Blast analysis using MM_ALE 2D Axisymmetric model

[Nishant Choudhary]

Dear All, 
I am currently modeling a spherical air blast using a 2D axisymmetric MM-ALE formulation in LS-DYNA, with TNT defined via *INITIAL_VOLUME_FRACTION_GEOMETRY (IVFG). My objective is to capture the incident pressure at specific radial distances; however, I am encountering significant numerical divergence from analytical benchmarks (UFC) beyond a scaled distance (Z) of 1.5 m/kg^(1/3).While the results demonstrate strong correlation in the 0.5 < Z < 1.5 range, the peak pressures consistently over-predict or drift beyond this threshold. I am interested to know if others have experienced similar far-field accuracy limitations with 2D MM-ALE or if there are specific recommendations for advection schemes or mesh refinement strategies to maintain fidelity at larger scaled distances.

Warm Regards, 

N. S. Choudhary

[gaurav mishra]

Hi Nishant ,

Pl try with finer mesh with second order advection. Also take pressure time history at different TRACER points and check improvement in results. 

Thanks and regards

Gaurav Mishra 

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[Nishant Choudhary]

The mesh is quite fine (1 mm) and the advection method is also of second order. The history data is also taken from tracer points. Fine meshes are converging the results, but again the issue is with the scaled distance outside the range of 0.5 to 1.5.

Regards,

N. S. Choudhary

[gaurav mishra]

Try the same model in quarter symmetry 3d and check if the result deviates from 2d and the pressure readings. Regards

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[James Kennedy]

Dear Nishant,

 

Perhaps of some interest:

 

This paper presented a validation study of the LS-DYNA MMALE approach with existing exper-

imental studies of blast wave clearing and blast in an urban environment, as well as numerical

results from the finite volume method software Air3d.  The overpressure histories, peak over-

pressures and impulses were compared:

 

Huang, Y., Willford, M.R., and Schwer, L., "Validation of LS-DYNA MMALE with Blast

Experiments", 12th International LS-DYNA Users Conference, Dearborn, Michigan, June, 2012.

 

http://www.dynalook.com/international-conf-2012/blast-impact20-c.pdf

 

Calculation of blast propagation in air from a high explosive detonation is an often-used feature of

LS-DYNA’s Eulerian capabilities.  To obtain credible results, a suitably fine mesh is needed, partic-

ularly in the vicinity of the explosive, to represent the nearly instantaneous rise of shock pressure and

its gradual decay.  In this paper, we aim to present a set of generally applicable guidelines for mesh

refinement, using both 2-D axisymmetric and fully 3-D models.  Models of the Composition B

spherical detonation were exercised using various mesh sizes and for charges of varying mass. 

Simulations made use of the high explosive burn material model and initial detonation card within

LS-DYNA:

 

Powell D.A., Bogosian, D., and Schwer, L., "Mesh Sensitivity of Blast Wave Propagation", 15th

International LS-DYNA Users Conference, Dearborn, Michigan, June, 2018.

 

https://www.dynalook.com/15th-international-ls-dyna-conference/fsi-ale/phase-change-equation-of-state-for-fsi-applications

 

Sincerely,

James M. Kennedy

KBS2 Inc.

February 23, 2026

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