Wrong Cb calculated in Maxsurf (problem with import from Rhino)

Discussion in 'Software' started by Xthesinos, Mar 8, 2015.

  1. Xthesinos
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    Xthesinos Junior Member

    Hello everyone, I'm a new member but you have helped me many times before. Thank you.

    So, i opened Maxsurf for the first time yesterday and i want to build a very simple barge-shaped FPSO. Not having access to the formsys tutorials yet, I tried to understand how the modeller works but after a while I migrated to rhino as the shape of the hull i need is very simple.

    I imported the attached file in Maxsurf modeller (import > rhino file) as it came out of rhino, and there is a problem with how Maxsurf ''reads'' the geometry. I put a draft of 18m and the Cb comes out as 0.436 which is wrong.

    I tried to change the rhino file (converted the surfaces to solids, joined surfaces in the region i think is the problem-see below, etc) but other problems occured during import.

    I also went to see the 'curves of form' diagram in the stability module and from the Cb curve i can see that there is a problem in the lower region (around z=2.3m) where i filleted the structure in rhino. However i cannot seem to find what i have to do.

    I thank you in advance for your help!
     

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  2. DCockey
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    DCockey Senior Member

    I imported the .3dm file you posted into Rhino. 44 surfaces, no polysurfaces. no solides. (By the way, a solid in Rhino is just a closed polysurface.) I discarded the surfaces representing the internal structure, joined the outer surfaces into a closed polysurface, and used Orca for analysis. Cb is 0.932 with draft of 18m.

    Create a barge without fillets or internal structure and try importing it into MaxSurf and see what happens.
     
  3. Xthesinos
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    Xthesinos Junior Member

    DCockey, thanks for the quick answer.

    Yes, the rhino file that i uploaded is the one i used in the first attempt. Then i tried to join surfaces etc but that made it worse. MaxSurf wasn't reading the whole structure.

    The Cb you calculated is what i was also expecting. Before moving to create the structure in rhino, i managed to make the same barge without internal structures or fillets in Maxsurf. Then i realised that i wanted fillets and i decided to do it in rhino as i didn't manage to find any thorough tutorials for Maxsurf.

    So, there is no way to run this model made with rhino (with fillets etc) in Maxsurf?

    Thanks again.
     
  4. DCockey
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    DCockey Senior Member

    I don't use MaxSurf so the following is just a guess.

    Try selecting and joining only the outer surfaces in Rhino into a single polysurface and export that polysurface as a model. Then import that model into MaxSurf.

    Trying to join both the inner and outer surfaces in Rhino will probably result in a mess.
     
  5. Xthesinos
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    Xthesinos Junior Member

    I also did exactly that, i.e. i joined all the external surfaces alone into one. It resulted in Maxsurf showing me an error and then displaying the structure in a mess and without some of the joined parts.

    The fillets seem to be the problem. However, it is strange that when the surfaces are separate (attached file), there is no visible problem with the import, but something is not interpreted well resulting in a wrong Cb calculation.

    Thanks again
     
  6. bhnautika
    Joined: Feb 2006
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    bhnautika Senior Member

    Xthesinos Importing trimmed surfaces and things like fillets into maxsurf never really, if ever, works well, you are far better off to build your basic model in maxsurf, get your info then export to rhino to finishing off. I re- did the main surfaces in maxsurf and got Cb of .93 without the fillets which DCockey got from the model in rhino/Orca. Rhino join command doesn't really join surfaces only groups them into single surface to do other things with.
     
  7. Dr34m3r
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    Dr34m3r Senior Member

    as suggested, try to build the model in maxsurf, that will give you more accurate results.
     
  8. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Xthesinos, import Rhino model into Maxsurf. This done, in Maxsurf, deletes all surfaces except the numbers 2, 3, 4, 6, 7, 8 and 43. Make breadth for all starboard points equal to zero. Declares these seven surfaces as symmetric about the center line.
    Forget all interior bulkheads. Tanks and compartments can be defined in Hydromax without consideration of these bulkheads.
    You must always ensure that the model is as simple as possible. There are details that are very time consuming to model and give no precise (and this is negligible) calculations. And intends to work, whenever possible, with just one side of the ship, port or starboard.
     
  9. bhnautika
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    bhnautika Senior Member

    Xthesinos have a look at this maxsurf file imported from rhino after I changed some of the surfaces to different types. I then did a little work in maxsurf (duplication etc.)
     

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  10. Xthesinos
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    Xthesinos Junior Member

    Thank you all for you help!

    On a side note, does anyone have the official tutorials which i have not access to? or any other ones (i have the manual). It would be very helpful for me if you could send them to me or provide a link.

    Thank you.

    xthesinos@gmail.com
     
  11. Xthesinos
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    Xthesinos Junior Member

    Bhnautika, i didn't see your reply before posting.
    Thank you a lot!

    I would appreciate very much if you could tell me what you did in rhino and maxsurf to make it work (other than deleting the inner surfaces and the deck).
    Also, by duplicate you mean offset-copy?
     
  12. bhnautika
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    bhnautika Senior Member

    The problem is the trimmed surfaces in the pic barge rebuild 1 I have turned on the control points for the fillet edge as you can see the red surfaces the points are off the ends so maxsurf see that is where the surface edge is. The green surfaces are ok the points are on the edges, so we can keep those and use them to rebuild the other edges. In the pic barge rebuild 2 I have deleted the red surfaces and using the Extrude command off the green edges, I re did the new surfaces (yellow). The pale blue surface was done with the Surface from 2,3 or 4 edge curves command. Then using the edges of these new surfaces I extruded to the mid point centre line (purple) and deleted the old surfaces (barge rebuild 3). The side surface is also a trimmed surface (barge rebuild 4 ) so I deleted that then used the extrude on those edges to get a surface (blue). There were two issues that popped up, one was that rhino would not extrude the bottom curve and the end of the surfaces weren't straight. To quickly fix the end issue I used the Setpoint/ xyz coordinates command in the transform menu. I turned on the control points for the two blue surfaces, selected the end points then set point command and using the X coordinate ( barge rebuild 5) I then snapped to the end of the yellow surface so all the points line up to that point. To finish off the surfaces I drew a line connecting the two corners of the surfaces at the end, then used the Surface from 2,3 or 4 edge curves command again (pale blue in barge rebuild 6). I then exported out the surfaces as IGES into maxsurf, then ticked the symetrical box for each surface. I then used the flip copy command to get both ends.
     

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  13. TANSL
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    TANSL Senior Member

    Congratulations, you got the model of the barge operating in Maxsurf. My question now is whether, from the point of view of construction shipyard, worth doing those rounded corners. A boat as simple as a barge, why do you need those soft curves?.
    Not to be negative, just realistic.
     
  14. Xthesinos
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    Xthesinos Junior Member

    Bhnautika, i thank you very much for the detailed procedure.
    TANSL, you are right, it doesn't make sense from a construction point of view.
    However, after designing it with fillets in rhino and not seeing it working, I just wanted to find out what caused the problem and then how can someone fix it. With Bhnautika's help, i can now use fillets in another application while modelling in rhino and then importing it in Maxsurf.

    Thank you all once again.
     

  15. TANSL
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    TANSL Senior Member

    Yes, good advices that will be very useful in the future. Bhnautika is an artists doing renderings, there is more to see his Gallery.
    Cheers
     
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