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Re: MATRIX ANALYSIS

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>But, what if the person that wrote the program had the program check for 
>equilibrium unbalance in these items and distributed the unbalance in some 
>manner just to make the statics work out?
I think you'd find that doing a statics check with member forces and then 
overall equilibrium. You could probably force either, but I don't think 
you can force them both and get a consistent answer. Somewhere I 
recollect that a statical (which includes the D'alembert form of a 
dynamic solution) solution is unique--no such thing as two different 
states of equilibrium for one configuration. It means checking both 
internal and external equilibrium. Then you check deformations to make 
sure the material constitutive relationship is followed and the element 
stiffness matrix is done properly.

>I agree with your final premise, but would add, "... or if both are wrong."
Too true. FEA validation is a joke, but no one understands the punchline. 
I've had people tell me that they validate with a convergence check and 
others who believe that you should validate by running two independent 
analyses with different software and compare answers. (If that actually 
happened on a practical problem, it'd be prima facie evidence of 
collusion.) 

Others run a couple of cantilever beam problems, write them up in a 4 
page report and call that program validation. I watched some poor soul 
from one of the A&E firms who was sent out to check some results from a 
time-history seismic analysis. He sat at a desk and paged through book 
after book of print-out for a couple of days, without a clue about what 
he was looking for or at. Then there are the QA auditors who don't even 
do that, just thumb through QA manuals until they find a hair to split, 
then ask their scripted questions, listen to the scripted answers, shake 
hands all around and stroll off on their way. Damn good thing all that 
hasn't turned me into a cynic.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw



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