• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.112-118
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• 2008

In the present study, the dependence of ultrasonic phase velocity on porosity and frequency in cancellous bone was predicted using the Biot model and the modified Biot-Attenborough (MBA) model for propagation in fluid-saturated porous media. It was also compared with previously published measurements in human and bovine cancellous bones in vitro. It was shown that the phase velocity in cancellous bone decreased with increasing porosity and frequency The dependence of phase velocity on propagation angle in cancellous bone as predicted using the Schoenberg model together with the Biot model and tile MBA model which were modified to include the effect of angle. The theoretical models used in the present study advance our understanding of the interaction between ultrasound and cancellous bone and can be expected to be usefully employed for the diagnosis of osteoporosis.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.2
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• pp.50-59
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• 1997

When a front head of train enters a tunnel at a high speed, compression wave is generated at tunnel entrance due to the confinement effect and propagated along the tunnel with sound of speed. The propagated compression wave is reflected at tunnel exit due to abrupt pressure change at passage. The reflected wave is expansion pressure wave. And when the rear head of train goes through the tunnel entrance, another expansion pressure wave is generated and propagated along the tunnel. The pressure drop occurs seriously around train when the two expansion pressure waves come cross on train in the tunnel. In order to reduce the pressure drop, the compression wave front must be controlled because the intensity and magnitude of pressure drop is nearly proportional to that of compression wave at tunnel entrance. This study relates to reduction of the pressure wave gradient with respect to tunnel entrance shape change with various kind of angle and rounding. The results show characteristics of wave propagation in tunnel, usefulness of characteristic curve to estimate proper time domain size in numerical study and measuring time in actual experiment. Also rounding is contributed to improve pressure wave front even if its radius is very small at tunnel entrance. In order to improve of pressure wave front at tunnel entrance, proper angle is prefered to rounding with big radius and an angle of around 14$^{\circ}$ is recommended according to this simulations, And it is expected to reduce additional pressure drop in tunnel when the location and the size of the internal space for attendant equipment are considered in advance.

• Journal of Power Electronics
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• v.5 no.2
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• pp.120-128
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• 2005

This paper deals with the analysis of switched reluctance motor drives for different drive circuit topologies used in automobile. So we attempt to improve the weaknesses associated with the asymmetric bridge converter in the limited internal environment of automotive application. Two kinds of c-dump converters are tested in terms of dump capacitor voltage, speed response according to the variation of advance angle and efficiency for the radiator cooling-fan drive of an automobile. They enable more economical and efficient converter topology for automobile industries. This paper describes the performance characteristics of 12V-250W-3000rpm SRM drives for automotive application. Computer simulation and experiment results are then presented to verify the performance of the two kinds of c-dump converters.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.828-830
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• 2002

Axial Flux Permanent Magnet motor could widely be used for low speed and high torque applications. In this paper, to analyse the sensor positioning effect of AFPM motor which has a new concentric winding method and to calibrate the switching timing according to speed, prototype motor is manufactured. As a result of experiment, advance angle from 30 degree to 45 degree of sensor position is more proper. So, this results can be used for design of sensor position to improve characteristic of the dual gap AFPM with coreless and slotless.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2518-2523
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• 2007

In this paper, thermo-flow characteristics of an outer-rotor type of a BLDC motor are numerically analyzed using three-dimensional turbulence modeling. In an advance design of BLDC motor, cooling blades and holes are preferred for the enhanced cooling performances. Rotating the blades and holes generates axial air flow passing through stator slots, which cools down stator by forced convection. For the present study, a new design of the BLDC motor has been developed and major design parameters such as the arrangement of cooling holes, the area of cooling holes, and cooling blades and the cooling blade angle, are analyzed for the enhanced convective heat transfer rate. It is found that the convective heat transfer rate of the new BLDC motor model is increased by about 8.1%, compared to that of the reference model.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.52-56
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• 2004

Unmanned Aerial Vehicles (UAVs) are remotely piloted or self-piloted aircraft by inputted program in advance or artificial intelligence. In this study Aileron and Elevator are used to control the movement of airplane for horizontal and vertical flights about its longitudinal and lateral axis. In an introduction, the drone was linearly modeled by extracting aerodynamic parameter through flight test and simulation, lift and drag coefficient corresponding to angle of attack, changes of pitching moment coefficient. In the main subject, the flight simulation was performed after constructing hardware using TMS320F2812 from TI company and PID with lateral and longitudinal controller for horizontal and vertical flights. Flying characteristics of two system were estimated and compared through real flight test with hardware equipped algorithm and adaptive algorithm that was applied to consider external factors such as turbulence. In conclusion the control performance of the controller with proposed algorithm was streamlined at lateral and longitudinal controller respectively, we will discuss guidance command to pass way point.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.136-138
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• 1996

This paper deals with the torque characteristic of AFPM Brushless DC motor, which is driven by 3 phase inverter and with the effect of phase of input voltage to the output by varying the input voltage to the induced voltage in stator of motor. To accomplish this, a prototype AFPM Brushless DC Motor was produced and phase variation was detected by a set of photo interrupter. In this realized system. method to maximize the output torque depend on the speed of motor is presented.

• Proceedings of the KIEE Conference
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• 2006.10d
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• pp.92-94
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• 2006

Single phase switched reluctance motor has a high speed capability, due to its very robust rotor, and requires only one electronic power switch in its control circuitry. The latter feature considerably reduces the cost of the drive system. But it involves starting problem and strongly torque ripple, which means that the motor is not suitable for application that require constant torque or speed. To solve torque ripple and region of these problem, this paper presents a single phase Switched Reluctance Motor model with a barrier rotor pole. Also it is simulated the designed prototype model by FEM for the prediction of characteristics.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.1
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• pp.22-31
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• 1993

Spark-ignition engine knock is affected by engine operating conditions such as engine speed, spark timing and intake air temperature. In this study the effect of intake air temperature on knock characteristics was studied experimentally using a 4-cylinder carburetor spark-ignition engine. The cylinder pressure data at 2000rpm were taken for intake air temperature range of $30^{\circ}C$ to $80^{\circ}C$ with $10^{\circ}C$ interval. And 80 consecutive cycles were taken at each experimental condition. As the same spark timing, as the intake air temperature increased by $50^{\circ}C$, the mean knock intensity increased about 20kPa. This effect corresponds to that of spark timing advance of 3 crank angle degrees.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.175-177
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• 2007

This paper presents for the torque characteristics and improving the efficiency of driving system of electric bicycle which applied IEWPM(Independently Excited Winding Permanent Magnet) motor. IEWPM motor can expand the number of phase from 3 phases to multiphase like SRM motor because stator windings are unconnected directly. BLDC motor raise rotor'-s electromagnetic torque per unit volume by using Spoke type permanent magnet. By using two photo sensor per phase and applying excited width, advance angle and bipolar control, we confirmed higher torque at a low speed, higher out-put at a high speed, and efficiency improvement at a wide speed control area.