• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.31-40
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• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• The Journal of the Acoustical Society of Korea
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• v.24 no.5
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• pp.271-281
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• 2005

An electromagnetic type shock wave generator suitable for extracorporeal shock wave therapy has been constructed by employing a solenoid coil. The Property of the shock waves produced by the shock wave generator was evaluated using a needle hydrophone. It was shown that, as the capacitor discharging voltage increased from 8 to 18 kV, the Positive Peak Pressure (P+) of the shock wave increased non-linearly from 10 to 77 Wa. In contrast. the negative peak Pressure (f) varied between -3.2 and -6.8 MPa. had its absolute maximum of -6.9 ma at 14 kV The peak amplitudes P+ measured repeatedly under the same voltage setting varied within $5\;\%$ from mean values and this is very small compared to about $50\;\%$ for electrohydraulic type shock wave generators. It could be observed, from the hydrophone signal recorded over 1 ms. several sequential acoustic impulses representing bubble collapses. namely. acoustic cavitation. induced by the shock wave. A technique based on wavelet transformation was used to accurately measure the time delay between the 1st and 2nd collapse known to be closely related to the shock strength. It was observed that the measured time delay increased almost linearly from 120 to $700\;{\mu}s$ with the shock wave Pressure P+ increasing from 10 to 77 MPa.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.350-355
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• 2012

Past few years have seen the growing importance of micro shock tubes in various engineering applications. A pharma ballistic technique is one such application which uses micro shock tube to accelerate drug particles and penetrate into skin, thus avoiding the usual injection drug delivery system. But for the efficient design of such instruments requires the detailed knowledge of shock characteristics and flow field inside a micro shock tube. Due to many factors such as boundary layer, low Reynolds number and high Knudsen number shock propagation inside micro shock tubes will be quite different from that of the well established macro shock tubes. In the present study, experimental studies were carried out on a micro shock tube of 3 mm diameter to investigate flow characteristics and shock propagation. Pressure values were measured at different locations inside the driven section. From the experimental values other parameters like shock velocity, shock strength were found and shock wave diagram was constructed.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.74-80
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• 2012

Past few years have seen the growing importance of micro shock tubes in various engineering applications like micro combution, micro propulsion, particle delivery systems. But in order to efficiently apply Micro Shock Tube to such areas require the detailed knowledge of shock characteristics and flow field inside a micro shock tube. Due to many factors such as boundary layer, low Reynolds number and high Knudsen number shock propagation inside micro shock tubes will be quite different from that of the well established macro shock tubes. In the present study, experimental studies were carried out on micro shock tubes of two diameters to investigate flow characteristics and shock propagation. Pressure values were measured at different locations inside the driven section. From the experimental values other parameters like shock velocity, shock strength were found and shock wave diagram was constructed.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.3
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• pp.36-46
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• 1998

Shock-wave in a supersonic diffuser flow cannot be stable even in the given pressure ratio which remains constant over time, and oscillates around a certain time-mean position. In the present study, oscillation of a normal shock-wave in a supersonic diffuser was analyzed by a small perturbation method. Upstream pressure perturbation was applied to a supersonic diffuser flow with a normal shock-wave. Stability of shock-wave was investigated by considering the diffuser pressure recovery and frequency of the pressure perturbation. The results obtained show that a stable oscillation of weak normal shock-wave is obtainable for the flow with the Mach number over 1.74. The ratio of sound pressures downstream to upstream of the shock wave increases with increase of the Mach number. The present results agree well with other analytical and experimental results.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.86-94
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• 1999

Measured shock wave effects were investigated by changing shock strength and position with particular emphasis on the stability limits of hydrogen-air jet flames. For this purpose, a supersonic nonpremixed, jet-like flame was stabilized along the axis of a Mach 2.5 wind tunnel, and wedges were mounted on the sidewall in order to interact oblique shock waves with the flame. This experiment was the first reacting flow experiment interacting with shock waves. Schilieren visualization pictures, wall static pressures, and flame stability limits were measured and compared to corresponding flames without shock-flame interaction. Substantial improvements in the flame stability limits were achieved by properly interacting the shock waves with the flameholding recirculation zone. The reason for the significant improvement in flame stability limits is believed to be the adverse pressure gradient caused by the shock, which can elongate the recirculation zone.

• Journal of Astronomy and Space Sciences
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• v.24 no.3
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• pp.219-226
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• 2007

Among the interplanetary shock (IP shock)s observed by ACE spacecraft at 1AU during 1997 to 2000, we have selected 31 IP shocks which had triggered the interplanetary type II radio bursts detected by the WIND spacecraft while those shocks were leaving the Sun. We compared the observed IP shock propagation speeds and the IP shock transit speeds estimated by time difference between the interplanetary type II radio burst detection and the IP shock observation. Then, we found that the mean acceleration of the IP shocks between the Sun and the Earth is about $-1.02m/sec^2$, which means the deceleration contrary to the positive acceleration predicted by Parker solar wind model. It is also verified that the acceleration of the IP shock does not show any linear correlation with the shock propagation speed and the Mach number of the IP shock.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.615-622
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• 2017

A normal shock wave is initially formed in the shock tube that migrates towards the closed end of the tube, which, in turn, leads to the reflection of shock. Due to the interaction of the reflected shock with the boundary layer, bifurcation of the shock wave takes place. A shock train will be generated after the bifurcated shock wave approaches the contact surface. Until now, only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study, a CFD analysis has been performed on a two dimensional axisymmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of the shock train phenomenon, quantitative studies have been performed by varying shock tube length, diameter under fixed diaphragm, and pressure ratio inside a shock tube.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.139-142
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• 2002

An experimental model and a conceptual model are investigated in this paper with both shock tube experiment and numerical technique. The shock-vortex interaction generated by this model is visualized with various methods: holographic interferometry, shodowgraphy, and numerical computation. In terms of shock dynamics, there are two meaningful physics in the present problem. They are reflective wave from the slip layer at the vortex edge and transmitted shock penetrating the vortex core. The discussion in this study is mainly focused on the two kinds of waves contributing to the quadrupolar pressure distribution around the vortex center during the interaction.

• Journal of Korea Water Resources Association
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• v.32 no.2
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• pp.185-195
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• 1999

The finite difference method and the method of characteristics are frequently used for the numerical analysis of kinematic wave model. Truncation errors cause the peak discharge dissipated in the solution from the finite difference method. The peak discharge is conserved in the solution from the finite difference method. The peak discharge is conserved in the solution from the method of characteristics, however, the shock may deteriorates the numerical solution. In this paper, distinctive features of each scheme are investigated for the numerical analysis of kinematic wave model, and applicability of shock fitting algorithm such as Propagating Shock Fitting and Approximated Shock Fitting methods are studied. Propagating Shock Fitting method appears to treat shock properly, however, it failed to fit the shock appropriately when applied to a sudden inflow change in a long river. Approximate Shock Sitting method, which uses finer elements, is found to be more proper shock-fitting than the Propagating Shock Fitting method. Comparisons are made between two solution from the kinematic wave theory with shock fitting and full dynamic wave theory, and the results are discussed.