FEA Software Again

Discussion in 'Software' started by FeaMan, Feb 13, 2008.

  1. FeaMan
    Joined: Feb 2008
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    FeaMan Junior Member

    Trying to avoid the risk of being called a "spammer", apologies to the moderators if this breaches the rules. I work for ANSYS in the UK, and just wanted to say that if anyone needs any advice regarding FEA software, please feel free to contact me: glenn.davis@ansys.com or 07968 855759. I must point out this is for UK only.

    ANSYS Products Include:

    ANSYS AQWA
    ANSYS ASAS
    ANSYS Mechanical
    ANSYS CFX (CFD)
    ANSYS FLUENT

    Many Thanks


    Glenn Davis
     
  2. yipster
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    yipster designer

  3. MikeJohns
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    MikeJohns Senior Member

    Glenn
    Are you happy answering questions here or do you want to restrict it to email?

    Cheers
     
  4. FeaMan
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    FeaMan Junior Member

    Happy to discuss here, as long as its not too technical!:!:
     
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  5. Aquaplanning
    Joined: Jun 2007
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    Aquaplanning Geert-Jan

    How to start with FEA

    Well, here's question nr. 1:

    I'm trying to figure out how much time it will take me to learn FEA on a basic level. For instance: I have a sailboat model in Rhino. I would like to find out what the stress levels are around the stanchions/ mast foundation.

    I guess I would heel the hull to the maximum righting moment, and put forces on winches, stanchions, mast compression etc. (It would be nice to work with Dutch shipping rules, that work with sudden windgusts!)

    So I look at the Strand7 package, read some very complimentary comments on the Rhino Wiki, only to find out that the manual has 262 pages, in a techno language I find hard to understand. Also, I miss information on how to model the force of water against the hull. Most information is about forces with a clear direction and magnitude.

    My question is: what is a good way to start with FEA? Are there sites like rhino.tv with video?
     
  6. MikeJohns
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    MikeJohns Senior Member

    FEA is a tool for people with a high level of structural engineering knowledge AKA engineers, It is not trivial and it is easy to get very correct results that are not very useful unless you really know what you are doing.

    A problem you must consider with an object on the water surface is that there are often considerable dynamic loads unless you are designing for sheltered water only.

    FEA on yachts should be considered a design tool rather than an analysis tool. Identifying stressed areas of the structure and designing to keep those stresses below the level where they become a fatigue issue and also within your factor of safety. Rules of thumb are a very valid design process.

    Having said that, in Strand/Straus the process is very easy and intuitive for this sort of simple multi-element design.

    Create your elements physical properties, spreaders, stays, mast, then create a point cloud corresponding to all the key positions (you can pull this in from a spreadsheet) put extra points in an element doesn't break it up but allows point loads and analysis at those points. Create elements between points ( simple; create element and click on points) . Fix the fixed ends of the elements.
    Loads are then applied to points or distributed along an element. Pre-stress in wires by making the initial length less than the model defined length. This will give you the tensions compressions and displacements and stress patterns, best run non-linear static. You may have to set up rotational restraints to keep the solver happy.

    This is multi element structural modeling. Solids is quite different and not as easy.

    Glenn may like to give the basic procedure for Ansys for comparisson

    You can email me directly engden@aapt.net.au

    Cheers
     
  7. yipster
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    yipster designer

    Mike, i'm no engineer, studied industrial design long ago and only a few year math and physics at university but now into boatdesign, scantling books etc have a quik peek into my gallery to get the idea i'm now also playing with inventor, nice drawingtool too but is there anything to be gained trying the FEA in inventor? any cool FEA book recomandation?
     
  8. MikeJohns
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    MikeJohns Senior Member

    There are two approaches that I use. Firstly an element based assessment of the structure, using individual elements, then a detailed solids model of the jointing of the structural members to ensure the stresses flow. The more indeterminate the loads the greater the FOS you must use, but understand the difference between FEA as a basic 'design' tool and FEA as a cutting edge 'analysis' tool. The latter does not lend itself well to marine engineering unless you are very specialized in a particular area.

    The embedded FEA in the likes of Solidworks and Inventer is oriented towards solids. This is not very useful for complex structural entities as the model gets too big (too long to solve) and the result is only as accurate as your assessment of the loads. They are good for bolted connections, components, individual frames, panel assesments, engine beds, mast steps etc

    There are no books I would recommend, if you look up 'Cadre' http://www.cadreanalytic.com/Cadrepro.htm people find it a good package for boat work , things like one way elements for rigging . Used to be some good tutorials available if you email them perhaps.

    Beste Groete
     
  9. lazeyjack

    lazeyjack Guest

    hey people
    anomoly in Rhino , try the length of the beam,. it is way out of whack? 1553, shud be 1482
     

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  10. sailaweigh
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    sailaweigh Junior Member

    I doubt it's the software. Check your work?
     
  11. MikeJohns
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    MikeJohns Senior Member

    Stu
    I just looked at your dwg, its not on a single plane.
    Look at your top view and you'll see.

    Cheers
     
  12. rapscallion
    Joined: Oct 2006
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    rapscallion Senior Member

    I know where you are coming from, I have been trying to teach myself FEA for several months now. I would start with the book "Boat Strength," it has the info you need for the most part. If you want to go deeper, read "principles of yacht design." That book goes into FEA enough to work your way through ISO 12215. There is a Spreadsheet in this forum that calculates scantlings based on Gerr's "boat strength" book, you might want to take a look at that too.

    I'm working on an ISO 12215 based scantling spreadsheet for trimarans. Gerr's book helped to a certain point. I wanted to consider nida and polycore, and there was no treatment for those core materials in his book.

    I also wanted to compare strength, weight, and cost of various material AND STRUCTURAL combinations. For example, I would like to compare a thin skin GRP with a frame reinforcement to a monocque construction. Gerr helps but is a bit limited in that respect as well.

    I have a feeling based on your post that Gerr's book will answer most if not all of your questions.
     

  13. FeaMan
    Joined: Feb 2008
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    FeaMan Junior Member

    Hi All

    Mike is right FEA is a tool for people who have at least a basic understanding of engineering principles. As the saying goes, you put SH*! in you get SH*! out. Although we have rededisgned our software to accomodate ease of use with standard windows drop down menus and input boxes.

    ANSYS offer a number of options to help with this, including our ANSYS AQWQ suite, which is a CFD code specifically for hydrodynamics, which can be couples to ANSYS FEMGV to calculate wave loadings on hull structures, beams etc.

    If you are UK based, and have a some spare time on the 17th June 08, you can come to our Marine day in Portsmouth. We will be showing FEA, CFD, AQWA and ASAS (Marine specific) as well as having a number of machines available for people to get hands on with the software on offer. (please see my seperate thread)

    Regarding publications, there are few specific to your particular area of expertise, however i have seen some good FEA publications on Amazon, which may be worth investigating.
     
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