Well, the learning was great, but the conclusion is no go for LISA.
I successfully learned how to model a finite element in vibration, using LISA, and managed to get reasonable results for WebPilot's example. Extremely glad I did.
But I finally learned enough to realize that the LISA program won't be able to handle pulsejet valve modeling, at least in its present level of sophistication.
Because I can't use shells to model a valve, I have to use bricks. But bricks work best when they are cubic -- with all sides equal. They become less accurate as they deviate from that.
Also, in a sheet material, the mesh should be divided, when using bricks, into at least one half the thickness, and preferably one third or even less. In other words, with say a valve of .006" thick material, the mesh should be .003" or preferably finer to adequately model the valve's flexibility. That means one side of every brick must be .003" or smaller in height. If we want to keep the bricks cubic, it means all three dimensions are .003"
Theoretically this would be possible. But practically, it isn't
For a half inch wide rectangular strip valve 1" long made from .006 material it would take (0.5 x1 x .006)/ (.003^3) brick elements to make up an accurate model. That's about 100,000 elements.
Even if it didn't crash or freeze up trying to display that many, my computer would probably take over a week of continuous computation to solve that problem, and LISA display and menu/mouse program function would crawl to a standstill.
LISA worked better on WebPilot's example because it was thick -- .1" is huge for a strip valve, but it was only intended as a test lesson. With 1600 bricks and a half hour LISA solved as many as 5 modes (loadcases) for that problem. And for thicker objects much simpler models would produce accurate results quickly.
But pulsejets are difficult to model, because they use thin materials -- just as they are difficult to weld.
So, learn and live.
Glad for the learning. I'll be looking for another FEA program, free or low cost, which can handle thin flat shells in dynamic vibrational modeling, and be run on Linux. I might have to learn engineering French following tufty's Code Aster suggestion, after all.
I've sent for a LiveCD of CAELinux 2008 (the last 32 bit proc version) to explore that possibility.
Où est la bibliothèque?
No problem is too small or trivial if we can really do something about it.