modal displacements of Diana

posted by aeam on Wed, 26/10/2011 - 17:58

Are the modal displacements presented by Diana normalized ?
I mean , is Diana (at each node) dividing all the dispalcements (x,y and z) by the maximum absolute displacement in the model.
 
for example, if I have a model of three nodes and I carried out modal analysis and I got the following
the first node modal vector is (0.02 -1.12 0.35)    (x y z displacements  respectively)
the second node modal vector is (-1.78 0.05 -3.20)
the third node modal vector is (2.22 1.53 -0.44)
from this data will diana select 3.20 and divide all the values by it, so it will present the following
the first node modal vector is (0.00625   -0.35   0.109)
the second node modal vector is (-0.56   0.016   -1.00)
the third node modal vector is (0.694  0.478   -0.138)  ???
 
or Diana will present the displacements without any normalization ????
 

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DIANA

On Mon, 31/10/2011 - 11:00

I assume that with "modal displacements" you refer to the eigenmodes of an eigenvalue analysis. By default, the eigenmodes are scaled in such a way that the largest translational displacement component has a value of 1 as you can see in Paragraph 27.4.7 of Volume Analysis Procedures (DIANA 9.4.3 manual).
Alternatively, it is possible to normalize the eigenmodes with respect to the matrix used in the eigenvalue analysis, e.g. the mass matrix in a free vibration analysis or the identity matrix for a standard eigenvalue analysis, or to output the participation vectors, i.e. weighted eigenmodes in a free vibration analysis.
For more information and background theory on this topic, please check Volume Analysis Procedures.

By Jonna Manie