Craig, are you talking about Earth, or a hypothetical water-world?

I'm not sure why you need a keel, and what part of a submarine urbanity would need a keel.

Wave propagation is really a non-issue below about 100m or so, and certainly not at all an issue at 500m. Below that the problem is pressure.
In fact this is the engineering problem of the first order, how to deal with the pressure.
This requires energy and a lot of it.

On re-reading your post, I just realised that you are not talking about a submarine structure but a surface one.
This creates several problem in that you need a design which must cope with two different environments simultaneously, but what you want to do is deal with just one envidonment. There is no need to make the design more complex than absolutely necessary.

Ac tually modern Earth cities are not 'large', but are collections of small urban 'cores' linked (eventually) by various means. In this they are quite modular, and the smame principal can be used for designs of submarine cities except they need not be static as the land-surface cities are. Internal navigation systems will allow finding one's way home even if home is not located in the same physical coordinates as it was when you left in the morning. There are massive advantages to building in 3D.

Greg C

On 31 December 2015 at 09:42, Craig Berry <xxxxxx@gmail.com> wrote:
Stability: Being big gives a structure more inertia, linear and angular, so it takes more force to move or rotate it a given amount. Also, deep waters tend to be calmer than the surface, so a big structure with a deep keel will be more stable. Further, a structure that is large relative to the wavelength of the, um, waves will experience less jostling than one that is comparable in size to or smaller than the wavelength. (Basically, if you're e.g. five wavelengths long, the highs and lows of all those five waves average out to little net force.)

Shared infrastructure: This is the same reason cities tend to be large and dense. There are economies of scale in matters such as power generation, sewage handling, food production and distribution, recreational facilities, and so forth. 

Easy transportation: Even in a world with g-craft, it's more convenient to move people around on a solid surface, or inside a solid matrix. People can walk to nearby places, and slidewalks, elevators, trolley networks, and so forth are efficient for longer distances. Also, with smaller floating habitations there will be more need for travel between them (via boat, g-craft, or whatever), because a small habitation won't support all the specialized services of a large city.

On Wed, Dec 30, 2015 at 2:14 PM, Greg Chalik <mrg3105@gmail.com> wrote:

How's that?

Greg C

On 31/12/2015 9:13 AM, "Craig Berry" <xxxxxx@gmail.com> wrote:
Building big buys you stability, shared infrastructure, and easy transportation.

On Wed, Dec 30, 2015 at 2:06 PM, Greg Chalik <mrg3105@gmail.com> wrote:

I don't think building big is an elegant solution for water worlds, or an affordable one.

Cheers

Greg C

On 31/12/2015 8:37 AM, "Craig Berry" <xxxxxx@gmail.com> wrote:
The chief engineer shook her head. "There's just no way that can be true. This city is bigger than a Tigress. Bigger than three of them, actually. Our keel goes down so far deeprays get tangled in it. It's sculpted to ride the currents, ocean and atmosphere. A damned typhoon isn't going to mean a thing to us."

The tech shook her head, too. "Chief, this isn't a normal typhoon. I don't know how the survey missed this, but we're seeing surface winds beyond anything in our models. I'm talking half a mach, and that's a thick atmosphere out there. And the waves...well, there's no land on Ulma to stop them, you know that. So they just keep building. They're breaking across the landing aprons on deck 74. That's two hundred meters above the waterline. Or where the waterline is supposed to be, anyway."

"So let 'em break," replied the chief. "It would take a nuclear strike to do any real damage to the superstructure. We'll repair some bent railings when this is over, and..." She trailed off.

"What?" the tech began to ask, then she felt it, too. Without a word, the chief reached into her desk and pulled out a ball bearing, placing it on the center of her desk. It slowly began to roll toward her.

Just then, the first lights began flickering from green to red on the wall status display.


On Wed, Dec 30, 2015 at 12:30 AM, Greg Chalik <mrg3105@gmail.com> wrote:

The big problem with most futuristic ocean-based designs is that the designers often go for spectacular architecture but impractical infrastructure. And, just as on ships, the greatest problem is power, I.e. energy generation.

One reason we don't have any on Earth now is that such urbanities would require massive amounts of energy, well beyond the capabilities of nuclear power plant tech.

One design consideration I was looking at a few years ago was to generate power via Massive Local Current Array generators which work just like standard turbines, but are much larger.

The real-world problem of constructing in international waters is a legal one. I suppose on a water world this isn't an issue.

Greg C

On 30/12/2015 8:47 AM, "Timothy Collinson" <xxxxxx@port.ac.uk> wrote:
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