AUV: CFDAnalysis

Discussion in 'Software' started by dtoshni, May 15, 2009.

  1. dtoshni
    Joined: May 2008
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    Location: Lisbon

    dtoshni Junior Member

    Hi!

    I would like to know that which one is a better software for doing CFD analysis of an AUV: Solidoworks (COSMOSFloWorks) or FLUENT?

    I know that Solidworks uses the k-epsilon model and that fluent gives the user more options as to the model to be used, but apart from that, COSMOSFloWorks just seems to be easier than FLUENT, as far as usage is concerned. Are there any drawbacks to using FloWorks? Or should I go with FLUENT only?

    And also, I calculated the horizontal component of the total force in a flow of 1m/s using FloWorks. Is this value equal to the total resistance of the vehicle? It just says "Horizontal component of the Force" and I had defined "Horizontal component of total Force" as a "global goal". Is the solution to this problem the resistance of the vehicle?

    I'd be highly obliged if you all can help me.

    Thank you.
     
  2. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Fluent is a professional CFD package which allows you to have a vast control of the physical parameters involved in the analysis. It has been used for the design of the winning Alinghi AC racing yachts, just to give you an example. But it is not easy to use for a beginner, particularly for one who doesn't have a firm background in aero/hydrodynamics.

    On the other hand, Cosmos FloWorks is a nice and well-done tool for quick CFD analysis of internal or external flows in a single-phase fluid with no surface effects. You can use it for the preliminary evaluation of your AUV design as long as it's geometry is not too complex and only if you are considering deep-dive conditions.
    If you want to be sure about the results, you need to perform first a number of CFD test runs with some UAV hull model (sufficiently similar to yours) with known resistance data. It will allow you to calibrate the simulatior parameters until the CFD output coincide with experimental data within desired accuracy. Then you can use these parameters for the evaluation of your design, and can be confident that the results are sufficiently close to the reality.

    P.S.
    Yes, the horizontal force component is what you are looking for - if your free-stream flow has only a Vx velocity component.
     
  3. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    I use Cosmos/M FEA and consider it the most user friendly FEA available on the market, i swear by it. I have not used their floWorks, but i can imagine it is 'of similar' layout.

    But just like FEA, the best software is the one that is most affordable and user friendly for you to use. Since all decent commercially available software must meet minimum requirements of consistency and accuracy.

    Whilst i favour Cosmos/M for my FEA there are many others out there just as good, some not so. But all of them pass the basic patch test and should at least to comply with NAFEMS.

    So i would say it is a matter of personal preference really.

    But as Daiquiri noted if you're getting serious about the actual results, then you can't beat a real tank test.
     
  4. alidesigner
    Joined: Nov 2006
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    Location: Australia

    alidesigner Senior Member

    Unfortunatley the Cosmos that you know Adhoc is no longer available. You can now only get cosmos as part of Solidworks, and its very different to what we used to use. The solidworks version doesnt even support offset beam elements!!

    Dtoshni - If you own Solidworks log in to your customer portal and check out the bugs list to see if any of them will affect you.

    If you are thinking of buying Solidworks to do flow simulation then you will need to create your model in solidworks so ask the sales rep to log in to the portal and show you the bugs list for both solidworks and cosmosflow. They will most likely make some excuse as to why they cant and that should make your decision easier. If your model will be made of surfaces get them to show you how it works with surfaces (remember solidworks is a solid modeller)

    Also google 'solidworks bugs' and see what solidworks users are saying.
     
  5. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    alidesigner

    yes, so i am learning. The cosmos we used to use way back in those "good old days", luckily i still have and use. No need for upgrades either, does the job well.
    Pity, is/was an excellent product.
     

  6. dtoshni
    Joined: May 2008
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    Location: Lisbon

    dtoshni Junior Member

    Thank you everyone. I shall keep this in mind whilst I am doing the analysis. :) Thanks a lot.
     
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