Ice region vessel design

Discussion in 'Boat Design' started by saeedfa, Jul 15, 2020.

  1. saeedfa
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    saeedfa Junior Member

    hello
    i want to design a vessel with Ice class (C) according to DNVGL
    Reference: DNVGL-RU-SHIP-Pt6-Ch6-Sec1
    in the structural requirement for ice class (C) rule have some subsection: plating, framing, stringer, web frame. i have 2 question:
    1- is "framing" same as stiffener? rule said longitudinal and transverse stiffener, is that mean the longitudinal and transverse stiffener ?
    2- in the calculation of web frames, rule refer to use sec.2. in the calculation of web frames there are 2 parameter that i cant understand: hs and ls ??
     
  2. saeedfa
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    saeedfa Junior Member

    so there is no one knowing about ice class vessel structure ?!
     
  3. TANSL
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    TANSL Senior Member

    Dear Saeed,
    "ls" and "hs" are not universal signs that everyone knows and uses several times a day. It is not possible, without knowing this regulation well, or without using our time to consult it, to know what the DNV-GL refers to when it uses those terms. So no one answers you.
    I'm sure that somewhere the regulation explains what it means when it uses those terms. Another thing is that, if the DNV-GL says "ls" is xxxxxx or "hs is yyyyyyyy, you don't understand what it means.
    If you explain yourself a little better, it is possible that someone can clarify your doubts.
     

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  4. Ad Hoc
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    Ad Hoc Naval Architect

    If you understand structures, this should be obvious. One is a transverse member - the Frame - the other is a longitudinal member - stiffener.
    You need to understand maritime terminology and then how these members are referenced in the rules.

    Look at Fig.1 in sec 2. That defines the ice belt for Hs.
    Ls is simply the distance between each structural member.

    You seem somewhat impatient?
     
  5. TANSL
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    TANSL Senior Member

    There are also longitudinal frames and transverse stiffeners.
     
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  6. Ad Hoc
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    Ad Hoc Naval Architect

    Well done.. you can read books with references to structural members.
    Take a house point! :rolleyes:
     
  7. TANSL
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    TANSL Senior Member

    Thanks for the point, you are always so kind.
    In relation to "read books with references to structural members", see attached picture.
    @saeedfa, forget all that nonsense. It only serves to confuse you even more.
    Simple :mad:
     

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  8. saeedfa
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    saeedfa Junior Member

    thank you for your reply
    as TANSL said there is longitudinal frames and transverse stiffener in the rule so ....
    frames and stiffener are some terms for secondary members and all of them can refer to a longitudinal or transverse member

    as TANSL send the reference, the hs and ls defined in the rule as below, but these are not sensible:
    hs: the distance to the ice belt, in m
    ls: the distance to the adjacent ice stringer, in m

    thank you
     
  9. TANSL
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    TANSL Senior Member

    It could be interpreted (although I do not affirm anything) as frames are primary members and stiffen are secondary members of the structure. But Ad Hoc, who always shows signs of knowing the English language well, could shed light on this matter, even if it means correcting himself (even the gods are sometimes wrong).
    Simple.

    Oooh, yes, the emoti : :rolleyes: (following my idol, technical reasoning must end with an emoticon)

    P.S. : Nothing to do with all of the above, @saeedfa, look for "intermediate frames" in the DNV GL regulation for ice.
     
  10. saeedfa
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    saeedfa Junior Member

    thank you for your reply
    in the rule there are two situation that use hs and ls:
    1- for stringer situated outside the ice belt but supporting ice strengthened frames
    2- for ice web frames In case the supported stringer is outside the ice belt

    in my case i dont use any ice stringer, because i dont use any transverse frames (stiffener) so there is no need to use of ice stringer to support them. in my case i used some longitudinal frames (stiffener) and some ice web frames that support the longitudinal frames. in this case these terms (hs and ls) not sensible for me. in my case the ice web frames at the shell plate extended to the main deck, so i think may be these two terms effect in calculation of side transverse web frames, because this girder have tow different part, the lower end have ice pressure and the upper end have just sea pressure. i attached a typical frame for better understand.
    as you see in the attached picture, i show the ice upper limit, i think these two terms may be effect in the calculation of side transverse girder (TB 245*10-120*10). as you see in the picture the longitudinal frame (stiffener) for ice region (ice upper limit in z=1610mm) according to pt6-ch6 of DNVGL, is FB75*6.
    i dont use any intermediate transverse frame, i just use ice web frame with 800mm spacing and some longitudinal frame (stiffener).
     

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  11. Ad Hoc
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    Ad Hoc Naval Architect

    Longitudinal structural members that are main supporting members are called girders, not frames. So you are referring to a girder, not a frame.

    You need to read the rule and understand what it is asking you. As noted above:-

    "...10.1.1 The gross section modulus of a stringer situated within the ice belt, see [8.1], in cm3 , shall be calculated by the formula:..."

    The clue is the terminology.

    "...10.1.1 The gross section modulus of a stringer situated within the ..."

    Thus, what direction does a 'stringer' run in a vessel, longitudinally, or transversely?
     
  12. TANSL
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    TANSL Senior Member

    On any of them or diagonally. You just need to understand maritime terminology and then how these members are referenced in the rules.
     
  13. saeedfa
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    saeedfa Junior Member

    sorry but i dont understand what you say
    i said longitudinal frames or stiffener these are similar!!
    stringer is a horizontal member in side shell and bulkhead, and i can not say that it is longitudinally or transversely run! it can be extended in both direction, but in this problem i think the direction of stringer is longitudinally. the stringer is extended from ice web frame to another ice web frame. but in my case, i dont use any stringer, in accordance with the above picture, i extended the ice web frames from keel to deck, and because of longitudinal stiffening i dont need to use ice stringer, if i consider the transverse stiffening then i use the stringer as support the transverse stiffeners.
    but i cant understand what did you said.
     
  14. TANSL
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    TANSL Senior Member

    What I mean is that an element of a structure can be vertical, horizontal, transverse, longitudinal or not follow any of the three main directions but have a certain inclination with respect to any of them. His position in the helmet does not define it as a stiffener. There can be frames, girders or stringers and they will be one thing one another depending on the role they play in the structure, it will never depend on their position in space.
    A very clear example, a pillar will never be a frame, for example, because, due to the mission it performs, how it works, its name is "pillar".

    Edited: Ad Hoc notice has let me know that where I wrote the word "helmet" it should have put "hull". I am glad that only my translation errors need correction, not my technical arguments. Thanks once again, master!
     
    Last edited: Jul 20, 2020

  15. Ad Hoc
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    Ad Hoc Naval Architect

    No, they are not.
    This is why I am suggesting you need to understand the terminology of structural members. This plays an important part of how to interpret what a rule is asking or informing you to do.
    I suggest you buy a book on Maritime Terminology - this is the source of confusion for many and for many, it leads to pointless arguments and posters resort to polemic attacks as a mean of reply simply because their limited knowledge on a subject - that they thought they knew - is exposed as not so knowledgeable and is lacking. Rather than accept that the day we stop learning is the day to retire and go sailing or fishing or whatever..!!

    That is the question. So ignore Class rules, it has nothing to do with Class rules.
    What does - structurally - a stringer do and mean?

    It is always a longitudinal structural member.
    Its origins come from shell plating or stakes at the gunwale and also during fabrication. When fabricating large shell plates off the boat... the edges can deform during welding. These edges that are always prone to this is and of course the longitudinal edge clearly the greatest amount. As this is the greatest length (in the L x B panel) and as such the greatest amount of expansion/contraction can occur. This means when the shell plate is 'offered' up for fighting to the boat, the edges can be distorted and not match the plate on the vessel. So the solution, is to add a temporary structural members to "hold" the long straight edge. These too, are called stringers. (They are also called strong backs too).

    And as noted, if in doubt check the definitions first....from structural theory, not, Class rules. Class follows the theory, not the other way around.

    So, any text book of maritime definitions will note this, such as:

    upload_2020-7-21_8-35-45.png

    So, now you understand that stringers run longitudinally, you realise that terms like a 'transverse stringer' is a misnomer and incorrect. Just because it may be written as - transverse stringer - in Class rules, does not make it correct. Class rules always have many errors in terminology. Because the rules, the written words, are usually not written by naval architects/structural engineers!

    Now, you understand the definition of a stringer, let's go back to the rule, which states:

    "...10.1.1 The gross section modulus of a stringer situated within the ice belt, see [8.1], in cm3 , shall be calculated by the formula:..."

    So, this rule is refereeing to a stringer - which means a longitudinal structural member.
    But, as you have noted already:


    Which means, this rule is not applicable to your design.

    Simple :cool: and you do not need to worry about falling and the need for a helmet for protection as you fall either!
     
    Last edited: Jul 20, 2020
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