Learning Forum

[Ahmed Taher]

Hello,

I am trying to define a charge of 1140 gm weight of Pentolite (density = 1.7 gm/cm3). I tried to define it as "box" shape in which it's dimensions were 75x75x120 mm3 (volume of the charge), everything is fine.

the problem is, when I try to redefine it as a "conical" shape, there is no tap for "conical" definition, it which i needed to use "cylinder" tap and tried to redefine the charge, it asked to enter some data like inner and outer radius along with the length. Now, the required volume of the charge after dividing the weight by the density of pentolite would be approximate to 670 cm3. In which, a cone volume would be pi x radius^2 x height.

i picked a radius of 6.5 cm, and height of 5 cm

entered the data as: 

1- start outer radius = 65 mm

2- end outer radious = 0.5 mm (since there is no "zero" value that can be entered"

3- start inner radius = 0.1 mm (since there is no "zero" value that can be entered)

4- end inner radius = 0.09 mm (since there is no "zero" value that can be entered)

5- Length = 50 mm

 

everything is fine EXCEPT, I start running the model, but I notice that there is a dramatic drop in charge effect and force relative to defining the charge as a box. The question is, why? aren't both charges having approximately the same weight? I can't find where the problem is.

Thanks,

[Chris Quan]

FIrst of all, volume of a conical shape is equal to 1/3 x pi x radius^2 x height. Thus, for a cone with base radius of 65 mm and height of 50 mm, its volume is 221 cm^3. Its mass is 376 g, 33% of the mass of a box shape.

Thus, the differece between two simulations is expected.

Next, it would be better if you use Solid, rather than Hollow to define the conical shape. See the picture below.

 

[Ahmed Taher]

Hello Chris,
Thanks for your reply. Yes, I haven't noticed that I have used the wrong equation for the cone volume, it increased the charge quantity of course, yet again, I can't figure out where my mistake is as I can't reach out to final damage state of the specimen that I am trying to model.
I use SPH particle defining the charge in AUTODYN, I don't know which is best and more accurate honestly, is it defining the charge as SPH particles, Fill, or Solid? However, I am trying to model a conical explosive charge attached to a columns to test the effect on many parameters, a previous research used same way to define the charge (SPH particles) in which, they acheived modeling the specimen and got to the desired final result and final damage state, this is the reason I use SPH particles. So, may I ask another question? which is, when modeling the charge as SPH paticles, do I need to add the gas produced by the detonation of the charge? or just add the particles representing the charge and that's all?

Thanks again.
Note: I am using AUTODYN only in this model, I didn't use workbench.