• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.2985-2992
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• 2015

In this study, the characteristics of heat transfer and pressure drop was theoretically analyzed by changing longitudinal pitch, bump phase, location of vortex generator about the staggered tube banks by applying SST (Shear Stress Transport) turbulence model of ANSYS FLUENT v.14. Before carrying out CFD (Computational Fluid Dynamics) analysis, It is presumed that the boundary condition is the tube surface temperature of 363 K, the inlet air temperature of 313 K and the inlet air velocity of 5-10 m/s. The results indicated that the heat transfer coefficient is not affected by the longitudinal pitch and the bump phase of circle type was more appropriate than serrated type in the characteristics of heat transfer and pressure drop. Additionally, in case of vortex generator location, the heat transfer characteristics showed that forward location of tube was more favorable 4.6% than backward location.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2341-2348
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• 2010

In this paper, strain and stress on space frame are analyzed at racing car under crash loads. As the deformation is reduced to a minimum during crash and the vulnerable parts are grasped, the safety of driver is ensured. The vehicle frame is modelled with truss structure by inputting the material property of carbon steel on finite element analysis. The increase of impulse momentum is due to speed change at frontal collision. This influence effected on vehicle frame is also analyzed by ANSYS program. The deformation of the frame is studied by applying the crash loads at front, side and rear directions. Though the influence on the seat of driver is small at frontal and rear crash, the deformation due to impact is progressed into this seat. The safety of frame is enhanced by making up for these weak deformations and these results of simulation analysis can be applied to the production of the actual vehicle frame.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.649-650
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• 2005

반도체는 고집적화, 고속도화, 저전력화를 목적으로 발전하고 있다. 이를 위하여 design rule의 감소, 새로운 물질과 프로세스의 적용 등 많은 연구가 이루어지고 있으며, RC delay time을 줄이기 위한 Cu 와 저유전율 재료의 적용이 그 대표적인 예라 할 수 있다. Cu 배선은 기존의 Al 배선에 비하여 높은 전자이동 (electro-migration)과 응력 이동 (stress-migration) 저항을 가짐으로써 전기적인 성능 (electrical performance) 에서 이점을 가지고 있다. 반도체에서의 Cu 배선 구조는 평탄화된 표면 및 배선들 사이에서의 좋은 전기적인 절연성을 가져야 하며, 이는 디싱(dishing)과 에로젼(erosion)의 중요한 인자가 된다. 기존의 평탄화 공정인 Cu CMP(Chemical Mechanical Polishing)에 있어서 이러한 디싱, 에로전과 같은 결함은 선결되어져야 할 문제로 인식되고 있다. 따라서 본 연구에서는 이러한 결합들을 감소시키기 위한 새로운 평탄화 방법으로 Cu gap-filling 을 하는 동시에 평탄화된 표면을 이루는 ECMD(Electro-Chemical Mechanical Deposition) 공정의 전기적 기계적 특성을 파악하였다.

• Archives of Plastic Surgery
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• v.37 no.6
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• pp.763-768
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• 2010

Purpose: Reconstruction of soft tissue defect using tissue expander can provide better flap which is more similar to surrounding tissue in color, skin texture and hair compared to other methods. Many pediatric patients need reconstruction of soft tissue defect because of giant congenital nevi, congenital or acquired malformations and burn scars. Reconstruction using tissue expander is adequate to minimize dysmorphism in these patients. We intended to assess outcomes of using tissue expander in pediatric patients by retrospective study. Methods: Total cases were 168 of pediatric patients who received soft tissue reconstruction using tissue expander by the same surgeon from February, 1982 to May, 2009. All patients who received soft tissue reconstruction were under 10 years old. Mean age was 4.3 years old, the youngest 13 months, the oldest 8 years. Eightynine cases were male and 79 cases were female. Most common cause was giant hairy nevi (67 cases, 39.9%), secondary cause was burn scar/scar contracture (61 cases, 36.3%). Trunk (38 cases, 22.6%) was most common anatomical location. Results: Soft tissue defects were successfully covered using tissue expander in 149 cases (88.7%) without major complications. There was infection on 8 cases (4.7%) and we treated by adequate antibiotics in these cases. There were tissue expander folding or valve displacement on 5 cases (3%). Conclusion: Usage of tissue expander is useful on pediatric patients because tissue expansion is rapid on children and there are less secondary contractures on operation site than full thickness skin graft. Because of psychological stress due to tissue expander, operation should be performed before school age.

• Tribology and Lubricants
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• v.31 no.6
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• pp.294-301
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• 2015

In this paper, we predict the rotordynamic force coefficients of tilting pad journal bearings (TPJBs) with rocker-back pivots, and we compare the predictions to recently published predictions and test data. The present TPJB model considers the rocker-back pivot stiffness calculated based on the Hertzian contact-stress theory, which is nonlinear with the application of a force . For the five-pad TPJB in load-between-pad and load-on-pad configurations, the predictions show the pressure- and film-thickness distributions, the deflection and stiffness of the individual pivots, and bearing stiffness and damping coefficients. The minimum film thickness and peak pressure occur at the bottom pad on which the applied load is directed. Because of the preload, the pres- sure is positive even at the upper pad in the opposite direction to the applied load. The pivot deflection and stiff- ness are maximum at the bottom pad that receives the heaviest pressure load. The predicted stiffness coefficients increase as the static load and rotor speed increase, while the damping coefficients decrease as the rotor speed increases, but increase as the static load increases. In general, the predicted stiffness coefficients agree well with the test data. The predicted damping coefficients overestimate the test data, particularly for large static loads. In general, the current predictive model considering the pivot stiffness improves the accuracy of the rotordynamic performance compared to previously reported models.

• Tribology and Lubricants
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• v.30 no.6
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.68-73
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• 2009

Recently, as titanium and titanium alloys are being increasingly used in wide areas, there are on-going researches to obtain high quality weld zone. In particular, growing interest is being drawn to laser welding, which involves low heat input and large aspect ratio in various welding processes and can facilitate shield in atmospheric condition compared with electron beam welding. The first report covered the analysis of embrittlement by the bead color of weld zone through quantitative analysis of oxygen and nitrogen and measurement of hardness as basic experiment to apply laser welding to titanium. Results indicated that the element that affect embrittlement the most was nitrogen, and as embrittlement and oxygenation go on, bead color changed to silver, gold, brown, blue and gray. This study performed butt welding of pure titanium and STS304 by using 1kW CW Nd:YAG laser, and to find out basic physical properties, evaluated welding performance by laser output, welding speed, root gap and misalignment etc, and examined mechanical properties through tensile stress and Erichsen test. The reason particles of pure titanium welded metal and HAZ are greater than STS304 is because they are pure metal and do not include many impure elements that work as nuclei in case of resolidification, thus becoming coarse columnar crystals eventually. In addition, the reason STS304 requires more energy during welding than pure titanium is because the particle size of base metal is smaller.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.352-357
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• 2008

The detection of micro cracks in materials at the early stage of fracture is important in many structural safety assurance problems. The nonlinear ultrasonic technique (NUT) has been considered as a positive method for this, since it is more sensitive to micro crack than conventional linear ultrasonic methods. The basic principle is that the waveform is distorted by nonlinear stress-displacement relationship on the crack interface when the ultrasonic wave transmits through, and resultantly higher order harmonics are generated. This phenomenon is called the contact acoustic nonlinearity (CAN). The purpose of this paper is to prove the applicability of CAN experimentally by detection of micro fatigue crack artificailly initiated in Aluminum specimen. For this, we prepared fatigue specimens of Al6061 material with V-notch to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results, we could see that the harmonic amplitude had good correlation with COD and it can be used to detect the crack depth in more accurately than the common 6 dB drop echo method.

• Current Research on Agriculture and Life Sciences
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• v.32 no.3
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• pp.155-158
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• 2014

Phytoextraction is a technique that uses plants to remediate metal-contaminated soils. However, this technique cannot be applied in highly metal-contaminated areas, as plants cannot normally grow under such conditions. Therefore, this study investigated the introduction of various biodegradable chelating agents to increase the bioavailability of metals in highly metal-contaminated areas. Mercury (Hg) was selected as the target metal, while cysteine (Cys), histidine (His), malate, succinate, oxalate, citrate, and ethylenediamine (EDA) were used as biodegradable chelating agents. Plants were grown on agar media containing various chelating agents and Hg to analyze the effect on plant root growth. Cys and EDA were both found to diminish the inhibitory effect of Hg on plant root growth, whereas His, citrate, and ethylenediamine tetraacetic acid (EDTA) did not show any significant effects, and malate, succinate, and oxalate even promoted the inhibitory effect of Hg on plant root growth. Thus, Cys and EDA would seem to be promising biodegradable chelating agents for highly Hg-contaminated areas.

• Journal of the Korean Society of Child Welfare
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• no.26
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• pp.113-137
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• 2008

Present study investigated the effects of poverty and poverty-co-factors in childhood. The effect of poverty status was measured by needs-income ratio. It compared its effect on children's socio-emotional development with that of poverty proxy variables such as recipient of public assistance, financial stress, subjective perception about social class, residence in public housing. It also examined the effects of poverty-co-factors after poverty status were controlled. Results show that poverty status has a more consistent negative relationship with socio-emotional development than other proxy variables. However, the relationship between them disappeared after poverty-co-factors were controlled. Findings from the present study suggest that targeted efforts for decreasing poverty-co-factor risks should be made along with financial support.