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Structural Modelling of Tensegrity Structures

  1. J by Jesusbill on 10 May 2020 #

    @brunopostle if you have Linux it should be more straightforward to install and use Salome_Meca, with Windows things are a bit more complicated as there is an unofficial version, which has small some problems however, otherwise you have to go with a Virtual machine.

    For thin shells like in this structure it would not make sense to model in 3D for the analysis, in any case, as one should mesh also "in-depth" to consider the bending behavior. Since they can be represented with planar quads (or any planar shape for that matter) I would say that also ifc2ca and BlenderBIM would not be that far to consider such a structure, essentially it would be a collection of IfcStructuralSurfaceMembers (the current algorithms won't work though for any non-zero curvature unless simplified in planar triangles).

  1. J by Jesusbill on 10 May 2020 #

    If you have any questions or issues with Salome_Meca or Code_Aster do not hesitate to ask @brunopostle , I will be happy to help.

  1. B by brunopostle on 10 May 2020 #

    @Jesusbill thanks, I'm downloading the Linux binary and watched a couple of YouTube videos, small steps

  1. J by Jesusbill on 10 May 2020 #

    @brunopostle Awesome! Don't forget to install the prerequisites first with apt-get install

  1. B by brunopostle on 11 May 2020 #

    @Jesusbill I'm trying the Salome_meca Linux binary. First problem is that the installation scripts are all python2, so on fedora I have to edit 'create_appli.sh' and change all the 'python' references to 'python2' to get it to install.

    Second problem is opengl errors running the salome application, but I can't track this down, my system seems to be otherwise working ok with the default radeon drivers (Blender is fine):

    Searching /Kernel/Session in Naming Service ++++++libGL error: MESA-LOADER: failed to open radeonsi (search paths /usr/lib64/dri)

    libGL error: failed to load driver: radeonsi

    libGL error: MESA-LOADER: failed to open swrast (search paths /usr/lib64/dri)

    libGL error: failed to load driver: swrast

    ..and a pop-up window:

    OpenGl_Window::CreateWindow: glXCreateContext failed.

  1. J by Jesusbill on 11 May 2020 #

    @brunopostle arghh yes I forgot to mention ... they have migrated to python3 for the application and have left the installation files with python2 ... no idea why they have done that really. But if you managed to overcome this step and install without errors you should be good.

    Regarding the second error I think you can try this

    
4) link libstdc++.so.6 Fedora has a different path

$ cd ${HOME}/salome_meca/V2019_univ/prerequisites/debianForSalome/lib

# backup original one

mv libstdc++.so.6{,.old}

# link the system library

$ ln -s /usr/lib64/libstdc++.so.6

    You may try first just renaming the libstdc++.so.6 file without linking cause it should try to look for the one in the system. If it does not work try the second step of linking it as well.

    I found this answer in this thread in the forum of CodeAster, where it says at the last post for Fedora 31 "Also, the renaming of libstdc++.so.6, that you have specified in your post, was necessary on machines with ATI display adapter, and no necessary on a machine with a NVIDIA display adapter, at least on those that I have tried"_

    Another thread for Xubuntu 20.04 but with a similar error (libGL error: MESA-LOADER...) cites in the end as a solution the same action proposed above.

    I hope it helps

  1. B by brunopostle on 11 May 2020 # +1 votes

    @Jesusbill thanks, seems to be running. Now I need to figure out how it works ;)

  1. J by Jesusbill on 11 May 2020 #

    @brunopostle Great! I will make a new thread when I have some time to gather some links to useful resources.

  1. J by Jesusbill on 29 May 2020, edited 29 May 2020 # +3 votes
  1. B by brunopostle on 29 May 2020 # +1 votes

    @Jesusbill very impressive. This is also my experience with tensegrity structures.

  1. J by Jesusbill on 29 May 2020 #

    @brunopostle with the right tools and the right modelling choices, in this case cable elements for cables with no stiffness in compression and large displacements/large rotations analysis settings to satisfy the equilibrium in the deformed configuration, one should be able to simulate the actual, or let's say a realistic, behavior of a structure. In this particular case it is also impressive to watch :) certainly a nice "eye-candy" for Code_Aster

  1. B by brunopostle on 29 May 2020 #

    @Jesusbill I meant this is my experience with real tensegrity structures

  1. J by Jesusbill on 29 May 2020 #

    Yes I thought so @brunopostle, sounds great. To be honest I didn't know about tensegrity structures until a few months ago.

    I would be curious to know what you have worked on

  1. B by brunopostle on 29 May 2020 #

    @Jesusbill we never got past the physical mockup stage. Even the most famous tensegrity designs are extremely elastic, we quickly realised from our 2m high models that a 20m high structure wasn't going to be feasible.

  1. J by Jesusbill on 29 May 2020 #

    @brunopostle Yes they look like quite unstable structures by design

  1. M by Moult on 29 May 2020, edited 29 May 2020 #

    I've heard somewhere (no idea if true) that NASA is very interested in intensegrity structures - because if a space frame could be designed with a tensegrity structure, that would allow very large structures to be fabricated in space, with a much lower weight payload to bring up from Earth, as half the elements are tensile. I also heard how they were considering some form of extruder that would extrude out modules of this tensegrity space frame.

    No idea how that might or might not work, but sounded fascinating to me ;)

  1. R by ReD_CoDE on 30 May 2020, edited 30 May 2020 #

    @Moult a solar farm designed in this way and will be implemented in the space by NASA

    However, maybe I'm wrong, but the solvers and the approach you use is not interesting for NASA :)) (A clue: Iso...?)

  1. B by baswein on 30 May 2020 #

    So in space the intensegrity structures would rely on centrifugal force instead of gravity? It does seem like it could be more stable if the forces where radial.

  1. B by baswein on 30 May 2020 # +1 votes
  1. R by ReD_CoDE on 30 May 2020 #

    Yes, I saw this one too.

    I think gravity doesn't matter because it has a structure that causes always the sum of stresses be zero

    For NASA these kinds of challenges are easy to solve

    I think the main focus is or could be "MATERIALS"

  1. J by Jesusbill on 30 May 2020 # +2 votes

    @baswein said:

    Looks like they where exploring rovers using tensegrity structures.

    Interesting video, that would be relevant to tensegrity robotics. I even found a relevant GitHub repo https://github.com/NASA-Tensegrity-Robotics-Toolkit/NTRTsim

    @Moult said:

    I've heard somewhere (no idea if true) that NASA is very interested in intensegrity structures

    I did a quick search and came up with this https://www.nasa.gov/feature/tensegrity-approaches-to-in-space-construction-of-a-1g-growable-habitat/. They call it "Growth-Adapted Tensegrity Structures (GATS)" and in some part it says:

    The critical enabling technology for our GATS technology is Tensegrity Engineering, where new design methods, new dynamic models, and new control approaches are specialized for networks of axially-loaded elements, allowing the structural mass to be minimized, while the dynamic response can be controlled with minimal energy, with repairable, growable structural methods, using tractable analytical tools that are now available.

    The fact that they mention that the dynamic response is controlled with minimal energy leads me to think about active control systems, where one for example would alter the tension in the cables real-time and based on a feedback loop of the response of the structure to control and dissipate vibrations, but that's only an interpretation.

  1. R by ReD_CoDE on 30 May 2020 #

    IGA: Isogeometric analysis is a computational approach that offers the possibility of integrating finite element analysis (FEA) into conventional NURBS-based CAD design tools. Currently, it is necessary to convert data between CAD and FEA packages to analyse new designs during development, a difficult task since the two computational geometric approaches are different. Isogeometric analysis employs complex NURBS geometry (the basis of most CAD packages) in the FEA application directly. This allows models to be designed, tested and adjusted in one go, using a common data set.

    https://en.wikipedia.org/wiki/Isogeometric_analysis

  1. J by Jesusbill on 30 May 2020 #

    @ReD_CoDE it looks like an interesting approach but I have not seen any robust practical applications yet.

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