• Journal of Institute of Control, Robotics and Systems
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• v.13 no.3
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• pp.218-223
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• 2007

The dissipation of high-power ultrasonic energy at the faces of the defect causes an increase in temperature. It is resulted from localized selective heating in the vicinity of cracks because of the friction effect. In this paper the measurement of size and direction of crack using UET(Ultrasound Excitation Thermography) is described. The ultrasonic pulse energy is injected into the sample in one side. The hot spot, which is a small area around the crack tip and heated up highly, is observed. The hot spot, which is estimated as the starting point of the crack, is seen in the nearest position from the ultrasonic excitation point. Another ultrasonic pulse energy is injected into the sample in the opposite side. The hot spot, the ending point of the crack, is seen in the closest distance from the injection point also. From the calculation of the coordinates of both the first hot spot and the second hot spot observed, the size and slope of the crack is estimated. In the experiment of STS fatigue crack specimen(thickness 14mm), the size and the direction of the crack was measured.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.380-387
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• 2000

In this paper, a successful result of modification of an axial flow fan and a shroud for noise reduction of a window type air conditioner is presented especially in order to verify the importance of blade shape improvement and the searching for the optimal shape of shrouds. Effective ways to work out the result as mentioned above are to make the tip of the blade varied in thickness and to have special shapes. From the viewpoint of the shape in a shroud, several cases were examined and the particular value of a design parameter of the shroud was acquired to get the best noise reduction of an air conditioner. Through the application of the methods, the air conditioner became less noisy by 4.5 dB(A) in terms of air-borne noise produced only by the axial flow fan and consumed less energy by 20.9% compared to the current one.

• Journal of computational fluids engineering
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• v.18 no.3
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• pp.51-59
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• 2013

A significant change in aerodynamic characteristics of wind turbine blade can occur by ice formed on the surface of the blade operated in cold climate. The ice accretion can result in performance loss, overloading due to delayed stall, and excessive vibration associated with mass imbalance. In this study, the impact of ice accretion on the aerodynamic characteristics of NREL 5MW wind turbine blade sections is examined by a CFD-based method. It is shown that the thickness of ice accretion increases from the root to the tip and the effects of icing conditions such as relative wind velocity play a significant role in the shape of ice accretion. In addition, the computational results are used to assess the degradation in the lift and drag coefficients of the blade sections.

• Journal of Astronomy and Space Sciences
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• v.2 no.2
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• pp.153-174
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• 1985

The one of critical factor in gas turbine engine performance is high turbine inlet gas temperature. Therefore, the turbine rotor has so many problems which must be considered such as the turbine blade cooling, thermal stress of turbine disk due to severe temperature gradient, turbine rotor tip clearance, under the high operating temperature. The purpose of this study is to provider the temperature distribution and heat flux in turbine disk which is required to considered premensioned problem by the Finite Difference Method and the Finite Element Methods on the steady state condition. In this study, the optimum aspect ratio of turbine disk was analysed for various heat conductivity of turbine disk material by Finite Difference Method, and the effect of laminating method with high conductivity materials to disk thickness direction by Finite Element Methods in order to cool the disk. The laminating method with high conductivity material on the side of the disk is effective.

• Tribology and Lubricants
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• v.18 no.1
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• pp.1-8
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• 2002

Nano adhesion and friction between a $Si_{3}N_{4}$ AFM(atomic force microscope) tip and thin silver films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM and LFM(lateral force microscope) modes in various range of normal loads. Thin silver films deposited by IBAD (ion beam assisted deposition) on Si-wafer (100) and other Si-wafers of different surface roughness were used. Results showed that nano adhesion and friction decreased with the surface roughness. When the Si surfaces were coated by pure silver, the adhesion and friction decreased. But the adhesion and friction were not affected by the thickness of IBAD silver coating. As the normal force increased, the adhesion forces of bare Si-wafer and IBAD silver coating film remained constant, but the friction forces increased linearly. Test results suggested that the friction was mainly governed by the adhesion as long as the load was low.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.292-297
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• 2001

Composite patch repair of cracked aircraft structures has been accepted as one of improving fatigue life and attaining better structural integrity. Analysis for the stress intensity factor at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels are developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior. In order to investigate the crack growth direction, maximum tangential stress(MTS) criteria is used. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stress intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. The research on cracked structure subjected to mixed mode loading is accomplished and it is evident that more work using different approaches is necessary.

• Journal of Sericultural and Entomological Science
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• v.36 no.1
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• pp.1-7
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• 1994

Four tetraploid mulberry lines, Sawonppon No.11, No.13 and No.14, were induced by the colchicine treatment on the shoot tips of seedlings originated from the cross between Yongchonppong and Kaeryanppong. The major characteristics of the tetraploid lines were as follows: Green tip sprouting stage was similar to Kaeryanppong, a medium budding variety. Leaves were medium- to large-sized cordate type. Leaf surface was rougher and stronger than that of the diploid parents. Leaf thickness, leaf area weight and leaf water content were higher than those of the diploid parents. Average branch length was shorter than that of the diploid parents. Internode length and number of lateral branches were similar to the average values of the two parents. Death atop rate of branch was 1.6%~2.5% indicating strong cold-hardiness of the tetraploid lines. Therefore, these lines could be used as sources of cold-hardiness in developing triploid lines.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.52-63
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• 1985

Fillet welded joints, specially in ship structure, are well known the critical part where stress concentrate or crack initiates and grows. This paper is concerned with the study of the behavior of fatigue crack growth t the root and toe of load carrying cruciform fillet welded joints under three points bending by the determination of stress intensity factor from the J-Integral, using the Finite Element Method. The stress intensity factor was investigated in accordance to the variation of the weld size (H/Tp). weld penetration (a/W) and plate thickness (2a'/Tp). As mixed mode is occurred on account of shearing force under the three points bending, Stern's reciprocal theory is applied to confirm which mode is the major one. The main results may be summarized as follows 1) The calculation formula of the stress intensity factor at the both of root and toe of the joint was obtained to estimate the stress intensity factor in the arbitrary case. 2) The change of stress field around crack tip gives much influence on each other at the roof and toe as H/Tp decreases. 3) Mode I is a major mode under the three points bending.

• Archives of Reconstructive Microsurgery
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• v.22 no.1
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• pp.38-41
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• 2013

A 31-year-old female patient presented with a skin and soft tissue defect measuring $8{\times}6cm$ in size with exposure of the extensor hallucis longus tendon and the first metatarsal bone after metatarsal lengthening for brachymetatarsia. The defect was covered with a distally based dorsalis pedis flap based on the distal communicating branch of the dorsalis pedis artery. Secondary defect was covered by a split thickness skin graft. There was congestion of the flap tip after the operation; however, it was resolved using medical leeches and anti-coagulants. No necrosis or infection was encountered and the contour of the flap was satisfactory. There was no donor site morbidity. Reverse dorsalis pedis flap has not been commonly used due to the anatomical variation and uncertainty, which is different from the reverse radial forearm flap. However, when faced with the challenge of a moderate soft tissue defect of the distal forefoot, we believe that the reverse dorsalis pedis flap offers a good option with various advantages.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.1
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• pp.65-73
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• 1986

Surface fatigue crack propagation tests by plane bending fatigue were conducted on the welding specimens of an aluminium alloy, A5083-0, having an edge through thickness notch to study the fatigue crack growth characteristics. Moreover, the experiments were performed in order to clarify the fatigue crack initiation and growth. The properties of fatigue crack growth were quantitatively inspected in welded metal, heat-affected zone and base metal of the welding specimens. The main results obtained are summarized as follows: 1. It is found that the hardness distributions of A5083-0 aluminium alloy weldments are quite different with those of steel material weldments, so that the hardness distribution becomes lower in the following order: base metal, heat-affected zone and weld metal. 2. It is observed that the grain size of this specimen weldment appears to be almost equal to the base metal, when TIC welding method is adopted. 3. In a surface fatigue crack initiation and growth, the fatigue crack does not begin by opening-closing mechanism until hardening is saturated at the crack tip. 4. The fatigue crack growth characteristics of A5083-0 alluminium alloy weldments can be concluded.$${\frac{da}{dn}}=C({\Delta}K)^n=3.8{\times}10^{-9}{({\frac}{1}{2}{\Delta}S_t{\sqrt{{\pi}a}})}^{2.4}$$