/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
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/LOAD/PBLAST/load_ID/unit_ID  
load_title  
surf_ID  Exp_data  I_tshift  N_{dt}  I_{Z}  
x_{det}  Y_{det}  Z_{det}  T_{det}  W_{TNT} 
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) 

N_{dt}  Number of intervals
for minimal time step. $\text{\Delta}{t}_{blast}=\frac{\mathrm{inf}\left({T}_{0}\right)}{{N}_{dt}}$ Where,
Default = 100 (Integer) 

I_{Z}  Scaled Distance Update
with time.
(Integer) 

X_{det}  Detonation Point
Xcoordinate. Default = 0.0 (Real) 
$\left[\text{m}\right]$ 
Y_{det}  Detonation Point
Ycoordinate. Default = 0.0 (Real) 
$\left[\text{m}\right]$ 
Z_{det}  Detonation Point
Zcoordinate. Default = 0.0 (Real) 
$\left[\text{m}\right]$ 
T_{det}  Detonation
Time. Default = 0.0 (Real) 
$\left[\text{s}\right]$ 
W_{TNT}  Equivalent TNT
mass. (Real) 
$\left[\text{Kg}\right]$ 
Comments
 At a given radius
$R$
from explosion center both incident and
reflected pressure wave are supposed to follow Friedlander’s
equation:
(1) $${\mathrm{P}}_{Friedlander}\left(t\right)={P}_{\mathrm{max}}\cdot {e}^{\frac{t{t}_{a}}{\text{\Delta}{t}_{+}}}\left(1\frac{t{t}_{a}}{\text{\Delta}{t}_{+}}\right)$$Where, ${P}_{\mathrm{max}},\text{\Delta}{t}_{+},{t}_{a}$ are experimentally known at a given scaled distance $\frac{R}{{W}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{1ex}{$3$}\right.}}$ ( $W$ is explosive mass). If the I_{z} = 1, then $R$ =constant, but if I_{z} =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) $${\mathrm{P}}_{BLAST}\left(t\right)=\{\begin{array}{c}{\mathrm{cos}}^{2}\theta \cdot {\mathrm{P}}_{reflected}\left(t\right)+\left(1+{\mathrm{cos}}^{2}\theta 2\mathrm{cos}\theta \right)\cdot {\mathrm{P}}_{incident}\left(t\right)\text{if}\mathrm{cos}\theta 0\text{}\\ \text{}{\mathrm{P}}_{incident}\left(t\right)\text{if}\mathrm{cos}\theta \le 0\end{array}$$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.
 If W_{TNT} 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 $T=0$ 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.
 The ${N}_{dt}$ parameter can impose a minimal time step if structural one is not large enough. Imposing $\text{\Delta}{t}_{blast}=\frac{\mathrm{inf}\left({T}_{0}\right)}{{N}_{dt}}$ ensures that there are sufficient time steps during positive phase, i.e. during the exponential decrease of the blast wave. By default, ${N}_{dt}=100$ .