raisim::blast

namespace

The air blast of a spherical TNT charge in a sea-level atmosphere (101325 Pa, 15 °C). Distances scale with the cube root of the charge (Hopkinson–Cranz): every quantity of a charge of mass W at distance R equals W^(1/3) times (for times and impulses) or exactly (for pressures) that of a 1 kg charge at the scaled distance Z = R / W^(1/3).

• Peak overpressure and positive-phase impulse: the free-air fits of Kinney and Graham, "Explosive Shocks in Air" (1985).
• Arrival time: the shock speed of the Rankine–Hugoniot relations, U = a0 sqrt(1 + 6 Ps / (7 P0)), integrated outward from the charge.
• Positive-phase duration: the Kinney–Graham hypothesis that the phase ends when a boundary moving at the sound speed behind the shock arrives, calibrated to Kingery–Bulmash surface-burst durations.
• Pressure history: the modified Friedlander pulse, its decay chosen to carry the fitted impulse. Reflected and dynamic pressures follow the Rankine–Hugoniot relations for air (gamma = 1.4). Scaled distances below 0.1 m/kg^(1/3) (inside the fireball) take the values at 0.1.

Classes

• struct Wave — The blast at one distance from a charge.

Functions

wave

#include <raisim/Explosion.hpp>

Wave wave(double distance, double chargeMass)

The blast of chargeMass kg of TNT in free air at distance m.

Parameters

Parameter	Description
distance (in)	distance from the charge's center (m)
chargeMass (in)	TNT-equivalent mass (kg), positive

reach

#include <raisim/Explosion.hpp>

double reach(double chargeMass)

Distance (m) at which a charge's blast stops loading objects: kMaxScaledDistance * chargeMass^(1/3).

Variables

kAmbientPressure

#include <raisim/Explosion.hpp>

constexpr double kAmbientPressure

Sea-level ambient pressure (Pa).

kAmbientSoundSpeed

#include <raisim/Explosion.hpp>

constexpr double kAmbientSoundSpeed

Sea-level sound speed at 15 °C (m/s).

kMinScaledDistance

#include <raisim/Explosion.hpp>

constexpr double kMinScaledDistance

Smallest scaled distance the model evaluates (m/kg^(1/3)).

kMaxScaledDistance

#include <raisim/Explosion.hpp>

constexpr double kMaxScaledDistance

Largest scaled distance at which a blast loads objects (m/kg^(1/3)): the peak overpressure has fallen to about 2 kPa.

kSurfaceBurstFactor

#include <raisim/Explosion.hpp>

constexpr double kSurfaceBurstFactor

A charge detonated on the ground drives a hemispherical wave as strong as that of a free-air charge this many times heavier (the ground reflects the other half, less what cratering absorbs).