• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.44-50
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• 2003

An experiment is conducted for measuring the performance of an air tool, which is operated at 100,000 RPM in an unloaded state with very low torque. A 551 kPa in gauge pressure is supply to the inlet of an air tool. An experimental apparatus is developed as a friction type dynamometer. Inlet total pressure, air flow rate, rotational speed and operating force are measured simultaneously. Torque, output power and specific output power are obtained with different rotational speeds. Those are compared with the experimental results which were obtained by a commercial dynamometer. However, no commercial dynamometers are available for measuring the torque above 30,000 RPM. In order to reduce the rotational speed, a reduction gear is applied between the air tool and the commercial dynamometer. Torque and power obtained by the commercial dynamometer show $55\%$ lower than those obtained by the developed friction type dynamometer, because the mass is added to the rotor of air tool for the braking system of the commercial dynamometer and power loss is generated by the reduction gear. From the compared results, the friction type dynamometer should be applied for measuring the performance of the air tool operating at low torque and high RPM.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.7
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• pp.756-759
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• 2014

DC/DC converters are commonly used to generate regulated DC output voltages with high-power efficiencies from different DC input sources. The converters can be applied in the regenerative braking of DC motors to return energy back to the supply, resulting in energy savings for the systems at periodic intervals. The fundamental converter studied here consists of an IGBT (Insulated Gate Bipolar mode Transistor), an inductor, a capacitor, a diode, a PWM-IC (Pulse Width Modulation Integrated Circuit) controller with oscillator, amplifier, and comparator. The PWM-IC is a core element and delivers the switching waveform to the gate of the IGBT in a stable manner. Display of the DC/DC converter output depends on the IGBT's changes in the threshold voltage and PWM-IC's pulse width. The simulation was conducted by PSIM software, and the hardware of the DC/DC converter was also implemented. It is necessary to study the fact that the output voltage depends on the duty rate of D, and to compare the output of experimental result with the theory and the simulation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2018-2023
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• 2003

An experiment is conducted for measuring the performance of an air tool, which is operated at 100,000 RPM at the unloaded state with the low torque. An experimental apparatus is developed as the power absorption type dynamometer. Inlet static pressure, flow rate, RPM and force are measured simultaneously. Torque, output power and specific output power are obtained. Those experimental results are compared with the experimental results obtained on a commercial dynamometer. However, no commercial dynamometers are available for measuring the torque above 30,000RPM. In order to use the commercial dynamometer, a reduction gear is applied to the shaft of dynamometer. Torque and power obtained on the commercial dynamometer show 50% lower than those obtained on a power absorption type dynamometer, because the inertia force is added to the air tool rotor for the braking system. Moreover, the starting RPM on the commercial dynamometer is less than 40,000RPM. From the compared results, they show that the power absorption type dynamometer should be applied for measuring the performance of an air tool operating at low torque and high RPM.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.7
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• pp.67-74
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• 2009

This paper describes the speed control functions of the typical steam turbine speed controllers and the test results of generator load rejection simulations. The goal of the test is to verify the speed controller's ability to limit the steam turbine's peak speed within a predetermined level in the event of generator load loss. During normal operations, the balance between the driving force of the steam turbine and the braking force of the generator load is maintained and the speed of the turbine-generator is constant. Upon the generator's load loss, in other word, the load rejection, the turbine speed would rapidly increase up to the peak speed at a fast acceleration rate. It is required that the speed controller has the ability to limit the peak speed below the overspeed trip point, which is typically 110[%] of rated speed. If an actual load rejection occurs, a substantial amount of stresses will be applied to the turbine as well as other equipments, In order to avoid this unwanted situation, not an actual test but the other method is necessary. We are currently developing the turbine control system for another nuclear power plant and have plan to do the simulation suggested in this paper.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.938-947
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• 2003

In this paper, we derived the formula for estimating the power of the electric motors needed to operate the Decanter-type centrifuge. In the derivation of the formula the sludge-removal torque is to be supplied from the formula derived in the first paper. The intricate nature of the transmission mechanism in the planetary gear trains of the sludge-removal power and torque has been clarified in this second paper. In particular we considered two-motor system, where the main motor drives the machine while the differential-speed control motor plays the role of braking in adjusting the differential speed. Sample calculation for the specific design treated in the first paper showed that the selection criterion for the main motor depends on the lower limit of the differential speed; when the lower limit is set low, it should be selected based on the steadily operating power, while it should be selected based on the starting power when the lower limit is set high. The total power required by both the main motor and the differential-speed control motor increases as the differential speed is decreased. It is suggested that the power loss in the differential-speed control motor could be minimized by attaching an electric generator to it.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2228-2234
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• 2000

Steering of the vehicles on a slippery highway is a difficult task for most passenger car drivers. The steering vehicles on slippery roads tend to slide outward with less lateral forces than on nor mal roads. When the drivers notice that their vehicles on a slippery highway start to depart from the cornering lane, most of them make a sudden steering and/or braking, which in turn may induce spin-out and instability on their vehicles. In this paper, an active steering control method is proposed such that the vehicles in slippery roads are steered as if they are driven on the normal roads. In the proposed method, the estimated lateral forces acting on the steering tires are compared with the reference values and the difference is compensated by the active steering method. A fuzzy logic controller is designed for this purpose and evaluated on a steering Hardware-In-the-Loop Simulation (HILS) system. Steering performance results on the slippery curved and sinus roads demonstrate the effectiveness of the proposed controller. This method can be realized with the steer-by-wire concept and is promising as an active safety technology.

• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.181-186
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• 2002

We study a role of the proto-accretion disk during the formation of the planetary system, which is motivated with recent X-ray observations. There is an observational correlation of the mass of extrasolar planets with their orbital period, which also shows the minimum orbital period. This is insufficiently accounted for by the selection effect alone. Besides, most of planetary formation theories predict the lower limit of semimajor axes of the planetary orbits around 0.01 AU. While the migration theory involving the accretion disk is the most favorable theory, it causes too fast migration and requires the braking mechanism to halt the planet~0.01 AU. The induced gap in the accretion disk due to the planet and/or the truncated disk are desperately required to stop the planet. We explore the planetary evaporation in the accretion disk as another possible scenario to explain the observational lack of massive close-in planets. We calculate the location where the planet is evaporated when the mass and the radius of the planet are given, and find that the evaporation location is approximately proportional to the mass of the planet as ${m_p}^{-1.3}$ and the radius of the planet as ${r_p}^{1.3}$. Therefore, we conclude that even the standard cool accretion disk becomes marginally hot to make the small planet evaporate at~0.01 AU. We discuss other auxiliary mechanisms which may provide the accretion disk with extra heats other than the viscous friction, which may consequently make a larger planet evaporate.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.145-150
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• 2017

Air brake valves are widely used in automotive braking systems and the Korean automobile industry depends on importing them. Therefore, we should develop the technical expertise for their domestic production. In this study, air brake valves were analyzed that can be used in a variety of automobiles. Computational fluid dynamics analysis, static structural analysis, and hyper-elastic analysis were carried out. Before production of an air brake valve system, the performance of different parts has to be evaluated, for instance by using finite element analysis. The structural stability of the product can be determined using static dynamics. The compression behavior of the O-ring is predictable by nonlinear hyper elastic analysis, although errors are possible due to one-way loading. This simulation study can both save time and reduce costs compared to the development of experimental prototypes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.486-491
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• 2013

Creak noise is kind of scratching noise which is usually generated in drum brake system on the vehicle. When driver brakes vehicle or applies parking lever, drum brake shoe moves to the drum side to stop the vehicle. And at that time, moving shoe scratches backing plate ledge surface, and that makes scratching noise in special condition. This study presents how we can generate creak noise in the laboratory and how we can reduce it by experimental approach. Through several and various type of tests, we could generate creak noise with damage on ledge area of the backing plate in the lab and we verified tab type shoe design can reduce this scratching noise. As a result of this study, we notified how creak noise happens in the vehicle, and that tab type design shoe has good performance of ledge area damage based on lab test(rig & dynamometer equipment), and that this can reduce potential risk of creak noise in the field.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.7
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• pp.603-609
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• 2015

Railway vehicles driven by wheels obtain force required for propulsion and braking by adhesive force between wheels and rails, this adhesive force is determined by multiplying adhesion coefficient of the friction surface by the applied axle load. Because the adhesion coefficient has a peak at certain slip velocity, it is important to determine the maximum values of the friction coefficient on the contact area. But this adhesive phenomenon is not clearly examined or analyzed. Thus we have developed new test procedure using the scaled adhesion test-bench for analyzing of the adhesion coefficient between wheel and rail. This adhesion test equipment is an experimental device that contacts mutually with twin disc which are equivalent to wheels and rails of railway vehicles.