free-form surface - form finding with mesh using GSA (Oasys) - troubles

Replies to This Discussion

Permalink Reply by Jon Mirtschin on May 21, 2011 at 4:54am

Hi Alessandro,

 

Here's some comments from my look at your model to keep you progressing.

 

Your sketch shows continuous curvature over the lines of support, in reality a membrane or fabric would crease and hang over these support lines (as my image shows).  If you wish to "form find" this type of geometry, you will need to find a way to apply upwards pressure at these regions.

 

 

It's easiest to work with a single mesh, so I reworked your line generation to loft a surface (there were some internal disjoint edges forming).  Also, I added an exaggerated gravity load case to give the surface shape (with settlement loads only, the surface will relax to a minimal surface, which will produce planar type surface in your example as it spans one way.  I also added an xy restraint to the internal nodes not vertically fixed, the surface was collapsing at some edges causing problems in calculating a result.

 

One other tip, if you right click on an ssiBake component, you can disable the placement of data into Windows Clipboard that will help accelerate the process.

 

I hope this helps you progress further closer to your objective, I'm happy to help advise further.

 

Cheers,

 

Jon

Attachments:

• AL86_geom gym.gh, 134 KB

Permalink Reply by Alessandro Liuti on May 21, 2011 at 3:22pm

Thank you so much Jon, you've been very kind and helpful! Thanks to your very good clarifications, next days I'll develop further aspects of the project, I'll think about the best strategy to deal with it and I'll keep you up to date if you wish.

 

Best regards, Alessandro.

Permalink Reply by Alessandro Liuti on May 31, 2011 at 5:46pm

Hi Jon,

I've been developing further stages of the project; my aim is to morphogenetically modify the initial shape I designed, in order to find an optimum structural shape with minimal bending stress, strain energy and deformation.

I can't understand what I'm missing, I worked following your suggestions but I have difficulties in getting good results, can you take a look at it?

 

thanks in advance, Best regards, Alessandro.

 

 

Attachments:

• base.3dm, 326 KB
• AL_try.ghx, 2.2 MB

Permalink Reply by Jon Mirtschin on June 1, 2011 at 2:09am

Hi Alessandro.

 

Great to see your progress.

In order to effectively troubleshoot this type of problem, I suggest disabling the "solving component" and using the ssiBake component to manually take model to GSA and try running the analysis task there when you can supervise it. 

 

When I did this, I first tried taking the planar restraint of the internal nodes (using a similar test that you did to place them on the perimeter).  Still no luck, the form finding was still producing strange and diverging results.  So the next thing I checked was your model units and it seems that's the issue.  You either need to adjust material units for an 80cm wide mesh, or I took the assumption it was 80m wide and changed the rhino document units.  Then I started getting results.

 

From your initial shape (and note to minimize flexural  stress), I'm assuming you might like a vaulted (shell) shape rather than a membrane, so I've form found against a positive gravity load in the attached.  I also increased the maximum acceptable cycles, it was so close to convergence for 10,000 

Hope this helps,

 

Jon

Attachments:

• base.3dm, 304 KB
• AL_try geomgym.gh, 388 KB

Permalink Reply by Alessandro Liuti on June 1, 2011 at 2:35am

Thanks again Jon, very helpful as always! Now, with your precious suggestions I hope to update you soon on further interesting developments.

 

Best regards, Alessandro.