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Mechanics of the spar design

Home Forums Archive Structure Designs Mechanics of the spar design

This topic contains 41 replies, has 9 voices, and was last updated by Avatar of Sundiver Sundiver 6 years, 1 month ago.

Viewing 12 posts - 31 through 42 (of 42 total)
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  • #2105
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant
    • One good thing with steel is that it can be incrementally built and still result in a one-piece structure (by welding). This makes it possible to build the spar while it is floating, which should make for cheap construction and no need for big docks and equipment.
    • Is it possible to do this with concrete? I think I´ve seen houses being built sort of like this, with a climbing platform that forms a concrete mold that is poured, then the platform climbs one story and the process repeats. Can you do this continually (for days/weeks/months) and end up with a one piece concrete spar?
    • And by concrete I mean reinforced concrete obviously.
    #2138
    Avatar of Anonymous
    Anonymous
    Participant

    What you are looking for is called a slipform. The CN Tower took about 8 months to pour the main column this way. It was the tallest freestanding structure in the world until last year, so I would hope it is reinforced concrete ;)

    #2150
    Avatar of portager
    portager
    Participant

    I think that the Spar Buoy could be made of Ferro Cement, but I question if it will be easier, lighter or cheaper. I think alternative materials should be considered.

    #2479
    Avatar of xoid
    xoid
    Participant

    This huge tower is expensive and requires a big ballast which decreases payload. We need more simpler and robust design like a box with a few internal sections, very like the ARK. In case of very bad weather people can hide inside as we do at land

    #2480
    Avatar of xoid
    xoid
    Participant

    Undersea part of tower contunues very deep , it makes repair difficult

    #2487
    Avatar of Jesrad
    Jesrad
    Participant

    If I remember correctly, the Ark used a reactive water ballast to remain steady in storms, in the form of a large water tank designed to have a flow period half of the rocking period of the boat itself. When the ark heaved, the water in the tank would rush from one side to the other and compensate. Or so I think. Maybe that’s completely implausible, but I would love to test that sort of thing in a wave tank.

    #2486
    Avatar of thebastidge
    thebastidge
    Participant

    Well, that sort of depends on the size, doesn’t it? 100 meters is pretty deep for divers to reach, but if a sizable bit of the lower portion is either solid ballast or a tank designed to be flooded, there is less to inspect. There’s also a current ly useful technology for inspections: a robotic camera, and this depth is hardly anything to that technology.

    #2537
    Avatar of xoid
    xoid
    Participant

    Even 35 meters is difficult to dive, and you need to dive not only for inspection, but to repair cracked concrete

    #2542
    Avatar of thebastidge
    thebastidge
    Participant

    True, but designs should take that into account.

    • Cracks in solid ballast compartments are not as much of an issue, as they don’t have to be water-tight.
    • Cracks in water ballast compartments depend on how big they are and if your pumps can keep up with them for the periods of time they need to be pumped out, and if the crackwill affect structural inetegrity under a changed condition susch as pumping them dry.
    • Cracks in buoyancy ares, particularly in living quarters are the biggest concern
    • The design lifetime may take it into account that eventually, this sea stead is going to be completely or semi-scuttled, and therefore when the predicted failure time is nearing, it is taken to its final position, i.e. shallow water where it becomes either an artificial reef or an artifical island

    It also depends on the material. Robotic undersea welding seems like a near-term possibility.

    #2564
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    Cool, thanks for that link and info. Looks like you can even build tapering and complex structures with this method.

    #2599
    Avatar of Sundiver
    Sundiver
    Participant

    35 meters is easy, very easy. 100 meters is getting difficult. Such an installation would certainly have onboard intervention technology like divers (professional, not scuba) and ROV’s. Really though, stability will govern, not diver depths.

    #2600
    Avatar of Sundiver
    Sundiver
    Participant
    • Maybe this is the wrong thread for this. Here’s a link to the Floatec site where there are some good illustrations that I’m using to comment.
    • Spar- http://www.floatec.com/spar.htm
    • TLP- http://www.floatec.com/tlp.htm
    • I agree that a spar can be made to work for a small platform. The spar has some really great advantages such as reduced heave. That’s great if you have a need to support a rigid structure to the stationary bottom, like a drill riser. Seems to me though that the TLP could provide a more suitable arrangement for a colony. The spar is vertically arranged, limiting solar area, greenhouse area, and personal space. The TLP with its more horizontal design instead of vertical, would possibly provide more usable, high value space than the spar.
    • There are already concrete TLP’s out there. The Heidrun field platform is one. http://www.km.kongsberg.com/ks/web/NOKBG0240.nsf/AllWeb/ABD72633D883B154C1256A530038BAA6?OpenDocument
    • The Hutton TLP is even older.
    • A colony platform would be considerably simpler than that. Might be more like a parking garage with each level smaller than the one below. Spaces could be customized as needed or prefabbed modules slid in. Like a trailer park in a parking garage. (just kidding sort of).
    • I think the cost would be lower than a spar on several counts. Deployment is one. The spar has to be built in deep water doesn’t it? The TLP can be built by pouring and launching the base and columns, submerging it to the bottom in a shallow harbor, and then continuing the construction. Then deballast, tow it to the site, ballast down, connect the tension leg anchor lines, and pump it out. Studies need to be done but I just can’t see a spar being cheaper per available area.
    • The TLP is a very nicely stable platform too. Think of it as an upside down pendulum. Now make it a box with 4 strings instead of one, put a lot of weight in it and immerse it in a viscous fluid.

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