TNT blast pressure

[­부지연 | 공과대학 공학교육혁신센터 | 장학조교 | 한양대(서울)]

Hello All

I am currently creating a model to measure pressure at a gauge located a certain distance from a concrete column after detonating TNT attached to the column.
For the blast modeling approach, I have adopted the Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE) method.

However, the measured pressure results show that the arrival time of the pressure is later and the peak pressure value is smaller compared to the actual experiment. 

What parts should I modify? 

I adjusted the TSSFAC value in CONTROL_TIMESTEP from 0.67 to 0.33, but there was no significant change. 

I also reduced the pressure measurement DT from 0.1 sec to 0.0001 sec, but it was ineffective. 

The keywords used include EOS_JWL, EOS_LINEAR_POLINOMIAL, CONTROL_ALE, ALE_MULTI_MATERIAL_GROUP, BOUNDARY_NON_REFLECTING, MAT_NULL, and MAT_HIGH_EXPLOSIVE_BURN. 

The air mesh size is 35mm, and when it was reduced below 25mm, the analysis time increased abnormally. 

What parts should I try to modify?  

Thank you very much for your time and support.

[l...@schwer.net]

1\ This sounds like a lack of mesh refinement. You should have a minimum of about 10 ALE cells across the radius (minimum distance) of your TNT charge to capture the blast initiation.

 

2\ What is the magnitude of the difference between measured and computed time of arrival and maximum pressure? Note: it is best to compare measured and computed impulse rather than maximum pressure.

 

3\ What is the mass of your TNT charge and the straight line distance to your point of measurement?

 

4\ What are your JWL EOS parameters for TNT and what is the reference for these values? Also please provide you MAT_HIGH_EXPLOSIVE_BURN parameters.

 

5\ Although likely not a factor in your present close in concerns, Note that BOUNDARY_NON_REFLECTING is not intended for air blast simulations. To eliminate boundary reflections you need to increase the mesh external dimensions.

 

                --len

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[­부지연 | 공과대학 공학교육혁신센터 | 장학조교 | 한양대(서울)]

Thank you for your response.  

1.  As you suggested, reducing the mesh size significantly improved the peak value and arrival time. However, as shown in the photo below, the graph abruptly cuts off and then drops below atmospheric pressure.  This phenomenon specifically did not occur on the gauge located 1 m above the ground, but it did occur on the gauge located 0.5 m above the ground (the gauge at the same height as the TNT).   The total number of gauges is six, consisting of three gauges located at a height of 1 m and three gauges located at a height of 0.5 m.  The ground was modeled as a rigid wall.

2. The paper only provides pressure data, and the impulse value is not included. The maximum error for the peak pressure is 33%, and the maximum error for the arrival time is 0.4 msec.

3. The TNT mass is 1 kg, and the measurement distances are 1 m, 1.5 m, and 2 m.

4. The EOW JWL and MAT_HIGH_EXPLOSIVE_BURN parameters are as follows. The same values as those in the paper were used.

*EOS_JWL_TITLE
EOS for tnt
$#   eosid         a         b        r1        r2      omeg        e0        vo
         5    371.25     3.231      4.15      0.95       0.3       7.0       1.0

MAT_HIGH_EXPLOSIVE_BURN_TITLE
tnt
$#     mid        ro         d       pcj      beta         k         g      sigy
         51.63000E-6    6950.0      21.0       0.0       0.0       0.0       0.0

5. Although the distance was sufficiently increased, there was no significant difference in pressure beyond a certain distance, and the analysis time increased considerably.

                             -- Boo

2025년 11월 5일 수요일 오후 10시 31분 1초 UTC+9에 leonarder...@gmail.com님이 작성: