• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.569-585
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• 2013

The use of the rigid polyurethane foam (RPF) to strengthen sandwich structures against blast terror has great interests from engineering experts in structural retrofitting. The aim of this study is to use the RPF to strengthen sandwich steel structure under blast load. The sandwich steel structure is assembled to study the RPF as structural retrofitting. The filed blast test is conducted. The finite element analysis (FEA) is also used to model the sandwich steel structure under shock wave. The sandwich steel structure performance is studied based on detonating different TNT explosive charges. There is a good agreement between the results obtained by both the field blast test and the numerical model. The RPF improves the sandwich steel structure performance under the blast wave propagation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.4
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• pp.71-77
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• 2001

In this paper, stress wave propagation characteristics of MR(Magneto-rheological) inserts are experimentally investigated. Generally, stress waves of structures such as warships or submarines are induced by shock waves from underwater explosion. Their fatal effects on the shipboard equipments or structures damage the performance of warships. But, such a problem can be solved by controlling the stress waves propagating through structures by means of MR inserts. MR insert consists of two aluminum layers and MR fluid filled in between. Two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of stress waves. Pulse waves are generated by the transmitter and they reach to the receiver through the MR insert. Permanent magnet and magnetic coil are used to produce magnetic field at the MR insert. In the presence of magnetic field, MR particles are arranged in chains parallel to the magnetic field such that the transmitted stress waves are reduced. Attenuation of stress waves is experimentally investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.440-444
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• 2017

Two-dimensional hydrodynamic analysis was performed to analyze the attenuating characteristics of shock waves generated by the detonation of the bulkhead initiator. Through the interlocking analysis between HNS and HMX stacking initiator and STS bulkhead, we have precisely simulated detonation growth and pressure wave attenuation phenomena. The free surface velocity at the surface of the bulkhead was measured for quantitative comparison with the test data by VISAR. As a result, it was confirmed that the pressure attenuating pattern of the shock wave exponentially decreased according to the bulkhead thickness. The observed inflection point at the particle velocity measured over time is due to the subsequent propagation of the shock wave due to the rapid spallation of the interface between the detonator and the bulkhead.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.3
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• pp.103-113
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• 2013

Shock wave model describes the propagation speed of kinematic waves in traffic flow. It was first presented by Lighthill and Whitham and has been deployed to solve many traffic problems. A recent paper pointed out that there are some traffic situations in which shock waves are not observable in the field, whereas the model predicts the existence of waves. The paper attempted to identify how such a counterintuitive conclusion results from the L-W model, and resolved the problem by deriving a new asymptotical shock wave model. Although the asymptotical model successfully eliminated the paradox of the L-W model, the validation of the new model is confined within the realm of the deceleration flow situation since the model was derived under such constraint. The purpose of this paper is to derive the remaining counter asymptotical shock wave model for acceleration traffic flow. For this, the vehicle trajectories in a time-space diagram modified to accommodate the continuously increased speed at every instant in such a way that the relationship between the spacing from the preceding vehicle and the speed of the following vehicle strictly follows Greenshield's model. To verify the validity of the suggested model, it was initially implemented to a constant flow where no shock wave exists, and the results showed that there exists no imaginary shock wave in a homogeneous flow. Numerical applications of the new model showed that the shock wave speeds of the asymptotical model for the acceleration flow tend to lean far toward the forward direction consistently. This means that the asymptotical models performs in a systematically different way for acceleration and for declaration flows. Since the output difference among the models is so distinct and systematic, further study on identifying which model is more applicable to an empirical site is recommended.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.548-559
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• 2015

We performed a numerical simulation based on the two-dimensional (2-D) unsteady Euler's equation with a single-step Arrhenius reaction model in order to investigate the detonation wave front propagation of an Argon (Ar) diluted oxy-hydrogen mixture ($2H_2+O_2+12Ar$). This simulation operates in the detonation frame of reference. We examine the effect of grid size and the performance impact of integrated quantities such as mass flow. For a given set of baseline conditions, the minimal and maximum grid resolutions required to simulate the respective detonation waves and the detonation cell structures are determined. Tertiary shock wave behavior for various grids and pre-exponential factors are analyzed. We found that particle fluctuation can be weakened by controlling the mass flow going through the oblique shock waves.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.249-257
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• 2007

A high resolution numerical method aimed at solving gas-liquid two-phase flow is proposed and applied to gas-liquid two-phase shock tube problem. The present method employs a finite-difference 4th-order Runge-Kutta method and Roe's flux difference splitting approximation with the MUSCL TVD scheme. By applying the homogeneous equilibrium cavitation model, the present density-based numerical method permits simple treatment of the whole gas-liquid two-phase flow field, including wave propagation and large density changes. The speed of sound for gas-liquid two-phase media is derived on the basis of thermodynamic relations and compared with that by eigenvalues. By this method, a Riemann problem for Euler equations of one dimensional shock tube was computed. Numerical results such as detailed observations of shock and expansion wave propagations through the gas-liquid two-phase media and some data related to computational efficiency are made. Comparisons of predicted results and exact solutions are provided and discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2066-2070
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• 2003

This experimental study describes the propagation characteristics and suppression of the impulse noise emitted from the exit of a perforated pipe attached to the open end of a simple shock tube. The experiment is performed through the systematic change of the shock wave Mach number and the geometrical parameters such as the porosity, hole diameter and length of the perforated pipe. The experimental results for the near and far sound field are presented and explained in comparison with those for a straight pipe. The results obtained show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the all directions, indicating that the directivity pattern is almost same regardless of the pipe type. Moreover, the noise reduction performance of perforated pipe depends upon the condition of sound field. For the near sound field the perforated pipe has a little performance to suppress the impulse noise, but for the far sound field the perforated pipe has little performance to suppress the impulse noise.

• Structural Engineering and Mechanics
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• v.60 no.3
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• pp.529-545
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• 2016

In this article, the generalized coupled non-Fickian diffusion-thermoelasticity analysis is carried out using an analytical method. The transient behaviors of field variables, including mass concentration, temperature and displacement are studied in a strip, which is subjected to shock loading. The governing equations are derived using generalized coupled non-Fickian diffusion-thermoelasticity theory, which is based on Lord-Shulman theory of coupled thermoelasticity. The governing equations are transferred to the frequency domain using Laplace transform technique and then the field variables are obtained in analytical forms using the presented method. The field variables are eventually determined in time domain by employing the Talbot technique. The dynamic behaviors of mass concentration, temperature and displacement are studied in details. It is concluded that the presented analytical method has a high capability for simulating the wave propagation with finite speed in mass concentration field as well as for tracking thermoelastic waves. Furthermore, the obtained results are more realistic than that of others.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.23-30
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• 1989

Propagation phenomena of nonlinear pressure waves in a bubbly mixture are studied. The governing equations for a bubbly mixture are derived heuristically and energy equation is incorporated with other governing equations to take thermal effects into consideration inside the bubble. This non-isothermal condition of the bubble inside is especially important when high amplitude pressure waves are treated. Keller's equation is adapted for the bubble dynamics as practical problem. Some numerical simulations are carried out for the shock tube problem using a computer program based on the above model. A comparison with experimental results of Noordzij and van Wijngaarden shows that the structure of the wave in the shock tube experiment seems to be much more significantly affected 요 the complex heat transfer phenomena inside the bubbles than by the relative translational motion between bubbles and surrounding liquid.

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