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Author Topic: Buoyancy calculations – making use of an exception to Archimedes' principle?  (Read 4482 times)

Tarsier_79

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I don't completely agree Willy. If you exclude water from the bottom of an upturned cup and place it on the bottom, it will stay there. It is no exception to the bouyancy rule though. Without pressure pushing up from the bottom, the pressure pushing down is going to win.

Novus. A big issue is the displacement of water. If your "exception" mechanism sits at the bottom position sealed at both sides, lets pretend that it is positively buoyant looking at your fig1 and fig2. As it rises, we have about 14 units of water that drop 2 spaces and 4 units that are displaced all the way to the top of the water surface, about 5 or 6 spaces. So around 22 units of Potential energy working against you vs 14 units moving down 2 spaces...28 units of PE. That is if the buoyant container volume is equal to air. If it weighs less than 6 units of water, it will float, any more (ie if it is neutrally buoyant), it will not rise. I don't think this "exception" will overcome this, but you would need to test.


Novus

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@ Tarsier, thanks for taking an interest in this topic and providing valuable feedback.

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It is no exception to the bouyancy rule though

I agree that the bottom case scenario seems pretty obvious (with an increasing downward Fb depending on dept). Below links provide an interesting read on why apparently it not so obvious?

https://www.scirp.org/journal/paperinformation.aspx?paperid=75679
https://www.scielo.br/j/rbef/a/w7VfCBmYgN46Wm77ttMmQ7d/?lang=en

The reason why it is an exception to the AP is on how the principle is worded. For the bottom and site case the wording would need to be changed to; a body fully immersed in a fluid, however this would exclude the scenario in which a body is partially submerged where AP is applicable.

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Archimedes' principle (also spelled Archimedes's principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces

In our case ^Fb will decrease with dept untill Fb is zero (as per picture 1 in the initial post) and becomes increasingly negative (vFb) at more dept.

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As it rises, we have about 14 units of water that drop 2 spaces and 4 units that are displaced all the way to the top of the water surface, about 5 or 6 spaces. So around 22 units of Potential energy working against you vs 14 units moving down 2 spaces...28 units of PE.

I believe your calculations are correct, however not sure why this would be ‘against you’. A downwards displacement of 28 units would be sufficient for a lift of 22 units?

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That is if the buoyant container volume is equal to air.

If this is correct it obviously will not work. However I don’t understand why only a slightly buoyant object A wouldn’t be able to rise with a downwards water displacement of 28 units exceeding the upwards lift of 22 units?



Tarsier_79

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Think about it. if it were neutrally buoyant and it moves upwards, there is no downwards displacement of mass, as the assembly weighs the same as the water, so we just displace water to the top, lifting PE. Those calcs (which might not be perfect) were based on the assembly weighing the same as air.

panyuming

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 :)
Rough calculations.

Tarsier_79

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Is it? The pontoons still displace the same amount of water.

How do you seal the pontoons against the shield without creating massive friction?

panyuming

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How do you seal the pontoons against the shield without creating massive friction?

The principle is the foundation, everyone determines that the principle is correct,
and then how to make the second layer.

It may be possible to use the nano fluff on the surface of the lotus leaf.

There are some situations that are correct but cannot be implemented, such as the space ladder.

Novus

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@Panyuming, interesting design. Thanks for sharing. Maybe it fails based on below site case scenario which whould be applicable to H1 in your design (aand probably partially to H2 and H3). It looks like Fb not only changes direction but also increases?

Novus

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Willy

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I don't completely agree Willy. If you exclude water from the bottom of an upturned cup and place it on the bottom, it will stay there.

So ? A playing card will keep the water in a over turned cup as well.

Try it with something other than a cup.

Question. is a buoyant in water, 5 sided pyramid, changed in buoyancy when its point faces down ?  Of course not.

Note...
   Precision mated, ground glass surfaces are what is needed in the ferris wheel design.
  The viscosity of water is too great for water to leak through the plunger and barrel fit
  in my syringe.  Even so, the sliding action is very low friction.

panyuming

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@Panyuming, interesting design. Thanks for sharing. Maybe it fails based on below site case scenario which whould be applicable to H1 in your design (aand probably partially to H2 and H3). It looks like Fb not only changes direction but also increases?

I also don't think it's possible that simple to succeed. ;) :P ::)

Willy

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But...

Seriously and sincerely, thanks for bringing the information and idea to
the forum.
  Very cool !

P.S.
   Overunity devices do exist. 

I know, I have one that sits on my bench at my home.

sm0ky2

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The key point, as per the exception to the Archimes principle, is that there are no lateral forces in step 1 and 2 and therefore object A will not compress to its minimum volume even when the 2 parts of the trapezium A are not locked.


This assumption only holds true while the inner vessel is in contact with the outer vessel
It is not a true exception to  Archimedes principle.
But rather that multiple vessels must be taken into consideration


Novus

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This assumption only holds true while the inner vessel is in contact with the outer vessel
It is not a true exception to  Archimedes principle.
But rather that multiple vessels must be taken into consideration

I won't argue you're point. One thing is for sure that, at least to my calculations, Fb behaves in a strange fashion in the sense that it decreases with dept, than at some point is equal to zero and becomes negative (similar to the bottom case scenario) at greater depts.

https://arxiv.org/pdf/1110.5264.pdf

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This downward force then increases linearly with depth, which clearly contrasts to the force predicted by AP, but agrees to experimental results [2, 15, 17]. In fact, the increase of this force with depth has been subject of deeper discussions in recent works [2, 15, 16, 33], in which it is suggested that the meaning of the word ‘immersed’ should be ‘fully surrounded by a liquid’ instead of ‘in contact to a liquid’, which would make the ‘bottom’ case, as well as all other ‘contact cases’, out of scope of the Archimedes original propositions, as well as AP modern statement [2, 15, 33]. Note, however, that this redefinition is deficient because it excludes some common cases of buoyancy such as, for instance, that of a solid (e.g., a piece of cork) floating in a denser liquid (e.g., water). In this simple example, the body is not fully surrounded by a liquid and yet AP works! More recently, other authors have argued that the definition of BF itself should be changed to “an upward force with a magnitude equal to the weight of the displaced fluid” [16]. However, I have noted that this would make AP a definition for the BF and then, logically, AP would not admit any exceptions at all. In face of the downward BF experiments already mentioned, it is clear that this is not a good choice of definition. Therefore, I would like to propose the abandon of such redefinitions, as they are unnecessary once we admit some exceptions to the AP, which is the natural way to treat the exceptional cases not realized by Archimedes in his original work.

Tarsier_79

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I know, I have one that sits on my bench at my home.

Could you elaborate a little?

In all my years of searching, I have never seen a successful OU device, mechanical, magnetic or electrical.

Novus

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Could you elaborate a little?

In all my years of searching, I have never seen a successful OU device, mechanical, magnetic or electrical.

It is discussed on the Free Energy RANT CAFFE tread.