# Variable Rotational Damper

Rotational damper with variable damping coefficient

## Library

Couplings & Drives/Springs & Dampers

## Description

The block represents a rotational viscous damper with a variable damping coefficient. A physical signal input port provides the magnitude of the damping coefficient. The magnitude of the damping torque is equal to the product of the physical signal input and the relative angular velocity between the two rotational conserving ports, R and C. A minimum damping coefficient prevents non-physical negative damping values.

The damping torque satisfies the following expression:

$T=\left\{\begin{array}{cc}B\cdot \omega & B\ge {B}_{\mathrm{min}}\\ {B}_{\mathrm{min}}\cdot \omega & B<{B}_{\mathrm{min}}\end{array},$

The parameters are:

• T — Torque transmitted through damper

• B — Viscous damping coefficient

• ω — Relative angular velocity measured between the two rotational conserving ports according to $\omega ={\omega }_{R}-{\omega }_{C}$

• ωR — Angular velocity of rotational conserving port R

• ωC — Angular velocity of rotational conserving port C

The block applies equal and opposite damping torques on the rotational conserving ports. The sign of the damping torque acting on port R is equal to the sign of the relative angular velocity. A positive relative angular velocity corresponds to a positive damping torque acting on port R, and a negative damping torque of equal magnitude acting on port C.

## Assumptions and Limitations

• The block represents only viscous damping

• The value of the damping coefficient must be equal to or greater than zero.

## Dialog Box and Parameters

### Parameters

Minimum damping coefficient

Minimum value allowed for the damping coefficient. The physical signal input saturates below this level. The parameter must be greater than or equal to zero. The default value is `0`. The default unit is `N*m/(rad/s)`.

### Variables

Specify the desired initial values of the block dynamical variables. These variables guide model assembly at simulation time zero. When two or more variables conflict with each other, the priority setting determines which of the variables to satisfy. For more information, see Set Priority and Initial Target for Block Variables.

Variables that you can specify include:

• `t` — Spring torque

• `w` — Relative rotational velocity

## Ports

PortDescription
BPhysical signal input port representing the variable damping coefficient
CRotational conserving port
RRotational conserving port