• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.717-720
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• 2002

An Amplitude Proportional Friction Damper (APFD) system is considered in order to improve the stick-slip characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. The free vibration analysis on an 1-DOF system has conducted to demonstrate the characteristics of the APFD system and the results show that the APFD system has similar damping characteristics to the viscous damper system. It is concluded that the APFD system may become a cost effective substitution for the viscous damper and it also has certain advantages over Coulomb damper system since the APFD system can be designed to work with no stick-slip.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.55-62
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• 2016

Nuclear fuels are always exposed to hot temperature and high speed coolant flow during the reactor operation. Thus the fuel rod accompanies small amplitude vibration due to the turbulent flow. The random vibration causes friction between the fuel rod and the grid structure which provides the lateral supports. The friction is critical to the fuel rod fretting wear, and it degrades fuel performance when a severe wear is developed. LuGre friction model is introduced in the paper, and the performance was evaluated comparing to the classical Coulomb model. It is shown that the developed friction force considering the Coulomb friction is not enough to stop or delay the motion while the stick-slip can be simulated using LuGre friction model. Numerical solutions of the two dimensional spacer grid cell model with the modern friction are also reviewed, and it is discussed that the new friction model simulates well the nonlinear mechanism.

• 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.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.516-520
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• 2011

본 논문에서는 먼저 흥인지문에 대해 상시진동실험을 수행하고, 그 데이터를 분석하여 흥인지문의 고유진동수, 모드, 감쇠비의 특성을 분석하였다. 그 결과로부터 흥인지문의 병진모드를 파악하였고, 병진모드에서 측정한 여러 기둥의 모드 상대크기와 위상이 동일함을 확인하였다. 저차 병진모드에서 모든 기둥이 같은 방향으로 강성을 발휘하기 때문에 각층의 강성을 합한 등가의 층강성을 가지는 2자유도의 동적강체해석모델을 제시하였다. 이 해석모델은 선형 범위 내에서 거동한다는 것으로 가정하여 층강성을 산정하였다. 실제 흥인지문의 접합부에는 부재간의 이음과 맞춤에 의한 마찰력이 작용한다. 접합부를 누르는 무거운 지붕하중에 의해 이 마찰력은 증가하게 되고, 이로써 횡하중에 저항하게 된다. 이러한 접합부에 강한 횡하중이 작용하게 되면, 접합부의 이완 및 마찰력의 저하 등으로 인하여 횡강성의 저하가 급격히 일어나는 비선형 특성을 갖게 된다. 이러한 흥인지문의 비선형적인 특성을 파악하기 위해 흥인지문 해석모델에 쿨롱 마찰력을 도입하여 비선형적인 해석모델을 제시하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.947-954
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• 2014

In general, Fracture of the material is not occurring of the maximum normal stress or the maximum shear stress failure in the state. Maximum normal stress and maximum shear stress in the state of Critical coupling from being destroyed based on the Mohr-Coulomb theory. Couple of different mixtures, including permeable asphalt pavement, SMA and dense-graded asphalt mixture, were used for compression triaxial test at $45^{\circ}C$ and $60^{\circ}C$. Mohr-Coulomb theory to the analysis of compression triaxial test result of the internal friction angle $38.9^{\circ}{\sim}46.9^{\circ}$ measured somewhat irregularly, but in the case of cohesion, depending on whether the temperature and immersion of the specimen appeared differently. In addition, Indirect tensile test and compression triaxial test of the asphalt mixture to determine the correlation between compression triaxial test results assessed as cohesion and internal friction angle calculated using the theoretical Indirect tensile strength and measured indirectly tensile strength were analyzed. The Measured & Predicted IDT St values tended to be proportional.

• 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.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.172-183
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• 2019

The generalized Hoek-Brown (GHB) failure criterion developed by Hoek et al. (2002) is a nonlinear function which defines a stress condition at failure of rock mass. The relevant strength parameter values are systematically determined using the GSI value. Since GSI index is a value quantifying the condition of in-situ rock mass, the GHB criterion is a practical failure condition which can take into the consideration of in-situ rock mass quality. Considering that most rock mechanics engineers are familiar with the linear Mohr-Coulomb criterion and that many rock engineering softwares incorporate Mohr-Coulomb criterion, the equations for the equivalent friction angle and cohesion were also proposed along with the release of the GHB criterion. The proposed equations, however, fix the lower limit of the minor principal stress range, where the linear best-fitting is performed, with the tensile strength of the rock mass. Therefore, if the tensile stress is not expected in the domain of analysis, the calculated equivalent friction angle and cohesion based on the equations in Hoek et al. (2002) could be less accurate. In order to overcome this disadvantage of the existing equations for equivalent friction angle and cohesion, this study proposes the analytical formula which can calculate optimal equivalent friction angle and cohesion in any minor principal stress interval, and verified the accuracy of the derived formula.

• Tunnel and Underground Space
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• v.25 no.3
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• pp.284-292
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• 2015

The generalized Hoek-Brown failure criterion, the strength parameters of which are determined by using the GSI index, is an empirical nonlinear failure criterion of rock mass and has been widely employed in various rock engineering practices. Many rock engineering practitioners, however, are still familiar with the description of the strength of rock mass in terms of friction angle and cohesion. In addition, almost all rock mechanics softwares incorporate the simple linear Mohr-Coulomb function. Therefore, it is necessary to provide a tool to implement the Hoek-Brown function in the framework of the Mohr-Coulomb criterion. In this study, the use of upper-bound solution of limit analysis for bearing capacity of a strip footing resting on the ground surface is proposed for the estimation of the equivalent friction angle and cohesion of rock mass incorporating the generalized Hoek-Brown failure criterion. The upper-bound bearing capacity is expressed in terms of friction angle by use of the relationship between tangential friction angle and tangential cohesion implied in the generalized Hoek-Brown function. The friction angle minimizing the upper-bound bearing capacity is taken as the equivalent friction angle. Through the illustrative implementations of the proposed method, the influences of GSI, $m_i$ and D on the equivalent friction angle and cohesion are investigated.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.35-42
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• 2004

The control systems with friction cause the steady state error and slow response, because friction is a sensitive to the change of system condition and has highly nonlinear characteristics. To overcome these problems and do precise position control for a ball-screw system, we use Coulomb friction estimator and the sliding mode control(SMC) to compensate its negative effect. The applied SMC for tracking position has a characteristics of robust stability and reducing chattering, and is derived from the Lyapunov stability theorem and reaching condition. Compensating the estimated friction torque to the bounded disturbance term of the SMC's equivalent control input, it has a tracking performance better than the PID from the experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.171-179
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• 2003

An Amplitude Proportional Friction Damper (APFD) is considered in order to improve the characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. A free vibration analysis on the 1-DOF system has made to demonstrate the characteristics of the APFD system. The results show that APFD system has similar damping characteristics to the viscous damper. Also, the solution for the response of a base-excited system with APFD is developed through the application of a Fourier series to represent the frictional force of APFD. It is assumed that no stick-slips occur during any portion of the steady-state oscillation.