• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1481-1486
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• 2007

Frictional laws are criticized with emphasis on their application to bulk metal forming simulation in this paper. Coulomb frictional law and constant shear frictional law are investigated in detail in terms of their effect on metal forming process. A friction sensitive bulk metal forming process, a long-pipe simultaneously shrinking and expanding process, is introduced and the problems of the constant shear frictional law are revealed comparing the predictions obtained by the Coulomb frictional law and the constant shear frictional law with the experiments. It is shown that the constant shear frictional law is improper in the case that the normal stress varies very much from position to position and that the normal stress is low compared with flow stress of the adjacent material. It is also shown that the Coulomb frictional constant is more or less affected by the normal stress.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1545-1551
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• 1992

This work is concerned with the prediction of turbulent friction factors in rod bundles. In this study, the Law of the Wall is assumed to be valid over the entire flow area. The flow channel is divided into element channels, and the algebraic form of the "Law of the Wall" is integrated over each element channel to yield an analytic expression for the pressure drop in the rod bundle. The method is applied to rod bundles with 1.2

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.102-109
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• 1996

Effects of frictional laws on finite element solutions in metal forming were investigated in this paper. A rigid-viscoplastic finite element formulation was given with emphasis on the frictional laws. The Coulomb friction and the constant shear friction laws were compared through finite element analyses of compression of rings and cylinders with different aspect ratios, ring-gear forging, multi-stage cold extrusion and hot strip rolling under the isothermal condition. It has been shown that two laws may yield quite different results when the aspect ratio of a process and the fractional contact region are large.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.23-30
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• 2011

본 연구는 산업용 열교환기 및 상용 파이프의 최적 설계를 위하여 열교환기 내의 사각형 단면 파이프의 shear-thickening 비뉴톤 유체의 압력강하 및 대류 열전달률을 수치해석적으로 수행하였다. shear-thickening 유체의 구성 방정식은 기존의 비뉴톤 유체 멱법칙을 보완한 확장 멱법칙 모델을 채택하였다. 파이프 내의 압력강하를 의미하는 마찰계수와 확장 레이놀즈 수의 곱은 기존 연구의 비교자료와 비교할 때 뉴톤 유체 영역과 멱법칙 영역에서 각각 0.018% 및 0.06% 내에서 일치함을 보였고, 대류 열전달률을 의미하는 뉴셀트 수는 문헌치와 비교할 때 뉴톤 유체 영역과 멱법칙 영역에서 각각 0.025% 및 0.14% 내에서 일치함을 보였다. 비뉴톤 확장 멱법칙 유체 모델의 형태를 띠는 shear-thickening 유체를 열교환기 또는 상용파이프 내의 사각형 단면 파이프 내에서 사용하면 유동지수(n)에 따라서 뉴톤 유체보다 최대 160%의 압력강하를 증가시켰고 최대 14%의 대류 열전달 감소를 발생시킬 수 있었다.

• Journal of Wetlands Research
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• v.21 no.3
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• pp.207-214
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• 2019

This study investigated the flow characteristics in an annular flume with a free water surface using the Acoustic Doppler Velocimeter(ADV) in the laboratory. The flow was driven by the rotation of the inner cylinder in a way designed not to interfere with flocculation of cohesive sediments. The effect of the inner cylinder for the longitudinal velocities showed highest near the moving boundary and decreased towards the outer wall. At the lower longitudinal velocity, there was a peak in turbulent kinetic energy near the bed, whereas it moved upward to with increasing of the velocity. The longitudinal velocities estimated using the power law were in good agreement with the measured values than the values predicted by the log-law with roughness lengths. The average friction velocities evaluated by Reynolds shear stress were smaller than the values calculated using the log-law and power law when increasing the longitudinal velocity.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.51-57
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• 2012

본 연구는 컴팩트한 열교환기의 설계를 위하여 열교환기 내의 원형 단면 도관의 유변 유체의 압력 강하 및 대류 열전달률을 수치해석적으로 수행하였다. 유변 유체의 구성방정식은 기존의 비뉴톤 유체 멱법칙을 보완한 수정 멱법칙 모델을 채택하였다. 도관 내의 압력강하를 의미하는 마찰계수와 수정 레이놀즈 수의 곱은 기존 문헌치와 비교할 때 뉴톤 유체 영역과 유변 멱법칙 영역에서 각각 0.01% 및 0.004% 내에서 일치함을 보였고 유변 수정멱법칙 유체 모델의 형태를 띠는 유변 유체를 열교환기 내의 원형 단면 도관 내에서 사용하면 뉴톤 유체보다 최대 58%의 압력강하를 감소시켰고 최대 9%의 대류 열전달 증가을 발생시킬 수 있었다.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.4
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• pp.264-269
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• 1996

본 논문에서는 디스트리뷰션 인테그랄 서브매니폴드에 의하여 표현되는 마찰이 없는 면을 따라 강체 로봇 매니퓰레이터의 모션 제어에 대한 새로운 힘.위치 제어법칙은 힘/위치가 제어되는 방향으로 투영된 앤드 이팩트의 비선형 항을 정확하게 상쇄하도록 설계하였으며, 미분기하학을 이용하여 스무스 디스트리뷰션의 인테그랄 서브매니폴드 상에서의 새로운 모션 방정식을 제안하고 제안된 힘/위치 제어법칙에 대한 타당성을 컴퓨터 시뮬레이션을 통하여 검증한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1513-1518
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• 1992

Numerical solution technique is suggested to analyze the vibration of a spring composed of stacked beams fastened together. Bernoulli-Euler beam theory for small deflection is used, and incremental Coulomb friction law is adopted for the interface friction. The validity of the present solution technique is checked for the perfectly bonded case and the perfect sliding case.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.3
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• pp.157-162
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• 2005

This paper presents an adaptive compensator using the fuzzy systems for robot manipulator with unknown frictions. In general, frictions are neglected or dynamic frictions are only considered in robot control theories. The proposed control method considers viscous frictions as well as dynamic frictions. Using the property that the frictions of joints are decoupled, SISO-fuzzy systems are utilized to approximate each friction. The stability of overall control system is proven and the adaptive laws are derived based on Lyapunov stability theorey. To verify the validity of the proposed control strategy, the results of computer simulations are shown for 2-link robot manipulator. The ability of approximating of the fuzzy system is also shown.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2026-2038
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• 1994

A numerical scheme is developed for the analysis of incipient sliding contact with orthotropic friction condition subjected to tangential load and twisting moment. The inherent nonlinearity in the orthotropic friction law has been treated by a polyhedral friction law. Then, a three-dimensional linear complementarity problem(LCP) formulation in an incremental form is obtained, and the existence of a solution is investigated. A Lemke's complementary pivoting algorithm is used for solving the LCP. The scheme is illustrated by spherical contact problems, and the effects of eccentricity of elliptical friction domain on the traction and stick region are discussed.