• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.539-543
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• 2011

Recently, to reduce the noise and vibration levels of ships, high skewed marine propellers with thinner thickness are adopted widely, however, such propeller design trend causes to reduce the strength of blades. Propeller blades are rotating continuously in irregular wake field of ships. So, it is necessary to examine the strength of them precisely including from a viewpoint of fatigue strength. In present paper, the fatigue strength of propeller blades was investigated. Firstly, fatigue tests for Al Bronze, the representative propeller material, were carried out. The S-N curve was obtained for the assessment of the fatigue crack initiation life. And the material properties C, m for the fatigue crack propagation analysis based on the Paris' equation were derived. For the 2nd stage, the structural responses of propeller blades in irregular ship wake field was carried out using the finite element analysis code. And the fatigue strength of propeller blades were considered based on the calculated stress levels and material characteristics for fatigue strength.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1195-1207
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• 1998

Periodic pulsations in the static pressure near turbine surfaces as blade rows move relative to each other is one of the important sources of turbine unsteadiness. The present experiment aims to investigate the effect of the static pressure pulsations on the interaction of film coolant flows from two rows of staggered holes with mainstream and its effect on film cooling heat transfer. Potential flow pulsations are generated by the rotating shutter mechanism installed downstream of the test section, The free-stream Strouhal number based on the boundary layer thickness is in the range of 0.033 - 0.33, and the amplitude of about 10-20%. Measured are time-averaged and phase-averaged velocity variations, pressure variations and temperature distributions of the flow field. Experimental conditions are identified by boundary layer measurements. Injectant behavior is characterized by the measurements of unsteady pressure in the plenum chamber and free-stream static pressure. The film cooling effectiveness is evaluated from the insulated wall temperature measurement. It has been found that bulk flow pulsation provides very large diffusion of the injectants and the effectiveness is significantly reduced by the flow pulsations.

• Applied Microscopy
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• v.28 no.3
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• pp.329-343
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• 1998

Early wound healing responses in the skin of the Korean fire bellied toad, Bombina orientalis, were examined using histochemical , scanning and transmission electron microscopical techniques. Cutaneous wounds were induced by sharp razor blade , and maintained in special cages for up to 3 days. By this treatment whole parts of epithelium and dermis were profoundly affected. After injury, retraction of damaged surface of the skin was observed. At 3 hours after injury, poly-band was form by mucous substance. The wound skin consisted of mucous gland secreted mucous substance which flows into wound cavity and the wound area was sealed by mucous substance which form thick layer at 6 hours. It appeared that natural disposition showed acid and neutral mucous substance by reaction of PAS and Alcian blue (pH 2.5) staining. After formation of the poly-band, epithelial cells were formed by migration of regenerating epithelial cells. These cells moved over the wound surface by migration at 12 hours after wounding. Poly-band was much increased in thickness and migrating cells were completely formed wound closure at 24 hours post-wounding. After 72 hours regenerated epithelial layer consists of four or five cell layers which are similar to clear, granular, and spinous layer.

• 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.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.29-40
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• 1999

A numerical method in frequency domain for the analysis of the acoustic wave equation governing the sound field generated by a non-cavitating propeller under a steady of unsteady loading condition is developed. Theory shows that only multiples of the blade passage frequency exist and that the wave number consists of the frequency component due to the nonuniformity of the wake and the Doppler effect originated from the rotation of the blades. Correlation with experiments for a two bladed propeller, designed to be load-free at a particular advance speed, indicate that the thickness effect can be significant in steady case, but can be negligible compared to the unsteady loading effect.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.775-780
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• 2013

In recent years, a notebook like an ultrabook gets thinner. Its thickness causes problems in cooling fan performance, system installation condition, and so on. In this study, we installed a small turbofan in notebook system with very narrow gap in order to generate similar condition to a real product. Experiments were performed to measure the fan's performance and the flow and noise characteristics, its results were compared with computational ones. Prediction of P-Q curve using CFD showed under about 5% error in high flow rate and its trend was agreed with experimental one over the flow field. Experimental data to measure the noise at a distance of 100 mm from a rotation axis direction of an impeller corresponded well with computational ones of broadband and BPF noise. The noise experiments to measure at a distance of 100 mm from a rotation axis direction of an impeller corresponded well with computational ones of broadband and BPF noise. Especially, tip part of impeller blade and part of exit and bottom near in an analysis by a commercial program(FlowNoise).

• Journal of Engineering Education Research
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• v.13 no.5
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• pp.8-14
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• 2010

This study intends to study about the blade performance loss occurred due to the variation in the shape of an airfoil from attachment/non-attachment of an erosion shield for the hovercraft. The model in this study has used NACA44XXseries, has designed NACA44XX-series by using the Auto CAD, and it designed the shape that has attached an erosion shield to this model according to the thickness and length. By using these models, a grid was generated by GAMBIT and the lift coefficient ($C_l$) and the drag coefficient ($C_d$) were calculated FLUENT code for flow analysis. Through this, the $C_l$ and $C_d$ have calculated and compared the lift-to-drag ratio that an indicator of airfoil performance according to the shape and attachment/non-attachment of erosion shield.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2612-2617
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• 2013

This study aims to develop hair cutter with zirconia($ZrO_2$) material whose machinability, corrosion resistance, wear resistance and bio-compatibility are excellent by comparing iron hair cutter. Ultra-thin zirconia cutter with the thickness of 0.253mm is manufactured through the optimization of design, molding, sintering, grinding and grinding process. With observation result of cutter specimen by use of scanning electron microscope(SEM), formability and process of cutting face are shown to be good. It is also evaluated with sufficient merchantability by cutting test results. The cutter process technology of thin zirconia can be utilized at the development of high value-added beauty appliances like razor, beauty-razor and eye brows-razor for woman by use of study result.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.2
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• pp.32-42
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• 1995

When the thickness becomes so small as in the case of the trailing edge of the propeller blade or when the curvature of the surface varies rapidly as in ship stem, the existing panel method employing a flat-surface panel, obtained by collapsing the original non-planar surface into its mean location, suffers the leakage problem and also gives inaccurate induction upon the field point very close to the panel. The hyperboloidal panel deals with the induction from the dipole distributed on the non-planar surface without approximation, overcoming the defects of the flat-surface panel. This paper introduces two distinct derivations of the formulae to compute the integral for the potential induced by a dipole of uniform density distributed on a non-planar hyperboloidal surface element. One method is based on the Gauss-Bonnet theorem and the other is based on the transformation of the surface integral into a line integral.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.1-10
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• 2010

The present study is a fundamental approach to develop the measuring technology for minute fluctuating pressures on the three-dimensional blade surfaces of the fan which rotates with an arbitrary rotation-axis direction. In this situation, we are required to correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures. The working fluid is air. A pressure transducer rotating with an arbitrary attitude is closely sealed by a twofold shroud system. The rotational motion with an arbitrary attitude is produced by fixing the pressure transducer to the cantilever which is connected to a motor-driven disc of 500mm in diameter and 5mm in thickness. As a result, we have quantitatively determined main governing effects upon the non-effective component of the pressure-transducer signal.