Software for flow analysis of moving boat

Discussion in 'Hydrodynamics and Aerodynamics' started by jsanchez0510, Nov 30, 2011.

  1. jsanchez0510
    Joined: Nov 2011
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    jsanchez0510 New Member

    I am a Mechanical Engineering student at University of Central Florida.

    I need to perform flow analysis on a moving hull profile. I downloaded Maxsurf but it only seems to calculate hydrostatics.

    Is there another boat design software with these capabilities ??

    Thanks in advance
     
  2. Leo Lazauskas
    Joined: Jan 2002
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    Leo Lazauskas Senior Member

    What type of boat/ship?
    What do you need from the software?
    Wave elevations a long way behind the boat?
    Close to the boat?
    Do you need wave resistance and other drag components?
    Do you want velocity vectors and other detailed output?
    The answers to these questions will determine whether you need to use CFD or simpler, classical hydrodynamic, methods.

    Leo.
     
  3. jsanchez0510
    Joined: Nov 2011
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    jsanchez0510 New Member

    we are making a
    L18.2ft x W5.75ft x H1.66ft
    Made out of thin lightweight fiberglass
    Gheen Manufacturing Inc. in Titusville FL
    http://www.gheenoe.net/
    is helping us with the manufacturing portion.

    However I need to analyze how the design as well as dimensions chosen affect speed and handling in still water.

    Perhaps be able to moify the dimensions and shape, run the analysis again and see if velocity and acceleration increase.

    Drag components will be useful. I now that adding hydrofoils reduces wet area so it would be good to test that as well.

    We are participating in a competition called solar splash
    http://www.solarsplash.com/index.php

    thank you
     
  4. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    There are two fundamentally different ways to analyze the hydrodynamic characteristics of boats.

    A) Regression The hull is described by a set of parameters which are typically dimensions and coefficients. This set of paremeters is then put into a formula which calculates various performance values such as resistance. There are many different formulas which can be used, and the applicability of a particular formula depends on the shape of the hull and the speed range. The formulas are generally derived using regrission on experimental results for a set of models. This method works well as along as the hull shape and speed range is sufficiently similar to the shapes of the models and the speed ranges tested which were used as the basis for the formulas. A common mistake is to try to use a formula for a boat shape and/or speed range for which it is not appropriate. Savitsky is popular for V-bottom planning hulls and Holtrop for displacement hulls but there are many alternatives.

    You can find various formulas in naval architecture literature. Various formulas have also been put into software including FreeShip and DelftShip. If you are using Rhino3D for hull geometry then Orca3D Level 2 is a plug-in which includes hydrodynamic analysis. Contact the Orca folks about getting a student version. http://www.orca3d.com

    B) Physics These methods attempt to the model the flow of water around the hull. These can be further divided into those which use an intergral approach and the finite difference / finite volume / finite element methods. If the hull is sufficiently thin and smooth then Michlet which is a thin-ship integral method can be used. Michlet is relatively easy to learn. There are other integral methods similar to aerodynamic panel methods which use varying levels of sophistication to model the free surface of the water.

    The finite difference / finite volume / finite element methods seem to be the more popular "physics" methods, and commercial codes are avaialble. Your school may even have one. But using these codes for boats is fundamentally more difficult than for something like an aircraft because the free surface of the water needs to be properly handled. On the other hand they can produce nice color pictures which look realistic even when they are fundamentally wrong.
     
  5. jsanchez0510
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    jsanchez0510 New Member

    I am not using Rhino. It costs $195 for students and I was hoping to find some free software such as Maxsurf.

    Is there any other??
     
  6. DCockey
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    Location: Midcoast Maine

    DCockey Senior Member

  7. Alik
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    Alik Senior Member

    The worst thing beginner can make is to start using software without knowledge on what is inside back box. In this case, the result is unpredictable.

    So, a) study prediction methods, to make justified choice and get ability to evaluate the result or b) involve an expert or just student/college who possess required knowledge.
     
  8. DCockey
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    DCockey Senior Member

    Excellent advice, though best if both a) and b) can be done.
     
  9. abdo
    Joined: Dec 2011
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    abdo Junior Member

    hello . i am using maxsurf just for design the hull and calculate hydrostatic . if you want to calculate the seakeeping in still water you can use seakeeper
     
  10. jsanchez0510
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    jsanchez0510 New Member

    How can I get Seakeeper?? I have the academic version of maxsurf but it seems not to have it.
    I have been trying to work with free ship+ but cannot get any analysis thus far.
     
  11. Alik
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    Alik Senior Member

    Don't look for magic software. There is none. Seakeeper? What can You get from it? Rows of numbers You do not understand? What is the accuracy? Do You know what is speed limitation for seakeeper? Study few methods of seakeeping predictions, start from simple - Savitsky-Brown, Hoggard-Jones, etc.
     
  12. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I agree with Alik and others

    If there was a magic button we could push that said "optimise hull" we'd all use it, and by implication be out of a job.

    The same applies to that guitar playing software you can download. It wouldn't turn me into Eric Clapton.

    I have to ask, "why does a mech eng student need to do a flow analysis? surely you have a fellow student doing naval arch who could do that part"

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  13. DCockey
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    DCockey Senior Member

    The University of Central Florida doesn't have naval architecture students. There are only a very few universities in the US with naval architecture or related programs. I'm not associated with University of Central Florida but may be able to help with some of the background for why some students not studying naval architecture pop-up on this forum asking about boat design.

    Why are teams of students from universities around the US without naval architecture programs designing and building solar powered boats? And why are over 200 teams of civil engineering students designing and building concrete canoes? Simple answer is it provides good experience in design, construction and project management in an enviornment with constraints on cost and time where the success (or failure) of the effort is readily apparent. Projects involving boats also force students who haven't studied naval architecture to think and work beyond what their course work has covered. Part of the competitions is the preparation and presentation of technical reports about the designs.

    These projects are one way students discover that engineering is more than finding the right software, providing the appropriate input, and clicking the "go" button. Some students learn that lesson quicker than others. Occasionally on this forum we have the opportunity to help students with that lesson, hopefully in a constructive manner.
     
  14. PAR
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    PAR Yacht Designer/Builder

    David has nailed it. The primary object of these "problems" are to teach the student to be resourceful and preform the necessary research. This is the hall mark of every good engineer: research.
     

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

    Agreed.

    However, there is a big difference between a student who comes on says:

    I have done some research...i found that X states Y and another that A states that B is correct...which would you advise or suggest is applicable.

    The inference here is that the student has already done some research and is asking for a wider opinion to assist.

    That is a far cry from those that pop up asking for detailed technical information, which, as you're both implying, is outside their course work and constantly ask follow up questions because it is not their field and are thus still confused. If they did the research to begin with, they would know. Isnt that what you're suggesting that they should be doing to begin with?

    Thus it appears that many are wishing to get a short circuit to a "click here for answer" button. Helping students along the way is fine as it is our prerogative to train up the next generation of naval architects. (I have been doing this for a long time now all ages, and also occasionally teaching post-grad students). But when part of the training is simply giving them the answer, as the student is unwilling to do the leg work themselves to begin with .. is another matter entirely.
     
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