• Tribology and Lubricants
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• 제24권6호
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• pp.355-361
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• 2008

In highly stressed machine elements such as angular contact ball bearings and toroidal type traction drives, the elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning motion are occur. In this paper, a finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various ellipticity parameter, dimensionless speed and load parameter. The results showed that the spinning motion has significant influence especially on the film shapes. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. Especially variations of the minimum film thicknesses with rolling velocity, load and ellipticity ratio are a great different from those of pure rolling. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• Tribology and Lubricants
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• 제23권2호
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• pp.49-55
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• 2007

A numerical analysis of elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning has been carried out. A finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. The velocity vectors resulting from combined spinning and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. The spin motion have large effect on variations of the minimum film thickness with load parameter which are small in pure rolling/sliding cases. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• 한국전산유체공학회지
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• 제14권4호
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• pp.48-55
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• 2009

In this study, roll lock-in phenomena of freely spinning tailfins were investigated by a CFD code. To analyze a motion of freely spinning tailfins, this research use a Chimera method, an Euler code and a 6 degrees of freedom analysis. The numerical results of aerodynamic characteristics and roll rates of a canard-controlled missile with freely spinning tailfins show a good agreement with wind tunnel test results. Using the roll rates calculation result of freely spinning tailfins, roll lock-in phenomena is confirmed. Roll lock-in phenomena and Roll lock-in states can be predicted through effects of the induced vortex of the canards control and the analysis of the rolling moments of tailfins due to the bank angle.

• 한국항공우주학회지
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• 제38권9호
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• pp.849-855
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• 2010

본 논문은 자유회전 테일핀을 갖는 커나드 유도 미사일에 대해 Falanga의 회전율 계산식을 자유회전 테일핀에 적용하여 자유회전 테일핀의 roll lock-in 현상을 예측하였다. 예측 결과의 정확도를 확인하기 위하여 Blair의 풍동시험 결과와 비교하여 검증하였다. 자유회전 테일핀의 회전율 계산 시에 필요한 테일핀의 롤링 모멘트는 풍동시험 결과를 이용하였고 롤 댐핑 모멘트는 missile DATCOM을 이용하여 계산하였다. 이를 자유회전 테일핀의 회전율 계산식에 대입하여 자유회전 테일핀의 회전율 및 Roll lock-in 현상을 예측하였으며 풍동시험 결과와 비교하였다. 검증결과, 자유회전 테일핀의 회전율 및 Roll lock-in 현상 예측 결과가 풍동시험 결과와 잘 일치하는 것을 확인 할 수 있었다.

• 한국항공우주학회지
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• 제36권3호
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• pp.220-228
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• 2008

반실험적 기법과 CFD 코드를 이용하여 자유회전 테일핀을 갖는 커나드 조종 미사일의 공력특성을 연구하였다. 반실험적 기법에서는 테일핀의 회전각에 따른 공력계수의 평균을 구한 후 자유회전 테일핀의 공력계수를 계산하였다. 또한 테일핀의 평균 롤링 및 롤 댐핑 모멘트계수를 이용하여 자유회전 테일핀의 회전율을 예측하였다. CFD 계산의 경우 중첩격자를 이용한 6-자유도 해석을 통해 테일핀의 회전율을 계산하였다. 미사일의 공력계수 예측 값들은 풍동실험 결과와 유사하게 나타났고, 커나드 롤 조종 및 요 조종시의 테일핀 회전율 또한 풍동실험결과와 근접하게 나타났다. 본 연구를 통해 자유회전 테일핀을 갖는 커나드 조종 미사일에 관한 공력해석에 반실험적 기법을 적용할 수 있음을 확인하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.310-315
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• 2001

The most general feature of contact zone among the mechanical components is elliptical circle. In particular, continuously variable transmission (CVT) of toroidal type has elliptical shape of contact zone under the elastohydrodynamic lubrication condition, where the power is transmitted by the shearing the efluid. Due to the traction of the shear behaviors of lubricant over the small elliptical contact zone, high power of torque is transmitted. During the power transmission, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spinning. The spinning effect that is not common contact behavior in tribological components frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of elastohydrodynamic lubrication with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.

• 한국정밀공학회지
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• 제13권8호
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• pp.13-27
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• 1996

소성가공이란 원재료를 소성변형(Plastic deformation)을 통해서 고체의 제품을 만드는 가공법이다. 가공중에 물체의 질량과 체적에는 크게 변화가 없다. 소성 가공중 주응력이 어떻게 작용하느냐에 따라서 소성가공을 여러가지로 분류하고 있다. 즉, Metal Forming은 다음과 같이 분류할 수 있다. 1) Compound Forming에는, Rolling, Free forming, Die forming, Stamping, Pressing 2) Tension compression forming에는, Drawing, Deep-drawing, Rimming, Spinning, Bulge forming 3) Tension forming에는 Lengthening, Widning, Deepening 4) Bending에는 Bending with linear tool motion, Bending with rotary tool motion 5) Thrust forming에는 Swaging, Twisting이 있다.

• 소성∙가공
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• 제21권4호
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• pp.234-239
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• 2012

This study examines the forming properties and forming loads needed to increase the edge thickness on the external face of a plate using finite element analysis(FEA). Recently, forming optimization techniques within FEA are being extensively used in designing the optimal forming conditions for processes like forging, extrusion, rolling, and spinning. Most of these existing forming operations involve reducing the volume per unit length, but research for increasing volume per unit length is not very extensive. For this study we chose an automotive engine flywheel which is a welded assembly of a plate and a gear with each component having a different thickness. We considered a forming technique to increase the thickness in order to allow the machining of the gear directly on the external face of plate alleviating the need for a weld. To study various forming techniques, we used the finite element method with the flow stress of material and incremental forming steps. We conclude from this study that the analysis of forming properties and forming loads by using the finite element analysis and testing is useful as a method to increase the thickness per unit length.