1
C H A P T E R 1
Guilty Until Proven Innocent
I repeatedly tell students that it is risky to accept
computer calculations without having done some
parallel closed-form modeling to benchmark the
computer results. Without such benchmarking and
validation, how do we know that the computer isn’t
talking nonsense?
Clive Dym
Principles of Mathematical Modeling
If you only make one predictive simulation, it will likely
be wrong.
Loren Lorig
CEO, Itasca International
1.1 GUILTY UNTIL PROVEN INNOCENT
One of the many advantages of the finite element method (FEM) is that it is relatively easy to
create a model and use the method to run an analysis. Often, for better or worse, the method has
become commonplace enough to be seen as a sophisticated calculator. In addition to enhanced
computational speed, this is due to the development and preponderance of graphical user inter-
faces (GUI) used as pre- and post-processors to nearly all commercial finite element software.
Yet a great hazard of FEM is also that, with the aid of commercial software, it can be
too easy to create a model and run an analysis. e ease of operation can foster “computational
complacency” [Paulino, 2000] in validating numerical results. It often appears that the myth that
“the computer must be right” is alive and well. While, indeed, algorithms in commercial codes are
well debugged and are unlikely to contain programming errors, the user is ultimately responsible
for making appropriate modeling assumptions and interpretations of the output.
Hand in hand with complacency is the “optimism bias,” in which people tend to believe
that they are correct in more situations than they really are [Conly, 2013]. In the context of
FEA, even honest users who intend to validate their work might mislead themselves, thinking
that results are correct because they appear to correspond to a simple theory that they might be
applying inappropriately (for example, out of its bounds of accuracy), or they might be missing
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