• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.4
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• pp.768-778
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• 1998

Human beings usually absorb a shock from terrain during walking through the damping effects of joints, muscles and skin. With this analogy, a robot-leg with a shock absorber is built to absorb the impact forces at its foot during high-speed walking on irregular terrain. To control the hip position while walking, the dynamic controller suitable for high speed walking is designed and implemented based on a dynamic model by Kane's equation. The hip position tracking performances of various controllers (PID controller, computed torque controller and feedforward torque controller) are compared through the experiments of the real robot-leg.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.112-122
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• 1996

A finite element scheme using the concept of PISO method has been developed to solve the Navier-Stokes viscous flows in all speed range. This scheme includes development of new pressure equation that retains both the hyperbolic term related with the density variation and the elliptic term reflecting the incompressibility constraint. The present method is applied to the incompressible two-dimensional driven cavity flow problems(Re=100, 400 and 1,000). For compressible flows, the Carter plate problem(M=3 and Re=1,000) is computed. Finally, we have simulated the shock-boundary layer interaction(M=2 and Re=2.96×10/sup 5/), a more difficult problem, and compared its results with the experiment to demonstrate the shock capturing capability of the present solution algorithm.

• 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.

• Journal of the Korean Society of Visualization
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• v.10 no.2
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• pp.32-38
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• 2012

In recent years a unique drug delivery system named as the transdermal drug delivery system has been developed which can deliver drug particles to the human skin without using any external needle. The solid drug particles are accelerated by means of high speed gas flow through a shock tube imparting enough momentum so that particles can penetrate through the outer layer of the skin. Different systems have been tried and tested in order to make it more convenient for clinical use. One of them is the contoured shock tube system (CST). The contoured shock tube consists of a classical shock tube connected with a correctly expanded supersonic nozzle. A set of bursting membrane are placed upstream of the nozzle section which retains the drug particle as well as initiates the gas flow (act as a diaphragm in a shock tube). The key feature of the CST system is it can deliver particles with a controllable velocity and spatial distribution. The flow dynamics of the contoured shock tube is analyzed numerically using computational fluid dynamics (CFD). To validate the numerical approach pressure histories in different sections on the CST are compared with the experimental results. The key features of the flow field have been studied and analyzed in details. To investigate the performance of the CST system flow behavior through the shock tube under different operating conditions are also observed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1229-1237
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• 1998

Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.389.2-389
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• 2002

Nonlinear aeroelastic characteristics of a missile control surface are investigated in this study. The wing model has freeplay structural nonlinearity at its pitch axis. Nonlinear aerodynamic flows with unsteady shock waves are also considered in high-speed flow region. To effectively consider a freeplay structural nonlinearity, the fictitious mass method (FMM) is applied to structural vibration analysis based on finite element method (FEM). (omitted)

• 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
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• v.18 no.10
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• pp.2686-2697
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• 1994

When 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. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• 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 Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.449-454
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• 2009

This paper presents an experimental study on the failure characteristics of SnAgCu lead-free solder balls. To estimate the effect of Ag, three types of SnAgCu balls are first prepared by varying the weight percent of Ag(1.0, 3.0, 4.0 wt%) and then analyzed by reliability tests such as thermal shock, high speed ball shear, and drop tests. Thermal shock test reveals that the higher the weight percent of Ag is, the longer the fatigue lift becomes. To the contrary, high speed ball-shear test and drop test show that the shear strength and the fracture toughness of solder balls are inversely proportional to the weight percent of Ag, respectively, Reasons for these observations will be further investigated In the future work.