Sugestion for sofware for stress calculation

Discussion in 'Software' started by kaptcatb, Feb 17, 2023.

  1. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    Hello all,

    I have started to work on tanker modernization project.
    The client is installing some new equipment into the ship funnel and in the engine room. Due to that ship casing doubles its size (the funnel is extended aft ). We have prepared various drawings for the Class, but also FEM analysis of the aft ship structure is needed.

    The software wer normally use for stress calculation is incapable to make simulations due to the complexity of the model ( the model is too large, the program gives a bunch of errors etc.).
    Our model extends from the lower engine deck to the top of the casing, all bulkheads, deck and their stiffeners and girders.

    Can you please suggest software for such calculations?

    Thank you in advance

    Best regards
    Todor
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Hi Todor,

    before thinking about another software, Im curious about this statement:-

    What errors/limitations are you experiencing?
    Do you have an image of the FEM to give an idea of what is being modelled?
    Have you thought of sub-modelling regions of it too?

    It is rarely the case of the modelling being too complex for the software, but the way the model is made and the elements selected.
     
  3. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    Hello and thanks for your reply.

    The project is typical tanker construction. Superstructure is located in the aft part of the ship, the funnel is located behind the superstructure. We extend the funnel backwards in order to have the volume to fit new equipment/pipes into the new funnel. That extension has pillars connected to the deck below, reinforcements are placed below the pillars.

    In past, we have used FEM software, but we no longer have access to it ( no licence ). Only available stress calculation tool that we have is Autodesk Inventor - I know it's limited, but I just wanted to run a simple simulation to check if the pillars/deck below can withstand load from the new funnel part above it. I exported a very small part of the model ( part of deck + pillars ), but Inventor gives an error ( degenerate bodies or something similar, maybe because the deck plate is recognized as a thin body ). I think that we also have Autodesk Robot ( or w/e its called ) - I have never used it and I think its more into civil engineering.

    We need to run a simulation of the existing funnel structure+funnel extension+decks below up to ER for Class approval. That's maybe 10-15 times bigger that my current 3d model export into Inventor. That's why I'm looking for another software. I can simplify the model and ignore all brackets, lugs for openings in girders, local stiffeners etc, but not sure if Inventor can handle that model. Not sure if the Class will accept simulation only for decks, bulkheads, and web girders...

    Best regards
    Todor
     

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  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Todor,

    Aahh...indeed, Autodesk Inventor's FEA is very limited and not very good. You have no control over the mesh or elements.
    However, what you can do, if really desperate, model the whole structure with beam elements only. From that run the calc, then identify the regions of interest.
    Then create a shell element more detailed model, only of the area/region of interest, and transpose the boundary conditions, such as displacements etc, from the beam elements, onto the ow more detailed mesh.
    This is just sub-modelling.

    However Im not wholly sure whether you can do that in Autodesk Inventor.

    If at the end, you still seek FEA software, try Ansys, it is very good and robust. But it is rather complex to learn - you wont do it in 5mins!
     
  5. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    IIRC, AutoDesk has (or had...been out of the loop for a few years) a NASTRAN plug-in. That could save having to re-model. Also I'd run down what the error really means. "Degenerate" usually means that there was a problem generating a mesh element from the model, could be a stitching problem.
     
  6. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    @jehardiman - from what I have read online, the degenerate error happens when there's an element with almost zero areas and the software is unable or mesh it properly. In addition to that, Inventor didn't say which element has this issue. The only error that I see in the simulation window dialog is that my deck plates are recognized as thin bodies. Not sure if I try to split the deck plate into smaller pieces.

    In past, I have used Ansys, but it was 10+ years ago. From what I see now, the interface is changed a lot.
    What I'm looking for is a list of FEM software, capable to run simulations for plate/beam(profile). We have FEM software, but they do simulation only for beam construction ( civil engineering ). So any suggestion for such software is highly appreciated!

    Regards
    Todor
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    That tends to occur when the meshing has coincident nodes. Thus a 3 element triangular element has 2 nodes which are the same.
    And since Inventor ONLY produces triangular elements - it is highly likely that it has created/generated elements with 3 nodes, where 2 nodes are coincident.

    In my FE programme, it tells me which element are as such.... if this occurs.
    Any modern FEA programmes will do what your seek.
     
  8. jehardiman
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    jehardiman Senior Member

    Again, it has been years, but I recall that for most meshing widgets there is a setting that merges nodes within a given radius just to manage that problem. <shrug>. Anyway, if you want a recommendation ANSYS is what we where using in the office when I retired. It worked well with SolidWorks and RHINO.
     

  9. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "Usually" in most FE programmes, one can elect a tolerance to merge nodes.
    The down side, if the tolerance is "too large" for the size of model and mesh, one can merge 2 nodes, that should be, 2 node.
    Thus, the element then has zero area and is flagged as an error.
     
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