Request for help meshing and and analysing a part {Solved}

About the development of the FEM module/workbench.

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Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

thschrader wrote: Sat Oct 02, 2021 1:09 pm OK, thanks for the info.
Here is a first try with FEM beams. You can merge the wedge-array (solid) and the hangers (lines)
with boolean-fragments. In gmsh, set mesher explicit to 1-D, gmsh extracts the edges of the wedge-array
by itself. No need to extract the lines "by hand" as I did before. Nice.
Loading each node 150 kg, no selfweight of structure. Round beams d=30 mm steel S235.
StPauls_02102021_FEM_frame.FCStd
Thomas you come across as a very modest man so I hope what I am about to post does not embarrass you but it would be absolutely remiss of me not to acknowledge the time and effort you have put into this thread and the wonderful work you have produced. I have had time to look through your file and I am in awe at the detail and techniques you have used. For that reason and for the benefit of the forum and aspiring engineers and forum members I would like to post three screenshots of your latest file. The images speak for themselves. I will leave it at that - thank you.
Attachments
St Pauls Spaceframe1_Tschrader.png
St Pauls Spaceframe1_Tschrader.png (119.71 KiB) Viewed 15473 times
St Pauls Spaceframe2_Tschrader.png
St Pauls Spaceframe2_Tschrader.png (394.55 KiB) Viewed 15473 times
St Pauls Spaceframe3_Tschrader.png
St Pauls Spaceframe3_Tschrader.png (675.24 KiB) Viewed 15473 times
Last edited by Laurie Hartley on Thu Oct 07, 2021 6:43 am, edited 1 time in total.
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

johnwang wrote: Sun Oct 03, 2021 5:24 am
Laurie Hartley wrote: Thu Sep 23, 2021 5:42 am
Follow this, I made an inp file to represent this shape. It could be imported by Open directly. Please remove '.txt' in the file name.
Hi John - I have been examining your file which is indeed beautiful and as a result I have as promised three questions for you:-

1.This may seem very naive but what can I do with this file which you very kindly made for me in response to my post about a parametric model and the node shape I was using.

2. How did you make it :) I can't find any detail.

3. If I try to transform it I can move it horizontally or vertically but it will not rotate - why is this so?

For more on the parametric model see my next post.
Attachments
JohnWangHiiSpaceFrame.png
JohnWangHiiSpaceFrame.png (23.19 KiB) Viewed 15449 times
JohnWangHiiSpaceFrameTransform.png
JohnWangHiiSpaceFrameTransform.png (44.59 KiB) Viewed 15449 times
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

I set off on an effort to create a parametric model of the spaceframe before I really delved into Thomas' St Paul's file after which I realised I was probably embarking on a folly - but by that time I had the bit between my teeth trying to discover the wonders of the octagon and how I might use them via the spreadsheet workbench to produce the parametric model.

This was a very interesting exercise even for someone like myself who has only a rudimentary understanding of mathematics, algebra and geometry. I found myself looking for equations that would produce the shapes I had in mind - note what I just said!!

I found myself recalling something that the English Mathematician G. Spencer Brown had written in a book that I came across many years ago which I knew was important but lacked the knowledge to understand. Look up "Canon" on this Wikipedia page. It seems to describe what I am talking about.

https://en.wikipedia.org/wiki/Laws_of_F ... n_of_canon

One thing I do understand is "how to put things together and make sure they stay together" :D

Originally it was inspired by the link Thomas posted about "hinges' - but I reached an impasse. I don't know what to do with it but it does seem to be fully parametric.

If the structure of my spreadsheet looks a bit convoluted and disjointed please make allowances.
Attachments
Parametric Spaceframe.FCStd
(135.53 KiB) Downloaded 324 times
Parametric Image.png
Parametric Image.png (415.04 KiB) Viewed 15421 times
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johnwang
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Re: Request for help meshing and and analysing a part

Post by johnwang »

Laurie Hartley wrote: Thu Oct 07, 2021 6:20 am 2. How did you make it :)
It's a FEA case file. Just trying to use the GRID and Element information in it to build a 3D model. Same as you specify these information using an Excel file. You can edit it with any txt editor program.

Here is another one. Use Mesh Design workbench to import, then add Triangles to fill the two holes, then it is a solid model.

But maybe you need the newest code. See here: https://forum.freecadweb.org/viewtopic. ... 20#p537628
mesh_hole2.jpg
mesh_hole2.jpg (45.98 KiB) Viewed 15234 times
mesh_hole5.jpg
mesh_hole5.jpg (19.46 KiB) Viewed 15234 times
mesh_hole4.jpg
mesh_hole4.jpg (37.73 KiB) Viewed 15234 times
HiSpaceFrame.bdf.txt
(5.16 KiB) Downloaded 307 times
hfc series CAE workbenches for FreeCAD (hfcNastran95, hfcMystran, hfcFrame3DD, hfcSU2 and more)
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

johnwang wrote: Fri Oct 08, 2021 11:46 pm
Here is another one. Use Mesh Design workbench to import, then add Triangles to fill the two holes, then it is a solid model.
Thanks John - I managed to fill the holes but it seems I haven't succeeded in creating a solid.
Attachments
Hispaceframe Shape Holes Closed.FCStd
(3.43 KiB) Downloaded 303 times
Holes Filled.png
Holes Filled.png (101.43 KiB) Viewed 15173 times
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

Laurie Hartley wrote: Thu Oct 07, 2021 6:42 am
"does seem to be fully parametric."
Hmm not quite - Missed a formula on the placement for the top longitudinal chord. Revision 1 attached
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Parametric Spaceframe_Rev1.FCStd
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Re: Request for help meshing and and analysing a part

Post by johnwang »

Laurie Hartley wrote: Sat Oct 09, 2021 5:19 am I haven't succeeded in creating a solid.
It is a closed surface mesh, but not a real 3d model yet. You could export it as an STL file. GMSH can mesh an STL file.
hfc series CAE workbenches for FreeCAD (hfcNastran95, hfcMystran, hfcFrame3DD, hfcSU2 and more)
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Re: Request for help meshing and and analysing a part

Post by thomas-neemann »

here a request from cad1234 (Holger)

https://forum.freecadweb.org/viewtopic. ... 73#p538931


thomas
Gruß Dipl.-Ing. (FH) Thomas Neemann

https://www.youtube.com/@thomasneemann5 ... ry=freecad
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Re: Request for help meshing and and analysing a part

Post by cad1234 »

thomas-neemann wrote: Sat Oct 09, 2021 5:28 pm
Many thanks thomas!! Great Video about a great FC-FEM model!
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

@ Thomas in response to your suggestion
https://forum.freecadweb.org/viewtopic. ... 79#p541579
This could get interesting :)
Geometry and Construction of Gothic Vaults – A Hypothesis – Part One

I had another look at the Gothic Vault video
https://www.youtube.com/watch?v=KokrF7dneXQ
at the beginning of which the investigating stonemasons expressed their desire to rediscover the work method and techniques by which the master stone masons of the past converted the ideas (plan, section and elevation drawings) of the master builders / architects, into the magnificent finished vaults that remain standing throughout Europe to this day.

At one point in the video (10:26) a member of the team expressed the opinion that the only three tools used were the “compass, square, and ruler. I humbly suggest that there were probably at least another three more tools which were used – the plum bob (or plummet), chalked string line, and hardwood wedges.

Many years ago I was awarded two contracts to design, supply and erect access scaffold to facilitate the restoration of The Royal Exhibition Building Melbourne.
External - https://www.kane.com.au/assets/_project ... _Web_1.JPG
Internal- see image below

The base of the dome was a regular octagon. As I was drawing up the scaffold plans I discovered amongst other things that
1. The sections across the diagonal “ribs” was greater than across the “faces”.
2. The sections formed a parabola from the base to the apex of the dome.
3. The drawings I had available were to scale and in imperial units (feet and inches).
Architectural scales imperial

3″=1′-0″ – Pronounced three inches to a foot
1 1⁄2″=1′-0″
1″=1′-0″
1⁄2″=1′-0″
(3⁄4″=1′-0″)
(3⁄8″=1′-0″)
(1⁄4″=1′-0″)
(1⁄8″=1′-0″)
(3⁄16″=1′-0″)
(3⁄32″=1′0″)

After completing the internal scaffold I was inspecting the scaffold with the builders project manager who had noticed that there was a very large “hook” fixed at the very centre point of the apex of the dome. He asked me if I thought it had been used to hang a chandelier. I realised immediately that it was placed their from which to hang a huge plum bob (plummet).

With this revelation came the understanding that the plumb line was used as the “datum line” from which to ensure that timber skeleton ("ribs") of the dome could be adjusted to be perfectly positioned throughout the 360 degrees of its circumference. Simply put if the point of the plumb bob was positioned directly above a “mark” on the floor indicating the centre point of the structure (or mid point on the diagonals between the four supporting columns, the centre of the dome at the apex was directly above it.

This "plumbing and leveling was achieved by driving wedges between the base of the dome ribs and their supporting structure. Simply put if, you drove a wedge into the underside of the left hand side of the structure, the apex would move to the right. Once “plumb” was achieved the structure supports were packed with hardwood timber inserts and permanently fixed to the octagonal ring beam (see image attached)

The relevance of this information for me and I hope of interest to readers, is that every Gothic vault I have viewed is symmetrical (like the dome) and has a central apex or keystone.

In part two and three I will endeavor to answer the question posed by the team leader – “how do you plan for each single stone?”
Attachments
Internal View of Dome.jpg
Internal View of Dome.jpg (52.88 KiB) Viewed 14096 times
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