Modeling the Effects of Detonations of High ExplosivesDetonations of High Explosivesto Inform Blast-resistant Designg

Andrew Whittaker Ph D S E Professor and ChairAndrew Whittaker, Ph.D., S.E., Professor and ChairAmjad Aref, Ph.D., P.E., Professor

Pushkaraj Sherkar, M.S., Thornton-Tomasetti, LA

Department of Civil, Structural and Environmental Engineering

University at Buffalo

Summary of workSummary of work

• Field trials at Woomera and Port Wakefield• Air-blast effects on structural shapes• Blast-tolerant ultra-high performance concrete

l telements• Effects of air and ground shock on nuclear structures• Modeling detonations• Modeling detonations• Influence of charge shape, orientation and point of

detonation on overpressure distributions• Importance of charge shape and orientation in blast-

resistant design

NEES-MCEER Annual Meeting, June 2011

Blast-resistant designBlast resistant design• UFC-3-340 • FE and CFD analysis

– Scaled distance– Spherical or hemispherical

charge

– Model detonation explicitly– Charge shape, orientation and

detonation point– SDOF analysis– Uniform loading– Idealized pressure history

– Fluid-structure interaction

Idealized pressure history– Dynamic increase factors

NEES-MCEER Annual Meeting, June 2011

Modeling detonationsModeling detonations

• Explicit modelsp– Lagrangian, Eulerian and Arbritrary-Lagrangian-

Eulerian (ALE) solvers– Finite element meshes: explosive, air, and structure– Materials, equations of state

LS DYNA– LS-DYNA– AUTODYN

• Air3D• Air3D– Balloon analog (Ritzel and Mathews, 1997) based on

Brode (1959)

NEES-MCEER Annual Meeting, June 2011

( )

Sample detonation problemSample detonation problem• Purpose• Free-air burst of 1000 kg of

TNTRi id l f fi it idth• Rigid column of finite width– Why?

• Transmitting groundTransmitting ground– Why?

• LS-DYNA, Air3D and AUTODYN

• Overpressure histories at points A B and C

NEES-MCEER Annual Meeting, June 2011

A, B and C

Point C

NEES-MCEER Annual Meeting, June 2011

Point A

Values of blast-wave parametersValues of blast wave parameters

Point CAir3D LS-DYNA AUTODYN UFC-3-340

Peak reflected overpressure (MPa) 7.13 12.5 8.33 11.1

Time of arrival (msec) 1.83 1.77 1.61 1.90

Point C

Time of arrival (msec) 1.83 1.77 1.61 1.90

Reflected impulse (MPa-msec) 3.41 6.33 3.73 5.40

Air3D LS-DYNA AUTODYN UFC-3-340

Peak reflected overpressure (MPa) 65.2 60.8 46.8 79.2

Point A

Time of arrival (msec) 0.86 0.80 0.70 0.65

Reflected impulse (MPa-msec) 23.4 25.1 20.5 32.0

NEES-MCEER Annual Meeting, June 2011

Summary remarksSummary remarks• Analysis and modeling in LS-DYNA

El t i ll f l i (10 ) d i– Element sizes small for explosive (10mm) and air (25mm)

– Input parameters for the coupling algorithm• Analysis and modeling in AUTODYN

– Use of remapping capabilities– Euler-FCT solver for air– Euler-Godunov solver for afterburning

• Analysis and modeling in Air3D• Analysis and modeling in Air3D– Cell size– Runtimes better than LS-DYNA and AUTODYN

NEES-MCEER Annual Meeting, June 2011

Summary remarksSummary remarks

• Mesh sensitivity is acute in LS-DYNAMesh sensitivity is acute in LS DYNA– Mesh sensitivity studies are important for blast analysis

• Clearing leads to a reduction in peak reflected g poverpressure and reflected impulse

• Afterburning of detonation products increases the reflected impulse– Rarely considered, if at all

Temperat res are er high and the ass mption of• Temperatures are very high and the assumption of constant γ is violated– Implications are an underestimation of pressure loading

NEES-MCEER Annual Meeting, June 2011

Implications are an underestimation of pressure loading

Influence of charge shapeInfluence of charge shape• Baseline analysis: 10 kg TNT spherical charge• 10 kg TNT cylindrical charges; L/D = 1, 3 and 5• Monitoring overpressure and impulse

NEES-MCEER Annual Meeting, June 2011Spherical charge Cylindrical charge

2 000

2,500a)

SphericalL/D = 1 1 600

2,000

a)

SphericalL/D = 1

1,000

1,500

2,000

over

pres

sure

(kPa L/D 1

L/D = 2L/D = 3L/D = 4L/D = 5

800

1,200

1,600

verp

ress

ure

(kPa

L/D 1L/D = 2L/D = 3L/D = 4L/D = 5

0 5 1 1 5 2 2 5 3 3 5 4-1000

500

Inci

dent

o

-1000

400

Inci

dent

o

0.5 1 1.5 2 2.5 3 3.5 4Time (msec) 0.5 1.0 1.5 2.0 2.5 3.0100

Time (msec)

60

Spherical50

Spherical

a) 10 cds (axial) Z = 1 m/kg0.33 b) 10 cds (radial) Z = 1 m/kg0.33

20

40

rpre

ssur

e (k

Pa) L/D = 1

L/D = 2L/D = 3L/D = 4L/D = 5 20

30

40

rpre

ssur

e (k

Pa) L/D = 1

L/D = 2L/D = 3L/D = 4L/D = 5

0

Inci

dent

ove

r

-10

0

10In

cide

nt o

ver

NEES-MCEER Annual Meeting, June 2011

10 12 14 16 18 20 22 24-20

Time (msec)

10 12 14 16 18 20 22 24-20Time (msec)

c) 40 cds (axial) Z = 4 m/kg0.33 d) 40 cds (radial) Z = 4 m/kg0.33

Charge shape and orientationCharge shape and orientation

• Response of a structural componentResponse of a structural component– A992 (Grade 50) W14x257 steel column, Johnson-Cook model

• 1000 kg of TNT; spherical and cylindrical charges– Aspect ratios of 1 and 5 for cylindrical charges

NEES-MCEER Annual Meeting, June 2011Spherical charge Cylindrical charge, A Cylindrical charge, B

Monitoring gauges

Spherical charge

NEES-MCEER Annual Meeting, June 2011

Pressure and temperatures at gauge 1 Shear force and displacement histories

NEES-MCEER Annual Meeting, June 2011

ConclusionsConclusions• For near-field detonations involving a large mass of TNT

– Results of analysis using UFC-3-340 and DYNA/AUTODYN andResults of analysis using UFC 3 340 and DYNA/AUTODYN and Air3D differ significantly

– Temperatures are high in the near-field region• Variable γ and afterburning

Cl i d b th k fl t d d i l– Clearing reduces both peak reflected overpressure and impulse for targets with finite dimensions

• Charge shape influences substantially the near-field overpressure distributionsoverpressure distributions

• Charge shape and charge orientation influence substantially the response of a structural component in the near-field region– Charge shape should not be assumed to be spherical per UFC-3-

340• Strain-rate and thermal effects do not affect substantially the

global response of the sample W14x257 column

NEES-MCEER Annual Meeting, June 2011

global response of the sample W14x257 column

Recommendations for future workRecommendations for future work• Studies on afterburning to better understand effects

M d li ft b i i FE/CFD d• Modeling afterburning in FE/CFD codes• Variation of γ with temperature and pressure; EOS calibration• Propagation of rarefaction waves and their effect (clearing)• Empirical design charts that address variations in charge shape,

charge orientation and point of detonation• Simplified procedures for design of structures to resist effects ofSimplified procedures for design of structures to resist effects of

near-field detonations• Extend scope of study beyond the simplified model of a W-shape

column used; variations in boundary conditions explosive locationcolumn used; variations in boundary conditions, explosive location• Controlled experimental studies

NEES-MCEER Annual Meeting, June 2011