Structural Analysis Software!?

Discussion in 'Software' started by TealTiger, Mar 23, 2012.

  1. TealTiger
    Joined: Sep 2009
    Posts: 83
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Toronto

    TealTiger Junior Member

    What software if any is used to do a structural analysis on a boat? I know it will have to be checked (at least) by an NA but I'd like to do as much as possible myself first. This is for a typical 38' ocean cruising cat using conventional materials, but in an unconventional mix/way.
     
  2. DCockey
    Joined: Oct 2009
    Posts: 5,229
    Likes: 634, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Who will model and mesh the boat in a manner suitable for structural analysis using the software?

    Where will the loads come from? This is a non-trivial question.

    Who will interpret the results?
     
  3. TealTiger
    Joined: Sep 2009
    Posts: 83
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Toronto

    TealTiger Junior Member

    Hi David,

    Thanks for the questions. I'm not up on this stuff yet, so I may not be using the best terminology. I'm not sure if I need the detail that your question seems to indicate to me. I certainly don't need FEA. I want to take a fairly conventional cat (like a lighter simpler Lagoon 380) and find out if my material choices and spec's are aprox. strong enough. If so, I can pay more to get it thoroughly to get it done. So before I throw a lot of money at doing a through job of what might be a waste, I'd like to do everything I can to minimize the job of finding out if I'm on the right track. I'm interested in hearing any advice the people here might have to say. Thanks.
     
  4. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Save yourself money and:

    1) download any of the Classification society rules that are now available for free, such as here: http://www.boatdesign.net/forums/classification/dnv-hslc-snc-2012-rules-42292.html

    and

    2) Buy a good book on composite design.

    No need for fancy FEA....unless you like looking at pretty coloured pictures?

    1) Will tell you if it is strong enough, since if Class accept the layup, then it is a good baseline minimum.
    2) A good book on composites shall highlight areas that Class does not, and also pointers for practical things to consider.

    If these are beyond you to begin with, then best seek a NA that deals with composite design. Good luck :cool:
     
  5. Alik
    Joined: Jul 2003
    Posts: 3,075
    Likes: 357, Points: 93, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    2AdHoc
    I would not use DNV HSLC for 38' cruising cat, as thickness of bottom sandwich skin would be excessive.

    Use ISO12215-5 is much better option; here on forum it was free calculator for these rules.
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Interesting.

    I designed a 15m cat to the DNV rules a few years ago...all came out ok. As I expected really. So, either the DNV rules are excess, as you say, or ISO is deficient. Either way...take your pick :p
     
  7. Alik
    Joined: Jul 2003
    Posts: 3,075
    Likes: 357, Points: 93, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    They have min glass weight requirement for skins. Those are a bit excessive, for sailboat of 38'.
     
    1 person likes this.
  8. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Depends upon your definition of ..."excessive" :p
     
  9. Petros
    Joined: Oct 2007
    Posts: 2,934
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    The vast majority of boats are built without a structural analysis, but rather using rules and design tables for hull thickness/frame size/spacing, etc. from one of the class rules. These are design rules based on long experience and observations on what works. Too much is impractical to design for, so these formulaic designs based on size of boat and usage is more practical.

    Burrow through those rules listed above to get an idea on how much structure you need.
     
    1 person likes this.
  10. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    That is not strictly correct. Rules, such as DNV or LR etc, whilst in the beginning (eons ago) were based upon "historical" evidence, today, there is a significant amount of R&D that is done to validate, justify and modify rules. It is no longer a hit and miss affair. There is sound engineering behind them.
     
  11. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Alik, I don't have statistics to demonstrate it, but I believe that the probability of grounding gets higher as boats gets smaller, primarily because of crew experience factor and tendency to sail closer to the coast. Large yachts are more likely to have a more experienced payed skipper and crew aboard, which (at least in theory) should diminish this probabilty.
    Well, it's also true that, from time to time, even on ships around 300 meters of LOA it happens to find a Schettino in command, but that's a bit out of this topic... :D

    So, I believe that for small boats it is more sound to stay on the "excessive" (to be defined, as Ad hoc noted) side of scantlings, unless you are designing a pure racer.

    Cheers
     
    1 person likes this.
  12. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    As for the OP's question, I use Strand7 software for the FEA (http://www.strand7.com), which allows me to perform linear and non-linear, frequency and modal, buckling, transient, inertial and thermal analysis, all in static or in time-domain analysis. But on the other hand I am an engineer trained in this kind of analysis. If you are not, then I'd advice you to follow DCockey's and Ad Hoc's advices and stick to the classification societies' and ISO scantling rules. Errors can cost very much in this job.
     
  13. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    :eek::eek::eek::eek:

    I first used Strand in 1991, hated it...was terrible. Full of bugs, non-intuitive, poor graphics interface. Although I'm sure it is somewhat better today 20 years later :)

    I use Cosmos/M, which is now sadly all wrap up in Solidworks as a CAD package, no longer stand alone. (http://www.solidworks.com/sw/products/fea-cfd-simulation-sofware.htm). But i still use my older stand alone package, does everything I need it to do...
     
  14. DCockey
    Joined: Oct 2009
    Posts: 5,229
    Likes: 634, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    From the original post: "This is for a typical 38' ocean cruising cat using conventional materials, but in an unconventional mix/way."

    What knowledge is needed to use classification society and ISO scantling rules with materials used in an unconventional mix/way ?
     

  15. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You were lucky to have a graphical interface at all, back in 1991! ;) I had to write my own software for nearly every task, back in those good old days. :p

    I'm pretty happy with Strand. It works well and is one of the most reliable software I have. It never ever crashed, hanged or similar stuff which happens from time to time to nearly every other program on my computer. Evidently, the software house has managed to considerably improve the quality of Strand over the decades.

    An off-topic rant:
    The AutoCAD used to crash every now and then just until 5-6 years ago. The newer versions crash very rarely, but at the cost of high frequency of automatic backup save instances. I have noticed that some commands which on older versions used to cause a software crash, now don't cause a crash but a backup save before the command executon. Guess that folks at Autodesk weren't too much confident that they have managed to resolve the problem, so they said "hey, we better save the drawing before we run this command". Or perhaps it is a concealed way of recovering from a command-module crash which has happened after the command button was pressed.
    It can be pretty annoying when I have to work on a server-based drawing, because of the time-lag in the access to the file. You hit a command button and then have to wait few seconds because AutoCAD want's to save the drawing first, so it slows down the work. Can that be considered a good software-programming practice? :rolleyes: Yet the AutoCAD is an industry standard, so one would expect the excellence in every regard...

    Ok, ok, I'm over now. ;)
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.