• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.493-499
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• 2015

The aerodynamic performance of blunt trailing edge airfoils was investigated. The flow fields around the modified NACA64-418, which consists of the tip blade of the wind turbine and Mexico model of IEA wind, were analyzed. To imitate the repaired airfoil, the original NACA64-418 airfoil, a cambered airfoil, is modified by the adding thickness method, which is accomplished by adding the thickness symmetrically to both sides of the camber line. The thickness ratio of the blunt trailing edge of the modified airfoil, $t_{TE}/t_{max}$, is newly defined to analyze the effects of the blunt trailing edge. The shape functions describing the upper and lower surfaces of the modified NACA64-418 with blunt trailing edge are obtained from the curve fitting of the least square method. To verify the accuracy of the present numerical analysis, the results are first compared with the experimental data of NACA64-418 with high Reynolds number, $Re=6{\times}10^6$, measured in the Langley low-turbulence pressure tunnel. Then, the aerodynamic performance of the modified NACA64-418 is analyzed. The numerical results show that the drag increases, but the lift increases insignificantly, as the trailing edge of the airfoil is thickened. Re-circulation bubbles also develop and increase gradually in size as the thickness ratio of the trailing edge is increased. These re-circulations result in an increase in the drag of the airfoil. The pressure distributions around the modified NACA64-418 are similar, regardless of the thickness ratio of the blunt trailing edge.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.74-83
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• 2001

In this study, internal fatigue crack initiation and propagation behavior were investigated by triple piece spot welded specimen. To estimate fatigue life of the specimen varied with shape and thickness, Crack tip opening angle(CTOA) correlated with stress intensity factor was used as the stiffness parameter. The relation between fatigue life and CTOA can be arranged by the quantitative equation for each specimen by experiment. In addition, the variation of stress distribution was solved and the effect on fatigue crack behavior was examined by finite element method(FEM).

• Proceedings of the KOSOMBE Conference
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• v.1993 no.11
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• pp.99-103
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• 1993

A monoleaflet polymer artificial heart valve which showed the remarkable improvement in pressure drop compared with other types of artificial valve was designed to decrease the deflection in vertical direction and the displacement or the valve tip in horizontal direction. Stress distribution change was studied as the location of the supporting members or the valve frame changed. And it was found that using the valve tip horizontal displacement the minimum valve thickness could be obtained in order to prevent the gap between the valve tip and the frame wall.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.673-677
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• 2004

The sensitivities of eigenvalues to the change of element thickness have been calculated for beams in the paper. For a cantilever beam the sensitivities fluctuate more for higher modes. When the thickness of the element near the fixed end increases, the eigenvalues for all modes increase. On the other hand, increasing of the thickness of the element at the tip decreases the eigenvalues for all modes. For a simply supported beam the sensitivities fluctuate more for higher modes, which is the same phenomenon as for a cantilever beam. The sensitivities are always positive for all modes

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.15-20
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• 1997

This study is to investigate the behavior of fatigue crack growth with ATOS 55 steel which can be applied to the commercial car Dump Frame. It is to obtain the material coefficients after tensile and fatigue crack growth test with the variation of thickness or heat treatment. Also, that is proved the Pari's law by experiment. The summarized results are as follows ; 1) Increasing thickness, tensile and yield strength measured highly regardless to heat treatment and measured lowly as variation of heat treatment temperature. 2) Specimen of thickness 8.0㎜ measured the faster of crack growth rate than another thickness according to the results of experiment. It was the different of stress conditions in crack tip. 3) It was found that the experimental constant m was range of 2∼5 to the relationship between fatigue crack growth rate and stress intensity factor range. Also, it was to prove the Paris's law by the experiment.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.772-776
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• 2001

The flow structures of turbulent shear layer behind oil fences with different tip configurations were investigated experimentally using flow visualization and PIV velocity field measurement. An oil fence was installed in a circulating water channel and the flow structure around the fence tip was mainly analyzed in this experiment. The four tip configurations tested in this experiment are knife edge; semi-circle edge, circular edge and rectangular edge. The 300 instantaneous velocity fields were measured using the single-frame PIV system and they were ensemble averaged to give the mean velocity field and spatial distribution of turbulent statistics. Free stream velocity was fixed at 10ms/sec and the corresponding Reynolds number based on the fence height was Re=4000. As a result, for the oil fence with rectangular edge, the streamwise velocity component was decreased. On the other hand it was increased for the oil fence with circular edge. For all four fences tested in this study, general flow pattern of the lower shear layer is analogous but the upper layer shows difference depending on the tip configurations. The oil fence with circular edge has more diffusive upper shear layer than that of the others. The shear layer of the oil fence with rectangular edge has relatively thin thickness. The oil fence with circular edge was found to be proper shape for tandem fence.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.111-116
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• 1991

주파수 영역에서 로터의 thickness noise는 블레이드의 여러가지 기하학적인 조건, 즉 블레이드 수, 블레이드의 사잇각, 에어포일의 모양 그리고 반경방향의 블레이드 끝모양에 따라서 해석되어진다. 본 논문은 비 등간격 로터의 기하학적 조건에 따른 음신호의 위상간섭 영향을 고찰하기 위해서 등간격을 이루는 로터에 대해서 해석된 Hanson의 방법을 확장하였다. thickness noise를 6개의 블레이드를 가진 로터에 대하여 15.deg., 30.deg., 45.deg., 비 등간격을 이루는 경우와 각각에 45 tip angle로 sweepback되었을 때 먼 거리의 음향학적 음신호와 그 스펙트럼을 계산하였다.

• Tribology and Lubricants
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• v.9 no.1
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• pp.45-54
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• 1993

The lubrication characteristics of line contacts between the vane and cam ring in an oil hydraulic vane pump with intravanes have been investigated. Variations of the radial acting force of a vane were calculated from previously measured results of dynamic internal pressures in four chambers surrounding a vane, and variations of the film thickness were estimated in both the rotational speed range from 500 to 1500 rpm and in the delivery pressure range from 1 to 14 MPa. The results indicate the variations of the radial acting force and film thickness. It is found that the regimes of lubrication in the vane tip contacts lover rigid-isoviscous to rigidvariable viscosities.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.112-120
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• 1993

Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode 1/3 stress intensity factors $K_{1}$ and $K_{3}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. the parameters used in this study were dimensionless crack length .lambda. crack slant angle .alpha, thickness ratio .betha. and width ratio .omega. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method proposed by Ingraffea and Manu. The effect of thickness ratio .betha. on $K_{1}$ is relatively great in comparison to $K_{3}$.

• Bulletin of the Korean Chemical Society
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• v.23 no.1
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• pp.71-74
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• 2002

The apparent barrier height for charge transfer through an interfacial water layer between a Pt/Ir tip and a gold surface has been measured using STM technique. The average thickness of the interfacial water layer inside an STM junction was controlled by the amount of moisture. A thin water layer on the surface was formed when relative humidity was in the range of 10 to 80%. In such a case, electron tunneling through the thin water layer became the majority of charge transfers. The value of the barrier height for the electron tunneling was determined to be 0.95 eV from the current vs. distance curve, which was independent of the tip-sample distance. On the other hand, the apparent barrier height for charge transfer showed a dependence on tip-sample distance in the bias range of 0.1-0.5 V at a relative humidity of approximately 96%. The non-exponentiality for current decay under these conditions has been explained in terms of electron tunneling and electrochemical processes. In addition, the plateau current was observed at a large tip-sample distance, which was caused by electrochemical processes and was dependent on the applied voltage.