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Showing papers on "Overpressure published in 2008"


Journal ArticleDOI
Neil S. Mancktelow1
01 Jun 2008-Lithos
TL;DR: The magnitude of tectonic pressure is determined by a non-dimensional pressure parameter, reflecting geometry and position, and a scaling factor, with units of stress (Pa), given by the strength of the rock as discussed by the authors.

157 citations


Journal ArticleDOI
TL;DR: In the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana, the pore pressure penetrometers did not reach the in situ pressure at the end of the deployment as discussed by the authors.

145 citations


Journal ArticleDOI
01 May 2008-Geology
TL;DR: In this article, a comprehensive database of combined gas permeability and fragmentation experiments was used to deduce a fragmentation criterion that incorporates gas permeabilities as well as porosity and internal overpressure, which implies that the energy required for fragmentation is less dependent on the actual pore geometry than on the way the void space is interconnected and thus on the contribution of permeable gas flow to decompression.
Abstract: Fragmentation of porous magma that is subject to gas overpressure is considered to be a crucial process in the generation of explosive volcanic eruptions. A decompressive event (e.g., rapid magma ascent, landslide, dome collapse) disrupts the stress equilibrium between the gas phase and the surrounding melt. When the gas in the pores is exposed to a pressure gradient, it may either fragment the surrounding magma or escape from the magma along an existing pathway of cracks and interconnected bubbles. Therefore, magma permeability can be a decisive parameter in determining if an eruption experiences fragmentation (i.e., whether it is explosive or effusive, or exhibits a temporal transition between the two eruptive styles). Despite the central role that gas permeability may play in the fragmentation of volcanic rocks, previous studies have not experimentally verified or quantified this influence. Based on a comprehensive database of combined permeability and fragmentation experiments, we show that high permeability substantially increases the overpressure required to fragment porous volcanic rocks. Our results allow us to deduce a fragmentation criterion that incorporates gas permeability as well as porosity and internal overpressure. This criterion implies that the energy required for fragmentation is less dependent on the actual pore geometry than on the way the void space is interconnected and, thus, on the contribution of permeable gas flow to decompression.

142 citations


Journal ArticleDOI
TL;DR: In this article, a free-lagrange numerical method is implemented to simulate the axisymmetric jetting collapse of air bubbles in water, which is performed for both lithotripter shock-induced collapses of initially stable bubbles and for free-running cases where the bubble initially contains an overpressure.
Abstract: A free-Lagrange numerical method is implemented to simulate the axisymmetric jetting collapse of air bubbles in water. This is performed for both lithotripter shock-induced collapses of initially stable bubbles, and for free-running cases where the bubble initially contains an overpressure. The code is validated using two test problems (shock-induced bubble collapse using a step shock, and shock–water column interaction) and the results are compared to numerical and experimental results. For the free-running cases, simulations are conducted for a bubble of initial radius 0.3 mm located near a rigid boundary and near an aluminium layer (planar and notched surfaces). The simulations suggest that the boundary and its distance from the bubble influence the flow dynamics, inducing bubble elongation and jetting. They also indicate stress concentration in the aluminium and the likelihood of aluminium deformation associated with bubble collapse events. For the shock-induced collapse, a lithotripter shock, consisting of 56 MPa compressive and ?10 MPa tensile waves, interacts with a bubble of initial radius 0.04 mm located in a free field (case 1) and near a rigid boundary (case 2). The interaction of the shock with the bubble causes it to involute and a liquid jet is formed that achieves a velocity exceeding 1.2 km s?1 for case 1 and 2.6 km s?1 for case 2. The impact of the jet on the downstream wall of the bubble generates a blast wave with peak overpressure exceeding 1 GPa and 1.75 GPa for cases 1 and 2, respectively. The results show that the simulation technique retains sharply resolved gas/liquid interfaces regardless of the degree of geometric deformation, and reveal details of the dynamics of bubble collapse. The effects of compressibility are included for both liquid and gas phases, whereas stress distributions can be predicted within elastic–plastic solid surfaces (both planar and notched) in proximity to cavitation events. There is a movie with the online version of the paper.

80 citations


Journal ArticleDOI
TL;DR: Ogden et al. as mentioned in this paper used a pseudogas approximation for a mixture of tephra and gas to simulate the effects of standing shock waves on the gas-thrust region and showed that overpressured jets produce vertical heat flux profiles that are drastically different than those of balanced jets.
Abstract: JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B02204, doi:10.1029/2007JB005133, 2008 Numerical simulations of volcanic jets: Importance of vent overpressure Darcy E. Ogden, 1 Kenneth H. Wohletz, 2 Gary A. Glatzmaier, 1 and Emily E. Brodsky 1 Received 24 April 2007; revised 5 October 2007; accepted 5 November 2007; published 29 February 2008. [ 1 ] Explosive volcanic eruption columns are generally subdivided into a gas-thrust region and a convection-dominated plume. Where vents have greater than atmospheric pressure, the gas-thrust region is overpressured and develops a jet-like structure of standing shock waves. Using a pseudogas approximation for a mixture of tephra and gas, we numerically simulate the effects of shock waves on the gas-thrust region. These simulations are of free-jet decompression of a steady state high-pressure vent in the absence of gravity or a crater. Our results show that the strength and position of standing shock waves are strongly dependent on the vent pressure and vent radius. These factors control the gas-thrust region’s dimensions and the character of vertical heat flux into the convective plume. With increased overpressure, the gas-thrust region becomes wider and develops an outer sheath in which the erupted mixture moves at higher speeds than it does near the column center. The radius of this sheath is linearly dependent on the vent radius and the square root of the overpressure. The sheath structure results in an annular vertical heat flux profile at the base of the convective plume, which is in stark contrast to the generally applied Gaussian or top-hat profile. We show that the magnitude of expansion is larger than that predicted from previous 1D analyses, resulting in much slower average vertical velocities after expansion. These new relationships between vent pressure and plume expansion may be used with observations of plume diameter to constrain the pressure at the vent. Citation: Ogden, D. E., K. H. Wohletz, G. A. Glatzmaier, and E. E. Brodsky (2008), Numerical simulations of volcanic jets: Importance of vent overpressure, J. Geophys. Res., 113, B02204, doi:10.1029/2007JB005133. 1. Introduction [ 2 ] In large, explosive volcanic eruptions, the eruptive fluid issues from the vent as a high speed, compressible gas with entrained solid particulates. It is important to quantify the behavior of this gas-thrust region because it provides a connection between the fluid dynamics in the conduit and that of the buoyant column. If the eruptive fluid velocity is at or greater than sonic and vent pressure is higher than atmospheric pressure, the dynamics will be complicated by the presence of standing shock waves that can drastically alter the distribution of the vertical heat flux necessary for eruption column stability. The fluid dynamics and structure of a compressible jet issuing from a sonic nozzle into an ambient atmosphere of lower pressure are well known from experimental, analytical and computational studies [e.g., Crist et al., 1966; Young, 1975; Norman et al., 1982; Figure 1]. Although application of compressible jet dynamics to explosive volcanic eruptions was first sug- gested over 25 years ago by Kieffer [1981], the concept has Earth & Planetary Sciences Department, University of California at Santa Cruz, Santa Cruz, California, USA. Los Alamos National Laboratory, Los Alamos, New Mexico, USA. Copyright 2008 by the American Geophysical Union. 0148-0227/08/2007JB005133$09.00 yet to be widely applied in modeling and analysis of explosive eruption columns. [ 3 ] In this paper, we present computational results that quantify the important effects of vent pressure on the fluid dynamics of volcanic jets and show that overpressured jets produce vertical heat flux profiles that are drastically different than those of pressure-balanced jets. (Note: to avoid confusion, here we use the physics convention and consider ‘‘heat flux’’ the thermal energy transfer per area per unit time (J m 2 s 1 ) and ‘‘heat flow’’ the thermal energy transfer integrated over an entire area per time (J s 1 ). In volcanology literature, the term ‘‘heat flux’’ is often used to mean either of these things [e.g., Woods, 1988; Mastin, 2007]). The simulations shown here are time-dependent, though they assume a steady vent condition. Through these simulations, we quantify the effects of vent pressure and radius on plume radius and heat flux distribution after expansion of the jet. This may allow the prediction of major features of the eruptive structure. We do not consider the effects of variations in conduit dynamics, buoyancy, or the presence of a crater in order to focus only on the effects of vent pressure and radius alone. This study is not a complete picture of the complicated flow dynamics of a volcanic eruption. Rather, the results presented here could be consid- ered the ‘‘simplest case’’ to which one could compare the dynamics resulting from more complicated simulations and observations of high-pressure volcanic jets. B02204 1 of 18

63 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new fragmentation criterion to explain the relationship between the gas overpressure at the fragmentation surface, the initial pressure and the porosity, and obtained satisfactory agreement between their simulation and experiment when they assume that the critical value is inversely proportional to the square root of bubble wall thickness.

60 citations


Journal ArticleDOI
TL;DR: In this paper, a large eddy simulation (LES) model of gaseous deflagration is applied to reproduce experimental data on uniform 20% and 30% hydrogen-air mixture explosions in a 78.5m long tunnel.
Abstract: A large eddy simulation (LES) model of gaseous deflagration, previously validated against the largest known 20-m diameter deflagration in the open atmosphere, is applied in this study to reproduce experimental data on uniform 20% and 30% hydrogen-air mixture explosions in a 78.5-m long tunnel. The model enables the transient modelling of deflagration dynamics with a laminar flamelet burning velocity which alters spatially and in time with mixture composition, pressure, and temperature. The turbulent burning velocity is computed using Yakhot's model of premixed turbulent combustion. Yakhot's transcendental equation is essentially customized to account for both the transitional phenomenon of turbulence generated by the flame front itself, and the fractal structure of the flame surface on an unresolved sub-grid scale (SGS) level. The LES model reproduced available experimental data for both 20% and 30% hydrogen-air mixtures in an unobstructed and an obstructed tunnel. The simulations gave insight into the dynamics of flame propagation and the pressure build up within and outside of the tunnel. The LES model enabled the analysis of phenomena that were not reported in the experimental study. For example, a significant increase in the maximum explosion overpressure was observed in the vicinity of obstacles due to obstacle side-on pressure wave reflection in later stages of the event.

49 citations


Journal ArticleDOI
TL;DR: In this article, the authors present empirical correlations between the flame speed and the burning velocity starting from the explosion indices K St and P max of the standardized 20-l sphere test and either the calculation of the explosion overpressure or the sizing of relief vents of an enclosure.
Abstract: Explosion relief vents on enclosures in powder-handling plants are currently designed according to technical standards that in some situations may overestimate the required vent area significantly. These technical standards sometimes do not take into account the real work conditions of industrial plants (e.g. turbulence intensity) and therefore explosion worst cases are not always foreseeable. The availability of methods either for the evaluation of explosion overpressure or sizing of relief vents, with involvement of the pre-ignition turbulence, could be very useful for a better estimate of these quantities. In this work two empirical correlations are presented: the first one allows the calculation of the flame speed and the burning velocity starting from the explosion indices K St and P max of the standardized 20-l sphere test. The second allows either the calculation of the explosion overpressure or the sizing of relief vents of an enclosure.

46 citations


Journal ArticleDOI
TL;DR: In this paper, the authors constrain overpressure (25-50% of hydrostatic effective stress) above 30 mbsf at two sites in the Mississippi Canyon region, northern Gulf of Mexico.
Abstract: [1] Laboratory experiments constrain overpressure (25–50% of hydrostatic effective stress) above 30 mbsf at two sites in the Mississippi Canyon region, northern Gulf of Mexico. Overpressure at site 2562 is less than that at site 2567; however site 2562 has accumulated faster. One-dimensional sedimentation-consolidation models cannot recreate the overpressure without external fluid sources. A fluid source (specific discharge, q = 2–7 mm/yr) is required for site 2567, whereas a fluid sink (q = 10–12 mm/yr) is required for site 2562 to simulate the constrained overpressure. Although basal conditions differ, specific discharge of 2.1–4.2 mm/yr occurs at the sea floor. Shallow upward flow at each site, deep upward flow at site 2567 and deep downward flow at site 2562 is consistent with a two-dimensional flow field where sites 2562 and 2567 are hydrologically connected at depth by a regional aquifer.

38 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used a soil model to determine that an extrapolation approach based on the inverse of square root of time ( 1 / t ) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation.

37 citations


Journal ArticleDOI
TL;DR: In this paper, empirical correlations for blast-wave overpressure and fragments initial velocity are presented, based on the basic hypothesis that BLEVE is a phenomenon driven by the excess heat stored in the liquid (overheated liquid) and some thermodynamic approximations are introduced.
Abstract: When a pressure vessel filled with a liquid is involved in a fire, a variety of effects are to be expected. If the vessel is filled with LPG, a boiling liquid expanding vapour explosion (BLEVE) is one of the possible effects, although it does not always happen. Actually BLEVE is a complex phenomenon resulting from many factors which are hard to summarize into mathematical formulations or models. Nevertheless it could be useful in order to assess the consequences of a BLEVE, to have access to simplified models lying on physical basis. In this paper empirical correlations for blast-wave overpressure and fragments initial velocity are presented. The basic hypothesis that BLEVE is a phenomenon driven by the excess heat stored in the liquid (overheated liquid) is assumed and some thermodynamic approximations are introduced. Despite these approximations and the empirical formulation simplicity, the results accuracy is good.

Journal ArticleDOI
TL;DR: In this paper, the pore pressure in shales is estimated using well-log or seismic data, and measured pressures in adjacent reservoir beds are used to calibrate the estimated shale pore pressures, a methodology that works well where reservoirs are restricted in volume and without significant leakage.
Abstract: Direct measurements of pore pressure in shales are usually not possible because of the low permeabilities, but shale pore pressures may be estimated using well-log or seismic data. Measured pressures in adjacent reservoir beds are used to calibrate the estimated shale pore pressures, a methodology that works well where reservoirs are restricted in volume and without significant leakage. Analysis of pressure data from many basins with substantial hydrocarbon reserves shows significant pressure drawdown due to lateral drainage along inclined reservoirs and through faults to shallower levels. When the direct measurements of pore pressure used for calibration have been made in reservoirs that have experienced lateral drainage, the shale pore pressures are underestimated. Consequently, mud weights selected for drilling may be too low, leading to the risk of fluid influx and blow out when encountering other reservoir beds that are sealed by encasing shales. Furthermore,understanding the geological context for overpressure development is useful in exploration because of the implications for hydrocarbon migration, hydrodynamic trapping, and hydrocarbon column height assessment.

01 Jan 2008
TL;DR: In this paper, a series of laboratory measurements were conducted to investigate the relationships between velocity/porosity/density/permeability versus effective stress for pure smectite, kaolinite, and silt, and their mixtures.
Abstract: A general way of predicting pore pressure in sedimentary basins is to use relationships of sonic travel time and/or seismic interval velocity versus depth / effective stress in mudstones. Pore pressure is then estimated from the divergence from generalized compaction trends. The key to a successful conversion of mudstone compaction trends to pore-pressure prediction is to characterize the mudstones as functions of lithology and textural variations and to establish relationships between porosity/density/velocity/ permeability versus effective stress. Sedimentary basins are awfully heterogeneous as functions of sedimentary facies, tectonic development, and diagenetic history. Fluid transport in sedimentary basins is therefore controlled largely by the heterogeneity of the basin fill. Overpressure generation is the function of fluid flux generated by compaction (porosity loss) and the permeability along the most permeable pathways to the surface. Generation of fluids from kerogen and dehydration of minerals may add to this fluid fluxes, but permeability is the most critical parameter determining the development of overpressure. A series of laboratory measurements were conducted to investigate the relationships between velocity/porosity/density/permeability versus effective stress for pure smectite, kaolinite, and silt, and their mixtures. Experimental compaction has shown that the permeability of clay minerals vary by a factor of 104 to 105 for the same porosity. The smectite-rich mudstones have very low permeability compared to others and have potentiality to develop overpressure even at shallow or moderate burial depth. Calculations assuming vertical flow show that fracture pressure will be reached if the effective permeability of the shale forming the seal is less than 0.1-0.01 nD (nanodarcies). The experimental results of relationships between velocity/porosity/ density/permeability versus effective stress of well-characterized mudstones were compared to the field data which demonstrated a close match, confirming that experimental data can be useful to distinguish mudstones for pore-pressure prediction.

Journal ArticleDOI
TL;DR: The lower Cretaceous Britannia Sandstone Formation is located below overpressured Sola Formation shales and above Jurassic reservoirs and represents a pressure regression, recording overpressure values ranging from approximately 100 psi in Block 15/30 (in the extensional Outer Moray Firth/Central North Sea basin) up to a maximum of approximately 1600 PS in Block 22/4.
Abstract: The Lower Cretaceous Britannia Sandstone Formation is located below overpressured Sola Formation shales ( c . 2800 psi overpressure) and above Jurassic reservoirs (up to 5700 psi overpressure) and represents a pressure regression, recording overpressure values ranging from approximately 100 psi in Block 15/30 (in the extensional Outer Moray Firth/Central North Sea basin) up to a maximum of approximately 1600 psi in Block 22/4. The Britannia Sandstone has an anomalously low overpressure when compared with deeper Cretaceous (Valhall) and Jurassic reservoir overpressures locally, and further afield in the Central North Sea at similar depths. The pore pressures in the Sola Formation shales have been estimated using conventional porosity/sonic-based prediction methods, indicating strong overpressure disequilibrium between the Sola Formation shales and the Britannia Sandstones, both in the Britannia Field area and in the laterally age-equivalent sands to the west referred to as the Kopervik Fairway (the Aptian sands of the South Halibut Basin, forming the reservoirs of the Blake, Captain and Goldeneye fields). Burial curve modelling indicates that it is likely that the Sola Formation shales have overpressured for the last 4 Ma, and likely much longer, suggesting an early history of pressure build up (now preserved in the Sola Formation shales and deeper, Jurassic reservoirs and associated sediments). The adjacent Britannia Sandstone Formation therefore lost fluid and pressure due to local availability of a fluid conduit. Resulting active fluid flow, driven by overpressure differences in the Britannia Sandstone Formation, has created a hydrodynamically tilted hydrocarbon–water contact with lateral flow from east to west. Well evidence indicates vertical flow from shallower reservoirs into the stratigraphically deeper, main Britannia reservoir. The fluid escape could be either laterally via the Kopervik Fairway and/or vertically through the Upper Cretaceous Chalk facilitated by fractures/faulting.

Journal ArticleDOI
Brandon Dugan1
TL;DR: In this paper, the authors used laboratory experiments and drilling observations to estimate vertically upward fluid flow rates of approximately 4mm/yr in Keathley Canyon, northern Gulf of Mexico.

Journal ArticleDOI
TL;DR: In this article, the authors show that realistic permeabilities can be assumed, provided that compressibilities describing the plastic process of compaction are used in the pressure equation instead of the elastic compressibilites that, for instance, can be derived from log data.
Abstract: Cretaceous–Paleogene overpressure distribution in the Danish Central Graben shows a remarkable coincidence with the thickness of the rapidly deposited middle Miocene to Holocene succession. Slow deposition of smectite-dominated clays in a deep-marine environment occurred from the late Paleocene until the middle Miocene, and the resultant mudstone succession constitutes the main barrier that delays pressure dissipation. Between the late Miocene and the Holocene, the Upper Cretaceous–Paleogene succession became overpressured, probably because of accelerated depositional rates. Quantification of this disequilibrium compaction mechanism relies mainly on a determination of permeability and effective compressibility of the Paleogene shales. This article shows that realistic permeabilities can be assumed, provided that compressibilities describing the plastic process of compaction are used in the pressure equation instead of the elastic compressibilites that, for instance, can be derived from log data. One-dimensional (1-D) modeling is applied in two cases: a well from the Dan chalk field, where accelerated deposition since the Tortonian (11.2 Ma) produced a present-day overpressure of 7.97 MPa (1156 psi); and a well from the South Arne chalk field, where accelerated deposition since the early Serravallian (14.6 Ma) produced a present-day overpressure of 13.9 MPa (2016 psi). This is based on an identical set of parameters and compares with the observed 7.7 and 14.8 MPa (1117 and 2147 psi ) overpressure at the two locations. The modeled development of the pressure profiles shows that an effective stress minimum occurred in the upper part of the Paleogene succession. This is consistent with the observed ubiquitous intraformational faulting at that level. About 80% of the added Neogene load is estimated to have been converted to overpressure.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the mechanism by which overpressure is generated and maintained in the Taiwan oil fields by using a one-dimensional basin model incorporating laboratory-approximated hydraulic parameters.
Abstract: [1] Overpressure, fluid pressure higher than hydrostatic pressure, has developed below the middle Miocene formations in the north central Western Foothills of Taiwan. To study the mechanism by which overpressure is generated and maintained in the Taiwan oil fields, we estimated the fluid pressure history and overpressure distribution by using a one-dimensional basin model incorporating laboratory-approximated hydraulic parameters. Transport properties of outcropping sedimentary rocks were measured at effective pressures of 5 to 200 MPa. All parameters showed apparent stratigraphic variation, decreasing with increasing burial depth. Permeability showed the strongest sensitivity to depth, decreasing by 6 orders of magnitude to 10−20 m2 at the bottom of the basin. A critical sealing layer was not identified in the geologic column. The basin model incorporates overburden loading due to sediment accumulation, aquathermal expansion of water, the dehydration reaction of expandable clay to nonexpandable clay, and oil generation. Predicted overpressure was generated dramatically from 3 Ma, when the accumulation rate increased rapidly as a result of tectonic collisions in the area. If we assume a fluid influx from the bottom of the basin, the predicted overpressure is consistent with the observed overpressure, implying that continuous inflow from depth, possibly along the decollement or normal faults, may be the main cause of overpressure generation in this area. Stratigraphic variation of transport properties, which decrease with depth, also influences overpressure trends in the Western Foothills, where overpressure is generated only in deeper horizons. The clay mineral distribution estimated by a kinetic smectite-illite dehydration model is consistent with the observed mineralogical data.

Journal ArticleDOI
TL;DR: In this article, a new method was proposed for suppressing gas-explosion propagation in a tunnel by using a vacuum chamber, which can absorb the explosion wave and explosion energy as much as possible at the beginning of the gas explosion and when the vacuum chamber is used the closer it is to the ignition source the more significant the suppression effect.

Journal ArticleDOI
TL;DR: In this article, the scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed, and the results point out the possibility of detecting source explosions from far-field pressure measurements.
Abstract: The scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed. Both point source explosions and high pressure gas explosions are considered. Test data on blast overpressure from the interaction and coalescence of spherical blast waves emanating from explosives in the form of shaped charges of different strength placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure. The results point out the possibility of detecting source explosions from far-field pressure measurements.

Journal ArticleDOI
TL;DR: In this article, a three-dimensional nonlinear dynamic simulation analysis for an explosion experiment inside tunnel was carried out with the help of the numerical simulation finite element software LS-DYNA.
Abstract: The explosion inside tunnel would generate blast wave which transmits through the longitudinal tunnel. Because of the close-in effects of the tunnel and the reflection by the confining tunnel structure, blast wave propagation inside tunnel is distinguished from that in air. When the explosion happens inside tunnel, the overpressure peak is higher than that of explosion happening in air. The continuance time of the blast wave also becomes longer. With the help of the numerical simulation finite element software LS-DYNA, a three-dimensional nonlinear dynamic simulation analysis for an explosion experiment inside tunnel was carried out. LS-DYNA is a fully integrated analysis program specifically designed for nonlinear dynamics and large strain problems. Compared with the experimental results, the simulation results have made the material parameters of numerical simulation model available. By using the model and the same material parameters, many results were adopted by calculating the model under different TNT explosion dynamites. Then the method of dimensional analysis was used for the simulation results. As overpressures of the explosion blast wave are the governing factor in the tunnel responses, a formula for the explosion blast wave overpressure at a certain distance from the detonation center point inside the tunnel was derived by using the dimensional analysis theory. By comparing the results computed by the formula with experimental results which were obtained before, the formula was proved to be very applicable at some instance. The research may be helpful to estimate rapidly the effect of internal explosion of tunnel on the structure.

Proceedings ArticleDOI
05 May 2008
TL;DR: In this paper, an extensive database of low-to normal-intensity booms (overpressures of 0.08 lbf/sq ft to 2.20 lbf /sq ft) was collected for propagation code validation, and initial results and flight research techniques were presented.
Abstract: An extensive sonic boom propagation database with low- to normal-intensity booms (overpressures of 0.08 lbf/sq ft to 2.20 lbf/sq ft) was collected for propagation code validation, and initial results and flight research techniques are presented. Several arrays of microphones were used, including a 10 m tall tower to measure shock wave directionality and the effect of height above ground on acoustic level. A sailplane was employed to measure sonic booms above and within the atmospheric turbulent boundary layer, and the sailplane was positioned to intercept the shock waves between the supersonic airplane and the ground sensors. Sailplane and ground-level sonic boom recordings were used to generate atmospheric turbulence filter functions showing excellent agreement with ground measurements. The sonic boom prediction software PCBoom4 was employed as a preflight planning tool using preflight weather data. The measured data of shock wave directionality, arrival time, and overpressure gave excellent agreement with the PCBoom4-calculated results using the measured aircraft and atmospheric data as inputs. C-weighted acoustic levels generally decreased with increasing height above the ground. A-weighted and perceived levels usually were at a minimum for a height where the elevated microphone pressure rise time history was the straightest, which is a result of incident and ground-reflected shock waves interacting.

Proceedings ArticleDOI
21 Jul 2008
TL;DR: In this article, numerical simulations of model solid rocket motor ignition overpressure wave were performed with the CEDRE unstructured reactive flow solver developed at ONERA to reproduce major trends such as the effects of nozzle shape and motor pressure build up rates.
Abstract: This paper presents numerical simulations of model solid rocket motor ignition overpressure wave. The computations are performed with the CEDRE unstructured reactive flow solver developed at ONERA. The flow description is two-dimensional axisymmetric and focuses on the effects of nozzle shape, motor pressure build-up rates and post-combustion of motor exhaust plume with ambient air. The results are compared to those of several experimental firings carried out at the ONERA CFM center in the South of France. It is demonstrated that the computations can reproduce majors trends such as the effects of nozzle shape and motor pressure build up rates. However directivity patterns and wave amplitude are not accurately reproduced. This is believed to be due to the limitations of the 2D approach that cannot properly describe the motor plume development. The role of postcombustion in the pressure wave patterns is studied through different chemistry models. Although limited by the 2D nature of the computations the conclusions seem to indicate a possible effect of plume post-combustion on the pressure wave characteristic. Further work is needed before concluding on that matter. In particular, 3D simulations seem to be necessary to properly describe the flow development and the details of the pressure wave patterns. The presented work has been supported through CNES-ONERA AEID program.

01 Jan 2008
TL;DR: In this article, a new formula has been summed up, and LS-DYNA has been used to simulate the spreading of shock wave in the air generated by TNT explosion on different conditions.
Abstract: Differences between several scholars′ forecasts of peak overpressure have been compared by the con-trastive analysis of research on TNT explosion shock wave spreading in the air.A new formula has been summed up,and LS-DYNA has been used to simulate the spreading of shock wave in the air generated by TNT explosion on different conditions.The numerical values are less than empirical formula′s.The results of the explosion with heavier load are more approximate than the forecasting results of empirical formula.So it′s necessary to do more research on explosion shock wave parameters.

DOI
01 Mar 2008
TL;DR: In this article, the authors investigated the flow structures inside and outside a rocket nozzle and found a simple function to analyze the flow structure inducing transition between free shock separation and restricted shock separation inside a nozzle.
Abstract: The objective of this study is to clarify flow structures inside and outside a rocket nozzle, which are indispensable for actual development of rocket engine. One is the transition of the flow structure between free shock separation and restricted shock separation inside a nozzle, which would sometimes generate a destruc- tive side-load. The transition is numerically reproduced under the experimental condition where the transition occurs. We also found a simple function to analyze the flow structure inducing transition. Another is ignition overpressure induced by engine ignition. The overpressure, which originates in shock wave, imposes high pressure load on the nozzle or rocket surface and also influence the ignition process especially under cluster- ing (two) nozzle configuration. The numerical results show that besides an overpressure, a vortex ring is gen- erated and propagated from the nozzle. Under clustering nozzle configuration, the interaction between the overpressure waves and the vortex rings occurs between the nozzles. This makes the force acting on the noz- zle asymmetric. We could estimate the side-load acting on the nozzle actuator in advance of the development and firing test.

Journal Article
TL;DR: In this paper, the effect of bifurcation on the flame velocity and overpressure is analyzed theoretically, and the authors show that the effects of the overpressure and flame velocity on the explosion wave overpressure of a methane explosion in a bifurlapse duct are clear.
Abstract: To master the propagation rule of methane explosion in bifurcation duct,the explosion wave overpressure and flame velocity of methane explosion in bifurcation duct were measured by means of experiment,and the propagation of methane explosion in bifurcation duct was analyzed theoretically.It shows that the effect of bifurcation on the flame velocity and overpressure is obvious,and the destruction in bifurcation is serious.So during the mine exploitation and laneway design,the bifurcation laneway should be avoided and the obstruction should be eliminated as possible.When the bifurcation is unavoidable,the relevant preventive measures should be adopted to suppress the methane explosion propagation,depress the intensity and diminish the loss due to gas explosion,according to the propagation rules.

Journal Article
TL;DR: In this article, the authors deduced the attenuation law of the shock wave in excavation roadway during gas explosion by combining with the theory of the conservation law of mass,momentum, energy and gas explosion dynamics.
Abstract: Combining with the theory of the conservation law of mass,momentum,energy and gas explosion dynamics,the attenuation law of shock wave in excavation roadway was deduced during gas explosion.The deduction shows that the maximum overpressure on the shock wave front is inversely proportional to the square root of the propagation distance and the roadway section,and in direct proportion to the square root of the accumulated volume of gas.Comparing the analysis between experiment and deduction,it is concluded that the theoretical data is fairly close to that of the experiment,which proves that the deduction of the overpressure on the shock wave front attenuating with the propagation distance is reasonable.

Proceedings ArticleDOI
TL;DR: In this article, an experimental set-up has been developed to support reduced scale structures as well as reduced scale detonating solid charges, which can be used to produce the entry data for numerical assessments of the structure resistance.
Abstract: The definition of blast loads applying to a complex geometry structure is, nowadays, still a hard task when numerical simulation is used, essentially because of the different scales involved: as a matter of fact, modelling the detonation of a charge and its resulting load on a structure requires one to model the charge itself, the structure and the surrounding air, which rapidly leads to large size models on which parametrical studies become unaffordable. So, on the basis of the Crank-Hopkinson’s law, an experimental set-up has been developed to support reduced scale structures as well as reduced scale detonating solid charges. As a final objective, the set-up must be used to produce the entry data for numerical assessments of the structure resistance. This set-up is composed of a modular table, sensors and targets and has been designed to conduct nondestructive studies. In the context of security, the general aim is to study the effects of detonation shock waves in the vicinity of test installations and to test various shock wave mitigation means that could be implemented for the protection of facilities in sensitive locations. In particular, the set-up offers the possibility of measuring the loading in terms of pressuretime curves, even for very complex situations like multiple reflections, combination and diffraction. The present paper summarizes the development of the set-up, as well as the first tests performed. The main features of the table, the instrumentation and the pyrotechnics are given. Also, the paper summarizes a first qualification test campaign that was conducted in the year 2006. In this campaign, free field blast tests (i.e. blast tests performed without structures) have been conducted. Overpressure maxima, arrival time of the shock wave and impulse are presented as nondimensional characteristics of the pressure time history. The results obtained have been found to be in good agreement with reference curves available from the open literature.

Patent
27 Jun 2008
TL;DR: In this article, a cylindrical chamber with a plurality of lateral holes is used for releasing gas in overpressure, and a fusible device is used to keep the spring compressed and contrast the thrust of the gas exclusively in normal pressure and temperature conditions.
Abstract: A safety valve (1), particularly for releasing gas in overpressure, which includes a cylindrical chamber (2) provided with a plurality of lateral holes (3) and with an opening (4) which is provided on the bottom and connects it to the inside of a tank which contains gas; the cylindrical chamber (2) accommodates a flow control means (5) which is biased in abutment against the opening (4) by a spring (6). A fusible device (10) is joined to the top of the cylindrical chamber (2) in order to keep the spring (6) compressed and contrast the thrust of the gas exclusively in normal pressure and temperature conditions.

Journal ArticleDOI
TL;DR: In this article, the characteristics of the mudstone overpressure were studied to reveal the relationship between reservoir distribution and overpressure, and several overpressure mudstone cap-rocks were found in the Turpan Depression.

Patent
20 Mar 2008
TL;DR: In this paper, a method and a device for preventing fast changes of the atmospheric pressure in an enclosed room induced by an external environment was proposed, where the internal pressure in the room was monitored by a sensor.
Abstract: The invention relates to a method and a device for preventing fast changes of the atmospheric pressure in an enclosed room (1) induced by an external environment. According to the invention, the internal pressure in the room (1) is monitored by a sensor (3). Fast changes of the internal pressure are at least partially compensated for by the targeted supply or removal of air. The supply and removal of air preferably occurs with overpressure and underpressure containers (5, 6).