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Currently, mixing hydrogen into natural gas networks is the most cost-effective method for transporting significant quantities of hydrogen over long distances. However, after mixing natural gas with hydrogen, the properties of the mixed gas will change significantly, manifested as faster diffusion rate, increased combustion rate, and wider flammability limit. In this paper, a CFD numerical simulation method is used to establish a numerical model for the leakage and diffusion of buried hydrogen-blended natural gas (HBNG) pipelines, and the concentration diffusion trend and velocity flow field distribution of HBNG in soil under different leakage conditions are studied, as well as the alarm time when HBNG diffusion reaches the lower flammability limit (LFL) at the ground surface. At the same time, the effects of hydrogen blending ratio (HBR), pipeline operating pressure, soil porosity and leakage diameter on HBNG leakage and diffusion are investigated. The simulation results indicate that increasing the HBR will increase the diffusion rate of the mixed gas and reduce the LFL, resulting in a decrease of the alarm time. The increase of pipeline operating pressure and leakage diameter will increase the mass flow rate, and the increase of soil porosity will reduce the resistance when HBNG spreads in the soil. All three cases will significantly reduce the alarm time. The results of this study will provide some references for the emergency response work of buried pipeline leakage and the risk assessment of HBNG leakage and explosion. • A numerical model of leakage and diffusion in a buried hydrogen-blended natural gas pipeline is established. • The concentration diffusion trend of hydrogen-blended natural gas in soil under different leakage conditions are studied. • The effects of hydrogen blending ratio, pipeline operating pressure, soil porosity and leakage hole diameter on HBNG leakage and diffusion are investigated. [ABSTRACT FROM AUTHOR]

• Statistical, Hurst, Shannon entropy and chaos analysis methods are used. • Flow regime transitions in an aerated stirred tank are identified. • Standard deviation and largest Lyapunov exponent are effective indicators. • The relationship between the flow regime and the degree of chaos is discussed. A novel method was proposed to determine the flow regime based on the bottom pressure fluctuations of the stirred tank. Statistical, Hurst, Shannon entropy and chaos analysis methods were used to analyze the pressure time series in an aerated stirred tank with a Rushton impeller, and the relationship between the characteristic parameters and the flow regimes was established. The results showed that the bubble motion in the loading regime was obviously stronger than that in the flooding regime, and the homogeneity of the system was rapidly improved. Compared with the first two stages, the chaotic extent of the complete dispersion regime was slightly weaker, and the benefit generated by continuously increasing the speed was limited at this time. In addition, considering the sensitivity of pressure pulsations to the gas–liquid dispersion state, the transition points of the three flow regimes were successfully identified by the standard deviation and the largest Lyapunov exponent. The data were well consistent with the measurements from the visual method and power method, with a maximum deviation of 16%. This demonstrated that it was a reliable non-invasive method for flow regime identification in gas–liquid stirred tanks. [ABSTRACT FROM AUTHOR]

Hydrogen storage vessels in hydrogen refueling stations are densely arranged, so high-speed fragments generated by explosion accidents may endanger adjacent vessels. It is of great significance to explore the dynamic responses and damage modes of hydrogen storage vessels under impact loads to promote the intrinsic safety development of hydrogen storage vessels. In this paper, a finite element analysis model is developed for simulating the dynamic responses of vessels under the impact of fragments. The influences of the number of winding layers, impact velocity, fragment mass, and fragment shape are investigated. The results show that fragment impact is a kind of local damage behavior with two typical stages of hitting and rebounding. The impact resistance of vessels increases with the number of winding layers. Impact velocity and fragment mass are positively related to deformation and damage. Conical fragments have stronger damage abilities, while spherical fragments cause greater deformation. [Display omitted] • The dynamic response and damage modes of vessels under impact were investigated. • The impact resistance of vessels increases with the number of winding layers. • Different factors have different effects on the damage and deformation of vessels. • System energy is mainly converted into internal energy. [ABSTRACT FROM AUTHOR]

Abstract: In the last few years, great achievements have been made in the field of peer-to-peer (P2P) streaming system. In mesh-based P2P streaming system, retrieving data from multiple parents simultaneously improves resilience of the streaming service. However, it also brings in playback lags. To improve users’ viewing experiences, we should consider both playback lags and resilience of the streaming service. However, it seems there is a natural trade-off between these two goals. In this paper we propose a viewing experience optimization algorithm which adjusts the position of the requesting window adaptively based on different requesting strategies. The novelty of the proposed method is that it utilizes heterogeneous real-time demands for different genres of videos, and can adjust requesting strategies adaptively. Under the condition of guaranteeing basic QoS (Quality of Service), the algorithm achieves a balance between playback lags and resilience. Finally, experiment results show the satisfactory performance of the proposed method. [Copyright &y& Elsevier]