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You want to use beams, not trusses. Trusses cannot take loading in their perpendicular direction via bending: all they can do is stretch or shorten: not a good representation of a metal tube used to make a bike frame.
Best,
Jeff

Thanks Jeff,

Although the tutorial is called Truss Bridge, it actually uses the beam interface along with shells (which I will also use farther down the road in a more complex model with some metal plates that are used to reinforce the structure).

Not sure if that's what you meant.

Thanks.

OK, my bad. My gut feeling remains that your problem is singular somehow (and therefore does not have a unique solution, leading to the solver's inability to converge to that unique solution). Have you checked that your boundary conditions remove all 6 rigid body motions?
Try attaching your model again after clearing the solution to reduce file size if needed.
Jeff

Hi,

No problem.

Tried uploading my file in different computers and at home but the "Attach File" button doesn't seem to work, it doesn't open any new window or any place to select the file, not sure why.

Anyway, I'm relatively new to COMSOL so, about the boundary conditions:
1) I added fixed constraints on 5 different points along the rear axle of the cab, I believe this should remove motion on all axes and also block rotation around the 'x' and 'y' axes (the rear axle runs along the 'z' axis)
2) Added prescribed displacement at the end of the front tube (known as headtube), it is set to zero on 'y' and 'z', allowing the endpoint to move only along 'x', besides being part of the load case, this should block rotation around 'z' axis.
3) Added loads at the top of the headtube, pedal axel and driver and passenger seats.

Let me know if you see anything is missing please, I will continue to investigate why I can't attach a file, maybe it's because this is my first post? Don't know.

Thanks again Jeff and anyone else who can help!

Hi Alfredo,
The "Attach" button seems to be misbehaving today on Firefox, but works on IE and Chrome. If you tried on Firefox earlier, can you try using one of those browsers to upload your file?
Sorry about this, I have reported the problem to our web team.
Best,
Jeff

Hi,

I was in fact using Firefox and it works in Chrome.

So, I attach the file, you'll see it's a pretty simple case I believe.

Again, thanks and any help is appreciated,

Alfredo

It looks like something is wrong with your imported CAD file around point 6 and edge 7, and also the geometry looks like it may be missing an entire beam (Edge 42 has no equivalent on the other side of the frame: I am guessing that is not intentional).
Note that if you fix point 6 (where the problem seems to be, see above) the solution converges nicely.
Jeff.

Perfect, yes, I had overlooked that tiny edge (edge 7) that should not be there, I deleted point 6 and edge 7 and in fact the solution converged. The other missing edge is on purpose due to an assymetrical force that must be added later.

I will continue to add complexity to the model and come back if I find any obstacles hehe

Thank you very much for your help Jeff and have a great day,

Alfredo

The Attach button seems to work again now that Firefox has updated to version 48.0.
Jeff

Thanks again,

Could you take a look at this model where I try to incorporate the shell interfece? I'm not sure if I'm missing some border condition to make it converge or if I'm using the beam connections as I should.

Also, suppose that some of the edges that represents the shells (edge 28, the long one along the z axis and edges 98, 104, 113, 114 and 119 and similar) is not supposed to be a beam, so I'm not sure what data to enter there, it should not be in the beam interfece but I know I should imput some properties on it, right? I can't delete them either as they define the region that represents the shells.

But even if I imput them as beams (the one that says "with all edges as beams"), the model will still not converge, so not sure what's happening.

Besides the Truss Bridge tutorial, are there any other examples that ilustrate the combination of beams and shelss?

Tailwinds,

Alfredo