Variable rotary friction

| C |
in the palette on the schematic

The block is designed to simulate the contact friction of two rotating surfaces with a variable pressing force.

The relative slip speed ω in rad/s is determined by the formula:

where ωC, ωR – angular speeds at ports "C" and "R", respectively, rad/s

Defining the friction curve is possible in two ways: the Stribeck curve and the tabulated curve.

Stribek curve

When using this method, the Stribeck friction curve [1] and viscous friction (Figure 1) are used to determine the friction torque.


Figure 1. Dependence of friction torque on relative speed
The friction torque is determined by the formula:



where:
  • TC and TC – torques applied to ports "C" and "R", respectively, Nm
  • Tbrk – breakaway friction torque, Nm
  • Tc – dry (coulomb) friction torque, Nm
  • ωth – breakaway angular speed, rad/s
  • C – damp ratio, s/rad
  • Fr – coefficient of internal friction, Nm·s/rad
Friction torques Tbrk and Tc are calculated depending on the value of the pressing force according to the formulas:



where:
  • N – pressing force, N
  • μ – breakaway friction factor
  • μs – dry (coulomb) friction factor
  • Reff – effective radius of the disk in meters which is set explicitly or calculated by the formula:

    where Ro – outer radius of the disk, m; Ri – inner radius of the disk, m

Tabulated curve

Using this method the friction factor is defined by interpolating a given table. If the slip speed exceeds the value specified in the table, extrapolation is not carried out.

The friction torque is determined by the formula:



where μ(|ω|) – friction factor value obtained as a result of interpolation.

Inputs

Name Description Connection line type
C Port for connecting a conditionally fixed case (case) Rotary mechanics
R Port for connecting a conditionally moving shaft (rotor) Rotary mechanics
N Specified pressing force Mathematical

Outputs

None.

Properties

Title Parameter Description By default Data type
Friction curve A group of properties that define the friction parameters
Friction model MType Friction model type The possible values are: "Stribek curve", "Tabulated curve” Stribek curve Перечисление
Breakaway friction factor Mu Breakaway friction factor. The property is available when selecting the model defining method as "Stribek curve" 0.3 Вещественное
Dry (coulomb) friction factor Mus Dry (coulomb) friction factor. The property is available when selecting the model defining method as "Stribek curve" 0.15 Вещественное
Damp ratio, s/rad C Damp ratio. The property is available when selecting the model defining method as "Stribek curve" 1 Вещественное
Coefficient of internal friction, Nm·s/rad Fr Coefficient of internal friction. The property is available when selecting the model defining method as "Stribek curve" 0.1 Вещественное
Array of speeds, rad/s Wx Array of slip speed values. The property is available when selecting the model defining method as "Tabulated curve" [0 , 0.1 , 0.2 , 0.3 , 0.4 , 0.5 , 1 , 2 , 5] Массив
Array of friction factors My Array of friction factor values. The property is available when selecting the model defining method as "Tabulated curve" [0.29 , 0.28 , 0.26 , 0.22 , 0.21 , 0.2 , 0.2 , 0.19 , 0.19] Массив
Geometry A group of properties that define the geometric parameters of surfaces
Disk geometry defining method R_type Disk geometry defining method. The possible values are: "Outer and inner radii", "Effective radius" Outer and inner radii Перечисление
Outer disk radius, m Ro Outer disk radius. The property is available when selecting the method of defining the disk geometry as "Outer and inner radii" 0.15 Вещественное
Inner disk radius, m Ri Inner disk radius. The property is available when selecting the method of defining the disk geometry as "Outer and inner radii" 0.1 Вещественное
Effective disk radius, m Reff Effective disk radius. Changing the property is only possible when choosing the method of disk geometry defining as the "Effective radius", otherwise the property is displayed in the "Read-only" mode and is for reference only 0.12667 Вещественное
Breakaway angular speed, rad/s Wth The threshold value of the speed below which the value of the friction torque is reduced to achieve the stability of the numerical solution 0.001 Вещественное
Maximum pressing force, N Pth The maximum pressing force limiting the value of defining pressing force 1000 Вещественное

Parameters

Name Parameter Description Data type
Angular speed differential, rad/s W Relative slip speed Вещественное
Friction torque, Nm T Torque at the port "R" Вещественное
Power of friction torque, W Q Power of friction torque, W Вещественное

Examples

Examples of block application:

Literature

  1. Richard Stribeck: Die wesentlichen Eigenschaften der Gleit- und Rollenlager, Z. Verein. Deut. Ing. Vol. 46 Seite 38ff. 1341–1348 (1902).