Rotational Friction
Friction in contact between rotating bodies.
blockType: AcausalFoundation.Mechanical.Rotational.Elements.Friction
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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, , is a characteristic with a negative slope that occurs 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 referred to as resting friction . The friction is approximated by the following equations:
where
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— the moment of friction;
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— the moment of dry (Coulomb) friction;
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— the moment of friction at rest;
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— critical speed;
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— speed threshold for Strobe friction;
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— the threshold of the Coulomb velocity;
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and — the absolute angular velocities of ports R and C, respectively;
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— relative angular velocity;
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— 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.
Variables
Use the parameter group Initial Targets to set the priority and initial target values for the block parameter variables before modeling. For more information, see Configuring physical blocks using target values.
Parameters
Parameters
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Breakaway friction torque —
moment of friction at rest
N*m | uN*m | mN*m | kN*m | MN*m | GN*m | kgf*m | lbf*in | lbf*ft
Details
The moment of friction at rest. Must be greater than or equal to the parameter value. Coulomb friction torque.
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Breakaway friction velocity —
critical angular velocity for Shtribek friction
rad/s | deg/s | rad/min | deg/min | rpm | rps
Details
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 parameter Breakaway friction torque. This parameter sets the speed threshold, which affects the trade-off between simulation accuracy and speed.
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Coulomb friction torque —
the moment of dry friction
N*m | uN*m | mN*m | kN*m | MN*m | GN*m | kgf*m | lbf*in | lbf*ft
Details
The moment of Coulomb friction, that is, the friction that counteracts rotation with constant torque at any speed.
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Yes |
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Viscous friction coefficient —
coefficient of viscous friction
N*m/(rad/s) | ft*lbf/(rad/s)
Details
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.
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