2015.13-17 ipsf cambridge

Blast and quasi-static pressure in

partially confined geometries:

Empirical, analytical and numerical modeling

IPSF - APRIL 2015

E. LAPBIE, A. OSMONT, L. YOUINOU, R. SOULI, A. GENOT : CEA/DAM/Gramat

S. BARROT : LCPP

Corresponding author : [email protected]

18 MAI 2015 | PAGE 1CEA | 10 AVRIL 2012

HEADLINES

CEA/Gramat overview

Main activities P.04

Blast-related studies P.05

Blast wave and QSP modelling

Empirical models P.08

Numerical models P.16

Analytical approaches P.20

Conclusions

Choosing a model P.27

Way forward P.29

18 MAY 2015 | PAGE 2CEA | APRIL 2015

CEA/Gramat overview

18 MAI 2015

| PAGE 3

CEA | 10 AVRIL 2012

CEA/Gramat overview

Main activities: weapon effects

CEA/G history began just after WW II with the study of nuclear weapons effects

through the use of large-scale experimental facilities:

Blast and thermal effects.

Ground shock propagation / interactions with buried structures.

E/M Impulse and X-Ray generation.

The activities extended to the effects of conventional weapons:

HE physics (initiation, detonation propagation, direct effects, ).

Lethality of warheads and vulnerability of systems (aircrafts, infrastructures, ).

More recently, our scope broadened to global safety:

Physics of transient CBR Source Terms.

Improvised explosives.

Effects of IEDs on light / unprotected structures.

Domino effects in chemical industries.

Our expertise is based on both experiments and modelling.

18 MAI 2015 | PAGE 4CEA | APRIL 2015

CEA/Gramat overview

Blast-related studies 1/2

Free-field:

Blast effect of OTS and improvised high explosives.

Characterization of blast (and fragments) from ammunitions.

Urban:

Various projects on the consequences of bombings.

Effects of VB-IEDs on buildings.

Prediction of collateral effects from air strikes.

Confined geometries:

Detonations in a vented bunker.

HE in commercial aircrafts.

Weapons effects in multi-room facilities, including EBXs.

Effects of IEDs in tunnels / metro stations (with LCPP).


Free-field HoB setup

Semi-confined setup

Bunker setup

Urban setup

CEA/Gramat overview

Blast-related studies 2/2

Free-field:

Overpressure time-history = f(R) or f(Z).

Second shock (modelling of afterburning ).

Empirical TNT equivalence for pressure and impulse.

Urban:

Reflection (normal, Mach ).

Canyon propagation.

Diffraction.

Interaction.

Confined geometries:

Superposition of:

- Blast waves (complex due to multiple reflections).

- Quasi-static Pressure (QSP) build-up.

Effects of:

- Venting (doors, windows)

- Collapse of partition walls / main walls.18 MAI 2015 | PAGE 6CEA | APRIL 2015

Free-field results

Bunker setup : QSP build-up

Bunker setup : venting


18 MAI 2015

| PAGE 7

CEA | 10 AVRIL 2012


Empirical models Free field (1/4)

Numerous empirical models

Friedlander shape only.

All parameters (P, I, t ) or some of them only.

Abaci / explicit formulations / Excel worksheet (BEC).

Assume TNT equivalence to compare HEs.

Issues

Scaling (Hopkinson, Sachs, ).

Reproducibility of experiments.

Nature of the HE & initiation train (booster ?).

Confidence in experimental setup / measures.

18 MAI 2015 | PAGE 8CEA | APRIL 2015Hopkinson scaling

(the simplest approach)

Historical abaci

Blast wave parameters

From Cooper 1994 see also MSIAC L-132

Modified Friedlander [from Baker]



Comparison of empirical models Overpressure

From spherical or hemispherical bursts (ground reflection coefficient < 2).

Huge discrepancies for small to intermediate Z values but reproducibility ?

Even worse for other parameters (I+, t+, ) when the models are available.


Comparison of some empirical overpressure models at intermediate (left) and long range (right).



Adding consequence models [TNO Green book]

Probabilistic models for casualties / injuries + levels of damage to buildings.

Models depend on DP and I+ (impulse scales with the lengthscale).

Zmin threshold for 100% casualties and 100% building collapse for a given GE mass

no need for precise computations below this limit (but still not sufficient to

compensate from variations among models).


Comparison of some empirical overpressure models

1,3

ton

100%

Death

100%

Collapse


Empirical models Free field (4/4)Scaling considerations : mass or energy ?

Cube-root scaling based on HE mass is the simplest scaling, and is prominently used for HEs.

Energy scaling is a true (non-dimensional) scaling and accounts for variations of P0 (many

experiments have been performed with P0 standard atmospheric pressure)Replacing mass scaling by energy scaling allows for comparison with other explosions (BLEVEs,VCEs, pressurized vessels bursts) provided that the proper energy is considered manyreferences in the literature on industry accidents.

Applications to high explosivesFor HEs, the energy transferred in the blast wave is only a fraction of the total energy released at

short times (radiation, etc.).

Comparing HEs using a measured of total energy assumes that the fraction of energy released in the

blast is the same for different formulations

Geometry considerations : 1D plane / cylindrical / spherical propagations.


Explosion types, from Strehlow and Baker, 1976

3/10PER

R

Sachs scaling

SPHERICAL CYLINDRICAL PLANE

Geometry parameter "n" 3 2 1

Characteristic dimension "R0" sphere radius cylinder radius slab half-width

"Mass" formula rho.4/3.Pi.R0^3 rho.Pi.R0^2 rho.2.R0

"Mass" unit kg kg/m kg/m^2

Scaled distance formula R/M^(1/3) R/M^(1/2) R/M

Scaled distance unit m/kg^(1/3) m^(3/2)/kg^(1/2) m^3/kg

Generic formula m^(3/n)/kg^(1/n)

Geometry considerations


Empirical models QSP (1/4)

Interests in QSP modelling for the consequences on buildings

Detonations in closed volumes result in the superposition of a transient signal (multiple

reflections and interactions of blast waves) and a quasi-static one (QSP build-up).

The characteristics QSP duration leads to a large QSP impulses.

Pressure discharge surfaces (venting) may help limiting structural damage.

| PAGE 12CEA | APRIL 2015

Typical pressure signal obtained

in the 2 m3 CEA-G bunker

Influence of a discharge surface in the damage resulting from an internal detonation

(CEA-Gramat experiments)



Interests in QSP modelling for the consequences on people

The studies of human vulnerability to blast usually focus on external detonation,

sometimes accounting for a nearby reflecting surface.

The analysis of terror bombings shows that primary blast injuries (PBIs) are much

more frequent during bombings in partially confined geometries (buses, trains, ).

Pressure discharge surfaces (venting) does not help that much

Katz & al. Primary blast injury after a bomb explosion in a civilian bus

The estimated QSP and duration are 3.8 to 5.2 bar and 2 to 3 ms.

Eardrum injury: 76%, Lung injury: 38%, Abdomen injury: 14%.

Much more than for open-space detonations [reflected pressures also play a role].


Frequency of blast lung injury in various studies Bombing forensics



The QSP depends on M/V AND atmosphere (afterburning).

Single room, no venting.

NATO AASTP-04 model

2 x 6 parameters for TNT (PQST in kPa, M/V in kg/m3))

PQST = exp(A+B.[ln(M/V)]+C.[ln(M/V)]2+D.[ln(M/V)]3+E.[ln(M/V)]4+F*[ln(M/V)]5)

Other HEs accounted for through TNT equivalence = f(M/V).


V M

PQST

QSP variables

Equivalence coefficients = f(M/V)

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0,001 0,01 0,1 1 10 100

ANFO

Comp A3

Comp B

Comp C4

Cyclotol 70/30

DESTEX

H-6

HBX-1

HBX-3

Poudre M1

MINOL-II

Octol 75/25

Pentolite 50/50

Picratol

Tritonal

AASTP-04

TNT coefficients

Comparison of the AASP-04 model with TNT experiments

Init

ial sta

tefi

na

l sta

te



Alternative approach : empirical fit to the results of a thermochemistry solver

US code CHEETAH (the widely available version 2 is sufficient) or other codes.

Considering HE mass + room atmosphere as an equivalent explosive.

Parametric constant volume explosion runs = f(M/V).

Physics-based fit for any (non-aluminized) explosive much easier than AASTP-04.

Large discrepancies at small M/V (solver problem).

| PAGE 15CEA | APRIL 2015Comparison of CHEETAH fits with TNT experiments

Pqst polynomial fit.

2 m3 CEA-Gramat Bunker


Numerical models (1/4)

Numerical models

From first-principles reliability.

Not limited to simple geometries (3D).

Added physics if required (multiphase ).

Possible integration of simple consequence models.

Handles reflections, diffractions, interactions, etc.

Current issues

Non ideal HEs.

Mesh size and peak pressure.

- AMR, shock capturing, a.s.o.

Weak or strong fluid / structure coupling.

Computational burden (no fast answer !).

Illustrations are from the HI2LO hydrocode

Developed by the RS2N company for CEA-Gramat.

Dedicated to the transient dispersion of pollutants (high Mach flows).

Checked against an almost exhaustive set of urban experiments from the literature.| PAGE 16CEA | APRIL 2015

18 MAI 2015

HI2LO results : blast propagation

in urban geometries from GIS data.

TOP : flat terrain; BOTTOM : with DEM.



Example: 1 ton HE in Paris.


18 MAY 2015HI2LO ; Pressure contours on the ground

(12 M cells, for the last step, after 2 remaps).

Examples of consequence models

(two large detonations):

TOP : % of broken windows.

BOTTOM: % of eardrum ruptures.


Numerical models (3/4)Example: Comparison with INSA-CVL experiments (propane-oxygen detonations).


18 MAY 2015

Sochet & Sauvan

Configuration 1 : Centered charge, with roof opening, with obstacle.

Configuration 2 : Centered charge, without roof opening, with obstacle.

Configuration 3 : Centered charge, without roof opening, without obstacle.

Configuration 4 : Charge in the upper-left corner, without roof opening, with obstacle.



Specificity of indoor detonations.

Afterburning MUST be modelled.

From models of intermediate complexity (no gas/gas interpenetration, mixed is burnt

approach with infinite rate chemistry) to full models including chemical kinetics

(computationally expensive and not always robust) Still a difficult problem !


18 MAY 2015

Temperature maps

[A. Milne, FGE]

Pressure evolution [A. Milne, FGE]


Analytical approaches (1/6)

CEA-Gramat interests in Fast-Running Models of blast consequences

Enhancement of our Vulnerability and Lethality Assessment Models as well as specific

tools developed for the Air Force.

Frequent interactions with end-users, asking for fast answers (but as accurate as

possible) for more and more complex problems.

CEA leads the DEMOCRITE project, funded by the French National Research Agency,

for the Paris Fire-fighters Brigade. Among many other things, the project aims at

developing of a fast-running algorithm for blast consequences in urban environments.

Strategy adopted since 2014

Database of results from the literature + development of new sets of experiments:

- Urban geometries and tunnels (up to a few kg of solid HE): CEA-Gramat

- Small-scale urban geometries at the Institute Von Karman (RP-80 detonators).

- Multi-room facilities (2015): parametric experiments at INSA-CVL (propane-O2).

Validation of the HI2LO code and parametric simulations on various geometries.

Analysis of existing works and development of our own approach for blast waves in

urban geometries, coupled to GIS tools.

Enhancement of an unstructured solver for multi-room geometries.| PAGE 20CEA | APRIL 2015

18 MAY 2015

DEMOCRI E



Existing (more or less) simplified approaches :

Theoretical : Geometrical Shock Dynamics (Whitham, 1957 !) and Shock Ray Theory.

Empirical: Neural network learning of simulated scenarios (Remnikov & Rose).

Empirical approaches based on volume equivalence: EVA (Equivalent Volume

Approach, Borgers, 2008) ECF (Energy Concentration Factor, Silvestrini 2009).

Analytical: Mirror-images for indoor explosions (from acoustic propagation).

Analytical: Shock waves addition rules from LAMB model (Hikida & Needham).

Numerically-based empirical approach: Coarse Grain Method (Flood): propagation of

Friedlander shape parameters on coarse grids (preliminary fits on numerical results).

Mixed approach: Ray-tracing & shortest path + specific rules for canyon detection

(Frank & al.).


18 MAY 2015

Mirror-image principle

[from Pope, 2010]Whitham book [1974]



A closer look at EVA / ECF Methods

A spherical P(Z3D) fit is chosen.

At a given distance X in tunnels, canyons, etc.:

- The total volume swept by the blast wave is V(X).

- Req is the equivalent sphere radius: 4/3.p.Req3 = V(X).

- Zeq is computed from Req and the HE mass M.

- The pressure at distance X is given by P(X)=P(Zeq).

Playing with EVA / ECF : blast in tunnels


18 MAY 2015

ISTSS 2008

Comparison of EVA results

with numerical simulations.

Assessment of ECF against data sets

[from Silvestrini & al, 2009]



First results of CEA-G model compared to experiments.

Mixed method with automated canyon detection.

Scale 1/10th , streets are 2m wide.

Run time < 1 second (HI2LO : 106 seconds).


Tir 1

A

B

Tir 4

A

B

2 kg

hemisphere,

T junction.

Zones with

100% damage

at real scale

Overpressure and impulse comparisons: Markers: experiments, Lines: CEA model.

1 kg

hemisphere,

L turn.


Analytical approaches - QSP (5/6)Remember the 2x6 coefficients for TNT in the AASTP-04 QSP model ?

CEA-Gramat QSP DAMOCLES model : all range of M/V, with NO PARAMETER.

The HE decomposition energy is used to heat the gases (Cv(T) from NIST data).

Decomposition energy means total combustion energy when oxygen is in excess

the combustion energy is measured in a combustion or a detonation calorimeter.

For large M/V ratios (oxygen-deficient atmospheres), decomposition energy means

(1-a).Edetonation + a.Ecombustion, a computed for total combustion with available O2.

the detonation energy is measured in a detonation calorimeter.

a decomposition scheme is required (empirical or from a thermochemistry code).


QSP comparisons (CEA model illustrated with combustion only)

CEA-Gramat

detonation calorimeter

Detonation + Afterburning of V401

(30 bar O2)

y = 2424,4x + 6250

R2 = 0,9982

0

10000

20000

30000

40000

50000

60000

0,00 5,00 10,00 15,00 20,00 25,00

m V401 (g)

Q(c

al)

Q cal

Linaire (Q cal)

Detonation of V401

(6 bar N2)

y = 1218,2x + 3378,3

R2 = 0,9958

0

5000

10000

15000

20000

25000

30000

35000

0,00 5,00 10,00 15,00 20,00 25,00

m V401 (g)Q(c

al)

Q cal

Linaire (Q cal)

Specific energy of detonation + afterburning

for octoviton. The value obtained by

combustion calorimetry Is 2314 18 cal/g

Specific energy of detonation

for octoviton.


Analytical approaches - QSP (6/6)

The icing on the cake: additional phenomena in DAMOCLES

Evaporation or evaporation + combustion in the room are accounted for.

Venting is modelled using a Riemann solver.

- Handles both sonic and subsonic venting regimes in a 0D = f(t) model.

Extension to N rooms (RS2N company for CEA-G, MUZO code).

Unstructured Eulerian code (1 cell / room), runs in seconds.

Ongoing work to extend the model.


Influence of the vent size on QSP evolution (DAMOCLES)

MUZO Multi-room geometry and DP maps

0 ms (a), 8 ms (b), 16 ms (c), 32 ms (d), 64 ms (e), 350 ms (f), 1050 ms (g)

Conclusions

18 MAI 2015

| PAGE 26

CEA | 10 AVRIL 2012


Choosing a model

You have a supercomputer, state-of-the-art hydrocodes and plenty of time ?

Run huge numerical simulations in order to get pretty 3D pictures for your report.

Wonder how you could draw a clear conclusion from billions of data

You are getting short of time ?

Be careful in extrapolating empirical models

Use the best available FREMs.

Then prepare for the next time and improve your tools.

An anthology of Murphys (and others) laws for modellers

Complex problems have simple, easy to understand wrong answers Be wise !

When working toward the solution of a problem, it always helps if you know the

answer Use first order solutions to check more refined results.

Sometimes, where a complex problem can be illuminated by many tools, one can be

forgiven for applying the one he knows best Practice your models to avoid errors.

Given any problem containing n equations, there will be n+1 unknowns Modellers

always have to make assumptions.

There is a solution to every problem; the only difficulty is finding it Good luck !| PAGE 27CEA | APRIL 2015


Choosing a model

Complex problems have simple, easy to understand wrong answers ?

Not always true back to the EVA / ECF approach.

HE charge at the entrance of a tunnel.

A simple EVA analysis gives a speed-up of 50.106 compared to the 3D simulation.

But not easily extended to complex geometries.

| PAGE 28CEA | APRIL 2015HPC results with AMR ISTSS 2012(1024 cores, 13 hours, 110 to 260 M cells)

EVA approach compared to 3D results

(Excel worksheet, < 1 s runtime)


Way forwardFast-running models for complex geometries

Specific experiments at CEA-G or in cooperation (LCPP, INSA-CVL, IVK, ).

Further work is required for blast consequences in urban environments.

- Importation of GIS geometries, improvement of sub-models, optimization

In parallel, development of a new version of the multi-room QSP solver.

- It would be interesting to add QSP and the first 2 or 3 dynamic waves

What about indoor / outdoor and outdoor / indoor propagations ?

Human response to complex pressure signals ???

Forensic approach (inversion of the direct model, planned in 2016)


[from Jeske Engineering Inc.]Oklahoma city bombing (1995): building damages Oslo bombing (2011) [from Christensen]


Thank you for your attention !


2015.13-17 ipsf cambridge

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