Operation Castle - Project 1.3, Report to the Scientific Director Dynamic Pressure Measurements

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This report i& o_rjeof the reports prswntlq the results of the 34 projects included six test -deixxtione. Tests Program of Operation Castle, which For readers interested in other pertinent tast information, reference is made to m-934, Smmary of Weapons Effects Tests, Military Effects Program. This summa tion of possible general Interest: (7 report includes the following infome1 an overall description of each detoration, including yield, height of burst, groud zero location, time of detonation, ambient atmospheric conditions at detonation, etc., for the six shots: (2) dfscussion of all project results; -(3) a sumary of each project, includin;: tives and results; and (4) .: complete listing of all reports covering the objec-

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The objectivee 2f FYoject 1.3 were to spotAmck the theoretical relatiorishlp between vc pressure and overpreasure in the lO-to-400 pal overpremire range and to evaluate (L group of gagea manuring various The one mwsurenent of me premzre la Shot 6 agreed vith that implied by the cmrp~emure; in thir cane the shock bad traveled 800 feet over laad lma&.ate~~ before reaching the gage, In Shot8 4 and 5 meame&s of me pr@&re bjr the gage gmup vere all !Qh; in this case the gages wre neaz--+A&watqr’e edge. These latter recoils alao alaed peculiar waveform, lndica!tig that the shock had picked q~ water and/or The force plate and Wiity gage mem to be suitable for field we) but their mqxme to du&%u+y~t be studied.

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Changes in the Experiment I>ynamicpresswe versus time, Shots 4, 5,:md 6 Overpressure versm tine, Shots 4, 5, azx.6; l Density ratio versus time, Shots 3 and 4

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:Ths principal objectlvs of Project 1.3 was to sfxiy the dyol;aio pressu&time characteristics of shock waves produced by high-yield surface 33&i&t @anage to militssg targets la due to viada in the shoak wava a~ vell 83 to~-gw3rpre33ure3;in fact, damage to such targets as twers, bridges, -ti~trucks is much better reCl.atedto dynamic pressure than to overpres&tie, Since the ext ,l?t of damage is r&ted to the time history of dynamic prossu-e aa well 3s to its peak value, measwanents as a function of ti.ze are needed. Such measurements vill alao serve as a check on the theoretical relation between peak vslues'of overpressureand C&M&O Another objective was to evaluate a group of gages for use cm future studies of blast winds ,and other parmeters associated with the precmsor. 3). Heasuremnts yhere no prec_&$or existed have been made both in rq@ar face bursts, measured values ofrthe peak dynamic pressure, q, have bean in fatily good agreezmnt with valuGs%alqulated from the masured oveqresswe, iiouevc~~, measurements have been tie only a~‘~'oveqMZssuresbelow 20 calculated valws. It is believed that thase high vain@j h&w the 4aEe explanationas t&t prcposed below for high values in khe’precymor. sure in the precurscr. Although many of the gage tcuers ver?c ddstxvyad,

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80 that most records were lntxmplete,the recorda did ahav that the mea6ured value6 of q were tvo to tventy thes thoas calculated fran the overpreasure using the above relatlonshQ, The explaaatlon for thaw high valuer aa devalcped mperixaentnlly and tlmmtlcally (Referugca 3) i.8that dust AH v&l a8 air registers on tie kind of gage usai. Subject to rather bmad l%aitatlom, dust cemried along by the bZati regi~tem pq$aqco that, at both tie timada Teat Site % AS) a& the Roifio Rmlng : ‘Sinoo this problrrp of dust interaction ir not at cll well uxrkwtood, bei;iAr dq$~e the Interaction of dust with gages and structures. At the mime time $* uaa suggested thfit a eet of data lncludlng overpressure, tqemture, density, and at least two dynamic prsesure measurcrments ueixq gagesjvlth different responses to dust wotild give more insight Into the nature of 9s precursor and would dllau the ef fecte of the air alvl the dust +.o be -separataL The various gages being evaluated are a reuult of thin suggeistkon.

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The pitot-etatic gage ~a8 the best c&Iurated dymmic pressure gage the-.bWrd inatrumnt for dynamic preesure measumnente. The pitot gage +o offered the advantap of measuring both dynanic preemre and the dperpreosure and both the positive and negative phase& Because of the shor%age of recording channels no pitot gage could be included in the group of gages being studied. Since the differential pressure q-tube had beg previously c&Tared to ‘,he pitot gage it was considered the standard in t!xis group. The group of gag es consisted of the following: to one used @raV?omly (Reference 1 but mdifled by mounting it in a“fi erature gage, similar in principle side-on baffle and by using a blower to draw a continuoue flow of air past the sensing wire, 2. A cent&petal density gage (Reference 3) modified by doublir?E; the rotor apeed and nounttig fn a smaller baffle. An element to masure overpressure pi8 also included. 2: A drag q-tube’ identical in dimensiom to the d?ff ererrtSal type, but inttmented to r&& the deflection of the sensing elmmt inetcad of the difference in$&@m_ro between the centers of the front and back of the element. z-Z-; [5%Le...-1 A force plate, W’*wh$@ a large diaphragm-type pressure head-on into the blast to measure the total or swtion preeaura. These gages have been tested in thg-XX@orato~y, but the cmbimtion of high thermal radiation, zero tine tra&ients, lorry duration of the ehock wave, and cl-tic conditions in a@a1 bursts required that they also be tested in such bursts. The pit&: ,ag$q and q-tllbee Ixwe been correction factors to obtain dynamic presnrre:firm measured differential pressured. A model of a force plate VBS alsoi&sted and the ca?lete calibration will be presented elaewhers (Ref&nce $.-G Figure 2.1 also) includes the correction factor for head-on orientation. All gtiges for this project were placed sdx feet above. g&xnd surface. heigi:,t WA chomn as a caxpronise betvwn the need to be far e3ough

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above ground to eliminate interference between the ground and the gage and thcl necessity of having a gage mount strong enough to uithstaad the high dynamic pressures to be measured. The plan for this experiment did not call for caqAete coverage of q&e vs. distance, but for spot checks at For Shot 3, three pitot g&pea were placed at distsncea correqonding to expected overpressures of 15 to 35 phi. It was expected that if a pre~ih$gr folmed, the closest hqe (Station 130.03) wuld be in it; therefore a temperature ard a density gage were added ?A tr,is station to bid in Interpretation of resulte, 1 canceled) gave an opportunity to measure dynamic pres@rea over two kinds of surfaces. Cnly one-half of Pearl Island had been !49ared, the other half having been left in Its native state of vegetati& Stations 130.04 and 130.05, each conalsting of a pitot gage and a tcqxrat$.zz$‘gage, were inctal1ed at about equal distances frm ground zerc, one iti .tkiie cloared area and one in the vegetation. This choice of gages was expected to znen~urc the different amounts of heating of the air and the diffFre_St amounts of duet picker3 up by the 8hoCk xstitirq from the differen$ep in surffice. These txo stations were ex+cted to be in a precursot :if

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Section 2.1 vas set up, Stations 131 and 130.@7 next to each other on George Island of northern Bikini. Cperation plans called for four nearby barge shots giving four trials of the gage group at cverpressures ranging from 8 to ?L psi. In a;lproaching the gages the shock voulci travel over water except for the last 20 to 30 feet, so that a fairly Ideal shock was expected for The study, I -:223 CHANCESIN THE MPERIMXI _ t i f: . ; eeration Castle uas notable for the fluidity of its plans made ‘- %ices,caxy by the veather and the fact that it ups primarily a veapons To set forth these changes and their effect on Project 1.3, atlist of the shots in the order in which they vere fired follover t ?I+ 1 vas fired as scheduled. Although no participation VRS planned by Projo@ l.3, the force plate already installed on George Island vas Shot.2 vas moved from its position off Dog Island to the same place as Shot I, thus removing one of the chances to test the gage group. The force plate vas bperated but again at an overprrtssure of only 3 psi, not at the higher value desired for the test. Shot 3 was detonated at its planned pos?ticn but was so much smaller in yield than ergected that the resultant dynamic pressures were not in the range dosired. ‘. At this stage of ..the operation, Echo, the second shot on vhich ~JWI,& prossuro measurements-v&e planral, vas canceled. Shot 4, the second shot_ on vhich the gage-group study vas planned, vent as schedrcled, and neasurments were made as intended. Shot 5, another shot ferjwhich the gage &u&J vas planned, went ae eq)ected and sane men,curem&ntswere obtained. The vater wave fraGI Shot 4 had washed *way the battery box %$+taicing the paver supply for the density gage and the temperatu$~e+pe blover. Because of the high radithese could not be rei~&alled, so t@density gage and the tcrperaturegage blover could not be run. Shot 6, another ahot ?n whith iq had been plcnned to make the gage study, was moved from Bikini to the I%y Mi&_erster at Eniuetok. Because of previous inability to obia:n desired data--for this project ati for Project 1.2a, a blast line vas set, up for this neJ pcsitlon. Constnzction problems and the limited time avalab:e al&$& only one station, cansisting of a pitot gage and a force klate,%t aq-evorpressure level of

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j %$3 obtain+ ..~t?presented in Figures 3.1 through 3.5 ad in Tables UL !Jk.@tz FressurC. The first objective of Project 1.3 was not filly ach~ev~d’bedsuse &ho shot was canceled and Shot 3 was so much smaller In vie&4 than expected that the dynamic pressures resulting were too small tu be read accurtltely. On Shots L and 5 measured values 01’ dynastic pressure and total or stagnation pressure ticre higher than those implied by the overpressure (Table 3.51, ati wavef.orrPsuers much distorted. For instance, on Shot 5 the dynmic pressure versus tine records had a hump immediately after the was essentially straight. Xvidently the shock wave was not an ideal shock The point of meawrement was fai-rfy; closo to the water’s alee. On the other hand on Shot G,~measurenents of dynamic prossure and pressure, arxl vavefozw were only sllghf.2y rounded (FQures 3.1, 3.2, and 3.3). At thp point of measurement t&-shock had traveled the last SC0 feet Thi:: observation. that a ahock wave uaq-aess id=1 over a water surface than over a land surface stands in direct +/ntrast to previous sqpositions. The forca plate aeema to have the required r&se time of from 1 to 3 msec, nti the ringing is not too objectionable. : 6 Shot 1 this page driftad badly before shock arrival because of hpdting? by-thermal rediation, but on ai!zLm foil, alld the drift was much =Iler. i i’hotoyrfiphy ohms t&t the shock wave in tra; sling across water :k$+s up spray uhic!: uobld f311oi4 the front at about this tizu interiraj

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to see the true form at all. The amplit:;;deodthe r1ngln.guas up to &4J percent of tho signal amplitude. Sines it do&fnot appear that this ringing can be daqxd out vith the prenant de$i@n nor that ite frequency can be raised to such a value that it gilI not--becbjectionabls,it muat be concluded for nbv that this pape Is not suitable!foF Its prcpoaed use. that measured by three types of dynazic pressure gag_& F&e the noise and high-frequencyringing of the gages has been smoothed,gu$. A 5O-qs ringing of the force plate ia much more prcxninenton She% 6:Chan on the othw shots. The corkpondence of t.+e*,otalpreu232ea i's‘v&y good on Shots 4 and 6, although the force pla+lsdiffers from the $&ki AP measure-

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7.zre 3.4~ Total pressure versus time, Shots 4, 5, IIM 6 ments by sllghtiy ‘&ore than the expected accuracy (5 percent) of the individual secords. ‘[;A~~2asec dip in the q ard b P rerm-d of Shot 5 appears to be a real. si&al from the q record, althoueZi the differential pressure q-tube does %I&~-sh_o~ it. The similar dip in -‘,c forze plete pressure of about 4 psi, th&neamxd cqrassion ratio $a4.j,, of shock density to ambient density) bei&; in good agreemen’; vith that. ir~‘zrsd gages. This ray mean that in at&e way it registers watei- or dc;.ot iz tha air. Leboratory tests in still air ah-~.:that the gage responcis to Ilust, but that in Rho& flow the dust goes by$he opening ard does rxt coiitribute significantly to the gage output. In Figure 3.3 the iencfty-tim insert is a true tracing of the recor&on Shot 3. For Shot 1, the g~.ga oscillations have been smoothed out. : I about any changes in air tezperature hefore shock arrival h;;t ~?th the hope that it might cnJerate at least part way tbcFg@ the shock, &lever, apparent came. This occurred j;lst before Shot 4. ‘so that the cage was not operated cn that shot. The battery power t’cr..the blaver could hot bt reinstalled in tine for Shot 5 so tkt the themal rad?at;cn had c chm-r* to hea.t the air stagnated around the element, and no .rtti_4 me~surment was obtdned on this shot either,

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The one 3~cce33ful meaaurment of dynamic pressure made specifically t $$$heck the relation between dynmic p.-easureand overpressurewas in ‘--goodap_ement uith the theoretical relation. This neaauremxt 9aa made on Shg~t$at an overpressureof 21.5psi alldat a position such that the shock:&& had had 600 feet of travel eve? land Imediately in fr0r.tof the g&e. &aou.renents were also obtaixd on Shots 4 ard 5 in connection with the”gaee_ evaluation study at overpressures of 14 and 20 p~11and at a position au&that the shock wave had traveled entirely over water except for the last $0 to 30 feet. These records gave hizhcr values of dynaxic and total pressure than implied by the overpressure,and had distorted wav8foms. Such nonideal behavior suggests that th? shock8 had picked q water and/or dust. in their travel; this was not expected of shock wave8 over water, a supposedly ideal surface. Fran the gage study it seems that the force plate and the density partially to ratcrial :&her than air carried by the shock wave and this respoxe requires furtheti investigationif it is to be used in the presence a.?dust. Further u&e .of=zthoresistance wire tqerature gage or of the drag-t,ypeq-tube is notrccozzended. On Shot L both q-tube3$&icate the huzp in dynamic pressure, but this is not at all clearly &G-ifient_$nthe force-plate record; hcuever, on Shot 5, the hu! in dynamic @@$ure correqords to the dip in overpressure so that no huq in to+&>--@%x!ssurevouLi be expect&. h %ot 5 the sum of the ovepressure and @&mic pressure exceeds the force plate reading behind the front. If thf??orcj6$platescale were isicrcasedor the dsmity static scale decreased, the va$.$esat 0.1 secoti after shock N‘- rival could te mtched and, as in shotid, have the farce plate rendiws slight& higher just behind the front b&t thereafter about equal to the The cqarison of propagation of a precursor~~aVeover EadY Soil and over vegetation (proposed on the canceled Sho$,Echo) should be cwriodi -* out when suitable test …