• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.14-17
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• 2004

A purpose of this visual experiment is to investigate the effect of reduced frequency qualitatively by examining wake pattern change for insect flying motion. Insect is composed of two pair wing with forewing and hindwing, flying motion of insect is performed pitching and plunging so it makes a separation over the wings. The separation affects at the wake pattern and changed wake pattern has an influence on lift, drag and propulsion. This experiment is conducted by using a smoke wire technique and a camera is fixed at hindwing to take a photograph of wake. An electronic device is mounted below test section to find exact the mean positional angle of wing. The reduced frequency in experiment is 0.15, 0.3 and 0.45. We obtained the result which that reduced frequency is closely related to wake pattern that determines flight efficiency.

• Tribology and Lubricants
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• 제29권4호
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• pp.223-227
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• 2013

A GAF (generated axial force) is produced at a plunging-type CVJ (constant velocity joint). A high GAF can cause vibrations in a vehicle. Grease is used to reduce friction between the roller and the track of the outer case of a CVJ. The grease performance depends on the surface conditions and operating temperature. The surface of the outer case is extremely rough and hard. In recent times, the maximum operating temperature of CVJs has crossed $140^{\circ}C$, because the exhaust line is now located close to the CVJ. In this study, we examined the friction characteristics of friction additives at $25-150^{\circ}C$ and determined an optimal formulation with a low friction coefficient. This formulation can be used to develop low-friction grease that can reduce the GAF produced at a CVJ by approximately 7-26%.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.183-185
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• 2005

In an attempt to optimize friction spot joining process of Mg alloys, effects of joining parameters such as rotating speed, plunging depth, and dwelling time on the joints properties were evaluated. Experimental tests were carried out for lap joined AZ31B-H24 sheets. A wide range of joining conditions could be applied to join Mg alloys without defects in the weld zone except for certain welding conditions with an insufficient heat input. The microstructures and hardness variations in the weld regions are discussed. For sound joints without defects, tensile shear strength of weld joints was higher approximately 116% than typical tensile shear strength of electrical resistance spot-welded joints for magnesium(Welding handbook, Vol 3, AWS).

• 한국항공운항학회지
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• 제14권2호
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• pp.39-44
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• 2006

The unsteady vortex lattice method is used to model lead-lag in flapping motions of a rectangular flat plate wing. The results for plunging and pitching motions were compared with the limited experimental results available and other numerical methods. They show that the method is capable of simulating many of the features of complex flapping flight. The lift, thrust and propulsive efficiency of a rectangular flat plate wing have been calculated for various lead-lag motion and reduced frequency with an amplitude of flapping angle(20o). To describe a motion profile of wing tip such as elliptic, line and circle, the phase difference of flapping and lead-lag motion was changed. And the effects of the motion profile on the aerodynamic characteristics of the flapping wing are discussed by examination of their trends.

• Journal of Welding and Joining
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• 제24권1호
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• pp.50-55
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• 2006

In an attempt to optimize friction spot joining process of Al alloys for automobiles, effects of joining parameters such as tool rotating speed, plunging depth, and joining time on the joints properties were investigated. A wide range of joining conditions could be applied to join Al alloys for automobile without defects in the weld zone except for certain welding conditions with a lower heat input. For sound joints without defects, tensile shear strength of joints was higher than acceptable criteria of tensile shear strength of resistance spot welded joints for aluminum.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.177-179
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• 2005

In an attempt to optimize friction spot joining Process of Al alloys for automobiles, joining parameters such as tool rotating seed, plunging depth, and joining time on the joints properties were investigated. A wide range of joining conditions could be applied to join Al alloys for automobile without defects in the weld zone except for certain welding conditions with a lower heat input. for sound joints without defects, tensile shear strength of joints was higher than acceptable criteria of tensile shear strength of resistance spot welded joints for aluminum.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.35-40
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• 2002

This paper deals with a thrust generation on flapping-airfoil by dynamic stall. Dynamic stall refers to a series of complicated aerodynamic phenomena accompanied by a stall delay in unsteady motion. In most cases, once it occurs, the dynamic stall may lead to an abrupt fluctuation of aerodynamic forces. An inverse $k\acute{a}rm\acute{a}n$ vortex has been considered as a main reason for a thrust generation. In this paper, however, we have found out that a thrust is closely related to reduced frequency and leading edge vortex in addition to inverse Karman vortex. In order to certify our opinion, picking and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

• Journal of Advanced Marine Engineering and Technology
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• 제33권6호
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• pp.873-879
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• 2009

The steady breakers at an infant stage are investigated through the numerical simulation. The appearing condition and characteristics of the sub-breaking waves are reviewed by analysing bow waves. The instability analysis is possibly done through the relationship between the free-surface curvature and circumferential force, which is obtained from the momentum equations. Navier-Stokes equations are solved by a finite difference method where the body-fitted coordinate system, the wall function and the advanced mesh system are invoked. The numerical result shows that the gradient of M/$U_s$ is greatly influenced by the Froude number and the decrease of M/$U_s$ indicates that the flows are unstable. Additionally flows with plunging or spilling are simulated successfully, but the application of breakers to the severely broken wave still remains to be settled in the future.

• 대한기계학회논문집
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• 제13권3호
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• pp.419-423
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• 1989

본 연구에서는 담금유의 냉각능에 관한 상세한 연구는 우리나라에서는 아직 미비한 상태에 있으나, 저자 등은 제1보에서 서술한 실험장치 및 은시편을 사용하여 여러 광.식물성유의 냉각곡선을 구하고, 이로부터 냉각성능을 나타내는 파라미터들을 구하여, 객관적인 냉각성능을 평가하였다.

• 한국수정란이식학회지
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• 제9권1호
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• pp.111-116
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• 1994

This study was carried out to investigate the aggregation rate of isolated mouse 2-, 4- and 8-cell stage blastomeres in phytohemagglutinin(PHA) solution. The morphologically normal embryos were collected from the oviduct of superovulated female mouse by flushing with M2 and the zona pellucida of embryos were removed with 0.5% pronase. The blastomeres were isolated by pipetting after plunging into Ca++-Mg++free PBS for 20 min. The result showed that aggregation rate in 0.5% (84.9~93.1%) was higher than that in 1.0% PHA(76.0~82.1%). Optimal aggregation time was 60min (83.9~100.0%) when compared with 30min (78.8~87.5%). Developmental to blastocyst in recombinated blastomeres was higher under conditions of 0.5% PHA solution and 60-min aggregation than that under other conditions.