geodetic submarine design

Discussion in 'Boat Design' started by tugboat, Feb 8, 2010.

  1. tugboat

    tugboat Previous Member

    and yet another thread on concrete or steel subs...

    ok so a geodetic lattice is perhaps the strongest framework possible for any enclosed structure- so why not apply that to submarine construction?. for instance- if you made a lattice out of rebar by making both the framing as a lattice and the whole structure in a geodetic pattern lattice, then it seems to me you could have an almost indestructable hull made from light guage steel.
    the conventional sub design method in steel is to use heavy guage steel roll it and use i-beam rings for the frames- i have yet to see a sub hull with longitudinal stiffeners. so, instead of very expensive and hard to work with material such as say 1/2 inch thick plate, you use maybe 1/8th inch but supported by this type of lattice work. the result would be stronger(in my opinion) than the heavy plate. but the reason for this type of construction would be 1. ease of construction for an amateur hull and 2. cost effective usage of steel.
    putting the problems of ballasting a given area to nuetral bouyancy aside, it should prove to be incredibly strong.

    now again use that with concrete and you have the same effiiency of strength in fact even great perhaps than steel. easily formable and extremely effective...

    i am going to investigate this further. would like to hear thoughts on this..
     
  2. Boston

    Boston Previous Member

    geodetic lattice is full of hard angles
    would have a high resistance I would think
    that and welding all those deep welds would be a *****

    my two cents
    B
     
  3. tugboat

    tugboat Previous Member

    Boston- yea for sure it would be labour intensive. but the benefits would be so great...think of it..in fact if there was a way to weld the lattice as a core between two lighter sheets of steel, you would have one hell of a strong composite...bear in mind there would not be many angles as the lattice itself would be in a compund curve over a mold. I got the idea from the geodetic design of the wellington bomber

    http://www.bomber-command.info/blwimpy6.htm

    i was thinking rebar trusses about 2 inches thick- again lattices with triangles. The problem i was thinking about is that the weight would be very light even after machinery etc since it is a civil sub design that the ballast needed would be an issue but if i made the nose cone out of one solid chunk of cement shaped to a conical/eliptical sub bow and balance that solid concrete again at the aft section where the stern tube runs out, i have greatly added ballast at no expense to structural deficits.
     
  4. Boston

    Boston Previous Member

    that they already do for satellite bases
    its kinda a sandwiched honey comb design
    like a bees nest kinda thing

    cheers
    B
     
  5. Luckless
    Joined: Mar 2009
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    Luckless Senior Member

    You're not thinking of geodesic are you? Slightly different concepts, and I can't find a single way to tie my understanding of geodetic into a structural system that makes sense.

    Either way the problem with something like you find in wellington bomber, even with fully curving members, is that you end up with dangerous tensions on your skins. Every time you put them under pressure from a dive the outer skin is going to want to flex to the middle of each 'cell' in your lattice. The problem is made worse by the fact that the tensions are non-linear as you have triangular sections, rather than round, and stresses become harder to predict.

    Of course the worst part of the problem stems from repeated dives leading to material stretch and fatigue. What starts out as a very strong structure may quickly become weaker over time. If the outer skin is too light then every time you dive the it will dimple at every cell, and stretch slightly.

    One way to get around this would be to use a variable thickness panel as a cover for each cell, sort of an arch, to better spread the load across the open space.

    Basically you end up playing between using more materials, or using way, way more construction effort.
     
  6. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    A geodetic structure is not the "strongest"; it is the lightest weight structure of flat panels for the enclosed volume and was not designed to resist extrenal pressure. And in a sense, a geodetic structure is just a degenerate sphere, which is the strongest structure for resisting pressure. See Submersible Vehicle Systems Design and the '67 edition of Principals of Naval Architecture, both by SNAME, if you want to delve into pressure hull design
     
  7. tugboat

    tugboat Previous Member

    Hmmm...stretching skin? does steel stretch that much???...ill take your thoughts under advisement...actually after i posted this i rethought it and realized that the design woulld not provide enough rigidity to make it worthwhile. works on a plane but not on a sub.
    nevertheless, what it would be great for is a concrete hull structure. In fact, my secondary idea which ive done more research on is to build a two inch ferro wall for the sub, then add another layer of two inches to form a 4 inch thick wall. I contacted an engineer about this and they do say that two walls would combine to have the strength of one. the strength of a 4 inch thick wall i.e. the two layers are additive in nature. Thus, if you used a lattice work of steel rod as in the geodetic(not geodesic) frame it would create a very good substitute for mesh. of course you could add mesh too, to increase strength. look at Hartkey truss method - its uses a latticed method.
    Mr Ellmer uses rebar and mesh for his subs. simple rugged concrete technology. Then it should work for ferro-cement taken to its extreme of about 2 inch wall thicknesse and add a secondary layer over the first of 2 inches using a bonding agent. the lattice should give awesome support...its too bad that the lattice could not work for steel since i would prefer steel but the costs are prohibitive for me.
    necessity is the mother of invention.
     
  8. Luckless
    Joined: Mar 2009
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    Luckless Senior Member

    All steel flexes and stretches, that is why it is so widely used. (If it didn't flex and stretch, and it would crack)

    And the problem isn't really with it stretching all that much. Under pressure you likely would be hard pressed to detect the dimpling by hand or eye, but the real problem is doing this repeatedly. Like taking a steel paper clip and bending it back and forth a over and over again. Eventually it gets harder and harder to bend, and then suddenly it snaps. This is something you really should consider in any construction.
     
  9. haru
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    haru Junior Member

    Why it's not used for subs?
    Well, it seems simple to me to answer.
    1. subs are big, a geodesic structure will be complicated, difficult to put ideally together, may offer a lot of weakpoints due to this
    2. there is a difference between structural integrity and pressure hull
    for pressure you simply want equal strength for every inch of the surface
    3. cost

    This may change if there are better materials.
     
  10. messabout
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    messabout Senior Member

    Jehrdiman told it like it is. A geodsic is NOT the strongest structure by a long shot. A sphere is the ultimate shape for resistng pressure within or without. The next best form is the cylinder as in current sub design. Rolling half inch plate is a no sweat deal. With the right machinery we can and do roll one inch plate. Rolled sections are a lot easier to join than all those lovely triangles. Curved or rolled sections resist deformation better than flat sections, far better. With that said I confess that I think geodesics are fascinating structures. I have built some interesting models using that concept. But not submarines.
     
  11. guzzis3
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    guzzis3 Senior Member

    I would have thought that type of skin was about the worst solution to the problem.

    The issue with predicting stresses within triangular spaces isn't that hard, but the argument is correct. The function of that skin in a distributed pressure situation would be extremely poor. You haven't even started thinking about the additional problems the welding would cause.

    I have not read the previous threads on submarines on this forum, so forgive me if I've missed something, but weight saving shouldn't be a big driving element in the design.

    Submarine design shouldn't be that hard. You start with much the same design process as for a pressure vessel, add hydrodynamics if you expect to attain any signifigant speed, add orifices as required then sort your bouyancy.

    Then you assault enviromental issues like engine oxygen requirements, crew, equipment etc.

    Unless your trying to do something "cutting edge" it should be a mature science.
     
  12. tugboat

    tugboat Previous Member

    I understand what people are saying- What i havent told you is i have already designed the systems -worked them out tested some of them, designed a concrete design of the uss skipjack taken the lines from a model and even designed a system to have 4 inch thick walls ferro-cement design. stronger than steel easy to form to a conical and compound surface. pressure resistant -non compressable. and monolithic. I was going to use pumps rather than blowing ballast. the pump i looked at i could have bought for 75.00 and would have pumped 900 gph. easily enough for ballast and it would take almost as little tiem to put her to her lines at the surface. also had a diesel electric system solved using a golf cart motor and charging the batts off the shaft using a series of truck alternators for effective fuel efficiency. I called engineers, talked to experts, got very creative myself with every system . found proper seals for penetrations i.e. dive planes rudders etc good to 250 psi rotational. so all of this is just elemtary to me. the geodteis again not geodesic design is based on practical alreayd proven methods for strength- if you dotn believe me do this experiment- get an I-BEAM and put three tons on it or until it buckles. then try that same with a truss type frame made form a lattice of trangles. see which is stronger??
    which one will bend first?..thus the psi for ther truss is greater than a uniform thick hull and in theory the geodetic design is better and stronger. as far as cost-i cant see that building the sub from rebar trusses would make it less strong, most likely stronger than just a rolled plate in the tube shape. btw steel does not stretch- it shears. it may bend and it may stretch a little but the effect should not be anough to es[ecially if the frames were close enough together and welded enough that you do not get diminished dispersal. then there would not be any issues at all...thats kinda like saying boats should be built out fo steel and franes because when the vessel hogs and sags the steel will stretch and not fit to the frames anymore...IMHO.

    all that aside im confident i could build my sub. however this week i did a mock up of the dimensions i was going to use--which was 51.5 ft loa and 7 ft dia. close to the UC3 nautilus. and for me that wasnt enough space. so im going with a tug design...as far as im concerned im closing this post..i wont be on again to answer it...simply because my project is closed too. I just was curious as to geodetic possibilities and i maintain it would work since there are compund structure made with it that are suprememly strong. check out the roof of the hong kong airport for example. but I was curious as to what people would say...interesting...

    good luck everyone on their projects..im going to open a new thread about industrial dc motors for tugs yachts...
     
  13. tugboat

    tugboat Previous Member

    I understand what people are saying- What i havent told you is i have already designed the hull and systems not using geodetic principles, -worked them out tested some of them, designed a concrete design of the uss skipjack taken the lines from a model and even designed a method to have 4 inch thick walls, ferro-cement. giving about 19 000 psi if im not mistaken. stronger compressive strength than steel, easy to form to a conical and compound surface. pressure resistant -non compressable. and monolithic. I was going to use pumps rather than blowing ballast. the pump i looked at i could have bought for 75.00 and would have pumped 900 gph. easily enough for ballast and it would take almost as little time to put her to her lines at the surface. also had a diesel electric system solved using a golf cart motor and a 75 hp d4600 cat charging the batts off the shaft using a series of truck alternators for effective charging and fuel efficiency. I called engineers, talked to experts, got very creative myself with every system. found proper seals for thru hull penetrations i.e. dive planes rudders etc good to 250 psi rotational. so all of this is just elementary to me. the geodetic, again not geodesic, design is based on practical already proven methods for strength- and they have been used on compound curved surfaces- if you dont believe me with regards to strength-do this experiment- get an I-BEAM and enough weight until it buckles. then try that same with a truss type (maybe 2/3rds the weight of the I-beam)frame made from a lattice of trangles. see which is stronger??
    which one will bend first then buckle??..thus the psi for the truss is greater than simply using unframed longitudinally rolled tubes for a sub design and uniformly thick hull. In theory the geodetic design is better and stronger. as far as cost- i cant see that building the sub from trusses would make it less strong and more costly, most likely stronger than just a rolled plate in the tube shape. btw steel does not stretch- when it does to any thing past a a workable tolerance, it shears. it may bend and it may stretch a little but the effect should not be enough to warp the plate especially if the frames were close enough together and welded enough that you do not get diminished dispersal. then there would not be any issues at all...if there were well, thats kinda like saying boats shouldnt be built out of steel and frame construction because when the vessel hogs and sags the steel will stretch and not fit to the frames anymore...IMHO.

    all that aside im confident i could build my sub succesfully. however this week i did a mock up of the dimensions i was going to use--which was 51.5 ft loa and 7 ft dia. close to the UC3 nautilus. and for me that wasnt enough space. so im going with a tug design...as far as im concerned im closing this post..i wont be on again to answer it...simply because my project is closed too. I just was curious as to geodetic possibilities (and yes i know the diff between geodetic and geodesic)and i maintain it would work since there are compund structure made with it that are suprememly strong. check out the roof of the hong kong airport for example. but I was curious as to what people would say...interesting...

    good luck everyone on their projects..im going to open a new thread about industrial dc motors for tugs yachts...
     
  14. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    get an I-BEAM and put three tons on it or until it buckles. then try that same with a truss type frame made form a lattice of trangles. see which is stronger??

    Fundamentally wrong. Your using a point load to assess a distributed load problem and confusing stiffness with strength. Force and pressure are not the same thing. Much of what you type above displayes a fundamental lack of understanding of the problems. I can't stop you, but if you go ahead with this please be careful. It's really easy to kill yourself in a submarine.

    Edit: concrete is not incompressable. Nor for that matter is water....
     

  15. Petros
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    Petros Senior Member

    I am an engineer and I have designed and have done structural analysis on geodesic structures. They have no advantage for a sub hull. They have a lot of seams to seal and to leak (and they always do!), and the shape would be very poor for efficiency (too much drag).

    The advantage in a building is the parts can be pre-made and are almost all simlar size and shape (but not all exactly alike), and you can make a sphere-like shape with strait members (straight lumber or metal beams) and flat panels, reducing the surface to volume ratio, using less materials for the same enclosed volume, and possibly requiring less insulation to heat the space efficiently (less surface to loose heat from). The problem is the interior shape is far less than ideal for habitation, the seams always leak, and the structure always ends up being more complicated to build compared to conventional construction, more labor involved and a lot of special fittings.

    A sub that moves through the water needs to have a good shape to reduce drag or you use way to much fuel or battery power. The most efficient structure for doing that is a smooth curved relatively thin skin, stringers and frames, just like conventional hulls, and just like aircraft structures (which I have also designed).

    Sorry, that is just the way the physics of a structure that has to move through a fluid works.

    There is one good way to use a geodesic structure in marine waters: to make a sightseeing sphere. You can buy relatively inexpensive heavy flat polycarbonate panels, all cut edges are straight lines, and have a riveted or bolted frame made from I-beam members, and you bolt the flat panels onto the frame with thick rubber gaskets. It would be lowered from a cable. The advantage is it would cost far less to make than to make a one piece polycarbonate sphere, and you can unbolt the panels for replacement or maintenance.

    Good luck
     
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