergence results for three Newton-like methods in Banach space are provided. A comparison is given between the three convergence radii. Then we show that using the largest convergence radius we can pick an initial guess from with we start the corresponding iteration. It turns out that after a finite number of steps we can always use the iterate found as the starting guess for a faster method, since this iterate will be inside the convergence domain of the new method.

• Convergence Security Journal
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• v.3 no.3
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• pp.51-57
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• 2003

The Real-time DBMS must provide the keeping, fabrication and control function which the data where the user requsets for processing inside the hour when it is restricted, it is quick most and safely[3]. In order lide this to take chare of the real-time control and fabrication function, details recording (log) of the control processing is very important in accomplished transactions from inside the Real-time DBMS. In this proposal, it sees recording which is like this in base and it proposes the new recovery function for transactions log. This recovery technique which it sees used the concept of the LIFO (Last-In-First-Out) method with basic. The proposed technique will becomes the technique which it will be able and to record to process efficiently with a same attribute and the continuous transactions log.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.140-143
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• 2001

Digital shearography, a speckle pattern method is based on the superposition of two laterally sheared images. Therefore, object points which are positioned in some distance from each other are superposed in the image plane. This shearography, one of NDT methods without contact, is able to inspect defects in pipelines and pressure vessels that are used in nuclear power plants. This is can inspect whole fields and has a low sensitivity to environmental noise. Because optical setting is very simple, it has a little exhaustion of time, cost and man power. And also it can find a defect position through real time monitoring of a part. This paper, finds out the relationship among shearing quantity image quality and defect size with this method.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.11a
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• pp.103-107
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• 2006

Decapsulation of EMC(Epoxy Molding Compound) in package device is a method used to inspect inside of device by removing plastic molding. So far, chemical etching and mechanical grinding methods have been used widely. Recently, several works using laser have been carried out. This method has advantages with fast process time and precision than conventional methods because of noncontact process. Also, laser process is a clean process because of removing EMC directly without using toxic chemicals. The wavelength of laser used in this study is 355nm. Key parameters of removing EMC are laser power, scan speed, and number of scans of laser. It if confirmed that laser decapsulation is a useful process to inspect inside a device with a small thermal damage to chip surface.

• Corrosion Science and Technology
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• v.12 no.3
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• pp.142-148
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• 2013

Safety is a major concern in Nuclear Power Plants (NPPs). Piping systems in NPPs are very complex and composed of many components such as tees, elbows, expanders and straight pipes. The high pressure and high temperature water flows inside piping components. As high speed water flows inside piping, the pipe wall thinning occurs in various reasons such as FAC (Flow Accelerated Corrosion), LDIE (Liquid Droplet Impingement Erosion) and Flashing. To inspect the wall thinning phenomenon and protect the piping from damages, piping components are checked by UT measurement in every overhaul. During every overhaul, approximately 200~300 components (40,000~60,000 UT data) are examined in NPPs. There are some methods from EPRI for evaluating wear rate of components. However, only few studies have been conducted to find out the raw data reliability for the wear rate evaluation. Securing the reliable raw data is the key factor for a reasonable evaluation. This paper suggests the reliability analysis method for the repeatedly measured data for wear rate evaluation.

• International Journal of Fluid Machinery and Systems
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• v.7 no.2
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• pp.80-85
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• 2014

In this study, we visualized the internal flow of a regenerative turbomachinery using the direct injection tracer method. For visualization, the working fluid was water and the tracer was oil colors (marbling colors). Droplets were injected at the inlet of the machinery and the streak were recorded using a high-speed camera with high-power light sources. While circulating inside the groove, the droplets were translated by the rotational motion of the impeller. When the droplets flow out of the impeller groove, relative to the impeller, they moved more slowly. And the droplets repeatedly reentered into the groove and circulated again. Then the droplets either flowed to the outlet or to the stripper. As a result, this experiment has confirmed the internal circulating flow of a regenerative turbomachinery.

• The KSFM Journal of Fluid Machinery
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• v.16 no.5
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• pp.24-28
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• 2013

Visualization of internal flow of a regenerative blower has been made by injecting a tracer directly into the flow. For the convenience of visualization, working fluid has been replaced by water and marbling color oil has been used as a tracer. Oil droplet has been injected near the inlet of the blower and the streak has been recorded using a high speed camera with the illumination of high power light sources. At first, droplets have irregular motion in the near inlet area and enter into a groove of the impeller. Then the droplets circulate inside the groove while translated by the rotational motion of the impeller. When the droplets get out of the impeller groove, their speed is lower than that of impeller. And the droplets repeatedly enter into the groove and circulate inside the grooves. Then the droplets either flow to the outlet or reenter into the inlet area through stripper. Through this experimental study, internally circulating motion of the flow inside a regenerative blower has been characterized.