5.1. Adding Damping

Damping is present in most systems and should be specified for your dynamic analysis. Bearings are one of the most common sources of rotordynamic damping. More information on how to specify your bearing damping characteristics is found in Modeling Bearings, also in this guide.

In addition, the following forms of damping are available:

  • Alpha and Beta Damping (Rayleigh Damping) ALPHAD BETAD

  • Material-Dependent Damping MP,BETD, MP,ALPD, TB,SDAMP,,,,BETD, TB,SDAMP,,,,ALPD

  • Constant Material Damping Coefficient MP,DMPS

  • Global Material Damping DMPSTR

  • Damping Ratio DMPRAT

  • Modal Damping MDAMP

  • Element Damping

  • Material Structural Damping Coefficient DMPSTR

See Damping in the Structural Analysis Guide. The accompanying tables provide more information on the types of damping that are available for your analysis.

The effect of rotating damping is specific to rotating structures and may induce stability issues. It is supported by all the elements which generate a gyroscopic matrix (see CORIOLIS for a list of elements) when proportional viscous or structural damping is defined. The viscous damping is defined via beta damping (BETAD) or the material-dependent damping (MP,BETD). Similarly, the structural damping is defined via DMPSTR or MP,DMPS.

It is also supported by the following elements:

  • Bearing element COMBI214 with real constants K11 = K22 and K21 = K12 = 0

  • 3D longitudinal spring-damper element COMBIN14 with KEYOPT(2) = 0 and KEYOPT(3) = 0

  • General joint MPC184 with 6 degrees of freedom, KEYOPT(1) = 16 and KEYOPT(4) = 0, and with stiffness characteristics (TB,JOIN,,,,STIF)

  • Stiffness matrix MATRIX27 with KEYOPT(2) = 0 and KEYOPT(3) = 4

  • Bushing element COMBI250 when stiffness characteristics are non-zero.

For COMBI214, the rotating damping effect comes directly from the damping characteristics (real constants C11 = C22 and C21 = C12 = 0).

The rotating damping effect is activated using the RotDamp argument of the CORIOLIS command. An example can be found in VM261 - Rotating Beam with Internal Viscous Damping.