Multipoint Random Vibration

[srjose]

Anybody knows how to considerer the cross terms during a multipoint Random analysis in Ansys?

 

[bagarbilla]

Can you explain cross terms ??

 

[pepelu2009]

Let imagine a Structure which presents 6 interface points with another one. From a dynamic analysis we get the acceleration time series of each interface point per axis, we get and amount of 18 acceleration time series. Then we build the AutoPSD and the CrossPSD from the time series, so our PSD matrix presents 18 AutoPSD and 144 CrossPSD:

A11XX
C21XX A22XX
C31XX C32XX A33XX
C41XX C42XX C43XX A44XX
C51XX C52XX C53XX C54XX A55XX
C61XX C62XX C63XX C64XX C65XX A66XX
C11XY C21XY C31XY C41XY C51XY C61XY A11YY
C12XY C22XY C32XY C42XY C52XY C62XY C21YY A22YY

... A66ZZ

Well the question is: How can I take into account the cross terms in an Ansys Random analysis?

 

[srjose]

Dear all.
Reading the Ansys Help I find out that in order to take into account the cross correlations between different signals in a multipoint Random Analysis I should use following commands:

Command(s):

COVAL for cospectral values
QDVAL for quadspectral values
PSDSPL for a spatial relationship
PSDWAV for a wave propagation relationship

Could any expert in this topics explain me how to use this parameters in order to take into account the cross correlations during a multipoint base excitation random analysis?

If none of previous commands is defined, how are the signals? correlated or uncorrelated?

Thanks everybody in advance.