Documentation

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.

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

Modeling Thermal Effects

You can model the effects of heat flow and temperature change through an optional thermal conserving port. By default, the thermal port is hidden. To expose the thermal port, right-click the block in your model and, from the context menu, select Simscape > Block choices. Choose a variant that includes a thermal port. Specify the associated thermal parameters for the component.

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.

Ports

B

Translational conserving ports associated with the driving shaft

F

Translational conserving ports associated with the driven shaft

N

Physical signal terminal through which you import the normal force

H

Thermal conserving port. The thermal port is optional and is hidden by default. To expose the port, select a variant that includes a thermal port.

Parameters

Friction

Friction model

Select a parameterization method to model the kinetic friction coefficient. The options and default values for this parameter depend on the variant that you select for the block. The options are:

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

    • Is only visible if you use the default variant of the block

    • Is the default method for parameterizing the default variant of the block

    • Affects the visibility of other parameters

     Fixed kinetic friction coefficient

  • Table lookup kinetic friction coefficient — Define the kinetic friction coefficient by one-dimensional table lookup based on the relative angular velocity between disks. This option:

    • Is only visible if you use the default variant of the block

    • Affects the visibility of other parameters

     Table lookup kinetic friction coefficient

  • Temperature-dependent kinetic friction coefficient — Define the kinetic friction coefficient by table lookup based on the temperature. This option:

    • Is only visible if you use a thermal variant of the block

    • Is the default method for parameterizing the thermal variant of the block

    • Affects the visibility of other parameters

     Temperature-dependent kinetic friction coefficient

  • Temperature and speed-dependent kinetic friction coefficient — Define the kinetic friction coefficient by table lookup based on the temperature and the relative angular velocity between disks. This option:

    • Is only visible if you use the thermal variant of the block

    • Affects the visibility of other parameters

     Temperature and speed-dependent kinetic friction coefficient

Velocity tolerance

Relative velocity below which the two surfaces can lock. The surfaces lock if the torque across the B and F rotational ports is less than the product of the effective radius, the static friction coefficient, and the applied normal force. The default value is 0.001 rad/s.

Threshold force

The normal force applied to the physical signal port N is applied to the contact only if the amount of force exceeds the value of the Threshold force parameter. Forces below the Threshold force are not applied, and there is consequently no transmitted frictional torque. The default value is 1 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 value is 0 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 option.

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

Thermal Port

These thermal parameters are visible only when you select a block variant that includes a thermal port.

Thermal mass

Thermal energy required to change the component temperature by a single degree. The greater the thermal mass, the more resistant the component is to temperature change. The default value is 50 kJ/K.

Initial temperature

Component temperature at the start of simulation. The initial temperature alters the component efficiency according to an efficiency vector that you specify, affecting the starting meshing or friction losses. The default value is 300 K.

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