Showing papers on "Overpressure published in 1978"

Subjective loudness of N-wave sonic booms.

Abstract: A loudspeaker‐driven simulation booth with extended rise‐time capability (down to 0.22 ms) has been used for subjective loudness tests of N‐wave sonic booms. The test series compared signatures over a range of 0.22–10 ms in rise time, 100–250 ms in duration and 0.5–2.5 psf (24–120 Pa) in peak overpressure. In one sequence, the tradeoff between rise time and overpressure was measured for equal loudness; in another, the tradeoff between duration and overpressure. For equal loudness 10‐ms rise time required 8‐dB higher overpressure than for 1‐ms rise time. Duration had little effect in the range 100–200 ms, but at 250 ms noticeably enhanced the loudness. These results confirm those measured by Shepherd and Sutherland made at 1‐ms rise time and above (except for the anomalous enhancement at 250‐ms duration), and extend the measurements down to 0.22 ms. There is also good agreement with theoretical predictions (Johnson–Robinson, Zepler–Harel methods) except for the 10‐ms rise time and 250‐ms duration cases.

Vibrational relaxation effects on the atmospheric attenuation and rise times of explosion waves

Abstract: The effect of vibrational relaxation processes on the rise times and overpressure decay of weak shock waves from explosions is investigated. Calculations have been performed which incorporate finite amplitude wave effects, spherical spreading, classical acoustic attenuation, and attenuation due to vibrational relaxation of oxygen and nitrogen. These calculations are compared to data and to the results of an empirically based calculation.

Pressure responding device

Abstract: PURPOSE:To realize a device equipped with an overpressure protective means without electrode shortcircuit having small over-range error by shutting off the chamber in the coating part in case a diaphragm is charged with an overpressure.

A wind-tunnel study of the applicability of far-field sonic-boom theory to the space shuttle orbiter

Abstract: Sonic boom characteristics of a 0.0004-scale model of the space shuttle orbiter were studied. Pressure signatures were measured at Mach numbers of 2.8 and 4.14 and at angles of attack of 0.3 deg, 19.0 deg, and 41.0 deg. To allow for observation of signature development and to provide data for extrapolation to larger distances, measurements were made at distances of from 8 to 32 body lengths. Relatively simple purely theoretical prediction methods provided reasonably accurate estimates of bow-shock overpressure and signature impulse.

Tactical nuclear slide rule

Abstract: A calculational aid is provided, in the form of a slide rule, to facilitate calculation of damages inflicted by a nuclear detonation. The particular apparatus permits calculation of the effects of an air blast, due to static overpressure, resulting from such a detonation. Appropriate scales, properly spaced in particular relationships, are provided on a slide rule, thus providing a means for performing the calculational functions described above. The calculations utilize five parameters, and the present invention provides an apparatus for determining any one of the five parameters once the other four are known.

Distortion of the sonic‐boom pressure signature by high‐speed jets

Abstract: Mach‐2.5 (0.30 caliber) projectiles were used to simulate supersonic aircraft; the acoustic impedance mismatch was provided by either of two rectangular nozzles having exit Mach numbers of 1.00 and 1.82 when delivering correctly expanded helium jets. These nozzles were operated from 40%–150% expansion at a fixed position relative to the presure transducer when the projectile miss distance was 36 or 108 body diameters from the transducer. Schlieren optical photographs demonstrated that the bow shock was always folded or ’’wrinkled’’ after passing through either of the jets. As exit Mach number decreased, the size of the shock‐front folds, as well as the divergent jet spread angle, increase and the bow shock becomes increasingly bent forward by the jet. Pressure signatures measured with a jet operating started 40–80 μs earlier than those measured without a jet. All pressure signatures obtained with a jet operating exhibited similar varieties of waveforms as F‐104, B‐58, XB‐70, SR‐71, and Concorde 002 flight test results. The wide variations in overpressure, rise time, duration, and wave shape are attributed to the velocity and density fluctuations of the turbulent jets.

HUFF, a One-Dimensional Hydrodynamics Code for Strong Shocks

Abstract: : HUFF is a one-dimensional Lagrangian hydrodynamics computer code developed from the basic principles of mass, momentum, and energy conservation for strong shock propagation in a solid or gas. Two equations of state are used - the adiabatic ideal gas law with a variable gamma and the Gruneisen solid equation of state with a constant Gruneisen ratio. The Richtmyer and Morton difference equations for strong shocks are used on a spatial mesh composed of up to 100 cells. Results for two problems are presented which show the usefulness and limitations of the code and also serve as sample problems. The results of a one kiloton nuclear explosion are compared to the Nuclear Blast Standard 1KT. The results were within 13 percent for shock overpressure and overdensity, 5 percent for shock material velocity, and 2 percent for shock position over a range of 20 meters to 2 kilometers from the burst point. The larger deviations occurred at early times being attributed to an absence of radiation transport calculations in the code. The second problem, a megabar compression of uranium, shows agreement within two percent for all parameters (peak shock pressure, density, material velocity and shock velocity) when compared with the Rankine-Hugoniot compression curves. The equation of state for a solid was limited to calculations below 100 megabars due to its simplicity and constant value for the Gruneisen ratio. A complete users guide and program listing are also provided. (Author)

Modeling of the UH-1B Tail Boom for Analysis by the NASTRAN Computer Program

Abstract: : A representative tail boom of the UH-1B helicopter is modeled for dynamic structural analysis by the NASTRAN computer program. The finite-element model employs beam and plate elements to construct the structural model, which will subsequently be used to study the effects of simulated nuclear detonations, subjecting the model to blast overpressure exposure with and without thermal effects. The lower mode shapes and frequencies of the structural model are generated and presented as a validation check.