DAMPING should be preceded by a *MATERIAL card

1

Hi,

I would like to apply some Rayleigh damping to some spring elements with a mass attached to one of the nodes of each one.

¿Is it possible.? Ccx is complaining.

*ERROR reading *DAMPING: *DAMPING should be preceded by a *MATERIAL card *WARNING in calinput: no elastic constants were assigned to material MASS in a (thermo)mechanical calculation

*ERROR in calinput: at least one fatal error message while reading the input deck: CalculiX stops.

This is a simple example.

*NODE
1,0,0,0
2,0,0,0.1
*ELEMENT,TYPE=SPRINGA
1,1,2
*ELEMENT,TYPE=MASS
2,2
*ELSET,ELSET=Default
1
*ELSET,ELSET=Mass_1
2
*SPRING,ELSET=Default

1.764000000000E+003
*BOUNDARY
1,1,,0
1,2,,0
1,3,,0
2,1,,0
2,2,,0
*MASS,ELSET=Mass_1
1
*INITIAL CONDITIONS,TYPE=DISPLACEMENT
2,1,0
2,2,0
2,3,0.05
*DAMPING,ALPHA=0.0062,BETA=0.0004
*STEP,INC=110,AMPLITUDE=STEP
*DYNAMIC
0.01,1,0,0.01
*NODE FILE,GLOBAL=YES
U
*EL FILE
S,NOE
*END STEP

¿What are those elastic constants I need to assign to the mass?

2

According to the documentation, this type of damping doesn’t have to be placed under *MATERIAL:

Keyword type: model definition, if structural damping: material

But in practice, it seems to be necessary for some reason. Maybe you could just use the dashpot element instead. It would fit your spring-mass system.

1 Like
3

Hi Calc_em and Thanks.

I’m interested in Rayleigh damping effect on my model, so I need to be able to play with those coefficients.

Note: I liked your last Prepomax YouTube video.

4

Perhaps there’s at least a way to convert Rayleigh damping coefficients to dashpot coefficient. Or you could model the mass as a solid cube and then define material damping.

Only the following damping options are available for *DYNAMIC analysis:

  • Rayleigh damping by means of the *DAMPING keyword card underneath a *MATERIAL card
  • Dashpot damping by defining dashpot elements
  • Contact damping by defining a contact damping constant and, optionally, a tangent fraction using the *CONTACT DAMPING keyword card

Thanks, it took me a while to finally realize this topic.

5

Manual p. 421, this is damping for continuum or structural elements, springs I guess you have to use dashpots for damping. alpha multiplies the mass matrix and beta the stiffness matrix to build the damping matrix, so if you want that combination for a 0D element just do the multiplication to create the C for the dashpot associated to same dofs as the spring.

Example:
*DAMPING,ALPHA=5000.,BETA=2.e-3
indicates that a damping matrix is created by multiplying the mass matrix
with 5000. and adding it to the stiffness matrix multiplied by 2 · 10−4
Example:
*DAMPING,STRUCTURAL=0.03
defines a structural damping value of 0.03 (3 %). This card must be part of
a material description.
Example files: beamimpdy1, beamimpdy2

6

Thanks to both of you,
I was preparing the proposal of the cube at the tip and …surprise. If a dumb cube is added to the system the matrix is assembled and the problem is solved with the springs. I am referring to a loose cube. I have yet to see if the result makes sense but it is surprising isn’t it?:joy:

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