For Questions That Don't Merit Their Own Thread

[K^2]

10 hours ago, kerbiloid said:

The temperature defines the speed of sound in the medium.

And when the average thermal energy of particles corresponds to a few hundred meters per second, and something's passing through this medium at a few kilometers per second, that matters absolutely naught. You should be looking up formulae for hypersonic flight. Not propagation of subsonic waves. There is a reason why supersonic and hypersonic are two different terms.

[wumpus]

13 hours ago, kerbiloid said:

The temperature defines the speed of sound in the medium.
https://en.wikipedia.org/wiki/Speed_of_sound#Practical_formula_for_dry_air

Only if the pressure is constant.  The link included (slightly above the linked section) even points that altitude is more important than raw temperature.

[ARS]

In theory, if the temperature of surrounding air decreases, does it also decrease the air's absolute humidity? Based from the experiment that I did to determine the fluctuations of absolute humidity of air cooled by ice (until the ice completely melts), it results in this curve: 

Here's the timeline of the air temperature and relative humidity (from the moment it's cooled inside the cooling box with ice until the ice completely melts), compared with outside the box:

 

I am confused. Realistically speaking, if the temperature drops, then the surrounding air should be condensating (thus, raising the humidity of air and in turn, the curve should point upwards, not downwards), but the data that I obtained results in a completely different value. The data that I obtained from the experiment is temperature and relative humidity, and I'm using that to determine the value of absolute humidity. Am I mistaken the meaning of absolute and relative humidity? Because it's very confusing for me to differentiate between the two. Can someone explain to me how the fluctuations of temperature affect the absolute humidity?

[Lisias]

 

15 minutes ago, ARS said:

In theory, if the temperature of surrounding air decreases, does it also decrease the air's absolute humidity? Based from the experiment that I did to determine the fluctuations of absolute humidity of air cooled by ice (until the ice completely melts), it results in this curve: 

Here's the timeline of the air temperature and relative humidity (from the moment it's cooled inside the cooling box with ice until the ice completely melts), compared with outside the box:

 

I am confused. Realistically speaking, if the temperature drops, then the surrounding air should be condensating (thus, raising the humidity of air and in turn, the curve should point upwards, not downwards), but the data that I obtained results in a completely different value. The data that I obtained from the experiment is temperature and relative humidity, and I'm using that to determine the value of absolute humidity. Am I mistaken the meaning of absolute and relative humidity? Because it's very confusing for me to differentiate between the two. Can someone explain to me how the fluctuations of temperature affect the absolute humidity?

It depends.

Google for Supercooled water, or Super Large droplets.

Under the right circunstances, water can remain in a liquid state at -45o C.

(source: https://www.discovermagazine.com/the-sciences/the-freaky-physics-of-supercooled-water )

Things get really nasty when that special circunstances change and the water get solid suddenly inside your ducts.

Edited February 3, 2020 by Lisias
Forgot to quote the guy

[kerbiloid]

4 hours ago, K^2 said:

And when the average thermal energy of particles corresponds to a few hundred meters per second, and something's passing through this medium at a few kilometers per second, that matters absolutely naught. You should be looking up formulae for hypersonic flight. Not propagation of subsonic waves. There is a reason why supersonic and hypersonic are two different terms.

At the  supersonic and hypersonic speed the Mach number is used in formulas.
The Mach number is the speed to sound speed ratio.
The temperature afects sound speed, and the Mach number via it.
It's simple.

Edited February 3, 2020 by kerbiloid

[K^2]

4 hours ago, kerbiloid said:

It's simple.

Cool. Since it's simple, what's the dynamic pressure on a R = 1m sphere traveling at 5km/s through diatomic gas with average molecular weight of 29AU as a function of temperature and pressure? You may plot temperature dependence as individual curves for pressure values from 1bar to 1μbar decreasing by factor of 10 between curves.

Edited February 3, 2020 by K^2

[kerbiloid]

10 minutes ago, K^2 said:

Cool. Since it's simple, what's the dynamic pressure on a R = 1m sphere traveling at 5km/s through diatomic gas with average molecular weight of 29AU as a function of temperature and pressure? You may plot temperature dependence as individual curves for pressure values from 1bar to 1μbar decreasing by factor of 10 between curves.

Take a calculator and calculate.

***

What I never do is trying to look too wise.

Edited February 3, 2020 by kerbiloid

[K^2]

4 hours ago, kerbiloid said:

Take a calculator and calculate.

Oh? You can do hypersonic flow computations on a calculator? THAT I got to see. Please, go ahead. Demonstrate this miracle of simple math to us.

[kerbiloid]

Just now, K^2 said:

You can do hypersonic flow computations on a calculator?

I believe, you can.

[DDE]

What's a major advantage of a double-hulled submarine?

There's no arguments after torpedo drills.

Spoiler

 

[magnemoe]

18 minutes ago, DDE said:

What's a major advantage of a double-hulled submarine?

There's no arguments after torpedo drills.

  Hide contents

 

Hard to argue if you was hit here  
But the real reason for the double hull is that the outer hull is streamlined and you use lots of the gap for ballast tanks 

Have you an story behind it, its an obvious training torpedo, however using them like paintball bullets in an exercise sounds risky, no its unlikely they can not hurt the pressurized hull but can easy hurt control surfaces or sensitive parts on the tower. 

[kerbiloid]

Spoiler

Maybe it's an inflatable torpedo to fool the opponent.

He sees a torpedo sticking out of hull, gets sure that the sub is shot down (or up? depends on buoyancy), then air bubbles when they deflate it.
And gets a sudden hit at close range.

On the opposite board there is also a painted hole with a toy crab looking from inside.

 

[DDE]

5 hours ago, magnemoe said:

Have you an story behind it, its an obvious training torpedo, however using them like paintball bullets in an exercise sounds risky, no its unlikely they can not hurt the pressurized hull but can easy hurt control surfaces or sensitive parts on the tower. 

Apparently B-454 was actually launching a torpedo at K-178; it was supposed to have depth guidance disabled, so I suppose it would've passed harmlessly above the target. It didn't.

And failing that, yes, the Soviets had small diesel-electric boats designed to take torpedo punches on a regular basis.

[kerbiloid]

Afaik, in the Hunt for Red October when one sub had launched a torpedo, another one (the target) turned to the collision course to catch the torpedo hit with its forehead before the torpedo let the safety off, to get a small hole instead of large one.

Edited February 4, 2020 by kerbiloid

[magnemoe]

1 hour ago, DDE said:

Apparently B-454 was actually launching a torpedo at K-178; it was supposed to have depth guidance disabled, so I suppose it would've passed harmlessly above the target. It didn't.

And failing that, yes, the Soviets had small diesel-electric boats designed to take torpedo punches on a regular basis.

I expect an practice torpedo to be designed to hit the target softer like having an rubber nose, the problem is not so much the target but the torpedo itself as the training torpedoes are reusable. 
Norwegian navy lost one training torpedo and asked if some had found it.
However I suspect the outer skin on an submarine is pretty much sheet metal far thinner than ship hulls. 

[magnemoe]

1 hour ago, kerbiloid said:

Afaik, in the Hunt for Red October when one sub had launched a torpedo, another one (the target) turned to the collision course to catch the torpedo hit with its forehead before the torpedo let the safety off, to get a small hole instead of large one.

Rater that in the front of an modern submarine you have an huge sonar array, then the torpedo room, an bulkhead who is is probably designed so that the sub can surface even if its flooded. As you have all the torpedo tubes trough the hull its an especially vulnerable area 

[kerbiloid]

34 minutes ago, magnemoe said:

Rater that in the front of an modern submarine you have an huge sonar array, then the torpedo room, an bulkhead who is is probably designed so that the sub can surface even if its flooded. As you have all the torpedo tubes trough the hull its an especially vulnerable area 

I had a feeling it's something wrong with that idea.

Edited February 4, 2020 by kerbiloid

[magnemoe]

3 hours ago, kerbiloid said:

I had a feeling it's something wrong with that idea.

No, another benefit is that if the torpedo hit you in the middle it can easy flood two bulkheads. Also your profile is smaller. 

[ARS]

If I'm on the warship in the middle of nowhere, can I cook by using ship's radar array? Like sticking a sausage on a stick and placing it in front of the radar dish?

[magnemoe]

1 hour ago, ARS said:

If I'm on the warship in the middle of nowhere, can I cook by using ship's radar array? Like sticking a sausage on a stick and placing it in front of the radar dish?

On an larger ship probably, mind you that the frequency will not be optimal as unlike microwaves you try to prevent the signal to be affected by water as much as possible. 
However powerful radar systems are dangerous and is knows to kill birds flying into the beam. 

[kerbiloid]

2 hours ago, ARS said:

Like sticking a sausage on a stick

Better cover it with foil. As engineers told, chocolate in foil melted if they were passing in front of ground radar.

[DDE]

9 hours ago, magnemoe said:

Rater that in the front of an modern submarine you have an huge sonar array, then the torpedo room, an bulkhead who is is probably designed so that the sub can surface even if its flooded. As you have all the torpedo tubes trough the hull its an especially vulnerable area 

Yes and no. Most submarines still have torpedo tubes sticking out of the torpedo rooms and above the sonar array. A design that has the entire cross-section occupied by the sonar is new, rare, and restricted to navies with blue-water ambitions.

Which brings me to my own question. Suppose I wanted to take another go at this thing:

What reactor design would I be using to maximize power density? Is PBi-cooled fast reactor still unbeatable? What about high-temp gas-cooled systems?

[ARS]

2 hours ago, DDE said:

What reactor design would I be using to maximize power density? Is PBi-cooled fast reactor still unbeatable? What about high-temp gas-cooled systems?

For submarine use, Lead-Bismuth cooled fast reactor (LBCFR) is currently still the best option. High-temperature gas cooled system might get power density equal to the LBCFR, but it has more drawbacks that makes it unsuitable for submarines, mainly because of high vibration and noise. While LBCFR that's used on Alfa-Class submarines is also noisy, it should be noted that this noise is only noticeable when operating at top speed (Alfa is one of the fastest submarines). At cruising speed, Alfas weren't any louder than other nuclear sub of her generation. LBCFR's drawbacks when used in submarines includes: inability to be turned off (doing so would solidify the core), cannot be refueled (the entire reactor is replaced like a battery at the end of it's life, which, while more expensive than refueling, in theory it allows quick reactor replacement), and short lifespan (15 years, compared to around 33 years for US submarines)

[DDE]

Usually it's you asking the miltech questions here. Nice role reversal )

6 minutes ago, ARS said:

High-temperature gas cooled system might get power density equal to the LBCFR, but it has more drawbacks that makes it unsuitable for submarines, mainly because of high vibration and noise.

Do the power density assumptions and the noise stem from a mechanical turbine? I was thinking about electrical transmission anyway - same as on the French boomers - and with gas-cooled it's possible to switch to a pure MHD with no moving parts.

9 minutes ago, ARS said:

At cruising speed, Alfas weren't any louder than other nuclear sub of her generation.

Problem being, of course, that ten years of development hell meant she was a second-generation boat cruisin' alongside third-generation submarines (in Soviet terms).

11 minutes ago, ARS said:

short lifespan (15 years, compared to around 33 years for US submarines)

Isn't the 'fueled-for-life' concept recent for US submarines?

[ARS]

37 minutes ago, DDE said:

Usually it's you asking the miltech questions here. Nice role reversal )

Well, being a graduate from naval engineering, I knew better about ships than tanks or aircraft :)

37 minutes ago, DDE said:

Do the power density assumptions and the noise stem from a mechanical turbine? I was thinking about electrical transmission anyway - same as on the French boomers - and with gas-cooled it's possible to switch to a pure MHD with no moving parts.

If that's the case, then it is possible to obtain similar or higher power density than LBCFR with an added advantage of better cooling due to high-temp gas cooled reactor allowing a larger coolant fraction in the core (due to the low number density of gas coolant)

37 minutes ago, DDE said:

Isn't the 'fueled-for-life' concept recent for US submarines?

The concept of 'fueled-for-life' isn't something new, it's already been around since the idea of putting nuclear reactors on ships, it's just that the nature of LBCFR's operation that makes it's lifespan shorter than other nuclear reactors for submarines. The use of lead has a benefit of higher boiling point, which provides safety advantages as it can cool the reactor efficiently even if it reaches several hundred degrees Celsius above normal operating conditions. However, because lead has a high melting point and a high vapor pressure, it is very difficult to refuel and service a lead cooled reactor. The melting point can be lowered by alloying the lead with bismuth, but lead-bismuth eutectic is highly corrosive to most metals used for structural materials, shortening their lifetime. All of these factors contributes to the reason why Soviets go for 'replace it like battery' approach

Edited February 5, 2020 by ARS