Rotational Friction
Friction in contact between rotating bodies.
blockType: AcausalFoundation.Mechanical.Rotational.Elements.Friction
|
Path in the library: |
Description
Block Rotational Friction It is the friction caused by contact between rotating bodies. The friction moment is modeled as a function of relative velocity and calculated as the sum of the components of liquid, viscous, and mixed friction, as shown in the following figure.
Mixed friction, or Shtribek friction, , represents a negative slope characteristic occurring at low speeds. Dry or Coulomb friction , results in constant torque at any speed. Viscous friction it counteracts movement with a torque directly proportional to the relative velocity. The sum of mixed and dry friction near zero velocity is often called the resting friction . The friction is approximated by the following equations:
where:
-
— the moment of friction.
-
— the moment of dry (Coulomb) friction.
-
— the moment of friction at rest.
-
— critical speed.
-
— the speed threshold for the friction of the Strobe.
-
— the threshold of the Coulomb velocity.
-
and — the absolute angular velocities of ports R and C, respectively.
-
— relative angular velocity.
-
— coefficient of viscous friction.
The exponential function used in the part of the Shtribek friction force equation is continuous and decays at velocity values exceeding the critical angular velocity.
The hyperbolic tangent function used in the Coulomb part of the equation ensures that the resulting function is smooth and continuous when passing through , but quickly reaches its full value at non-zero speeds.
The positive direction of the block is from port R to port C. This means that if the speed of port R is greater than the speed of port C, the block transfers power from R to C.
Ports
R — mechanical rotary port
rotational mechanics
Mechanical rotary port, corresponds to a moving body.
C — mechanical rotary port
rotational mechanics
Mechanical rotary port, corresponds to a stationary body.
Parameters
Breakaway friction torque, N*m — resting friction moment
25.0 Nm (default)
The moment of friction at rest. Must be greater than or equal to the value of the Coulomb friction force parameter.
Breakaway friction velocity, rad/s is the critical angular velocity for the friction of the Strobe
0.1 rad/s (default)
The angular velocity at which the friction of the Strobe reaches its maximum. At this point, the sum of the Shtribek and Coulomb friction is equal to the value of the Breakaway friction torque parameter. This parameter sets the speed threshold, which affects the trade-off between simulation accuracy and speed.
Coulomb friction torque, N*m — dry friction moment
20.0 Nm (default)
The moment of Coulomb friction, that is, the friction that counteracts rotation with constant torque at any speed.
Viscous friction coefficient, N*m/(rad/s) — coefficient of viscous friction
0.001 Nm/(rad/s) (default)
The coefficient of proportionality between the moment of friction and the relative angular velocity. The parameter value must be greater than or equal to zero.
Initial value of rotational velocity, rad/s is the initial value of the angular velocity of
0.0 (default)
The initial value of the angular velocity.
Initial value of torque, N*m — the initial value of the torque
0.0 (default)
The initial value of the torque.