Showing papers on "Overpressure published in 1981"

Nonlinear solution for an applied overpressure on a moving stream

Abstract: A boundary-integral method is given for the numerical solution of the exact equations for steady two-dimensional potential flow past a fixed pressure distribution on the free surface of a fluid of infinite depth. The variation in wave-resistance coefficient with overpressure and Froude number is presented. A drag-free nonlinear profile is obtained.

Bubble formation in supersaturated gelatin: A further investigation of gas cavitation nuclei

Abstract: Recently, a new cavitation model has been proposed in which bubble formation in aqueous media is initiated by spherical gas nuclei stabilized by surface‐active membranes of varying gas permeability. The data which originally motivated this development were obtained mainly by subjecting shallow gelatin samples to rectangular pressure schedules consisting of a rapid compression, equilibration of the sample at some constant increased pressure, and a rapid decompression. Since the initial pressure was ordinarily less than or equal to the final pressure, the magnitude of the initial compression was ordinarily greater than or equal to the magnitude of the final decompression. An equivalent statement for this type of schedule is that the initial overpressure was generally greater than or equal to the final supersaturation. The purpose of the experiment reported here is to test the surfactant cavitation model in the unexplored domain for which the reverse is true, i.e., for which the maximum overpressure is less ...

Detection and Assessment of Secondary Sonic Booms in New England.

Abstract: Measurements in summer 1979 and subsequent analysis demonstrate that secondary sonic booms frequently reported by New England residents are caused by inbound Concord flights to New York. Ray trace computations, based on meteorological data and FAA radar tracking of Concord flights, predict signal arrival times within 20 s and predict wave front azimuthal angles with 4°. Present paper focuses on analysis and is based on comprehensive report (FAA‐AEE‐80‐22) with same title. Sound paths leaving aircraft trajectory normal to Mach cone that reach New England classify as (1) ground wave (plane to ground, then diffracted creeping wave), (2) type I secondary sonic boom (plane to mesophere to ground), and (3) type II secondary sonic boom (plane to ground to mesophere to ground). Refraction in the mesosphere back to the ground is possible only when mesospheric winds cause effective sound speed at some altitude above aircraft to exceed that at ground. The ground wave, which has very low amplitude but is discernible in infrasonic pressure records, arrives first and is explained by Ingard‐Pridmore‐Brown theory of penetration into a shadow zone. Geometrical acoustics predicts type I and II secondary sonic boom arrivals only at and beyond focus lines (where ray‐tube areas vanish), but a diffraction model based on theory of wave phenomena near caustics yields arrivals on near side of focus lines. [Work supported by Federal Aviation Administration.]

Propulsion system ignition overpressure for the Space Shuttle

Abstract: Liquid and solid rocket motor propulsion systems create an overpressure wave during ignition, caused by the accelerating gas particles pushing against or displacing the air contained in the launch pad or launch facility and by the afterburning of the fuel-rich gases. This wave behaves as a blast or shock wave characterized by a positive triangular-shaped first pulse and a negative half-sine wave second pulse. The pulse travels up the space vehicle and has the potential of either overloading individual elements or exciting overall vehicle dynamics. The latter effect results from the phasing difference of the wave from one side of the vehicle to the other. This overpressure phasing, or delta P environment, because of its frequency content as well as amplitude, becomes a design driver for certain panels (e.g., thermal shields) and payloads for the Space Shuttle. The history of overpressure effects on the Space Shuttle, the basic overpressure phenomenon, Space Shuttle overpressure environment, scale model overpressure testing, and techniques for suppressing the overpressure environments are considered.

Method for compensating for the tolerances in the production of overpressure measuring instruments with elastic measuring element

Abstract: The movement of the measuring element end in the plane of movement under pressure load is measured two-dimensionally and the transfer to the indicating mechanism is determined accordingly in such a manner that the measurement error is minimised.

Simulation of Blast Fields by Hydraulic Analogy

Abstract: : The blast wave emanating from the rear of most shoulder-launched recoilless weapons can be literally deafening. To reduce the blast over-pressure a number of different silencers have been proposed. The cost of field trials on the actual weapon is considerable so the hydraulic analogy has been used to investigate over 70 configurations, and to try to understand the various mechanisms that reduce the overpressure at the relevant 'ear position'. Measurements have also been made using a 32 mm air-driven, open-ended shock-tube fitted with a variety of silencers and exhausting into the atmosphere. Comparisons have been made between the two-dimensional hydraulic analogy and the three-dimensional shock tube results in order to check hydraulic analogy has also been used to simulate the effects of one or more reflecting surfaces when firing recoilless weapons in rooms, streets and passageways.

Charts for determining potential minimum sonic-boom overpressures for supersonic cruise aircraft

Abstract: Charts which give an estimation of minimum achievable sonic-boom levels for supersonic cruise aircraft are presented. A minimization method based on modified linear theory was analyzed. Results show several combinations of Mach number, altitude, and aircraft length and weight. Overpressure and impulse values are given for two types of sonic boom signatures for each of these conditions: (1) a flat top or minimum overpressure signature which has a pressure plateau behind the initial shock, and (2) a minimum shock signature which allows a pressure rise after the initial shock. Results are given for the effects of nose shape.

Far Field Overpressure from TNT Explosions: A Survey of Available Models.

Abstract: : Available mathematical models for peak blast wave overpressure at large distances from TNT explosions were surveyed. Analytical and empirical models are discussed. (Author)

Sonic boom measurement test plan for Space Shuttle STS-1 reentry

Abstract: Formal documentation for measurement procedures and system specifications, and general information are relating to the Space Shuttle STS-1 Sonic Boom Measurement Program are supplied. This test plan is designed to provide information, guidance, and assignment of responsibilities for the acquisition of sonic boom and atmospheric measurements, timing correlation, communications and other necessary supporting tasks. Specifically included are details such as mobile data acquisition station locations, measurement systems calibration levels, predicted sonic boom overpressure levels, overpressure level assignment for each data acquisition station, data recording times on and off, universal coordinated time, and measurement system descriptions.

Sonic boom measurement test plan for Space Shuttle STS-2 reentry

Abstract: Procedures and system specifications associated with the space shuttle STS-2 sonic boom measurement program are described. Specifically included are details such as mobile data acquisition station locations, measurement systems calibration levels, predicted sonic boom overpressure levels, overpressure level assignment for each data acquisition station, data recording times on and off, universal coordinate time, and measurement system descriptions.

Abnormal Formation Pressures: Recognition, Distribution, and Implications for Geophysical Prospecting, Brazoria County, Texas: ABSTRACT

Abstract: The Frio and Anahuac Formations in east-central Brazoria County, Texas, were deposited in deltaic to prodeltaic environments during the active and waning stages of growth of a piercement-style salt diapir, Danbury dome. Growth faulting is prominent in the area and abnormal pore-fluid pressure is present in much of the section. Borehole shut-in pressure measurements, drilling mud density records, and shale transit times are used to interpret distribution of subsurface pressures. Three pressure regimes are defined in terms of vertical pressure gradients: normal pressure (0.465 psi/ft), soft overpressure (0.465 to 0.70 psi/ft), and hard overpressure (>0.70 psi/ft). Distribution of these pressure regimes is controlled by the distribution of sands in the sedimentary section and the extent of flow continuity within them. Flow continuity can be cut off by stratigraphic pinch-out or by faulting. Comparisons of stratigraphic thicknesses measured in boreholes with those derived from seismic reflection data show significant mis-ties if a single velocity function is used for time-depth conversion throughout the area. These mis-ties result from lateral variations in acoustic velocity which can be related to the distribution of normally and abnormally pressured zones in the subsurface. Abnormally pressured zones have lower acoustic velocities than the normally pressured zones above and below them. Where these abnormal zones exist and dip significantly, lateral velocity variations should be expected.

X-ray and pressure conditions on the first wall of a particle beam inertial confinement reactor

Abstract: Because of the presence of a chamber gas in a particle-beam reactor cavity, non-neutron target debris created from thermonuclear burn will be modified or stopped before it reaches the first reactor wallThe resulting modified spectra and pulse lengths and the cavity overpressure created by the momentum and energy exchange between the debris and gas need to be calculated to determine their effect on the first wallThe purpose of this paper is to present results of the debris-background-gas problem obtained with a one-fluid,two-temperature plasma hydrodynamic computer code model which includes multi-frequency radiation transportSpherical symmetry, ideal-gas equation-of-state, and LTE for each radiation frequency group were assumedThe transport of debris ions was not included, and all the debris energy was assumed to be in radiation The calculated X-ray spectra and pulse lengths and the background overpressure are presented The impact of the initial target spectra on these chamber conditions is discussed

Investigation of Environment and Response Phenomena for Buried Target Structures in Crater Margins

Abstract: : There are situations in which peak overpressure on the surface may be a conservative or even a misleading kill criterion To kill structures which are hardened to withstand the effects of several thousand psi overpressures may require such small miss distances for a blast-only kill that the structure will be within or very near the crater Other effects - notably direct ground shock and cratering action will then become substantial, if not overwhelming, factors in the structure kill This report concludes: (1) Using simulated MIDDLE GUST III dynamic environment, response of representative structures at various ranges near the crater were analyzed For example, the MX-B vertical shelter (l/d = 7) is predicted to be destroyed in the crater margin due to decoupled effects of peak ground shock pressure (crushing), dynamic ground shock gradient (plastic hinge), and late-time differential displacement (plastic hinge) (2) Distinct layering in the MIDDLE GUST III geology (probably typical of many target sites) substantially affects structure vulnerability to dynamic ground shock gradient and late-time differential and late-time differential displacement from cratering flow (3) Environment near nuclear craters will be more severe than near HE craters, due to effects of 5-10 times higher peak overpressure at crater radius Thus, HE sources alone will not simulate the combined environment effects near nuclear craters (4) If test sites which are chosen have no strong relective interface at a relatively shallow depth, the near-crater environnent for model structures will probably not be as severe as for full-scale structures near nuclear craters in typical layered geologies