• Elastomers and Composites
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• v.38 no.4
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• pp.334-341
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• 2003

A bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is a hollow cylinder, which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the force applied to the shaft and the relative deformation of a bushing is nonlinear and exhibits features of viscoelasticity. A force-displacement relation for bushings is important for multibody dynamics numerical simulations. For the nonlinear viscoelastic axial response, Pipkin-Rogers model, the direct relation of force and displacement, has been derived from Lianis model and the sinusoidal input was used fer Pipkin-Rogers model, and the affection of displacement with frequency change was studied with Pipkin-Rogers model.

• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.183-194
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• 2014

Recently, a CANDU digital reactivity computer system (CDRCS) to measure the worth of the liquid zone controller in a CANDU-6 was developed and successfully applied to a physics test of refurbished Wolsong Unit 1. In advance of using the CDRCS, its measureable reactivity range should be investigated and confirmed. There are two reasons for this investigation. First, the CANDU-6 has a larger reactor and smaller excore detectors than a general PWR and consequently the measured reactivity is likely to reflect the peripheral power variation only, not the whole core. The second reason is photo neutrons generated from the interaction of the moderator and gamma-rays, which are never considered in a PWR. To evaluate the limitations of the CDRCS, several tens of three-dimensional steady and transient simulations were performed. The simulated detector signals were used to obtain the dynamic reactivity. The difference between the dynamic reactivity and the static worth increases in line with the water level changes. The maximum allowable reactivity was determined to be 1.4 mk in the case of CANDU-6 by confining the difference to less than 1%.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.566-574
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• 2005

Reduction of a ship's rolling is the most important performance requirement for improving the safety of the crew on board and preventing damage to cargos as well as improving the comfort of the ride. A mass driving anti-rolling system (MO-ARS) might be one candidate of several systems against the ship's rolling. As the movable range of the mass on the ship is finite, the control system must include restriction on the mass position to protect the device and the ship. This restriction usually causes windup phenomenon and control performance is deteriorated seriously. Two control algorithms, anti-windup control and saturated sliding mode control, are studied in this paper. Control performance and robustness problem are checked out by numerical simulations.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.384-390
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• 2012

This paper proposes a fault diagnosis method of the line-to-line voltage sensors in 3-phase AC/DC pulse width modulation (PWM) converters. The line-to-line voltage sensors are an essential device to obtain the information of the grid voltages for controlling the 3-phase AC/DC PWM converters. If the line-to-line voltage sensors are mismeasured by various faults, the voltage sensors can obtain wrong information of the grid voltage. It has an adverse effect on the control of the converter. Therefore, the converter causes the unbalance input AC current and the DC-link voltage ripple in the 3-phase AC/DC PWM converter. Hence, fast fault detection and fault tolerant control are needed. In this paper, the fault diagnosis method is proposed and verified through simulations and experiments.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.1
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• pp.14-21
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• 1998

In the conventional GaAs MESFET circuit simulation, the DC and transient simulation results are often failed due to the discontinuities of the first and second order derivatives arising from the use of separate models in linear, saturation, and transition regions. In this paper, we propose a unified drain current-voltage model by using a unified channel length modulation effect that is derived by extending the channel length modulation effect in the saturation region to the linear region. Calculated results from the proposed drain current-voltage model agree well with the results of Shur model. Also, we propose a unified capacitance model for linear, transition, and saturation regions by using a unified channel length modulation effect. Its results from the proposed capacitance model agree well with 2-D device simulation results. Thus, the proposed models are expected to be useful in circuit simulations.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.1
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• pp.156-163
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• 2010

A nonequilibrium molecular dynamics(NEMD) simulation method is developed and applied to study shock waves propagating through argon gas. In this simulation method, shock waves are generated by pushing a piston at a constant speed from one side of a simulation box filled with argon molecules. A linear relationship between piston speeds and shock speeds is observed. Thermodynamic properties including density, temperature, and pressure before and after the shock front are obtained from the simulations and compared with the well-known Rankine-Hugoniot equations based on ideal gases. The comparison shows an excellent agreement, indicating that this NEMD simulation method can be employed to investigate various physical properties of shock waves further.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.199-206
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• 2010

Matrix converter is an energy conversion device of controlled power semiconductor switches that directly connects the three-phase source to the three-phase load. With no dc-link components for energy storage in the matrix converter the input current depends directly upon the load currents and the switch state of the converter. Therefore the unbalanced and distorted input voltages can result in unwanted output harmonic currents. This paper presents a current compensator based on neural network to improving output current quality for matrix converter under abnormal input voltage conditions. The effectiveness and feasibility of the proposed technique has been proven through numerical simulations and experimental tests.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.11
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• pp.646-654
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• 1999

This paper deals with PWM patterns for harmonic reduction in inverter fed traction motors and the gear changing techniques for the variable speed drive of traction motor. GTOs are used as switching device of inverter because traction motor is a large load. To derive PWM rattern which can minimize the harmonics with the limited switching frequency, the output current and torque characteristic of SPWM and SHE PWM was analyzed. GTO inverter used for traction motor drive includes harmonics in the output current and torque by the limitation of switching frequency. However, the hybrid PWM method that adopt SPWM in the range of low frequency and SHE PWM in upper frequency range can achieve less harmonic characteristics in GTO inverters. If the traction motor is driven in variable speed by the proposed PWM pattern, 7 times of gear changing is needed. At the instant of the mode change, magnetic flux and torque may be altered and the large current flow. To reduce such an undesirable transient behavior, it is also presented the technique for the gear changing of inverter fed traction motor drive operated with the hybrid PWM. The results are verified by simulations and experiments.

• Journal of Magnetics
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• v.22 no.2
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• pp.286-290
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• 2017

The effects of loss of torque on magnetic fluid seals with rotating-shafts and the general difficulty of studying magnetic fluid seals are the focus of this work. The mechanism underlying loss of torque on such seals is analyzed using theoretical methods that show that loss of torque can be affected by several factors, including the velocity of the rotating-shaft, the structure of the sealing device, the characteristics of the magnetic field, and the characteristics of the magnetic fluid. In this paper, a model of the loss of torque is established, and the results of finite element analysis and testing and simulations are analyzed. It is concluded that (i) the viscosity of the magnetic fluid increased with the intensity of the magnetic field within a certain range; (ii) when the magnetic fluid was saturated, the increase in loss of torque tended to gradually slow down; and (iii) although the axial active length of the magnetic fluid may decrease with increasing speed of the rotating-shaft, the loss of torque increased because of increasing friction.

• ETRI Journal
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• v.35 no.4
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• pp.632-637
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• 2013

In this paper, we propose a superjunction trench gate MOSFET (SJ TGMOSFET) fabricated through a simple p-pillar forming process using deep trench and boron silicate glass doping process technology to reduce the process complexity. Throughout the various boron doping experiments, as well as the process simulations, we optimize the process conditions related with the p-pillar depth, lateral boron doping concentration, and diffusion temperature. Compared with a conventional TGMOSFET, the potential of the SJ TGMOSFET is more uniformly distributed and widely spread in the bulk region of the n-drift layer due to the trenched p-pillar. The measured breakdown voltage of the SJ TGMOSFET is at least 28% more than that of a conventional device.