• 드라이브 ㆍ 컨트롤
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• 제9권1호
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• pp.1-9
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• 2012

Nowadays, various researches about eco-friendly vehicles such as hybrid electric vehicle, fuel cell vehicle and electric vehicle have been actively carried out. Since most of these green cars have electric motors, the regenerative energy technology can be used to improve the fuel economy and the energy efficiency of vehicles. The regenerative brake is an energy recovery mechanism which slows a vehicle by converting its kinetic energy into electric energy, which can be either used immediately or stored until needed. This technology plays a significant role in achieving the high energy usage. However, there are some technical problems for controlling the regenerative braking and the electro-hydraulic brake during switching at transient region. In this paper, the performance simulator for fuel-cell vehicle is developed and transient response characteristics of the regenerative braking system are analyzed in the various driving situations. And the hardware-in-the-loop simulation of electro-hydraulic brake is performed to validate the transient characteristics of the regenerative braking system for fuel-cell electric vehicle.

• 한국자동차공학회논문집
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• 제1권3호
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• pp.1-11
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• 1993

An experimental study was carried out to evaluate the characteristics of transient performance of carburettered gasoline engine under rapid accelerating transient driving conditions. In order to evaluate the characteristics of transient performance quantitatively, the concept of dead time $t_d$ response delay time $t_r$ are introduced. Performance parameters such as air mass fiowrate Gat, engine speed N, manifold boost pressure Pb, and output torque T are measured simultaneously during the rapid opening of the throttle valve by the stepping motor. During the rapid opening of the throttle valve, air mass fiowrate Gat is increased immediately without delay time, but response of engine revolution N, and output torque T are delayed. Therefore hesitation, and stumble phenomena are occurred. Dead time $t_d$ and response delay time $t_r$ of engine revolution N, which is extremely delayed comparing to other performance parameters, are respectively 0.2-0.3sec., 3.0-4.6sec., and dead time rate $t_d/{\Delta}t$ and response delay time rate $t_r/{\Delta}t$ are linearly increased with the throttle valve opening rate ${\theta}$ during the acceleration from 12 degree to 20 degree at 1250rpm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2242-2247
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• 2008

A series of experiments have been performed in a vertical tube of 9.4 mm inner diameter using the Freon, HFC-134a as working fluid medium under the supercritical pressure range. Two kinds of experiments, i.e. steady-state and pressure transient, have been carried out. As for the steady-state heat transfer experiment, the mass flux was in the range between 600 and $2000\;kg/m^2s$ and the maximum heat flux was $160\;kW/m^2$. The selected pressures were 4.1, 4.3 and 4.5 MPa which correspond to 1.01, 1.06 and 1.11 times the critical pressure, respectively. In the pressure transient experiments, the inlet pressures were varied from 3.8 to 4.5 MPa and vice versa in the pressure transient simulations. In this study, heat transfer correlation and criterion for the heat transfer deterioration are suggested under the supercritical pressures. And also heat transfer characteristics during the pressure transient are examined.

• 마이크로전자및패키징학회지
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• 제12권4호통권37호
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• pp.331-338
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• 2005

The rapid advances in high power light sources and arrays as encountered in incandescent lamps have induced dramatic increases in die heat flux and power consumption at all levels of high power LED packaging. The lifetime of such devices and device arrays is determined by their temperature and thermal transients controlled by the powering and cooling, because they are usually operated under rough environmental conditions. The reliability of packaged electronics strongly depends on the die attach quality, because any void or a small delamination may cause instant temperature increase in the die, leading sooner or later to failure in the operation. Die attach materials have a key role in the thermal management of high power LED packages by providing the low thermal resistance between the heat generating LED chips and the heat dissipating heat slug. In this paper, thermal transient characteristics of die attach in high power LED package have been studied based on the thermal transient analysis using the evaluation of the structure function of the heat flow path. With high power LED packages fabricated by die attach materials such as Ag paste, solder paste and Au/Sn eutectic bonding, we have demonstrated characteristics such as cross-section analysis, shear test and visual inspection after shear test of die attach and how to detect die attach failures and to measure thermal resistance values of die attach in high power LED package. From the structure function oi the thermal transient characteristics, we could know the result that die attach quality of Au/Sn eutectic bonding presented the thermal resistance of about 3.5K/W. It was much better than those of Ag paste and solder paste presented the thermal resistance of about 11.5${\~}$14.2K/W and 4.4${\~}$4.6K/W, respectively.

• Transactions on Electrical and Electronic Materials
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• 제16권6호
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• pp.328-333
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• 2015

Squirrel cage induction motors have mostly been used for their small capacity because the starting torque is smaller than the starting current during start-up. However, as more and more mid-to-large capacity motors are developed, the demands for improvements in performance characteristics have also increased. In this study, the starting characteristics of squirrel cage induction motors were analyzed based on the rotor materials and shapes using a finite element method to provide design data suitable for different use purposes and capacities. We further completed analysis by combining electromagnetic equations deduced from Maxwell’s equations and the circuit equations of stators and rotors. A moving coordinator was introduced to rotate the rotor during the analysis, and the torques calculated via the finite element method were combined with the motion equations to calculate the position and angular velocity of the rotors at the next time, thereby analyzing the transient characteristics. The analysis results of the transient characteristics were applied to a 3-phase 4-pole 5-hp induction motor to calculate the starting torque, speed, and rotation angle of the rotors. In the reference model, the materials and shapes of the rotor slot were changed to copper and silicon copper and a deep slot, shallow slot, and long-neck-shaped slot.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.385-390
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• 2006

A fast response $CO_2$ analyzer has been developed to study transient characteristics on an SI engine. The analyzer has the delay time of 4.5 ms and time constant of 2.8 ms, which is fast enough to measure $CO_2$ concentration on a transient condition. Wide range of A/F(Air/Fuel) ratio can be estimated using the analyzer with an additional switch type oxygen sensor. The results of measurement of $CO_2$ concentration and A/F ratio on a transient condition including rapid acceleration/deceleration and EGR(Ehxaust Gas Recirculation) on/off are presented and compared with a commercial exhaust gas analyzer and UEGO(Universial Exhaust Gas Oxyzen) sensor.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.89-91
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• 1996

In dry-winding(unfilled) superconducting magnets, the behavior of liquid helium occupying the extremely small void space within the winding is contributed as a primary factor for transient stability of magnets. Therefore, numerical experiments have been carried out concerning the influences of transient heat transfer of liquid helium ocupying the void space in the winding and thermal properties of insulation at the conductor surface on the transient stability of magnets, by using three-dimensional finite element method(FEM). In this paper, we are going to consider three different cases for heat transfer characteristics of liquid helium to observe the influences of the rest of liquid helium in void space within the winding on the transient stability.

• Journal of Mechanical Science and Technology
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• 제15권5호
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• pp.656-664
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• 2001

A theoretical analysis is performed to describe the qualitative behavior of transient buoyant flows in a vertical channel. Consideration is given to the case of a fluid with a pre-existing stratification. The fluid motion is generated by giving impulsive anti-symmetric step-changes in temperature at the vertical left ad right sidewalls. The qualitative character of the flow is shown to be classified in the Rayleigh number (Ra)-Prandtl number ($sigma$) diagram. The transitory approach to the steady state can be monotonic or oscillatory, depending on ($sigma$-1)$^2$$pi$$^4$ 4$sigma$$R_a$. The prominent characteristics of time-dependent flow are discussed for large $R_a$. The profiles of temperature and velocity in the transient phase are depicted, which disclose distinctive time scales of motion. The transient process is shown to be sensitive to the Prandtl number. The detailed evolutions of flow and temperature fields are illustrated for large $R_a$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.490-491
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• 2011

This paper describes the EMTP/ATP Draw modeling HVDC submarine cable. HVDC submarine cables consist of conductor, lead sheath and amore. It is different from general cable which is composed with just conductor and aluminium sheath. Therefore, the transient characteristics are totally different between HVDC submarin cable and general cable. However, the study on HVDC cable modeling and Transient are insufficient. In this paper, characteristic and effectiveness of HVDC Submarine Cable through Transient analysis. Therefore it is evaluated that the application of HVDC Submarine cable at the field should be considered cautiously when more detailed transient analysis, another electrical testes and economic evaluations are implemented.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.240-243
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• 2005

This paper presents the transient behaviors of grounding system impedance against lighting impulse currents. The dynamic characteristics of the deeply driven ground rod and grounding grid subjected to the impulse current with various rise time were investigated. It was found that the transient ground impedance strongly depends on the configuration and size of grounding electrodes and the shapes of impulse currents, and the inductance of grounding electrodes has a significant affect on the transient ground impedance of grounding system in the short time domain.