Having learned how to create neato pictures, you can now design real-life neato products. Now power up you Silcon Graphics workstations, load your zillion dollar software, scroll down, and watch closely.
First, of course, you need a neato idea. This usually requires that you create a ream of doodles, separated into piles marked "stupid," "no way," "getting there," and "damn, I thought I had it." Then you need a 3D CAD model . . .sort of like this.
Now you need a workstation and a BMW's worth of software. OK, now you can import the model into your kilobuck FEA package. Of course, chances are your CAD program won't talk to your FEA package, and you'll have to create it all over again. (Hey, if this was as easy as we make it look, everyone would do it.) Now you need to generate the mesh. The nuts and bolts of the calculations performed by the computer are beyond the scope of this course, but the basic idea is that the computer calculates the stresses at the intersections, or nodes, of the short line segments in the mesh. The more nodes you use, the better your model.
The tradeoff with building a mesh is speed vs. accuracy. Get much past 1000 nodes and you can read War and Peace waiting for the analysis to run on your average PC. (In the dark ages it took Mr. Bebop 24 hours just to print out a 3D wireframe drawing on a 386.) But if the mesh is too coarse, it won't tell you what is really going on. So to do it right, don't skimp on the RAM -- 128 Megs is ok for openers, but half a gigabyte of RAM is better. Anyway, here is a portion of our mesh:
Now you need to figure out the loads and constraints you want to impose on your model. This is a big part of the skill of good FEA. You want to make sure the test properly represents the real world stresses you expert the part to face.
At last . . . . .the results. The computer generates results in the form of thousands of numbers, which are the results of millions of calculations. In the old days, engineers just interpreted those numbers. Now the graphic capabilities of workstations allow us to create graphic representations of those numbers. Each color represents a different stress level: blue is lowest, red highest. The computer scales the output so that all drawings will show the full range of colors. (In other words, some red will always show up if you are doing it right.) The point is to keep altering the design until the magnitude of the stress is reduced for a given load, and to make the transitions to and from the high stress areas as gradual as possible. Here is Mr.Bebop's final project:
The bottom line is that this design lowered the peak stresses by 8X relative to the original Bebop design with no weight penalty. So you get a free lunch, and all it took was $50,000 of techno juice, a generous friend in a high place, and a few reams of scrap paper.
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