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Second order ODE application question

by cue928
Tags: stiffness matrix
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Apr16-11, 09:03 AM
P: 131
We are doing mass spring problems that stem from second order ODE's. I think my lack of linear algebra is hurting me once again in this section so any help would be greatly appreciated.
We are using a stiffness matrix of K = [ -(k1+k2), k2 (row 2) k2, -(k2+k3)]
Our first problem has the following values: m1=m2=1; k1=0, k2=2, k3=0
Setting up the stiffness matrix I got the following:
-2 2
2 -2
So this is my first stopping point: I thought you were supposed to then take the inverse of that but can you do that with a matrix that has a determinant of zero?
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Apr16-11, 09:52 AM
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hi cue928!

not really my subject, so i'm going to risk asking what could be a really dumb question

if there's only two degrees of freedom, how come there's three parameters?
(and your general formula doesn't have rows summing to 0

maybe these are just the top triangle of a 3x3 matrix?)
Apr16-11, 09:54 AM
P: 131
I don't know how to answer that. Since there is a zero value for two of them, maybe that has something to do with it? I honestly don't know.

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