HEST for STP 3.5A Experiment · 2011. 5. 14. · SIMULATION DEVELOPMENT FOR SILO TEST PROGRAM (STP)...

AD-A 163 274 DNA-TR.84-219.V1

SIMULATION DEVELOPMENT FOR SILO TEST PROGRAM(STP)Volume I-Design and Evaluation of a Variable HEST for STP 3.5AExperiment

M. SanaiJ.D. ColtonSRI International333 Ravenswood AvenueMenlo Park, CA 94025

31 March 1984

Technical Report

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SIMULATION DEVELOPMENT FOR SILO TEST PROGRAM (STP)

VolumeI-Desien and Eveluation of a Variable HEST for STP 3.5A Exoeriment12 PERSONAL AUTHOR(S)

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FIELD GROUP SUB-GROUP Airblast Simulation Simulation of Weapon EffectsGround Shock Simulation

16 1 High Explosive Simulation Technique (HEST)

19 ABSTRACT (Continue on reverse if necessary and identify by block number)

In support of the Defense Nuclear Agency (DNA) Silo Test Program (STP), we designedand evaluated the performance of a variable high explosive simulation technique (HEST) tosimulate the airblast environment resulting from a 1.95-kt (1/8-scale of 1 MT) nuclearsurface burst ovel a pressure range of 500 MPa (5 kbar) to 7 MPa (1000 psi). Our finaldesign consisted of a variable HEST in which Iremite-60 explosive is used predominantly

in the pressure range from 500 to 100 MPa, and 0.085 kg/m (400 grain/ft) primacord explo-sive is used in the pressure range from 100 to 7 MPa. The overburden height increases

linearly with range from 0.64 to 1.15 m. The cavity height increases linearly with therange from 38 mm to the 500-MPa location to 70 mm at the 35-MPa location. Beyond thispoint, the cavity height remains constant at 70 mm.

The above HEST simulator was used in the STP 3.5A experiment performed by WES atFort Knox. On the basis of photopole, airblast, and near surface soil stress gage data,

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19. ABSTRACT (Continued)

the impulse from the HEST agreed, to within measurement error, with the design goals

for both short (10 ms) and long (90 ms) time frames. Hence, the full positive phaseof a 1.95-kt surface burst was successfully simulated by the HEST.

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PREFACE

This is one of two reports on investigations performed for the

Defense Nuclear Agency (DNA) under Contract DNAO01-82-C-0103 during the

period 11 January 1982 to 31 March 1984. Technical monitors for this

work were Major M. E. Furbee (now at BMO) and Dr. K. Goering.

Most of the experiments reported here were performed by the

Waterways Experiment Station (WES) under the supervision of Mr. R. Welch

and Mr. J. Balsara. Mr. J. Gran and Mr. C. Romander from SkI supervised

the gdge placement and participated in the evaluation of the data in theSTP 3.5A experiment.

The two-dimensional calculations reported here were performed by

Mr. T. Cooper of SRI. Dr. L. Seaman provided support for the one-

dimensional PUFF calculations, and Mr. J. Kempf and Ms. B. Lew performed

the one-dimensional and the TIGER calculations.

Mr. R. Port from RDA was the chairman of the Simulation Working

Group for the Silo Test Program (STP). He provided constructive

leadership as well as technical and moral support throughout the work

"I presented here. We dedicate this report to his memory.

NTIS__

V vTIC V'3

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."A, %P 9 D13t

TABLE OF CONTENTS

Section Page

PREFACE .................................. ... ..... .. *. 1

LIST OF ILLUSTRATIONS ....................... *....*.. . ... .... 4

1. INTRODUCTION AND SUMMARY o.............................. 9

2. PARAMETRIC INVESTIGATION OF HEST ................... .... .... 12

2.1 Equation of State of Explosive Products ............... 12

2.2 Charge Initiation Scheme ............................. 20

2.3 Adjustable HEST Parameters ............................ 20

2.3.1 Explosion Pressure ........ . .................... 242.3.? Charge Areal Density ........................... 242.3.3 Cavity Height ................ *................. 272.3.4 Overburden Height ............... . .... .. ........ 27

2.4 Charge Placement ........... . ........... . .............. 27

2.5 Tailored Overburden ................................. . 31

2.6 Loads on Buried Silo Structures ....................... 31

2.7 Edge Effects ................... 38

3. DESIGN CALCULATIONS FOR STP 3.5A EXPERIMENT ................ 43

3.1 Design Criteria . 43

3.2 STP 3.5A Variable HEST Design ......................... 45

4. CALIBRATION EXPERIMENTS .................................... 54

4.1 1000-MPa Experiment ................................... 54

4.2 IO0-MPa Experiment .................................... 57

4.3 35-MPa Experiment ................................. *. 60

4.4 DISK HEST Experiment . 64

4.5 Relationship Between Explosion Pressure andCharge Density ........................................ 64

5. STP 3.5A MAIN EVENT ..................... ...... ... .. ...... . 68

5.1 Overall Test Bed Layout ........................... 68

5.2 Data from Airblast Gages ............................. 70

2

TABLE OF CONTENTS (Continued)

Section ?Me

5.3 Data from Near-Surface Stress Gages ................... 79

5.4 Conclusions on the Simulator Performance ............ , 79

REFERENCES . ................ . . .... . ........ .... ... . . 84

APPENDIX: CALIBRATION OF HEST EXPLOSIVE CHARGE INHIGH-PRESSURE CYLINDRICAL CALIBRATOR (HPC 2 ) .......... 85

3

LIST OF ILLUSTRATIONS

Figure Y-9g0

1 Weapon Effects and a Conventional HEST for Simulatingthe Airblast-Induced Ground Shock ..................... 10

2 A Typical Foam HEST Experiment ......................... 13

3 Equations of State for Equilibrium Expansion of0.085 k /m (400 gs/ft) Primacord Explosives and16 kg/mK (1 lb/ft ) Foam from DifferentExplosive Pressures ... .... ........... .... ... . 14

4 Impulse Histories from an Iremite HEST Baoed on TIG"and Ideal (Constant-y) Equations of State . 16

5 TIGER and JWL Equations of State for Equilibri.mExpansion of ANFO and Chapman-Jouguet DetonationPressure ........................ i7

6 Stress Histories at Various Depths fo: a 0.92-uANFO Charge Based on TIGER and JWL Equationa ofState ......................... V......... .. .. ......... 18

7 Impulse Hiatories from a 0.92-rm ANYO Charge gaeedon TIGER and JWL Equations of State ............ 19

8 Cavity Pressure and Impulse Histories for ThreeInitiation Schemes of an ANFO HEST .......... 21

9 Variation of Peak Stress with Depth for ThreeInitiation Schemes of an ANFO HEST ................. . 22

10 Pressure Histories at 35 m gelov an ANFO RESTfor Three Initiation $chemes ................. 23

11 Pressure and Impulse Histories for DffferentInitial Explosion Pressures P ... ........ ...... 25exp

12 Pressure and Impulse Histories ror Different

Charge Areal Densities m ............................... 2E

13 Pressure and Impulse Histories for DifferentCavity Heights h ................ ........ 28

LIST OF ILLUSTRATIONS' (Continued)

Figure Page

14 Pressure and Impulse Histories for DifferentOverburden Heights H ........ . .... . ...... . .............. 29

15 Pressure and Impulse Histories for DifferentCharge Placements ............ . ..... , ................ . 30

16 Pressure Histories for Different TailoredFoam/Sand Overburdens ...... . ...................... . • . 32

17 Pressure and Impulse from a HEST with a Foam/SandOverburden Tailored to Match the Brode-SpeicherSimulation Objective at l00-MPa Peak Pressure ........ , 33

18 Test Configuration Assumed for Calculating theDifference in Loads Applied by a HEST to a SoilSurface or a Buried Structure .......................... 34

19 Displacement and Cavity Height Histories of theTop and Bottom Surfaces of a HEST Placed Over aSoil Test Bed and Over a Generic Structure ............. 36

20 Pressure and Impulse Histories Resulting from aHEST Placed Over a Soil Test Bed and Over aGeneric Structure ............................... .. 37

21 Two-Dimensional Axisymmetric Calculation of HESTExpansion . . . . . . . . . . . . . . . . . . . . . ... 39

22 Pressure Histories from One-Dimensional and Two-Dimensional HEST Calculations for (a) Simulta tousInitiation and (b) Center Initiattin of theExplosive Charge ...... ......... ...... ...... ... .. ... 40

23 Impulse Histories from One-Dimensional and Two-Dimensional HEST Calculations ........... ....... 42

24 Comparison of Calculated Pressure Histories (HeavySolid Lines) with Typical Pressure Measurement Madein the STP 2.5 Expetiment ................... ...... 44

25 Stress-Strain Data from Uniaxial Compression TestsPerformed by WES on fort Knox Crush-4 Limestone ....... 47

26 Pressure aa.d impulse Histories Calculated forDifferent Explosion Pressurc Pexp in a Nominal35-MPa HIST ......................... . ...............W. 48

LIST OF ILLUSTRATIONS (Continued)

Figure Tage

27 STP 3.5A Variable HEST Design Covering the PressureRange of 7-500 MPa (1000 psi-5 kbar) .......... ......... 49

28 HEST Pressure and Impulse (Using Iremite Explosive)Compared with Simulation Objective at 500-MPa andlO0-MPa Peak Pressures . ................ . ......... 51

29 HEST Pressure and Impulse (Using Primacord Explosive)Compared with Simuiation Objective at 100-MPa and7-MPa Peak Preisures ................................... 52

30 Calculated Total Impulse Versus the Product ofCharge Areal Density and Overburden Height forPrimacord HEST (7-100 MPa) and for Iremite 60HEST (100-1000 MPa) . ........ ..................... . . .... 53

31 Pretest REST Calculations and the SimulationObjective for the 1000-MPa Iremite HESTCalibration Experiment .......................... . .... . 55

32 HEST Calculations and Data from the lO00-MPaIremite HEST Calibration Experiment .................... 56

33 Explosion Pressure Versus Charge Density forIremite-60 Explosive ................................... 58

34 Calculations, Simulation Objective, and Data fromtae 100-MPa Primacord HEST Calibration Experiment ...... 59

35 Data from 100-MPa HEST Calibration Experiment andTwo Other Similar HEST Experiments in which 0.085kg/m (400 gr/ft) Primacord was Used .................... 61

36 P:atest HEST Calculatiou and Simulation Objectivefor the 35-MPa HEST Calibration Experiment ............. 62

37 Calculations and Data from the 35-MPa PrimacordHEST Calibration Experiment . ............. ........ 63

38 Data from the nISK REST Experiment (Light SolidCurves), 35-MPa Simulation Objettive (Heavy SolidCurves), and 2-Dimensional Finite DifferenceCalculations (Heavy Dashed Curve) ...... V ............... 65

39 Explosion Pressure Versus Charge Densityv forPrimacord Explosive ... .......... ........................ 66

6

LIST OF ILLUSTRATIONS (Continued)

Figure Page

40 Layout of Striptest and STP 3.5A HEST Experiments ...... 69

41 Airblast Data from 3oTP 3.5A Experiment andSimulation Objectives (Dashed Lines) ................... 73

42 Impulse Versus Range from Airblast Gage Measurementsin STP 3.5A Experiment and Simulation Objective at5, 10, 50, and 90 ms After Shock Arrival Time .......... 78

43 Simulation Objective and Airblast and Near-SurfaceSoil Stress Gage Measurements in STP 3.5A Experiment .,. 80

44 Simulation Objective and Impulse Versus Rangefrom Airblast and Near-Surface Soil Stress GageMeasuremer~s in STP 3.5A Experiuent at 10 and 90 asAfter Shock Arrival Time .............................. 81

45 Photo Pole Total Impulse Versus kange Compared toSimulation Objectives at 90 ms ......... .............. 82

A.1 An Overview of Jhe SRI High-Pressure Cylindrical

Calibrator (HPC&) ................................... 86

A12 Schematic of Hilh-Preesure CylindricalCalibrator (HPC ) . 87

A.3 Time of Arrival Pins Used to Measure theDisplacement History of the Movable Pieconin tht HPC2 Facility ................................... 88

A.4 Typical Ggcilloscope Trace frow a Set ofFour TOA P' I s . . . . . . . .. . . . . . . . . . . . . . . . . . . 89

A.5 Cavity Pressure History for Five InitialExplosion Pressures ................ ............. 91

A.6 Piston Displacement History for Five InitialExplosion Pressures ............ ......................... 92

A.7 Piston Displacement History for Five InitialExplosion Pressures (log-73g plot) ..................... 93

A.8 Normalized Pressure-Volume Relationshtp for TwoValues of Specific Heat Ratio, y ...... ...... 94

LIST OF ILLUSTRATIONS (Concluded)

Figure

A.9 Piston Displacement Histories for Two

Values of the Specific Heat Ratio, ................... 95

A.10 Schematic of Charge Calibration Experiments ...... ,.... 97

A.11 Piston Displacement Histories Measured in HpC2

Experiments . . . ......... ,,.. . .,,,,,,.,,,.... 98

"A.12 Data from HpC2 Experiments Compared to TIGERCalculations and the Fit to HEST CalibrationExperiments ............ ,•,•.•..,,,,,. 99

:.8

.58

SECTION 1

INTRODUCTION AND SUMMARY

In support of the Defevse Nuclear Agency (DNA) Silo Teat Program

(STP), we designed and evaluated the performance of a variable high

explosive simulatfon technique (REST) to simulate the alrblast environ-

ment resulting from a 1.95-kt (1/8-scale of 1 MT) nuclea, surface burst

over a pressure range of 500 MPa (5 kbar) to 7 HP& (1000 psi). Figure

l(a) shows the weapon effects and Figure l(b) shows the schematics of a

HEST used to simulate the surface ai-hlst. The HEST consists of an

explosive charge inside a cavi't that is tamped with a soil overburden.

The explosive charge usually consists of high explosive cords placed

inside the groove. of rigid foam plates. The Impulse applied to the

test bed is contralled mainly by the areal density of the explosives,

and the pulse width is determined mainly by the initial height of the

explosive cavity. The overburden height influences both the impulse andthe pulse width.

In a nuclear blast, the peak pressure attenuates and the pressure

pulse widens with increasing renge from ground zero. To simulate the

airblast environment at all ranges, we designed a variable REST in which

the explosive loading density, cavity height, and overburden height

varied with range. The design criterion is to match at all ranges the

positivr phase of the impulse history of the reference Brode-Speicher

nuclear environment. This implies that the pressure history is also

matched at all ranges. The peak pressure, however, may not match

exactly because of the familiar pressure spikes produced by the HEST.

The first step in our design procedure was to perform a parametric

series of calculations to determine the effects on the HEST impulse of

adjustable parameters such as the explosive areal density, charge

density, and cavity and overburden heights (Section 2). The one-

"dimensional PUFF finite-difference hydrocode was used to model the HEST

9

1 -MT AirblastNuclearSurface 6 GPa 1 J3Pa 100 MPa 35 MPa

Burst (47.2 m) (85.6 m) (185 m) (266 m)

Airblast- Induced"Ground Shock

Direct- inducedGround Shock

"(a) Weapon Effects

~~~~~~~~~~~~. . . . . . ".-.. .. . ....." ,''. S i;'.. '. ', " . . '. "..

'.° * , . o . Soil,. . .° € ',. • • , , , . ° I • • , °

r High Explosive '

(b) Conventional HEST

JA-4015-4

Figure 1. Weapon effects and a conventional HEST for simulatingthe airblast-induced ground shock.

10

cavity expansion and mction of the berm and the loaded medium. The SRI

TIGER code wav used to calculate equilibrium states of the explosive and

foam products during -xpansion to establish an expansion isotrope for

each explosive/foam ratio used in the REST cavity. We also performed a

series of two-dimensional calculations to determine the extent to which

the boundaries of a finite-size REST affect the pressure and impulsehistories.

From the preliminary calculations discussed above, we determined

the REST configuration that produced the impulse history of the refer-

ence environment at several discrete ranges and then developed a design

curve that allowed us to interpolate the REST design at other ranges of

interest. Our final design (Section 3) consists of a variable REST in

which Iremite-60 explosive is used predominantly in the pressure rangefrom 500 to 100 MPa, and 0.085 kg/m (400 grain/ft) primacord explosiveis used in the pressure range from 100 to 7 MPa. The overburden height

increases linearly with range from 0.64 to 1.15 m. The cavity height

increases linearly with range from 38 mm at the 500-HPa location to

70 -m at the 35-MPa location. Beyond this poln', the cavity height

remains cinstant at 70 m.

To check the REST designs, Waterways Experiment Station (WES)

performed calibration experiments that represented the HEST designs at

the 1000-, 100-, and 35-MPa peak pressures (Section 4). Iremite-60

explosive was used in the 1000-MPa experiment and primacord explosive

was used in the other experiments. By comparing the calculations and

the experimental data, we deduced a relationship between the explosion

pressure and the charge density. This relationship was then used to

adjust the amount of the explosives in the final design of the STP 3.5A

experiment.

The variable REST simulator was used in the STP 3.5A experiment

(Section 5). On the basis of photopole, airblast, and near surface soil

stress gage data, the impulse from the REST agreed, to within measure-

ment error, with the design goals for both short (10 ms) and long

(90 ms) time frames. Hence, the full positive phase of a 1.95-kt

surface burst was successfully simulated by the HEST.

11

SECTION 2

PARAMETRIC INVESTIGATION OF HEST

A parametric series of one-dimensional and two-dimensional hydrocode

calculations was performed to determine the effect of various parameters

on the performance of a HEST. To put the calculations in prospective,

we show in Figure 2 the setuo in a typical foam REST experiment. High

explosive cords are placed in a foam cavity and tamped with a soil

overburden. As shown in Figure 2(b), the foam holds the explosive

strands in place and provides the desired initial cavity height. We

expect the areal density of the explosives to determine the impulse

applied to the test bed, and the initial cavity height to determine the

pulse width. The overburden height should influence both the impulse

and pulse width.

The parameters discssed here are the expansion characteristics of

the explosive products (Section 2.1), charge initiation schemes (Section

2.2), adjustable HEST parameters such as the explosion pressure and

charge areal density (Section 2.3), charge placement in the cavity

(Section 2.4), tailoring of the overburden for pulse shaping (Section

2.5), comparison of loads on a sand test bed with those on a buried

structure (Section 2.6), and relief waves generated at the edges of the

HEST cavity (Section 2.7). We used the SRI version of the PUFF computer

code 1 for the one-dimensional calculations and the TDL computer code 2

for the two-dimensional calculations.

2.1 EQUATION OF STATE OF EXPLOSIVE PRODUCTS

We used the TIGER computer code 3 to characterize the expansion of

the explosive products. Figure 3 shows the relationship between the

pressure and specific volume for equilibrium expansion of a 0.085 kg/m

(400 gr/ft) primacord and 16 kg/m 3 (1 lb/ft 3 ) foam from explosion

pressures of 91, 35, and 9.5 MPa. The plastic and binding materials

12h"

Explosive Cavity .

(See Detail Below)'.

(a) HEST Configuration

S. 40.7

t25.4 F oam Primacord Strand19.1 0.085 kg/rn (400 gr/ft)

Foamm 3. Ikgm3. k g/2

(b) Detail of Explosive Cavity(STP 2.5 Calibration Experiment)

(Dimensions in mm) JA-401 5-5

Figure 2. A typical foam HEST experiment.

13

100 - - 7lO I , I I I II 1 1111 1 iExP 91 MPa

50

\ EXP =35 MPa

20

: 10 XP 9.5 MPa

U,L

a. 5

2

I-5 10 20 50 iO0 200 500

SPECIFIC VOLUME (m3 /kg x 10-3)

JA401 5-6

Figure 3.. Equa,:ion of state for equilibIiu- expansion of 0.085 ki/m(400 gr/ft) pdrmacord explosives mid 16 kgim 3 (1 )b/ft0)foam from different explosive pmessores, 'The middle curve(solid line) corr•eýponds to the STP 2.5 HEST experimentshown in Figure 2(b).,

14

ased in the construction of the primacord are included in these

calculations. The straight lines in the log-log plot of Figure 3

indicate that, for pressures below 100 MPa, the expansion states of the

explosive products can be described by the equation of states of an

ideal gas with a constant specific heat ratio of y = 1.18.

To determine the adequacy of the constant-y law in REST calculations,

we calculated the impulse from a primacord/foam charge for expansions

from initial explosion pressures of 58 and 270 MPa using the ideal and

TIGER equations of state. For the 58-MPa case [Figure 4(a)], the

calculated impulses are essentially identical, whereas for the 270 MPa

case (Figure 4(b)], the constant-y equation of state overestimates the

impulse at 10 ms by abnut 18%. This corresponds to about a 30% error in

the explosive weight and indicates that a more complete equation of

state must be used in the design of a HEST with above 100 M•a.

We also compared the TIGER calculations against the JWL4 model

using an amonium nitrate/fuel oil (ANFO) explosive, which is similar to

the Iremite-60 explosive used in the STP experiments. Figure 5 shows

the TIGER and the JWL equations of state, and Figure 6 shows the stress

histories resulting from a 0.92-m-thick bare ANFO charge using the two

models. The waveforms appear to be very similar, but the peak stress is

"higher and the pulse width is smaller for the TIGER model. Figure 7

shows the impulse histories on the surface of the test bed and indicates

that both models predict the same total impulse at 10 ms.

Results of the present calculations may be regarded as an indirect

verification of the TIGER code against experiments because the JWL model

is based on an extensive series of experiments in which the measured

motion of a cylindrical shell surrounding the explosive charge is

matched by hydrocode calculations. Direct comparison with experimental

results are discussed in Section 4.1 where the l000-MPa Iremite

calibration experiment is discussed.

15

0.101Ida I I(V=1.18; 0 =4 MJ/kg)

0.08

0.006

C,,

0. HEST Dimensions

h -50.8 mm0.02 H -0.75 mn

m4.7 kg/rn

0I0 2 4 6 8 10

TIME (ins)(a) 58-MPa Explosion Pressure

0.16 Ideal(,y 1. 18 Ql0=4 MA/Og 100 100

-0.12

CL TIGER

0.0

_ HEST Dimensionsh = 32.2 mm

0.04 H =0.63 m

rn= 18.1 kg/rn

0 2 4 6 8 10TIME (ins)

(b) 270-MPa Explosion PressureJA-401 5-7

Figure 4. Impulse histories from an lre~nite HESTbased on TIGER and ideal (constant-yequations of state.

16

10 t._

1.0- TIGER

.JWL

cc 0.1

0.01

0.001 l I I I I I l l I I0.1 0.2 0.5 1 2 5 10 20 50 100

SPECIFIC VOLUME (m3 /kg x 10-3)JA-4015-8

Figure 5. TIGER and JWL equations of state for equilibrium expansionof ANFO from Chapman-Jouget detonation pressure.

17

6 0 -x "0.1

x 0.2Depth in Meters ANFO 0.92 m

x 0.5x

Saturated

4 Sand

x 1.0

0c%3

x -2.0 TIGER

JWL

2 (100-ps Time Shift)

x -5.0

1x 10.0

0-10 2 4 6 8 10 12

TIME (ms)JA-4015-9

Figure 6. Stress histories at various depths for a 0.92-m ANFOcharge based on T IG E R and JWL equations of state.

18

1.6

X 0

I I --

-- TIG ER Vo, wwo .- WIM

1.2 /. / JWL

ANFO 0,92 mn

Uj 0.8 ,

CL Saturated x

Sand

0.4

pr

I wo

0 2 4 6 8 10TIME (ins)

JA-.401 5-10

Figure 7, Impulse histories from a 0.92-m ANFO charge basedon TIGER and JWL equations of state.

19

2.1 CHARGE INITIATION SCHEME

We compared different schemes of initiation of a HEST charge based

on one-dimensional calculation of the cavity pressure. Figure 8 shows

the cavity pressure and impulse histories resulting from a 0.92-m ANFO

charge initiated simultaneously throughout the volume, at the top, or at

the bottom. The pressure waveforms are different from each other,

although the impulse delivered by the explosive is identical. This

indicates that different initiation schenes significantly modify the

HEST pressure history, but do not change the impulse ultimately

delivered by the explosive.

It is expected that the details of the initiation scheme should

become less discernible as the stress wave propagates into the soil.

Figure 9 shows the peak stress versus depth for the three ii.itiation

schemes of the ANFO charge. Close to the charge, the peak stresses are

quite different from each other, but at about 32 tH-es the charge height

(30 m depth), the peak stresses become equal and remain the same with

further propagation. Figure 10 showr that the waveforms at this point

are also identical.

The present calculations therefore indicate that the details of a

HEST waveform do not propagate to locations that are beyond 30 times the

initial cavity height. The propagation distance required to "clean up"

the waveform depends strongly or the geology (saturated sand in the

present calculations) and is expected to be much shorter (ten times

cavity height, say) for a drier geology.

2.3 ADJUSTABLE HEST PARAKMTERS

The three main parameters that can be adjusted in a REST design to

match given pressure and impulse histories are the initial explosion

pressure Pexp' the cavity height h, and the overburden height H. The

explosion pressure is related to the initial charge density p , definedas the mass of the explosive per unit cavity volume. The total

The relationship between Pex- and j is obtained separately from TIGERcalculations or from cylinldr excal calibrator (C2) experiments. See

Section 4.5 for more detail.

20

1.4 3.0

Top -

Initiation-1.2 V

j Simultaneousi Initiation

1.0 *HEST Dimensions 2.0

h 0.92 m

H 1.5 mc08 m "754 kg/n 2

I Bottom. /Initiation== 0.6 L•

1.0

0.4

0.2 -- _

000 2 4 8

"riME (ins)JA-4015-11

Fitgow 8. Cavity pressure and impulse histories for three initiationsdhemes of an ANFO HEST,

21

1.2 I

Top HEST Dimensions7 niiop o h -0.92 m

a,~~ -- H 1.5 ma.2o0.8 Bottom m - 754 kg/rn

08

LU

< 0.4 Simultaneous0.4

0 Iniiaion

0 5 10 15 20 25 30 35 40 45

DEPTH (inJA-4015-12

Figure 9. Variation of peak stress with depth for three initiationschemes of an ANFO HEST.

22

I

800 1 1

HEST Dimensigns700 - h 0.92 m

H a 1.5 mn600 754 kg/m2

600.

z500

E 400

!"IL

(: Top300 Initiation

200 - Bottom/S Initiation -

100 I SimultaneousI Initiation

0I10 12 14 16 1T 20 22 24

TIME (ms)

JA-4015-13

Figure 10. Pressure histories at 35 m below an ANFO HEST for threeinitiation schemes.

23

explosive mass per unit area m is then determined by m p ch and the

spacing, between explosive strands is determined by s t/m, where t is

the linear density (mass per unit length) of the explosive strands.

2.3.1 Explosion Pressure

Figure 11 shows the pressure and impulse histories resulting from

different initial explosion pressures of an ideal explosive charge

(constant specific heat ratio of 1.18). An increase of 94% in the

explosion pressure from 17 to 33 HPa has resulted in a 65% increase in

impulse at 5 ma and a 49% increase in impulse at 20 ms. These increases

are consistent with the familiar rule that the total impulse from a one-

dimensional HEST is proportional to the square root of the explosionpressure.

2.3.2 Charge Areal Density

Figure .2 shows the pressure and impulse histories from a HEST with

four explosive areal densities ranging from m - 2.29 kg/m2 to m - 4.57

kg/m 2 . The charge density and explosion pressure are constant in all

cases (Pc - 90 kg/O 3, Pexp ' 100 MPa), so the charge areal density is

directly proportional to the cavity height. The calculations show that

a 100% increase in charge areal density (from 2.29 to 4.°57 kg/m2 )

results in a 48% increase in impulse at 5 ms. Also, the width of the

pressure waveform at half the peak pressure (50 MPa) increases by 93%

from 0.14 to 0.27 ma, which is roughly the same as the 100% increase in

cavity height from 25.4 to 50.8 mm. This increase is consistent with

the familiar rule that, for equal explosion pressures, the wtdth of a

HEST pulse is nearly proportional to the height of the cavity.

*This rule follows from equating the kinetic energy of the overburden

to the initial internal energy of the explosives.

24

140 1- 0.14

120 HEST Dimensions PEXP -33 MPa 01h -0.19m 01

H - 0.91 mn26MI

100 22Ma 0.10

17 aI

Lu 600.6 L

Sa.

40 0.04

20 P X 3Ma0.02

00 ~EXP 17 MI~a 10 1200

JA-401 5-14

Figure 11., Pressure and impulse histories for different initial5' explosion pressures Pewp

25

100 1 0.10(5) m - 4.57 kg/m 2 ; h a 50.8 mm

(4) m 4.00 kg/m 2 ; h - 44.5 mm

(3) m 3.43 kg/m 2 ; h -38.1 mm

80 (2) m -2.86 kg/m 2 ; h - 31.8 mm 0.08' 1) m -2.29 kg/m2; h -25.4 m

a60 0.06w

Ilg w

it 40 -H - 0.51 mn 0.04 CLo.0 Pc "90 kg/m 3 -CL ~ ~~(5) m =4.57 kg/m2 PCa0 gm

h =50.8 mm

20 ) m 2.29 kg/m2 0.02h =25.4 mm

0 00 1 2 3 4 5

TIME (ms)JA-401 5-15

Figure 12. Pressure and impulse histories for different charge3real densities m.

26

2.3.3 Cavity Height

Figure 13 shows the pressure and impulse histories from a HEST with

initial cavity heights of 25.4 mm (1 in.), 50.8 mm (2 in.), and 101.6 mm

(4 in.). The areal density of the explosives is constant in all

calculations (m - 3.36 kg/m2 ), but the charge density varies according

to M m/h. The calculations show that the reduction in cavity heightc

leads to an increase in peak pressure, but the impulse at 20 ms remains

essentially unchanged. This result indicates that the total impulse is

controlled mainly by the areal density of the explosive weight and is

essentially independent of the details of the HEST cavity.

2.3.4 Overburden Height

Figure 14 shows the pressure and impulse histories from an ANFO

HEST with overburden heights ranging from H - 0 (bare charge) to

H - 3.0 m. The trend is a substantial increase in impulse with increas-

ing overburden height. For example, compared with the case of bare

charge, the impulse at 8 ms increases 2.8 times when a 3-m (3.3 times

the cavity height) soil berm is placed on top of the explosives.

2.4 CHARGE PLACEMENT

In the calculations presented so far, we have assumed that the

explosive is uniformly distributed throughout the HEST cavity. To

investigate the limitation of this assumption, we performed the three

calculations shown at the top of Figure 15 in which the same amount of

explosive is assumed to be (1) uniformly distributed throughout the

cavity, (2) concentrated in 25% of the cavity near the top, and

(3) concentrated in 25% of the cavity near the bottom. The calculated

pressures for the concentrated charges show repeated oscillations due to

the reflection of the pressure waves from the top and bottom of the

cavity. The impulse, however, is essentially the same for all three

cases, except for about the first 0.2 ms after charge initiation.

We therefore conclude that the overall impulse is essentially

independent of the explosive configuration inside the REST cavity.

27

120 0.12

"100 0.10

80 - h =25.4 m .000IO,

S0.08

=: 0 I101.6 mm -

S0 00.06wm Ih =50.8 mm u

40 HEST Dimensions - 0.04

h = 25.4, 50.8, 101.6 mm

H - 0.76 m20 m 3.36 kg/m 2 -0.02

20 00 5 10 15 20

TIME (ms)JA-4015-16

Figure 13. Pressure and impulse histories for different cavity heights h.

28

1.81 1 1 1 11 1 - 3.

HEST DimensionsH 3.m1.6 h -0.92mr

H - 0, 0.3, 1.5, 3.0 mn 3.0

1.45

1.2 2.5

LU. 2.0k

H 03 n

0.6H 0

4.1.

0.4H 30

H 1.0.50.2

0.

H 0

40 1 2 3 4 5 6 7 8

TIME (ins)JA-401 5-17

Figure 14. Pressure and impulse histories for differentoverburden heights H,~

29

SSand Sand Sand 38.1

0.76 Overburden Overburden Overburden mm

f 77777777 1" "\\ -f"

50.8 Soil Soil Soil -2mm Test Bed Test Bed Test Bed mm

mm

(1) " 66 kg/m 3 (2) Pc - 264 kg/m 3 (3) Pc -264 kg/m3

300 0.06

250 0.05CL.

200 0.0 4

150 0.03

(1) Uniformly Distributedv Charge

100 (2) Charge Concentrated - 0.02--- (3) Charge Concentrated

on Bottom50 -0.01

0 0

0 0.5 1.0 1.5 2.0

TIME (ms)JA-4015-18

Figure 15. Pressura and impulse histories for different charge placements.

30

This further supports the conclusion that, for equal overburden height,

the HEST impulse is determined mainly by the explosive areal density and

is not sensitive to such cavity design details as the detonation point

(Section 2.2), cavity height (Section 2.3.3), or charge placement.

2.5 TAILORED OVERBURDEN

The modified Brode-Speicher nuclear environment, which is used as

the simulation objective in the present program,5 is characterized by a

very rapid decay from peak pressure immediately after the shock arrival.

To simulate the rapid pressure decay, we designed a REST with a tailored

overburden that consists of layers of sand and foam. The immediate

crush of the foam layers would result in a rapid expansion of the cavity

volume and a rapid decay of the cavity pressure.

Figure 16 shows the pressure histories for two thicknesses of a

16 kg/m 3 (1 lb/ft 3 ) foam layer placed above a HEST cavity. Compared

with the reference case with no foam (F - 0), the cavity pressure for

the foam/sand overburden decays faster and results in a narrower pulse.

For example, at 60 MPa, the pulse width for a foam/sand overburden is

about one half of the reference case.

Figure 17 shows a generic design for simulating the Brode-Speicher

pressure history at the lO0-MPa peak pressure. Both the pressure and

impulse are closely matched by the HEST. Note that use of a tailored

overburden may not be appropriate in a conventional HEST because the

pressure spikes typically seen in conventional HEST produce deviations

from the ideal nuclear waveforms that are much more significant than the

improvements provided by a tailored overburden. Thus, the use of a

tailored overburden should probably be limited to a high-fidelity HEST

in which the spikes are removed by, for example, using a dilute

explosive that fills the cavity uniformly.

2.6 LOADS ON BURIED SILO STRUCTURES

When a buried silo structure is loaded with a HEST (Figure 18), the

cavity expansion above the silo will be slightly smaller than the free-

31

100

17

Sand t ' 0.76 rn80

16 kg/m 3 (1 ib/ft 3 ) Foam FSand "12.7 mm

Explosives (m - 4.6 kg/ 2 ) 50.8 mmS60

w SSoil Test Bed

C/)W F=0cr-40

20

0 1 1 1 -

0 1 2 3 4 5TWME (ins)

JA-401 5-19

Figure 16. Pressure histories for different tailored foam/sand overburdens.

32

100 1110.10

-, HEST Calculations

| --- Brode-Speicher80 Simulation Objective 0.08

460 0.06 0.2

-JHEST Dimensions

wJ 40 h-5.mm0.04ct

0 0

0 1 2 3 4 5TIME (ins)

JA-4015-20

Figure 17. Pressure and impulse from a HEST with a foam/sandoverburden tailored to match the Brode-Speichersimulation objective at 100-MPa peak pressure.

33

P-

.4�... *..**.� *5*0.. * ,* � � ,t * .* I.

4*5.9,'' 9

� S* . 0.7Cm*..y,.*t''''.h'.t's'.'o.' I': ',q' and � Iver

Explosive � * � *.*., 0. ________

Cavity""""� V�,�:h.'r' 85.5 mm

'I 'I Generic ' .Structure Soil 6.35 m* .'. p.4

4t

'''"'.3 p

K\ Co npetent Rock

L

LJA-401 5-21

Figure 18. Test configuration assumed for calculating the differencein loads applied by a HEST to a soil surface or a buriedstructure.

VaI-

34

field expansion because the silo is stronger than the soil and therefore

does not move down as much as the surrounding soil does. This leads to

a higher pressure over the silo and riay result in an overtest of the

structure.

We performed two separate one-dimensional calculations to determine

the loads on a generic silo structure and on a soil test bed. The

calculations correspond to vertical expansion of the flow over the

structure (region between the two dashed lines in Figure 18) and the

vertical expansion of the flow over the soil test bed (region outside

the dashed lines). These one-dimensional calculations in which no

lateral flow is allowed give an upper bound to the difference of HEST

pressures in the free-field and over silo structures, because in an

actual experiment, a lateral flow occurs in the cavity, which tends to

equilibrate the pressures.

Figure 19 shows the cavity expansion of a 35-MPa HEST placed over ageneric structure (dashed curves) and over a generic soil test bed (fullcurves). At 10 'as, the bottom surface of the cavity has moved down

170 mu for the soil test bed, but only 10 mu for the structure (a net

difference of 160 mu). The cavity height at this time, however, is

different by only 90 m= (750 m over soil compared with 660 mm over

structure) because a smaller cavity height results in a higher pressure,

which in turn, results in a more rapid expansion of the cavity. This

self-correcting mechanism tends to equalize the HEST pressure over a

buried silo structure and the surrounding free-field.

Figure 20 shows the calculated pressure and impulse histories for

I) the two cases. The impulse at 12 ms is 12% higher over the structure

than over the 3oil test bed. As mentioned earlier, this is an upper-

bound estimate of the overtest. Experimental data reported in Reference6 tend to indicate that the impulse over a concrete pad (representing a

generic structure) is, to within the spread of the HEST data, the same

as the free-field impulse.

35

80U0

-Over Soil 'rest Bed-E Over Generic Structure

x 600

Cavity HeightToSufc

~400U

zHEST Dimensions

~200 H-07LU

2

0-

0 initial Cavity Height (85.5 mm)<----------------------------------------

U.

-200 I0 2 4 6 8 10 12

TIME (ins).JA-401 5-22

Figure 19. Displacement and cavity height histories of the top and bottomsurfaces of a HEST placed over a soil test bed and over a genericstructure.

36

35 1 1 10.15

Over Soil Test Bed HEST Dimensions

30 - Over Generic Structure h a 85.5 mmH a 0.76 m

ma2.1 kg/rn2

25-0.10

!20

I W15 0L

0..G

a' 10

5

0 0..J40 2 4 6 8 10 12

TIME (ins)

JA-401 5-23

Figure 20. Pressure and impulse histories resulting from a HEST placed over a soiltest bed and over a generic structure.

37

2.7 EDGE EFFECTS

Near the edges of a HEST cavity, the pressure drops faster than the

free-field pressure because of the lateral expansion of the cavity.

This results ini a lower total impulse than that obtained from one-

dimensional calculations.

To estimate the edge effects in a typical HEST, we performed a

series of two-dimensional axisymmetric calculations using the SRI TDL

computer code.2 Figure 21 shows the cavity expansion 10 me after thedetonation for a nominal HEST design. The initial charge cavity (shown

as a dashed lines in Figure 21) is 1.5 m in radius and 70 mn high. The

charge is center-initiated with an explosion pressure 18.5 MPa, which

corresponds to the REST design in STP 3.5A experiment at the 35-MPa

range. We note that the cavity contour at 10 ms (shown as a heavy solid

line in Figure 21) is not straight near the edge. The depression

observed at the radius of 1.4 m indicates a high-pressure zone due to

the reflection and focusing of the wave near the edge.

Figure 22 shows the pressure histories calculated for simultaneous

and center initiation of the charge. For comparison, pressure histories

from a one-dimensional calculation representing an infinite HEST are

shown as dashed curves in Figure 22. For the case of simultaneous

initiation, Figure 22(a), a relief wave propagates !rom the edge coward

the center. The arrival of the wave is manifested !u Figure 22(a) by a

deviation of the two-dimensional calculation (solid curves) from the

reference one-dimensional calculation (dashed curves). the geometric

focusing of the relief wave enhances the relative drop in pressure as

the center of the charge is approached. For example, the relative

pressure drop when the wave arrives at R - 1.4 m is about 18%, whereas

the pressure drops by about 30% for R = 0.8 m.

When the charge la initiated at the center [Figure 22(b)], the

relief wave from the edge is preceded by the reflection cf the outward

running wave from the edge, which shows as a second peak on the pressure

histories. As before, geometric focusing has enhanced the magnitude of

the second peak at R = 0.2 m over that at R 1.4 m.

38

J- I- AI I i J 4-I~..

1.0 0 Sad a . Cavity Contour

•Overburden W at 10 ms

0z

0 0

icc

U.LUzIL

':Soil Initial HEST

W Test Bed -Cavity Contour

-1.0 1 I I I0 0.5 1.0 1.5 2.0

RADIAL DISTANCE (m)JA-4015-24

Figure 21. Two-dimensional axisymmetric calculation of HEST expansion.(Initial radius of 1.6 m, initial cavity height of 70 mm, andcharge areal density of 2.1 kg/m 2).,

39

20 R 0.2 m R =0.2 m

0 15 2 n- n -

S. One-Dimensional ---- One-DimensionalCC 10 Two-Dimensional - Two-Dimensional

cc 5S~~~.. .. ... .. ,. .. . . .0.

20R 0.8 .m Ru 0.8 m

M\

6- 15

2

" 10

c c 5 i" .

0 1 .. ".•.' ..............

0 2.5 5.0 7.5 10.0 0 2.5 5.0 7.5 10.0TIME (ins) TIME (ins)

(a) Simultaneous Initiation (b) Center InitiationJA-4015-25

Figure 22. Pressure histories from one-dimensional and two-dimensional HESTcalculations for (a) simultaneous Initiation and (b) center initiationof the explosive charge., (Initial radius of 1.6 m, initial cavity height

pWof 70 mm, charge areal density of 2.1 kg/in2 ,, and detonation velocityof 6200 m/s).-

40

The impulse histories calculated from the six pressure histories

shown in Figure 22 are compared in Figure 23 with the one-dimensional

reference calculation. The impulse from both of the two-dimensional

calculations are nearly identical (5% spread at 10 ms), indicating that

the detonation scheme modifies the pressure histories but does not

change the overall impulse. This result is consistent with our previous

conclusion that the overall impulse is determined mainly by the charge

weight and not by the charge configuration or the detonation scheme.

Compared with an infinite HEST (dashed curve in Figure 23), the

impulse at 10 ms is reduced by about 18% due to the lateral expansion at

the edges. This estimate may be regarded as typical of the edge effects

in small HEST experiments. For a larger HEST calibration experiment,

such as the 6.1-m-radius DISK HEST experiment discussed in Section 4.4,

the calculated impulse at 10 ms is only 9% lower than the reference one-

dimensional calculation.

41

0.06

0.05 -.

- 0.04

wu 0.03

I.'

0.02

One-Dimensional

0.01 Two-Dimensional Center InitiationTwo-Dimensional Simultaneous Initiation

--00 2.5 5.0 7.5 10.0

TIME (ms)

JA-4015-26

Figure 23., Impulse histories from one-dimensional and two-dimensionalHEST calculations. (Initial radius of 1.6 m, initial cavityheight of 70 mm, charge areal density of 2.1 kg/m 2 , anddetonation velocity of 6200 m/s),

42

SECTION 3

DESIGN CALCULATIONS FOR STP 3.5A EXPERIMENT

In this section, we present the methodology and the design

calculations for the variable HEST used in the STP 3.5A experiment.

3.1 DESIGN CRITERIA

The ultimate objective of a HEST simulator would be to match

exactly a desired nuclear pressure history throughout the simulation

time. The HEST pressure, however, includes many oscillations and spikes

due to reflections from the cavity walls and interaction of pressure

waves from the explosive strands. Figure 24 shows typical pressure

histories measured in the STP 2.5 experiment and a comparison with one-

dimensional PUFF calculations. The desired peak pressure for this HEST

design was 35 MPa (5 ksi), which is the same as the initial explosion

pressure assumed in the calculations. The measured peak pressures of

% 117 MPa in Figure 24(a) and 85 MPa in Figure 24(b) are, respectively,

3.3 and 2.4 times higher than the 35-MPa explosion pressure. The

impulse history, however, matches the calculated impulse very well.

The present comparison shows that the peak pressure measured in a

conventional HEST is not the same as the initial explosion pressure that

must be used in one-dimensional calculations to match the measured

impulse history.

The above discrepancy between the measured HEST peaks and the

explosion pressure suggests that the HEST design criterion should not be

based on matching the peak pressure. The criterion we chose is to match

the pressure waveform (excluding its peak) and the impulse history

throughout the desired simulation time. Even though our criterion does

not require a match to the peak pressure, we do not expect a degradation

of the fidelity of the resulting REST simulator, especially if the HEST

is intended to simulate the airblast-induced ground shock. Calculations

43

120 - 0.1216 16

100 - I- 0.10"• 0--12 Il 12 .. "

80 1• - - - 0.08•InI

uc'60 cc L .bLUn

0..• O.0o..

2" 40 -- i - 0.02 M

0 0

0 2 4 6 8 10TIME (ins)

(a) Free-field (Gage BP-15)

120 - 16 - 0.12

100 - 0.1004 80 12 -- 120 0.08

W CL

w160 -0.12

*cc D 88LD, 00 (

cc CC

20 0.02

"0 2 4 6 8 10TIME (ins)

( Over Structure (Gage 5)JA-40145-27

Figure 24. Comparison of calculated pressure histories (heavy solidlines) with typical pressure measurement made in theSTP 2.5 experiment..

44

discussed in Section 2.2 show that two pressure waveforms with different

peaks but the same impulse become identical after a propagation distance

of about 35 times the cavity height. In other words, the peak stress

that occurs in soil at distances far enough from the explosive cavity is

insensitive to the peak pressure initially applied to the soil surface.

Because most of the HEST waveforms in the STP experiments arrive at the

test structure after traveling a distance that is large compared with

the initial cavity height, we conclude that a discrepancy in peak

pressure on the soil surface does not measurably impair the fidelity of

the ground shock simulation.

The criterion discussed above should lead to a reasonable simulation

of the ground shock. However, if a REST is used to simulate the direct

airblast loads on a responding structure, the pressure spikes must be

considered in determining an equivalent pressure-yield combination and

in assessing the simulation fidelity. This topic is under investigation

in the simulation development community. Several fitting routines, in-

cluding the SRI shock spectrum method, 7 are discussed in Reference 8.

We have observed that any of the fitting routines applied to a HEST

pressure record result in a higher equivalent pressure than the explo-

sion pressure used in our one-dimensional calculations. For example,

the average equivalent pressure calculated by WES for the STP 2.5

experiment is about 48 MPa, which is 37% higher than the explosion

pressure of 35 MPa. This indicates that, if the HEST design is based on

an explosion pressure that is about 35% lower than the simulation

objective, the equivalent pressure of the resulting HEST should then

approach the simulation objective. This rule is used as a guide in

"designing the HEST for the STP experiments.

3.2 STP 3.5A VARIABLE HEST DESIGN

We designed a variable BEST for the STP 3.5A experiment based on

the criterion that the airblast pressure (excluding the peak) and

impulse are matched throughout the desired simulation time. The over-

burden and test bed materials were represented by pressure-density

"45

relationships in our calculations. The relationship for the crushed

limestone overburden was based on the stress-strain data provided by WES

(Figure 25). A generic unsaturated soil with 3% void ratio was used to

represent the HEST test bed at Fort Knox. 6

Our design methodology was to determine the REST configuration at

several discrete ranges based on one-dimensional calculations of the

cavity expansion. The areal density of the explosive, m, and the

overburden height, H, were determined such that the total impulse from

the REST matched the total positive impulse of the reference nuclear

environment. We then obtained a "best" match to the desired pressure

and impulse historiis by varying the cavity height while keeping m and

H constant.

Figure 26 shows the results of such calculations for a nominal

35-MPa HEST. Comparison of the impulse histories shows that the

reference impulse, designated as the simulation objective in Figure 26,

is best matched by the 70-mm-high cavity (Pexp - 18.5 MPa). We also

note that a good match with the simulation objective would not be

possible with an initial explosion pressure of 35 MPa (long-dashed

curves in Figure 26). The calculated impulse for Pexp - 35 MPa always

lies above the simulation objective throughout the 20-ms-window shown in

Figure 26, and at 2.5 ms it is about 50% higher than the simulation

objective.

We repeated similar one-dimensional calculations for several other

ranges and then interpolated the HEST variables at other ranges based on

these calculations. Figure 27 shows a schematic of our final design of

the variable REST for the STP 3.5A experiment covering the pressure

range of 500 to 7 MPa (5 kbar to 1000 psi). Iremite-60 explosive is

used for the pressure ranges of 500 to 100 MPa, and primacord explosive

is used for the lower pressure ranges. We found that the overburden

height could be chosen to vary linearly with range from 0.64 m at the

500-MPa location to 1.15--m at the 7-MPa location. The cavity height

increases linearly with range from 38 mm at the 500-MPa location to

70 mm at the 35-MPa location. Beyond this location, the cavity height

remains constant at 70 mm.

46

15

1001 Initial Density =1790 kg/m 3 IS- (112 Ib/ft 3 )I

13 - 90

12 -Extrapolation - 80

11 - to 100 MPa_'-II

10 -70Test D4----.,.

Loading Curve Used 60(n in HEST CalculationsW. 8 W l

I-- I--- 7 50 (n

x x< 6 D2-A 40

//5 5D3 30

4/D2 D3

2S

1 1 10

0 -0

0 5 10 15 20 25

AXIAL STRAIN (%)JA-4015-28

Figure 25. Stress-strain data from uniaxial compressiontests performed by WES on Fort Knox crushedlimestone.. (The loading curve used in STP 3.5AHEST design calculations is shown as a heavysolid line.

47

35 10.07

HEST Dimensions30 h =37, 48, 70, 96 mm 0.06

H =0.9 mM 18.gm

25 0.05

ICM 20 0.04C

w

10 =6, 185 MPa, h=37 mm 00

Pexp = 13.5 MPa, h = 96mm

5 - 0.01

0 00 5 10 15 20

TIME (ins)JA-401 5-2q

Figure 26. Pressure and i'mpulse histories calculated for different explosionpressure Pex in a nominal 35-MPa HEST,.

48

O.~ 2~~i~~IaCrushed Limestone 1 .115

13.5 20 23 25 30 33 35 40 45 50 55 58RADIAL DISTANCE FROM GROUND ZERO (in)

JA-401 5-30

Figure 27. STP 3.5A variable HEST design covering the pressure range of 7-500 MPa(1000 psi-S kbar).

49

Figures 28 and 29 show typical comparisons between our calculations

and the simulation objective for two segments in which Iremite-60

(Figure 28) and primacord (Figure 29) explosives are used. The differ-

ence between the calculated impulse and the simulation objective is less

than 5% at all times and ranges.

Figure 30 shows that the discrete primacord and Iremite-60 HEST

designs (including those shown in Figures 28 and 29) can be correlated

by plotting the total impulse from the HEST versus the product of charge

areal density and overburden height, mH. The plot shows that the total

impulse is roughly proportional to the square root of MH. The dashed-

point line indicates a theoretical limit for the HEST impulse and

represents the case in which all the explosive energy is transformed

into the kinetic energy of the overburden. The plot in Figure 30 was

used to interpolate the value of mlH at all ranges in the ITEST design and

resulted in the variable HEST design shown in Figure 27.

50

-" HEST Calculation

-- '-- Simulation Objective375 0.15

c 250 0.0

0 00 2 4 6 8 10

TIME (ins)

(a) 500-MPa Pressure

- HEST Calculation

125 H- .6 - 0.08-~~~ -Simlaio Objetiv

800

* 4000 O0.06

so1.1 SiultinObeci m2 0CL.

40

0 2 4 6 8 10TIME (ns)

(b) 100-MPa PressureJA-4015-31

Figure 28.. HEST pressure and impulse (using Iremite explosive)

compared with simulation objective at 500-MPa::and 100-MPa peak pressures.

151

100 0.10

-HEST Calculation

80 -- Simulation -0.08Objective

~60 -0.06~w w

S40 -0.04 Dw HEST Dimensions 0

0. h - 50.8 mmr20 H - 0.75 m 0.02

mn - 4.12 kg/in

0 2 4 6 8 10TIME (ins)

(a) 100-MPa Pressure

7 1 1 1 0.035

6 -HEST Calculation0.3-- Simulation-

I ~~Objective V ~002

w 4 0.020w wD HEST Dimensions 001I0.010 -D

0h 0TIME (ens)

Fiur 29 HEH presur an mpus (usngpmaor

5200

1.0 111111 I1 I I 11 Ii11

-- Primacord0.6 Iremite-60

0.4

0.2 - , ,a

CCA5 0.1 e-j ,70 MPa 100 MPa

•; -3. MPa

-- 70 10 MM-J0.06 17.2 MPa

0- 0.04 7MPa

0.02

0.01 i i ilt ill0.2 0.4 0.6 1 2 4 6 10 20

CHARGE AREAL DENSITY x OVERBURDEN HEIGHT, mH (kg/m)

JA-401 S-33

Figure 30. Calculated total impulse versus the product of charge areal densityand overburden height for primacord HEST (7-100 MPa) and foriremite-60 HEST (100-1000 MPa).

I.5." 53

SECTION 4

CALIBRATION EXPERIMENTS

We designed four uniform REST calibration experiments to validate

our code calculations and obtain a relationship between the charge

density and explosion pressure. The calibration experiments represent a

constant-pressure segment of the STP 3.5A variable HEST design at 1000,

100, and 35 MPa peak pressure ranges (two calibration experiments were

designed at the 35-MPa range). These experiments were performed by WES

at Fort Knox near the site of the STP 3.5A main event.

4.1 1O00-HPA EXPERIMENT

The 1000-MPa HEST calibration experiment consisted of a 7.9-m

(26-ft) square charge placed directly over the in situ soil at Fort

Knox. The explosive used was 28.6-mm-diameter (1.125 inch) Iremite-60

placed on 41.3-mm (1.625 inch) centers. (Details of the charge design

4.re given in Reference 5.)

Figure 31 shows a comparison between the pretest REST calculations

and the simulation objective. In this calculation, the SRI TIGER code

was used to generate a tabular equation of state for the Iremite/foam

explosive charge.

Figure 32 shows a comparison between the calculations and the data

from a flatpack ytterbium gage. Because of an uncertainty in the

density of the overburden used in this experiment, Figure 32 shows the

results of two separate calculations based on probable maximum and39 3minimum overburden densities of 1840 kg/m 3 and 1360 kg/m . Also shown

is an error bar representing the uncertainty in the measured impulse.*

%**

Hysteresis and strain effects most be accounted for to obtain stressand impulse data from ytterbium gages. Details of data reductionprocedure and the level of uncertainties involved ate discussed inReference 5.

54

1000 0.20

800 0.16

Simulation

S600 - Objective -- 0.12 -.

CL

wcr•" Pretest LU

/ Calculation-J

cc 400 0.08

HEST Dimensions200 h = 54 mm (2.125 in.) 0.04

H = 0.51 m (20 in.)

m = 17.3 kg/m 2 (3.5 lb/ft 2 )

0 00 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

TIME (ms)JA-4015-34

Figure 31. Pretest HEST 7;culations and the simulation objectivefor the 1000-ftPa Iremite HEST calibration experiment.

55

0.4 BarDuError Bar Due

to BaselineCorrection

Posttest Calculation Crci0.3 -(Berm Density ofData

"1840 kg/m 3 or 115 lb/ft3 )-

w 0.2 -Bar Gage -, -

0.. Pretest Calculation'Flatpack Gage (Berm Density of

0.1 1360 kg/m 3 or 85 lb/ft 3 )

00 5 10 15 20

TIME (ms)JA-4015-35

V Figure 32. HEST calculations and data from the 1000-MPa"77, Iremite HEST calibration experiment,.

56

The agreement between the predicted and measured impulse is reasonably

good after about 10 ms. The impulse at earlier times does not agree as

well, possibly due to the measurement errors.

We used the calibration experiment discussed above and several

other uniform Iremite REST experiments at lower pressures to obtain a

relationship between the charge density p c and explosion pressure Pexp"

For each HEST design, we performed several calculations with different

explosion pressures and found the value that best matched the impulse

measurements.

The explosion pressures obtained in this manner are plotted versus

the as-built charge density in Figure 33 and compared with the TIGER

calculations. The agreement is very good for the l000-MPa HEST, but

differs as much as 50% for the low pressure experiments. This differ-

ence seems to be a manifestation of nonequilibrium effects at low

pressures, which is not accounted for in the equilibrium calculations of

the TIGER code. The solid curve in Figure 33 is a fit to the experi-

mental points and was used in the design of the STP 3.5A experiment.

4.2 100-MPA EXPERIMENT

The 100-MPa HEST calibration experiment consisted of a 5.0-m

(16.4 ft) square charge placed directly over the in situ soil at Fort

Knox. The explosive used was 0.085 kg/m (400 grains/ft) primacord

placed on 25.4-mm (I inch) centers. (Details of charge design are given

in Reference 5.)

Figure 34 shows a comparison between the pretest calculations,

simulation objective, and data obtained from a WES airblast gage. The

measured impulse is significantly lower (about 40%) than the calculated

impulse or the simulation objective. As shown in Reference 5, this

large difference could not be accounted for by either the edge effects

from the test bed (also discussed in Section 2.7) or by varying the

properties of the overburden or test bed materials within reasonable

bounds. The most probable cause for the discrepancy between calcula-

tions and measurements was found to be the lack of performance of the

primacord explosives used in this experiment.

57

0.6

TIGER CalculationsPUFF/TIGER Fit

to HEST Experiments0.5 - *. AFWL Double-Exponential

Fit to TAHEST

/-u- 1000-MPa HEST/4Calibration•.0.4 -" Experiment -

0

CC,uJ= /7

oC

cc 0.00 -

X 0.2/w '" /

P = P3.076 x10-6 p2 +3.83 x10-4 P// p= 10 [/38.76 +3251 P -6.23

0.1 -

TA" AFWL TA1S�-� �hES STP DEMO

00 100 200 300 400 500

"CHARGE DENSITY (kg/m 3 )JA-4015-36

Figure 33. Explosion pressure versus charge density for Iremite-60explosive.

58

0.07

200 Pretest 0.06

Calculation -. , -

Simulation 0.05160 Objective

"CL WES Data "

0.04 07

w- 120D Cn(n -Ju)n HEST Dimensions -- 0.03 D

Cr h = 50.8 mmr (2 i n.) :O. 80 H = 0.76 m (30 in.)

m = 3.36 kg/m 2 (0.7 lb/ft3 ) - 0.02Simulation

40 Objective WES Data Pretest - 0.01

0 02 3 4 5 6

TIME (ms)JA-4015-37

Figure 34. Calculations, simulation objective, and data from the 100-MPaprimacord HEST calibration experiment..

59

As a check on explosive performance, measured impulse-time histories

for three similar tests are compared in Figure 35. The highest curve is

the simulation objective for which the l00-MPa HEST was designed (left-

hand diagram in the figure). As previously indicated, the measured

impulse is lower than the objective by 40%. The ACID test has a

slightly higher overburden and only 70% of the explosive areal density,

but gives an impulse comparable to the l00-MPa experiment. The STP 2.5

test has 60% less overburden and the same amount of explosives, but

gives 50% more impulse than the 100-MPa test. This result indicates

that the performance of the primacord explosive in the lO0-MPa test was

lower than in other tests in which primacord explosive of same size was

used.

To verify the accuracy of the charge weight, WES measured the

weight of some of the primacord that was left over from the calibration

experiments. The measured weights from some of the samples were as much

as 30% lower than the manufacturer's specification of 0.085 kg/m (400

grain/ft). However, the question of what was actually used in the

calibration experiments could not be resolved because the primacord

charge had not been weighed before the experiments.

4.3 35-MPA EXPERIMENT

The 35-MPa REST calibration experiment consisted of a 7.9-m (26-foot)

square charge placed directly over the in situ soil at Fort Knox. The

explosive used was primarily the 0.085 kg/m (400 grain/ft) primacord

from the same batch used in the 100-MPa experiment. The spacing between

the primacord strands was 50.8 mm (2 inch). (Details of the charge

design are given in Reference 5.)

Figure 36 shows a comparison between the pretest calculation and

the simulation objective, and Figure 37 shows a comparison between the

pretest calculations and the measured impulse histories from nine of the

WES airblast gages. A typical pressure history (from Gage 418) is also

shown for comparison. The data shows a 20% spread and the mean impulse

is about 40% lower than the simulation objective. The discrepancy seen

60

100-MPa HEST

Calibration AFWL Acid STP 2.5

0.89 1i84090.76 1840 89 1840m kgm3: ." kg/m3 " - ---1840

r • ........ 0.46 11 4m kg. kg/m3

50.8 69.9- ' .. .952•mm - mm mm T -

3.36 kg/m 2 2.24 kg/m 2 3.36 kg/m2

I I I I100-MPa

0.10 Simulation Objective

-STP 2.5

w 0.06 -

D0-/-• 0.04 10M a AFWL Acid _

H EST Calibration

0.02

II0 I I I I

0 2 4 6 8 10 12 14

"TIME (ms)

JA-4015-38

Figure 35. Data from 100-MPa HEST calibration experiment and twoother similar HEST experiments in which 0.085 kg/m (400gr/ft) primacord was used.

61

35 ...... ...0.07

30 Calculations

0.05

25 Objective -

w0,0

cc 0E.03o

Wion

H-ESTD DimeniOns 00

10 ~h =70 mm (2.75 in.)

H =0.86 m (34 in.) 2m= 1.79 kg/rn2 (0.37 lb/f t) 0.01

50

00

TIME (ins) JA-401 5-39

Figure 36. Pretest NEST calculation and simulainojciefrte3-~HEST calibration experiment.

62

45

S40 41 S 0.035 /Pretest 41I • .•-

Calculations

"• 0 4 12 4126 20

",,,. Gage Numbers=:20 0.02 w

TIM (ins)I .2.J

HES cairtoDxeiet

w 15

10 0.01

0 " 0

-50 48 12 16 20

TIME (ms)

JA-4015-40

•" !Figure 37. Calculations and data from the 35-MPa primacord,', H EST calibration experiment.

63

here again appears to be due to the lack of performance of tne primacord

charge similar to that observed in the lO0-MPa experiment.

4.4 DISK HEST EXPERIMENT

Because of the uncertainties in the amount of explosives used in

the 35- and 100-MPa calibration experiments, results from these experi-

ments could not be used for validating the code calculations. Therefore,

WES performed another 35-MPa WEST calibration experiment, designated as

DISK HEST, in which the explosives were weighed before being placed in

the cavity. Results of this experiment are compared in Figure 38 with

one-dimensional and two-dimensional calculations. The agreement between

the data and the calculations is within the accuracy of the measurements.

4.5 RELATIONSHIP BETWEEN EXPLOSION PRESSURE AND CHARGE DENSITY

Using the procedure discussed in Section 4.1, we deduced a relation-ship between the as-built primacord charge density and the explosion

pressure based on all the calib-ation experiments after a posttest

correction was made for the ci 'rge weight and the STP 2.5 experiment

(Figure 39). Because the maa&ufacturer's specification for weight

tolerance is ±20% of 0.085 kg/m (400 grain/ft) primacord, we assumed a

20% lower charge weight to account for the lo,; performance of the

explosives in the 35- and IO0-MPa HEST experiments and a 20% higher

charge weight to account for the extra high performance of the charge in

the STP 2.5 experiment. This appears reasonable from the resulting

smooth solid curve in Figure 39 fit to the experimental points. This

curve was used in the design of the variable HEST in the STP 3.5A

experiment.

Also shown in Figure 39 are the results from TIGER calculations for

a p-imacord/foam charge and the data from AFWL C2 experiments. At a

charge density of 15 kg/m3 the effective explosion pressure deduced

from the calibration experiments is about 40% lower than the TIGER

predictions and about 251% lower than the C2 data. We believe that the

discrepancy observed here is characteristic of a HEST with a thin cavity

64

50 0.05

40 ~(Heavy Lines) --

WUt1-- 0.03 ;

cc 2 --- 0.02 wDNumbers 13,8, 7-I

0 1 2 3 4 5 6 7 80 .10TIE(is

1Z II-5 A

AFigr 380aafc h ikHS xprmn lgtstdcre)

Figur 38.Daase curve).. ikHETeprmnt(ih dcre)

65

90

80 TIGER CalcuiationsPrimar~ord with Foam .,•

AFWL C2 Experiments

to HEST Experiments 0 !

60 - F T R i

"•50 100-MPa Experiment( (-20% Charge) /

z 40 - S T P 2 .5 / , , IO ,;, •

0 (+20% Charge), S

0

x 30

20 -H

1 -/DISK HEST Experiment

0 10 20 30 40 50 60 70 80

CHARGE DENSITY (kg/m 3)

JA-4015-42

Figure 39.. Explosion pressure versus charge density for primacordexplosive.

66

(less than 100 m, say). In such a HEST, the jetting between the

explosive strands tends to penetrate into the soil that surrounds the

cavity, thus dissipating part of the explosive energy. The net result

is a loss of impulse delivered by the charge, which is represented by a

lower effective explosion pressure in Figure 39. This conclusion is

also supported by the HPC 2 experiments reported in the Appendix.

Regardless of the actual reasons for the lack of agreement with

TIGER calculations or C2 experiments, the solid curve in Figure 39

represents the combination of measured explosive density in the as-builtexperiment and the explosion pressure required to give the best match to

the measured impulse history. This result was therefore used in

conjunction with the one-dimensional calculations to design the STP 3.5A

variable HEST discussed in Section 5.

.4

I67

SECTION 5

STP 3.5A MAIN EVENT

In this section, we first discuss the layout of the test bed and

then evaluate the performance of the variable HEST by comparing the

simulation objective with the data from the airblast and near-source

stress gages.

5.1 OVERALL TEST BED LAYOUT

The overall layout of the STP 3.5A experiment is shown in Figure

40. The location of the perimeter of the HEST was specified by ARA. 9

The central strip covers four structures as shown. Iremite (denoted by

I) was used in the closer ranges of the central strip (down to 23.2 m or76 feet) and in the side (down to 39.4 m or 129 feet). The angle of the

side zones was chosen to be 22.5* relative to the central zones so that

the length of the side zone at the 35-MPa range is normal to a radius

from GZ through the center of this zone.

The variation with range R of the explosive areal density m and

the cavity height h were obtained from the conceptual design shown in

Figure 27 and the explosi3n pressure-charge density relationship shown

in Figure 39. The curves of m versus R and h versus R were then

discretized into zones of constant m and constant h. For ease of

construction, all zone widths were chosen to be multiples of 1.22 m

(4 feet). The zones over the structures (zones 13P, 15P, and 21BP) were

selected to be at least 2.44 m (8 feet) wide and centered over the

1.22-m-diameter (4-foot) structures. The remaining zones were chosen to

reasonably approximate the m versus R curve.

For each zone, the primacord spacing was calculated according to

the explosive areal density required in that zone. A similar procedure

was used for selecting spacing for Iremite-60 explosive. The cavity

height for each zone was chosen to be a constant and a multiple of

6.35 mm (0.25 inch).

68

(60 ft)

BLESTField

12.2 m 0 RadialG@ (40 f t)E

0. 0.a. 0.A.0c. 0.0A. 0. 0. 0.0

0

18.3 m(60 f t) A

0 2 40 60 0 10 10 10 10 1 0 200

RANGE/ft)(1i 1211

0 10 20 30 40 50 60

RANGE (in)

JA-401 5-43

Figure 40.. Layout of striptest and STP 3.5A HEST experiments.

The parameters calculated for each zone are shown in Tables I

and 2. In most zones, the explosive was parallel to the zone length

("circumferential"). In zones 13A through 15P, the explosive was

parallel to the zone width ("radial") so that the load ran over the

structures at the detonation velocity of the primacord (6100 m/s), which

is approximately equal to the air shock velocity of the airblast

environment at these ranges. The primacord in zone 21BP was oriented as

shown so that the load swept the structure at a velocity of about 3050

m/s, which is approximately the air shock velocity of the airblast

environment at this range.

5.2 DATA FROM AIRBLAST GAGES

Twenty airblast gages (8 over the structures and 14 in the free-

field) produced usable waveforms. Figure 41 compares the airblast data

(solid lines) with the simulation objective (dashed lines) over 10, 20,

and 100 ms time windows. The distance from ground zero is given at the

top of the plots for each of the gages.

Except for Gage AB-3, which shows an impulse about four times lower

than the expected values at this range, the remaining 21 airblast gages

compare reasonably well with the simulation objective. There appears to

be a late-time cavity flow caused by the horizontal pressure gradients

in the cavity. This flow is manifested as low-amplitude ripples visible

on some of the pressure records at late times. An example of cavity

flow can be seen in the data from gages AB-I or AB-9. A good match with

the simulation objective is obtained in the 20-ms plots. At about 20

ms, the measured impulse rises above the simulation objective due to the

arrival of a pressure ripple, signalling the passage of a compression

wave from the upstream higher-pressure zone.

The overall performartce of the simulator can be assessed by

plotting the impulse measured by a gage at a given time versus the gage

location. Figure 42 shows the impulses measured from the airblast gages

at 5, 10, 50, and 90 ms after the time of shock arrival. For ,omparison,

the simulation objective is shown as the solid line with the 13% band

70

Nn 0 U, , U, Ln F, LM LM 0 ~O U 0 Mn

416

A N N .4 4 .4 -1 - -. -. -. -. -. - . % '.

0

0. i4? N .. 4 n C 0.4 m0 NW en ' r- N tn MO 4?

0 ' 0 ? ,a'.4 0m ? ' N Lm in N a' U, .4 a ? , 4? ý4

C4 U %D. '0.4 '4 N V, , W U, ' 4? F- N tn N l -2 0.4.4.

r 0 1 0 N a' P4 r% 8 a'N .40 Ch LM Ma' U, 4 U,

0' ' . _ _ _ _ _

U, Xe .0 a' 4 n &I ON ' N O 4A) 'j? 0 M ' 0 4 N ? 0a 4U 0 N 0 U

v 0 - n en 44 . .4 4 4 4. .4 N N e MO

* ~ (~qU SZT Uj U,1, N 000 N0 , N N N

0

'0W 4 0 '04 4 0 0 0 N N; N n a1' a 'a'a 'a '

-TS 0 0 P N Nmm m .4 l10 r w w N N D

km I LA LO 6n '04 '0 'n0 '0.4.4.4.M 4 '0

.4. .4. 4. LM... .4N N N N ene ne

1-1. U, a' M N ., U, V' en Ns -4 U, a, CO O N n 4h' 0 e

61 .4 4 ?U U,' '0' N N '0 a .. 4 .4 .44 4 .4 A 4 A N

" 'n a, m 4, '0 V0 0 en U, "N U a' , C.. en ' ? a n ' -n

r n 4 ? '0 N Wa . Nen V? U, DN, W O 4? ' ay4 , a' a

E34. . N' NM N N? M M W MM It4W? U,

a; 0P1 A 9 A (1a

al4 CL 91, -4 C44 ow CL. CL 0. P.. 0. .0 0. 0.. m. w CLU,~L rL N a' 0 NM 4 U, 0 Nw a, 0 C14

71

.0 ~ ~ ~ ~ ~ % in4~0 0 E' . .. N ' ,U M r44 N d 4 0 0.4 N N N - 4 4 -- -- -. -. -. -. *

0

be 4 0; V; N z N ý .- ; A. C.4 I

4.4~ ~ ~~ U,0 ý % N 4 E4 .4 00 0 UN N N .

o0u , NV Nn .1 .4 . 4 0 0 0 00 0- 4 S.. S. 4 S. ' S' S ." S' S' ' S' . . .

0N1 .00. '0 .0 .-4 TNOa '00 0% NO %

00

N

w

a,

N N 4 .4ý

20 0- -

v4 u

.0l~ . 4.. 4 .4 U, A, 4 A

-40. . 4 N 0 N N CU, 444,U '0 0 0 00 N N V N C-% 4

m. m% .0. N LA '0 N 44 4n uN N N0 .0.0 U '0.4.0

C4 - - - - - -Q 40 4 N 0 40 UU N 4 U U 4 . NM

- U, -4. '0 N -0 0 -4 -, -, U 0 N.434 . '4 . .4 N ,.

in ~ _n tn Ln an va an an ai an an v

-'~ ~~~ -, U a U , U , U, U , U ,

U, W ,U ,N N 0 0 N N N Ur.. " HC4 Hý ý

>.&4*i .4 4m . . N' N0 Nl Nn N, N7 N N N4. -c -. -i - -. -. . . . . . . . . . . S' S . ~ .

'-472

R =22.3 m (73.1 ft) R 26.5 rn (87 ft)

80 AB-9" 0.08 80 0.08

"40 0.04 " 40 .: 0.04

S"------• 0

0-0 0 0 i.1

2 4 6 8 10 12 3 5 7 9 11 13

TIME (ms) TIME (ms)

80 -------- 0.16 80 AB-1 008

60 AB-9 0.12 60-- -- /S -- 0.06

-40 .0.08 M 40 0.040

3AS-2 ----20 . 0.04 20--J/- -- -- 0.02

00 000 4 8 12 16 20 0 4 8 12 16 20

TIME (ms) TIME (ms)

80 -.1 80 6AB-9 jAB-1

60 0.12 60 - 0.12

4- 40 -- 00.08 .08240 0:•AB-2 0.08 0,•"

20 •/0.04 20 1Y _B3--I• 0.04

0 0 ' 0

0 20 40 60 80 100 0 20 40 60 80 100

TIME (ms) TIME (ms)

JA-4015-44

Figure 41. Airblast data from STP 3.5A experiment and simulation objectives(dashed lines)..

73

R =29.7 mn (97.4 ft) R =31.9 mn (104.6 ft)

80 0.08 80 00

~40 0.04 Am 0- 40 -0.02 '0C00 0 - - -

3 5 7 9 11 13 3 5 7 9 11 13TI ME (ins) TIME (ins)

80 0.08 80-----------08

60.660 -- 0.06

40AB-17 0.04k m -40--- --- 0.4o

20.220 - - - - - - 0.02

0 4 8 12 16 20 0 4 8 12 16 20TIME (ins) TIME (ins)

80 -AB-11- 0.16 80------------0.16

60------------0.12 60-----------0.12

CL40 -- AB-17- 0.Cn M 4 a-.~ 4000

20~ ~-- - 0.04 20 0.04

2 0 1------00

02040 6080 100 0 2040 6080 100-'IM E (ins) TIME (ins)

JA-401 5-45

Figure41.. Airblast data from STP 3.5A experiment ;1nd simulation objectives(dashed lines)., (Continued),

74

R = 38.7 m (127 ft) R = 41.8 m (137.3 ft)

0.06 1 1 1 1 140 80 1 1 11 " 0.04

a- 20 ,0 40 0.02

0.020,0 0

710, 4 6 8 10 12 14 5 7 9 11 13 15

TIME (ms) TIME (ms)

- ~I-------80 -0.08 80--- 0.04

60 - - - - - - 0.06 60-- 0.03

" 40 A0.04 0 . 40 0.02 m.

20 -- 0.02 20 , 0.01

00 0 0-- V0 4 8 12 16 20 0 4 8 12 16 20

TIME (ms) TIME (ms)

80- - - - - 0.16 80 -- 0.08

In60 0.,12 60 • "0.06

40 - 0.08 .40 ,-0.04

20 0.04 20 0.02

0 ... .. 0 0 i 0

0 20 40 60 80 100 0 20 40 60 80 100

TIME (ms) TIME (ms)

JA-4015-46

Figure 41., Airblast data from STP 3.5A experiment and simulation objectives(dashed lines). (Continued).

75

R = 44.6 m (146.4 ft) R = 47.9 m (157.2 ft)

A" I I. I 0.030 , 4.. .

20i20 0.04

..r I 1 0.020 10I. 0I" II.. " -" .2 •10- 10M. 100020

0.010 AB-19--0 . 0

0 t 0 0.

6 8 10 12 14 16 7 9 11 13 15 17

TIME (ms) TIME (ms)

40 - - -0.04 40 -I 0.04-AB-4 1

30- - - -0.03 30 - -- - 0.03I --. O2

0 0 - 0.0

0 4 8012 16"20 0 4 81 2162 20TIME (ins) TIME (ins)

40----- 0.08 40 0.08

""" I0 1 0 0 4081206L 2

20 0.02 40 24B-69 0.04tit ..1; -,- 0.02 10 /I0.02

"20 /004 0. E #,0

0 20 40 60 80 100 0 20 40 60 80 100

TIME (ms) TIME (ms)

JA-4015-47

Figure 41. Airblast data from STP 3.5A experiment and simulation objectives(dashed lines). (Continued)..

76

R 51.1 m (167.7 ft) R = 52.6 m (172.5 ft)

0.030 1 1 1 120 2020 20 =l :0.020

0.02010 L 10 0.010 .

0.0100 0 0-o

8 10 12 14 16 18 8 10 12 14 16 18TIME (ms) TIME (ms)

16 -- 0.04 16 - - 0.04

12 0.03 12 - 0.03• ~I - ,

8- 8 0-.0 0.02 .

4 0.01 4 0.01

0 0

0 4 8 12 16 20 0 4 8 12 16 20TIME (ms) TIME (ins)

16 0.08 16-- - 0.04

12 0.06 12 --- 0.03

C- 8 0.04 o! (- 8 0.02 , L

4 .•/ 0.02 4 0.01

011 0z0 0

0 20 40 60 80 100 0 20 40 60 80 100TIME (ms) TIME (ms)

.A-4015-48

Figure 41.. Airblast data from STP 3.5A experiment and' simulation objectives(dashed lines). (Concluded)..

77

0.20 1 1 1 1 1

* Freefield Airblasto Structure Airbiast

0.15

__ Simulation Objective0.10 ±15% Lines

0~

C.0.05

(a) 50 ms (b) 90 ms

0.201 -4

Fiue4.Iplevessrnefo.1r5s aeriauriet nSP35exeietadsmltobe~v t5 0 0 n 0m fe

sh ockarvalie

U. 78

above and below the simulation objective shown as dashed lines. The

data points are seen to mostly fall within the 15% band for each of the

time windows, indicating satisfactory agreement with ihe simulation

objective at all times and ranges.

5.3 DATA FROM NEAR-SURFACE STRESS GAGES

A similar ;onclusion is reached when the simulation objective is

compared with the data obtained from the soil stress gages placed near

the surface of the test bed. Figure 43 compares the simulation objec-

tive at the 28.4-m range and the impulses measured by all the horizontal

and vertical stress gages that were fielded at this range to a depth of

about 0.6 m (2 feet) below the test bed. Result i from the airblsst

gages placed at the same ranges are also plotted for comparison. The

horizontal and vertical stress measurements are virtually identical,

indicating a sta.e of hydrostatic loading of the soil. A good corre-

lation of stress and airblast measurement is elso foand. Within the

experimental errors, the measurements agree with the simulation

objectives. Also, the impulse histories measured by gages 3-1 SV,

3-2 SV, and 3-3 SH uider a primacord HEST are ident._al (to within the

measurement errors) to those measured by gages 8-1 SV and 8-2 SV, which

were placed under an equivalent Iremice HEST. This sh^ws the

consistency of the procedures vsed to design the HEST.

?igure 44 compares the measurea impulses at 10 and 90 ms with the

simulattoi objectives. Again, thte data suggest a reasonable agreement

w;,.n the simulation objective at all times and ranges. This conclusion

also conckirs with the data from 'he photopoles presented in Figure 45.

5.4 CONCLUSMONS ON THE SIMULATOR PERFORMANCL

The HEST simulator for the 3.5A event was designed to produce the

overpressure environment from a l.95-kt nuclear surface burst for the

overpressure range of 500 MPa (5 kbar, 72,000 psi) ti 7 MPa (1000 psi).

Based on photopole, airblast, and near surface soil stres:, sage data,

the impulse from the REST agreed, to within measurement error, with the

79

90 - 0.18f 13-1 SVI80 --- -s- -- - -\ ~803-3 SH 0.16,

I0 I Ab-17GAGE NUMBERS 8-i SV

70 3- ,2 0.14AB-1I ., 8-i.SV --- : _

6u1 1 .

c 50-••---• ,. t'• 0.10

W;/ Simulation DC. 3 Objective0.6_.

4/.

20 0.04

10

-10 -0.02

0 20 40 60 80 100

TIME (ms)

R =28.4 m (97.9 ft)JA-4015-50

Figure 43. Simulation objective and airblast and near-surface soil stress gage

measurements in STP 3.5A experiment. (Gages 3-I SV, 3-2 SV,and 3-3 SH were located under primacord HEST, and gages 8-1 SVand 8-2 SV were under an equivalent Iremit- HESt.)

80

0.20 1 I l[ S Free-field Airblast

I \ I Structure Airblast

0.15 0 Backfill Soil Stress

U Near-field Soil Stress

Simulation Objective0. 10 ± ±15% Lines

0.05 "

( (a) 10 ms

w- 0.20 \

0.15 Z\ zZ\••>.

0 .10N ,

Simulation Objective

±15% Lines

o -I I

10 20 30 40 50 60

RANGE (m)

(b)JA-401 5-51

Figure 44. Simulation objective and impulse versus range from airblastand near-surface soil stress gage measurements in STP 3.5Aexperiment at 10 and 90 ms after shock arrival time.

81

0.20

Simulation Objective

05 -- t - 15% Lines

0.50 Photo Poles

0 Polystyrene Poles

'" 0.10

0.05

0 I I I10 20 30 40 50 60

RANGE (m)JA-4015-77

Figure 45. Photo pole total impulse versus range compared tosimulation objectives at 90 ms.,

82

design goals for both short (10-ms) and long (90-ms) times. Hence the

full positive phase cf a 1.95-kt sutface burst was successfully

simulated by the HEST.

The above conclusion also represents the concensus of the

Simulation Working Group involved in the Silo Test Program. 6

83

REFERENCES

1. L. Seaman and D. R. Curran, "SRI PUFF 8 Computer Program for One-Dimensional Stress Wave Propagation," SRI International FinalReport on DNA Contract No. DAAKlI-77-C-0083 (August 1978).

2. T. Cooper, "A Computer Code for Numerical Simulation of Shock Wavesin Fluids and Solids," SVEDEFO Report No. DS 1980:16 (December1980).

3. M. Cowperthwaite and W. H. Zwisler, "TIGER Program Documentation,"SRI Publication No. 2106 (January 1973).

4. E. L. Lee, H. C. Hornig, and J. W. Kury, "Adiabatic Expansion ofHigh Explosive Deconation Products," Lawrence Livermore NationalLaboratory, Livermore, CA, UCRL-50422 (1968).

5. R. J. Port, "STP HEST/BLEST Quick Look Report," R&D Associates,Marina Del Rey, CA (4 October 1982).

6. Waterways Experiment Station, "Quick Look Report on Silo TestProgram 3.5A Event, Volume I: The Test Environment" (March 1983).

7. J. R. Bruce and H. E. Lindberg, "Interpretation of AirblastSimulation Tests," SRI International Final Report on DNA ContractNo. DNAO01-80-C-0059 (January 1982).

8. Don Simmons, "Draft Report on Pressure-Yield EstimationTechniques," R&D Associates, Marina Del Rey, CA (January 1984).

9. J. Shinn, ARA, private communication.

84

Appendix

CHARACTERIZATION OF HEST EXPLOSIVE CHARGEIN HIGH-PRESSURE CYLINDRICAL CALIBRATOR (HPC2 )

INTRODUCTION

To evaluate and characterize the performance of various explosives

in HEST experiments, we- designed and constructed a high-pressure (up to

500 MPa) expanding explosives chamber. Explosives to be tested are

placed inside a thick-walled steel cylinder, and a piston is inserted

from each end to confine the explosive products after detonation. The

displacement histories of the pistons are measured either photographi-

cally or by time-of-arrival (TOA) pins. The initial explosion pressure

is then inferred from one-dimensional calculations that match the piston

displacement.

We used the above facility, designated as HPC 2 (for high-pressure

cylindrical calibrator), to determine the relationship between the

charge density and the effective explosion pressure of a primacord

charge as used in the STP 3.5A experiments. In particular, we inves-

tigated the apparent lack of performai.ce of a HEST charge due to the

penetration of the explosive products into the soil pores.

EXPERIMENTAL SETUP

Figure A.1 shows an overview of the HPC2 facility with typical

dimensions shown in Figure A.2. The ptstons and cylinders were con-

structed from high-strength stainless steel. Figure A.3 shows a set of

four quartz TOA pins used to measure the piston displacement and Figure

A.4 shows a typical oscilloscope trace from the TOA pins. The piston

arrival is indicated by a sharp drop in the signal to about -40 volts.

85

10

142

* NC.)

0.

.0

0L.

8,

MovablePiston 0.1/b m of 21.29 g/m (100 grain/ft) Primacord

Thick-wall PC 30.1 kg/m3Steel Cylinder

1----609.6--I ToDetonation

Unit

t56.15 - __

157.7 ID -

OD ___

50.8

(a) Primacord Charge25.4 25.4

(Dimensions are in mm) JA-4015-1B

Figure A.2. Schematic of high-pressure cylindrical calibrator (HPC 2 ).

87

I',

1..I 0LA* C03E-a.LA

* -0>0

El00

pI.-.

I-

NICOLET SCOPE - 2 Ms/pt.,

10 Pin #1 Pin #2 Pin #3 Pin #4r Detonation 25.4 mm 50.8 mm 76.2 mm ,101.6 mm

/(0 ms) P(2888 ts) (4366 js)/(5622 ps) (6740 p,)

.- 1

S-20

-30

-40

-50

0 2 4 6 8 10TIME (ms)

JA-4015-54

Figure A.4. Typical oscilloscope trace from a set of four TOA pins.

89

BACKGROUND CALCULATIONS

We used the SRI PUFF hydrocode to calculate the cavity pressure and

piston displacement time histories for the setup shown in Figure A.l.

Because PUFF is a one-dimensional Lagrangian hydrocode, the effects of

mixing of the explosive products or leakage from the explosive chamber

are not included in these calculations.

Figure A.5 shows the calculated cavity pressure as a function of

time for five explosion pressures ranging from 14 to 30 MPa. The cavity

length is 50.8 mm and the piston length is 304.8 mm (Figure A.2). The

pressure waveforms have rounded peaks because of the piston inertia.

The peaks become sharper with increasing explosion pressures.

The piston displacements calculated for the same five explosion

pressures are shown in Figure A.6. The same results are shown on a log-

log plot in Figure A.7. The displacement-time histories on the log-log

plot form nearly a straight line with a slope of about 2. These plots

facilitate the match with the piston arrival times measured in the

experiments and were used to estimate the effective explosion pressuresof each charge.

"The explosive products in the present calculations are treated as a

perfect gas. Figure A.8 shows a log-log plot of the cavity pressure

(normalized with respect to the initial pressure) as a function of the

cavity volume (normalized with respect to the initial cavity volume) for

two values of the specific heat ratios of y - 1.1 and y - 1.2. The

pressurp-volume relationships are found to be straight lines with slopesvery nearly equal to the y initially specified in the calculations.

This indicates that the explosive products expand isentropically for the

pressure ranges considered (below 40 MPa).

The sensitivity of the calculated piston displacement to the choice

of y is shown in Figure A.9 by plotting piston displacements for the

same two cases of y = 1.1 and y 1.2. The two curves are virtually

identical, although the pressure that drives the piston is proportional

to y - 1, and y - 1 changes by a factor of two (from 0.1 to 0.2) in the

90

4

"30.0

InitialExplosion

25.0 Pressure

30 MPa

26 MPa

, 20.0 22 MPa

K 18 MPawc.Jc 14 MPac/)

wu 15.0

I-aI..

< 10.0

5.0

0 2 4 6 8 10

TIME (ms)JA-4015-55

Figure A.5., Cavity pressure history for five initial explosion pressures.

91

140

120

E

-- 100I--

z

-J 80

0..

0 6 0

0

40

20

0 24 6 8 10TIME (ms)

JA-401 5-56

Figure A.6. Piston displacement history for five initial explosion pressuies.

92

120

,100 e

90.J 80-/-

E 70

I-z 60w

< 50-JAC

z 400U,a-

30

20 ,/iI1

2 3 4 5 6 7 8 9 10

TIME (ms)JA-4015-57

Figure A.7., Piston displacement history for five initial explosion pressures(log-log plot).

qq

100

90

80

70

60 -#21

E 50 - ' 1.10°"•,/'

E #3

C.)wwI. // 1.20Uz 40W

-J 30a.

z0

20

* I.-

10 I , I I

1 2 3 4 5 6 7 8 910

TIME (ms)

JA-4015-59

Figure A.9, Piston displacement histories for two values of the specificheat ratio, .

two calculations. This indicates that the explosion pressure estimated

on the basis of the piston-displacement is not sensitive to the choice

of y used in the PUFF calculations.

EXPERIMENTAL RESULTS

We uied the HPC 2 facility to investigate the effect of various

field parameters on the HEST performance. Figure A.1O shows the

schematics of the experiments performed to determine the effective

explosion pressure from (a) primacord charge in an air cavity, (b)

primacord charge in a foam cavity, (c) primacord charge next to v asnd

column, and (d) prir-acord charge next to a capped sand column. lie

experiment with the sand column was performed with both wet and d&y

sands.

Figure A.11 shows the picton displacement histories measu:.d for

the configurations shown in Figure A.10. The explosion pressures

requi.ed in the PUFF calculations to match the measured displacement

histories were found to range from a maximum of 28.5 MPa for the

primacord charge in an air cavity [configuration (a) ir Figure A.1O] to

a minimum of 18 MPa for the primacord charge next to a dry sand column

[configuration (c) in Figure A.10.

"Figure A.12 compares the maximum and minimum explosxon pressure

"measured in the present Axperiments with the explosion p. ssure/charge

density relationship used for the design of the STP 3.5A experiment

(Figure 39). The present data roughly span the results of the TIGER

calculations and the fit to HEST experiments. This comparieon suggests

that the field parameters in HEST experiments are responsible for the

discrepancy observed between the expected explosion pressure (from TIGER

calculation and C2 experiments) and the effectiw explosion pressure

inferred from the calibration experiments.

CONCLUSIONS

The data presented here indicate that the performance of a HEST

charge (represented by its effective explosion pressure) depends not

"96

0.178 m of 21.29 g/m (100 grain/ft) PrimacordPC = 30.1 kg/m3

9 NI ToDetonation

I jj Unit56.15

157. ODID157"7D II 50.8

(a) Primacord Charge

25.4 25.4

50.8

(b) Primarc.ord in 16 kg/r 3 Foam

Sand Column 3-mil Mylar

,•,50.8 50.8

Wc Primacord with Sand Column

[ [ Sand Column Aluminum " ]Cap

50.8 50.8

(d) Primacord with Capped Sand Column

All dimensions are in mm. JA-4015-1A

Figure A.10. Schematic of charge calibration experiments.

97

120

100 A

90

80 -8A ¢,

E 70E One-DimensionalI- PUFF Calculationsz 60-,/-

< 50o-

_ DATAz 40

z 40 + Primacord in AirCavity

P r("L• z Primacord in Foam30b Cavity

00 Dry Sand Column30 / oo Dry Sand Column

t, Moist Sand Column,, v v Dry Sand Column

with Cap

202 3 4 5 6 7 8910

TIME (ms)JA-4015-60

Figure A.1 1., Piston displacement histories measured in HPC2 experiments.

98

90

80 .. . TIGER CalculationsPrimacord with Foam ,o,

AFWL C2 Experiments

70 PUFF/TIGER Fit --

to HEST Experiments ^

. 60

W/

u) 50 - 100-MPa Experiment /.U (-20% Charge) /

z 40 STP 2.5 /0 (+20% Charge)/ /0- I /

X 30 (28.5 MPaW I Data from

HPC2 'ILExperiments I , I MP20 1E!.0 MPa l

/ DISK HEST Experiment

* / . --- 35-MPa Experiment/ (-20% Charge)

00 10 20 10 40 50 60 70 80

CHARGE DENSITY (kg1'm3,

JA-4015-42A

Figure A.12. Data from HPC 2 experiments compared with TIGER calculationsand the fit to HEST calibration experiments.

only on the charge density but also on other field parameters such as

the presence of foam in the cavity or penetration and mixIng of the

explosive products with the soil surrounding. We can also infer that

the data obtained from conventional C2 experiments or TIGER calculations

provide only an upper bound to the performance of a REST charge because

they do not account for the field parameters mentioned above.

The results further indicate the necessity of REST calibration

experiments, such as the DISK REST, or C2 experiments nimilar to those

discussed here so that the charge perforwance data used to validate and

adjust the HEST design calculations are obtained under realistic field

conditions.

100

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