• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.4
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• pp.294-304
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• 2003

An experimental analysis using three-dimensional laser Doppler velocimetry(LDV) measurement and computational analysis using the Reynolds stress model in FLUENT are conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition ($\Phi$=0.25) and two off-design conditions ($\Phi$=0.21 and 0.30). As the blade loading increases, the onset position of the rolling-up of tip leakage flow moves upstream and the trajectory of tip leakage vortex center is more inclined toward the circumferential direction. Because the casing boundary layer becomes thicker and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with the blade loading increasing. A distinct tip leakage vortex is observed downstream of the blade trailing edge at $\Phi$=0.30, but it is not observed at $\Phi$=0.21 and 0.25.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.322-329
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• 2005

The flow characteristics in the blade passage and in the wake region of a low speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. The tip leakage vortex interfaces with blade pressure surface, and results in high velocity fluctuation near the pressure surface. From axial velocity distributions downstream of the fan rotor, large axial velocity decay near the rotor tip is observed at near stall condition, which results in large blockage compared to that at the design condition. Although the wake flow downstream of the rotor blade is clearly measured at all operating conditions, the trough of the high velocity fluctuation due to Karmann vortex street in the wake flow is mainly observed at a higher flow condition than the design flow rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.5
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• pp.65-73
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• 2006

When a satellite separates from the launch vehicle, an initial high angular rate or a tip-off rate is generated. B-dot logic is generally used for controlling the initial tip-off rate. However, it has the disadvantage of taking a relatively long time to control the initial tip-off rate. To solve this problem, this paper suggests a new detumbling control method to be able to adapt to micro/nanosatellite with the pitch bias momentum system. Proposed detumbling method was able to control the angular rate within 20 minutes which is significantly reduced compared to conventional methods. Since the previous wheel start-up method cannot be used if the detumbling controller proposed by this paper is used, a method is also proposed for bringing up the momentum wheel speed to nominal rpm while maintaining stability in this paper. The performance of the method is compared and verified through simulation. The overall result shows much faster control time compared to the conventional methods, and achievement of the nominal wheel speed and 3-axes stabilization while maintaining stability.

• Archives of Plastic Surgery
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• v.36 no.1
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• pp.66-74
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• 2009

Purpose: The importance of the deformities in alar - columellar complex has been underestimated in Asian ethnic groups for the last decades. Fortunately, with increasing familiarity of the open rhinoplasty techniques, the anatomic details of the nasal tip have been pointed up. Definitely, having an interest and demand for improving the sub - normal relationship between the alar rim and columella are indebted for such growing of knowledge about nasal tip anatomy. However, it is true that any single procedure is not settled as versatile and fully confident modality to correct the retracted notching of the alar rim. With this article, I should like to propose another useful option for treating retracted ala. Methods: The author has tried to correct alar rim retraction by means of: (1) Triangular onlay septal cartilage graft on the lower lateral cartilage with the medial end fixed to the anterior surface of the lateral crus(Alar extension graft), (2) Inserting lateral end of the alar extension graft to the vestibular skin pocket in the form of a finger - in - groove, (3) using the vestibular skin in the form of an advancement flap, and (4) using the soft shield graft to prevent possible visible step - off of the alar margin. Results: The author applied an alar extension graft to 16 patients in order to correct a retracted ala for the last 27 months (August, 2003 - October, 2005). The distances from alar rim to long axis of nostril were improved to be within 2 mm in all of the cases, and also the shape of the alar rim changed to a round form. Nostril asymmetry (6%) in one case, temporary palpable step - off (18%) in three cases, temporary visible step - off (6%) in one case, and temporary paresthesia of the tip (25%) in four cases were observed. Conclusion: The alar extension graft is simple and efficacious. It does not need donor sites other than the operative field, and its results are predictable. In particular, since it may give structural intensity to a weak lower lateral cartilage, it may be preferentially used for the correction of a retracted ala that arises from hypoplastic lower lateral cartilage. Moreover intensified lower lateral cartilage also improves the esthetic shape of lobule.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.56-62
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• 2008

In this paper, elastic and plastic adhesion index was very important in deciding adhesive characteristics and varying elastic and plastic index, dimensionless load and pull-off force were analyzed and simulated. Finally, using AFM, experimental surface roughness parameters of substrates and pull-off force between tip and substrates were produced. Using these values, pull-off forces were calculated and were compared with experimental pull-off forces. Through simulation and experiment, it was found that interaction of asperity also had very important influence on adhesive contact.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.181-188
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• 2004

The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the velocity fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating velocity. The results show that the spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high velocity fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.66-71
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• 2008

Two cases with circumferential grooves were designed for a transonic compressor, and 3-D numerical simulations were conducted for stall mechanism at three representative speeds. A conclusion can be drawn from the comparison between compressors with or without casing treatment that: with the rising of rotation speed, stall margin increases dramatically under the help of casing treatments, and the case with middle grooves has reasonable compromise between stall margin increment and efficiency cutting. At lower speed, the increment reduces, and grooves at the back of blade tip have more influence on stall margin. Further investigation shows there is a transition in mechanism of compressor stall with the decline of rotational speed: at high rotation speed, the expansion of stall margin mainly results from the suppression of tip leakage vortex by casing treatments, yet it benefits more from the depression of boundary layer separation from suction surface of blade tip.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.57-58
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• 2002

Asperity arrays and Independent asperities were fabricated on a silicon plate. Then pull-off and friction forces were measured on each asperity pattern by using AFM (atomic force microscope) in humid air and high vacuum of $2{\times}10^{-5}$ Pa. The probe of AFM cantilever has a flat square of about $1\;{\mu}m^2$ on its tip. The results showed that the pull-off force was proportional to the curvature radius of asperity peak in each ambient condition. The friction force was proportional to the pull-off force and was slightly higher in the humid air than in the high vacuum.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.6
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• pp.615-621
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• 2013

The robot calibration has greatly improved the absolute accuracy of the industrial robot. However, the accuracy of the relative positions of robotic tool-tip at work-points on a work-piece is only slightly corrected by the robot calibration since there has been no practical method to eliminate the elements of the setup position errors at a robotic workplace. A robotic workplace calibration is demonstrated in this paper to minimize the relative position errors between a robot tool-tip and the work-point on a work-piece. The existing teaching and playback method has been developed for the robotic workplace calibration. This paper uses the work-piece fixed in a robotic work-place as measurement equipment instead of a special robot measurement equipment for the robotic workplace calibration. The positive effect of the robotic workplace calibration is supported by the results of computer simulation on an ideal robotic workplace model and an experiment at the actual robotic workplace.

• Bulletin of the Korean Space Science Society
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• 2006.04a
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• pp.121-124
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• 2006

B-dot logic is generally used for controlling the initial tip-off rate. However, it has the disadvantage of taking a relatively long time to control the initial tip-off rate. To solve this problem, this paper suggests a new detumbling control method to be able to adapt to micro/nanosatellite with the pitch bias momentum system. Proposed detumbling method was able to control the angular rate within 20 minutes which is a significant reduction compared to conventional methods.