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EXPLOSION AIRBLAST PROGRAM ”BLASTO”, FOR WEATHER-DEPENDENT PREDICTIONS ON A
PERSONAL COMPUTER
J. Reed
To cite this version:
J. Reed. EXPLOSION AIRBLAST PROGRAM ”BLASTO”, FOR WEATHER-DEPENDENT PRE-
DICTIONS ON A PERSONAL COMPUTER. Journal de Physique Colloques, 1990, 51 (C2), pp.C2-
1193-C2-1196. �10.1051/jphyscol:19902280�. �jpa-00230613�
ler Congres Franqais d'Acoustique 1990
EXPLOSION AIRBLAST PROGRAM "BLASTO", FOR WEATHER-DEPENDENT PREDICTIONS ON A PERSONAL COMPUTER
J . W . REED
JWR, Inc., 5301 Central Ave. N E , Suite 220, Albuquerque, New Mexico 87108, U.S.A.
Abstract
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An airblast prediction program for explosions, called BLASTO has been written for use with IBM-PC (or compatible) computers, to produce overpressure-distance curves for a variety of interactive input conditions. Several common units are allowed for each input, but calculation and output are in SI metric units. Explosion yield (chemical or nuzlear) and ambient atmospheric pressure are used to generate a referenced 'Standard' overpressure-distance curve. Explo- sives may be point charges at any height above ground or depth below the earth surface. Buried charges may also be distributed in a sheet, or 'HEST' configuration, but a mining model for a number of point charges with firing delays has not yet been developed.If upper air weather data or forecasts are available, they can be used to generate directed (wind effects) sound velocity versus height structures which are interpreted to give attenuated or enhanced over- pressure-distance curves. These are calculated for incremented direc- tions around the compass or toward specified targets or communities.
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INTRODUCTIONPredicting atmospheric influences on explosion airblast propagation has evol- ved from a two-hour process of number-punching on an electro-mechanical desk calculator in 1951 / I / , through analog computer processing 1 2 1 in about 15 minutes with five 3-m relay racks of electronic components, for atmospheric nuclear tests from 1 9 5 5 to 1 9 6 2 , to general assessments of atmospheric struc- ture which can be made on a programmable pocket calculator that allow quali- tative safety conclusions. Detailed numerical evaluations for expected dam- age still require main frame computations for yield-scaled overpressure-dis- tance curves and bookkeeping functions of damage assessment for the distribu- tion of neighbors around a typical explosion test site 1 3 1 . The recent pro- liferation of desk-top personal computers, with large memories and user- friendly operations, now makes feasible a relatively complete airblast pre- diction program, BLASTO, that is transportable by floppy disk to any PC that is IBM-compatible and uses the MS-DOS operating system.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19902280
COLLOQUE DE PHYSIQUE
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PROCEDUREBLASTO begins with an input explosion definition, considers the burst envi- ronment and its effect on airblast source strength, and generates several typical overpressure-distance curves for various weather effects At this point in planning exercises it is possible to tell whether weather needs to be watched during a countdown. If so, input weather data are used to show directional refractive enhancements or attenuations of airblast propagation with expected overpressure-distance curves for incremental or targeted direc- tions. From these, an off-line estimate of damage may be made for each com- munity of concern. Diskette copies of BLASTO, along with necessary instruc- tions and input-output examples, are available for field test evaluation.
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COMPUTATION MODELA flow diagram for BLASTO is shown in Figure 1. An input explosion defini- tion consists of a yield, W, in any of several units for selected explosives, and an environment, a location, elevation, and height-of-burst (HOB). HOB may be zero for a surface burst, positive for an airburst, or negative for an underground burst. Certain distributed buried charge configurations may also be used, when simultaneously detonated. The positive HOB function shown in Figure 2 141 begins with a 2-W apparent yield value for a surface burst, curves up to 5.6-W at optimum HOB, and reduces to a free-air burst 1-W value above 5.4 m for 1-kg HE. Source strength for buried charges depends on the amount of overburden per unit of charge weight 151, as shown in Figure 3.
Ambient pressure at the burst is obtained from a weather report, if avail- able, or from the Standard Atmosphere 161 and elevation.
Apparent yield (free-air burst) is then used to scale distances 171 in calcu- lating a Standard /4,8/ overpressure-distance function. Typical weather ef- fects on propagation include attenuation by upward acoustic refraction as shown in Figure 4 , enhancement by acoustic ducting, and amplification by focusing in complex atmospheric conditions as shown in Figure 5. Empirical functions were derived 191 for simple sound velocity versus height conditions where the overpressure-distance decay ratge depends on the increase or de- ,
crease of sound velocity between the surface and a yield-scaled height about 40 m above 1-kg HE, as shown by Figure 6. When there is focusing, focal dis- tance cannot be accurately predicted because of its great sensitivity to mea- surement and turbulent errors in defining sound velocity. For those cases, the envelope of overpressure in Figure 6 contains about 90% of the relatively few data points that have been acquired from tests. The world record focused overpressure magnification of 9.6-X was found during French sonic boom tests
1101. A window damage threshold was established by incidents from atmospher- ic nuclear tests 121.
Input weather data requirements are for pressure, temperature, and wind vec- tors to such altitudes as may cause propagation problems /I!. Sound speed depends on air temperature, and directed sound velocity is the sum of sound speed plus the directed wind component. Vertical structure of directed sound velocity then determines the airblast overpressure-distance curve expectation for that direction. This is as far as BLASTO goes at the present time.
Damage prediction requires another empirical approximation., for window damage probability versus incident overpressure 141 derived from accident analyses / 1 1 / , as shown in Figure 7. Window surveys or estimates based on population census values give the number of exposed window panes, which are multiplied by appropriate probabilities to give the number of broken panes. This may or may not frighten test management into calling a delay for better weather.
These manipulations will eventually be included in BLASTO to compute expectations for numbers of broken panes.
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FUTURE MODIFICATIONSPlanned expansions for BLASTO include detailed damage and hazard evaluations, pending final analyses of glass breakage tests at MISTY PICTURE, a large ex- plosion test at White Sands Missile Range in 1987 1121. For countdown
1 1 4 1 . One really needs to know, when conditions look agood, how close the weather may be to causing a serious incident. Or, when conditions look bad, how much diurnal or statistical change is needed to make a test safe.
Finally, in response to recent requests, a source model for underwater bursts is planned. There has been no attempt to generate graphic outputs, since each PC installation is likely to have its own graphics capability and sys- tem. A choice is presented, however, between immediate output to a terminal or creation of an output data file which may be read and rewritten in a local format for graphics preparations. We welcome comments or suggestions about other specific useful modifications to this program.
Fig. 1
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Computation flow chart for BLASTO Airblast Predictions.OVERBURDEN FACTOR (Cu.fI.nb HE)
Fig. 3
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Reference overpressures( 9 1 4 m from 1 8 Mg HE) vs *overbur-
den factors for buried explosions.
Fig. 2
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Explosion height-of-burst effect on apparent airblast yield.T E M P O U N E A N D
SWND SPED Dl-
X C
3
BlnAw S W N D SKED
P i g . 4
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Blast wave distortion byatm'ospheric refraction.
COLLOQUE DE PHYSIQUE
W
2
F2
RANGE
Fig. 5
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Typical explosion ray paths under complex conditions.Legend
M a i n
!'9:!% ...
P1.9.!!: ...
?5.?.q:'1. ...
E'S!!: ...
x PlRECI CouL.%
V LII!N!?RS.C^!E..
DISTANCE (kilometres) OVERPRESSURE (kPa)
Fig. 6
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Overpressure vs distance Fig. 7-
Window damage probability curves, 1-kt NE airburst standard vs incident airblast overpressure.explosion, in various atmospheric conditions.
REFERENCES
Il/ Cox, E.P., Plagae. H.J., and Reed, J.W., Bul. Amer. Meteor. Soc.
35 (1954) 95.
/ 2 / K x , E.F., and Reed, J.W., US-AEC Weapon Test Rep. WT-303 (1957).
1 3 1 Reed, J.W., Sandia Lab. Rep. SC-RR-69-572 (1969).
/ 4 / Am. Natl. Std. Inst., ANS1 S2.20-1983, Acoust. Soc. Amer., (1983) / 5 / Reed, J.W., Proc. MABS-8 Symp., 1, 1983.
161 NASA, USAF, and USWB, U.S. standard Atmosphere, 1962, USGPO.
1 7 1 Glasstone, S. (Ed.), The Effects of Nuclear Weapons, Rev. Ed.,
USGPO, (1977).
181 Needham, C.E., Havens, M.L.. and Knauth, C.S., USAF Weapon Lab.
Rpt. AFWL-TR-73-55 (1975).
/ 9 / Reed, J.W., Min. 19th DOD Explos. Safety Sem., (1980).
1101 Wanner, J.L., Vallee, J . , Vivier, C. and Thery, C . . J. Acoust.
Soc. Amer.
52
(1972).1111 Reed, J.W., Pape. B.J., Minor, J.E., and DeHart, R.C., Ann. N.Y.
Acad. Sc. 152 (1968) 565.
1121 ~ i l l i n ~ h a m 2 . A . (Ed.), Tex. Tech. Univ. Rep. (1987).
/ 1 3 / Reed, J.W., Sandia Lab. Rep. SAND 79-0626 (1980).
