TNT model Validation

[Shubham Sharma]

Hi all,

I am validating a 2D axisymmetric TNT model so it can be used to map 2D to 3D ale simulations.

 The expected overpressure at 400mm standoff should be around 3 MPa.

 The research paper that I am validating has a cylindrical TNT with a diameter-to-height ratio of 2.

When IVFG CONTTYP 4 was used to model a cylindrical TNT  in 2d axisymmetric model, it was not giving the correct blast wave propagation. Instead, CONTTYP 5 was used to define a rectangle in 2D with length and breadth proportional to the cylinder, but this simulation consistently overpredicts the pressure by at least a factor of 3, I am attaching .k file so you can have a look.

I need to understand why the cylindrical TNT made through IVFG does not give the desired wave propagation and also the rectangular charge's overprediction of blast overpressure. Also when spherical shape was used it gave overpressure values to some accuracy.

[l...@schwer.net]

Have you read this Remark 6 under the keyword *INITIAL_VOLUME_FRACTION_GEOMETRY:

 

“Two-dimensional geometry. If the ALE model is 2D (*SECTION_ALE2D instead of *SECTION_SOLID), CNTTYP = 4 defines a quadrilateral. In this case, the fields which, in the 3D case define a cone, are interpreted as the corner coordinates of a clockwise defined (inward normal) quadrilateral having the vertices: (X1, Y1), (X2, Y2), (X3, Y3), and (X4, Y4). The CNTTYP = 4 input fields X0, Y0, Z0, X1, Y1, Z1, R1, and R2 becomes X1, Y1, X2, Y2, X3, Y3, X4, and Y4 respectively. CNTTYP = 6 should be used to fill a circle.”

 

               --len

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[Shubham Sharma]

I tested giving coordinates to IVFG according to the 2d ale, and it is giving the same result as given by CONTYP5 that is a rectangle, the issue I am facing is that for same weight and same scaled distance the spherical charge gives a peak overpressure value of 3 Mpa which is closer to the research paper's theoretical value of 2.88 Mpa, but the research paper uses cylindrical charge, and when I am using the cylindrical charge it is giving a value of 8.4 Mpa (for same weight and same scaled distance).