Hello
I'm doing my first generative design and have run into problems:
- I've done 2 studies, with 3 outcomes in each, and each time it stops at 32 iterations, I don't understand why it doesn't do more?
- I have set fos to 3, but in the result fos is approx. 450,000. Why is it so far from the 3 I set it to?
- When I go in and look at the results, it says "out of date results" even though I haven't changed anything - why?
I hope someone can help me here 🙂
Hi @sisam20 ,
Welcome to generative design!
I'll try to provide satisfying answers to your questions below, but I highly recommend going through a tutorial (official ones are here and here though plenty of others are available on YouTube) or even a full training course to get the most out of this technology.
Now, to your questions:
32 iterations is actually pretty typical for a generative run. Generally, the earliest iterations are the thickest/bulkiest in a generative run and as mass is removed the part gets thinner in subsequent iterations.
A generative solve stops running when the shape is no longer changing for some reason, or when a maximum amount of material has been removed from the initial design (first iteration). I'd have to see your study to be sure, but I suspect you've hit the maximum amount of material removal limit here. You can get a thinner design by providing a starting shape that is smaller than a box around your preserves. In your situation you might consider something like an upside-down "U" shape:
I got that by looking at your outcome and thinking about removing a chunk of geometry from the first iteration where no material was present in the last iteration. Note that a starting shape that's too thin or pushes generative towards a bad solution to the design problem can cause the results to look pretty poor. I would recommend you not mess with the starting shape and fix issue #2 first:
FOS of 450,000 is definitely way up there. Recall that FOS stands for Factor of Safety, and is the ratio between the yield strength of the material being used (an Aluminum alloy in this case) and the maximum stress experienced in your part when the load you specify are applied. So an FOS of 450,000 with a yield strength of 240 MPa means the maximum stress on your design is 1.8 kPa, which is very small for most engineering structures (it's about the same stress as a pencil-sized piece of aluminum experiences when it's used to hold up a slice of bread). So why is the design so under-stressed?
Again I don't know for sure, but I suspect you've provided loads which are very small, or loads and constraints on the same preserves. Think of a load as a "faucet" that spills energy into the shape and a constraint as a "drain" that absorbs mechanical energy. If there is no distance between the faucet and the drain, the energy "water" doesn't flow through the structure and create stress which in turn is used to compute factor of safety. Similarly, if the magnitude of the load is very small, there's only a trickle of energy flowing from the faucet which creates very small stress (and correspondingly high factor of safety values). Force loads in generative are specified in Newtons, which is a relatively small unit of force (roughly the weight of a 100-gram object). Double-check that you're put in the loads correctly for the problem you're trying to solve. Generative will work best when the FOS limit you specify (2) is on the same order as the factor of safety of the design you're simulating, so tune your loads and constraints and re-run the solve until you get down below at least 10, and ideally all the way to 2, by the final iteration.
Fusion often displays the "out of date results" warning, sometimes for no reason that I can tell. The intent is to warn you when you've made changes to your design or to the generative setup after you ran a generate job such that the design you have now is different than the design you used to generate outcomes. Sometimes, though, it flags this for super tiny (or invisible?) design changes. You can safely ignore this warning so long as you haven't changed the generative setup or the design.
Hope that helps!
Ben
