culated from the ideal curve.
It was also possible that dynamic pressure might assume
added significance with the high-yield devices because of the increased positive-phase
duration.
2.3.1 Overpressure.
A fact of major significance noted on the records of both over-
pressure and dynamic pressure was the non-ideal shape of the wave forms.
It had been
thought—-the possibility of precursor notwithstanding — that considering the long dis-
tances of water travel inherent in the instrumentation of long blast lines at the proving
ground, most wave shapes would appear nearly as the ideal: a fast rise followed by a
TABLE 2.1
SCALING FACTORS
enet
1
(Surface,
Reef)
2
(Surface,
Crater)
3
(Surface,
Land)
4
(Surface,
Lagoon)
5
(Surface,
Lagoon)
6
(Surface,
Crater)
Sield, Mt
Py, mb
Po, pai
To. ¥
15.0
1006.1
14.53
80.0
11.0
1012.4
14.67
80.0
0.130
1009.7
14.63
81.0
7.0
1007.4
14,60
81.0
13.0
1010.8
14.65
80.8
1.7
1906.4
14.58
79.9
To, C
Sp
Sa
&
y
26.66
1.0078
0.0405
0.0409
6.0412
26 .66
1.0016
1.0450
9.0458
0.0255
27.22
1.0046
0.1973
0.1957
0.2006
27.22
1.0068
0.0522
0.6523
0.0532
27.12
1.0038
0.0425
0.0430
0.0431
26.61
1.0078
0.0836
0.0845
0.0854
smooth decay.
This was not observed.
shown in Figure 2.1.
A typical series of overpressure records is
The low-pressure records, after an initial sharp rise, exhibit a
continuing slower rise to peak before the decay——a hump-back appearance.
In the highcr-
pressure regions, this second rise is not prominent; however, the front is rounded and
peak pressures are smaller than would be obtained by extrapolating the decay back to the
arrival time.
The cause appears to be associated with the water-laden medium through
which the blast wave was propagated: specifically, the water cloud picked up by passage
of the shock over the water surface. Shock photography along the surface showed what
appears to be spray behind the shock fronts, particularly on Shots 2 and 4. It may be
concluded that water does not constitute or approximate the ideal surface—it sometimes
had been assumed asideal.
Precursors that could be identified as such were not observed on any of the records.
Two shots on which this phenomenon might have been detected were modified: one was
cancelled entirely and the other experienced a much-~-lower yield than planned and instrumented for.
2.3.2 Dynamic Pressure Free-Field Measurements. Various types of gages were
selected for those measurements, recording either dynamic pressure, q, directly or
some related parameter—density, temperature, total pressures-——that would aid in the
interpretation of results. All gages were placed 6 feet aboveground, a compromise to
eliminate interference effects from the ground yet allowing a strong enough mount to
withstand the high dynamic pressures. Gages were placed on each shot to span the 10to-40-psi range of overpressure. Self-recording gages mounted 3.feet above groundlevel
were also located in this pressure range.
Participation on Shots 1 and 2 was a minimum effort, and the low yield of Shot 3 pre-
cluded effective results. Shots 4 and 5 gave dynamic pressures higher than those computed from the measured overpressure.
As in the overpressure records, the wave forms
24