• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.8
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• pp.963-972
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• 1997

As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfortableness of the passengers in the train. In the present study, the pressure transients were calculated numerically for a wide range of train speed and compared with the previous tunnel tests. The calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.8
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• pp.983-995
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• 1997

As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect backward at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves can give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfort for the passengers in the train. In the present study, the pressure transients and aerodynamic drag for two-trains running in a tunnel were calculated numerically for a wide range of train speed, and compared with the results of the previous tunnel tests and calculations for one train. The present calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.149-155
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• 2011

The viscous flow in an axisymmetric nozzle was analyzed while accounting for the mesh sizes in both in the free stream and the boundary layer. The Navier-Stokes equations were resolved using the finite volume method in order to determine the supersonic flow parameters at the exit of the converging-diverging nozzle. The numerical technique in the aforementioned method uses the flux vector splitting of Van Leer. An adequate time stepping parameter, along with the Courant, Friedrich, Lewis coefficient and mesh size level, was selected to ensure numerical convergence. The boundary layer thickness significantly affected the viscous flow parameters at the exit of the nozzle. The best solution was obtained using a very fine grid, especially near the wall at which a strong variation of velocity, temperature and shear stress was observed. This study confirmed that the boundary layer thickness can be obtained only if the size of the mesh is lower than a certain value. The nozzles are used at the exit of the shock tube in order to obtain supersonic flows for various tests. They also used in propulsion to obtain the thrust necessary to the displacement of the vehicles.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.213-220
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• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• The Korean Journal of Nuclear Medicine Technology
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• v.25 no.1
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• pp.41-43
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• 2021

Purpose In nuclear medicine blood tests, hemolysis samples are considered as inappropriate sample and are recommended not to be used for blood test. So, the lab are required to collect the blood again in the blood collection room However, The effect of hemolyzed samples on radioimmunoassay has not studied yet. This study was designed to evaluate effects of hemolysis on radioimmunoassay. Materials and Methods The kit manuals of 23 test items were reviewed to confirm whether hemolyzed samples were used. The subjects were 19 general applicants(male : 9, female : 13) and the samples were collected by each two SST tubes, one tube was obtained by centrifugation normally, and the other was obtained hemolyzed sample by centrifugation after external shock. It has been known that highly hemolyzed samples can affect the test results, so the test was performed using the severe hemolyzed sample. The test was performed for each test item using 23 normal serum and hemolysis serum, and SPSS19 program was used for statistical comparison of the test result. Results There was no significant difference between normal serum and hemolysis serum in 21 of 23 test items, but the results of insulin and C-peptide were significantly different(P<0.05). Conclusion It has been known that hemolysis in blood samples can affect the results of biochemical and hematological test, However, hemolysis effect is relatively low. Similarly, this study showed that hemolysis had not much effect on most of immunological radioimmunoassay except for some tests. Therefore, it is thought that the demand for re-collection due to hemolysis will be reduced in the laboratory, which will improve the work process of the laboratory.