Showing papers on "Overpressure published in 2006"

Thrust wedges and fluid overpressures: Sandbox models involving pore fluids

Abstract: The well-known model for the critical taper of an accretionary wedge includes overpressure as a first-order parameter. Fluid overpressures reduce frictional resistance at the base of a wedge but they also act as body forces on all material particles of the wedge, in addition to that of gravity. By means of sandbox modeling, many workers have tried to verify the predictions of the critical taper model, but few of them have so far incorporated true fluid pressures. We have used scaled experiments, in which compressed air flows through sand packs, so as to model the deformation of overpressured wedges. A new apparatus provides for a horizontally varying fluid pressure, for example, a linear variation, as in the critical taper model. We have done three series of experiments, involving horizontal shortening of homogeneous or multilayered sand models for various gradients of fluid pressure. As predicted by the critical taper model, the apical angle of the resulting wedge depends on the overpressure gradient. In homogeneous sand at a high overpressure gradient, deformation becomes diffuse and looks ductile. In multilayered models, detachments form beneath layers of low permeability, so that thrusts propagate rapidly toward the undeformed foreland. The efficiency of a detachment and its ability to propagate depend not only on the fluid pressure but also on the permeability ratios between the various layers.

Supersonic Inlet Shaping for Dramatic Reductions in Drag and Sonic Boom Strength

Abstract: An alternate approach has been identified for defining supersonic inlet compression surface geometry, the use of which increases the design latitude for lofting the inlet cowling region while permitting control over other key inlet design variables. Through this approach, a novel inlet design space is analytically shown to significantly improve supersonic aircraft performance and reduce sonic boom overpressure compared to high-speed inlets designed using traditional methods and constraints. Installed specific fuel consumption improvements of up to 11 percent and sonic boom overpressure reductions of 16 percent were observed for a podded axisymmetric external compression inlet designed for Mach 1.8 cruise. A theoretical discussion and physical description of the alternate inlet design concept is provided along with a summary of the analysis methodology used to judge the concept’s merit against conventional configurations. Inlet performance metrics, presented as a function of key design variables, are compared; and CFD solutions of the compression and diffusion flow environment are included. Drag characteristics at off-design Mach number are also presented. An extended range, low sonic boom vehicle concept is used as an aircraft study platform for which installed CFD-based drag and sonic boom comparisons are made.

Vented confined explosions in Stramberk experimental mine and AutoReaGas simulation

Abstract: Research Mining Institute, Inc., Ostrava-Radvanice, in cooperation with Dept. of Theory And Technology of Explosives of University of Pardubice and Klokner Institute of CTU in Prague, has performed three series of experiments examining methane–air mixture explosions and their impact on 14 and 29 cm thick wall. The project was named ‘Modeling Pressure Fields Effects on Engineering Structures During Accidental Explosions of Gases in Buildings’ and was sponsored by Grant Agency of Czech Republic (project No. 103/01/0039). The project is aimed at deeper understanding of pressure field effect upon the structures. Methane-air mixture explosion was used to generate the blast wave. The geometrical configuration of the environment resembled a room of an average size, such as larger kitchen. Preliminary simulations were made by AutoReaGas code (Century Dynamics and TNO). The design phase was followed by tests in an experimental mine in Stramberk. Two masonry dams were build in the mine, with cross-section areas of 10.2 m2 and longitudinal distance of 5.7 m, creating an explosion chamber with a volume of 58 m3. Two vent openings with an adjustable free cross-section were used to control the maximum overpressure inside the chamber. The concentration of methane-air mixture was approximately 9.5% (vol.) and the volumes of the clouds were 5.25, 10.2 and 15.3 m3 respectively. The generated blast wave overpressures inside the chamber ranged between 1 and 150 kPa. According to experimental results a calibration of the code was performed. After the calibration it is possible to make relatively accurate simulations in similar geometry and to calculate the pressure loading of the structure at any spot in the simulated space. This paper describes the experiments performed and compares experimental and computational results.

Characteristic overpressure–impulse–distance curves for the detonation of explosives, pyrotechnics or unstable substances

Abstract: A number of models have been proposed to calculate overpressure and impulse from accidental industrial explosions. When the blast is produced by explosives, pyrotechnics or unstable substances, the TNT equivalent model is widely used. From the curves given by this model, data are fitted to obtain equations showing the relationship between overpressure, impulse and distance. These equations, referred to here as characteristic curves, can be fitted by means of power equations, which depend on the TNT equivalent mass. Characteristic curves allow determination of overpressure and impulse at each distance.

Experiments on the influence of pre-ignition turbulence on vented gas and dust explosions

Abstract: Experiments were performed on the influence of pre-ignition turbulence on the course of vented gas and dust explosions. A vertical cylindrical explosion chamber of approximately 100 l volume and a length-to-diameter ratio (l/d) of 4.7 consisting of a steel bottom segment and three glass sections connected by steel flanges was used to perform the experiments. Sixteen small fans evenly distributed within the chamber produced turbulent fluctuations from 0 to 0.45 m/s. A Laser-Doppler-anemometer (LDA) was used to measure the flow and turbulence fields. During the experiments the pressure and in the case of dust explosions the dust concentration were measured. In addition, the flame propagation was observed by a high-speed video camera. A propane/nitrogen/oxygen mixture was used for the gas explosion experiments, while the dust explosions were produced by a cornstarch/air mixture. It turned out that the reduced explosion pressure increased with increasing turbulence intensity. This effect was most pronounced for small vents with low activation pressures, e.g. for bursting disks made from polyethylene foil. In this case, the overpressure at an initial turbulence of 0.45 m/s was twice that for zero initial turbulence.

Studies on Internal Flow Choking in Dual-Thrust Motors

Abstract: Adetailed picture of the internal flow during the starting transient of high-performance solid rocket motors (SRMs) is of topical interest for several reasons in addition to the motor performance itself [1–12] Despite the fact that many of the existing models could predict the internal flow features of certain classes of SRMs, none of these models could capture the unusual starting transient flow features such as pressure overshoot and pressure-rise rate often observed during the initial phase of operation of the dual-thrust motors (DTMs) [1] Ikawa and Laspesa [8] reported that during the first launching of the space shuttle from the Eastern Test Range, the launch vehicle experienced the propagations of a strongly impulsive compression wave This wave was induced by the SRM ignition and was emanating from the large SRM duct openings The analysis further showed that the compression wave created by ignition of the main grain was the cause of the ignition overpressure on the launch pad [9] Alestra et al [10] reported that Ariene 5 launcher experienced overpressure load during the liftoff phase The overpressure is composed of the ignition overpressure, which emanates from the launch pad, and the duct overpressure, which emanates from the launch ducts Of late, Sanal Kumar et al [1,2] reported that abnormal high-pressure overshoot in certain class of DTMs during the startup transient is due to the formation of shock waves because of the fluid-throat effect, which has received considerable attention in the scientific community This manuscript is the continuation of the previous connected note for establishing the intrinsic flow physics pertinent to internal flow choking in inert simulators of dual-thrust motors [1] Note that the illustration of ignition pressure spike is deliberately set aside in this note for explaining the intrinsic flow physics pertinent to internal flow choking without complications arising from the propellant combustion

Rapid Sedimentation, Overpressure, and Focused Fluid Flow, Gulf of Mexico Continental Margin

Abstract: Expedition 308 of the Integrated Ocean Drilling Program (IODP) was the fi rst phase of a two-component project dedicated to studying overpressure and fl uid fl ow on the continental slope of the Gulf of Mexico. We examined how sedimentation, overpressure, fl uid fl ow, and deformation are coupled in a passive margin setting and investigated how extremely rapid deposition of fi ne-grained mud might lead to a rapid build-up of pore pressure in excess of hydrostatic (overpressure), underconsolidation, and sedimentary mass wasting. Our tests within the Ursa region, where sediment accumulated rapidly in the late Pleistocene, included the fi rst-ever in situ measurements of how physical properties, pressure, temperature, and pore fl uid compositions vary within low-permeability mudstones that overlie a permeable, overpressured aquifer, and we documented severe overpressure in the mudstones overlying the aquifer. We also drilled and logged three references sites in the BrazosTrinity Basin IV and documented hydrostatic pressure conditions and normal consolidation. Post-expedition studies will address how the generation and timing of overpressure control slope stability, seafl oor seeps, and large-scale crustal fl uid fl ow. The operations of Expedition 308 provide a foundation for future long-term in situ monitoring experiments in the aquifer and bounding mudstones.

Test of Thermal Transport Models through Dynamic Overpressure Stabilization of Ablation-Front Perturbation Growth in Laser-Driven CH Foils

Abstract: Heat-flow-induced dynamic overpressure at the perturbed ablation front of an inertial confinement fusion target can stabilize the ablative Richtmyer-Meshkov-like instability and mitigate the subsequent ablative Rayleigh-Taylor (RT) instability. A series of experiments was performed on the OMEGA laser to quantify the dynamic overpressure stabilization during the shock transit. Analysis of the experimental data using hydrocode simulations shows that the observed oscillatory evolution of the ablation-front perturbations depends on D{sub c}, the size of the thermal conduction zone, and the fluid velocity in the blowoff region V{sub bl} that are sensitive to the thermal transport model used. We show that the simulations match the experiment well when the time dependence of the heat-flux inhibition is taken into account using a recently developed nonlocal heat-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)].

Study of the ignition overpressure suppression technique by water addition

Abstract: The main objective of this study is to gain an understanding of the mechanisms responsible for the suppression of the ignition overpressure observed when water is injected through discrete nozzles into a rocket exhaust A simplified launch-vehicle/launchpad configuration of relevant importance is selected for this study This configuration is then numerically modeled using two-phase computational fluid dynamics with a representative motor startup sequence and a series of water addition configurations The study focuses on the interaction between the ignition overpressure wave and the injected water Chemical reactions are not included in the model; therefore, the effect of afterburning of fuel-rich exhaust is omitted in this study A total of 11 water addition configurations were studied The study demonstrated that ignition overpressure is strongly affected by the cooling of the plume and the amount of obstruction restricting the expansion of the plume Also, the study suggests the existence of an optimal water addition rate with a weak dependence on the water nozzle pressure drop

Flight Demonstration Of Low Overpressure N‐Wave Sonic Booms And Evanescent Waves

Abstract: The recent flight demonstration of shaped sonic booms shows the potential for quiet overland supersonic flight, which could revolutionize air transport. To successfully design quiet supersonic aircraft, the upper limit of an acceptable noise level must be determined through quantitative recording and subjective human response measurements. Past efforts have concentrated on the use of sonic boom simulators to assess human response, but simulators often cannot reproduce a realistic sonic boom sound. Until now, molecular relaxation effects on low overpressure rise time had never been compared with flight data. Supersonic flight slower than the cutoff Mach number, which generates evanescent waves, also prevents loud sonic booms from impacting the ground. The loudness of these evanescent waves can be computed, but flight measurement validation is needed. A novel flight demonstration technique that generates low overpressure N‐waves using conventional military aircraft is outlined, in addition to initial quantitative flight data. As part of this demonstration, evanescent waves also will be recorded.

Finite-rate interphase heat-transfer effects on multiphase burning in confined porous propellants

Abstract: Deflagrations in porous solid propellants are often affected by an increasing pressure difference, or overpressure, between the burned-gas region and the gas deep within the pores of the material. As a result, there appears to be a relatively rapid change in the burning-rate response over a certain range of overpressures in which the sensitivity, or slope, of the propagation speed as a function of overpressure transitions from relatively small to large values. This is often referred to as a transition from “conductive” to “convective” burning, corresponding to the increased role played by convective gas transport relative to thermal diffusion in determining the propagation speed of the deflagration. In the present work, we consider the analysis of a two-temperature model in which finite-rate interphase heat-transfer effects also play an important role in determining the burning-rate eigenvalue. In particular, we revisit a physically relevant scenario in which the first effects of temperature nonequilibriu...

Computer-aided modeling of the protective effect of explosion relief vents in tunnel structures

Abstract: This paper aims at contributing to the efficient design of explosion protection systems against confined explosions. The issue addressed concerns the quantitative estimation of the protective effect of explosion relief vents in the case of confined explosions inside tunnels. A series of virtual experiments performed by computer simulation, revealed how the number of vents, their diameter, as well as the angle between the vents and the tunnel, influences the blast wave attenuation. The computational study was performed considering a complicated large-scale tunnel configuration with branches on its half portion. The purpose was the calculation of the attenuation effect due to the presence of vents by comparing the total explosion-specific impulse developing at antidiametric positions inside the tunnel. Simulations were carried out via a three-dimensional numerical model built in the computational fluid dynamics code CFX 5.7.1, which has been validated in previous papers against experimental overpressure histories data demonstrating reasonable performance. Computer results showed that the use of branch vents provides an effective method for shock wave attenuation following an explosion, whereas their statistical elaboration revealed that the attenuation is mainly affected by the number of vents and their diameter. In contrast, the angle between the side vents and the main tunnel appeared to slightly affect the pressure wave weakening. Eventually, the quantitative influence of the above parameters was effectively illustrated in functional diagrams, so that the total attenuation effect may be promptly estimated, if the design variables are known. In addition, two statistical models with reasonable fitting to the calculated data are proposed, which express the attenuation effect as a dependent variable of the design variables including their interactions.

Simulation Assisted Risk Assessment: Blast Overpressure Modeling

Abstract: A probabilistic risk assessment (PRA) approach has been developed and applied to the risk analysis of capsule abort during ascent The PRA is used to assist in the identification of modeling and simulation applications that can significantly impact the understanding of crew risk during this potentially dangerous maneuver The PRA approach is also being used to identify the appropriate level of fidelity for the modeling of those critical failure modes The Apollo launch escape system (LES) was chosen as a test problem for application of this approach Failure modes that have been modeled and/or simulated to date include explosive overpressure-based failure, explosive fragment-based failure, land landing failures (range limits exceeded either near launch or Mode III trajectories ending on the African continent), capsule-booster re-contact during separation, and failure due to plume-induced instability These failure modes have been investigated using analysis tools in a variety of technical disciplines at various levels of fidelity The current paper focuses on the development and application of a blast overpressure model for the prediction of structural failure due to overpressure, including the application of high-fidelity analysis to predict near-field and headwinds effects

Overpressure protection device

Abstract: The present invention relates to overpressure protection systems and methods for use on a production system for transferring hydrocarbons from a well on the seafloor to a vessel floating on the surface of the sea. The production system includes a subsea well in fluid communication with a turret buoy through a production flowline and riser system. The turret buoy is capable of connecting to a swivel located on a floating vessel. The overpressure protection device is positioned upstream of the swivel, to prevent overpressure of the production swivel and downstream components located on the floating vessel. The device may include one or more shut down valves, one or more sensors, an actuator assembly, and a control processor.

Process transmitter with overpressure vent

Abstract: An overpressure vent (160) in a transmitter housing (112) of a process transmitter (102) . The transmitter (102) is configured for coupling to an industrial process and measuring a process variable. The transmitter (102) includes an enclosure having a cavity (146) formed therein. A process coupling (114) is configured to couple the cavity (146) to the industrial process. The overpressure vent (160) is arranged to vent an overpressure in the cavity (146) to outside of the transmitter enclosure.

Simulations of the hydrogen migration out of intermediate-level radioactive waste disposal drifts using tough2

Abstract: Corrosion and radiolysis processes cause hydrogen to be generated in a repository for intermediate-level radioactive waste (ILW) for at least 10’000 years after the closure of the facility. Two model configurations have been used for the TOUGH2 simulations to investigate the impact of the hydrogen in terms of the pressure build-up and the gas saturation level in the disposal drift and in the surrounding argillaceous rock formation. 1. Cross-section (2D) through the disposal drift, perpendicular to its axis: The overpressure caused by the hydrogen has been found to be less than the expected frac pressure, for the production rate and scheme considered. 2. Longitudinal vertical section (3D) through the disposal, access and main drifts: The flow of gas/water from the disposal drift through/around the sealing plug in the access drift has been found to have limited impact on the overpressure inside the disposal drift.

Method for quantitative evaluation of fluid pressures and detection of overpressures in an underground medium

Abstract: Method for evaluating fluid pressures in an underground zone by means of seismic and well data. The zone studied is divided into several time analysis intervals. For each of these intervals, a pre-stack stratigraphic inversion of the seismic data is then carried out using geological a priori information, and a lithoseismic facies cube is determined by lithoseismic analysis. Then, for each facies, relations connecting the seismic impedances of wells to differential pressures in wells are determined in each analysis interval. Finally, a differential pressure cube is determined using the previous relations, as well as a confining pressure cube, in order to determine the fluid pressures in the subsoil by simple difference between these two cubes. Application: petroleum sphere for the detection of overpressure zones during drilling for example.

Condensate drainage with maintenance interface

Abstract: The present invention relates to a steam trap for draining off condensate from a collecting chamber in which condensate resulting in a pressure gas system is collected, the collecting chamber being pressurized by a gas pressure which, depending upon the operating state of the pressure gas system, may be a negative pressure below the atmospheric pressure, an overpressure above the atmospheric pressure or an atmospheric pressure itself. The steam trap may be separated via an interface into an integral first assembly unit and an integral maintenance assembly unit which comprises the essential wear and tear parts.

Influence of suspension generation on dust explosion parameters

Abstract: Combustion mechanisms of a suspension of solid particles in a gaseous mixture are studied with the aim of correlating the constant volume explosion characteristics with the initial state of the suspension at ignition time. Two vessels have been specially designed, one transparent with an octagonal cross section, allowing visualization and, the other steel made, able to support 50 bar overpressure to measure combustion characteristics. Particle dispersion in the chamber is achieved by means of the turbulent flow created by the discharge of pressurized air. Experiments were made with cornstarch particle suspensions. Evolution of the flowfield and dust distribution were recorded with high-speed imaging, LDV and PIV. The required delay to obtain an optimal mixture is between 500 and 700 ms. For a stoichiometric cornstarch dust-air mixture, explosion characteristics are in satisfactory agreement with results obtained by other researchers. Theses values decrease with initial rms velocity.

Pore pressure prediction using an Eaton's approach for PS‐waves

Abstract: Mapping overpressure prior to drilling is critical for safe and successful hydrocarbon exploration (Caricone and Helle, 2002). Lack of predictability of abnormal pressures results in cautious drilling, and this leads to slow penetration rates, excessive bit wear and increased well cost and risk while drilling (Mukerji et al., 2002). The excess drilling cost in regions with abnormal pressure can amount to over $20 million per well (Mukerji et al., 2002) or $1.08 billion per year worldwide (Dutta et al. 2002).