rigg calc: searching Software for 3d Framework Analysis

Discussion in 'Software' started by CBRA, Aug 14, 2013.

  1. CBRA
    Joined: Aug 2013
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    Location: Germany

    CBRA New Member

    Hi,
    Does anybody know a free or low cost software for calculating simple 3d Framework with (truss or Beam Elements).
    I want to use it for basic rigg calculations.

    thanks
    Chris
    _________________________________________
    NEW Scangaard 26 Classic Daysailer
    https://de-de.facebook.com/scangaard
     
  2. Olav
    Joined: Dec 2003
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    Olav arch. nav.

    Hey Chris,

    I can recommend CAMMPUS by Prof. Dr. Jürgen Dankwart.

    The downsides are: It will run on 32 bit systems only and - sorry for you other guys out there - it's only in German afaik.
     
  3. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    most of the rigging is designed by class rules based on a long history of data. It seems to me it would be nearly impossible to second guess what the maximum loads your rigging will experience in actual usage, if you assume too low, it will fail, if you assume too high than it will add extra weight and cost, and all of the calculations just become a math experiment.

    IOW, you do not really know what you are design for unless you are doing a "point" design for a very limited application (such as an inland lake racing dingy where the race is called off if the wind or waves are above a certain threshold).

    The German Lloyd's rules are available on-line, only down load the chapters applicable to your design, or use the design rules outline in Elements of Yacht Design by Llarson and Elisson. Little to no calcualtions required, you just stick to the rules for the size of boat you are building. You will get a strong and reliable design.

    Otherwise, if doing a completely new rig design (or experiment), than your strength will only be as good as your design assumptions.
     
  4. CBRA
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    CBRA New Member

    @ Olav: Thanks for that. I will try the CAMPUS program. Just downloaded it.

    @ Petros: I know the German Lloyd Rules and also the calculation in Larsson Eliasson, but what i am looking for is also flexing of the Rigg with big masthead Downwind sails and the loose of the forestay when sailing upwind.
    With the loads to apply you are right. It is crucial to get them right and to use the right safety factors.

    Any suggestions for the design loads for multihull riggs. Especially the additional loads for slamming and abrupt stopping when pitchpoling are hard to get right?
    Any suggestions for the strain/Young's Modulus of Dyneema ropes?
     
  5. CBRA
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    CBRA New Member

    A second thing i want to calculate is the actual benefits or drawbacks in rigg loads when changes in shroud and stay attachment point positions on the hulls are made.
     
  6. Petros
    Joined: Oct 2007
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    Petros Senior Member

    it would not be difficult to develop a model for pitchpoling loads I would think, but again they are only as good as your assumptions. the level of your uncertainty determines the size of your safety factor, 2 or 3 to one are not uncommon, but when maximum loads are well known, a safety factor of 1.2 to 1.5 is more common.

    the manufacturer of the rope should have that data, if not it would not be too difficult to rig up some weights on a length of rope, and a fairly accurate way of measuring strain/elongation.

    impact loads are much more difficult to predict, and are highly materials dependent. For example, on wood structures you are allowed to double the nominal allowed loads for impacts because of the wood's ability to flex and absorb the impacts as compared to steel or aluminum. Cyclic loading is another issue that is highly material dependent, wood, fiberglass and steel have very good and predictable fatigue properties, but aluminum has no fatigue limit and has a very unpredictable cyclic loading life, and that even varies greatly between the various alloys and heat treat conditions.

    It would be easy I would think to compare loading conditions for different attachment points. Compare the geometric load transfer between the different locations and you can get a ratio, either higher or lower, from which you can either up-size or down size the fittings, cables and fasteners.
     
  7. CBRA
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    CBRA New Member

    Right, but as i remember EN ISO 12215-9 has pretty good load assumptions for ring loads.

    The fatigue should be considered in the allowable design stresses for aluminum of the ISO.

    It could also be done by hand, but a rigg structure in reality has geometric non-linear behavior and i want to consider that to.
     

  8. quequen
    Joined: Jul 2009
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    Location: argentina

    quequen Senior Member

    AXIS VM light is free, limited to 40 linear elements and 20 load cases, may be enough for a standard sail rigging:

    http://axisvm.eu/axisvm_download_free_light.html

    There's a free and full version for students that runs by 180 days under registration.
     
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