• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.879-886
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• 2004

A numerical optimization has been carried out to determine the shape of the three-dimensional channel with oblique ribs attached on both walls to enhance turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Numerical results fur heat transfer rate show good agreements with experimental data. four dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, streamwise rib distance on opposite wall to rib pitch ratio, and the attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related coefficients with a weighting factor. D-optimal method is used to determine the training points as a means of design of experiment. Sensitivity of the objective parameters to each design variable has been analyzed. And, optimal values of the design variables have been obtained in a range of the weighting factor.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.3
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• pp.229-234
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• 2021

In this paper, a study was conducted on the power amplifier control required to design an eLoran transmitter system using a low-height antenna. The eLoran transmitter developed during the eLoran technology development project conducted in Korea used a small 35 m antenna due to the difficulty of securing a site for antenna installation. This antenna height is very low compared to the height of 750 m which is required for eLoran 100 kHz signal transmission without any radiation loss. In the case of using such a small antenna, not only the radiation efficiency of the transmission is lowered, but also the power module control must be performed more precisely in order to transmit the eLoran standard signal. The equivalent RLC circuit of the transmitter system was implemented and transient analysis was conducted to derive the input required voltage for satisfying the output requirement. The voltage waveform was also generated by the RLC circuit analysis to generate the eLoran signal. Furthermore, we suggest power width modulation method to control eLoran power amplifier module more sophisticatedly.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.361-364
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• 2002

This paper discusses the influencing factors such as coring position, height to diameter ratio of core specimen(h/d) and coring torque on the strength estimation of concrete by small site coring method in order to verify the validities of small size core method. According to results, as for the influence of drilling position, when core specimens are obtained from the place parallel to placing direction, compressive strength of core specimens are higher than those perpendicular to placing direction. This is due to the loss of the area of core specimen perpendicular to plating direction by bleeding. And in case of $\phi$ 24mm core specimen, when vertical drilling against placing direction is taken. compressive strength of core specimen obtained at the bottom of the structure is higher than that at the top of the structure. As for the influence of height to depth ratio, as h/d ratio increases compressive strength shows to be decreased. As for the influences of rotation speed of drilling machine, as its speed goes up, compressive strength decreases, regardless of core diameter.

• Journal of Korean Foot and Ankle Society
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• v.16 no.2
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• pp.79-86
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• 2012

Calcaneal fractures account for 2% of all fractures and approximately 60 to 70% of tarsal fractures. These fractures typically are the result of high-energy injury, such as a motor vehicle accident or a fall from a height. The potential for disabling malunion following intrarticular displaced calcaneal fracture is high, regardless of treatment. Fracture displacement typically results in loss of hindfoot height, varus and widening of the hindfoot, with possible subfibular impingement and irritation of the peroneal tendon and/or sural nerve. Frequently, subtalar joint develops posttraumatic arthritis. In symptomatic patients with calcaneal malunion, systemic evaluation is required to determine the source of pain. Nonsurgical treatment, such as activity and shoe modification, bracing, orthoses, and injection, is effective in many patients. Surgical treatment may involve simple ostectomy, subtalar arthrodesis with or without distraction, or corrective calcaneal osteotomy. A high rate of successful arthrodesis and of patient satisfaction has been reported with surgical manamgent.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.245-248
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• 2005

In this paper, small sized half-wavelength circular loop antenna which attached beneath a visor of helmet is designed and fabricated at the resonant frequency of 449MHz. To reduce the size of the antenna, double series-shorted stubs are inserted inside the loop for practical use of a vacant space of loop inside. Also, It is designed for the printed type to install the helmet easily. The size of antenna on helmet is reduced to 87.75%(diameter : 70mm, height :.36mm) compare with general type antenna(diameter : 200mm height 101mm). The return loss, -10dB bandwidth and gain are -13.2dB, 17.6MHz(3.9%), and -1.78dBd. And, radiation pattern is omni-directional pattern at H-plane. Therefore, it can be seen that the half-wavelength circular loop antenna using double series-shorted stubs is proper structure for the miniaturization and the installed antenna of the helmet.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.112-117
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• 2004

The effects of laser heating on soot formation and oxidation of propylene diffusion flames have been studied experimentally under nearly sooting conditions. The non-sooting flame can be converted to a sooting flame when the laser light heats up a flame at 7 mm height, while a sooting flame can be changed to a non-sooting flame when a flame is heated with laser light at flame height of 13 mm. The selective heating at the soot formation and/or oxidation region determines the sooting behavior of a diffusion flame. The increased soot/flame temperatures are most likely to be responsible for both the decreased and increased soot formation/oxidation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05b
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• pp.133-136
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• 2011

This study concerned with the steel beam of bonding method and bonded steel beams by this method and both ends of different height, steel beams and steel beams in the center makes the junction. Both ends and the central part of steel beams connecting the lower flange by additional combining steel plates to convey stress, the stress to focus on the beam connections are passed to both ends of steel beams, and strength of beam connections is improved and steel structural beams is proposed to minimize the loss by Incision. If you use the developed method, the construction period is shortened, and reducing the amount of material can decrease the cost and reduction in floor height can be maximized business feasibility.

• Journal of computational fluids engineering
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• v.15 no.3
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• pp.16-23
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• 2010

Shape optimization of an upper plenum of a PBMR type gas cooled nuclear reactor has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) analysis and surrogate modeling technique. The objective function is defined as a linear combination of uniformity of flow distribution in the core and pressure drop in the upper plenum and the core. The ratio of thickness of slot to diameter of rising channels, ratio of height of upper plenum to diameter of rising channels, and ratio of height of the slot at inlet to outlet, are used as design variables for optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results show that the optimum shape represent remarkably improved performance in flow uniformity and friction loss than the reference shape.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.613-616
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• 2002

Luminance and contrast ratio is one of the most fundamental and important parameters of plasma display panel. Understanding the effects of cell design parameters on the display and background luminance is inevitable for improving the contrast ratio. We report the experimental results on the relationships between cell parameters and contrast ratio of the ac PDP driven by ADS scheme. It was found that the contrast ratio is the most significantly affected by rib height and optimum range of the rib height simultaneously affects the facing discharge during the reset periods, diffusion loss of plasma and shadowing of the visible light emitted from phosphor.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.407-407
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• 2011

태양전지에서 Fill Factor를 저하시키는 직렬저항의 성분들은 베이스저항, 에미터 저항, contact 저항, finger 저항, busbar 저항 등이 있다. 각각의 저항 성분은 전극의 width및 height, 그리고 전극과 전극 사이의 spacing을 가변함에 따라 각기 다른 값을 나타내는데, 낮은 직렬저항 값을 달성하기 위해 전극의 면적을 크게 하는 것이 바람직하지만, 이는 cell의 shading loss를 증가시켜 cell의 JSC를 저하시킨다. 그러므로 cell의 면적과 전면 에미터의 면저항을 고려하여 shading loss와 직렬저항을 최소화 하는 최적의 전면 전극의 설계가 중요하다. 본 논문에서는 시뮬레이션을 통해 전면 전극의 height, spacing 및 width를 가변하여 1 by 1, 2 by 2, 3 by 3의 cell 면적에서의 전면 전극의 설계를 최적화 하였다. 시뮬레이션 결과 각각의 cell면적에서 단위면적당 저항 값이 500 $m{\Omega}$ 이하, shading loss가 4% 미만인 전극을 설계하였다.