topic Re: Desperately seeking help adding ribs to chair for testing in Fusion Design, Validate & Document Forum

Desperately seeking help adding ribs to chair for testing

cyangaze — Wed, 13 Mar 2019 00:30:11 GMT

I've really gone full circle with this problem...I followed Lars Christensen's tutorial on making airplane ribs

to apply to my hollow aluminum chair and although I can combine them with the chair into one body, when I test the chair for static stress in Simulation, it give me meshing errors like "face boundary". I tried adding a filet around all the edges of the ribs and tried scaling them to be a bit smaller (as well as scaling the chair to be larger than the ribs) but I keep getting the same errors. I am relatively new to Fusion, so this forum really is my only source of help. I hope I have given enough information.

Essentially, I just want to be able to mesh the chair to be able to test static stress without any errors. I attached the file without any of the changes I mentioned above (fillet, resizing).

I would be very grateful for anyone who could find a solution. I have attached the file.

Re: Desperately seeking help adding ribs to chair for testing

TrippyLighting — Wed, 13 Mar 2019 00:58:59 GMT

I am going to tag @Anonymous and @MikeSmell_ADSK and hope they can help out.

My first guess is that for such thin walled structures, with or without ribs, you need a very fine mesh. I am not sure that Fusion 360 is the right tool to conduct a static stress on such a structure.

Then of course the ribs and the chair shell are separate pieces/bodies. In that case you'd have to define how they are connected. I believe in general it is better to use the combine tool to join them into one body for this particular model.

Re: Desperately seeking help adding ribs to chair for testing

Anonymous — Wed, 13 Mar 2019 01:15:20 GMT

Thanks for the shout @TrippyLighting....I gave it a quick look and noticed a few things.

There are several separate bodies and surfaces in this simulation that are interfering...typically when you have bodies and surfaces like this that interfere there is going to be difficulties with the meshing.
There are some surfaces that have no thickness...those can have difficulties meshing as well because there is no volume and Fusion 360 does not allow for shell elements at this time.
There are a lot of hidden surfaces and bodies that aren't actually removed from the simulation. You have to use the simplify workspace to remove those hidden surfaces and bodies.
It doesn't look like you have combined all of the bodies in the manner you thought you did.

There may be more issues...but without fixing all of the issues above I would never expect to get simulation results. If you clean up the model a little more and need another look please feel free to post it.

Best of luck!

Re: Desperately seeking help adding ribs to chair for testing

cyangaze — Wed, 13 Mar 2019 15:45:20 GMT

@TrippyLighting wrote:

I am going to tag @Anonymous and @MikeSmell_ADSK and hope they can help out.

My first guess is that for such thin walled structures, with or without ribs, you need a very fine mesh. I am not sure that Fusion 360 is the right tool to conduct a static stress on such a structure.

Then of course the ribs and the chair shell are separate pieces/bodies. In that case you'd have to define how they are connected. I believe in general it is better to use the combine tool to join them into one body for this particular model.

Thanks for the tags! Yes it might have to be very fine meshing...I managed to get down to at least one face boundary error though. Now they are combined and unused bodies deleted in Simplify.

Re: Desperately seeking help adding ribs to chair for testing

cyangaze — Wed, 13 Mar 2019 15:48:41 GMT

@Anonymous wrote:

Thanks for the shout @TrippyLighting....I gave it a quick look and noticed a few things.

There are several separate bodies and surfaces in this simulation that are interfering...typically when you have bodies and surfaces like this that interfere there is going to be difficulties with the meshing.

There are some surfaces that have no thickness...those can have difficulties meshing as well because there is no volume and Fusion 360 does not allow for shell elements at this time.

There are a lot of hidden surfaces and bodies that aren't actually removed from the simulation. You have to use the simplify workspace to remove those hidden surfaces and bodies.

It doesn't look like you have combined all of the bodies in the manner you thought you did.

There may be more issues...but without fixing all of the issues above I would never expect to get simulation results. If you clean up the model a little more and need another look please feel free to post it.

Best of luck!

Oh man thanks for the tips! I followed your steps and deleted unwanted bodies in Simplify as well as combined them. I did a section analysis and didn't find anything with zero thickness so I'm not sure why there is still one more face boundary error. I have attached the cleaned up file for you. Again, thanks very much for your help!

Re: Desperately seeking help adding ribs to chair for testing

laughingcreek — Wed, 13 Mar 2019 17:39:57 GMT

try taking rib 1 out of the equation and running it again. rib 1 looks kind screwed up. Keep trying with other ribs till you isolate what is causing problem. There is also a weird wrinkle that could be causing a problem, but my gut says it's rib 1. Attached is a screen shoot with possible problem area's circled.

Re: Desperately seeking help adding ribs to chair for testing

cyangaze — Thu, 14 Mar 2019 19:54:00 GMT

@laughingcreek wrote:

try taking rib 1 out of the equation and running it again. rib 1 looks kind screwed up. Keep trying with other ribs till you isolate what is causing problem. There is also a weird wrinkle that could be causing a problem, but my gut says it's rib 1. Attached is a screen shoot with possible problem area's circled.

Sorry it took a while to get it to work. Yes that was it! That worked. I'm not sure what was wrong with it though or why it caused that bizarre wrinkle.