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Showing papers on "Overpressure published in 1992"


Patent
05 Oct 1992
TL;DR: In this paper, an overpressure stop bridge is formed utilizing deep X-ray lithography to form a well-defined bridge structure and the gap between the membrane and the bottom surface of the bridge is established with a sacrificial layer, such as polyimide film, which dissolves in a solvent.
Abstract: Microminiature pressure transducers are formed on semiconductor substrates such as silicon and include a membrane which spans a cavity over the substrate, with the membrane being mounted to and sealed to the substrate at the peripheral edges of the membrane. The bottom of the cavity forms an overpressure stop to prevent over deflections of the membrane toward the substrate. An overpressure stop formed as a bridge of a material such as nickel extends above the membrane and is spaced therefrom to allow the membrane to deflect freely under normal pressure situations but prevent over deflections. The thickness of the polysilicon membrane and the spacing between the membrane and the overpressure stops is preferably in the range of 10 micrometers or less, and typically in the range of one micrometer. The overpressure stop bridge is formed utilizing deep X-ray lithography to form a well-defined bridge structure. The gap between the membrane and the bottom surface of the bridge is established with a sacrificial layer, such as a polyimide film, which dissolves in a solvent. The transducer is formed utilizing processing techniques which do not affect the performance of the membrane as a pressure sensor and which allow the substrate to have further micromechanical or microelectronic devices formed thereon.

82 citations


Patent
20 Mar 1992
TL;DR: In this paper, a turbine which generates overpressure for a breathing gas is controlled by detecting recurring variations in the operation of the turbine and correspondingly modifying the control signal which is set to a level which determines the overpressure of turbine, thereby modulating the supplied by the turbine.
Abstract: The turbine which generates overpressure for a breathing gas is controlled by detecting recurring variations in the operation of the turbine and correspondingly modifying the control signal which is set to a level which determines the overpressure of the turbine, thereby modulating the overpressure supplied by the turbine.

47 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the importance of overpressure mechanisms using the Institut Francais du Petrole Temispack model, which integrates compaction, hydraulic fracturing, fluid flow, heat transfer and the formation and migration of hydrocarbons.
Abstract: We used a basin-scale model to reconstruct the development of overpressures in a sedimentary basin. The area of application is the Venture gas field, Nova Scotia, Canada. It is in an overpressured zone in which sedimentation rates have been relatively low since 90 Ma, and where large horizontal stresses have been evidenced. We investigated the importance of overpressure mechanisms using the Institut Francais du Petrole Temispack model, which integrates compaction, hydraulic fracturing, fluid flow, heat transfer, and the formation and migration of hydrocarbons. We first constructed a reference model using geological, geochemical, and physical data. Second, we studied sensitivity of the model to several input parameters and, from this, deduced additional constraints. The modeled permeability along faults and of shaly beds interlayered in the reservoirs must be very low to enable both the local and regional distributions of overpressure and gas to be reproduced. Several runs of the reference model studying the relative importance of possible overpressuring mechanisms and the relative contribution of plausible source rocks to gas accumulations showed that gas generation and accumulation, and lateral compression contribute little to overpressuring, which is mainly accounted for by compaction disequilibrium in spite of low sedimentation rates. Faults and shaly beds play an important role in maintaining the overpressure. Gas generation in the reservoir units or close to them does not contribute significantly to the field gas accumulations. Gas sources are likely to be found in the underlying formations.

33 citations


Journal ArticleDOI
TL;DR: In this article, the quasilinear hyperbolic partial differential equations of continuity and momentum are used to model trap seal response and retention in a building drainage system and vent network.

31 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported that a significant amount of energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave, and that a distinct topography such as a mountain range was found to be effective to couple the wave energy to ground.
Abstract: Shock waves generated by the space shuttles Columbia (August 13, 1989), Atlantis (April 11, 1991) and Discovery (September 18, 1991) on their return to Edwards Air Force Base, California, were recorded by TERRAscope (Caltech's broadband seismic network), the Caltech-U.S.G.S Southern California Seismic Network (SCSN), and the University of Southern California (USC) Los Angeles Basin Seismic Network. The spatial pattern of the arrival limes exhibits hyperbolic shock fronts from which the path, velocity and altitude of the space shuttle could be determined. The shock wave was acoustically coupled to the ground, converted to a seismic wave, and recorded clearly at the broadband TERRAscope stations. The acoustic coupling occurred very differently depending on the conditions of the Earth's surface surrounding the station. For a seismic station located on hard bedrock, the shock wave (N wave) was clearly recorded with little distortion. Aside from the N wave, very little acoustic coupling of the shock wave energy to the ground occurred at these sites. The observed N wave record was used to estimate the overpressure of the shock wave accurately; a pressure change of 0.5 to 2.2 mbars was obtained. For a seismic station located close to the ocean or soft sedimentary basins, a significant amount of shock wave energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave. A distinct topography such as a mountain range was found effective to couple the shock wave energy to the ground. Shock wave energy was also coupled to the ground very effectively through large man made structures such as high rise buildings and offshore oil drilling platforms. For the space shuttle Columbia, in particular, a distinct pulse having a period of about 2 to 3 seconds was observed, 12.5 s before the shock wave, with a broadband seismograph in Pasadena. This pulse was probably excited by the high rise buildings in downtown Los Angeles which were simultaneously hit by the space shuttle shock waves. The proximity of the natural periods of the high rise buildings and the modal periods of the Los Angeles basin enabled efficient energy transfer from shock wave to seismic wave.

30 citations


Journal ArticleDOI
TL;DR: In this article, a technique combining a quasilinear extrapolation theory and a three-dimensional parabolized Navier-Stokes (PNS) code has been used to calculate the supersonic overpressure from three different geometries at near and mid-fields.
Abstract: A technique combining a quasilinear extrapolation theory and a three-dimensional parabolized Navier-Stokes (PNS) code has been used to calculate the supersonic overpressure from three different geometries at near- and mid-fields. Wind-tunnel data is used for code validation. Comparison of the computed results with different grid refinements, and different extrapolation distances, are shown in this article. It is observed that a large number of grid points is needed to resolve the tail shock/expansion fan interaction. Therefore, an adaptive grid approach is employed to calculate the flowfield. The effects of a thin, attached boundary layer and the sting of the wind-tunnel model to the sonic boom have also been studied in this article. The agreement between the results and the wind-tunnel data confirms that this technique can be applied to the problem of sonic-boom prediction.

29 citations


Journal ArticleDOI
TL;DR: In this article, the maximum mechanical energy extractable from a material as it reversibly moves into equilibrium with the environment is defined as the maximum amount of energy that can be extracted from the material.
Abstract: Thermodynamic availability represents the maximum mechanical energy extractable from a material as it reversibly moves into equilibrium with the environment. Since blast overpressure is a form of mechanical energy, thermodynamic availability provides a new and completely general technique for determining the energy of explosion. This paper presents the fundamental basis and shows how thermodynamic availability is used to determine the energy of explosion. It is shown that the method is applicable for any process conditions, including systems at elevated temperatures and pressures and systems composed of many materials, and for reactive explosion and explosions of inert compressed gases. The calculations are quite simple, even for the most complex cases. A table of thermodynamic data and a number of worked examples are provided.

25 citations


01 Oct 1992
TL;DR: In this paper, the bow shock amplitude and rise time distributions were measured under different atmospheric turbulence conditions for the same test aircraft and the effect of turbulence was more readily seen in the rise time distribution.
Abstract: Sonic boom bow shock amplitude and rise time statistics from a recent sonic boom propagation experiment are presented. Distributions of bow shock overpressure and rise time measured under different atmospheric turbulence conditions for the same test aircraft are quite different. The peak overpressure distributions are skewed positively, indicating a tendency for positive deviations from the mean to be larger than negative deviations. Standard deviations of overpressure distributions measured under moderate turbulence were 40 percent larger than those measured under low turbulence. As turbulence increased, the difference between the median and the mean increased, indicating increased positive overpressure deviations. The effect of turbulence was more readily seen in the rise time distributions. Under moderate turbulence conditions, the rise time distribution means were larger by a factor of 4 and the standard deviations were larger by a factor of 3 from the low turbulence values. These distribution changes resulted in a transition from a peaked appearance of the rise time distribution for the morning to a flattened appearance for the afternoon rise time distributions. The sonic boom propagation experiment consisted of flying three types of aircraft supersonically over a ground-based microphone array with concurrent measurements of turbulence and other meteorological data. The test aircraft were a T-38, an F-15, and an F-111, and they were flown at speeds of Mach 1.2 to 1.3, 30,000 feet above a 16 element, linear microphone array with an inter-element spacing of 200 ft. In two weeks of testing, 57 supersonic passes of the test aircraft were flown from early morning to late afternoon.

19 citations


01 Oct 1992
TL;DR: A new, empirical modification of the Seebass and George minimum-nose-shock sonic boom F-function and signature has all the inherent flexibility of application and enhanced this flexibility and applicability with neglegible increase in nose and/or tail shock strength.
Abstract: A brief resume of sonic boom minimization methods is given to provide a background for a new, empirical modification of the Seebass and George minimum-nose-shock sonic boom F-function and signature. The new 'hybrid' F-function has all the inherent flexibility of application found with the Darden-modified Seebass and George F-function. In addition, it has enhanced this flexibility and applicability with neglegible increase in nose and/or tail shock strength. A description of this 'hybrid' F-function and signature is provided, and the benefits of using them to design high-performance, low-boom aircraft are discussed.

14 citations


Proceedings ArticleDOI
01 Jan 1992
TL;DR: In this paper, the UTA (University of Texas at Arlington) shock tunnel at high Reynolds numbers for perfect gas simulation of hypersonic flow and boundary layer studies is described.
Abstract: Initial experience in operating a small UTA (University of Texas at Arlington) shock tunnel at high Reynolds numbers for perfect gas simulation of hypersonic flow and boundary layer studies is described. Particular attention is given to tradeoffs between various constraints for achieving the test requirements, and methods for obtaining precise control of test conditions and protecting low-range pressure transducers from overpressure damage.

13 citations


Journal ArticleDOI
TL;DR: In this paper, a field-scale experimental study has been performed in an attempt to reproduce, in a 1 5 geometrical scale replica rig, the results of a previous study of large-scale explosion experiments involving mixtures of air and a predominantly methane fuel gas.

Journal ArticleDOI
TL;DR: In this paper, a simplified thermochemical analysis and supporting experiments were conducted to investigate the mitigation of quasistatic overpressure occurring in such systems, and reasonable agreement between a simple analysis and the experimental results demonstrated that foam decreases the overpressure by a factor of 3-30.

Patent
09 Mar 1992
TL;DR: In this paper, a device for controlling the overpressure generating turbine is described, which comprises means (15, 17, 18, 20, 22) for detecting periodic variations in the regime of the turbine and means (I, E) for fixing two reference levels of the pressure delivered in order to modulate the over pressure provided by the turbine as a function of the respiratory parameters of the user which are detected in situ by a pressure sensor.
Abstract: The device for controlling the overpressure generating turbine (3) comprises means (15, 17, 18, 20, 22) for detecting periodic variations in the regime of the turbine and means (I, E) for fixing two reference levels of the pressure delivered in order to modulate the overpressure provided by the turbine as a function of the respiratory parameters of the user which are detected in situ by a pressure sensor (8). Application in particular to respiratory aid for individuals suffering from respiratory disorders when sleeping.

01 Oct 1992
TL;DR: In this article, a series of sonic boom flight tests were conducted by the US Air Force at Edwards AFB in 1987 with current supersonic DOD aircraft and the measured peak overpressures to predicted values as a function of lateral distance are compared.
Abstract: A series of sonic boom flight tests were conducted by the US Air Force at Edwards AFB in 1987 with current supersonic DOD aircraft. These tests involved 43 flights by various aircraft at different Mach number and altitude combinations. The measured peak overpressures to predicted values as a function of lateral distance are compared. Some of the flights are combined into five groups because of the varying profiles and the limited number of sonic booms obtained during this study. The peak overpressures and the lateral distances are normalized with respect to the Carlson method predicted centerline overpressures and lateral cutoff distances, respectively, to facilitate comparisons between sonic boom data from similar flight profiles. It is demonstrated that the data agrees with sonic boom theory and previous studies and adds to the existing sonic boom database by including sonic boom signatures, tracking, and weather data in a digital format.

ReportDOI
01 Jan 1992
TL;DR: In this paper, the overpressure field around an M68 tank cannon firing an M735 round was studied, where pressure transducers were located from 15 to 400 calibers from the muzzle and at 30 degree increments around the gun.
Abstract: : The overpressure field around an M68 tank cannon firing an M735 round was studied. Pressure transducers were located from 15 to 400 calibers from the muzzle and at 30 degree increments around the gun. The investigation yielded a detailed picture of the flow field, as displayed by overpressure traces. Comparisons of the overpressure data with a prediction method show better agreement for the measured points nearer to the muzzle. The peak overpressure, time-of-arrival, and positive-phase-duration data will be used together with other gun blast data to modify and improve the present prediction method. Observed anomalous pulses were also investigated but their origins remain unknown.

01 Apr 1992
TL;DR: In this article, the rise time is defined as the time for the waveform to rise from 10 percent of its peak value to 90 percent of the peak value, and it is shown that a longer rise time typically implies a less loud shock.
Abstract: The rudimentary theory of sonic booms predicts that the pressure signatures received at the ground begin with an abrupt shock, such that the overpressure is nearly abrupt. This discontinuity actually has some structure, and a finite time is required for the waveform to reach its peak value. This portion of the waveform is here termed the rise phase, and it is with this portion that this presentation is primarily concerned. Any time characterizing the duration of the rise phase is loosely called the 'rise time.' Various definitions are used in the literature for this rise time. In the present discussion the rise time can be taken as the time for the waveform to rise from 10 percent of its peak value to 90 percent of its peak value. The available data on sonic booms that appears in the open literature suggests that typical values of shock over-pressure lie in the range of 30 Pa to 200 Pa, typical values of shock duration lie in the range of 150 ms to 250 ms, and typical values of the rise time lie in the range of 1 ms to 5 ms. The understanding of the rise phase of sonic booms is important because the perceived loudness of a shock depends primarily on the structure of the rise phase. A longer rise time typically implies a less loud shock. A primary question is just what physical mechanisms are most important for the determination of the detailed structure of the rise phase.


01 Oct 1992
TL;DR: In this article, a near-field analysis of the near field sonic boom environment of several low-boom HSSC concepts is presented using a multi-block Euler marching code within the context of an innovative mesh topology.
Abstract: A CFD analysis of the near-field sonic boom environment of several low boom High Speed Civilian Transport (HSCT) concepts is presented. The CFD method utilizes a multi-block Euler marching code within the context of an innovative mesh topology that allows for the resolution of shock waves several body lengths from the aircraft. Three-dimensional pressure footprints at one body length below three-different low boom aircraft concepts are presented. Models of two concepts designed by NASA to cruise at Mach 2 and Mach 3 were built and tested in the wind tunnel. The third concept was designed by Boeing to cruise at Mach 1.7. Centerline and sideline samples of these footprints are then extrapolated to the ground using a linear waveform parameter method to estimate the ground signatures or sonic boom ground overpressure levels. The Mach 2 concept achieved its centerline design signature but indicated higher sideline booms due to the outboard wing crank of the configuration. Nacelles are also included on two of NASA's low boom concepts. Computations are carried out for both flow-through nacelles and nacelles with engine exhaust simulation. The flow-through nacelles with the assumption of zero spillage and zero inlet lip radius showed very little effect on the sonic boom signatures. On the other hand, it was shown that the engine exhaust plumes can have an effect on the levels of overpressure reaching the ground depending on the engine operating conditions. The results of this study indicate that engine integration into a low boom design should be given some attention.

Journal ArticleDOI
TL;DR: In this paper, a variable pressure wave propagation velocity is developed and analyzed in ground materials which may be characterized by an exponential density -pressure relationship, and the peak overpressure dependence is minor in the low pressure range and the propagation velocity of the pressure wave is essentially a constant, in fact, it is the seismic P-wave propagation velocity.
Abstract: A variable pressure wave propagation velocity is developed and analyzed in ground materials which may be characterized by an exponential density - pressure relationship. The peak overpressure dependence is minor in the low pressure range and the propagation velocity of the pressure wave is essentially a constant, in fact, it is the seismic P-wave propagation velocity. Pressure dependence becomes increasingly more significant at peak overpressures exceeding 1 kbar (108 Pa). At very high pressure levels encountered only in shockwaves at and above 10 kbar (109 Pa), the initial mechanical characteristics of the ground materials become less significant, and the propagation velocity depends primarily upon the peak overpressure.

Journal ArticleDOI
TL;DR: In this paper, a method was developed to calculate the overpressure needed to ensure seal integrity, during thermal processing, of semi-rigid packages that contain a liquid food or drug.
Abstract: Heat processing semi-rigid packages with a steam/air mixture requires an overpressure to ensure seal integrity. A method was developed to calculate the overpressure needed to ensure seal integrity, during thermal processing, of semi-rigid packages that contain a liquid food or drug. An equation was derived relating total retort pressure (steam and air) required during sterilization to retort temperature, product water activity and tensile seal stress at the sterilization temperature. The proposed method was tested, under commercial sterilization conditions (123–127°C for 30min), with individual packages containing a dilute saline solution. The method was found useful for predicting the total retort pressure (steam and air overpressure) needed to ensure seal integrity and to prevent leakage of packages.

01 Apr 1992
TL;DR: In this article, the authors measured the sonic boom characteristics near Edwards Air Force Base from 11/66 to 1/67 using two microphones placed on the ground directly under the fight track.
Abstract: NASA measured sonic boom characteristics near Edwards Air Force Base from 11/66 to 1/67. Thirty four flights by an F-104 were recorded at an altitude of about 31,000 feet and flying speed of Mach 1.3. Forty two microphones were placed on the ground directly under the fight track. Each microphone recorded boom shape, rise time, peak overpressure, total boom duration, positive duration, and positive impulse.


Book ChapterDOI
01 Jan 1992
TL;DR: In this paper, a two-dimensional interior ballistics computer code was developed to solve the viscous two-phase flow in a combustion chamber of a gun tube during the ignition phase beginning with primer discharge and ending with projectile motion.
Abstract: A two-dimensional interior ballistics computer code has been developed to solve the viscous two-phase flow in a combustion chamber of a gun tube during the ignition phase beginning with primer discharge and ending with projectile motion. The motivations are to achieve a better understanding of the physical processes occuring during this phase and to predict overpressures which can occur under certain ignition conditions and configurations of loading. Calculations are presented for axisymmetric two-phase flow in a model combustion chamber assuming grain fracture or not. Predicted results indicate that grain fracture due to high compaction may generate substantial local pressure peaks along the combustion chamber. In extreme cases of severe grain fracture, the result is a catastrophic overpressure which can explain structural gun-damage and spontaneous deflagration-to-detonation transition.

Journal ArticleDOI
TL;DR: In this paper, the effect of As overpressure on the diffusion of Mn into an AlGaAs-GaAs superlattice using MnAs as the diffusion source was investigated.
Abstract: Data are presented showing the effect of As overpressure on the diffusion of Mn into an AlGaAs-GaAs superlattice (SL) using MnAs as the diffusion source. Arsenic overpressure has been shown to play a significant role in both impurity-induced layer disordering (IILD) and the microstructure of the Mn-diffused samples. The degree to which layer disordering occurs decreases as As overpressure increases. Furthermore, dislocation loops are observed for the diffusion of Mn under Ga-rich conditions at prolonged diffusion times. Both results, in addition to the effect of As overpressure on the Mn diffusion profile, indicate that Mn diffusion into GaAs or GaAs-AlGaAs heterostructures takes place by an interstitial-substitutional mechanism involving column III vacancies under As-rich conditions and a "kick-out" mechanism involving column III interstitials under Ga-rich conditions.