Search

• Full-field experiment for blast-induced ground vibration of gas transmission pipeline was performed. • Dynamic mechanism relating to blast-induced PPVs, GVAs, frequency response, and displacement were analyzed. • Failure mechanism was revealed for gas transmission pipeline and its integrated systems. • Data-supporting modified equations of blast-vibration characteristics improved performance of prediction. • Damage recognition and safety design reference for anti-blasting ground vibration in gas transport system. Natural gas pipeline network is a highly integrated network that moves natural gas throughout the continental and global services. Pipelines play a major role for the onshore and offshore gas transport, maintaining the record levels built up in recent years. However, once a rupture appears on a pipeline, the consequences of blast-induced incidents can pose a deadly threat in the vicinity of the failure location. Blast-induced ground vibration is the most significant impact that can seriously affect the surrounding parallel pipelines. In the present study, an experiment combined with a numerical investigation on the effect of blast-induced ground vibration of gas pipeline was undertaken. Dynamic characteristics such as peak vibration velocity, ground vibration acceleration, frequency response of blast-induced ground vibration were analyzed. Further, the modified prediction equations for blast-induced ground vibrational characteristics with distance were proposed. Ultimately, blast-induced displacement with the parallel pipeline was simulated, with a focus on risk vulnerability of gas pipeline. The main purpose of this paper is to facilitate a better understanding of the mechanical systems and dynamic characteristics governing the blast-induced ground vibration when the gas pipeline bursts, which is expected to be reliable for the safety spacing of buried integrated pipeline systems. [ABSTRACT FROM AUTHOR]

• An evaluation index system was proposed to evaluate the deployment rationality of outburst-prone coal mines. • A Bayesian network model for evaluating the deployment rationality of outburst-prone coal mines was established. • Accident prediction and cause diagnosis were carried out by posterior probability reasoning for Nantong Coal Mine. The safe and efficient operation of coal mines is inseparable from rational production deployment. As for outburst-prone coal mines, the production deployment is more complicated due to the introduction of gas disaster control processes, which can easily cause continuity tension and even coal and gas outburst accidents. Therefore, it is necessary to establish an evaluation system for the rationality of production deployment of outburst-prone coal mines. In this paper, based on the production experience of coal mines in Chongqing, China and the summaries of experts, a production deployment evaluation system with eleven indices for outburst-prone coal mines is established. In addition, a Bayesian network is used to establish a corresponding evaluation model. The result shows that the evaluation index system for the production deployment rationality of outburst-prone coal mines, which is composed of the excavation advance indices and the validity indices of regional measure engineering, can systematically diagnose the rationality of each link of the production deployment for outburst-prone coal mines. The results of the case study show that the established Bayesian network model can be used to evaluate the deployment rationality of outburst-prone coal mines. The sensitivity analysis shows that the development coal reserve is the most sensitive to the reasonable deployment of outburst-prone coal mines. The accident prediction and cause diagnosis through the posterior probability reasoning indicate that in the absence of other evidence, the most likely reason for the unreasonable mine deployment is the insufficient development coal reserve. The observations and findings in this research have considerable practical significance for the smooth production of outburst-prone coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]

Mining-induced microseismicity has been extensively used to evaluate the potential for rock bursts and coal and gas outbursts in underground coal mines. In a research project completed a few years ago, it was observed that characteristics of microseismicity around a working longwall panel were fairly consistent over the monitoring period until a lithological heterogeneity zone with a relatively high coal strength was reached. The current research presented in this paper aims at achieving a better understanding of the effect of lithological heterogeneity on microseismic activity in longwall coal mining. The heterogeneous zone inferred from the tomography measurements was first digitalised and implemented into a 3D geomechanical model. A microseismicity modelling approach which combines deterministic stress and failure analysis together with a stochastic fracture slip evaluation was used to simulate the evolution of microseismicity induced by the progressive face advance passing through the heterogeneous zone. The heterogeneity was taken into account by varying the material strength and the fracture attributes of the elements within the high strength zone. Results have shown that both the high rock strength of coal lithotype and low power law scaling exponent of fractures within this zone contribute to the reduction in fitted b values from frequency-magnitude distribution of microseismicity and the increase in fitted Gaussian distribution parameters to the logarithmic event energy. These deviations are believed to result from the combined effects of increased stress drops and slipped fracture sizes when the heterogeneous zone is approached. • Mining-induced microseismicity influenced by lithological heterogeneity was modelled. • Heterogeneities in both material strength and fracture attributes were considered. • Both high coal strength and low fracture scaling exponent lead to elevated seismic energy level. • The recorded seismic anomaly results from increased stress drops and slipped fracture sizes. [ABSTRACT FROM AUTHOR]

Understanding the dynamic mechanical behaviors and microstructural properties of outburst-prone coal is significant for preventing coal and gas outbursts during underground mining. In this paper, the split Hopkinson pressure bar (SHPB) tests were completed to study the strength and micro-structures of outburst-prone coal subjected to compressive impact loading. Two suites of coals—outburst-prone and outburst-resistant—were selected as the experimental specimens. The characteristics of dynamic strength, failure processes, fragment distribution, and microstructure evolution were analyzed based on the obtained stress-strain curves, failed fragments, and scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) images. Results showed that the dynamic compressive strength inclined linearly with the applied strain rate approximately. The obtained dynamic stress-strain responses could be represented by a typical curve with stages of compression, linear elasticity, microcrack evolution, unstable crack propagation, and rapid rapture. When the loading rate was relatively low, fragments fell in tension. With an increase in loading rates, the fragments fell predominantly in shear. The equivalent particle size of coal fragments decreased with the applied strain rate. The Uniaxial compressive strength (UCS) of outburst-prone coal was smaller than that of resistant coal, resulting in its smaller equivalent particle size of coal fragments. Moreover, the impact loading accelerated the propagation of fractures within the specimen, which enhanced the connectivity within the porous coal. The outburst-prone coal with behaviors of low strength and sudden increase of permeability could easily initiate gas outbursts. [ABSTRACT FROM AUTHOR]

Highlights from the article: The fluid flows through both the fractures and pores in deep-seated rock masses, which is of special importance for the performance of underground facilities such as groundwater use and nuclear waste disposal [[1]]. Many researchers have contributed to modeling fluid flow through pores, fractures, and dual-porosity media, using the developed laboratory experimental systems, theories and numerical methods [[6]]. This paper investigated the effect of wet-dry cycling on the evolutions of elastic modulus and compressive strengths of sandstone and mudstone. 8 Mora P., Wang Y., Alonso-Marroquin F. Lattice solid/Boltzmann microscopic model to simulate solid/fluid systems - A tool to study creation of fluid flow networks for viable deep geothermal energy.

The FU Ori–type young stellar objects are characterized by a sudden increase in luminosity by 1–2 orders of magnitude followed by a slow return to the pre-outburst state on timescales of ∼10–100 yr. The outburst strongly affects the entire disk, changing its thermal structure and radiation field. In this paper, using a detailed physical-chemical model, we study the impact of the FU Ori outburst on the disk chemical inventory. Our main goal is to identify gas-phase molecular tracers of the outburst activity that could be observed after the outburst with modern telescopes such as ALMA and NOEMA. We find that the majority of molecules experience a considerable increase in total disk gas-phase abundances due to the outburst, mainly due to the sublimation of their ices. Their return to the pre-outburst chemical state takes different amounts of time, from nearly instantaneous to very long. Among the former, we identify CO, NH3, C2H6, C3H4, etc. Their abundance evolution tightly follows the luminosity curve. For CO, the abundance increase does not exceed an order of magnitude, while for other tracers, the abundances increase by 2–5 orders of magnitude. Other molecules, like H2CO and NH2OH, have longer retention timescales, remaining in the gas phase for ∼10–103 yr after the end of the outburst. Thus, H2CO could be used as an indicator of the previous outbursts in the post-outburst FU Ori systems. We investigate the corresponding time-dependent chemistry in detail and present the most favorable transitions and ALMA configurations for future observations. [ABSTRACT FROM AUTHOR]

MAXI/GSC (Monitor of All-sky X-ray Image/Gas Slit Camera) observed 21 outbursts from Circinus X-1 between 2009 August and 2013 December. Although 14 outbursts showed ordinary gradual decays, in seven others we found a sudden drop in luminosity on a time scale of a few hours around the periastron, and then the outbursts terminated. These sudden drops started at the estimated luminosity of a few times 1037 erg s−1 and their luminosities dropped to ≲3 × 1036 erg s−1. We offer three interpretations of the sharp luminosity decrease: (1) the end of the outburst during its dip, (2) the propeller effect, and (3) the stripping effect by the stellar wind of the companion star. It is difficult to explain the phenomenon by any of these interpretations alone. The interpretation of (1) is possible for only two outbursts on the assumption of rapid decay. The propeller effect (2) is expected to occur at a constant luminosity, which is incompatible with the observed facts. In the stripping effect (3), the ram pressure of a typical stellar wind is not sufficient to blow most of the accretion disk off. In this paper, we discuss the possibility of a modified stripping effect by assuming other additional conditions such as wind clumping and disk instability. [ABSTRACT FROM PUBLISHER]

Pressure gradient driven m = 1 internal kink mode destabilization that follows an L-H transition is observed in the operational region of the EAST tokamak, which manifests in periodic oscillations in soft x-ray (SXR) and Mirnov coil signals. Using tomography with the high resolution soft x-ray detection array, we find that the rotation direction of the 1/1 kink mode is in the ion diamagnetic drift direction in poloidal cross-section. A large displacement of the hot core is attributable to the shift of the 1/1 internal kink mode. In contrast to stationary oscillations with fixed frequency, various frequency chirping behavior is observed with this 1/1 kink mode. Furthermore, we also occasionally observe that a 2/1 neoclassical tearing mode (NTM) is triggered by a 1/1 internal kink mode via mode coupling in a high-performance plasma. The spatial structure of a 2/2 mode, which is the harmonic mode of the 1/1 kink mode, is also presented in this paper. Large amounts of medium-Z impurities accumulate in the central plasma region where the 1/1 kink mode instability bursts. Finally, we also find that the frequency beating associated with a 1/1 kink mode is a consequence of plasma rotation. Based on all of these observations, we propose that the plasma pressure gradient, the driving force in kink modes, is plausibly the product of an intense concentration of impurities, which are related to plasma rotation. [ABSTRACT FROM AUTHOR]

Aims. We present new results from optical photometric and spectroscopic observations of the eruptive pre-main sequence star V2493 Cyg (HBC 722). The object has continued to undergo significant brightness variations over the past few months and is an ideal target for follow-up observations. Methods. We carried out CCD BVRI photometric observations in the field of V2493 Cyg ("Gulf of Mexico") from August 1994 to April 2012, i.e. at the pre-outburst states and during the phases of the outburst. We acquired high, medium, and low resolution spectroscopy of V2493 Cyg during the outburst. To study the pre-outburst variability of the target and construct its historical light curve, we searched for archival observations in photographic plate collections. Both CCD and photographic observations were analyzed using 15 comparison stars in the field of V2493 Cyg. Results. The pre-outburst photographic and CCD photometric observations of V2493 Cyg show low-amplitude light variations typical of T Tauri stars. The recent photometric data show a slow light decrease from October 2010 to June 2011 followed by an increase in brightness that continued until early 2012. The spectral observations of V2493 Cyg are typical of FU Orionis stars absorption spectra with strong P Cyg profiles of Ha and Na I D lines. On the basis of photometric monitoring performed over the past two years, the spectral properties at the maximal light, as well as the shape of long-term light curves, we confirm that the observed outburst of V2493 Cyg is of FU Orionis type. [ABSTRACT FROM AUTHOR]