• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.4 s.142
• /
• pp.330-340
• /
• 2005

Compressible two-phase flow is analyzed based on the arbitrary Lagrangian-Eulerian (ALE) formulation. For water, Tamman type stiffened equation of state is used. Numerical fluxes are calculated using the ALE two-phase Godunov scheme which assumes only that the speed of sound and pressure can be provided whenever density and internal energy are given. Effects of the approximations of a material interface speed are Investigated h method Is suggested to assign a rigid body boundary condition effectively To validate the developed code, several well-known problems are calculated and the results are compared with analytic or other numerical solutions including a single material Sod shock tube problem and a gas/water shock tube problem The code is applied to analyze the refraction and transmission of shock waves which are impacting on a water-gas interface from gas or water medium.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.1
• /
• pp.89-98
• /
• 1997

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.

• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.1
• /
• pp.38-47
• /
• 2017

This paper presents experimental data on water droplet breakup in high-speed air flows. Exact-time-dependent evolution of wave and droplet interaction as well as breakup processes were optically visualized using a shadowgraph technique. Droplet experiments were conducted in a shock tube. Five flow conditions were used with an incident shock wave Mach number from 1.40 to 2.19 with Weber number based on the droplet initial diameter from 2300 to 38000, respectively. This corresponds to post-shock flow speeds varying from subsonic to supersonic. The considered droplet diameters were 2.0 mm to 3.6 mm. Some interesting wave patterns in the near wake were found. The present data shows that with an increase in the Weber number the droplet acceleration coefficient decreases and the level of decrease was weaker for the case of higher Mach numbers. This state of affair is different to the existing data in literature. Possible reasons are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.9
• /
• pp.1139-1148
• /
• 1997

Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.

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

• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.5
• /
• pp.439-446
• /
• 2017

This paper deals with an experimental study of the dynamics of an underwater bubbles and shock waves, generated by rapid underwater release of highly compressed gas. Aribag inflators, which are used for automobile's airbag system, are used to generate the extremely-rapid underwater gas release. Experimental studies of the complex underwater bubble dynamics as well as underwater shock wave were carried out in a specifically designed cylindrical water tank. The water tank is equipped with a high-speed camera and pressure sensors. The high-speed camera was used to capture the expansion and collapse of the gas bubble created by inflators, while pressure sensors was used to measure the underwater shock propagation and magnitudes. The experimental results were compared against the results of explosion of pentolite explosive. Several physical phenomena that has been observed and discussed, which are different from the explosive underwater explosion.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.13 no.1
• /
• pp.156-163
• /
• 2010

A nonequilibrium molecular dynamics(NEMD) simulation method is developed and applied to study shock waves propagating through argon gas. In this simulation method, shock waves are generated by pushing a piston at a constant speed from one side of a simulation box filled with argon molecules. A linear relationship between piston speeds and shock speeds is observed. Thermodynamic properties including density, temperature, and pressure before and after the shock front are obtained from the simulations and compared with the well-known Rankine-Hugoniot equations based on ideal gases. The comparison shows an excellent agreement, indicating that this NEMD simulation method can be employed to investigate various physical properties of shock waves further.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.11
• /
• pp.1943-1947
• /
• 2016

Korea Electrical Safety Cooperation(KESCO) have provided the electrical safety speed-call service from 2007 year. Purpose of the service is to reduce discomfort of electricity use and to prevent electrical accident like as electrical fire and shock accident by providing emergency treatment service on fault of the residential electrical facilities notified in the specific house like as a lower-income group and a social welfare facility. But efficiency and economic evaluation of the electrical safety speed-call service is impossible because analysis on the quantitative effect of the service is difficult. This paper presents cost-benefit analysis method and result of the electrical safety speed-call service. The presented cost-benefit analysis method has a two-step process: the first step is to measure quantitative electrical fire prevention effect of the service by using electrical accident statistics and developing outcome analysis logic model of the service effect, and the second step is to analysis cost-benefit(B/C)of the service by calculating quantitative benefit analysis on the measured quantitative electrical fire prevention effect. The results showed that cost-benefit(B/C)of the electrical safety speed-call service is over 4 after 2010 year.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.214-215
• /
• 2005

Naval equipments are installed and used for naval vessel with different environmental conditions comparing to the commercial vessel, for example, high engine power per ship displacement size, severe vibration and shock due to high running speed and explosion from naval gun's bombardment and underwater weapons. Therefore, those equipments must be installed on shipboard with small spaces, high ambient temperature around engine room and which are required be fabricated with high resistances of vibration, shock and heat resources. But in case of commercial vessel, the performances of their recent equipments naval have been improved continuously due to the technology development of domestic shipbuilding and shipboard equipment industries, together with the related fundamental industries i.e, metal, steel and electronic industries, to an international level since 1970. With these results, it became possible to unify the specifications of shipboard equipments for the commercial and military vessels(Dual-Use). In this study, vibration and shock test standards for the commercial and military vessels will be compared and reviewed technically.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.121-126
• /
• 2001

This paper presents the experimental study for the reduction of transmitted shock waves in smart structures incorporating MR insert. MR fluid is filled within the two aluminum layers and two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of the shock wave. Pulse wave generated by the transmitter is transmitted to the receiver through the MR insert and the plate. By applying magnetic field to the MR insert, the amplitude of the transmitted shock wave is reduced remarkably. The attenuation performance is tested by changing the applied magnetic field on MR inserts in two ways: by changing angle of permanent rubber magnet from 90 to 5 with 5 decrements, by using electromagnet in which magnetic field is controllable. The propagating wave speed of MR insert is also investigated.