Underwater explosions

[Spinosaurus75DinosaurFan]

Previous thread.

Kinetic energy can be used in some cases when the water is blown back, but if not...

This site Kepekley23 linked helps.

10,000 psi is 689 bar

An explosion with 100m radius underwater would have a yield of:

W = 100^3*((27136*689 + 8649)^(1/2)/13568 - 93/13568)^2 = 97.286 kilotons of TNT (Town level+) Overpressure is S-tier, but this is a high end.

This paper says that

According to Cole's correlations (Ref. 2) for free-field underwater TNT explosions, the peak shock wave pressure (in psi) and integrated impulse per unit area (in psi•s) are given by:

Pm = 2.16 × 10^4(W1/3)/R)1.13 I/A = 1.46 W<su9>0.63</sup>/R0.89 where W is the charge weight in pounds and R is the range in feet. Therefore, for a given charge weight the peak shock wave pressure would be expected to vary as (1/R)1.13.

This is the Cole thing the article keeps on referencing, so I guess we can research that. Someone would have to read it though.

 

[Spinosaurus75DinosaurFan]

Also I want to ask for an explosion that explodes on land, but a character dives into water and the explosion reaches him. How should that be calculated?

 

[Mr._Redic]

I found a formula for underwater explosions from XKCD, or a paper they link to more specifically.

Radius = (3/4pi)^(1/3) x ((40% x explosion energy) / (ocean depth pressure + 1 standard atmosphere pressure))^(1/3)

Reworking that to find the energy, since we can usually guess the radius/diameter of the explosion and depth/pressure.

Joules = ((Radius in Meters^3) x (Pascals at specific depth + 101,325) / (3/4pi or just 0.23873241463)) x 2.5

Math seems to check out when I did the Tsar Bomb Mariana Trench example.

 

[Spinosaurus75DinosaurFan]

What would be the "standard" pressure though.

 

[Mr._Redic]

I guess we can use the average halfway point of 5,497 Meters / 55,321,110 Pascals for standard/unknown depths.

If this gets put up in the calculations page or somewhere else, we should link this calculator if anyone has a way of knowing its actual depth and therefore its pressure, it's pretty convenient since it has both freshwater and saltwater options.

We could list the the bottom and average depths/pressures of the oceans and major seas/gulfs/lakes for common references. We could also maybe add submarine test depths as well (think they're around 400-600 meters), though I'm pretty sure we'd already know the yields of any torpedoes they launch, and any sci-fi or fantasy submarine would have unknown depths. It's ultimately going to have to be on the calcer to find a reasonable depth and pressure, though.

 

[Spinosaurus75DinosaurFan]

Can you ask the rest of the calc group members to comment here

 

[Spinosaurus75DinosaurFan]

Bumping to remind myself.

Imma ask some calc group members later.

 

[Crimson_Azoth]

Math seems to be ok regarding the formula. And as for standard depth/pressure, I honestly doubt that there is any we can really use. That will have to be moderated on a case-by-case basis

 

[Therefir]

I think there shouldn't be any problem with using the underwater overpressure with that formula in this kind of feats.

 

[DMUA]

This should work

 

[TataHakai]

Looks good i suppose, and i agree with Azoth on the depth scenario.

 

[Spinosaurus75DinosaurFan]

For depth I don't think there's a standard thing. For pressure I think it's fine to use a standard value.

 

[Kepekley23]

I think using 5,000+ meters to get the standard depth is an extreme high-end.

The average ocean depth is 3,680 meters or so, but that's for the very bottom of the ocean. If you're talking about a sea, a lake, or a river, it would be vastly lover.

 

[Spinosaurus75DinosaurFan]

bump

 

[Huesito88]

Bump