Showing papers on "Overpressure published in 1983"

Blast Waves in Free Air

Abstract: Simple equations are given which can be used for calculating the approximate values of peak overpressure and positive phase impulse of blast waves generated by the detonation of military high explosive charges in the free atmosphere. To the practitioner, these equations may be useful in the quick and simple design of protective systems, or in calculating the amount of explosive required to achieve a certain desired effect. Moreover, an outline is given of the derivation of simple equations for the damaging effect of blast waves as a function of distance and charge weight. A useful formula, which had been given by Westine, encompasses the following three main causes of a damaging effect: peak overpressure, if the blast duration is long as compared to the natural vibration period of the target structure; pressure impulse, if the blast duration is short as compared to the natural vibration period of the target structure; product of peak overpressure multiplied by impulse in the intermediate range, i.e., if the duration of the pressure pulse is comparable to the natural vibration period of the target structure.

Protective breathing aid device for diving or other operation under pressure

Abstract: A protective exhaling device of the circulating path type with exhaling protection, with its exhaling duct connected, in the circulating path through a CO 2 absorber and a gas volume equalizing chamber containing a variable volume of gas, to an inhaling duct to which there is connected a reservoir of compressed gas supplying oxygen for breathing, has a cylinder and piston unit connected to the pressure bottle pressure or to an intermediate regulator pressure for pneumatically producing a force applied to the variable volume chamber. That assures that the force determining the overpressure level is always exerted at the same magnitude independently of the amplitude of the content of the equalizing chamber of variable volume. There is an automatic switchover from overpressure operation to normal underpressure operation in the case of a major leakage. For this purpose the cylinder and piston unit is provided with an outlet valve that opens when the piston goes beyond a predetermined stroke position, so that the overpressure diminishes through the piston and at the same time the supply of pressurized gas is blocked. Thus, in the case of major leakage there is no risk that the compressed gas supply will empty quickly without the user of the apparatus noticing it. After elimination of the leak overpressure can be reinstated manually or automatically. The equipment is suitable both for diving and for compressed air breathing protection equipment generally.

Reflected Overpressure Impulse on a Finite Structure

Abstract: : The effect of angle of incidence of the shock front on reflected impulse loading on a finite structure is presented in this report. Impulse reflection factors have been developed for angles of incidence from zero to ninety degrees. Reflected impulse on a finite structure is much less than reflected impulse on an infinite plane because of the unloading due to rarefaction waves propagation from the sides of the structure which lowers the reflected overpressure.

Overpressure valve made of plastic on a package

Abstract: An overpressure valve for a package is proposed, which consists of a polymer plastic. In order to be able to check by machine in a simple manner whether an overpressure valve (3) is arranged on a package (1) which contains a product which is perishable by atmospheric oxygen, the valve contains a substance with a special property which can be recognised physically, for example luminescent or magnetic properties. The substance is contained in at least one of the parts of the valve or in the adhesive which connects these parts. It can also be applied as a coating on one of the parts.

Random Choice Solutions for Weak Spherical Shock-Wave Transitions of N-Waves in Air with Vibrational Excitation.

Abstract: : In order to clarify the effects of vibrational excitation on shock-wave transitions of weak, spherical N-waves, which were generated by using sparks and exploding wires as sources, the compressible Navier-Stokes equations were solved numerically, including a one-mode vibrational-relaxation equation. A small pressurized air-sphere explosion was used to simulate the N-waves generated from the actual sources. By employing the random-choice method (RCM) with an operator-splitting technique, the effects of artificial viscosity appearing in finite-difference schemes were eliminated and accurate profiles of the shock transitions were obtained. However, a slight randomness in the variation of the shock thickness remains. It is shown that a computer simulation is possible by using a proper choice of initial parameters to obtain the variations of the N-wave overpressure and half-duration with distance from the source. The calculated rise times are also shown to simulate both spark and exploding-wire data. It was found that, in addition to the vibrational-relaxation time of oxygen, both the duration and the attenuation rate of a spherical N-wave are important factors controlling its rise time. The effects of the duration and the attenuation rate of a spherical N-wave on its rise time, which are designated as the N-wave effect and the nonstationary effect, respectively, are discussed in more detail pertaining to Lighthill's analytical solutions and the RCM solutions for nonstationary plane waves and spherical N-waves. (Author)

Development of space shuttle ignition overpressure environment and correlation with flight data

Abstract: The Space Transportation (STS) launch vehicles are more complex than other launch vehicles. A comprehensive analysis of the lift-off event is required so that the responses of the vehicle and payloads can be predicted. The transient overpressure induced by ignition of the solid rocket motors (SRM's) is one of the critical design factors assessed for lift-off. The STS-1 ignition overpressure design environment was developed from 6.4-percent scale-model tests in which the Tomahawk solid rocket motors were used to simulate the start-up process of the SRM's. The overpressures measured during STS-1 lift-off were much more severe than predicted. The reasons for this anomaly are discussed in this paper. The 6.4-percent scale model was redesigned and used as a tool to develop an effective ignition overpressure suppression system for STS-2 and subsequent flights. Also presented are advancements in subscale-model simulation and theoretical understanding of this transient overpressure phenomenon that led to the successful development of the fix.

Attenuation of shock parameters in air and water

Abstract: This paper describes the results of shock pressure measurements in the range of 1–25 MPa in water and in the range of 60–500 kPa in air. Pressure pulses were generated by exploding wire technique and measured with a quartz piezo-electric transducer. The attenuation with distance of shock overpressure, impulse and energy in shock front has been studied. Experimental data on shock attenuation in air is scarce and the results presented here confirm the attenuation behaviour derived from theoretical considerations.

Method for thickening mass or suspension and disk filter for implementation of this procedure

Abstract: A method and device for thickening mass or suspension by means of one rotating disk filter immersed in the mass or suspension where overpressure is applied to the outside of the plates' filter surface. Overpressure air is also used during filtration to loosen filtered mass from the plates' filter surface by directing overpressure air to a sector for each plate to be loosened. From there the air penetrates through the filter surface to the filter surface's outside. The disk filter is equipped with a vessel 1, a cover 7 above the vessel and sectors 3 arranged on the axis 5 forming rotating filter disks 4 in the vessel. In order to effect the overpressure outside the disks' 4 filter surface, the longitudinal cavity 14 or 19 inside the axis 5 is connected with the overpressure source 15 and the disk sector 3 which is located at the loosening place of each respective disk.

Simulation of Pressure Waves and Their Effects on Loaded Objects. Part 1. Outlining the Problem, Description of the Simulation Device,

Abstract: : Blast wavs generated by detonations of HE or fuel-air-mixtures are characterized by their peak pressure and their overpressure phase duration, i.e. by two parameters. But normally unconfined fuel-air-mixtures will deflagrate generating a pressure time history of a quite different shape. In contrast there is a relatively slow pressure rise up to a peak value followed by a sudden decay into a suction phase the minimum value of which is of the order of the overpressure peak value. The overall duration of this pulse there are more than two parameters necessary for a complete description. Despite the small peak pressure value these waves proved rather dangerous as numerous accidents have shown. Therefore it is desirable to get some insight into the destructive mechanism of these pulses. To be able to do that a special simulation device was developed which will be described. (Author)

Over-pressure preventing apparatus for geothermal power plant

Abstract: PURPOSE:To enable to prevent occurrence of overpressure in the main steam piping system, by making combined use of a blow-off valve for releasing superfluous steam in response to overpressure and an atmosphere relief means for releasing superfluous steam to the outside of the system by rupturing a diaphragm when overpressure is produced. CONSTITUTION:From setting of pressure, a blow-off valve 10 functions as a first protective means so as to protect pressure in a main steam pipe 6 by releasing steam to the outside of the system. Here, if the blow-off valve 10 becomes inoperative due to sticking of scale or by other reason, pressure in the main steam pipe 6 is further increased. When the pressure in the pipe 6 is raised to the burst pressure of an atmosphere relief means 13, a diaphragm 13b of the atmosphere relief means 13 is ruptured to release steam to the outside of the system. Thus, it is enabled to prevent occurrence of overpressure in the main steam pipe 6.

Capacitor arrangement having a device for monitoring and disconnecting an electrical capacitor

Abstract: A capacitor arrangement having a device for monitoring and disconnecting an electrical capacitor, especially a heavy-current capacitor, which is arranged in a gasproof housing inside which there is an overpressure resulting from excessive heating of the capacitor, from which the operation of an electrical switch, which is connected in the supply circuit of the capacitor, is derived. The switch is controlled by a pressure sensor which senses the pressure inside the housing and triggers when the maximum permissible overpressure is reached. In addition, self-monitoring of the disconnection protection and monitoring of the capacitor housing for leakage points that occur can take place by means of the pressure sensor or a second pressure sensor. To this end, a small minimum overpressure is set for the inside of the capacitor housing, so that the switch is also triggered as soon as the internal pressure falls below the minimum overpressure.