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How to extract the "strain modal matrix"

How to extract the "strain modal matrix"

How to extract the "strain modal matrix"

(OP)
Hey!

I am studying the linear displacement strain transformation by applying FEM solutions and experimental data. Several references make the following approximation:

{d} = [Phi]{q},
{s} = [Ksi]{q},

in which d refers to displacement vector, s to strain, Phi to modal displacement matrix and Ksi to modal strain matrix and q is the modal coordinates.

Therefore via least square approximation

{d} = [Phi]([Ksi]^T[Ksi])^(-1)[Ksi]^T {s}

But to accomplish this I need to reconstruct modal strain matrix [Ksi] from FEM computations. (I am using Nastran/Patran) I can easily obtain displacement modal matrix which comes immeadiately as a result of a modal frequency solvers...but how about the Ksi then?



Any idea???

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