Overpressure

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

Submarine slope failure due to overpressure fluid associated with gas hydrate dissociation

Abstract: The dissociation of gas hydrates can increase pore pressures greatly, thereby causing the shallow layers of submarine slopes to fail. Given the high failure risk of shallow subsea soils, it is important to understand the stratum response mechanisms after hydrate dissociation. In this paper, submarine slope failure triggered by overpressure fluid associated with gas hydrate dissociation is investigated in laboratory experiments. A two-layer geological model is built based on actual geological data, and pressurised air is injected into the model to simulate the overpressure fluid. The pore pressures, surface displacements and internal deformations of soils are measured and compared under different conditions, and their evolution processes are analysed for various parameter values. The results show that the accumulation of pore pressure increases with the thickness of the soil layer and leads to layered fractures. The failure pattern can be generalised into two types: (a) disc-shaped failure and (b) penetration failure. In disc-shaped failure, a major failure occurs when the shear stress reaches the shear strength, whereas tensile fracturing is a major effect in penetration failure. This achievement is very important for a deep understanding of submarine landslides induced by overpressure fluid, as well as for risk assessments of ocean engineering sites.

Experimental study on explosion characteristics of ethanol-gasoline blended fuels

Abstract: In the present work, a series of experiments have been performed to analyze the explosion characteristics of ethanol-gasoline with various blended ratios (0%, 5%, 10%, 15%, 30%, 50%, 70%, 80%, and 100%). A vented rectangular vessel with a cross-section of 100 mm × 100 mm, 600 mm long and a 40 mm diameter vent on the top is used to carry out the experiments. The flame propagation is recorded by a phantom high-speed camera with 5000 fps, while the histories of the explosion overpressure are measured by two PCB pressure sensors and the explosion sound pressure level is obtained by a CRY sound sensor. The results indicate that the maximum overpressure and flame propagation speed increases linearly as the blended ratio increases when the initial volume of blended fuel is 1.0 mL; While the change of explosion overpressure and flame propagation speed shows a trend of decreasing at first and then increasing as the concentration increases to 1.8 mL. It is also found that the peak of the sound pressure level exceeds 100 dB under all tests, which would damage the human's hearing. What's more, relationships between explosion overpressure and sound pressure level are examined, and the change of the maximum overpressure can be reflected to some extent by the measurement of the maximum sound pressure level. The study is significant to reveal the essential characteristic of the explosion venting process of ethanol-gasoline under different initial blended ratios, and the results would help deepen the understanding of ethanol-gasoline blended fuels explosion and the assessment of the explosion hazardous.

Experimental characterization and mondeling of hazards, BLEVE and BOILOVER

Abstract: The present thesis is conducted in the frame of a research project involving the ‘von Karman Institute (VKI Belgium)’ and the ‘Ecole des mines d’Ales (EMA France) with the support of the CEA Gramat. This project is about theoretical study, experimental characterization and modeling of hazards from pressurized or atmospheric reservoirs, containing liquids, flammable or not. The objective of this thesis is to study the apparition criteria and the consequences of an accident involving a container of pressure liquefied gas (BLEVE phenomenon) or liquid fuels (Boilover phenomenon). After a bibliographic research on the two phenomena, an experimental study in laboratory scale is conducted and from the results, the phenomena and their hazards are modeled. Small scale experiments are performed in the BABELs facility (Bleve And Boilover ExperimentaL setup) that consists of a cylindrical chamber of 2m diameter and 3m high, with round shape flanges, made out of steel with a rated pressure of 0.5 MPa. It has 3 series of 7 optical accesses, an entrance door, and an optional air venting system. A Boilover is a violent ejection of fuel due to the vaporization of a water sublayer, resulting in an enormous fire enlargement and formation of fireball and ground fire. Small scale experiments with cylindrical reservoirs of 0.08 to 0.3m diameter in glass or metal, filled with a mixture of diesel and oil have been performed. Instrumentation of the measurements consists of thermocouples rake, Medtherm radiometers, load cell and CCD or high-speed camera with a fisheye. During the quasi-steady combustion prior the Boilover, the typical variables describing a pool fire like burning rate, flame size, puffing frequency and radiation can be predicted with semi-empirical correlations available in the literature. At Boilover onset, high speed visualizations in glass reservoir show that the growth of one big bubble leads to a boiling front that propagates radially all along the fuel-water interface, ejecting the upper fuel layer and leading to the increase of flame size. LS-PIV technique applied to high-speed camera images shows that the flame enlargement is directly linked to the velocity of the flame. A BLEVE (or Boiling Liquid Expanding Vapour Explosion) is an explosion resulting from the catastrophic failure of a vessel containing a liquid at a temperature significantly above its boiling point at normal atmospheric pressure. Small scale experiments are performed with cylinders of 42g of propane, laid horizontally and heated from below by an electrical resistor. A groove of the reservoirs on the upper part allows better reproducibility of the rupture. High speed visualization and shadowgraphy are helping in visualizing the rupture and the content release. Thermocouples and PCB are also used to measure respectively the temperature and the blast wave overpressure. These experiments show that the fluid behavior during rupture differs with the size of the weakened part and therefore with the rupture pressure. The internal pressure measurement showed that the rupture pressure and temperature are supercritical, leading to the definition of a new type of BLEVE since there is no distinction between liquid and vapor phases prior rupture. © Copyright 2012 Delphine Laboureur

Effects of obstacle position and number on the overpressure of hydrogen combustion in a semi-confined compartment

Abstract: During a severe accident in a pressurized water reactor, large quantities of hydrogen can be produced and released into the containment. The hydrogen mixed with air may be ignited. Rapid pressure rise is likely to occur during hydrogen combustion in a semi-confined compartment because the length–diameter ratio of the compartment is relatively large and there generally are some devices and components in the compartment. Obstacle position and number have a significant and complex effect on combustion pressure. In this paper, a numerical analysis of the effects of obstacle position and number on the overpressure of hydrogen combustion in a semi-confined compartment was carried out to identify the arrangement of obstacles that can decrease the pressure loads generated by hydrogen combustion. The overpressure in the compartment with a single obstacle was found first increases to a maximum value and then decreases as the obstacle moving from the closed end to the open end. When there are multiple obstac...