Modeling the Effects of Detonations of High Explosives Detonations of High Explosives to Inform Blast-resistant Design Andrew Whittaker Ph D SE Professor and Chair Andrew Whittaker, Ph.D., S.E., Professor and Chair Amjad Aref, Ph.D., P.E., Professor Pushkaraj Sherkar, M.S., Thornton-Tomasetti, LA Department of Civil, Structural and Environmental Engineering University at Buffalo
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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
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
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