# Hand grenade's effect on nearby objects.

• posted

Hi, I'm new here, and I'm checking to see if someone could help me with a problem. I've searched google a lot, but I'm still pretty much clueless.

I'm assisting a colleauge (who's a conceptually oriented artist) with an installation. My task is to build and animate a simulation of a hand grenade exploding in her kitchen in 3d.

What I need to know is, given some attributes of the hand grenade, how does the shock wave affect the motion of an object? Note that this is a purely artistic task, I have no interest whatsoever in using real explosives :)

I'm disregarding the heat part, confining the simulation to the shock wave's effect on the objects. All in all, I'm trying to simplify the simulation, so I might substitute the shock wave with a particle system shooting radially from the location of the grenade, or even better, if I could find an equation how to calculate the velocity of an object after the shock wave has hit it, based on the shape, size and mass of the object, its distance from the grenade, and the properties of the grenade.

Known stuff (grenade info after some serious googling):

*The weight of the objects (ranging from a few grams for a coffee mug to about 20 kg for a table) *The detonation velocity of the grenade (about 7000 m/s) *The solid mass of the explosives (about 0.2 kg) *The detonation pressure of the shock wave (about 20 GPa)

Unknowns:

*How fast the shock wave pressure drops *How fast the velocity drops (the kitchen is only about 3x4x3 m in size, but the effect must obviously fade out)

So, how do I use this info to calculate/simulate the shock wave's effect on the motion of the objects? If I'm gonna use particles to simulate the shock wave, in wich case simple collision will be used, how do I determine the mass of the particles?

Would really appreciate any help I could get on this. Thanks in advance.

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• posted

Dear Anders Egleus:

Your kitchen air contains 36 m^3 of air. At STP (0 °C) this would be 1.295 kg * 36 = 46 kg. At 20 °C, this would be only 46 * 273.16 / 293.16 = 43 kg. The grenade's contents going to "equivalent" gas would be a small part of this (even at elevated temperature), but would be enough to take out the windows.

About 1 meter from the grenade, it should be inconsequential. The shrapnel will be far more destructive.

Bullets travelling this fast can go for kilometers before losing stopping power. The shrapnel from a grenade is much less aerodynamic, but will easily go through the walls/doors/windows/contents of the kitchen.

Why? Nothing "artistic" about human caused destruction.

David A. Smith

• posted

One possible modelling approach.... May be nothing like it actually is...:-)

assume the grenade is a point energy source, work out the proportion of the energy an object is exposed to ( area of object / surface area of sphere with radius equal to distance of object from grenade ) Assume a proportion of the energy is converted to kinetic energy in the object. ( say 10% ??? ).

It may not be in any way accurate, but it is a model you can feed into a simulation reasonably easily.

Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.