Streamline Simulation

An engineer studying for this year's exam emailed me an interesting question about Streamline Simulation.

It's regarding an apparent contradiction. The Guidebook quotes TS7 stating: "...there is no requirement the fluids be incompressible". Found under the "basics" section in TS7 this is fair game (author Gupta).

However, HS5 clearly states (in seeming contradiction): "...one of the key underlying assumptions in streamline simulation is that the system be close to incompressibility" (author Batycky & Thiele).

Read carefully, there is no contradiction. TS7 is clear. The quote from TS5 P1437 only says that the "system" must be "close" to incompressibility. These are not quite the same thing; note one is about "fluids", the other about the "system" (and merely "close").

I post this to show how tricky word problems can be. Be very, very careful with words. Look for exact quotes, and then carefully check for slight word change within a direct quote. And of course, check and recheck "simple" problems. Remember: a seemingly easy word problem has exactly the same weight as a 10 minute long reservoir calculation problem.

By the way, this is why many who think they did well on the PE exam still fail, and others who think they failed often pass. Paranoia is a good thing on the PE exam.

This is also why I recommend dividing each half exam into 8, 30 minute "mini-exams" of 5 problems each. One is thus forced to spend at least some extra time on these supposedly "easy" problems. And thus recheck problems otherwise deemed too easy to waste time on.