Pour your brains here on how to build this contraption...

[Externet]

Hi all.

 

Picture a glider model, ballasted to stay near horizontal and near neutral buoyant when placed in the sea.

 

When placed in the warmer water surface, with daylight and little depth pressure, some mechanism makes the nose go down, slightly decreases buoyancy and advances while dives.

 

When reaches a set depth pressure, darkness and cold water, those cause the mechanism to toggle back towards being slightly buoyant and tilt nose up.

It will rise and advance.

 

When surfaces, little depth pressure, daylight and warmer sea temperature cause the mechanism to toggle towards slightly decreased buoyancy and nose down.

It will sink again and advance. Repeat and repeat...

 

The lengthwise center of gravity shifting and the buoyancy are the mechanisms that can be actuated by solar cells, pressure collapsible chambers/piston, temperature actuators, or whatever else you think may work .

 

Some mechanism that increases buoyancy with cold/depth pressure/darkness/hitting bottom would be needed. Bubble generation and purge... or other clever methods.

 

Come up with ideas,,,

 

 

[John Cuthber]

Since the mechanism needs to supply the energy needed to push the craft forward, why not just call it an engine?

[Externet]

Hi John. There is no need to have an engine to propel it forward. The sinking action with nose slightly down will make it advance forward.
Same when rising, the nose slightly up will make it to continue advancing forward.
Like an airplane with no engine (glider)

The mechanism to make it buoyant and nose up could be an electrolysis bubbler running from a seawater battery.
When the craft surfaces, bubbles bleed by either a solenoid or a needle valve held closed by its own float, repeats the cycle starting to dive.

But there have to be other ways...

http://i588.photobucket.com/albums/ss323/Innernet/P1010038_zps089b92e7.jpg

[John Cuthber]

Even if you say it's driven forward by swimming pixies I can call them an engine.

Whatever engine you choose will need to obey the laws of thermodynamics and will therefore need power.

It could be wave powered or wind powered if you like but that's just just a fancy engine.

 

What are you actually trying to achieve?

[Externet]

Hi.

OK, call it engine. No problem there. But the word 'pixies' does not click in my poor English.

An underwater contraption that will travel powered by delta pressure, delta light, delta temperature, delta whatever supplied by sea environment.

 

To simplify, to come up with a device that endlessly dives and surfaces periodically by some clever automatism using the above deltas.

 

I believe would take a 'snap' hysteresis action mechanism triggered from the delta extremes.

Like a liquid that vaporizes under pressure and liquifies when not pressurized, as ideal dream.

 

The 'snap' 'toggling' action is what I believe would make it work. Nitinol, solar cells and electrical actions, pressure driven actuators, anything in that line. Sample attached.

But open to any suggestions

 

Edited. Unable to attach a picture. Will retry.

 

Edited2 : Lost in space on how to attach a picture on this new forum format. It was just a 'party clicker' image.

Edited January 23, 2013 by Externet

[StringJunky]

If you want to upload a file from your computer. Click More Reply Options (bottom right of text input box) then look at the steps in the following image.

 

[Externet]

Thanks.

It does not always show the "Attach this file" capability. [image below] This time did ¿?

See attached.

 

 

Retrying... perhaps will attach. Seems does not work on 'quick' replies...

Edited January 23, 2013 by Externet

[StringJunky]

No, it doesn't show in Quick Reply. You have go to the fully-featured Input box by clicking More Reply Options.

 

Wouldn't your vessel descend on a diagonal path but ascend on vertical one...you'll have no forward motion on the ascension?

Edited January 23, 2013 by StringJunky

[Enthalpy]

This gliding submarine does exist and is put at work for oceanic research.It does not need an engine because differences in water temperature between depth and surface bring the energy. I read a report several years ago.

 

Though, its design is a little bit tricky, because warmer temperature must reduce its total volume, as opposed to what thermal expansion uses to do. If I remember properly, it has one working volume full of liquid or solid, that expands little but delivers much pressure and force, to forcibly change the volume of a bladder that reacts with less pressure and force than a solid does.

 

And this, despite depth changes the pressure on the bladder...

 

Maybe a void ellipsoid made of bimetallic spring would suffice. Or even, a dome of one metal sitting at a circle of a different metal. Or a bimetallic truss: combines well with a piston, classical engineering then, done.

 

Or put the solid/liquid "in series" with the bladder, and both in a frame that expands little.

 

There are also a few materials that contract at heat, at least in one direction: carbon fibre, latex, many high-perf polymer fibres...

 

And of course, it needs something to stop the submarine diving, at a convenient depth.

 

-----

 

One fascinating aspect is that it's the first object that can really produce some meaningful work from the Oceanic thermal gradient. Many attempts want to make electricity and sweet water from the temperature gradient, but this challenge is very difficult, and both designs and results aren't fully convincing.

 

Though, I doubt a big wheel with wany submarines attached is a better design...

[Externet]

Thanks, Enthalpy. Very interesting.

Such depth pressure piston actuated bimetal dome could shift the ballast position for nose up when a depth is reached, to reverse its action for nose down when reaching zero pressure at surfacing. Nice and 'simple'.

 

The buoyancy cycling is left to deal with.

If solar cells on wings/fuselage of the glider charge a battery, could bubbling at an electrolysis chamber triggered by a depth switch work? * ; purging them when reaching surface is sensed , enabling next dive.

Surfacing at night, halts everything if battery sensors do not detect full charge.

 

Unless other opinions come up with a bubbler/expanding chamber actuated by depth/temperature/light deltas.

 

*Would bubbling volume by electrolysis be seriously impaired at depth, as to not consider such method ?

[Enthalpy]

Electrolysis produces gas amounts that are always very disappointing. Even more so with weak photovoltaic cells and if needing volume at depth to make buoyancy. My intuition shouts: no hope. Use the temperature difference.

 

If the bladder is located before the wings, its volume change will not only provide the net up or down force, it will also put the nose up or down.

 

For pitch stability, you have to adapt the stabilizer setting: it must pull the nose up during descent and down during ascent. Or adapt the wing's setting and keep the stabilizer immobile: this would keep the body parallel to the flow, reducing drag. The bladder's movement might set the wing, perhaps - but this lacks flexibility, so I prefer an electric motor.

 

For roll stability, since the wing can't be V-shaped, the centre of gravity must be low.

 

A different design would put the submarine on its back during ascent. Then the stabilizer can be immobile and the wing V-shaped. An eccentric bladder, near the belly, would do it. Less convenient for data comms etc.

 

In all cases, you need a brake that stops the bladder's movements during descent and ascent, to release it only at the desired depth, to change the direction. Say, a slit ring can block a rod: an electric motor +gear +screw tightens the slit ring at will.

 

============================================================

Three design families for the bladder that expands at cold:

 

 

Solids give great forces to contract or expand the bladder despite water's pressure; their thermal expansion is amplified by the dimensions or the shape.

 

I prefer solids to an expanding liquid: no seal, easier thermal contact with water.

 

All designs need a brake, though displayed only at the left design. The piston's seal must work between two liquids for long-term tighness, so the gas is in an elastomer bladder (not displayed!) within the cylinder, the rest being filled with a liquid.

 

The left design gives the necessary engineering flexibility (consider e-beam to weld different alloys), the others are very doubtful. The two holed cylinders at the middle design would have to be long, even with a polymer; pendulum clocks had several parallel rods in series, but this gets boring if exaggerated. The right design would need many trials and isn't adjustable.

 

Marc Schaefer, aka Enthalpy

============================================================

 

And this is how the oceanic glider can look like:

Here a fixed stabilizer and an oriented wing, so the body is always parallel to the flow.

The wing orients by flaps, better for the curvature and against algae. Sweep the wing.

The center of mass is always low, but goes to the prow for descend and to the aft for ascend.

 

It's important that the wing orients at the same time as the center of mass moves, so maybe the bladder should better control the flaps; elastic coupling and stops to define precise positions?

 

Produce some electricity from the bladder's actuator, when the brake is released. Or from a water turbine. Or have magnesium+seawater batteries if possible.

 

The glider needs a safeguarding ballast, as every submarine, to be thrown away in a situation of uncontrolled sinking.

 

Marc Schaefer, aka Enthalpy

Edited January 26, 2013 by Enthalpy

[Externet]

Thanks again, Marc.

 

Am thinking on your good suggestions, will be back.

 

So far I see a problem with your paragraph " If the bladder is located before the wings, its volume change will not
only provide the net up or down force, it will also put the nose up or down."

 

The air volume change due to depth pressure or lower temperature in the nose bladder would not provide surfacing force, as the pressure will reduce the volume, making it dive instead.

-----> The root of the problem is that at depth, there is lower temperature, and that causes air volume reduction, sinking it more, and;

at depth, there is high pressure, and that causes air volume reduction, sinking it more.

 

Then, to my poor brain, depth pressure and temperature are not useable to provide air expansion to rise to surface. We need the opposite action.

 

I came up with an hysteretic mechanism for nose up/down :

A long sealed pipe lengthwise to the fuselage, with a ball bearing inside and weak magnet end caps.

 

Seems to me, sealed bellows are preferable to piston/cylinders.

 

Will be back after digesting your post and evaluating the availability of fancy materials with expanding when cold property.

Edited January 26, 2013 by Externet

[Enthalpy]

The behaviour of gas in the bladder alone would go indeed in the wrong direction, contracting at depth. That's why I have solids, like the truss of two different metals, that impose their behaviour to the bladder. Provided that the solids are properly combined, they let the bladder expand at cold and contract at warmth.

 

To obtain the depth oscillation, it also needs hysteresis, here provided by the controlled brake to let the bladder's volume change only at the surface and full depth.

 

Combining both, the bladder's volume shrinks at once at the warm surface, letting the glider sink, and expands at once at the cold depth, letting the glider rise again.

[Externet]

Hi. In an attempt of exploring less complexity and difficult solid materials, let me make a parenthesis at this point, will return to the main solids expansion later.

 

What is your opinion on following the electric route, and as bubbling from electrolysis is not promising, what about using ethanol or an even better behaving liquid in a thermally insulated sealed bellows. Heating it up will become gas causing expansion and buoyancy. Something like 'hand boiler' toys.

 

A volatile liquid that can be easily gasified with little energy from a battery powered heating element. Which could be as simple/available or better performing enthalpy of evaporation than ethanol ? Propane, Acetone, Ethane, Carbon tetrachloride, Chloroform, Ether, Methane .... ? Under depth pressure of ~ 7atm = ~200 feet

 

Will be back...

Edited January 27, 2013 by Externet

[Externet]

Hi Marc.

Having difficulty to discern solids which show significant expansion. If you have suggestions, please come forward.

 

The force exerted by this one at a delta of ~20 degrees Celsius may not be useable to force enough expansion.

 

http://i00.i.aliimg.com/photo/v0/449280688/Bi_metal_thermostat_spiral_coil_on_silicone.jpg

 

Please comment on post #14 above.

[Enthalpy]

Imposing the volume to a bladder at depth means some force and energy, sure. But the solids that shall do it can have the necessary volume.

 

Generally, stiffer materials can provide more force but expand less - but there are exceptions like Invar or Pyrex. So once you have an efficient pair of materials, the shape you design must match the material to the blade's force and displacement - and it must guarantee a quick heat exchange with water.

 

A factor of merit for the expanding solid is E*K², where E is Young's modulus and K the coefficient of thermal expansion. This characterizes the available mechanical energy per volume unit. You can try a few metals and plastics - plastics look better but must be thin to react quickly.

 

The truss I sketched is an intuitive approach, which needs backing or adjustment by numbers, to matching the bladder's behaviour. It is stiffer than the bimetal you linked in order to, as you told, give more force. The angle of the truss adjusts this; stack seeral ones if needed.

 

Tubes react to heat more quicky and resist buckling better.

 

-----

 

A rough first glimpse, without the factors of 2 and 3:

 

Imagine a 10dm³ change bladder that works between 0m and 30m: it absorbs 3kJ if gas pressure varies little.

 

Aluminium (70GPa, 24ppm/K) provides 8kJ/m3 so you need 0.4m³ or 1000kg of it, plus the other metal, not very good.

 

A plastic (2GPa, 200ppm/K, must withstand 12MPa for long!) needs 0.18m³ or 180kg, better. Consider polypropylene.

 

At 20K*200ppm/K, a truss of 200mm length and 40mm height moves by 3.7mm which would fit a D=1.8m bladder, so a flater truss or several stages are better. You must also fit the 0.18m³ somewhere.

 

Levers and pulleys can contribute to the design.

 

-----

 

The design I heard of long ago used the expansion of a liquid in a cylindre instead of plastic parts. A liquid would need a good heat exchanger with water, like water tubes passing through the cylinder, or many liquid tubes in water making the tank (converging to one single piston).

 

If you find a strongly expanding liquid, fine. The ones I know (petrol) are somewhat better than plastics but polluting.

 

Marc Schaefer, aka Enthalpy

Edited January 30, 2013 by Enthalpy

[Enthalpy]

To compress the bladder by a thermal expansion, solids would impose a sturdy unflexible design. Liquids take less room, a design follows. A nearly-perfect gas would be bad; a gas just above the critical point (SF6), a liquid just below (SiF4), a liquid-vapour equilibrium or better a dissolved gas might improve, but I won't check that.
http://de.wikibooks.org/wiki/Tabellensammlung_Chemie/_Dichte_gasf%C3%B6rmiger_Stoffe sort by Kritische Temperatur
A shape memory alloy, or the change of Young's modulus with temperature, might improve. Later maybe.



The liquid here is soybean oil: 746ppm/K and 2.05GPa (near 1atm). Pure biodiesel would be more efficient but leaks more polluting. Better choices must exist.

The container and heat exchanger is a set of stainless tubes, ID=6mm OD=8mm, purchased as coil, totalling 1670m. Wound with D=0.6m, it takes 14 layers of 63 turns on 0.76m length. Oil then follows with 2K delay a gradient of 20K in 500s.

0.34dm³ expansion are exploited between 89b and 211b ("impedance matching") on a small piston, say D=46mm, which pushes a big piston, say D=204mm, to control the buoyancy. Steel expansion and elasticty are factored in, plus little margin. Via soybean oil, CO₂ is compressed between 80dm³ 6b and 70dm³ 7.13b, while water counter-pressure varies between 3b and 0b. The gas is isolated from water and has 288K at 75dm³.

The controlled brake allows action at both extreme programmed depths, better than hysteresis. Maybe a valve. An oil throat makes for smooth moves.

Bladders can be multiple (but mind moving liquid mass), their location modified and the exchanger's one as well... Hydraulic designs are flexible. Please remember that hydraulic and maritime design must be made or helped by experienced people (protect the heat exchanger), and seal design is a specialist's job.

The glider's design must boast adjustment for buoyancy (at each campaign), position of the center of mass, position of the bladder(s). The salvage ballast must more than compensate flooded bladders and exchanger plus all compressible parts; it can test the glider without the bladder. The operation team must comprise one person with clear ideas about gas, thermodynamics, buoyancy. Have a tether for each first dive.

Marc Schaefer, aka Enthalpy

Edited February 3, 2013 by Enthalpy

[Externet]

Thanks Marc for your elaborated and thoughtful post using purely delta temperature and fluid contraction. Deserves all the merit.

Maritime environment as you say, is very agressive and there is never enough precautions in redundant sealing. Been a scuba diver for 30 years and experienced several unexpectations.

 

Currently, am evaluating components sourcing to build the key buoyancy part of the contraption on two or three different schemes, test them as standalone (tether yes !) and much later to see housing in a PVC pipe fuselage.

 

Something I must also consider is the delta T may not be enough at all locations the glider encounters while travels, as delta depths could be restrictive. So the contraption may work in open seas but to reach there from a 'shallow' waters launch will pose a challenge.

[Enthalpy]

I imagined launch from a boat only. The glider needs, as you noted, depth as soon as it is freed.

[Enthalpy]

The variation of Young's modulus with temperature isn't more compact than the thermal expansion of oil.

 

Shape memory alloys and polymer can be more compact than oil, with alloys possibly faster as well if the elements are thin. Transition between +5°C and +25°C needs to be checked.

 

Marc Schaefer, aka Enthalpy

[Enthalpy]

Still for an expanding liquid like oil, this heat exchanger works faster than the set of tubes.

At the oil side, I've considered fins 29mm long, 2mm thin and spaced by just 2mm, so the oil temperature follows with only 1.5K lag a water gradient of 20K in 100s. Now the glider is fast enough to swim against a strong stream.

The fins at oil and water side are milled by a disk cutter or several disks on one shaft, the tips completely deburred, cleaned and covered with a layer of excellent filler, then an upper and a lower set of fins are interleaved and pressed (vertically on the sketch) to the proper overlapping. The interleaved zone is pressed together (horizontally here) and the filler molten.

This needs proper tolerance at fin spacing. The tips must be tapered and filler drops extend only there. Consider etching chemically the tips, for instance with lukewarm FeCl3, which can deburr and, when dipping deeper, adjust finely the interleaving tolerance. Some additional (or all) filler can be flown in from two sides, or preset as a powder between the cold fins above the interleaved zone.

The end caps must be really stiff and leave little dead oil volume. If considering elastomer joints, check their compliance. Void and heat help filling without bubbles and outgas the oil.

I take Cu-Cr1Zr for the fins, possibly for the caps. It may need additional anticorrosion protection, especially at the joints.

If the fins zone is 0.25m wide and 0.8m long, the previous bladder needs 8 such exchangers. The exchangers could be the glider's stabilizer, but if put instead in a hull recess, they drag less and can be protected from dirt. All ends should be tapered against algae and may extend more than the fins.

 

Such an exchanger has uses beyond the oceanic glider.

Marc Schaefer, aka Enthalpy

Edited February 8, 2013 by Enthalpy

[Enthalpy]

Fusion of a solid, especially of an alloy for stiffness and fast heat transfer, brings volume at a big potential pressure, and makes the design about as compact as shape memory materials.

The 75.5-24.5% Ga-In eutectic melts at +15.7°C - other proportions warmer, but cooler with added Sn. Lacking data, I suppose here 3% expansion and 62kJ/kg latent heat at melting, and both for the solid and liquid, 25W/m/K heat conductivity and 25GPa bulk modulus.

A D=10mm cylinder freezes and thaws in just 15s from ambient +5°C and +25°C, and the pressure increase at constant volume would be 7500b, demanding a stiff design. If used at 1500b, the volume change is 3% -0,6% (Ga-In) -0,3% (tube) -0,2% (hydraulic fluid) -0,2% (others) = 1,7% and the available energy 2500kJ/m3, yeah. The same bladder needs only a total of 23m of D=10mm thawing alloy.

The thick tube (OD=20mm, ID=10mm) is plated Cu-Be2 while the brazed fins can be Cu-Cr1Zr or cold-drawn Cu. The hydraulic fluid is glycerine with some anti-freeze water, or a PEG-base fluid, hold in a collapsable polymer tube (of shrinkable sleeve?) of D=2mm according to the alloy's melting expansion. A spacer (for instance thin spring wire) leant against the wall holds the polymer tube at the center from place to place, while a small metal tube (not sketched here) inside the polymer tube, with tiny performations, ensures the fluid can pass, and connects to the use.

Catalogue static and even mobile joints exist for 1500b but not for 7500b. I'd say: brazed metal tubes everywhere, short and thick, and a ball-and-cone valve.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Shape memory alloys are faster and perhaps a bit smaller than the melting alloy, but apparently their transition doesn't fit between +5°C and +25°C. Only Ni-Ti is available commercially if I searched well, and its transfomation range is for instance +23°C to +35°C in one direction and +6°C to -3°C in the other. The range is shifted by the precise composition, with a 10K additional tolerance, but stays wide; Ni-Ti-Cu would improve by 15K, still too wide.

So melting remains the best candidate for the Ocean's temperature gradient. By the way, a pressure that lets harvest work in a cycle must shift the melting temperature significantly.

Melting actuators have been used for decades as thermostats. They base on wax, which eases the design so I may have a look, but the stiffness of an alloy lets me suppose it offers more work, and its conductivity allows a wider tube.

The melting actuator or motor is good for the glider, say at Ocean research, and generally to exploit small temperature differences like the Oceanic gradient. I don't expect a better ideal efficiency than with a gas or a vapour, but a net power output is easier to obtain.

Autonomous mechanical power is sometimes more important than efficiency. For instance to harvest cold water from the depth of the Ocean or a lake, it takes little power to lift the denser water, the temperature difference is available at the engine-pump, and the engine avoids to mingle electricity with water. Once at the shore, cold water can cool houses, say in Canarias, Baleares, Hawaii, the Great Lakes...

Marc Schaefer, aka Enthalpy

[Externet]

Thanks, Marc, for your very elaborated and time consuming posts #21 and #22 above. Clearly show your involvement in the subject, your knowledge and expertise. The exposure of alternatives where you poured your brains onto it.

 

Once I learned that simple projects do not yield huge successes; complex problems do. Complex tasks requiere of these complex engineering considerations.

 

Currently in the pursuit of parts to build a few alternates to test and evaluate, hampered by imminent moving to another state and holding back progress and working with more dedication to the glider model. But will be back with more adrenaline when settled.

[Externet]

Did a quick preliminary qualitative test; based in gas production, about a spoonfull of acetone in a -say non-latex bladder- with a 5 watt immersed bulb in it as heater element. Initially there is no gas in it, just the liquid acetone. Power would come from a battery/solar cells on the glider wings.

 

 

After a few minutes, bubling was very active. One hour later, gas was about six times the amount of liquid acetone. Too long for a preferred 'snapping' action of immediate surfacing. Yes, it would surface anyway as there is some buoyancy provided, but too late?

 

 

The bouyancy, small and took too long to produce with five wattshour, could be increased with more power, BUT that test was at atmospheric pressure (not at ocean depths pressure onto the bladder, and at room temperature, not at cold depth temperatures) which both together would greatly impair the gas expansion amount.

 

To follow some day, based in a micro compressor. Sucking gas from a bladder to a lesser volume vessel to promote sinking. Instantaneously releasing it back to the bladder to start surfacing. Will see...

-Not ready yet for complex materials quicky tests-