From time to time I lurk around CFD related forums – just to see what people are talking about. A couple of weeks ago I found a posting on the subtleties of meshing and its relation to accuracy. The discussion rapidly became quite heated – there were some folks who believed that unless simulation gives you 100% accuracy then it is useless while others didn’t believe that accuracy is the only factor in the equation. In my mind’s eye I could see the whole conversation taking the shape of Budweiser’s campaign of “Less Filling, Great Taste” from a few years ago. One of the engineers on the forum finally said: “designers are interested in lowering the surprise ratio … not in getting an answer to another order of magnitude in accuracy. They are just trying to get it in the ballpark of success.”
Reading this conversation made me realize that from time to time we all need to remind ourselves that the correct answer to the question of which is more important: accuracy or getting a usable answer, is both!
I touched on the subject of meshing in my previous post. A lot of people consider meshing a “black art” especially when using traditional CFD tools. You need to tinker with it and coax it until it rewards you with a fine enough mesh so you’d get 100% accuracy. But there’s a price to pay for that kind of accuracy — time. I remember hearing about an engineer at an aerospace company who would spend 3 months on creating a “good enough” mesh.
In the fast-paced world of design, there’s very little room for any activity that distracts the design engineer from what they need to do: design. So it stands to reason that any activity that is spent on other things is not a good spend of time. Transferring data back and forth … waste of time. Deciding when to use which mesher … waste of time. Refining meshes for days… is a waste of pure design time. During the design process, engineers are mostly concerned with doing sanity checks … figure out if they’re going in the right direction. This iterative process doesn’t require 100% accuracy – a 5 to 10% deviation is OK. Once a few good candidates are chosen then the design engineer can go for broke. Now FloTHERM, FloVENT and FloEFD users are quite lucky because they get to take advantage of both speed and accuracy simultaneously (please look for one of these products under the Mechanical Analysis Multimedia tab to see what I mean).
Now I betcha you’re asking yourself, what’s this got to do with ROI (the main theme behind this blog)? It all goes towards making sure that the investment that you’ve made or will make in simulation software, pays for itself by enabling you to do what you do best: design in a timely manner.
Until next time,