• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.23-26
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• 2012

Experimental study was conducted to elucidate flame extinction phenomena in counterflow flame. Using a curtain helium flow significantly reduced buoyancy such that the flame can be positioned at the center between the upper and lower nozzles even at the velocity ratio of 1.0. The curves of critical diluent mole fraction versus global strain rate have C-shapes. The flame oscillation was observed prior to low strain rate flame extinction at both flame conditions with and without minimizing buoyancy force. The results show that, at low strain rate flame, the self-excitation frequency with the order of 1.0 Hz in the case of utilizing pure helium gradually decreases in increase of $N_2$ mole fraction in the curtain flow, meaning that buoyancy suppresses the self-excitation of the outer edge flame.

• Tribology and Lubricants
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• v.29 no.2
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• pp.98-104
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• 2013

Cu-matrix-sintered brake pads and heat-resistant low-alloy steel are commonly applied to basic brake systems in high-energy moving machines. We analyzed how the tribological characteristics are influenced by the inertial mass. A high inertial mass decreased the friction coefficient by about 15% compared to a low inertial mass under all velocity conditions. The wear rates of the friction materials increased with the inertial mass. Thus, the inertial mass influences the friction coefficient and wear rate of the friction materials and disk but not the friction stability.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.115-115
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• 2014

First, We will briefly introduce early science results of AGN observations with KVN and KaVA. KaVA is the combined array of the Korean VLBI network (KVN) and VLBI Exploration of Radio Astronomy (VERA). These include KaVA monitoring of M87, Sgr A* and a few bright blazars and KVN Search for circular polarized Blazars. Furthermore, we will present our future plan of monitoring observation of Sgr A* and M87 with KaVA and Low Radio Power AGN multi frequency polarization survey with KVN. Because of the largeness of their centralsuper-massive black holes, we select them as top-priority sources of our key science program (KSP). The main science goals of the KaVA KSP are (1) mapping the velocity field of the M87 jet and testing magnetically-driven-jet paradigm, and (2) obtaining tightest constraints on physical properties of radio emitting region in Sgr A. High sensitivity achieved through simultaneous multifrequency phase referencing technique of KVN will allow us to explore Low Radio Power AGN cores which build majority of AGNs and therefore are important for undestanding the evolution of AGNs and of their hosts.

• Journal of Ocean Engineering and Technology
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• v.14 no.3
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• pp.41-45
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• 2000

In solving the unsteady potential flow problem of the ship in waves with the panel method, in general one can consider the basic flow as the free stream or double body solution. For the double body solution, the body boundary condition has the 2nd derivatives of the velocity potential. Low order panel methods are known to suffer from the significant error in the 2nd derivatives computed at the body surface. This paper analyzes the numerical error in the 2nd derivatives for a 2-D cylinder and a 3-D sphere problem, and an extrapolation method to obtain the correct derivatives on the body surface is suggested.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.43.3-43
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• 2002

$\textbullet$ A high performance motion controller can be applied to a wider range areas. $\textbullet$ Users can easily add, delete, or modify the library functions in this motion controller $\textbullet$ users can easily create, delete, or change GUI menu in this motion controller $\textbullet$ The motion related libraries base on IEEE/NEMI low-cost open architecture controller specification. $\textbullet$ Many low-level libraries and GUI that can make users easily interface with hardware are developed. $\textbullet$ Various velocity profiles are generated for performing given tasks efficiently. $\textbullet$ The hardware of a high performance motion controller is developed with using DSP and PLD.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.519-526
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• 1995

Experiments have been performed to test the analytical tools developed concurrently for the motion-related unsteady pressure in annular passages. The outer cylindrical body was oscillated by a shaker in either rocking motion about a hinge-point or lateral translation motion. In the equilibrium configuration the two bodies are either concentric or eccentric, in the plane of oscillation or normal to it. The unsteady pressure generated by the oscillatory motion with low amplitudes (displacement/radius) was measured on wall of the fixed inner cylinder at various axial and azimuthal locations. The unsteady pressure were compared with theoretical predictions, and agreement was found to be within 10%. Experiments have been shown that the effect of flow velocity on the unsteady pressure is minimal and the pressure increases more or less with oscillatory motion, for low flow velocities (Re = 2 900).

• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.1054-1062
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• 2003

The numerical simulations of flow and pollutant particle dispersion are described for two-dimensional bell shaped hills with various aspect ratios. The Reynolds-averaged incompressible Navier-Stokes equations with low Reynolds number $\kappa$-$\varepsilon$ turbulent model are used to simulate the flowfield. The gradient diffusion equation is used to solve the pollutant dispersion field. The code was validated by comparison of velocity, turbulent kinetic energy, Reynolds shear stress, speed-up ratio, and ground level concentration with experimental and numerical data. Good agreement has been achieved and it has been found that the pollutant dispersion pattern and ground level concentration have been strongly influenced by the hill shape and aspect ratio, as well as the location and height of the source.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.774-779
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• 2012

MILD (Moderate and Intense Low Oxygen Dilution) combustion is a technology that uses the recirculation of combustion gas to increase thermal efficiency not only by keeping down the concentration of Nitric Oxides and temperature but also by uniformizing the internal temperature of the combustion furnace. This study is a trial to obtain MILD combustion characteristics by adjusting the equivalence ratio with the air flow rate in the conical combustor while keeping the fuel flow rate and measuring the exhaust gas of the combustion furnace.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.3
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• pp.26-36
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• 1989

Recently digital governor system is commonly adapted for the speed control of the marine diesel engine because of too much fluctuation of rpm resulted by the low speed, long stroke, high efficiency and a small number of cylinder of it, and versatile studies on the development of digital governor system are progressed. On this subject the new control method in which the fuel is controlled by feedforwarding the change of load as well as the feedback of angular velocity in case of disregarding the engine dead time and influence of scavenging air was proposed by the authors, and found the method has shown quite a good control performance in comparision to the conventional control method by the simulation using a digital computer for various load change. In this paper the speed control system of a diesel engine is simulated in case of regarding the engine dead time by the proposed method, and also confirm a good control performance of it under even more realistically simulated environment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.284-292
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• 1981

The flow of fluid with low prandtl number in the entrance region of a circular pipe has been considered, where the wall temperature is maintained to be constant. A finite difference method is used for the integral form of the governing equations in order that they satisfy the conservative properties of the numerical solutions. It is confirmed that the hydrodynamic entrance length and be divided into growing boundary layer region and fully viscous region, which is compared with existing results obtained by using boundary layer approximations. By assuning the developing velocity profile in the entrance region, the thermal entrance length is estimated and the local Nusselt number is obtained at various locations along the axial dirction.