Re: [PSUBS-MAILIST] Thought experiment

From what I gather, the standard method of 'blowing' a ballast/bouyancy tank is to push the water out using compressed air. The air pressure thereby having to be higher than the ambient water pressure.

I've been thinking... what if instead of using gas to displace the water, you simply remove the water, and leave behind a vacuum. For instance, using a hydraulic ram to push a sealed piston which forces water out of a cylindrical tank. Instead of back-filling with air, just leave a vacuum behind the piston. You'd need the energy to run a hydraulic pump (or other mechanism) against the water pressure, but you'd never be limited by air capacity (or nasty-ol lead shot).

Instead of a simple pliable bag operating at ambient pressure, you now have some rather high pressure components.

----- Original Message -----

From: Joseph Perkel

To: personal_submersibles@psubs.org

Sent: Thursday, July 19, 2007 2:08 PM

Subject: RE: [PSUBS-MAILIST] Thought experiment

Phillip,

Sorry for the delayed response but, I had to think about the question and, take a peek at C-BUG again. I find the question itself interesting because fine buoyancy control, is of particular interest to me, (although by different methods). So this is an exercise in basic buoyancy control for me as well.

In our application, we have buoyancy and thrust as our 2 ways of changing depth....correct? For the glider method,...... eliminate thrust.

I'm not quite clear on the "suspending" piston idea but, in thinking about this "non-powered" mode of changing depth, we're left only with manipulation of buoyancy...correct?

This had me thinking about , what manner of "ballast control", would I personally feel comfortable with in this application and,... like you,.... I feel air is unattractive for the ascent phase as..."failure is not an option".

So for my "glider", in the negative buoyancy phase, descent would be initiated from a positive buoyancy condition on the surface by, standard venting of soft tanks. The positive buoyancy ascent phase, would be by releasing lead shot via some type of failsafe release mechanism, (electromechanical).

Hope to be of some help and, thanks for the mind bender!

Joe

From:  Philip Ridenauer <akula151@yahoo.com>
Reply-To:  personal_submersibles@psubs.org
To:  personal_submersibles@psubs.org
Subject:  [PSUBS-MAILIST] Thought experiment
Date:  Sun, 15 Jul 2007 13:47:00 -0700 (PDT)





I've been running a thought experiment in my head for an ambient dry glider (though I suppose a 1atm sub could do the same). The idea is to have
the sub ballasted negatively and use gravity as the propulsion source. At max depth (depending upon how much pressure the pilot was willing to risk/withstand) enough ballast is expelled to provide positive bouyancy. The ballast taken on and expelled should be forward of the CG to provide nose down attitude at neg. bouyancy and nose up at pos.

Query: is there a means of expelling ballast water mechanically so that one does not have to carry an inordinate amount of compressed air to achieve this effect?

I have an idea for a suspended weight acting as a piston but don't know if this is feasible.

Just toying with an idea.

PR

ps My computer and server are sloooow, so I don't ck my email every day. It might take me a while
to reply to any questions.




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