Factor analysis and GA-BP-ANN prediction of nitrogen diffusion behavior in underground laboratory under ventilation conditions.

Nitrogen is widely used in various laboratories as a suppressive gas and a protective gas. Once nitrogen leaks and accumulates in a such confined space, it will bring serious threats to the experimental staff. Especially in underground tunnels or underground laboratories where there is no natural wind, the threat is more intense. In this work, the ventilation design factors and potential leakage factors are identified by taking the leakage and diffusion of a large liquid nitrogen tank in China Jinping Underground Laboratory (CJPL) as an example. Based on computational fluid dynamics (CFD) research, the effects of fresh air inlet position, fresh air velocity, exhaust outlet position, leakage hole position, leakage hole size, and leaked nitrogen mass flow rate on nitrogen diffusion behavior in specific environments are discussed in detail from the perspectives of nitrogen concentration field and nitrogen diffusion characteristics. The influencing factors are parameterized, and the Latin hypercube sampling (LHS) is used to uniformly sample within the specified range of each factor to obtain samples that can represent the whole sample space. The nitrogen concentration is measured by numerical value, and the nitrogen diffusion characteristics are measured by category. The GA-BP-ANN numerical regression and classification regression models for nitrogen concentration prediction and nitrogen diffusion characteristics prediction are established. By using various rating indicators to evaluate the performance of the trained model, it is found that models have high accuracy and recognition rate, indicating that it is effective in predicting and determining the concentration value and diffusion characteristics of nitrogen according to ventilation factors and potential leakage factors. The research results can provide a theoretical reference for the parametric design of the ventilation system.

Molecular Dynamics Study on Hugoniot State and Mie-Grüneisen Equation of State of 316 Stainless Steel for Hydrogen Storage Tank.

To promote the popularization and development of hydrogen energy, a micro-simulation approach was developed to determine the Mie-Grüneisen EOS of 316 stainless steel for a hydrogen storage tank in the Hugoniot state. Based on the combination of the multi-scale shock technique (MSST) and molecular dynamics (MD) simulations, a series of shock waves at the velocity of 6-11 km/s were applied to the single-crystal (SC) and polycrystalline (PC) 316 stainless steel model, and the Hugoniot data were obtained. The accuracy of the EAM potential for Fe-Ni-Cr was verified. Furthermore, Hugoniot curve, cold curve, Grüneisen coefficient (γ), and the Mie-Grüneisen EOS were discussed. In the internal pressure energy-specific volume (P-E-V) three-dimensional surfaces, the Mie-Grüneisen EOSs show concave characteristics. The maximum error of the calculation results of SC and PC is about 10%. The results for the calculation deviations of each physical quantity of the SC and PC 316 stainless steel indicate that the grain effect of 316 stainless steel is weak under intense dynamic loads, and the impact of the grains in the cold state increases with the increase in the volume compression ratio.

Study on Overpressure Propagation Law of Vapor Cloud Explosion under Different Building Layouts.

To determine and optimize the emergency evacuation path of personnel in the case of vapor cloud explosion caused by pipeline leakage and improve the safety control measures in the high-consequence areas of gas pipelines, this study was conducted. This work mainly studied two questions: whether various research methods applicable to the solid explosive explosion are also applicable to vapor cloud explosion and the influence of different building layouts on the overpressure propagation law of vapor cloud explosion. First, the applicability of several empirical models and computational fluid dynamics (CFD) methods in vapor cloud explosion overpressure prediction is systematically compared and analyzed. Second, the finite element models based on the fluid-structure interaction are established to study the overpressure propagation law under the influence of different building layouts. Finally, based on the overpressure propagation law, the determination and optimization principle of the emergency evacuation path of personnel when an accident occurs are given. The results show that the CFD method and empirical model based on equivalent assumption between trinitrotoluene and combustible gas are not suitable for the study of gas-phase explosion, while the mixed gas method based on CFD is more suitable for exploring the overpressure problem of vapor cloud explosion. Buildings arranged perpendicular to the direction of blast wave have the most obvious enhancement and weakening effect on overpressure, and the maximum increase rate and decrease rate are about 90%. The maximum increase rate of overpressure between two vertical layout buildings is more than 60% higher than that between two horizontal layout buildings. When determining the emergency evacuation path, the non-explosive side of the building perpendicular to the shock wave layout should be given priority. If it is necessary to pass through the building gap, the gap between the two horizontal layout buildings should be preferred to ensure that the damage of overpressure to personnel is minimized. The research results can provide a theoretical basis for the improvement of personnel safety control measures in high-consequence areas of the gas pipeline.