# Features of the Altair Bushing Model

The Altair Bushing Model supports many different representations of bushing stiffness and damping as illustrated below:

All stiffness models, constant damping and rubber or hydromount damping models are exported to the .gbs file for each direction. At run time, you can select the specific model that you want to use.

The following table explains the various models:

Component Method Description
Stiffness Constance Stiffness F=-K*x; used when the bushing’s stiffness behavior is linear. The value, x, is the deformation in the direction of interest.
Cubic Stiffness F=-h(x); where h(x) is defined by a pair of cubic polynomials whose coefficients are derived from the measured Force vs. Displacement data in the .gbs file.
Spline Stiffness F=-g(x); where g(x) is a cubic interpolation of Force vs. Displacement data in the .gbs file. Linear extrapolation is used when the data is outside the range of specified data.
Damping Constant Damping F=-c*v; used when a bushing’s damping behavior is linear. The value, v, is the deformation velocity in the direction of interest.
Rubber Damping An amplitude and frequency dependent bushing model, whose coefficients are fit to measured data using a tool such as the Altair Model Identification Tool. This is primarily used for fitting rubber bushings.
Hydromount Damping An amplitude and frequency dependent model for hydrodynamic mounts, whose coefficients are fit to measured data using a tool such as the Altair MIT.

You can include stiffness and damping selections in the ACTIVITY BLOCK of the bushing property file. To learn more about how to make these selections, see: Bushing Property File.