Showing papers on "Overpressure published in 1973"

Pressure waves generated by steady flames.

Abstract: Analysis of pressure waves that can be generated by clouds of explosive gas mixtures in a free atmosphere which is initially at a uniform state. The treatment is restricted only to the final stage of constant flame velocity when the flowfield is self-similar. By the introduction of reduced blast-wave parameters as phase-plane coordinates, the problem is resolved into the determination of the appropriate integral curves on this plane. Results, including space profiles of gasdynamic parameters, have been computed for a specific case of a hydrocarbon-air mixture characterized by a specific heat ratio of 1.3, sound speed at NTP of 345 m/sec, and volumetric expansion ratio corresponding to constant pressure deflagration of 7. Maximum overpressure ratios that can be generated by such flames in point-and line-symmetrical waves range from .00053, for the lower bound in the burning speed, up to 6 for the deflagration, while, for the average speeds of 5 to 10 m/sec, they are at a level of 0.05 to 0.10.

Prediction of Inlet Duct Overpressures Resulting from Engine Surge

Abstract: A semiempirical method has been developed for predicting the peak surge-induced overpressures in the vicinity of the engine face as a function of engine cycle variables. The method is applicable to relatively long inlets, such as those typically used on supersonic airplanes. (For the shorter inlets typical of subsonic airplanes pressure relief is obtained at the inlet entrance before the peak overpressures are reached in the inlet.) A correlation of existing overpressure data is obtained by combining an analytical solution for the effect of engine bypass ratio with an empirical evaluation of the effect of over-all compressor pressure ratio. The resulting method can be used to obtain boundary conditions for inlet dynamic simulation programs that predict the effects of inlet duct geometry and auxiliary air systems on overpressure characteristics. The method predicts that higher engine bypass ratios lead to significant reductions in peak overpressures.

Statistical Prediction Model for Glass Breakage from Nominal Sonic Boom Loads.

Abstract: : A statistical model was developed which can be used to estimate the probability of glass breakage from sonic booms as a function of their nominal overpressure. Other parameters which can be taken into account in breakage probability calculations with this model include window size, aircraft vector, boom duration, and whether the glass was previously in good condition or cracked. A model window population has been devised from available data which includes the distributions of dynamic amplification factors and breaking pressures for seven window types. Provision has been made in the model to treat .61% of the window population as cracked glass. From computer generation of histograms from test data, the distribution of both sonic boom stresses and glass strengths were found to be lognormal. By use of the model, it was estimated that there would be 1.1 breaks per million panes in good condition boomed at a nominal overpressure of 1 psf. This estimate agrees well with sonic boom claims data. (Author)

A study to determine the feasibility of a low sonic boom supersonic transport.

Abstract: A study was made to determine the feasibility of supersonic transport configurations designed to produce a goal sonic boom signature with low overpressure. The results indicate that, in principle, such a concept represents a potentially realistic design approach assuming technology of the 1985 time period. Two sonic boom goals were selected which included: (1) A high speed design that would produce shock waves no stronger than 48 Newtons per square meter (1.0 psf); and an intermediate Mach number (mid-Mach) design that would produce shock waves no stronger than 24 Newtons per square meter. The high speed airplane design was a Mach 2.7 blended arrow wing configuration which was capable of carrying 183 passengers a distance of 7000 km (3780 nmi) while meeting the signature goal. The mid-Mach airplane designed was a Mach 1.5 low arrow wing configuration with a horizontal tail which could carry 180 passengers a distance of 5960 km (3220 nmi).

Gas-blast HV cct. braker - uses gas pressure gradient in pressure gas chamber for arc quenching, produced by suction system

Abstract: The circuit breaker has a hermetically closed, gas-filled housing, in which a gas pressure gradient is generated for the breaking light arc quenching. The circuit breaker uses a suction system which generates both a relative overpressure and a relative vacuum in the housing. The overpressure flows through open contacts of an auxiliary switching device, electrically in series with the main switching device, into the housing part in which the main switching device is located. The moving contact of the main switching device has a bore whose end, away from the switching device, opens into the suction part of the system. The stationary contact is in the form of a nozzle, engaged gas-tightly by the moving contact.

Shuttle sonic boom - Technology and predictions

Abstract: Because the shuttle differs significantly in both geometric and operational characteristics from conventional supersonic aircraft, estimation of sonic boom characteristics required a new technology base. The prediction procedures thus developed are reviewed. Flight measurements obtained for both the ascent and entry phases of the Apollo 15 and 16 and for the ascent phase only of the Apollo 17 missions are presented which verify the techniques established for application to shuttle. Results of extensive analysis of the sonic boom overpressure characteristics completed to date are presented which indicate that this factor of the shuttle's environmental impact is predictable, localized, of short duration and acceptable. Efforts are continuing to define the shuttle sonic boom characteristics to a fine level of detail based on the final system design.

Sonic boom reduction through aircraft design and operation.

Abstract: Means of reducing or eliminating the sonic boom through aerodynamic design or aircraft operation are discussed These include designing aircraft to minimize or eliminate certain features of the overpressure signature, operating aircraft at slightly supersonic speeds so that the sonic boom does not reach the ground, and seeking reductions through the high altitude-high speed flight conditions of hypersonic transports

Oblique-wing sonic boom

Abstract: An investigation was conducted to determine the magnitude of the groundtrack overpressure generated by an oblique-wing transport cruising at Mach 1.4 at 45,000 ft. A conventional swept-wing configuration was included in the study to provide a basis of comparison for the oblique-wing configuration. The results of the investigation have shown that the oblique-wing configuration produces less sonic boom overpressure at cruise lift coefficient than the swept-wing vehicle.

An Experimental Study of the Reverse Percolation Lofting Process in a Sand Medium.

Abstract: : A vertical shock tube was used to approximate the time dependent overpressure at 1 km from a nominal 1 Mt source, in order to study the lofting response of a porous sand medium, arising from the gas flow into and out of the medium. The basic shock wave form applied to the sand surface in the vertical shock tube, had a peak value of 100 psig, and a positive duration of approximately 0.75 seconds. The corresponding Brode function has an estimated positive duration of 1.1 sec, but was closely approximated by the experimental shock over the first 0.4 microseconds. (Modified author abstract)

Apparatus for reducing shock and overpressure

Abstract: Apparatus for reducing shock and overpressure particularly useful in connection with the sequential detonation of a series of nuclear explosives underground. A coupling and decoupling arrangement between adjacent nuclear explosives in the tubing string utilized to emplace the explosives is able to support lower elements on the string but yields in a manner which absorbs energy when subjected to the shock wave produced upon detonation of one of the explosives. Overpressure is accommodated by an arrangement in the string which provides an additional space into which the pressurized material can expand at a predetermined overpressure.

The design or operation of aircraft to minimize their sonic boom

Abstract: Means of reducing or eliminating the sonic boom through aerodynamic design or aircraft operation are discussed. These include designing aircraft to minimize or eliminate certain features of the overpressure signature, operating aircraft at slightly supersonic speeds so that the sonic boom does not reach the ground, and seeking reductions through the high altitude-high speed flight conditions of hypersonic transports. A simple computer program has been developed that determines the area development of the equivalent body of revolution required to minimize various sonic boom signature parameters.

Effects of pressure on electronic bubbles in liquid neon

Abstract: A calculation is performed for the ground state energy of an electronic bubble in liquid neon as a function of temperature and pressure, and using experimentally determined electron-neon scattering cross sections. The density of the compressed liquid is calculated from an equation of corresponding states. It is found that the electronic bubble should collapse at temperatures near Tc with a few atmospheres of overpressure.

Characteristic overpressure of a supersonic transport of given length in a homogeneous atmosphere

Abstract: In recent years many investigations have been made into ways of reducing the pressure jumps across the shock waves resulting from supersonic transports. Lately Warren has stated that a quantity which typifies a sonic bang and in particular with regard to its effect on structures is the characteristic overpressure. The characteristic overpressure is the ratio of four times the running integral of the overpressure to the time interval between the first and last shock in the signature. The work on the pressure jumps across the shock waves and the resulting lower bound values have to be modified when the characteristic overpressure is considered. This note describes a preliminary investigation into methods of obtaining the lower bound values for the characteristic overpressure.

Preliminary study of supersonic-transport configurations with low values of sonic boom

Abstract: A parametric study of low-boom supersonic transport airplanes with conventional configurations was made to identify the features of specific configurations that promise relatively low sonic boom overpressures (less than 47.9 N/sq m). The range of values considered was gross weight from 28,300 to 170,000 kg; cruise Mach numbers of 2 to 3.2; and wing loadings of 1436, 2870, and 4309 N/sq m. Fuselage length was varied from 49.1 to 102.4 m and fuselage diameter from 2.75 to 3.98 m. A nominal Mach 2 configuration weighing 56,700 kg and having a wing loading of 2870 N/sq m was selected; and its gross geometric, aerodynamic, and structural features were estimated. At a cruise altitude of 18,300 m, lift-drag ratio was estimated to be 7.35, while sonic boom overpressure was 41.7 N/sq m. Takeoff thrust loading using four afterburning turbojet engines at maximum dry thrust was 0.32. Payload for a 4440-km range was 16.7 percent of gross weight, giving a direct operating cost of 0.82 cent per seat statute mile.