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How Do You Calculate Buoyant Energy? 
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#1
Dec2712, 02:23 PM

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Buoyancy is an artifact of gravity that moves mass up away from the center of the earth in a fluid whenever the specific gravity of the object is less than the surrounding fluid.
Buoyant Force is calculable. Gravitational Potential Energy is calculated by the formula: mgh Is Buoyant Potential Energy calculated mg'h? Here is how I have calculated it so far; mass = 100,000 kg height or depth = 100 meters g' = 1  (1000 / 1028) = 1  0.97276265 = 0.02723735 (The density of the solid object is 1,000 kg/m. The density of the fluid is 1,028 kg/m) By this calculation the Buoyant Potential Energy would be 272,373.54 Joules Is this correct? Could it be improved on? 


#2
Dec2712, 03:02 PM

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BTW, would there be more "bouyant energy" stored if you pushed a solid object down to a depth, or pushed an airfilled object down, where the object shrinks in size as it gets to greater pressures at lower depths? 


#3
Dec2712, 03:08 PM

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P: 11,589

You can define g' such that the potential energy is mg'h, but this would be an odd definition as the density of the object would contribute to g'. I would change m to m' which is the difference of the mass of the object and the corresponding mass of water. If you just know the density, but not the total mass or volume of the object, all you can calculate is an energy density: ##\frac{E}{V}=\rho'gh = (\rho_{object}\rho_{water})gh## where ρ are density values.



#4
Dec2712, 04:17 PM

P: 14

How Do You Calculate Buoyant Energy?



#5
Dec2712, 04:23 PM

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Aside  it is *very* disconcerting when you are in trouble and have to pull your Bouyancy Compensator (BC) vest's ripcord, to inflate it to take you to the surface  if you are at any depth, you barely start to accelerate to the surface at all. As you rise, you go faster and faster, which is finally reassuring. 


#6
Dec2712, 04:32 PM

P: 14

Net Gravitational Acceleration g' 0.315072129 m/s2 1p'/p 0.032128514 m/s2 Object Density p 996 kg/m3 Fluid Density p' 1,028 kg/m3 Buoyant Force Fb 1,013,473 N The idea was that I could back in F=MA and multiply the Buoyant Force * g' * the mass and come up with the energy potential. Should I put in m'  the differential mass  instead of the mass? 


#7
Dec2712, 04:42 PM

P: 14

Buoyant Force Calculator Gravity ("g") Force 9.80662 m/s2 Mass 100,129 kg Force 981,925 N Density 996 kg/m3 Submerged Volume 101 m3 Volume 101 m3 Fluid (Seawater) Density 1,028 kg/m3 Buoyant Force 1,013,473 N Net Buoyant Force Upwards 31,548 N Buoyant Path Distance 244.8 m Buoyant Joules (N m) 7,722,903 J Buoyant Potential Energy 2.15 kWh Buoyant Power 198 kW 


#8
Dec2812, 09:21 AM

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P: 11,589

Looks right, but I did not check the numbers in a calculator.



#9
Dec2812, 09:46 AM

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Does that seem good? 


#10
Dec2812, 10:22 AM

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P: 11,589

Depends on the setup. And if you let that thing float upwards, it depends on the water resistance, which depends on the shape of the object.



#11
Dec2812, 03:28 PM

P: 14

http://hyperphysics.phyastr.gsu.edu/hbase/lindrg.html I plugged the variables into Excel and ran the formula. Now that it is in Excel, (theoretically if I did not make any mistakes copying) I can adjust the size of the radius and the density. Is this page a standard or are there different variations of how to estimate the drag on a sphere ascending by buoyancy? I have heard of Reynolds Number, Laminar Flow, Cavitation, and a lot more variables: very complex and over my head calculations. But, I am hoping that this gives me a good ballpark estimate. 


#12
Dec2812, 04:23 PM

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I am quite sure that an object with that size and velocity in water will not follow Stoke's law.



#13
Dec2812, 05:28 PM

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#14
Dec2912, 01:54 AM

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#15
Dec2912, 09:12 AM

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P: 11,589

There are formulas for turbulent flow, with force proportional to the velocity squared. You can solve this for the equilibrium velocity. 


#16
Dec2912, 01:16 PM

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#17
Dec3112, 01:26 PM

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