Re: xkcd: Tukey

On 6/22/2025 2:50 AM, Thomas Koenig wrote:

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:
 

The worst thing is getting the young inexperienced engineers to
understand that even though we are first principles simulation software,
they think that any simulation is good for making billion dollar
decisions on.  They need to validate that simulation with a pilot plant
and extreme laboratory data first.  Few do nowadays.

 Judging the quality particular model is definitely part of the
art of engineering; judging if errors are on the safe side or
not also plays a large role.
 A colleague of mine once stated, ironically, "Convergence means
correct", which has become a favorite quip in our group.
 If I were to write a new simulation program from scratch, (which
I'm not), I would probably include sensitivity analysis into the
model right from the start, so people can now (if they care to know)
how a difference in composition, temperatre, pressure or material
properties will affect their results.  This could also provide a
guideline to those young engineers where the problems are.
 Plus (as much as this pains me to say, as you know I'm a Fortran
person) I would probably build this package on Julia, which can do
autodifferentiation and analytic Jacobians right out of the box,
has cool ODE solvers and is reasonably fast because functions
are compiled.
 Maybe a little anecdote:  Once upon a time, some people wanted to
build a distillation column.  The did the calculation using the
material properties provided by a well-known simulation package.
Somebody noted that things were a little too close for comfort
to an azeotrope, and asked the thermodynamics people to do some
measurements to confirm the design.  The thermodynamics people
measured and found that the azeotrope was indeed much closer than
previously calculated, and that the column actually needed a factor
of four more theoretical stages than been originally simulated.
The column started up on time and delivered in-spec product.
 They caught this in time, but less experienced engineers might
not have, and sensitivity analysis could have pointed a less
experienced engineer into the right direction.

Michael Michelsen wrote a really good book about stability analysis.  We have incorporated some of it in our software over the years, trying to stabilize our four phase kvalue solver that is about 250,000 lines of Fortran spread across 2,000+ subroutines.  Solving three kvalue equations simultaneously has proven to be ... difficult ... and easily unstable.  Using the partial stability analysis is good but, cpu time has greatly increased by almost a factor for four.
I do not have the second edition yet, as I have written notes all over my first edition.  Here is the second edition: "Thermodynamic Models: Fundamentals & Computational Aspects" by Michael L. Michelsen and Jorgen M. Mollerup.
  https://www.amazon.com/Thermodynamic-Models-Fundamentals-Computational-Aspects/dp/8798996118
Lynn