Showing papers on "Overpressure published in 2015"

Blast-induced air and ground vibration prediction: a particle swarm optimization-based artificial neural network approach

Abstract: Mines, quarries, and construction sites face environmental damages due to blasting environmental impacts such as ground vibration and air overpressure. These phenomena may cause damage to structures, groundwater, and ecology of the nearby area. Several empirical predictors have been proposed by various scholars to estimate ground vibration and air overpressure, but these methods are inapplicable in many conditions. However, prediction of ground vibration and air overpressure is complicated as a consequence of the fact that a large number of influential parameters are involved. In this study, a hybrid model of an artificial neural network and a particle swarm optimization algorithm was implemented to predict ground vibration and air overpressure induced by blasting. To develop this model, 88 datasets including the parameters with the greatest influence on ground vibration and air overpressure were collected from a granite quarry site in Malaysia. The results obtained by the proposed model were compared with the measured values as well as with the results of empirical predictors. The results indicate that the proposed model is an applicable and accurate tool to predict ground vibration and air overpressure induced by blasting.

Tectonic overpressure and underpressure in lithospheric tectonics and metamorphism

Abstract: The lithostatic pressure concept is most commonly applied on a geological scale for lithospheric processes and related evolution of metamorphic rock complexes. Here, various aspects of non-lithostatic overpressure and underpressure phenomena in lithospheric tectonics and metamorphism are reviewed on the basis of recently published literature. The main conclusion from this short review is that these phenomena certainly exist in nature on all time and space scales including geological ones. They are, in particular, responsible for some geological processes, which are otherwise difficult to explain, such as downward water suction into the interior of subducting slabs. Magnitudes of overpressure and underpressure are strongly variable and may potentially reach up to ±100% of the lithostatic pressure and up to a GPa-level. These magnitudes depend mainly on the rheology of deforming rocks and on the nature of related tectonic process. Rheological heterogeneity of deforming rock units, which is common in nature, has a tendency to enhance overpressure and underpressures. Large overpressure can typically be expected in rheologically strong (dry) bending rock units, in particular in the mantle lithosphere. However, rheological weakness of rocks and small local deviatoric stresses do not guarantee the absence of large overpressures in these rocks. Therefore, the influence of significant tectonic overpressure and/or underpressure cannot be excluded for any metamorphic complex a priori but should be instead tested by exploring realistic thermomechanical models for envisaged tectono-metamorphic scenarios. Many lithospheric rocks subjected to large overpressures and underpressures cannot be studied as they do not exhume to the surface. Some controversy exists concerning overpressure magnitudes for the ultrahigh-pressure (UHP) rocks and several conflicting hypotheses are proposed, which need to be thoroughly tested in the future. In this respect, the Alpine region may offer a unique opportunity for the testing of geological-scale overpressures in (U)HP rocks by combining structural-geological and petrological data with realistic lithospheric-scale numerical modelling.

Vent burst pressure effects on vented gas explosion reduced pressure

Abstract: The overpressure generated in a 10 L cylindrical vented vessel with an L/D of 2.8 was investigated, with end ignition opposite the vent, as a function of the vent static burst pressure, P stat , from 35 to 450 mb. Three different K v (V 2/3 /A v ) of 3.6, 7.2 and 21.7 were investigated for 10% methane–air and 7.5% ethylene–air. It was shown that the dynamic burst pressure, P burst , was higher than P stat with a proportionality constant of 1.37. For 10% methane–air P burst was the controlling peak pressure for K red > P burst in the literature and in EU and US standards. For higher K v the overpressure due to flow through the vent, P fv, was the dominant overpressure and the static burst pressure was not additive to the external overpressure. Literature on the influence of P stat at low K v was shown to support the present finding and it is recommended that the influence of P stat in gas venting standards is revised.

Fluid budgets along the northern Hikurangi subduction margin, New Zealand: the effect of a subducting seamount on fluid pressure

Abstract: We estimate fluid sources around a subducted seamount along the northern Hikurangi subduction margin of New Zealand, using thermomechanical numerical modelling informed by wedge structure and porosities from multichannel seismic data. Calculated fluid sources are input into an independent fluid-flow model to explore the key controls on overpressure generation to depths of 12 km. In the thermomechanical models, sediment transport through and beneath the wedge is calculated assuming a pressure-sensitive frictional rheology. The change in porosity, pressure and temperature with calculated rock advection is used to compute fluid release from compaction and dehydration. Our calculations yield more precise information about source locations in time and space than previous averaged estimates for the Hikurangi margin. The volume of fluid release in the wedge is smaller than previously estimated from margin-averaged calculations (∼14 m3 yr−1 m−1), and is exceeded by fluid release from underlying (subducting) sediment (∼16 m3 yr−1 m−1). Clay dehydration contributes only a small quantity of fluid by volume (∼2 m3 yr−1 m−1 from subducted sediment), but the integrated effect is still significant landward of the seamount. Fluid source terms are used to estimate fluid pressures around a subducting seamount in the fluid-flow models, using subducted sediment permeability derived from porosity, and testing two end-members for decollement permeability. Models in which the decollement acts as a fluid conduit predict only moderate fluid overpressure in the wedge and subducting sediment. However, if the subduction interface becomes impermeable with depth, significant fluid overpressure develops in subducting sediment landward of the seamount. The location of predicted fluid overpressure and associated dehydration reactions is consistent with the idea that short duration, shallow, slow slip events (SSEs) landward of the seamount are caused by anomalous fluid pressures; alternatively, it may result from frictional effects of changing clay content along the subduction interface.

Study of Shock and Induced Flow Dynamics by Nanosecond Dielectric-Barrier-Discharge Plasma Actuators

Abstract: The shock wave behavior generated from a single shot of pulsed nanosecond dielectric-barrier-discharge plasma actuator with varying pulse voltages in quiescent air was studied by experiments and numerical simulations. The experiments included using the schlieren technique, a fast response pressure transducer, and a two-velocity-component particle image velocimetry system to measure the propagation of the shock wave, the shock overpressure, and the shock induced flow, respectively. For the numerical simulation, a simple “phenomenological approach” was employed by modeling the plasma region over the encapsulated electrode as a jump-heated and pressurized gas layer. The present investigation revealed that the behaviors of the shock wave generated by the nanosecond pulsed plasma were fundamentally a microblast wave, and their speed and strength were found to increase with higher input voltages. The blast wave occured about 1 to 3 μs after the discharge of the nanosecond pulse, which was dependent on the inpu...

Analysis of the boiling liquid expanding vapor explosion (BLEVE) of a liquefied natural gas road tanker: The Zarzalico accident

Abstract: The road accident of a tanker transporting liquefied natural gas (LNG) originated a fire and, finally, the BLEVE of the tank. This accident has been analyzed, both from the point of view of the emergency management and the explosion and fireball effects. The accidental sequence is described: fire, LNG release, further safety valves release, flames impingement on vessel unprotected wall, vessel failure mode, explosion and fireball. According to the effects and consequences observed, the thermal radiation and overpressure are estimated; a mathematical model is applied to calculate the probable mass contained in the vessel at the moment of the explosion. The peak overpressure predicted from two models is compared with the values inferred from the accident observed data. The emergency management is commented.

Effects of premixed methane concentration on distribution of flame region and hazard effects in a tube and a tunnel gas explosion

Abstract: Study of flame distribution laws and the hazard effects in a tunnel gas explosion accident is of great importance for safety issue. However, it has not yet been fully explored. The object of present work is mainly to study the effects of premixed gas concentration on the distribution law of the flame region and the hazard effects involving methane-air explosion in a tube and a tunnel based on experimental and numerical results. The experiments were conducted in a tube with one end closed and the other open. The tube was partially filled with premixed methane-air mixture with six different premixed methane concentrations. Major simulation works were performed in a full-scale tunnel with a length of 1000 m. The first 56 m of the tunnel were occupied by methane–air mixture. Results show that the flame region is always longer than the original gas region in any case. Concentration has significant effects on the flame region distribution and the explosion behaviors. In the tube, peak overpressures and maximum rates of overpressure rise (dp/dt) max for mixtures with lower and higher concentrations are great lower than that for mixtures close to stoichiometric concentration. Due to the gas diffusion effect, not the stoichiometric mixture but the mixture with a slightly higher concentration of 11% gets the highest peak overpressure and the shock wave speed along the tube. In the full-scale tunnel, for fuel lean and stoichiometric mixture, the maximum peak combustion rates is achieved before arriving at the boundary of the original methane accumulation region, while for fuel rich mixture, the maximum value appears beyond the region. It is also found that the flame region for the case of stoichiometric mixture is the shortest as 72 m since the higher explosion intensity shortens the gas diffusion time. The case for concentration of 13% can reach up to a longest value of 128 m for longer diffusion time and the abundant fuel. The “serious injury and death” zone caused by shock wave may reach up to 3–8 times of the length of the original methane occupied region, which is the widest damage region.

Angle of Incidence Effects on Far-Field Positive and Negative Phase Blast Parameters

Abstract: The blast overpressure acting on a rigid target is known to vary between the normally reflected overpressure and the incident overpressure as a function of the angle between the target and the direction of travel of the blast wave. Literature guidance for determining the exact effects of angle of incidence are unclear, particularly when considering the negative phase. This paper presents the results from a series of well controlled experiments where pressure transducers are used to record the pressure-time history acting on the face of a large, rigid target at various angles of incidence for varying sizes of hemispherical PE4 charge and stand-off distances. The test data demonstrated remarkable repeatability, and excellent agreement with semi-empirical predictions for normally reflected overpressures. The oblique results show that peak overpressure, impulse and duration are highly dependent on angle of incidence for the positive phase, and are invariant of angle of incidence for the negative phase.

Methane–air explosion characteristics with different obstacle configurations

Abstract: To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations, an experimental study has been conducted, taking account of the number of obstacles, obstacle distance from ignition source, and stream-wise and cross-wise obstacle positions. The results show that the flame speed and peak overpressure increase with the increasing number of obstacles, while the time to reach the peak is not fully determined by it. And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak, but a slower flame propagation speed is obtained. Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions. Furthermore, the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher, which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.

Factors controlling petroleum accumulation and leakage in overpressured reservoirs

Abstract: This paper reviews the hydrocarbon-retaining properties of overpressured reservoirs and discusses the mechanisms for petroleum accumulation, preservation and loss in overpressured reservoirs, and the factors controlling hydrocarbon column heights in overpressured traps. Four types of overpressured traps (filled, underfilled, unfilled, and drained) are recognized. The diversities in petroleum-bearing properties reflect the complexities of petroleum accumulation and leakage in overpressured reservoirs. Forced top seal fracturing, frictional failure along preexisting faults, and capillary leakage are the major mechanisms for petroleum loss from overpressured reservoirs. The hydrocarbon retention capacities of overpressured traps are controlled by three groups of factors: (1) factors related to minimum horizontal stress (tectonic extension or compression, stress regimes, and basin scale and localized pressure–stress coupling); (2) factors related to the magnitudes of water-phase pressure relative to seal fracture pressure (the depth to trap crest, vertical and/or lateral overpressure transfer, mechanisms of overpressure generation); and (3) factors related to the geomechanical properties of top seals or sealing faults (the tensile strength and brittleness of the seals, the natures and structures of fault zones). Commercial petroleum accumulations may be preserved in reservoirs with pressure coefficients greater than 2.0 and pore pressure/vertical stress ratios greater than 0.9 (up to 0.97). The widely quoted assumption that the fracture pressure is 80%–90% of the overburden pressure and hydrofracturing occurs when the pore pressure reaches 85% of the overburden pressure significantly underestimates the maximum sustainable overpressures, and thus, potentially the hydrocarbon-retention capacities, especially in deeply buried traps. Lateral and/or vertical water-phase overpressure transfer from deeper successions plays an important role in the formation of unfilled and drained overpressured traps. Traps in hydrocarbon generation-induced overpressured systems have greater exploration potential than traps in disequilibrium compaction-induced overpressured systems with similar overpressure magnitude.

Blast Injuries and Blast-Induced Neurotrauma: Overview of Pathophysiology and Experimental Knowledge Models and Findings

Abstract: Explosions are physical phenomena that result in the sudden release of energy; they may be chemical, nuclear, or mechanical. This process results in a near-instantaneous pressure rise above atmospheric pressure. The positive pressure rise (“overpressure”) compresses the surrounding medium (air or water) and results in the propagation of a blast wave, which extends outward from the explosion in a radial fashion. As the front or leading edge of the blast wave expands, the positive phase is followed by a decrease in pressure and the development of a negative wave (“underpressure”) before subsequently returning to baseline. Figure 45.1 shows an idealized form of a shock wave (Friedlander wave) (Friedlander, 1955) generated by a spherical, uncased explosive in the air in free field conditions. The extent of damage from the blast wave mainly depends on five factors: (1) the peak of the initial positive-pressure wave (an overpressure of 690–1,724 kPa, for example, 100–250 psi, is considered potentially lethal) (Champion et al., 2009); (2) the duration of overpressure; (3) the medium of explosion; (4) the distance from the incident blast wave; and (5) the degree of focusing because of a confined area or walls. Intensity of an explosion pressure wave declines with the cubed root of the distance from the explosion. Thus, a person 3 m (10 ft) from an explosion experiences nine times more overpressure than a person 6 m (20 ft) away. Additionally, explosions near or within hard solid surfaces can be amplified two to nine times because of shock wave reflection (Rice and Heck, 2000). Indeed, it was observed that victims positioned between a blast and a building often suffer injuries two to three times the degree of the injury of a person in an open space. People exposed to explosion rarely experience the idealized pressure-wave form. Even in open-field conditions, the blast wave reflects from the ground, generating reflective waves that interact with the primary wave, thus changing its characteristics. In a closed environment (such as a building, an urban setting, or a vehicle), the blast wave interacts with the surrounding structures and creates multiple wave reflections, which, interacting with the primary wave and between each other, generate a complex wave (Ben-Dor et al., 2001; Mainiero and Sapko, 1996).Blast injuries are characterized by interwoven mechanisms of systemic, local, and cerebral responses to blast exposure (Cernak, 2010). When a blast generated by explosion strikes a living body, part of the shock wave is reflected and another fraction is absorbed becoming a tissue-transmitted shock wave. The transferred kinetic energy causes low-frequency stress waves that accelerate a medium from its resting state, leading to rapid physical movement, displacement, deformation, or rupture of the medium (Clemedson, 1956; Clemedson and Criborn, 1955). Thus, a militarily relevant blast injury model should be able to capture and measure these phenomena based on sufficient knowledge of shock wave physics, the characteristics of the injurious environment generated by an explosion, and the clinical manifestations and sequelae of the injuries. The purpose of this chapter is to outline the pathophysiology of blast-body/blast-brain interactions and to summarize the scientific evidence to date for the selection of appropriate experimental models for characterizing and understanding these interactions.

Predicting Blast Waves from the Axial Direction of a Cylindrical Charge

Abstract: Bare, cylindrical, explosive charges produce secondary shock waves in the direction of least presented area. Whilst the source of these shock waves was explored in the 1940’s, no attempt was made to predict them. This paper describes the detonation of bare, cylindrical charges of PE4 (RDX binder 88/12 %), mass 0.2 to 0.46 kg and with a length to diameter ratio of 4 to 1. High speed camera footage showed (i) the formation of the separate, primary, shock waves from the sides and ends of the charge, (ii) Mach reflection of these separate shock waves, giving rise to reflected, secondary shock waves, and (iii) the secondary shock waves catching and merging with the primary shock wave. In the axial direction, the secondary shock wave’s peak overpressure and impulse exceeded that of the primary shock wave for scaled distances, Z=R/M1/3 ≥3.9 m kg−1/3, where M is the mass in kg and R the distance from the charge in m. It was found possible to predict the primary peak overpressure, P, at all distances in the axial direction, for a constant length to diameter ratio, using P=3075 Z−3−1732 Z−2+305 Z−1. Close in the primary peak overpressure is proportional to M/R3 in the axial direction. It was not possible to predict the secondary peak overpressure with the data obtained. The total impulse from both shock waves, I, in the axial direction can be predicted using I=746(M2/3/R)3−708(M2/3/R)2+306(M2/3/R).

Flame behaviors and pressure characteristics of vented dust explosions at elevated static activation overpressures

Abstract: Dust explosion venting experiments were performed using a 20-L spherical chamber at elevated static activation overpressures larger than 1 bar. Lycopodium dust samples with mean diameter of 70 μm and electric igniters with 0.5 KJ ignition energy were used in the experiments. Explosion overpressures in the chamber and flame appearances near the vent were recorded simultaneously. The results indicated that the flame appeared as the under-expanded free jet with shock diamonds, when the overpressure in the chamber was larger than the critical pressure during the venting process. The flame appeared as the normal constant-pressure combustion when the pressure venting process finished. Three types of venting processes were concluded in the experiments: no secondary flame and no secondary explosion, secondary flame, secondary explosion. The occurrence of the secondary explosions near the vent was related to the vent diameter and the static activation overpressure. Larger diameters and lower static activation overpressures were beneficial to the occurrence of the secondary explosions. In current experiments, the secondary explosions only occurred at the following combinations of the vent diameter and the static activation overpressure: 40 mm and 1.2 bar, 60 mm and 1.2 bar, 60 mm and 1.8 bar.

Complex explosion development in mines: Case study—2010 upper big branch mine explosion

Abstract: On April 5th, 2010, a methane explosion occurred within the Upper Big Branch mine south of Charleston, WV. Twenty-nine men lost their lives as a result of a flammable concentration of methane that built up in the enclosed space and ignited, resulting in a methane explosion that transitioned into a coal dust explosion. This study used the FLACS computational fluid dynamics solver to conduct a detailed explosion analysis to evaluate the complex overpressure development throughout the mine as a result of the flammable cloud ignition. As a result of the accident investigation, unique explosion patterns were found in the mine where certain “blast indicators” within the mine shafts were deformed in such a manner that was inconsistent with the likely flow of the expanding blast wave. The FLACS analysis will analyze the explosion dynamics and shed light on the damage observations made after the blast. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 286–303, 2015

A numerical study of the evolution of the blast wave shape in rectangular tunnels

Abstract: When the explosion of condensed materials occurs in square or circular cross-section tunnel, the subsequent blast wave reveals two patterns: three-dimensional close to the explosive charge and one-dimensional far from the explosion. Pressure decays for these two patterns have been thoroughly studied. However, when the explosion occurs in rectangular cross-section tunnel, which is the most regular geometry for underground networks, the blast wave exhibits a third, two-dimensional, patterns. In order to assess the range of these three patterns, several numerical simulation of blast waves were carried out varying the width and the height of the rectangular cross-section as well as the mass of the charge. Laws are presented to localize the transition zones between the 3D and the 2D patterns, and between the 2D and the 1D patterns, as functions of non-dimensional width and height. The numerical results of the overpressure are compared to existing 3D and 1D laws. An overpressure decay law is proposed to represent the 2D pattern. Knowing the two transition zones and the overpressure decays within these zones, an algorithm is presented to efficiently predict an overpressure map. This algorithm is validated by comparison with experimental data.