An alternative method for the measurement of the mechanical impulse of a vertically directed blast.
An alternative method for the measurement of the total mechanical impulse of a vertically directed blast due to an explosive charge is presented. The method differs from apparatus that employ a vertically displaced mass (similar in principle to the ballistic pendulum) in that a relatively compact spring-damper system is employed to constrain the movement of the mass. The mechanical impulse is determined by integrating, with respect to time, the net force applied to the spring-damper system. The details of an explosive impulse measuring instrument rated to 12 kN s are presented.
The influence of the height of burial of buried charges – Some experimental observations
Abstract This paper presents the results of an experimental investigation to determine the effect of the height of burial (the amount of sand beneath the buried charge) on a buried charge in terms of impulses imparted onto a rigid steel target plate (suspended from a vertical pendulum). The 40 mm rigid target plate of exposed area 400 mm × 400 mm is located at a constant stand-off distance of 47 mm above the surface of the sand. Tests conducted at a height of burial of 0 mm (placed flush on a steel base plate) resulted in the largest impulse transfer for all depth of burial (amount of sand above the buried charge) values tested. The optimal depth of burial for impulse transfer was observed to occur within 50–70 mm irrespective of the height of burial (0–110 mm). Semi-infinite height of burial conditions are attained when any further increase in the height of burial does not influence the impulse transfer to the target plate. The height of burial representing semi-infinite conditions observed in the experiments is a function of the depth of burial.
Control of the homopause level
Abstract This paper reviews the hypothesis that internal gravity wave breaking in the factor responsible for upper atmosphere turbulence generation and control of the number density at the homopause level. Available data from Mars and Earth support the hypothesis, originally introduced by Lindzen, that breaking thermal tides are responsible for the necessary turbulence. The lowest-order, equatorially trapped, westward-propagating diurnal tidal mode is the primary cause on the Earth, and lower-order westward-propagating semidiurnal modes are the primary cause on Mars. The frequencies and vertical wavenumbers of the responsible modes determine the eddy diffusion coefficients; energy density is only indirectly involved by determining which modes can break. A general scale relationship between tidal heating and velocity amplitude can be used to assess the breaking potential of tidal modes, and is used here as the basis for arguing that the number density at the Martian homopause is likely to have been stable over much of geologic time. Difficulties with this approach arise in the cases of Venus and Titan because of their peculiar zonal winds. For Jupiter and Saturn, internal gravity waves generated by nontidal mechanisms probably control the homopause.