Author Topic: Common bulkhead vs. nested bulkhead difference  (Read 10530 times)

Offline rocketman99

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Common bulkhead vs. nested bulkhead difference
« on: 11/03/2006 03:11 PM »
I'm doing some IV+V  on CL:V 2nd stage concepts, and see references to common vs. nested bulkhead
designs--what is the difference in twerms of load path/load sharing??--anybody know?

Thanks

Offline Jim

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #1 on: 11/03/2006 03:54 PM »
Quote
rocketman99 - 3/11/2006  10:54 AM

I'm doing some IV+V  on CL:V 2nd stage concepts, and see references to common vs. nested bulkhead
designs--what is the difference in twerms of load path/load sharing??--anybody know?

Thanks

Defined nested

Offline rocketman99

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #2 on: 11/03/2006 07:40 PM »
as i understand nested, and i guess that's my question, it is two separate bulkheads in close proximity--
by that definition there would be no load sharing--but this is what i'm trying to clarify

Offline Jim

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #3 on: 11/03/2006 07:49 PM »
Quote
rocketman99 - 3/11/2006  3:23 PM

as i understand nested, and i guess that's my question, it is two separate bulkheads in close proximity--
by that definition there would be no load sharing--but this is what i'm trying to clarify

which is the standard config.

Bulkheads are not in the load path.   The load paths are the same, the walls of the vessel.  As long as the right pressure differential is maintained.

Offline bombay

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #4 on: 11/04/2006 12:14 AM »
Quote
rocketman99 - 3/11/2006  2:23 PM

as i understand nested, and i guess that's my question, it is two separate bulkheads in close proximity--
by that definition there would be no load sharing--but this is what i'm trying to clarify
When you say, "close proximity", do you mean one bulkhead is shoved into another?

Bulkheads are independently connected to the tank wall.  So by rule, the tank wall, not the bulkead is subjected to longitudinal mechanical loading.  The bulkheads are of course subjected to meridional and hoop pressure loading.  

It wouldn't make much sense to have two structural bulkheads shoved up next to one another such that under pressure they are pressing hard against each other.  If that were the case, then you could make an argument that the two bulkheads share pressure loading no different than having one bulkhead equal to the combined thickness of the two.

Offline quark

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #5 on: 11/04/2006 04:22 AM »
Current Centaur common bulkhead could be described as nested.  The bulkhead is double wall with a vacuum pulled in between for insulation.

Offline bombay

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #6 on: 11/04/2006 06:08 PM »
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quark - 3/11/2006  11:05 PM

Current Centaur common bulkhead could be described as nested.  The bulkhead is double wall with a vacuum pulled in between for insulation.
A vacuum unto itself does not provide insulation.  If two metallic components are pressed tight against each other, there wouldn't be much of a insulation affect.  It would however prevent pressure from building between the two bulkhead walls, which would prevent them from wanting to separate and possibly callapse.

Offline Jim

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #7 on: 11/04/2006 06:25 PM »
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bombay - 4/11/2006  1:51 PM

Quote
quark - 3/11/2006  11:05 PM

Current Centaur common bulkhead could be described as nested.  The bulkhead is double wall with a vacuum pulled in between for insulation.
A vacuum unto itself does not provide insulation.  If two metallic components are pressed tight against each other, there wouldn't be much of a insulation affect.  It would however prevent pressure from building between the two bulkhead walls, which would prevent them from wanting to separate and possibly callapse.

There IS a vacuum between the 2 walls of the Centaur bulkhead and they don't touch

Offline Nick L.

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #8 on: 11/04/2006 08:37 PM »
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bombay - 4/11/2006  12:51 PM

A vacuum unto itself does not provide insulation.

Yes it does. The lack of air inhibits heat transfer. A Thermos or similar vacuum flask works the same way.

Nick
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Offline bombay

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RE: Common bulkhead vs. nested bulkhead difference
« Reply #9 on: 11/04/2006 09:03 PM »
Quote
Jim - 4/11/2006  1:08 PM

Quote
bombay - 4/11/2006  1:51 PM

Quote
quark - 3/11/2006  11:05 PM

Current Centaur common bulkhead could be described as nested.  The bulkhead is double wall with a vacuum pulled in between for insulation.
A vacuum unto itself does not provide insulation.  If two metallic components are pressed tight against each other, there wouldn't be much of a insulation affect.  It would however prevent pressure from building between the two bulkhead walls, which would prevent them from wanting to separate and possibly callapse.

There IS a vacuum between the 2 walls of the Centaur bulkhead and they don't touch
Without a vacuum, the expansion and contraction of air would apply a dynamic stress within the cavity between the 2 walls.  You would run into a differential pressure condition (the pressure within the cavity versus the pressure within the tank) that could be avoided by pulling a vacuum.  Obviously the cavity pressure would have to exceed the tank pressure for a serious problem to occur.
If a generic insulator was incorporated between the tank walls along with pulling a vacuum on the cavity, then the best of both worlds is accomplished.  
   

Offline yinzer

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #10 on: 11/04/2006 09:05 PM »
Is the gap between the bulkheads filled with anything solid, like a honeycomb or batting?  If not, what stops the LH2-side bulkhead from reversing?
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Offline bombay

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #11 on: 11/04/2006 10:35 PM »
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yinzer - 4/11/2006  3:48 PM

Is the gap between the bulkheads filled with anything solid, like a honeycomb or batting?  If not, what stops the LH2-side bulkhead from reversing?
The opposite LO2 side would have to be of a higher pressure.

Offline yinzer

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #12 on: 11/04/2006 11:35 PM »
Quote
bombay - 4/11/2006  3:18 PM

Quote
yinzer - 4/11/2006  3:48 PM

Is the gap between the bulkheads filled with anything solid, like a honeycomb or batting?  If not, what stops the LH2-side bulkhead from reversing?
The opposite LO2 side would have to be of a higher pressure.

But if there's no way to transfer load from the LO2 bulkhead to the LH2 bulkhead, the LH2 bulkhead should start to reverse until it hits the LO2 bulkhead, which will restrain it via the pressure in the LO2 tank.  Unless the LH2 bulkhead is stiff enough to act as a dome in compression, which seems unlikely to me.

Is there a way to transfer load between the bulkheads?

(to clarify: the LO2 dome is concave with respect to the inside of the tank and so the internal pressure loads are tensile, so the dome is stable.  The LH2 dome is convex toward the inside of the tank, so the pressure loads on it are compressive.  It's a very thin shell and so seems like it should buckle very easily.  I read somewhere that the space between the bulkheads is filled with fiberglass, but am now wondering if this is loadbearing or not).
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Offline Gus

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #13 on: 11/04/2006 11:49 PM »
For all you fellow Lockheed Martin employees posting on this subject, this is just a reminder to remember your compliance training on sensitive information.  You are posting on a public forum and you are delving into proprietary information on how the Centaur design uses a common bulkhead.

Offline bombay

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #14 on: 11/05/2006 12:01 AM »
Quote
yinzer - 4/11/2006  6:18 PM

Quote
bombay - 4/11/2006  3:18 PM

Quote
yinzer - 4/11/2006  3:48 PM

Is the gap between the bulkheads filled with anything solid, like a honeycomb or batting?  If not, what stops the LH2-side bulkhead from reversing?
The opposite LO2 side would have to be of a higher pressure.

But if there's no way to transfer load from the LO2 bulkhead to the LH2 bulkhead, the LH2 bulkhead should start to reverse until it hits the LO2 bulkhead, which will restrain it via the pressure in the LO2 tank.  Unless the LH2 bulkhead is stiff enough to act as a dome in compression, which seems unlikely to me.

Is there a way to transfer load between the bulkheads?

(to clarify: the LO2 dome is concave with respect to the inside of the tank and so the internal pressure loads are tensile, so the dome is stable.  The LH2 dome is convex toward the inside of the tank, so the pressure loads on it are compressive.  It's a very thin shell and so seems like it should buckle very easily.  I read somewhere that the space between the bulkheads is filled with fiberglass, but am now wondering if this is loadbearing or not).
There's probably someone out there in cyber space that's more familiar with the nesting of bulkheads than me, but here's how I see it as an outsider looking in.

One bulkhead is shoved into another with some type of thin batting between them.  A vacuum is pulled and the bulkhead that's shoved into the other is essentially sucked against the more structurally sound bulkhead only separated by the thin batting thickness.  The pressure on the LO2 side is say 60 psi and the pressure on the LH2 side is say 50 psi.  Being that the two bulkheads are intimately contacting one another, as long as the LO2 pressure remains higher than the LH2 pressure, the (2) bulkheads that are acting as (1) will not buckel.

Does this make sense or am I sounding stupid?  In my mind it makes sense.  


Offline yinzer

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #15 on: 11/05/2006 12:25 AM »
It makes sense, as long as the batting can take the compressive loads across the gap between the bulkheads while still conducting little enough heat across the gap.  I would have expected that anything that could withstand tens of psi of compressive force would conduct heat well enough that the presence or absence of air between the bulkheads wouldn't change much, but my thermodynamic intuition is poorly developed.

And Gus, party-pooper though he may be, makes a good point.  Although it's amazing what one can read in the right books, like how the vacuum between the bulkheads is actually created - by filling the space with dry nitrogen, which then freezes out when the LH2 tank is filled.  Clever stuff.
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Offline Gus

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #16 on: 11/05/2006 04:30 AM »
Sorry for being a party pooper.  The problems being discussed here are definitely the ones the old-timers at GD Astronautics had to tackle.  I tip my hat to them for the elegant solutions they developed.  

Just want to make sure my fellow employess do not reveal anything that is not already in the public domain.

Offline Propforce

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #17 on: 11/05/2006 07:51 PM »
Quote
Gus - 4/11/2006  4:32 PM

For all you fellow Lockheed Martin employees posting on this subject, this is just a reminder to remember your compliance training on sensitive information.  

Damn... you guys had to take those "mandatory training" too?

My favorite one was on the Foreign Corrupt Practice Act ...

A good reminder for ALL here, Gus.

Offline Gus

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Re: Common bulkhead vs. nested bulkhead difference
« Reply #18 on: 11/09/2006 03:37 AM »
I thought my favorite was going to be TINA until I found out it was an acronym (Truth In Negotiations Act) :(

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