• 대한기계학회논문집
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• 제3권4호
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• pp.173-180
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• 1979

Temperature distriburion in a hollow chlinder has been analyzed mathematically. Unsteady condition considered assumed a constant heat flux input from the inside. The results are compared with experimental results of surface temperature rise of a gun barrel during continuous firing. Their agreements are acceptable. Effects of various dimensionless parameters on the surface temperature rise are discussed. For small Biot numbers, the external survface temperature approaches more rapidly to the steady temperature. Temperature difference between internal and external surfaces becomes greater for small Biot number. Steady solution assumed that the gas temperature inside the cylinder varies periodically. Relative amplitude and phase angles between the gas temperature and the internal or external surface temperature are obtained. Phase angles become smaller for large radiancy of gas temperature variation, small external Biot number, or large internal biot number. Relative amplitudes become samller as radiancy of gas temperature variation and internal Biot number become smaller. or external Biot number becomes larger. The solution obtained in this paper can be applied to gun barrels, heat pipes used in heat excangers, and reciprocation engines.

• 전기학회논문지P
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• 제58권4호
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• pp.557-562
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• 2009

Recently, researchers are developing a new, clean, renewable and sustainable energy to the industrial areas and the residential areas. Solar cell and fuel cell energy are presented in this paper. The paper shows the P-I and I-V characteristics of fuel cells which are connected in parallel and series. And the voltage drop of internal resistance of the fuel cell decreases with the increasing of the current of the fuel cell. A voltage drop at the internal resistance is increased according to the current, thus the terminal voltage is decreased. The internal resistance is calculated $0.3[\Omega]$ from maximum power transfer condition.

• 대한기계학회논문집B
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• 제21권8호
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• pp.1077-1085
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• 1997

The use of "clean fuels" such as butane, propane, and mixtures of these (LPG) is an attractive way to reduce exhaust emissions. In this study internal flow of the pintle type injector for LPG engine is studied. The breakup of liquid jet is the result of competing, unstable hydrodynamic forces acting on the liquid jet as it exits the nozzle. The nozzle geometry and up-stream injection conditions affect the characteristics of flow inside the nozzle, such as turbulence and cavitation bubbles. A set of calculations of the internal flow in a pintle type nozzle were performed using a two dimensional flow simulation under different nozzle geometry and upstream flow conditions. The calculation showed that the turbulent intensity and discharge coefficient are related to needle leading angle(.alpha.) and needle lift.edle lift.

• 대한기계학회논문집
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• 제16권2호
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• pp.191-199
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• 1992

This paper presents in experimental study of the dynamic internal pressure within an oil hydraulic vane pump. The measurements of the dynamic internal pressures near the vane of a pressure balance type of an oil hydraulic vane pump with intravanes has been made to provide the essential information for the study of the pump dynamics and control, the pump design and the analysis of tribological problems in the sliding components. The influences of the discharge pressure and rotating speed of the vane on the dynamic pressure in four chambers surrounding a vane have been investigated. The results indicate that the surge pressures of the chambers at the instant moment of discharge and closure are affected by the rotating speed. The pressure in the intravane chamber maintains almost constant values, which remarkably effects the pulsating discharge pressure.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1501-1513
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• 2001

Disturbance observer, adaptive robust control, and enhanced internal model control are model based disturbance attenuation methods famous for robust motion controller which can satisfy desired performance and robustness of high-speed/high-accuracy positioning systems. In this paper, these are shown to be the same scheme with different parameterizations. To do this, a generalized framework, called as RIC(robust internal-loop compensator) is proposed and the conventional schemes are analyzed in the RIC framework. Through this analysis, it can be shown that there are inherent similarities between the schemes and advantages of the RIC in the viewpoint of controller design. This is verified through simulations and experiments.

• 대한기계학회논문집A
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• 제27권2호
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• pp.294-301
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• 2003

It is of often important to accurately predict the flow-induced vibration or dynamic instability of a pipeline conveying internal high speed flow in advance, which requires a very accurate solution method. In this study, first the dynamic equations for the axial and transverse vibrations of a pipeline are reduced from a set of pipe-dynamic equations derived in the previous study and then the spectral element model is formulated. The accuracy of the spectral element method (SEM) is then verified by comparing its results with the results obtained by finite element method (FEM). It is shown that the present spectral element model provides very accurate solutions by using an extremely small number of degrees-of-freedom when compared with FEM. The dynamics of a sample pipeline is investigated with varying the axial tension and the speed of internal flow.

• 한국자동차공학회논문집
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• 제4권3호
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• pp.199-210
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• 1996

The measurements of velocities of internal flow in a scaled-up nozzle were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. The investigated length to diameter ratio(L/d) of the orifice were 1, 3, 4, 5 and 8, and inlet radius to diameter ratio(r0/d) were 0 and 0.5. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds number ranging between 15,000 and 28,000, and L/d ranging between 1 and 8 in sharp and round inlet nozzle. The turbulent intensity and turbulent kinetic energy at exit in a sharp inlet nozzle were higher than that in a round inlet nozzle. For sharp inlet nozzle, fluctuating velocities near exit were decreased with increasing L/d.

• 한국공작기계학회논문집
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• 제13권2호
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• pp.112-119
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• 2004

This paper discussed on the effect of an internal damping on the stability of an elastic material subjected to dry friction force. Dry friction forces act tangentially at the contact surface between a moving belt and elastic material. The elastic material on a belt moving is modeled for simplicity into a cantilevered beam subjected to distributed follower force. In the analysis, the discretized equations derived according to finite element method are used. The impulse response of the beam are studied by the mode superposition method to observe the growth rate of the motion. It is found that the internal damping in cantilevered beam subjected to distributed follower force may act destabilizing.

• KIEE International Transactions on Power Engineering
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• 제4A권3호
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• pp.146-151
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• 2004

The most widely used primary protection for the internal fault detection of the power transformer is current ratio differential relaying (CRDR) with harmonic restraint. However, the second harmonic component could be decreased by magnetizing inrush when there have been changes to the material of the iron core or its design methodology. The higher the capacitance of the high voltage status and underground distribution, the more the differential current includes the second harmonic during the occurrence of an internal fault. Therefore, the conventional second harmonic restraint CRDR must be modified. This paper proposes a numerical algorithm for enhanced power transformer protection. This algorithm enables a clear distinction regarding internal faults as well as magnetizing inrush and steady state. It does this by analyzing the RMS fluctuation of terminal voltage, instantaneous value of the differential current, RMS changes, harmonic component analysis of differential current, and analysis of flux-differential slope characteristics. Based on the results of testing with WatATP99 simulation data, the proposed algorithm demonstrated more rapid and reliable performance.

• 소성∙가공
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• 제9권1호
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• pp.35-42
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• 2000

In this paper, we developed the hydroforming simulator which can apply an axial compressive force and high internal pressure to bulge a tube. Experimental dtudies have been performed to investigate the effect of each parameters such as internal pressure and axial compression stroke required for the forming of circular components. Under the improper forming conditions there were two forming failures. One was the axial buckling due to excessive axial compressive load and the other was the circumferential necking fracture due to relatively high internal pressure. A safe forming zone without any failures exists between these two extreme zones. Also the condition of forming failure such as fracture is examined throughout the theoretical analysis. This paper covers a brief overview of the mechanism of hydroforming process as well as the design of die and tools.