Friday night joke: dynamicists

Three engineers are applying for a job: a designer, a structural analyst, and a dynamicist.  The interviewer calls in the designer first, and asks him "what's 2+2"?  The designer gets out his design guide, flips to the right design standard table, and says "well given your tolerance, it should be 4 to the second decimal place."  The interview thanks him, and the structural analyst goes in next to answer the same question.  He opens up his laptop, builds a model for a few minutes, runs his simulation, and says "with a few more runs I could say more certain, but I'd say about 4.2."  The interviewer thanks him, and the structural dynamicist comes in.  Again the same question is asked: what's 2+2?  The dynamicist thinks for a moment, leans over, and whispers "what do you want it to be?"

This one was told to me by a designer around the time of my first interfacing with a dynamicist, less than two years into my first structural analysis job.  It honestly helped understanding the oracle like nature of these high level analysts and their vague feedback about the quality of my design.

Like all good jokes, this one has a glimmer of truth to it that highlights the accumulating uncertainties in the design and analysis process.  At the design level, there are uncertainties in tolerance that stack up to make compound uncertainties that affect overall dimensions.  For a structural analyst, all the designers uncertainties are there, but in addition there's now statistical variability in material properties and strengths, uncertainties in FEA detail, element type, geometric nonlinearity, fixity of supports, and uncertainties in applied load.  For a dynamicist, they must consider all the uncertainties of both the designer AND the structural analyst, in addition to their own uncertainties!  These uncertainties become even more exotic, uncertainties in damping, bearing properties, load dependence on design configuration, etc.  So to an outsider, one would think that as more educated and specialized engineering professionals are being interviewed they would be even more certain about an answer, but the fact is they typically won't be.

I'll save the tall tales about dynamicists through aerospace history for another friday.