• Title/Summary/Keyword: Coulomb friction

Search Result 226, Processing Time 0.02 seconds

Estimation of Equivalent Friction Angle and Cohesion of Near-Surface Rock Mass Using the Upper-Bound Solution for Bearing Capacity of Strip Footing (줄기초 지지력 상계해를 활용한 천부 암반의 등가마찰각과 등가점착력 산정)

  • Lee, Youn-Kyou
    • Tunnel and Underground Space
    • /
    • v.25 no.3
    • /
    • pp.284-292
    • /
    • 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.

Friction tuned mass damper optimization for structure under harmonic force excitation

  • Nasr, Aymen;Mrad, Charfeddine;Nasri, Rachid
    • Structural Engineering and Mechanics
    • /
    • v.65 no.6
    • /
    • pp.761-769
    • /
    • 2018
  • In this work, an optimization method of Friction Tuned Mass Damper (FTMD) parameters is presented. Friction tuned mass dampers (FTMD) are attached to mechanical structures to reduce their vibrations with dissipating the vibratory energy through friction between both bodies. In order to exploit the performances of FTMD, the determination of the optimum parameters is recommended. However, the presence of Coulomb's friction force requires the resolution of a non-linear stick-slip problem. First, this work aims at determining the responses of the vibratory system. The responses of the main mass and of the FTMD are determined analytically in the sticking and sliding phase using the equivalent damping method. Second, this work aims to optimize the FTMD parameters; the friction coefficient and the tuned frequency. The optimization formulation based on the Ricciardelli and Vickery method at the resonance frequencies, this method is reformulated for a system with a viscous damping. The inverse problem of finding the FTMD parameters given the magnitude of the force and the maximum acceptable displacement of the primary system is also considered; the optimization of parameters leads to conclude on the favorable FTMD giving significant vibration decrease, and to advance design recommendations.

Seismic response control of a building complex utilizing passive friction damper: Analytical study

  • Ng, C.L.;Xu, Y.L.
    • Structural Engineering and Mechanics
    • /
    • v.22 no.1
    • /
    • pp.85-105
    • /
    • 2006
  • Control of structural response due to seismic excitation in a manner of coupling adjacent buildings has been actively developed, and most attention focused on those buildings of similar height. However, with the rapid development of some modern cities, multi-story buildings constructed with an auxiliary low-rise podium structure to provide extra functions to the complex become a growing construction scheme. Being inspired by the positively examined coupling control approach for buildings with similar height, this paper aims to provide a comprehensive analytical study on control effectiveness of using friction dampers to link the two buildings with significant height difference to supplement the recent experimental investigation carried out by the writers. The analytical model of a coupled building system is first developed with passive friction dampers being modeled as Coulomb friction. To highlight potential advantage of coupling the main building and podium structure with control devices that provide a lower degree of coupling, the inherent demerit of rigid-coupled configuration is then evaluated. Extensive parametric studies are finally performed. The concerned parameters influencing the design of optimal friction force and control efficiency include variety of earthquake excitation and differences in floor mass, story number as well as number of dampers installed between the two buildings. In general, the feasibility of interaction control approach applied to the complex structure for vibration reduction due to seismic excitation is supported by positive results.

A Study on the Large Deformation of Silicon Rubber Gasket with Hollow Circular Section (실리콘 중공 가스켓의 대변형에 관한 연구)

  • 이태원
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.20 no.11
    • /
    • pp.150-157
    • /
    • 2003
  • In this paper, the large deformation of hollow silicon rubber gasket is treated. The frictional contact occurs between groove and the outer part of hollow gasket, and the frictional self-contact exists in the inner parts of hollow gasket. The silicon rubber has the nonlinear elastic behavior and its material property is approximately incompressible. Hence, the stress analysis requires an existence of a strain energy function, which is usually defined in terms of invariants or stretch ratio such as generalized Mooney-Rivlin and Ogden model. Considering large compressive deformation and friction, Mooney-Rivlin 3rd model and Coulomb's friction model are assumed. The numerical analysis is obtained by the commercial finite element program MARC. But, due to large deformation, the elements degenerate in the inner parts of hollow gasket. This means that the analysis of subsequent increments is carried out with a very poor mesh. In order to continue the analysis with a sufficient accuracy, it is necessary to use new finite element modeling by remesh. Experiments are also performed to show the validity of present method. As a conclusion, numerical results by this research have good agreements with experiments.

A Study on the Structural Stiffness and Coulomb Damping of Air Foil Bearing Considering the Interaction among Bumps (범프들의 상호작용을 고려한 공기 포일 베어링의 구조적 강성 및 쿨롱 감쇠에 대한 연구)

  • Lee, Yong-Bok;Park, Dong-Jin;Kim, Chang-Ho
    • Tribology and Lubricants
    • /
    • v.22 no.5
    • /
    • pp.252-259
    • /
    • 2006
  • Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performances, stiffness, damping coefficient and load capacity, depend on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1 mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.

A Study on the Structural Stiffness and Coulomb Damping of Air Foil Bearing Considering the Interaction among Bumps (범프들의 상호작용을 고려한 공기 포일 베어링의 구조적 강성 및 쿨롱 감쇠에 대한 연구)

  • Park, Dong-Jin;Kim, Chang-Ho;Lee, Sung-Chul;Lee, Yong-Bok
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2006.05a
    • /
    • pp.1135-1141
    • /
    • 2006
  • Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performance, stiffness, damping coefficient and load capacity, depends on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.

  • PDF

Vibration Analysis of a Stacked beam Including Frictional Contact Force (마찰 접촉력을 고려한 다발 보(Stacked Beam)의 진동 해석)

  • 이기수;임철호
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.8
    • /
    • pp.1513-1518
    • /
    • 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.

Evaluzation of Model equation Predicting Roll Force and Roll Power during Hot Rolling (열간압연중 압연하중 및 압연동력 예측 모델)

  • 곽우진;황상무
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • 1999.08a
    • /
    • pp.308-312
    • /
    • 1999
  • Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

  • PDF

Anisotropic Version of Mohr-Coulomb Failure Criterion for Transversely Isotropic Rock (횡등방성 암석의 강도해석을 위한 이방성 Mohr-Coulomb 파괴조건식)

  • Lee, Youn-Kyou;Choi, Byung-Hee
    • Tunnel and Underground Space
    • /
    • v.21 no.3
    • /
    • pp.174-180
    • /
    • 2011
  • An anisotropic version of Mohr-Coulomb failure criterion is proposed in order to provide a strength criterion for transversely isotropic rock. The concept of fabric tensor introduced by Pietruszczak & Mroz (2001) is employed to define the friction angle and cohesion as scalar functions of the fabric tensors. The anisotroy in these two strength parameters are calculated in association with the consideration of the relative rotation between the principal stress coordinate and the principal material triad. The critical plane on which the anisotropic function maximized is found by an optimization technique based on the Lagrange multiplier method. To demonstrate the performance of the anisotropic failure criterion, conventional triaxial tests on the samples having various inclinations of weakness plane are simulated and the resulting triaxial strength and dip angle of failure plane are discussed.

Anti-Sway Tracking Control of Container Cranes with Friction Compensation (마찰 보상을 갖는 컨테이너 크레인의 흔들림 억제 추종 제어)

  • Baek, Woon-Bo;Shin, Jin-Ho
    • Journal of the Korean Society of Manufacturing Technology Engineers
    • /
    • v.21 no.6
    • /
    • pp.878-884
    • /
    • 2012
  • In this paper, we consider the sway suppression control problem for container cranes with the frictions between the trolley and the rail. If the friction effects in the system can be modelled, there is an improved potential to design controllers that can cancel the effects. The proposed control improves the trolley positioning and sway suppressing against various frictions. The proposed synthesis combines a variable structure control and the adaptive control to cope with various frictions including the unknown constants. First, the variable structure control with the simple switching action is designed, which is based on a class of feedback lineariztion methods for the fast stabilization of the under-actuated sway dynamics of container. Second, the adaptive control with a parameter estimation is designed, which is based on Lyapunov stability methods for suppressing the oscillation of the trolley travelling, especially due to Coulomb friction in the vicinity of the target position. The asymptotic stability of the overall closed-loop system is assured irrespective of variations of rope length. Simulation are shown under initial sway, external wind disturbances, and various frictions.