• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2375-2385
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• 1996

As a compression wave is emitted from a duct, an impulsive wave generates and causes an impulsive noise that is at present a serious environmental noise pollution. In order to clarify the acoustic characteristics of the noise and to reduce their pressure levels, a series of model experiments were conducted on the impulsive waves emitted from an open end of a shock tube. The impulsive waves with various intensities were obtained by controlling the operation pressure ratio of the shock tube. Various kinds of silencers such as the exit boxes with baffle plates, were applied to the duct exit to reduce the impulsive noises. The effects of geometry of silencers and shock Mach number on the noise reduction were clarified. From the measurements of sound pressure level, it was found that installing the baffle plate into the exit box is effective in lowering the noise level at far fields, and that the recommendable geometries of silencer are L/D=1, H/D=1 and H/D=0.75.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.355-360
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• 2001

This study addresses a computational work of the impulsive wave which is discharged from the open end of a pipe. An initial compression wave inside the pipe is assumed to propagate toward atmosphere. The over pressure and wave-length of the initial compression wave are changed to investigate the characteristic values of the impulsive wave. The second order total variation diminishing (TVD) scheme is employed to solve the axisymmetric, compressible, unsteady Euler equations. The relationship between the initial compression wave form and impulsive wave is characterized in terms of the peak pressure of the impulsive wave and its directivity. The results obtained show that for the initial compression wave of a large wave-length the peak pressure of the impulsive wave does not depend on the over pressure of the initial compression wave, but for the initial compression wave of a very short wave-length, like a shock wave, the peak pressure of the impulsive wave is increased with an increase in the over pressure of the initial compression wave. The directivity of the impulsive wave to the pipe axis becomes significant with a decrease in the wave-length of the initial compression wave.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1095-1104
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1294-1302
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• 1997

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4036-4043
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• 1996

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.987-994
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• 2008

The optimal structure of the Tonpilz transducer was designed. First, the FE model of the transducer was constructed, that included all the details of the transducer which used practical environment. The validity of the FE model was verified through the impedance analysis of the transducer. Second, the resonance frequency, the sound pressure, the bandwidth, and the impulsive shock pressure of the transducer in relation to its structural variables were analyzed. Third, the design method of $2^n$ experiments was employed to reduce the number of analysis cases, and through statistical multiple regression analysis of the results, the functional forms of the transducer performances that could consider the cross-coupled effects of the structural variables were derived. Based on the all results, the optimal geometry of the Tonpilz transducer that had the highest sound pressure level at the desired working environment was determined through the optimization with the SQP-PD method of a target function composed of the transducer performance. Furthermore, for the convenience of a user, the automatic process program making the optimal structure of the acoustic transducer automatically at a given target and a desired working environment was made. The developed method can reflect all the cross-coupled effects of multiple structural variables, and can be extended to the design of general acoustic transducers.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.115-119
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• 2009

We numerically investigated propagation of various waves in the two-phase flows such as sound wave, shock wave, rarefaction wave, and contact discontinuity in terms of pressure, void fraction, velocity and density of the two phases. The waves have been generated by a hydrodynamic shock tube, a pair of symmetric impulsive expansion, impulsive pressure and impulsive void waves. The six compressible two-fluid two-phase conservation laws with interfacial friction terms have been solved in two fractional steps. The first PDE Operator is solved by the HLL scheme and the second Source Operator by the semi-implicit stiff ODE solver. In the HLL scheme, the fastest wave speeds were estimated by the analytic eigenvalues of an approximate Jacobian matrix. We have discussed how the interfacial friction terms affect the wave structures in the numerical solution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1403-1412
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.

• Journal of KSNVE
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• v.10 no.6
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• pp.1035-1040
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Computations predicted the experimented results with a good accuracy. The peak pressure on the flat plate was not strongly dependent of the shock wave Mach number in the present range of Mach Number from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1972-1981
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• 1995

As a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. The impulsive noise is closely related to the pressure gradient of the compression wave propagating the tunnel. In order to investigate the characteristics of the compression waves, in the present study an experiment was made using a shock tube. The results show that the strength of a compression wave decreases with the distance from the tunnel entrance and the nonlinear effect of compression wave appears to be significant if strength of the initial compression wave is greater than 7 kPa. Furthermore if the wave pattern is known, attenuation of the compression wave propagating in a tunnel can be reasonably predicted by a theoretical equation considering viscous action and heat transfer in boundary layer.