There is a clear distinction between the "manufactured" CAD assembly and the "simulation" CAD assembly. When using simulation "Upfront" in the design process, we prefer to have a conceptual model that does not include all of the nuts, bolts, interferences etc. We would rather only include those parts and features that are critical to the type of analysis being conducted. So, for a flow analysis, we only really care about the "flow path", everything else is just additional info that may take time to address with little to no value to the analysis. If we include the thermal effects, than we need only the critical components and can ignore tiny components (bosses, fillets, chamfers etc) that will only make the model larger but can be simplified or ignored. Often times, this can reduce the solution time by up to 1000%. So in real numbers, this can result in a model taking less than an hour vs. overnight. To go one step further, this can result in doing 10 Upfront CFD simulations in a day or two rather than a week or two. Pretty signicant.
Sometimes, we are lucky enough to start with a clean sheet and build a conceptual model from scratch. But more often than not, we have a legacy model that needs to be redesigned or the next generation design will leverage legacy parts. So, what are the things we are looking to simplify or eliminate so that our models will run as fast as possible? The easiest question to ask yourself "if I get rid of it, will it alter my results by more than 5%"? If you don't know, than you should probably keep it.
So, here is a quick checklist if you are doing an Upfront CFD analysis...
Always, always start simple and work to the more complex.
Get rid of all fillets, chamfers and small edges. Keep only those that are in the "flow path" and will alter the flow behavior substantially.
Get rid of interferences and tiny gaps. Best to ensure that parts are coincident and/or concentric.
Leverage "alternative" assemblies (simplifid reps in Pro/e, configurations in SW, Levels of detail in Inventor etc).
Don't be afraid to re-assemble a simulation-only assembly. It is sometimes quicker to assemble a model from scratch rather than simplifying the original.
These are obviously guidelines. You have to weigh the time needed to simplify the model versus that of the time we are saving. I have found that time spent on simplifying almost always pays off in the end. Being able to identify the"ideal" model may take some experience. But the vendor you choose should be able to give you quick guidelines that should be able to get you there. Make sure that they understand your design process.
Much more to come on this in the coming weeks. I'd love to spark a discussion on which product has the best tools for simulation folks. I definitely have my own opinions. Also sparks the question, how about a tool for the simulation guys that do not drive CAD? Well, appears as though SpaceClaim boys are here to save the day. http://www.spaceclaim.com/
No comments:
Post a Comment