Wednesday, 30 November 2011

Nurbs To Structural Analysis Profile

At the request of the user, I've advanced the routines to convert arbitrary profiles (including nurbs perimeters) into the structural analysis section profiles capable of approximating this shape.

I've started with GSA, and will look into the other software equivalents shortly.  In GSA the perimeter is defined as a polyline (I have enabled an input to define acceptable deviation from original curve), and properties such as area and inertia are computed from the polyline bounds.

The torsion property is not calculated, so I also enabled a section property modifier component to allow user specification of this value (as well as the others).  There is a means to compute the torsional stiffness using soap film (which was the original reason I started coding mesh inflation), and I'll try to test this approach soon.  If you have any papers or technical explanations/demonstrations of this technique, it can only help accelerate this if you can share it.  Grasshopper definition can be accessed from here.

Wednesday, 23 November 2011

Tributary Areas and Variable Loading

I've finally got some final improvements made to some useful functionality that can save hours of spreadsheet processing (or the like thereof).
I've enabled functionality within Grasshopper to compute tributary areas for nodes contained within a structural grid, as well as generating node loads from varying loading phenomena such as snow drifting or wind pressure.

This algorithm was used (in a more time consuming and specific way) for the 2012 velodrome roof in applying wind pressures from wind tunnel testing advice.  At the time we were still optimizing cable spacing but still wishing to test multiple loading scenarios.  This routine can work out tributary areas for arbitrary grids (based on mid distance from adjacent nodes), grid normals (although load can be applied in a uniform direction if desired) and utilize a varying loading intensity at different locations.  This can be defined (or checked) intuitively from a surface (or polysurface) relative to a reference plane (the local z from datum defines the magnitude of loading pressure).

If you download the models below, you'll see it uses a reference plane from the structure (required for non-planar grids), and the relative position from the loading plane.  I haven't yet developed grasshopper visualization of the generated node loads (it's on my todo list along with boundary conditions, releases etc) so you'll have to visualize in the analysis software.  I also plan to implement face loading for finite elements in a similar manner, and any other suggestions that might arise from users, so don't hesitate to send them through.

Please check the results carefully, I hope you find it useful.  I'm also very happy to assist in applying or testing this with your own applications to projects.
GSA model,  SAP model (others to be added shortly).

Tuesday, 8 November 2011

Grasshopper Mesh to Finite Elements

The ability to convert Mesh from Grasshopper (it could have been generated or imported into Rhino) into finite elements with ability to triangulate quad faces failing shape checks has been in the Geometry Gym plugin for some time.  Recent requests from users recently enabled for the GSA plugin have included orthotropic material generation, nomination of finite element shape acceptance criteria (warning, severe warning, all) and ability to nominate varying orientation and property assignments throughout extent of mesh.  Update from and study this file for GSA, and this file for SAP.

Thursday, 3 November 2011

SAP2000 Point Local Axis

For the Geometry Gym plugin users, remember that I encourage and look forward to receiving suggestions and ideas for improvements and new features to the tools.

Here's a fairly simple one that where identification of node local axis can be straight forward in Grasshopper, but not so easy to do within the Structural Analysis software.  This user wants to be able to apply a local coordinate system to the points (nodes) generated to SAP2000.

You can try for yourself here Download