Bulk Data Parameter Entries - Rayleigh Damping Alpha1 and Alpha2

[jacksonfem]

I would like to import Rayleigh Damping for Advanced Nonlinear Transient (SOL601). My steps are:

- In the "Analysis Set Manager", I press "Preview Input" and then I click "Edit Preview"

- At the exististing PARAM commands I write for example "PARAM,ALPHA1,0.5"

- Click on "Analyze" and I take the following massage (6011):
"THE NDDL DEFAULT TYPE OF PARAMETER ALPHA1 DIFFERS FROM THE TYPE DETERMINED FROM PARAM CARD DEFINITION.NDDL TYPE IS S.P. COMPLEX, PARAM TYPE IS S.P. REAL".

I read in the DMAP guide aboyt these types but still I can' t understand the right way to write it.

Can anyone help??? Please....
For months I 'm trying to find it....

 

[mrfemap]

From the head of NX Nastran Development -

The alphas need to be written as a complex number using a format like this

PARAM ALPHA1 0.0 0.0
PARAM ALPHA2 1.0-5 0.0

Mark.

 

[jacksonfem]

Thank you very much for your help mrfemap!

But...what symbolize 1.0-5??? And why the 2 parameters have 2 values?

The equation is C=aM+b?. And the manual says a=Alpha1 and b=Alpha2.

From the theory they are just 2 numbers...

Why each one has 2 values?

 

[BlasMolero]

Hello!,
Please note that ALPHA1 & ALPHA2 parameters are used as well in frequency and transient response analysis with NX NASTRAN Dynamic module (SOL108 till SOL112), where if PARAM,ALPHA1 and/or ALPHA2 are not equal to complex zero, then Rayleigh’s damping is added to the viscous damping. ALPHA1 is the complex scale factor applied to the mass matrix and ALPHA2 to the stiffness matrix. The scale factors are applied to the d-set or h-set matrices. Do not confuse with Advanced Nonlinear dynamic implicit/explicit modules.

In Rayleigh damping with Advanced Nonlinear Module of NX NASTRAN (SOL601,129), parameter alpha1 dampens the low frequencies (and the rigid body modes), and parameter alpha2 dampens the high frequencies.
• The damping ratio caused by Rayleigh damping depends on the frequency.
• The two damping parameters should be chosen to fit experimental data.
• The program computes the Rayleigh damping matrix from the stiffness and mass matrices at the time of solution start. The Rayleigh damping matrix is not updated during the solution.
• Structural damping is not supported for individual elements. Hence, GE field in the supported Bulk Data entries is not used. Rayleigh damping is supported and specified with PARAM ALPHA1 and ALPHA2.
• Only ALPHA1 is supported for Advanced Nonlinear Dynamic "explicit" module (SOL 701).

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

 

[jacksonfem]

Thaks Blas again for your help!! But...I 'm a little confused with all these. I have read the second paragraph in the manual. I didn 't knew about the things you wrote at the first paragraph.

I 'm just interesting about Rayleigh Damping - SOL601/701. I know that ?=?/2?+??/2 for 2 desired eigenfrequences, where ?=ALPHA1 and ?=ALPHA2. I would expect for example to set ALPHA1=?=0.56 and ALPHA2=b=0.012 at the PARAM commands. I can 't understand the form

ALPHA1 0.56 0.56
ALPHA2 1.0-5 0.0

What is the meaning of these??

I also read in the dmap manual that complex type (ALPHA1,2 parameter type is complex)represents a pair of real and imaginary part such as (1.D0,3.5D1).....I can 't understand all these.