Engineering talk

by

The talk I held at the 2009 Seasteading conference is up! Thanks everyone who was there, for the interesting discussions we have had afterwards.

Some comments on the then and now: I unfortunately no longer have the confidence in this concept I had back then, for the reasons explained below:

 

Connecting seasteads in such a manner is more difficult than I supposed, because the horizontal forces involved are much larger than I anticipated on an intuitive basis. To get a bit technical: the horizontal forces on a submerged body can be estimated by Morrison’s equation. Not only does it contain a drag component, being a function of the relative velocity, but also a component proportional to the acceleration of the water. It’s a little bit harder to see why this must be so, but if one considers the boundary of the displaced water, and the fact that this is the acceleration the displaced water would have experienced had it still been there, a body of non-water on the same position would either undergo the same acceleration, or would have to be held in place by a force proportional to it.

I had looked at these issues before, but committed a fallacy ‘ad linearisatum’: the effect is small for short waves, and the effect is small for long waves, so at the time I supposed it was probably reasonably small for all waves. Unfortunately, not so. Under worst case conditions , these horizontal acceleration forces are of the same order of magnitude as the weight of the entire structure itself. the components required to withstand such thousands of tons forces get a little bit out of hand; perhaps it is not impossible, but taking this effect into account, it simply no longer feels like a conceptually elegant solution.

Secondly, I underestimated the effect of heave motion on comfort. I had been reading some literature that suggested heave is not that bad as long as it is not combined with any significant roll motions, but it appears the rest of the world does not agree. Given that heave suppression for this concept is not very strong, its comfort characteristics will not suffice in the open ocean.

 

I am somewhat disappointed by these discoveries, as it nudges up the minimum scale of open-ocean seasteading which I believe to be plausible, but as someone commented, ‘that’s progress’, and I suppose it is. Its unfortunate that progress doesn’t always come in the direction you wish it would, but such is life. There are still other options which are being explored at the moment that I feel confident about, so no lack of work ahead!

 

A happy new year to you all, 

Eelco

5 comments

  1. Wayne Gramlich 12:37 am

    Since you are up to speed on Morrisons equations.  How does a structure like the Flip Ship perform in the comfort department?

  2. OCEANOPOLIS 8:12 am

    A Happy New Year to you too.

    I would like to comment a bit on the subject.The problems with connected seasteads arises only when trying to maintain a stationary position in hurricane force winds and seastates…Why keep that fix when you have a category 5 coming towards you? Why not run 300nm away? Why this conceptual "rigidity" in design and engineering efforts @ TSI to find technical solutions of how to ride a "Big One", when its a known fact that no good captain would take his boat (no matter if 25′ or 1000′) into a storm, but instead will try to avoid it and go for sheltered or calmer waters? Why not look into full displacement type structures, highly stable and modular, easy to connect  (and disconnect), highly mobile (up to 18-20 knts speeds) that can be easily rafted up to 2000′-3000′ x 1000′-1500′ to form floating artificial islands type structures? If a major storm closes in, eigther get out of there as a whole (which wiould be a bit slow), or disconnect all modules, run @ maximum speed as a flotilla and regroup in calm waters.

    Octavian

  3. wesley_Bruce 8:01 am

    We may need one of these to inspect our vessels and to get a look at the bay stead sea bed.

    http://www.gizmag.com/httpwwwgizmagcomneptune-sb-113768/13768/

    It looks like fun too. The price of this technology is falling amazingly fast.

    There is going to be as much action under the water as there is on top and the images would be very useful from a promotional point of view.


    For everyone’s information I was involved with the original Oceania Project in a small way. I’m also in several space organisations. And I have a Degree in sustainable Development, sustainable agriculture and renewable energy, water and sewerage.

  4. Eelco 2:06 pm

     Wayne: The vertical motion response of FLIP is fine under all circumstances, but the horizontal response is nowhere noted (vertical motion is their main concern wrt their scientific experiments). It isnt easy to derive from first principles either. From looking at model test videos, it seems as if the horizontal response is substantial, and may well cause comfort issues in rough seas, even though there is hardly any heave.

  5. Eelco 2:16 pm

     Ocean:

    From what I understand, outrunning storms requires a fairly fast vessel (~10 knots at least). The only type of vessels that could concievably reach those kinds of speeds are vessels completely optimized for movement; ships, or elongated shiplike constructions. Shiplike elongated shapes have other advantages too, f.i. they are optimal for withstanding the effects of wave-drift and other external forcing. Demanding modularity in only one direction makes the problem of connecting it all a lot more managable too.

    The type of structure you describe is close to my current favorite solution; some form of simplified but modular concrete barge/ship

The comments are closed.