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)
surf_ID Exp_data I_tshift Ndt IZ
xdet Ydet Zdet Tdet WTNT

## Definitions

Field Contents SI Unit Example

(Character, maximum 10 digits)

surf_ID Surface identifier

(Integer, maximum 10 digits)

Exp_data Experimental data flag.
1 (Default)
TM5-1300 Free Air, Spherical charge of TNT.
2
TM5-1300 Ground Reflection, Hemispherical charge of TNT.

(Integer, maximum 10 digits)

I_tshift Time shift flag.
1 (Default)
No shift.
2
Shift time to skip computation time from 0 to ${t}^{*}=\mathrm{inf}\left({T}_{arrival}\right)$ .

(Integer)

Ndt Number of intervals for minimal time step.

$\text{Δ}{t}_{blast}=\frac{\mathrm{inf}\left({T}_{0}\right)}{{N}_{dt}}$

Where,
${T}_{0}$
Duration of positive phase

Default = 100 (Integer)

IZ Scaled Distance Update with time.
=1
Scaled Distance is computed at initial time and does not change with time.
=2 (Default)
Scaled Distance is updated at each time step.

(Integer)

Xdet Detonation Point X-coordinate.

Default = 0.0 (Real)

$\left[\text{m}\right]$
Ydet Detonation Point Y-coordinate.

Default = 0.0 (Real)

$\left[\text{m}\right]$
Zdet Detonation Point Z-coordinate.

Default = 0.0 (Real)

$\left[\text{m}\right]$
Tdet Detonation Time.

Default = 0.0 (Real)

$\left[\text{s}\right]$
WTNT Equivalent TNT mass.

(Real)

$\left[\text{Kg}\right]$

1. At a given radius $R$ from explosion center both incident and reflected pressure wave are supposed to follow Friedlander’s equation:(1)
${\mathrm{P}}_{Friedlander}\left(t\right)={P}_{\mathrm{max}}\cdot {e}^{\frac{t-{t}_{a}}{\text{Δ}{t}_{+}}}\left(1-\frac{t-{t}_{a}}{\text{Δ}{t}_{+}}\right)$
Where, ${P}_{\mathrm{max}},\text{Δ}{t}_{+},{t}_{a}$ are experimentally known at a given scaled distance $\frac{R}{{W}^{1}{3}}}$ ( $W$ is explosive mass). If the Iz = 1, then $R$ =constant, but if Iz =2, then $R=R\left(t\right)$ is changing with time.
Radioss proceeds to a fitting to match experimental data. 1
These fitted time history function ${\mathrm{P}}_{incident}\left(t\right)$ and ${\mathrm{P}}_{reflected}\left(t\right)$ are also used to compute blast loading ${\mathrm{P}}_{BLAST}\left(t\right)$ at a given face centroid Z’ (Figure 3). 2(2)
Where,
$\theta$
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.

2. 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.
3. 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.
4. It is possible to skip computation time from $T=0$ to ${t}^{*}=\mathrm{inf}\left({T}_{arrival}\right)$ . The shift value is automatically computed during Starter execution. To disable computation up to ${t}^{*}$ , then I_tShift value must be equal to 2.
5. The ${N}_{dt}$ parameter can impose a minimal time step if structural one is not large enough. Imposing $\text{Δ}{t}_{blast}=\frac{\mathrm{inf}\left({T}_{0}\right)}{{N}_{dt}}$ ensures that there are sufficient time steps during positive phase, that is, during the exponential decrease of the blast wave. By default, ${N}_{dt}=100$ .
1 Structures to resist the effects of accidental explosions. Departments of the Army, Navy, and Air Force, TM 5-1300/NAVFAC P-397/AFR 88-22, November 1990.
2 Randers-Pehrson, Glenn, and Kenneth A. Bannister. Airblast Loading Model for DYNA2D and DYNA3D. No. ARL-TR-1310. ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD, 1997.