• 제어로봇시스템학회:학술대회논문집
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• 1988.10b
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• pp.858-863
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• 1988

A micro-processor based control system for a brushless DC motor used in the motor-driven electromechanical total artificial heart was developed. Functionally, the control system is composed of two parts. The first part is the velocity and position controller to assure that the motor follows a predetermined optimal velocity profile with minimal energy consumption, and to guarantee the full stroke length. This part also utilize the passive adaptive control method to be robust against the load disturbance, system parameter variation, and uncertainty which is the environment of artificial heart system. The pump output control is the second part, and this part provides the required responses of the artificial heart to the time-varying physiologic demands. The basic requirements of these responses are preload sensitivity, afterload insensitivity, and the balanced ventricular outputs. The performance and reliability of this control system was evaluated through a series of mock circulation tests and animal implantation, and the results are very encouraging.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1736-1745
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• 2002

The objective of this study is to predict the roll wear in hot rod rolling process. In this study hot rod rolling process for round and oval passes has been investigated. In order to predict the roll wear, the wear model is reformulated as an incremental form and then wear depth of roll is calculated at each deformation step on contact area using the results of finite element analysis, such as relative sliding velocity and normal pressure at contact area. Archard's wear model was applied to predict the roll wear. To know the thermal softening of DCI (Ductile Cast Iron) roll according to operating conditions, high temperature micro hardness test is executed and a new wear model has been proposed by considering the thermal softening of DCI roll expressed in terms of the main tempering parameter curve. 3D wear program developed in this study might be used for adjusting the gap of rolls to set up a suitable rolling schedule for keeping dimensional tolerance of the product.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.887-890
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• 1997

Recently micromachining using DPSSL(Diode Pumped Solid State Laser) with 3rd harmonic wavelength is actively studied in laser machining area. Micromachining using DPSSL have outstanding advantages as UV source comparing with excimer laser in various aspect such a maintenance cost, maskless machining, high repetition rate and so on. In this study micro-drilling of PCB type substrate which consists of Cu-PI-Cu layer was performed using DPSS Nd:YAG laser(355nm, wavelength) in vector scanning method. Experimental and numerical method(Matlab simulation, FEM) are used to optimize process parameter and control machining depth. The man mechanism of this process is laser ablation. It is known that there is large gap between energy threshold of copper and that of PI. Matlab simulation considering energy threshold of material is performed to effect of duplication of pulse and FEM thermal analysis is used to predict the ablation depth of copper. This study could be widely used in various laser micromachining including via hole microdrilling of PCB, and micromachining of semiconductor components, medical parts and printer nozzle and so on.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.559-563
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• 2011

Drop impact reliability assessment of solder joints on the flip chip is one of the critical issues for micro system packaging. Our previous researches have been showing that new solder ball compositions of Sn-3.0Ag-0.5Cu has better mechanical reliability than Sn-1.0Ag-0.5Cu. In this paper, dynamic reliability analysis using Finite Element Analysis (FEA) is carried out to assess the factors affecting flip chip in drop simulation. The design parameters are size and thickness of chip, and size, pitch and array of solder ball with composition of Sn1.0Ag0.5Cu. The board systems by JEDEC standard including 15 chips, solder balls and PCB are modeled with various design parameter combinations, and through these simulations, maximum yield stress and strain at each chip are shown at the solder balls. It is found that larger chip size, smaller chip array, smaller ball diameter, larger pitch, and larger chip thickness have bad effect on maximum yield stress and strain at solder ball of each chip.

• Structural Engineering and Mechanics
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• v.65 no.1
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• pp.33-41
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• 2018

In this paper, using modified couple stress theory in place of classical continuum theory, and using shell model in place of beam model, vibrational behavior of nanotubes is investigated via the finite element method. Accordingly classical continuum theory is unable to correctly compute stiffness and account for size effects in micro/nanostructures, higher order continuum theories such as modified couple stress theory have taken on great appeal. In the present work the mass-stiffness matrix for cylindrical shell element is developed, and by means of size-dependent finite element formulation is extended to more precisely account for nanotube vibration. In addition to modified couple stress cylindrical shell element, the classical cylindrical shell element can also be defined by setting length scale parameter to zero in the equations. The boundary condition were assumed simply supported at both ends and it is shown that the natural frequency of nano-scale shell using the modified coupled stress theory is larger than that using the classical shell theory and the results of Ansys. The results have indicated using the modified couple stress cylindrical shell element, the rigidity of the nano-shell is greater than that in the classical continuum theory, which results in increase in natural frequencies. Besides, in addition to reducing the number of elements required, the use of this type of element also increases convergence speed and accuracy.

• Korean Journal of Optics and Photonics
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• v.27 no.5
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• pp.181-187
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• 2016

We report on the parameter-dependent optical characteristics of the unidirectional single-mode lasing square ring cavities. Using the taper-step section in the square cavities, the resonant direction can be selected and we characterize the optical losses by changing the taper lengths. Various kinds of square ring cavities are fabricated, based on InGaAsP/InGaAs multiple quantum well semiconductor materials. From the experimental results we obtain the optimized taper length for a given device structure, while maintaining unidirectional single-mode lasing.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.2-5
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• 2008

This study describes the numerical simulation of three-dimensional droplet formation and the following motion in a cross-junction microchannel by using the Lattice Boltzmann Method (LBM). Our aim is to develop the three-dimensional binary fluids model, consisting of two sets of distribution functions to represent the total fluid density and the density difference, which introduces the repulsive interaction consistent with a free-energy function between two fluids. We validated the LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we applied our code to the numerical simulation of a binary fluid flow in a cross-junction channel focusing on the investigation of the droplet formulation. Due to the pressure and interfacial-tension effect, one component of the fluids which is injected from one inlet is cut off into many droplets periodically by the other component which is injected from the other inlets. We considered the effect of the boundary conditions for density difference (order parameter) on the wetting of the droplet to the side walls.

• Journal of Sensor Science and Technology
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• v.21 no.1
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• pp.53-58
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• 2012

Biological and chemical assays(e.g., clinical tests for medical diagnosis) are needed to handle small liquid volume with high accuracy and high reliability. Many micro-dispensing systems using various actuation methods have been developed and applied. In this research, we confirm repeatability of the cartridge-type dispensing system with various measuring methods for guarantee of an acceptable reliability. We systematically examine the dispensed volume variation and dispense rate during 500,000 shots of sequential actuation. Using the same method, we confirm the repeatability of dispensed volume while varying operating conditions and design parameter(i.e., outlet size) of the dispensing system. Also, we examine the consistency of the dispensed volume of droplet while varying the operating pressures. Furthermore, we repeatedly measure differences between an actual dispensed volume and a target volume. According to our results, it is expected that the stable and reliable performance of our dispensing system can effectively be used in various applications containing bio-solutions.

• New & Renewable Energy
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• v.10 no.2
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• pp.5-11
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• 2014

Squirrel cage induction motor is the main driving system of industrial field and familiar with its use in a large variety of applications. The structure and operating characteristics of induction generator is almost identical to induction motor, but the induction generator part is used restrictively from hydropower power and wind power development etc. Recently induction generator is commonly used for micro & small hydro power applications due to its simplicity, reliability, low cost and robustness. Input and output of induction motor has turned against at the induction generator operation. Rotation speed of induction generator is small faster than synchronous speed of induction motor. As output of induction machines increases with the increasement of speed, so loss is same. Actually, generator efficiency is lower than motor at this condition. If induction generator is connected with mechanical load such as increaser, total efficiency is decreased. Consequently the quality in compliance with an induction motor parameter applying like that in the generator is a possibility of having the error of some. In this paper, we analyzed that input, output, torque and efficiency of induction machine is different from each other above and below synchronous speed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.519-528
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• 1994

Degradation problem due to long term service in machine or structure is now one of important problems in whole industrial field. In this study, pressure vessel steel, Cr-Mo steel, which was used more than 60,000 hours, was surface-modified by laser beam radiation for the improvement of fatigue strength. To find out optimum radiation condition, hardness, residual stress measurement and fatigue tests were carried out with the specimen of different radiation conditions. Experimental results show that micro-hardness values on the surface of the radiated specimens were approximately 2.2 times higher than those of un-radiated ones. In the depth direction of the specimen, hardness on the surface showed maximum value and was decreased at the inside the specimen. Different hardness values are due to the energy density Q which was absorbed by the specimen. Fatigue tests show that fatigue life was improved by the compressive residual stress after laser beam radiation. However, some specimens with differednt conditions show the shorter fatigue life. It means that laser beam radiation with optimum parameter can improve thae fatigue strength.