Venus Atmosphere

[davidsinn]

I was inspired by the floating Venus base that is under development, to come up with my own. What I need to know is how to calculate the lifting force of N2/O2 mix by volume for the Earth range in the Venusian atmosphere. If possible I'd like a general formula so I can play around with different lifting gases and altitudes in the Venusian atmosphere.

Thanks,
David

 

[Quick_Nick]

First find the mass of the air in the balloon minus the mass of the air(Venus atmosphere) displaced by the balloon. The mass of the air displaced is determined by the volume of balloon and the density of the air around the balloon. The 'apparent mass' is derived from the subtraction stated earlier. The force can be determined by the apparent mass of the balloon by multiplying by the gravitational acceleration.(negative apparent 'mass' would lead to an upward force, and positive 'mass' would result in a fall)
I think this is correct.

Basically:
Mi - Mass of air inside balloon
Md - Mass of air displaced by balloon
Ma - Apparent mass of balloon ('weight' after bouyancy is applied)
Di - Density of air inside balloon
Do - Density of air outside balloon
V - Volume of balloon
g - Acceleration due to gravity
F - Apparent weight of balloon (the downward force that should be applied)

F = Ma*g
Ma = Mi-Md
Mi = V*Di
Md = V*Do
----OR----
F = (V*Di - V*Do) * g

If you're familiar with programming in Orbiter, the Orbiter API should be able to give you the density of the air around your vessel (the balloon) and give the acceleration of gravity at the balloon's location. You can probably find the density of various mixtures of gases by researching on the internet. (wikipedia says the density of Earth atmosphere at sea level is 1.2kg/m^3)

 

[David]

First find the mass of the air in the balloon minus the mass of the air(Venus atmosphere) displaced by the balloon. The mass of the air displaced is determined by the volume of balloon and the density of the air around the balloon. The apparent mass is derived from the subtraction stated earlier. The force can be determined by the apparent mass of the balloon by multiplying by the gravitational force.(negative apparent mass would lead to an upward force, and positive mass would result in a fall)
I think this is correct.

Basically:
Mi - Mass of air inside balloon
Md - Mass of air displaced by balloon
Ma - Apparent mass of balloon (weight after bouyancy is applied)
Di - Density of air inside balloon
Do - Density of air outside balloon
V - Volume of balloon
g - Force of gravity
F - Force of buoyancy

F = Ma*g
Ma = Mi-Md
Mi = V/Di
Md = V/Do
----OR----
F = (V/Di - V/Do) * g

If you're familiar with programming in Orbiter, the Orbiter API should be able to give you the density of the air around your vessel (the balloon) and the force of gravity at the balloon's location. You can probably find the density of various mixtures of gases by researching on the internet. (wikipedia says the density of Earth atmosphere at sea level is 1.2kg/m^3)

I would correct, a bit. g would be the acceleration of gravity, and F would be the "total" downward force (weight of balloon - buoyant force). If I recall correctly, Archimedes' Principle is that the buoyant force is equal to the weight of fluid (e.g. - atmosphere), displaced (by the balloon, or whatever). And since your last formula seems intended to simplify to F=Wb-Wa, where F is "total" force, Wb is Weight of Balloon and Wa is Weight of Air (Atmosphere, and displaced by the balloon), therefore this formula makes sense to me.

Also, it is good that you have complicated it with consideration of densities, since these will vary with altitude (actually, the mass of the balloon should remain constant, so that Wb=Mb*g, where Mb is the [constant] mass of the balloon, while I'm not sure how Wa would be calculated, with changing altitude and thus air density; perhaps the volume, of the balloon, could be calculated from local atmospheric pressure and temperature, and the Ideal Gas Law [assuming an initially known volume of the balloon, for its initially known pressure and temperature], while the atmospheric density, at a specified altitude, could be calculated from an exponential relationship - although, for Orbiter purposes, I imagine that local atmospheric pressure, temperature and density are available as accessible variables within the program; then, Volume of Balloon, times Atmospheric Density, times g, would provide Wa, since Volume of Balloon is also volume of displaced atmosphere).

We are both assuming, of course, that g (for a specified planet) is constant - which is reliable, I suppose, for this purpose.

 

[Quick_Nick]

Good points. I've corrected g and F. And g doesn't really have to be 'constant'. (should vary slightly with altitude) Also, I'm certainly no bouyancy expert. I'm going heavily on a few minutes of 'research' and what sounds right.
EDIT: My last edits on this post were surely incorrect so I've removed them.

 

[David]

Also, change to M=V*D, since D=M/V.

 

[Quick_Nick]

Also, change to M=V*D, since D=M/V.

:lol: I didn't think about that one very long. Thanks for pointing that out.

 

[David]

I've done that one, a few times, myself. And I didn't even notice it, here, at first.

 

[Cairan]

A while back I had coded a buoyancy plug-in module (DLL) which calculated buoyancy forces for any and all vessels inside an atmosphere. It was an alpha/borderline beta release at the time but it's out there on Orbiter Hangar...

Unfortunately the HD on which my source was crashed and I just don't have the time nowadays to recode it

But still a word of warning: be weary of time acceleration effects on your vessels... You'll see why when you get there!

 

[Quick_Nick]

Oh yeah, I remember seeing that addon! And here it is. Strangely I think I was thinking about this addon while reading another thread but kept forgetting about it when reading this one.
But... does this addon do any of the calculations or have user-input?

 

[Cairan]

Oh yeah, I remember seeing that addon! And here it is. Strangely I think I was thinking about this addon while reading another thread but kept forgetting about it when reading this one.
But... does this addon do any of the calculations or have user-input?

Everything's taken care of inside the module, no user input whatsoever... It correctly takes into account the real gravity field for the vessel, not just the surface value, and the density at the vessel's altitude... everything taken from the API atmospheric values query functions... The point I left at was that I did not calculate the volume of the vessel with it's mesh, but by using a rough estimate based on a "box" model... Close enough but still not accurate for complex shapes...

 

[Quick_Nick]

Everything's taken care of inside the module, no user input whatsoever... It correctly takes into account the real gravity field for the vessel, not just the surface value, and the density at the vessel's altitude... everything taken from the API atmospheric values query functions... The point I left at was that I did not calculate the volume of the vessel with it's mesh, but by using a rough estimate based on a "box" model... Close enough but still not accurate for complex shapes...

Cool! Too bad the source is gone. But it shouldn't be too hard for someone to recreate something like it.(and add variable volume and density!)
And... um... where did davidsinn go??? :blink:

 

[davidsinn]

Cool! Too bad the source is gone. But it shouldn't be too hard for someone to recreate something like it.(and add variable volume and density!)
And... um... where did davidsinn go??? :blink:

I'm here. Been following along. I work 4 ten hour days so I don't have much time at the beginning of the week. I've been collecting data and working up a spreadsheet. I'm having to relearn HS chem as it's been 5 years since I graduated. I don't supposed I could talk any of you programmers into a partnership with me on this project? It'll be a long term slow thing especially because I'm getting married in 3 weeks. I would love to learn how to program but I have no time for the foreseeable future.

 

[Cairan]

It'll be a long term slow thing especially because I'm getting married in 3 weeks. I would love to learn how to program but I have no time for the foreseeable future.

Congratulations, and I really know the time issue with a wedding... I got married myself this summer on July 12th... The moment you say "I do!", it's not so much the words but the fact that you tell yourself "Aw, finally all that stress for the preparation of the ceremony is gone!"

That's how me and my wife felt, a big sigh of relief

 

[davidsinn]

Ok so here's what I come up with:
Venus g at surface 8.87 m/s2
Venus air 1.9516 kg/m3 at 101.325 kPa
Earth Air 1.2934 kg/m3 at 101.325 kPa
apparent mass of balloon -.6582
lifting force of approx 5.8 kg per cubic meter

 

[davidsinn]

That sounds high to me but I'm not sure can some one check me please?

 

[Quick_Nick]

Actually the result should be about 5.8 N per cubic meter.
The subtraction of densities gives a kg result, which is multiplied by a m/s/s number to give (kg*m)/s/s which is a Newton.
Also, remember that this is only true when you are at an altitude where the Venus air is actually 1.9516 kg/m^3.
It will vary with altitude.
Congratulations on the upcoming wedding!

 

[davidsinn]

Thank you. I calculated for 50km. So 5.8N. How many kg will that support per cubic meter?

 

[Quick_Nick]

Well, it will lift 5.8N for every cubic meter. At 8.87m/s^2 gravitational acceleration, 1kg weighs 8.87N. This means that about 0.65kg (5.8N/8.87N) can be lifted per cubic meter. Of course you may want to get some of these numbers more precise, but it should be a good estimation.
And, needless to say, a mixture with a lower density may be desirable for use in this balloon.
(I don't know about that density at pressure stuff though... or what the pressure is at various altitudes)