Rhinoceros and Orca3d plugin

Discussion in 'Stability' started by mizkuzi, Jul 7, 2011.

  1. mizkuzi
    Joined: May 2011
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    mizkuzi Junior Member

    has anybody of u have used Rhinoceros program with Orca3d plugin? I wanted to ask for those who have used.. Can orca3d compute all the necessary stability calculation needed after inclining experiment? I really need to know, i have checked the website already but i still want to ask those who have been using it. I need to do the stability calculations after we incline our boat by mid of this month but i want to try using this Orca3d software to generate all the calculations since we are using Rhino in the company. I will buy a copy but i need to get feedbacks first from those who have tried using Orca.

    Thanks everyone!
  2. Mark Cat
    Joined: Jun 2011
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    Mark Cat Senior Member


    I use Rhino + T-Splines + Orca3D for preliminary hull/vessel 3D concepts for first cut conceptual design. The focus is on hydrostatics and styling.

    I am unaware of any large firm using Orca3D for production release of hydrostatics, hydrodynamics, and stability.

    However, Rhino + Orca3D + T-Splines is very fast for concepts for the NAs. Using a very rough estimate on required specs, a design can be done quickly per hull type and hydrostatics checked. Then the overall styling concept is completed by the designers.

    This is a good and fast first cut for the customer. I believe it is more effective to provide a viewable 3D model in addition to the basic 2D drawings for concept approval. Many 3D viewers are free, and run on a PC.

    So I believe Orca3D is very useful and provides good value to the company.

    The approach to stability depends greatly on the lead NA's techniques and tools. Usually, in my experience, a mix of CAD software and spreadsheet analysis. So the Rhino 3D hull surface would be translated and imported into other 3D CAD for continued work on the proposed hull form. Once the final form is completed it can then be moved back to Rhino or any other 3D packaged used for continued design and manufacture.

    Orca3D support is very good, they also have good webinars. Just send them an email.

  3. mizkuzi
    Joined: May 2011
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    mizkuzi Junior Member

    thats great thanks for the idea...were going to buy it. ^_^
  4. mizkuzi
    Joined: May 2011
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    mizkuzi Junior Member


    I have found that orca3d gives VCG value (VCG=KG) and GM but cannot find KM. Ive been calculating something for the inclining weight to be moved and i used the value of GM in lightweight condition from orca3d.

    w = (GM x disp x tan theta)/d

    where d: distance of weights to be shifted.
    w = weight to be shifted

    My classmates asked me were i got KG value so i told them i got it from the orca report. Now she makes me confused coz she told me i can never get a KG value from the hydrostatic calculation but only during the inclining exp and thats the inclining purpose... but orca does gave me this value? i believed the KG i will need to get on the actual is just to compare how different the KG i got from the design.
    Anybody knows please let me understand.

    by the way regarding my calculation i need to know if i got it correct:
    datas: calculating the inclination weight to incline the boat at least 2 degrees.

    power catamaran
    LOA = 12.48m
    BOA=5.90 m
    Depth (overall) = 2.63m
    disp. = 7 tonnes
    assumed inclination angle = 2 degrees
    GM = 13.59 m (as shown from orca3d hydro calc report)
    VCG or KG = 1.1 m
    distance to which w will be move = 2 m


    w = (GM x disp. x tan theta)/d

    w = (13.59m x 7t x tan 2 degrees) / 2 m

    w = 1.66 tonnes (do u think this is acceptable?)

    i need ideas coz this is my first time to do the inclination experiment hopefully by the end of this month as the boat will be finished. thanks!

    regards to all!
  5. bbfm
    Joined: Dec 2010
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    bbfm New Member

    Post Inclining Calcs

    I do not any experience with Orca3d. It appears it can produce the required hydrostatics properties needed, but to show compliance with any stability requirements will require post analysis and reporting. Also, I believe it does not handle liquid cargo which means the volume and centers of tanks will need to be computed separately and a free surface correction applied.

    Is the VCG from Orca3d from the Weight and Cost module? That would be an estimate of the actual VCG that is a result of the inclining. Useful for estimating the weight needed for the inclining. I have seen inclinings where there wasn't enough weight available and some with too much. Depending on your confidence in the estimated VCG, you might allow some wiggle room. It might not be possible to get 1.66 mtons, you may only have 1.5 or 2.0. Will that give enough or too much heel.

    Crane operators like it when the engineers look like they don't know what they're doing.
  6. lleibman
    Joined: Jul 2011
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    lleibman New Member

    Orca3D and Hydrostatics Calcls

    Hello Mizkuzi,

    As one of the developers of Orca3D I thought it would be appropriate to comment here and hopefully provide some clarification.

    Orca3D provides two different approaches to compute the hydrostatics properties of a vessel. One approach involves specifying the location and orientation of the floatation plane (via a sinkage, heel, and trim) for which the hydrostatics are to be computed. This approach requires knowledge only of the geometry of the vessel and does not require knowledge of the vessels mass properties. The second approach involves specifying the mass properties of the vessel including its weight (mass) and CG (center of mass) location. This approach obviously requires the user to have knowledge of the vessel's mass properties and performs an iterative computation to determine the equilibrium condition of the vessel.

    Orca3D does not inherently know what the mass properties of the vessel are. However, the weight/cost tracking capabilities in Orca3D can assist you in estimating the mass and CG location. When the Orca3D hydrostatics output reports the VCG location, it is just the value that was input. You will note that when performing an Orca3D hydrostatics computation using the first approach described above, no VCG location is reported as none was input. Note also that when Orca3D makes reference to a location such as the CG, we use the Rhino origin as the reference for that location and use terms like VCG as opposed to KG. This is done because the location K, typically meaning the keel or baseline, can be ambiguous on many vessels while the location of the Rhino origin is never ambiguous.

    Now in regard to the incline experiment, as you noted the principal purpose of the experiment is to establish the vessel's weight and VCG location (and initial GMt). Referring to the formula you present, it can be similarly written as,

    Heeling Moment = w * d = GMt * displacement * tan(heel angle)

    Ultimately what you will be trying to compute from the incline experiment is GMt by moving a known weight (w) a known distance (d) to induce a heel angle that can be measured. The displacement is obtained by measuring the starting draft marks to determine the floatation plane. As noted above this together with a known vessel geometry, allows Orca3D to compute vessel displacement (you use the draft marks to define equivalent sinkage, heel, and trim values for input to Orca3D). As noted by the previous poster, Orca3D does not currently account for free surface effects so you will need to either ensure full or empty tanks during the incline or account for any partially filled tank via a free surface correction.

    Once you've computed GMt by the above formula, you can compute the VCG value. As described earlier, Orca3D does not output the height of the metacenter as KM because K is ambiguous. Instead it provides the height of the metacenter as Mt (for transverse metacenter or Ml for longitudinal metacenter) which is referenced to the equilibrium flotation plane, an unambiguous reference. Using the formula below

    VCG' = Mt - GMt

    where the prime denotes that the VCG value is relative to the equlibrium flotation plane. In order to make this value relative to the Rhino origin in your model,

    VCG = VCG' + LCG * sin(trim angle) + sinkage (watch the signs depending on the orientation of your model with respect to Rhino axes)

    Without getting into the details of the specific inclining procedure (which you can find in any of a number of references), you can also use Orca3D with the formula above to get an idea of what size weight and/or how far you need to move that weight to induce a particular heel angle. Too small a weight and you may not be able to induce a large enough heel angle to be accurately measured. Too large of a weight and you may exceed the range of heel angles for which the approximation GZ = GM * sin(heel angle) is valid. To do this you need to estimate a displacement and VCG based on your most recent weight estimate. Use these as input to Orca3D hydrostatics and you will obtain an estimate of GMt as a result. This together with and idea of what heel angle you would like to induce will allow you to determine what heeling moment you need to produce during the experiment.

    Hopefully this helps to clarify how you can use Orca3D to both prepare for an inclining experiment as well as analyze the results.

    Kind Regards,

    Larry Leibman
    DRS Defense Solutions, AMTC
    3 people like this.
  7. Mark Cat
    Joined: Jun 2011
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    Mark Cat Senior Member


    After you get a feel for the hydrostatics and stability, I think you will find it is a good first cut per vessel concept (requirements). I have been doing more "final" C2 (G2) surface work in Solidworks for the proposed final hull shape rather than Rhino. I find myself doing final lofts in SW which is faster at working with the 2 point splines than Rhino when working from a set of lines from the NA.

    As early as possible it is good to establish the base hull final shape with the NAs and Designers (styling) at a point where the waterline and major equipment locations are standardized for a proposed version of the vessel. This allows a floor plan to be adopted so the other team members can start work on the different compartments as soon as project contract sign off.

    So look at a work flow that gets you quickly to the milestones per your process, and work to streamline for best efficiency for the project leader.

    At some point you will need to move the concept into other 3D packages. I was wondering what 3D CAD tool chain you were targeting?



  8. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Thanks for your post Larry. Welcome to the forum.
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