/LOAD/PBLAST
Block Format Keyword Provides a fast way to simulate air blast pressure on a structure.
The Air Blast incident pressure is fitted from experimental data, then blast pressure is deduced from surface orientation to the detonation point. You must provide detonation point, detonation time and equivalent TNT mass.
This is a simplified loading method because the arrival time and incident pressure are not adjusted for obstacles. It also does not take into account confinement or ground effects.
Format
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
---|---|---|---|---|---|---|---|---|---|
/LOAD/PBLAST/load_ID/unit_ID | |||||||||
load_title | |||||||||
surf_ID | Exp_data | I_tshift | Ndt | IZ | Iform | Node_ID | |||
xdet | Ydet | Zdet | Tdet | WTNT | |||||
Pmin |
Definitions
Field | Contents | SI Unit Example |
---|---|---|
load_title | Load
title. (Character, maximum 10 digits) |
|
surf_ID | Surface
identifier. (Integer, maximum 10 digits) |
|
Exp_data | Experimental data flag.
(Integer, maximum 10 digits) |
|
I_tshift | Time shift flag.
(Integer) |
|
Ndt | Number of intervals
for minimal time step.
Where, is the duration of positive phase. Default = 100 (Integer) |
|
IZ | Scaled Distance update
with time.
(Integer) |
|
Iform | Modeling flag.
(Integer) |
|
Node_ID | Node identifier
defining detonation point. If defined, the flags Xdet, Ydet and Zdet are ignored. |
|
Xdet | Detonation Point
X-coordinate. Ignored if Node_ID ≠ 0 Default = 0.0 (Real) |
|
Ydet | Detonation Point
Y-coordinate. Ignored if Node_ID ≠ 0 Default = 0.0 (Real) |
|
Zdet | Detonation Point
Z-coordinate. Ignored if Node_ID ≠ 0 Default = 0.0 (Real) |
|
Tdet | Detonation
time. Default = 0.0 (Real) |
|
WTNT | Equivalent TNT
mass. (Real) |
|
Pmin | Minimum
pressure. Default = -1020 (Real) |
Comments
- At a given radius
from explosion center both incident and
reflected pressure wave are supposed to follow Friedlander’s equation:
- If
Imodel = 1
(Friedlander model)
(1) - If
Imodel = 2
(modified Friedlander model)
(2)
Where, are experimentally known at a given scaled distance ( is explosive mass). With modified Friedlander model (Imodel = 2) ‘b’ is a decay parameter introduced to fit the positive impulse.
'b’ is solved such as:(3) If the Iz = 1, then =constant, but if Iz =2, then is changing with time.
Figure 1. Blast profile from Friedlander equationRadioss proceeds to a fitting to match experimental data. 1
Figure 2. Wave parameter from spherical TNT explosion in free air at sea levelThese fitted time history function and are also used to compute blast loading at a given face centroid Z’ (Figure 3). 2(4)
Figure 3. Blast pressure applied on a face centroid Z’ . Depends on Face OrientationWhere, is the angle between the surface segment (centroid Z’) and the direction to detonation point.
This means that blast pressure is equal to reflected pressure if segment is directly facing the detonation point, and equal to incident pressure if segment is not facing the detonation point. This modeling is simple because arrival time and incident pressure are not adjusted with shadowing of the related structure. It also does not into account confinement and tunnel effect.
This also requires the surface to have outward normal vector.
- If
Imodel = 1
(Friedlander model)
- If WTNT is not set, then mass is zero and no pressure will be loaded on the related surface. If modeled explosive is not TNT, then an equivalent TNT mass must be provided.
- The experimental data uses the unit system {cm, g, µs}. The units defined in /BEGIN will be used to convert the experimental data units to the model units. Therefore, the units defined in /BEGIN must correctly match the units used in the model.
- It is possible to skip computation time from
to
. The shift value is automatically computed
during Starter execution. To disable computation up to
, then I_tShift value must be
equal to 2.
Figure 4. I_tShift enables to skip computation time up to first wave arrival time - The
parameter can impose a minimal time step if
structural one is not large enough. Imposing
ensures that there are sufficient time steps
during positive phase, that is, during the exponential decrease of the blast
wave. By default,
.
Figure 5.