Loaded-Contact Translational Friction

Loaded-contact friction between two sliding bodies

Library

Brakes & Detents/Translational

Description

The Loaded-Contact Translational Friction block simulates friction between two sliding bodies loaded with a normal force.

The block is implemented as a structural component based on the Fundamental Friction Clutch block. From the locked state, the clutch unlocks if the friction force exceeds the static friction, as defined by the static coefficient of friction and current normal force. For details on how the locking and unlocking are modeled, see the Fundamental Friction Clutch block reference page.

Friction force is transmitted for normal forces larger than the Threshold force parameter.

Ports

B and F are translational conserving ports associated with the base and follower, respectively. N is the physical signal terminal through which you import the normal force.

Dialog Box and Parameters

Friction

Friction model

Select how to specify the kinetic friction coefficient. The default is Fixed kinetic friction coefficient.

  • Fixed kinetic friction coefficient — Provide a fixed value for the kinetic friction coefficient.

    Kinetic friction coefficient

    The kinetic, or Coulomb, friction coefficient. Must be greater than zero. The default is 0.3.

  • Table lookup kinetic friction coefficient — Define the kinetic friction coefficient by one-dimensional table lookup based on the relative angular velocity between disks. If you select this option, the panel changes from its default.

     Table lookup kinetic friction coefficient

Static friction coefficient

The static, or peak, value of the friction coefficient. Must be greater than the kinetic friction coefficient. The default is 0.35.

Velocity tolerance

Relative velocity below which the two surfaces can lock. For the surfaces to lock, the force across the B and F translational ports must be less than the product of the static friction coefficient and the applied normal force. The default is 0.001.

From the drop-down list, choose units. The default is meters/second (m/s).

Threshold force

The normal force applied to the physical signal port N must exceed the Threshold force parameter value to be applied to the contact. Forces below the Threshold force are not applied, and there is consequently no transmitted frictional torque. The default is 1.

From the drop-down list, choose units. The default is newton (N).

Viscous Drag

Viscous drag force coefficient

Viscous drag coefficient μvisc for computing the drag force. The coefficient depends on the type of operating fluid, fluid temperature, and the maximum distance between the sliding bodies. The default is 0.

From the drop-down list, choose units. The default is newton/(meters/second) (N/(m/s)).

Initial Conditions

Initial state

Select the initial condition applied to the Fundamental Friction Clutch state inside the block:

  • Locked — Translational ports B and F are initially locked together. This is the default.

  • Unlocked — Translational ports B and F are initially sliding relative to each other.

Loaded-Contact Translational Friction Model

The block simulates friction between two sliding bodies loaded with a normal force. When the two sliding bodies are not locked, the friction force is determined with the following equations:

Ffr = N · μ· sign(vrel) + Fvisc ,

Fvisc = μvisc · vrel ,

where:

FfrFriction force
NNormal force
μFriction coefficient
vrelRelative velocity
FviscViscous drag force
μviscViscous drag force coefficient

Limitations

  • The model does not account for body mass. Add mass terms externally to the B and F ports as required.

  • The model computes the friction force assuming a uniform distribution of the normal force.

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