Showing papers on "Overpressure published in 2014"

Relationship between tectonic overpressure, deviatoric stress, driving force, isostasy and gravitational potential energy

Abstract: We present analytical derivations and 2-D numerical simulations that quantify magnitudes of deviatoric stress and tectonic overpressure (i.e. difference between the pressure, or mean stress, and the lithostatic pressure) by relating them to lateral variations in the gravitational potential energy (GPE). These predictions of tectonic overpressure and deviatoric stress associated with GPE differences are independent of rock rheology (e.g. viscous or elastic) and rock strength. We consider a simple situation with lowlands and mountains (plateau). We use a numerical two-layer model consisting of a crust with higher Newtonian viscosity than that in the mantle, and also a three-layer model in which the two-layer lithosphere overlies a much less viscous asthenosphere. Our results (1) explain why estimates for the magnitude of stresses in Tibet, previously published by different authors, vary by a factor of two, (2) are applied to test the validity of the thin sheet approximation, (3) show that the magnitude of the depth-integrated tectonic overpressure is equal to the magnitude of the depth-integrated deviatoric stress if depth-integrated shear stresses on vertical and horizontal planes within the lithosphere are negligible (the thin sheet approximation) and (4) show that under thin sheet approximation tectonic overpressure is required to build and support continental plateaus, such as in Tibet or in the Andes, even if the topography and the crustal root are in isostatic equilibrium. Under thin sheet approximation, the magnitude of the depth-integrated tectonic overpressure is equal to the depth-integrated horizontal deviatoric stress, and both are approximately 3.5 × 10 12 N m −1 for Tibet. The horizontal driving force per unit length related to lateral GPE variations around Tibet is composed of the sum of both tectonic overpressure and deviatoric stress, and is approximately 7 × 10 12 N m −1 . This magnitude exceeds previously published estimates for the force per unit length required to fold the Indo-Australian Plate south of India, and hence the uplift of the Tibetan plateau could have folded the Indian Plate. We also discuss the mechanical conditions that are necessary to achieve isostasy, for which the lithostatic pressure is constant at a certain depth. The results show that tectonic overpressure can exist at a certain depth even if all deviatoric stresses are zero at this depth, because this tectonic overpressure is related to horizontal gradients of vertical shear stresses integrated across the entire depth of the lithosphere. The magnitude of the depth-integrated tectonic overpressure of 3.5 × 10 12 N m −1 implies that the pressure estimated from observed mineral assemblages in crustal rocks is likely significantly different from the lithostatic pressure, and pressure recorded by crustal rocks is not directly related to depth. In case of significant weakening of the entire lithosphere by any mechanism our analytical and numerical studies provide a simple estimation of tectonic overpressure via variations in GPE.

Detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the Krishna-Godavari Basin, India

Abstract: Abnormally high pressures, measured by repeat formation tester (RFT) and detected by well log data from 10 wells in the Krishna-Godavari (K-G) Basin, occur in the Vadaparru Shale of Miocene and Raghavapuram Shale of Early Cretaceous age. Overpressures generated by disequilibrium compaction, and pore pressures have been estimated using the conventional Eaton sonic equation with an exponent of 3.0. The observed abnormal pore pressure gradient ranges from 11.85 to 13.10 MPa/km, whereas fracture pressure gradient varies from 17.40 to 19.78 MPa/km. The magnitude of vertical stress (Sv) has a gradient from 21.00 to 23.10 MPa/km. The minimum horizontal principal stress (Sh) magnitude is found to vary from 64 to 77% of the Sv in normally pressured to overpressured sediments. A multiple linear regression model with a squared multiple correlation coefficient (R2) of 0.94 is proposed for pore pressure prediction from gamma ray, density and sonic logs to focus on efficient drilling operations and to prevent borehole instability. The statistical model has been calibrated with the RFT data from five wells covering about 3400 sq. km area of the onshore K-G Basin. The model predicted pore pressure values are in close agreement with the actual RFT data for another four wells including a well in the offshore K-G Basin. Hence, the proposed regression model may be useful for predicting pore pressure from other well logs in the K-G Basin.

Partitioning of Seismoacoustic Energy and Estimation of Yield and Height‐of‐Burst/Depth‐of‐Burial for Near‐Surface Explosions

Abstract: Explosions near the Earth’s surface excite both seismic ground motions and atmospheric overpressure. The energy transferred to the ground and atmosphere from a near‐surface explosion depends on yield ( W ) as well as the height‐of‐burst/depth‐of‐burial (HOB/DOB) for above/belowground emplacements. We report analyses of seismic and overpressure motions from the Humble Redwood series of low‐yield, near‐surface chemical explosions with the aim of developing quantitative models of energy partitioning and a methodology to estimate W and HOB/DOB. The effects of yield, HOB, and range on amplitudes can be cast into separable functions of range and HOB scaled by yield. We find that displacement of the initial P wave and the integral of the positive overpressure (impulse) are diagnostic of W and HOB with minimal scatter. An empirical model describing the dependence of seismic and air‐blast measurements on W , HOB/DOB, and range is determined and model parameters are found by regression. We find seismic amplitudes for explosions of a given yield emplaced at or above the surface are reduced by a factor of 3 relative to fully contained explosions below ground. Air‐blast overpressure is reduced more dramatically, with impulse reduced by a factor of 100 for deeply buried explosions relative to surface blasts. Our signal models are used to invert seismic and overpressure measurements for W and HOB and we find good agreement ( W errors <30%, HOB within meters) with ground‐truth values for four noncircular validation tests. Although there is a trade‐off between W and HOB for a single seismic or overpressure measurement, the use of both measurement types allows us to largely break this trade‐off and better constrain W and HOB. However, both models lack resolution of HOB for aboveground explosions.

Explosion and flame characteristics of methane/air mixtures in a large-scale vessel

Abstract: In this study, experiments of explosions and flame characteristics in methane/air mixtures are performed in a 10-m3 vessel. Pressure gauges and a high-speed camera are utilized to record the pressure trajectories and the flame propagation process of ignition growth. The experimental results show that the maximum value of overpressure and the maximum rate of the explosion pressure rise are 0.596 MPa and 1.82 MPa/s for the methane (9.5% in volume)/air mixture at atmospheric conditions, respectively. Both values are higher than for other mixtures with different compositions. The results also indicate that the overpressure from the large-scale vessel in this study is lower than that of a smaller apparatus (e.g., 5-L closed cylindrical vessel). This difference occurs due to the cooling effect and because the reflected sonic disturbances by the vessel wall affect the explosion process and weaken the energy during the pressure attenuation stage, thus rendering the value of overpressure in the large-scale apparatus lower than in the tiny cylindrical vessels. The maximum overpressure is observed at 0.75 m for C = 7% (“C” means the methane concentration) and 9.5% but at 1.3 m for C = 5%, 6.5%, 11.2%, and 13%. These results indicate that methane/air is an easier means to generate overpressure and that the overpressure is higher near the stoichiometric condition. Based on the analysis of the flame propagation process, the mean value of the flame speed of methane (C = 9.5%)/air is calculated to be approximately 2.43 m/s because the nonuniformity of the chemical reaction at the flame front results in a maximum fluctuation of flame speed of approximately 28.5%. The flame thickness (θ) of methane (C = 9.5%)/air fluctuates between 9.84 and 10.95 mm, with a mean value of 10.53 mm. © 2014 American Institute of Chemical Engineers Process Saf Prog 33: 362–368, 2014

Shock wave generated by high-energy electric spark discharge

Abstract: Shock wave generated by electric spark discharge was studied experimentally and the shock wave energy was evaluated in this paper. A pressure measurement system was established to study the pressure field of the electric spark discharge process. A series of electric spark discharge experiments were carried out and the energy of the electric spark used in present study was in the range of 10 J, 100 J, and 1000 J, respectively. The shock wave energy released from the electric spark discharge process was calculated by using the overpressure values at different measurement points near the electric spark discharge center. The good consistency of shock wave energies calculated by pressure histories at different measuring points in the same electric spark discharge experiment illustrates the applicability of the weak shock wave theory in calculating the energy of shock wave induced by electric spark discharge process. The result showed that shock wave formed at the initial stage of electric spark discharge process, and the shock wave energy is only a little part of electric spark energy. From the analysis of the shock wave energy and electric spark energy, a good linear relationship between shock wave energy and electric spark energy was established, which make it possible to calculate shock wave energy by measuring characteristic parameters of electric spark discharge process instead of shock wave. So, the initiation energy of direct initiation of detonation can be determined easily by measuring the parameters of electric spark discharge process.

Enhancement effects of methane/air explosion caused by water spraying in a sealed vessel

Abstract: Experiments about the influence of ultrafine water mist on the methane/air explosion were carried out in a fully sealed visual vessel with methane concentrations of 8%, 9.5%, 11% and 12.5%. Water mists were generated by two nozzles and the droplets' Sauter Mean Diameters (SMD) were 28.2 μm and 43.3 μm respectively which were measured by Phase Doppler Particle Anemometer (PDPA). A high speed camera was used to record the flame propagation processes. The results show that the maximum explosion overpressure, pressure rising rate and flame propagation velocity of methane explosions in various concentrations increased significantly after spraying. Furthermore, the brightness of explosion flame got much higher after spraying. Besides, the mist with a larger diameter had a stronger turbulent effect and could lead to a more violent explosion reaction.

Water hammer in the pump-rising pipeline system with an air chamber

Abstract: Water hammer following the tripping of pumps can lead to overpressure and negative pressure. Reduction in overpressure and negative pressure may be necessary to avoid failure, to improve the efficiency of operation and to avoid fatigue of system components. The field tests on the water hammer have been conducted on the pump rising pipeline system with an air chamber. The hydraulic transient was simulated using the method of characteristics. Minimizing the least squares problem representing the difference between the measured and predicted transient response in the system performs the calibration of the simulation program. Among the input variables used in the water hammer analysis, the polytropic exponent, the discharge coefficient and the wave speed were calibrated. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system. The correct selection of air chamber size and the effect of the inner diameter of the orifice to minimize water hammer have been investigated by both field measurements and numerical modeling.

A parametric approach to shape field-relevant blast wave profiles in compressed-gas-driven shock tube.

Abstract: Detonation of a high explosive produces shock-blast wave, shrapnel, and gaseous products. While direct exposure to blast is a concern near the epicenter, shock-blast can affect subjects even at farther distances, which is termed as primary blast injury, which is the theme of this work. The shock-blast profile is characterized with blast overpressure, positive time duration, and impulse as shock-blast wave parameters (SWPs). These parameters in turn are a function of field factors, such as the strength of high explosive and the distance of the human subjects from the epicenter. The shape and magnitude of the profile determine the severity of injury to the subjects. As shown in some of our recent works (Chandra et al., 2011;Sundaramurthy et al., 2012;Skotak et al., 2013), the profile not only determines the survival of the animal but also the acute and chronic biomechanical injuries along with the following bio-chemical sequelae. It is extremely important to carefully design and operate the shock tube to produce field relevant SWPs. Furthermore, it is vital to identify and eliminate the artifacts that are inadvertently introduced in the shock-blast profile that may affect the results. In this work, we examine the relationship between shock tube adjustable parameters (SAPs) and SWPs that can be used to control the blast profile; the results can be easily applied to many of the laboratory shock tubes. Further, exact replication of shock profile (magnitude and shape) can be related to field explosions and can be a standard in comparing results across different laboratories. 40 experiments are carried out by judiciously varying SAPs such as membrane thickness, breech length (66.68 to 1209.68 mm), measurement location, and type of driver gas (nitrogen, helium). The relationships between SAPs and the resulting shock-blast profiles are characterized. Finally, shock-blast profiles of a TNT explosion from ConWep software is compared with the profiles obtained from the tube.

Background-oriented schlieren with natural background for quantitative visualization of open-air explosions

Abstract: This study describes an attempt of quantitative visualization of open-air explosions via the background-oriented schlieren method (BOS). The shock wave propagation curve and overpressure distribution were extracted from the obtained images and compared with the results of the numerical analysis. The potential of extracting the density distribution behind the shock front is also demonstrated. Two open-air explosions were conducted; one with a $$36$$ -kg emulsion explosive and the other with a $$7.89$$ -kg composition C4 explosive. A high-speed digital video camera was used with a frame rate of $$10{,}000\,\mathrm{Hz}$$ and a pixel size of $$800 \times 600$$ . A natural background, including trees and grass, was used for BOS measurements instead of the random dots used in a laboratory. The overpressure distribution given by the passing shock was estimated from the visualized images. The estimated overpressures agreed with the values recorded by pressure transducers in the test field. The background displacement caused by light diffraction inside the spherical shock waves was in good agreement, except at the shock front. The results shown here suggest that the BOS method for open-air experiments could provide increasingly better quantitative and conventional visualization results with increasing spatial resolution of high-speed cameras.

Porosity trends in the Skagerrak Formation, Central Graben, United Kingdom Continental Shelf: The role of compaction and pore pressure history

Abstract: This paper describes reservoir properties in the Triassic Skagerrak Formation in the Central North Sea. This prolific sandstone reservoir often possesses anomalously high porosity for its depth of burial. Simple statistical analysis of wire-line-log-derived porosity data is used to derive empirical trends as a function of both depth and vertical effective stress that show variations between neighboring hydrocarbon fields and between different parts of the basin. Porosity data from the Josephine (J) Ridge (Quadrant 30 of the United Kingdom Continental Shelf [UKCS]) show a marked degradation with depth, but the porosities are significantly higher than in similarly deeply buried areas such as the Puffin high to the west (Quadrant 29) or the Forties–Montrose high to the north (Quadrant 22). To understand the porosity patterns better the data have been analyzed by plotting against vertical effective stress. This allows a better comparison to be made between fields and wells within the high-pressure–high-temperature (HPHT) realm. High pressure here refers to fluid pressures above 10,000 psi (), whereas high temperatures are above 300°F (149°C). Results show that porosity and fractional effective reservoir (the proportion of net sandstone with a porosity greater than a predetermined cutoff) decrease systematically with increasing vertical effective stress. Data from the different J Ridge fields fall on a common compaction trend even though they are derived from structures with marked variations in present-day depth of burial and static formation overpressure. Trends from the other areas of the Central Graben (the Puffin and Forties–Montrose highs) indicate more indurate reservoir states. The observed porosity trends are independent of fluid type within the reservoir and the absolute magnitude of overpressure. The main observed hydrocarbon effect is the result of buoyancy forces. The analysis supports the contention that, after accounting for facies-related grain-size variations, compaction controls average reservoir properties. Differences in compaction state between areas are postulated to relate primarily to structurally controlled timing of overpressure development relative to burial, and how these affect the resultant vertical effective stress history. Both the Puffin and Forties–Montrose highs are directly attached to the basin margins across stepped faults. These marginal terraces were open to lateral fluid flow for longer probably because across-fault seals were only established late in the burial history when higher temperatures promoted cementation and the destruction of permeability within fault cores. As a result, they developed overpressures in the last 5–10 m.y. or so and are largely normally compacted. The J Ridge horst block is hydrologically more isolated within the basin center by across-fault juxtaposition seals. Here, overpressure development appears to have started earlier, possibly between 50 and 60 Ma, retarding compaction and allowing preservation of higher porosities. Compaction continues to present day driven by the large static vertical effective stress gradients in these deeply buried reservoirs. The observed empirical trends offer a means of predicting average reservoir properties in deep untested exploration targets.

Environmental impact of blasting at Drenovac limestone quarry (Serbia)

Abstract: In present paper, the blast-induced ground motion and its effect on the neighboring structures are analyzed at the limestone quarry "Drenovac" in central part of Serbia. Ground motion is examined by means of existing conventional predictors, with scaled distance as a main influential parameter, which gave satisfying prediction accuracy (R > 0.8), except in the case of Ambraseys–Hendron predictor. In the next step of the analysis, a feed-forward three-layer back-propagation neural network is developed, with three input units (total charge, maximum charge per delay and distance from explosive charge to monitoring point) and only one output unit (peak particle velocity). The network is tested for the cases with different number of hidden nodes. The obtained results indicate that the model with six hidden nodes gives reasonable predictive precision (R ≈ 0.9), but with much lower values of mean-squared error in comparison to conventional predictors. In order to predict the influence level to the neighboring buildings, recorded peak particle velocities and frequency values were evaluated according to United States Bureau of Mines, USSR standard, German DIN4150, Australian standard, Indian DMGS circular 7 and Chinese safety regulations for blasting. Using the best conventional predictor, the relationship between the allowable amount of explosive and distance from explosive charge is determined for every vibration standard. Furthermore, the effect of air-blast overpressure is analyzed according to domestic regulations, with construction of a blasting chart for the permissible amount of explosive as a function of distance, for the allowable value of air-blast overpressure (200 Pa). The performed analysis indicates only small number of recordings above the upper allowable limit according to DIN4150 and DMGS standard, while, for all other vibration codes the registered values of ground velocity are within the permissible limits. As for the air-blast overpressure, no damage is expected to occur.

BLEVE overpressure: Multiscale comparison of blast wave modeling

Abstract: BLEVE overpressure modeling has been already widely studied but only few validations including the scale effect have been made. After a short overview of the main models available in literature, a comparison is done with different scales of measurements, taken from previous studies or coming from experiments performed in the frame of this research project. A discussion on the best model to use in different cases is finally proposed.

Investigation of Blast Performance and Solid Residues for Layered Thermobaric Charges

Abstract: The confined explosion of an annular layered charge composed of a phlegmatized RDX (RDXph) core and an external layer consisting of aluminum powder (Al) or a mixture of ammonium perchlorate (AP) and Al was studied. Experiments were carried out in fully and partially closed structures, i.e., in the explosion chamber of 150 dm3 in volume and in the 40 m3 volume bunker with four small holes and a doorway. Two types of aluminum powder were used in the mixtures. Signals of overpressure from two piezoelectric gauges located at the chamber wall were recorded and the influence of aluminum contents and particle size on a quasi-static pressure (QSP) was studied. Moreover, the solid residues from the chamber were analyzed by using SEM, TG/DTA and XRD techniques to determine their structure and composition. Pressure and light histories recorded in the bunker enable us to determine the blast wave characteristics and time-duration of light output. The effect of the charge mass and aluminum particle size on blast wave parameters were investigated. For comparison, the test for RDXph and TNT charges were also carried out.

Numerical simulations on the attenuation effect of a barrier material on a blast wave

Abstract: This paper numerically modeled previous experimental results and quantitatively revealed the attenuation effect of a barrier material on a blast wave. Four fluids were considered in the present study: the detonation products, water, foamed polystyrene, and air. These fluids were modeled by Jones-Wilkins-Lee (JWL), stiffened gas, and ideal gas equations of state. A mixture of water and foamed polystyrene was used as a barrier to encircle a 0.1 kg mass of spherical pentolite, and the interface problem between the barrier and the blast wave was investigated. The simulation parameters were the radius and the water volume fraction of the barrier. To elucidate the effect of the barrier, we conducted two series of numerical simulations; one without a barrier, and another with a barrier of 50 or 100 mm in outer radius and 0–1 in the water volume fraction. Peak overpressure, positive impulse, and pressure history all agreed well with the previous experimental results. We focused on the energy transfer from high-pressure detonation products to other fluids. The sum of the kinetic energies of the detonation products and the barrier induced by the blast wave could quantitatively estimate the attenuation effect of the blast wave and was minimized when the water volume fraction was 0.5, as was the case in the previous experiment.

Impact of copper overpressure on the synthesis of hexagonal boron nitride atomic layers.

Abstract: Hexagonal boron nitride (h-BN) atomic layers are synthesized on polycrystalline copper foils via a novel chemical vapor deposition (CVD) process that maintains a vapor-phase copper overpressure during growth. Compared to h-BN films grown without a copper overpressure, this process results in a >10× reduction of 3-dimensional BN fullerene-like surface features, a reduction of carbon and oxygen contamination of 65% and 62%, respectively, an increase in h-BN grain size of >2×, and an 89% increase in electrical breakdown strength.

Study of shock and induced flow dynamics by pulsed nanosecond DBD plasma actuators

Abstract: The shock wave behaviour generated from a single shot of nanosecond DBD plasma actuator with varying pulse voltages in quiescent air was studied by experiments and numerical simulations. The experiments includes Schlieren technique, a fast response pressure transducer and a two-velocity-component PIV system to measure the propagation of the shockwave, the shock overpressure and the shock induced flow, respectively. For the numerical simulation, a simple “phenomenological approach” is employed by modelling the plasma region over the covered electrode as a jump-heated and pressurized gas layer. The present investigation reveals that the behaviours of the shock wave generated by the nanosecond pulsed plasma is fundamentally a micro blast wave and its speed and strength is found to be increased with higher input voltages. The blast wave occurs in about 1 to 4 μs after the discharge of the nanosecond pulse, which is dependent on the input voltages, and decays quickly from supersonic to sonic level within about 5μs (2-3mm from the actuator surface). The shock induced burst perturbations (overpressure and induced velocity) is found to be restricted to a very narrow region (about 1mm) behind the shock front and last only for a few microseconds. While a fairly weak induced vortex flow is observed in a relative long time period after the discharge of the plasma. These results imply that the pulsed plasma actuators have stronger local effects in time and spatial domain.

Analysis of the field test results of ammonium nitrate: fuel oil explosives as improvised explosive device charges

Abstract: When the over pressure of a blast wave is calculated and its effects on valuated objects are set, many approximations are used. Basic relationships, used to calculate the maximum blast overpressure, safety distances and building damage, are created for industrial accidents or for objects where explosives and munitions are stored. This method is invalid in public spaces. More than 95% of all terrorist attacks are carried out using ANFO (ammonium nitrate – fuel oil) explosives in three different variants (ammonium nitrate with oil, ammonium nitrate with oil and aluminium powder or ammonium nitrate with oil and trinitrotoluene (TNT)).The commonly used method to calculate the overpressure uses a scaled distance. The value of the scaled distance is derived from heat created by combustion. A theoretical value for the combustion heat of an industrialproduced ANFO explosion does not represent the real history of explosion or the size of overpressure. For example, the heat of combustion of Slovak-produced DAP-E is the same as TNT. From the relationship used, it emerges that the explosions have the same capacity. We have conducted more than 130 field tests of the ANFO explosive, where the history of blast wave was recorded. The results of the measurements clearly show the invalidity of this theory. The values of the calculated and measured overpressure are significantly different. It is necessary to choose a different approach for the TNT equivalent method. In the first part of this paper, we present the results of the conducted field tests. The experimental results are analysed using commonly-used methods. At the end of our paper we present a new relationship, used to calculate the maximum blast overpressure, which is based on the measured overpressure. This paper presents the results of scientific research at the Faculty of Special Engineering, University of Zilina.

Numerical Study of Solid-Rocket Motor Ignition Overpressure Wave Including Infrared Radiation

Abstract: DOI: 10.2514/1.B34824 The ignition overpressure wave generated during the pressure build-up of a solid-rocket motor is numerically investigated in this study. Numerical simulations are compared to the LP10 experiments, consisting of the horizontal firing of a scaled-down model for the Ariane 5 P230 booster. The present work aims at the prediction of the main characteristics of the ignition overpressure in the far field and the assessment of afterburning influence on both its formation mechanisms and its alteration by the jet plume. Two three-dimensional large-eddy simulations are performed, one considering inert flow and one modeling the afterburning. Infrared images of the plume are also computed with a dedicated radiation transfer solver. An overall good agreement with the experimental results is reported on amplitude and duration. Nevertheless, the reactive case is found to provide better results on amplitude and directivity. The signature is also better reproduced on the microphones near the jet centerline, and the emitted infrared intensity is well captured. Computations indicate that the formation of the shock wave is obtained by coalescence of compression waves emitted by the accelerating jet at early times. For the reactive case, computations show an increased interaction between the jet and the overpressure wave.

Displacement and stress fields around rock fractures opened by irregular overpressure variations

Abstract: Many rock fractures are entirely driven open by fluids such as ground water, geothermal water, gas, oil, and magma. These are a subset of extension fractures (mode I cracks; e.g., dikes, mineral veins and joints) referred to as hydrofractures. Field measurements show that many hydrofractures have great variations in aperture. However, most analytical solutions for fracture displacement and stress fields assume the loading to be either constant or with a linear variation. While these solutions have been widely used, it is clear that a fracture hosted by heterogeneous and anisotropic rock is normally subject to loading that is neither constant nor with a linear variation. Here we present new general solutions for the displacement and stress fields around hydrofractures, modelled as two-dimensional elastic cracks, opened by irregular overpressure variations given by the Fourier cosine series. Each solution has two terms. The first term gives the displacement and stress fields due to the average overpressure acting inside the crack; it is given by the initial term of the Fourier coefficients expressing the overpressure variation. The second term gives the displacement and stress fields caused by the overpressure variation; it is given by general terms of the Fourier coefficients and solved through numerical integration. Our numerical examples show that the crack aperture variation closely reflects the overpressure variation. Also, that the general displacement and stress fields close to the crack follow the overpressure variation but tend to be more uniform far from the crack. The present solutions can be used to estimate the displacement and stress fields around any fluid-driven crack, that is, any hydrofracture, as well as its aperture, provided the variation in overpressure can be described by Fourier series. The solutions add to our understanding of local stresses, displacements, and fluid transport associated with hydrofractures in the crust.

Numerical investigation of propellant leak methods in large-caliber cannons for blast overpressure attenuation

Abstract: In this study, we numerically investigate a novel means to reduce blast overpressure to the rear of a muzzle-loaded cannon. Reduction in blast overpressure, and thus peak overpressure, leads to an increase in the number of allowed rounds that can be fired over a given period of time for the crew manning the system. New propellant leak methods are studied using numerical simulations, where the propellant gas is intentionally allowed to leak in front of the projectile into the precursor region (while the projectile is still in the bore). This is done through the addition of a bulge or leak channels in the tube. The focus of this work is on a large-caliber muzzle-loaded cannon at $$80^{\circ }$$ (1,422 angular mils) elevation and with firing done at the max zone with the round and charge conditioned to ambient. We employ a hydrocode (ALE3D) to predict the blast overpressure for three types of geometries comprising five geometric configurations in total. These include one baseline configuration (i.e., with no modification) as well as four additional configurations with bulges and channels to allow propellant leak. The leaking of propellant gas into the precursor region leads to changes in the flow field associated with the precursor. In the case of channels, propellant leak results in a significantly reduced exit pressure ratio during projectile separation, and thereby, leading to a weaker primary blast wave. This in turn attenuates the peak overpressure to the rear of the muzzle without the aid of a muzzle device. For the channel leak method, at one monitored location, with the largest peak overpressure, a reduction of about 38 % was observed in peak overpressure as compared to the baseline case.

Experimental modeling of infrasound emission from slug bursting on volcanoes

Abstract: The acoustic signal produced by gas slugs bursting at volcano vents is investigated by means of laboratory experiments. In order to explore the transition between linear and nonlinear acoustics, we model the bubble by an overpressurized cylindrical cavity closed by a membrane. We find that the acoustic waveform inside and outside the cavity, produced by the membrane bursting, is well described by the linear acoustics equations and a monopole source model up to an initial overpressure inside the cavity of about 24 kPa. For higher overpressure, the amplitude inside the conduit is smaller than the linear prediction, whereas the amplitude measured outside is larger. The frequency content remains harmonic, even at high initial overpressure. Changing the bursting depth in the conduit does not change the scaling of the amplitudes but affects the waveform and energy partitioning. We show that the energy of the first signal period is about 30% of the total acoustic energy and can be used as a good estimate, with a geometrical correction to account for the bursting depth.

Internal explosion experiment based test method for quantitative evaluation on thermobaric effect of thermobaric explosive

Abstract: The invention belongs to the field of explosives, and provides an internal explosion experiment based test method for quantitative evaluation on thermobaric effect of thermobaric explosive. The method comprises the following steps: using a pressure sensor and a thermocouple to obtain benchmark TNT explosives, a curve for evaluation of shock overpressure of thermobaric explosive in an explosion tank, a thermocouple response temperature curve and a tank quasi-static pressure curve; then processing the experimental data to obtain a shock wave overpressure peak value, impulse, a thermocouple response temperature peak value and a quasi-static pressure peak value; and calculating TNT ratio of characteristic parameters of the thermobaric explosive and evaluating the thermobaric effect of the thermobaric explosive. The invention employs the explosion tank as an evaluation test carrier and uses TNT explosive with the same weight as a benchmark to quantitatively evaluate thermobaric effect of the thermobaric explosive, so as to provide technical basis for the development and power evaluation of thermobaric warhead.

Effect of the bifurcating duct on the gas explosion propagation characteristics

Abstract: The explosion wave overpressure and the flame propagation velocity of the gas explosion in a bifurcating duct are experimentally measured and theoretically analyzed. The results show that the effect of the bifurcation on the flame velocity and overpressure is obvious. Especially, the explosion wave overpressure and the flame propagation velocity increase sharply at the bifurcation point, and the surface at the bifurcation location is destroyed seriously. The gas explosion propagation is verified to suffer a dual effect of sudden expansion of the area and obstruction induction.