Learning Forum

[Mustapha EL MLILES]

Hello everyone,

 

I want to model a shock wave for exp with an overpressure of 10kPa and a positive phase duration of 0.3s, is there a way to model this shock wave directly (injecting a function of the shock wave), or the only way is by finding the equivalent TNT mass?

 

Thank you!

[Reno Genest]

 

 

Hello Mustapha,

What do you mean by shockwave? Are you modeling a blast from some sort of explosive? If so, one way to model a blast load (pressure) on a structure without explicitly modeling the explosive and the air is to use the keyword *LOAD_BLAST_ENHANCED to apply a pressure load directly on the structure. You will have to define the equivalent mass of TNT with the “M” parameter for this keyword. You will find more information here:

https://ftp.lstc.com/anonymous/outgoing/support/PRESENTATIONS/blast_slavik_ucsd.pdf

https://www.dynalook.com/conferences/european-conf-2009/J-I-03.pdf/view

You will find more papers by searching on dynalook.com

 

If you know the pressure vs time profile for each element of the structure or if you can assume a constant pressure vs time profile for a group of elements, you can apply the blast load pressure using one of the following keywords:

*LOAD_SEGMENT

*LOAD_SEGMENT_SET

You can define the pressure vs time profile using LCID and *DEFINE_CURVE. See the LS-DYNA user manual vol I for more information:

https://lsdyna.ansys.com/manuals/

 

Let me know how it goes.

 

Reno.

 

 

[Mustapha EL MLILES]

Hello Reno,

 

Thank you I really appreciate your response. In fact, I want to model a shock wave caused by an explosion with the following parameters (overpressure of 10kPa and a positive phase duration of 0.3s) and visualize its impact on a structure.

 

I have already done the mass calculation of the equivalent TNT, and I found that the shock wave corresponds to a TNT of 170 tonnes situated at a distance of 660 meters from the structure. I want to know if I can use these values with the *LOAD_BLAST_ENHANCED, if yes, where can I find this keyword on LS Dyna workbench, please.

 

Regarding the second way, I don't think it will work, since this method doesn't reflect the physics of the shock wave like the reflected wave...

 

Thank you again.

[Reno Genest]

Hello Mustapha,

You can check the validity of *LOAD_BLAST_ENHANCED using the following formula:

See the LS-DYNA user manual vol I for more details.

 

To use *LOAD_BLAST_ENHANCED in WB LS-DYNA, you can create a command snippet:

To specify the faces of the structure  where the blast load will be applied, you can create a named selection with an ID:

Let me know if this helps or not.

 

Reno.

[Reno Genest]

Note that you can use LS-PrePost to create the *LOAD_BLAST_ENHANCED keywords to ensure you have the correct format. You can download LSPP here:

https://ftp.lstc.com/anonymous/outgoing/lsprepost/4.9/

 

Then, you can save the .k file using LSPP and open the .k file with a text editor to retrieve the keyword.

 

Let me know how it goes.

 

Reno.

[Mustapha EL MLILES]

Hello Reno,

 

Thank you a lot, I followed your instructions (creating keywords on LSPP and copying them to LS workbench) and it worked perfectly. 

 

Thank you again.

[Reno Genest]

Hello Mustapha,

Sounds good. I'm glad it worked well for you.

 

Have a good day!

 

Reno.