• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.311-318
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• 2010

In this study, the conventional plane tip, double squealer tip, and various groove tip blades were tested in a linear cascade in order to measure the effect of the tip shapes on tip surface heat transfer coefficient distributions. Detailed heat transfer coefficient distributions were measured using a hue-detection based transient liquid crystals technique. Two tip gap clearances of 1.5% and 2.3% of blade span were investigated and the Reynolds number based on cascade exit velocity and chord length was $2.48{\times}10^5$. Results showed that the overall heat transfer coefficients on the tip surface with various grooved tips were lower than those with plane tip blade. The overall heat transfer coefficient on grooved along suction side tip was lower than that on the squealer tip.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.7
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• pp.553-559
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• 2012

A plate-fin heat exchanger is a type of heat exchanger widely used in air conditioners, and tubes and fins are tightly assembled by the mechanical expansion process of tubes. The tube expansion process deforms the grooves inside the tube, and the groove shapes also affect the adhesion between tubes and fins. In this study, the adhesion and heat transfer performance affected by the tube expansion of the non-uniform groove shape tube with different heights are investigated by both analysis and experiments. From the analysis method, it was shown that the contact pressure of non-uniform groove tube is higher than that of the uniform groove tube, and the most appropriate high groove number of the non-uniform groove tube is designed for the maximum contact pressure. From the experimental results, the decreasing rate of the condensation heat transfer coefficient is smaller in the non-uniform groove tube with different heights, compared to the conventional uniform groove tube. Also, the air-side heat transfer coefficient of the non-uniform groove tube with different heights is higher than that of the uniform groove tubes.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.135-143
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• 1999

This investigation evaluates effects of notch depth, fatigue precrack length and side groove in impact specimen for estimation of a valid K1d by instrumented Charpy impact test. Specimen material is 6005-T6. for notch depth 2.0mm and 2.5mm specimens or within about 2mm fatigue precrack length with notch depth 2.0mm and 2.5mm specimens or within about 2mm fatigue precrack length with notch depth 2.0mm , dynamic fracture toughness [$K_{1d,(1)}$] obtained by crack initiation load($P_m$) should be used. Dynamic fracture toughness of side grooved specimens are overestimated to that of standard impact specimen about 15 %-20%. It is confirmed that the formula of dynamic fracture toughness obtained by impact absorbed energy is inappropriate for ductile materials.

• Journal of the Korean Graphic Arts Communication Society
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• v.20 no.1
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• pp.113-122
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• 2002

We designed the illumination optical system to use Fresnel lens which is the most general type of large aperture system. The normal construction of Fresnel lens is a thin molded piece of material, usually some kind of plastic, with one side flat and the other comprising a series of concentric segments each angled in a way to provide for optimum focusing for a pair of conjugate points. The 155 mm Marine Signal Lantern is the approved for use on buoys and a maximum omnidirectional range of 8 nmi, can be obtained with standard 12V equipment, respectively. Finally, Fresnel lens with 155 mm diameter was designed and evaluated. Also, we re-designed groove "out" of Fresnel lens and compared results of groove "in" type with groove "out" type. According to the results, Fresnel lens is obtained best optical results when grooved side faces the longer conjugate.de faces the longer conjugate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.494-503
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• 1986

본 연구에서는 저강도.고연성재인 일반구조용압연강 SB41의 평골 CT 시험편과 양측면홈이 있는 CT시험편을 사용하여 ASTM R유선법, JSME R유선법,SZW법, 초음파법 및 전입차법에 따라 J$_{IC}$를 종합적으로 평가하였다. 복수시험편법인 ASTM 및 JSME 및 JSME R유선법을 상호 비교고찰하므로써 저강도.고연성재에 대한 파환인성평가 의 적용한계를 명확히 하였으며 단일시험편법인 초음파 및 전입차시험법은 효율적이고 간편한 J$_{IC}$평가법임을 확인하였다.

• ETRI Journal
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• v.20 no.2
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• pp.231-240
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• 1998

We report, for the first time, the fabrication of vertically stacked InGaAs/GaAs quantum wires (QWRs) on V-grooved substrates by chemical beam epitaxy (CBE). To fabricate the vertically stacked QWRs structure, we have grown the GaAs resharpening barrier layers on V-grooves with (100)-(322) facet configuration instead of (100)-(111) base at 450 $^{\circ}C$. Under the conditions of low growth temperature, the growth rate of GaAs on the (322) sidewall is higher than that at the (100) bottom. Transmission electron microscopy verifies that the vertically stacked InGaAs QWRs were formed in sizes of about $200{\AA} {\times} 500{\sim}600 {\AA}$. Three distinct photoluminescence peaks related with side-quantum wells (QWLs), top-QWLs and QWRs were observed even at 200 K due to sufficient carrier and optical confinement. These results strongly suggest the existence of the quantized state in the vertically stacked InGaAs/GaAs QWRs grown by CBE.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.161-166
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• 2008

In general structures, cleavage fracture may develop under the low constraint condition of larger scale yielding with a shallow surface crack. However, standard procedures for fracture toughness testing require very severe restrictions of specimen geometry. So the standard fracture toughness data makes the integrity assessment irrationally conservative. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with varying crack depth, The constraint effects on the crack depth ratios are quantitatively evaluated by scaling model and Weibull stress method using 3-D finite clement method, After correction of constraint loss due to shallow crack depths, the statistical size effect are also corrected according to the standard ASTM E 1921 procedure, The results snowed a good agreement in the geometry correction regardless of the crack size, while some over-corrections were observed in the corrected values of $T_0$.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.26-34
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• 2001

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.8
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• pp.795-800
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• 2014

In this paper, a vibrotactile pad system, T-mobile, is developed to provide vibrotactile cues for hand-held devices. A grooved and slim design is adapted to the back-side plane of the T-mobile, and the contact part consists of 12 vibrotactile panels which can operate independently and separately. To be isolated among vibrotactile actuators, the surface of the cover is divided into several pieces. Each vibrating module consists of a linear resonant actuator, a section of covering surface, and a vibration isolator. In order to provide spatial and directional information, sensory saltation and phantom sensation are applied to the T-mobile. To evaluate the developed device, two experiments were conducted to test whether directional information and spatial information can be successfully displayed by the device. Additionally, in order to find optimal stimulation by sensory saltation, an empirical test was conducted. As a result, spatial and directional information would be useful for displaying intuitive information for hand-held devices with vibrotactile feedback and reasonable near-optimal value for sensory saltation was obtained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.409-416
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• 2009

Standard procedures for a fracture toughness testing require very severe restrictions for the specimen geometry to eliminate a size effect on the measured properties. Therefore, the used standard fracture toughness data results in the integrity assessment being irrationally conservative. However, a realistic fracture in general structures, such as in nuclear power plants, may develop under the low constraint condition of a large scale yielding with a shallow surface crack. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with various crack depths. The constraint effects on the crack depth ratios were evaluated quantitatively by the developed scaling method using the 3-D finite element method. After the fracture toughness correction from scaling model, the statistical size effects were also corrected according to the standard ASTM E 1921 procedure. The results were evaluated through a comparison with the $T_0$ of the standard CT specimen. The corrected $T_0$ for all of the PCVN specimens showed a good agreement to within $5.4^{\circ}C$ regardless of the crack depth, while the averaged PCVN $T_0$ was $13.4^{\circ}C$ higher than the real CT test results.