Mesh an irregular surface for further structural analysis purpose

Hello, can anyone help me with the mesh generation? Thank you!

The attached 3dm file is the outline of a roof, which is going to be an ETFE cushion roof.

For further structural design and analysis, my plan is to
1) transform the 2D roof shape into a mesh (Rhino + GH),
2) use this mesh to construct beam structure for GSA (GH GSA plugin),
3) then in GSA I could apply external loads, and eventually do the form finding
4) after form finding, I will have reaction forces etc. results from GSA, modify the shape if necessary >> loop

Currently I am struggling in transform the shape into a proper mesh. As shown in the 1st screenshot, with certain gh plugins I can generate good-looking mesh (purple on the right) but not usable for structural analysis.

The left one (black) was generate by rhino mesh command, there are still tricky parts along the edge/thin area. The 2nd screenshot shows the beams transferred from this mesh exported to Oysis GSA, with help of a gh GSA plugin.

I'd like to know if there a way to generate a more proper mesh for later use?

Thank you very much for your advise and help!

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Replies to This Discussion

Permalink Reply by Jing on November 9, 2017 at 1:52am

Hello, can I understand that the mesh I have is already good enough?? Thanks.

Permalink Reply by peter fotiadis on November 9, 2017 at 3:25am

This is the most challenging parametric thingy known to man ESPECIALLY if your "envelope" (let's say: roof) is made via a W depth truss. In real-life is 120% impossible to do it without code nor even achieving some preliminarily/conceptual Academic solution that "may" qualify as "realistic". I have several defs that do similar stuff ... but this is an Academic forum and as you can understand a real-life solution would never appear here.

But let's forget the W task (truss out of relaxed mesh with depth, known as W in our trade). See for instance a step prior the "thickness".

General guideline:

1. Create a boundary (a BrepFace) and attempt to do some "reasonable" Mesh via Mesh Machine.

2. Mastermind a policy to manage anchors (naked and/or clothed vertices). This appears easy but is impossible without code IF you want to do it interactively.

3. Separate naked edges from clothed ones (as we do in real-life in tensile membranes etc etc) in order to apply different goal parameters.

4. Relax the mesh (K231 engine).

5. Either work with a "geodesic" structure (W = 0) or make a truss out of the mesh in 4. In either case decide the real-life system in use (say a Mero KK or some other).

6. Check clash truss members issues and interactively vary vertices in order to resolve them.

7. Create all the required connectivity Trees (VV, VE, EV).

8. Mastermind the skin solution (only for experienced pros: avoid at any cost that one).

My advice? Unless you are very determined ... well ... what about choosing an easier design task?

Permalink Reply by peter fotiadis on November 10, 2017 at 12:51am

BTW: A sequel using a totally different way for making the mesh (not MM):

Topics:

1. Although a W zero structure is doable ... I would strongly suggest a W depth load bearing structure. There's lot's of similar/WOW buildings that failed (or leaked) including a very famous one.

2. You must use instance definitions for the truss parts (sleeves, cones, rods and the likes) otherwise the whole thing could become an unworkable nightmare.

3. You must address clash issues otherwise doing it is out of question. These affect the skin parts as well (but as I said: this is 100% pro territory).

4. Your structural analysis (in order to make any sense) must deal with real life components either commercially available or bespoke things designed for the specific project.

5. Wind/Seismic effects can cause skin component issues/failures/leaks as it happened ... well ... in a variety of contemporary famous buildings.

6. Vapor condensation yields (in most of similar cases) buildings that "rain from the inside" - nothing serious, mind: just have an umbrella ready.

Permalink Reply by Jing on November 10, 2017 at 2:30am

Hi Peter,

First of all, thank you very much for your detailed instructions!!! I do appreciate your time and help. Thank you!

Let me explain more about what I was doing and what I am struggling with :)

In last semester I did the architectural design part of a given assignment. On top of the building (in the open space) there is a cloud-like roof >> ETFE cushion.

Above: The top view of the roof.

Below: The front elevation of the roof.

Now I am working on the structural design part of this roof. I used the mesh (mentioned in my original post) and transferred it into beams, baked the result directly to GSA using the plugin developed by Jon Mirtschin.

I did the initial form finding using this beam mesh in GSA. See below (the cushion not mirrored yet, so just one side)

I set the curve boundaries as restrictions and add pressure to surface elements. I got a bubble shape and all the reaction forces along the edge.

>> Form find of the ETFE bubble and reactions.

For the "green middle part" (the compression component in the cushion), the steel part, I am trying to find its shape in Abaqus.

I used the same curve shape to create a solid steel plate. Add reactions I found in GSA to this plate as loads, set the positions of supporting columns as restrictions. Run the topology optimization, below is a result with volume eliminating up to 33%:

>> Form find of the middle steel compression part.

Then is the interaction/combination of both cushion and steel frame. But import/export between Abaqus/GSA/Rhino_GH........... .........

So I am thinking to use Abaqus topology optimization as a guideline, print the result out and draw those holes with marker, assume it works with certain algorithm, then do all the stuff in Rhino/GH/GSA.

Therefore, currently I am not really working on generating a 3D mesh for the entire cushion. Indeed is a solution to find the form of the cushion/steel frame and their corresponding forces.

Last but not least, the gh components you used look quite unfamiliar with me, and not really readable... what's the name of it?

Thank you.

Permalink Reply by peter fotiadis on November 10, 2017 at 2:50am

These things captured are not components they are C# code that does what I want. I always work solely with code for a vast variety of reasons - teamwork/.../efficiency/"portability" (my main platform is AECOSim + Generative Components + Bentley Systems Verticals).

Other than that ... well ... I always see things like these having in mind strictly real-life constructions (I'm 1M+++ miles away from Academic thinking) and thus all my comments/notes are focused accordingly.

Other that that forces applied to "abstract" metal parts ?? (what about joints?/nuts?bolts?). How you address assembly puzzles?

Other than that ETFE ages over time: quite temporary approach (although the easy one) on a structure that costs an arm and a leg.

Permalink Reply by Jing on November 11, 2017 at 3:21am

I see, thank you. I am not really into coding yet, thus a bit difficult for me ///口\\\

I just started working with the part, still thinking and trying. Let's see what will happen to those puzzles. :)

Permalink Reply by peter fotiadis on November 11, 2017 at 3:38am

Well ... I wish you the best BUT have in mind that the "theoretical" (should I call it academic ?) approach on these matters usually guides you into BIG problems when the ugly part happens (get hired by someone in some practice and start doing real-things under huge pressure etc etc).

That's a malicious virus: it works under cover ... and the moment that you realize the impact is too late. I've seen this happening in 90% of students who from time to time are asking my help on this or that.

But then again I'm an amoral, greedy and cynic pro who only cares about optimized results and nuts and bolts, he he.

Permalink Reply by Hyungsoo Kim on November 9, 2017 at 3:53am