• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.2
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• pp.33-40
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• 2010

In this paper, we consider three macroscopic traffic flow monitoring indices, Travel Time Index(TTI), Acceleration Noise(AN) and Two Fluid(TF) and investigate how to determine a proper rate of probe cars for producing reliable values of these indices. For the analysis, we use classical sampling theories and provide numbers of probe rates using simulation data.

• Journal of ILASS-Korea
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• v.1 no.4
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• pp.46-53
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• 1996

The present study is aiming at improving the performance of main nozzle of an air jet loom with a modified reed and auxiliary nozzles. The double coaxial pipe jets consisting of a central air jet and an annular air jet have been experimentally investigated. The duter jet has a potential core and a constant velocity. The inner jet through an inner long pipe is induced by the subatmospheric pressure near the inner nozzle edge, and the jet velocity of an inner pipe is always lower than that of a outer pipe. The static pressures of the main nozzle over a wide range of the nozzle tank pressure were measured, and the nozzle velocity and Mach numbers were analytically calculated. Experiment81 results indicate that the critical condition of Mach number of unity to occur at the two positions in a main nozzle; one of them is the needle tip and the other is the acceleration tube exit An increase in the tank pressure causes the critical throat condition to occur at the two positions above. The velocity of acceleration-tube exit is maximum at the critical length L* and flow patter in acceleration-tube over critical lengh remains unstable.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.323-334
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• 2008

According to the delivery condition, the breakage of a product occurs when it is delivered to the customers. Therefore product's makers evaluate the durability under the delivery process by accelerated life testing. In order to conduct this accelerated life testing accurately, it is very important to identify the acceleration-factor exactly between on-road and accelerated life test condition. In this paper, the acceleration-factor is identified by applying linear damage summation law, rain-flow cycle counting and Dirlik theory under the conditions of the random vibration. And approximated FEM model of the connecting-pipe to the compressor is developed for fatigue analysis. This model is finally verified by comparing the experiment results to the numerical analysis results.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.6
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• pp.390-395
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• 1987

There is a variety not only of research topics but also of research techniques in electric power problems. It is well known that a significant increase in the rate of convergence can be obtained for the Gauss-Seidel method using the bus admittance matrix by applying acceleration factors determined empirically. The acceleration factor is calculated theoretically by using the bus voltage sensitivity (buses voltage interact each other) in this paper. It is observed that the proposed method using calculated acceleration factor gives better results than those of the method using calculated acceleration factor gives better results than those of the method using empirical one.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.1
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• pp.23-30
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• 2005

The air-jet loom represents a major step in the development of shutterless weaving due to its ability to weave a wide range of yarns at high speeds. The air-jet weaving involves inserting a pre-measured length of yarn through the wraps, which is shed by means of compressed air. The analysis of air flow characteristic of the main nozzle and acceleration tube is required for improving the loom performance. In this paper, we examined the effects of the main nozzle with different acceleration tubes as well as diameters. Also, we compared the performance of a straight-type tube with a Laval-type tube and the effect of installing a suction hole on the acceleration tube.

• 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.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1936-1941
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• 2003

Characteristics of the high frequency and pulsatile flow investigated experimentally to understand the flow phenomena in the hydraulic system. In the study, I axis fatigue tester which are widely used for automobile filed are selected. 4 Pressure transducer, amplifier, A/D convertor are used to analyse and to obtain the pulsatle pressure waveform with high frequencies in hydraulic system. Matlab are used. to analyse the characteristics of frequency. Variation of pump input pressure and actuator acceleration frequency, pressure wave are measured with or without accumulators. For with accumulator, frequency amplitude of pressure are very lower than those of without accumulator due to absorbing function of accumulator. As the actuator acceleration frequency increased, effect of accumulator are very important to decrease the pulsatile pressure waveform with high frequencies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.859-866
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• 2003

The Lagrangian dispserion of fluid particles in inhomogeneous turbulence is investigated by a direct numerical simulation of turbulent channel flow. Fluid particle velocity and acceleration along a particle trajectory are computed by employing several interpolation schemes such as linear interpolation, high-order Lagrange polynomial interpolation and the Hermite interpolation schemes. The performances of the schemes are evaluated through comparison of errors in computed particle positions, velocities and accelerations against spectral interpolation. Adopting the four-point Hermite interpolation in the homogeneous directions and Chebyshev polynomials in the wall-normal direction appears to produce most reliable Lagrangian statistics including acceleration correlations with a reasonable amount of computational overhead.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.556-561
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• 2003

Flight bodies are subject to highly unstable and severe flow conditions during taking-off and landing periods. In this situation, the flight bodies essentially experience accelerating or decelerating flows, and the aerodynamic characteristics can be completely different from those of steady flows. In the present study, unsteady aerodynamic characteristics of an aerofoil accelerating at subsonic speeds are investigated using a computational method. Two-dimensional, unsteady, compressible Navier-Stokes simulations are conducted with a one-equation turbulence model, Spalart-Allmaras, and a fully implicit finite volume scheme. An acceleration factor is defined to specify the unsteady aerodynamics of the aerofoil. The results show that the acceleration of the subsonic aerofoil generally leads to a variation in aerodynamic characteristics and it is more significant at angles of attack.

• Wind and Structures
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• v.5 no.2_3_4
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• pp.329-336
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• 2002

The along-wind response of a surface-mounted elastic fence under the action of wind was investigated numerically. In the computations, two sets of equations, one for the simulation of the unsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solved alternatively. The resulting time-series tip response of the fence as well as the flow fields were analyzed to examine the dynamic behaviors of the two. Results show that the flow is unsteady and is dominated by two frequencies: one relates to the shear layer vortices and the other one is subject to vortex shedding. The resulting unsteady wind load causes the fence to vibrate. The tip deflection of the fence is periodic and is symmetric to an equilibrium position, corresponding to the average load. Although the along-wind aerodynamic effect is not significant, the fluctuating quantities of the tip deflection, velocity and acceleration are enhanced as the fundamental frequency of the fence is near the vortex or shedding frequency of the flow due to the occurrence of resonance. In addition, when the fence is relatively soft, higher mode response can be excited, leading to significant increases of the variations of the tip velocity and acceleration.