Overpressure

About: Overpressure is a research topic. Over the lifetime, 3236 publications have been published within this topic receiving 34648 citations.

Numerical Simulation of Pipeline-Pavement Damage Caused by Explosion of Leakage Gas in Buried PE Pipelines

Abstract: In order to investigate the damage influence of the leakage explosion in urban gas pipeline on the surrounding environment, the numerical models of buried PE (polyethylene) pipes under urban pavement were established by using ANSYS/LS-DYNA in this study. The reliability of the numerical models was verified on the basis of the explosion experiments. According to the amount of gas leakage, the TNT explosive equivalent was determined. The gas leakage explosion process of buried PE pipes was studied, and the pressure and stress changes of pipes and pavements under different explosive equivalents and buried depths were analyzed; at last, the deformation law of pipes and pavements were discussed. The results show that the PE pipes are fractured during the leakage explosion and a spherical explosion cavity is formed in the soil. The pavement above the explosion point bulges upward and forms a circle. The maximum pressure of pipe near the explosion point increases linearly with the increase of explosive equivalent, and a proportional relation is observed between the fracture width of pipe and the explosive equivalent. The degree and duration of pavement deformation increase significantly with the increase of explosive equivalents. The dynamic response of the pipes is rarely affected by the buried depth, and the change of maximum effective stress is no more than 7%. However, the buried depth is of great influence on the damage degree of pavement. When the buried depth increases from 0.9 m to 1.5 m, the pavement deformation can be reduced effectively. The variation rule of pavement deformation is similar to the change rule of maximum overpressure and effective plastic stress; they change in the form of concave functions with the increase of buried depth. The results can provide theoretical basis for municipal pipeline construction design and urban safety planning and provide references for the risk assessment of gas explosion in buried pipelines.

A Parametric Investigation of Muzzle Blast

Abstract: : Weapons that vary greatly in their bore lengths are fired over a wide range of projectile velocities. Pressure transducers are located from 15 to 400 calibers from the muzzle and at 30-degree increments around the gun. The investigation yields a detailed picture of the flow field, as displayed by overpressure traces. Comparisons of the overpressure data with an older established prediction method show better agreement for the measured points nearer to the muzzle. Here, a scaling approach combined with a parametric least squares investigation is used to model the peak overpressure, which asymptotically approaches the far field behavior yet gives the nonlinear behavior nearer the muzzle. Using the shock wave expression, which depends on the fitted peak overpressure results, an expression for the time of arrival is obtained which in turn is fitted to the time of arrival data. The positive phase duration is then obtained by subtracting the time of arrival from the zero pressure point of the wave, which is traveling at the approximate speed of sound. The shape of the positive phase of the wave is then assumed to correspond to a Friedlander wave. Assuming the shape, an expression for the impulse of the positive phase is obtained that depends on the fitted peak overpressure and the value of the positive phase duration. The parameters describing the positive phase duration are then fitted by using the impulse data. In summation, the physics of the blast wave is used to construct the time of arrival, positive phase duration, and impulse models. Fluid dynamics, Impulse noise, Muzzle blast, Noise management, Overpressure.

Shock growth of ice crystal near equilibrium melting pressure under dynamic compression.

Abstract: Crystal growth is governed by an interplay between macroscopic driving force and microscopic interface kinetics at the crystal-liquid interface. Unlike the local equilibrium growth condition, the interplay becomes blurred under local nonequilibrium, which raises many questions about the nature of diverse crystal growth and morphological transitions. Here, we systematically control the growth condition from local equilibrium to local nonequilibrium by using an advanced dynamic diamond anvil cell (dDAC) and generate anomalously fast growth of ice VI phase with a morphological transition from three- to two-dimension (3D to 2D), which is called a shock crystal growth. Unlike expected, the shock growth occurs from the edges of 3D crystal along the (112) crystal plane rather than its corners, which implies that the fast compression yields effectively large overpressure at the crystal-liquid interface, manifesting the local nonequilibrium condition. Molecular dynamics (MD) simulation reproduces the faster growth of the (112) plane than other planes upon applying large overpressure. Moreover, the MD study reveals that the 2D shock crystal growth originates from the similarity of the interface structure between water and the (112) crystal plane under the large overpressure. This study provides insight into crystal growth under dynamic compressions, which makes a bridge for the unknown behaviors of crystal growth between under static and dynamic pressure conditions.

Blast Wave Mitigation by Water

Abstract: : Safety systems designed to mitigate blast wave effects are absolutely vital in the explosives industry. As a general rule, barricades made of soil, sand or concrete are used, but these systems cannot be moved once they have been constructed. Since plants or installations are frequently required to change location the concept of a mobile barricade is of considerable interest. The effect of a water wall on blast wave mitigation was studied in scale model tests. The influence of different parameters such as the thickness of the wall and the distance between the explosive charge and the water barricade was also calculated. This methodology enabled the use of nomographs giving excess pressure (overpressure) as a function of wall thickness, charge/wall distance and charge/location distance. The results showed the effectiveness of the water wall and confirmed its interest. This study was carried out by performing tests in a reduced scale model plant. The purpose of the tests was to: 1. Confirm the effect of the weight of the water wall on far-field blast mitigation. 2. Measure the effect of the water wall with regard to reflected pressures on rigid walls. In these cases water walls were created in front of the rigid walls.