• Journal of the Korean Society for Precision Engineering
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• v.28 no.8
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• pp.975-983
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• 2011

A microfin on a heated surface and its effects of the heat transfer has been investigated. The thickness of the fin is about 8 micrometer to allow the flexible up-down motion of the fin. Two-way complete FSI (Fluid-Structure Interaction) method has been applied for the analysis. Firstly, the deformation of a microfin due to the pulsating flow is evaluated using structure analysis. The flow and temperature patterns are predicted by CFD (Computational Fluid Dynamics) method. At each time step, using the pressure force and temperature distribution from CFD, the deformation of the wing is evaluated by FEM. Also in order to estimate the resonance probability, the natural frequency of the wing structure is calculated by modal analysis. The proposed numerical procedure was validated through experiment using a single fin. Through this work, we show that the increase of 40% in heat transfer capacity using the microfin has been compared with that of flat plate case.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.259-265
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• 1997

An analytical study has been peformed to investigate the unsteady ignition characteristics of pulse combustion. In many combustion applications, strain rate of the flow can significantly affect the combustion features; ignition, extinction, and reignition. In the pulse combustion, two jets (hot combustion gases and fresh mixtures) coming from the opposite side of the combustor will collide in the combustor forming a stagnation region where the chemical reaction is suppressed by the strain rate until this becomes below the critical value. In this research, the method of large activation energy asymptotic is adopted with one step irreversible kinetics to examine the ignition response to the periodic variation of the strain rate of flow. The results show the variation of the maximum value of strain rate can determine whether the ignition or extinction occur.

• Journal of Chest Surgery
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• v.22 no.4
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• pp.687-692
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• 1989

Aneurysm of the sinus of Valsalva is an uncommon cardiac anomaly, usually congenital in origin, which may occur as an isolated defect or in conjunction with other cardiac malformation. This report is a case of a ruptured sinus of Valsalva aneurysm with ventricular septal defect in a 18-year-old female patient who complained progressive exertional dyspnea. She underwent operative management using total cardiopulmonary bypass. The fistula originated from the right coronary sinus and ruptured into the right ventricle and coexistent lesion was supracristal ventricular septal defect. The repair was done through aortic and right ventricular approach. The ruptured sinus of Valsalva was closed with pledget suture and the ventricular septal defect was closed with patch. The postoperative result was good.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.10 no.6
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• pp.81-87
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• 1996

This paper is to develop a digital inverter using microcontroller for a Switched Reluctance Motor (SRM) driver. The closed-loop speed control system with fixed switching angle and variable voltage control is used to from a flat-topped phaes current and to simplfiy the drive system. This could be driven in a wide speed range with flat-topped current. Mifcrocontroller os used to be compact and to have a flexbility in the control system.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.4
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• pp.179-189
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• 1996

An unstructured grid finite-volume method has been applied to predict the linear and nonlinear attenuation characteristics of the expansion chamber silencer system. In order to achieve a grid flexibility and a solution adaptation for geometrically silencer system. In order to achieve a grid flexibility and a solution adaptation for geometrically complex flow regions associated with the actual silencers, the unstructured mesh algorithm in context with the node-centered finite volume method has been employed. The present numerical model has been validated by comparison with the analytical solutions and the experimental data for the acoustic field of the concentric expansion chamber with and without pulsating flows, as well as the axisymmetric blast flowfield with open end. Effects of the chamber geometry on the nonlinear wave attenuation characteristics is discussed in detail.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.101-109
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• 2000

Mutual torque ripple in a brushless DC motor is the main source of acoustic noise, especially fur motor operation with high speed and torque. This paper presents a method to obtain mutual torque ripple to identify acoustic noise source. Mutual torque ripple can be determined by analyzing phase current shape and magnetic circuit with different lead angles. Current shape is determined by state space model of voltage equation with the use of inductance calculated by FEM, and confirmed by experimental results. Mutual torque ripple is also determined by FEM analysis for the calculated current shape. Acoustic noise experiment reveals that mutual torque ripple with different lead angle is one of the main sources for noise generation in a brushless DC motor.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.132-140
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• 2001

A universal motor is a small dc series machine motor that is designed to operate from an ac machine. The characteristics of universal motors are high no-load and staring torque. Because of the high operating speed, the size of these motors for a given hp rating is typically smaller that other fractional hp ac machine, making it ideal for hand-held tools and appliances where weight, compactness, and speed are importance factors. A phase-angle control with AC drive system gains a high popularity due to their simple implementation, but contains the disadvantage of their poor input power factor, subharmonic current. Pulse width modulation control with DC drive systems increase the power factor as without delay phase angle. This paper analyzed the subharmonic characteristics of the phase angle control system that is controlled by zero voltage crossing similar to traditional method, and the dc chopper system that is used PWM.

• The Journal of Korean Physical Therapy
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• v.14 no.2
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• pp.162-171
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• 2002

The purpose of this study was to examined whether high voltage pulsed current stimulation(HVPCS) enhances the migration and proliferation of fibroblasts from tendon biopsies to provides evidence that the cellular activities of fibroblast are enhanced by HVPCS. Flexor digitorum profundus tendon of chickens were excised, biopsied and cultured in M199 medium for a day. The biopsies through which a cathodal HVPC with 100 pps, 50 V for 30 minutes was passed in medium. A day after treatment, the biopsies embedded in fibrin clot were covered by the addition of 1ml of M199 medium to the well, and placed in the $CO_2$ incubator for the duration of the experiment. The migration distance of cells from tendon biopsies were measured at 6 days after treatment, and proliferation of cells from tendon biopsies were measured at 7 days after treatment. The migration distance of cells from tendon biopsies in the HVPCS group demonstrated significantly greater than the shame treated control group (t=-2.675, p<0.05). Also HVPCS had significantly increased optical density of fibroblasts from tendon biopsies (t=-2.136, p<0.05). These results indicate that the HVPCS with 100pps, 50V for 30minutes enhanced either the migration and proliferation of fibroblast from tendon biopsies. These results supposed that the HVPCS activates cellular responses in fibroblasts from tendon biopsies. This suggests that enhanced the migration and proliferation of fibroblast by HVPCS may be one of the mechanism involved in tendon healing.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.5
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• pp.395-403
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• 2006

This paper has proposed a new dead time compensation method for a voltage-fed PMW inverter. In the voltage-fed PMW inverter, a voltage distortion is generated by the dead time effect and the nonlinear characteristics of the switching devices. Especially, the distorted voltage causes 5th and 7th harmonics in the stationary phase currents, and 6th harmonic in the synchronous phase currents. As a result, the integrator output of the synchronous PI current regulator has the ripple corresponding to six times of the inverter output frequency. In this paper, the signal of the integrator output of the d-axis current regulator is used as the control signal for the dead time compensation. The experimental and simulation results are presented to verify the validity of the proposed method.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2204-2206
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• 1997

A novel zero voltage and zero current switching (ZVZCS) full bridge (FB) PWM converter with a low output current ripple is proposed. The proposed circuit improve the demerits of the previously presented ZVBCS-FB-PWM converters[5-8] such as use of lossy components or additional active switches. A simple auxiliary circuit which includes neither lossy components nor active switches provides ZVZCS conditions to primary switches, ZVS for leading-leg switches and ZCS for lagging-leg switches. In addition, this proposed circuit reduces a output current ripple considerably. Many advantages including simple circuit topology, high efficiency, low cost and low current ripple make the new converter attractive far high power (> 1kW) applications.