Underground hydrogen storage has gained interest in recent years due to the enormous demand for clean energy.Hydrogen is more diffusive than air,with a smaller density and lower viscosity.These unique properties intro...Underground hydrogen storage has gained interest in recent years due to the enormous demand for clean energy.Hydrogen is more diffusive than air,with a smaller density and lower viscosity.These unique properties introduce distinctive hydrodynamic phenomena in hydrogen storage,one of which is fingering.Fingering could induce the fluid trapped in small clusters of pores,leading to a dramatic decrease in hydrogen saturation and a lower recovery rate.In this study,numerical simulations are performed at the microscopic scale to understand the evolution of hydrogen saturation and the impacts of injection and withdrawal cycles.Two sets of micromodels with different porosity(0.362 and 0.426)and minimum sizes of pore throats(0.362 mm and 0.181 mm)are developed in the numerical model.A parameter analysis is then conducted to understand the influence of injection velocity(in the range of 10^(-2)m/s to 10^(-5)m/s)and porous structure on the fingering pattern,followed by an image analysis to capture the evolution of the fingering pattern.Viscous fingering,capillary fingering,and crossover fingering are observed and identified under different boundary conditions.The fractal dimension,specific area,mean angle,and entropy of fingers are proposed as geometric descriptors to characterize the shape of the fingering pattern.When porosity increases from 0.362 to 0.426,the saturation of hydrogen increases by 26.2%.Narrower pore throats elevate capillary resistance,which hinders fluid invasion.These results underscore the importance of pore structures and the interaction between viscous and capillary forces for hydrogen recovery efficiency.This work illuminates the influence of the pore structures and the fluid properties on the immiscible displacement of hydrogen and can be further extended to optimize the injection strategy of hydrogen in underground hydrogen storage.展开更多
Accidental surcharge,a type of uncertain manmade hazard,poses a huge threat to the safe operation of shield tunnels.In this regard,a vulnerability assessment framework is proposed in this paper to evaluate the damage ...Accidental surcharge,a type of uncertain manmade hazard,poses a huge threat to the safe operation of shield tunnels.In this regard,a vulnerability assessment framework is proposed in this paper to evaluate the damage state of a shield tunnel subjected to sudden extreme surcharges,accounting for the effect of soil uncertainty and tunnel burial depths.A two-dimensional numerical model of the shield tunnel in soft soil under surcharge loading is established and verified by the field monitoring data.Then,joint opening and horizontal convergence of the shield tunnel are chosen as damage indices,and the corresponding fragility curves and vulnerability curves are established based on the Monte Carlo calculation.The influences of surcharge loading and buried depths on the vulnerability are discussed.Finally,the proposed vulnerability assessment framework is applied in a real case in Shanghai to make a quick judgement on the dangerous sections of shield tunnels.The research results show that the vulnerability of shield tunnels increases with the surcharge loading.Deep shield tunnels have higher initial vulnerability but are not sensitive to surcharge loading.The study sheds light on the robust design,post-hazard decision-making,and rapid risk identification for shield tunnels subjected to surcharge loads.展开更多
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.42320104003,42477168).
文摘Underground hydrogen storage has gained interest in recent years due to the enormous demand for clean energy.Hydrogen is more diffusive than air,with a smaller density and lower viscosity.These unique properties introduce distinctive hydrodynamic phenomena in hydrogen storage,one of which is fingering.Fingering could induce the fluid trapped in small clusters of pores,leading to a dramatic decrease in hydrogen saturation and a lower recovery rate.In this study,numerical simulations are performed at the microscopic scale to understand the evolution of hydrogen saturation and the impacts of injection and withdrawal cycles.Two sets of micromodels with different porosity(0.362 and 0.426)and minimum sizes of pore throats(0.362 mm and 0.181 mm)are developed in the numerical model.A parameter analysis is then conducted to understand the influence of injection velocity(in the range of 10^(-2)m/s to 10^(-5)m/s)and porous structure on the fingering pattern,followed by an image analysis to capture the evolution of the fingering pattern.Viscous fingering,capillary fingering,and crossover fingering are observed and identified under different boundary conditions.The fractal dimension,specific area,mean angle,and entropy of fingers are proposed as geometric descriptors to characterize the shape of the fingering pattern.When porosity increases from 0.362 to 0.426,the saturation of hydrogen increases by 26.2%.Narrower pore throats elevate capillary resistance,which hinders fluid invasion.These results underscore the importance of pore structures and the interaction between viscous and capillary forces for hydrogen recovery efficiency.This work illuminates the influence of the pore structures and the fluid properties on the immiscible displacement of hydrogen and can be further extended to optimize the injection strategy of hydrogen in underground hydrogen storage.
基金the support of the National Natural Science Foundation of China(Grant Nos.52478410 and 42477168)Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0808)+1 种基金Shanghai Science and Technology Committee Program(No.22dz1201202)the Key Laboratory of Performance Evolution and Control for Engineering Structures(Tongji University),Ministry of Education(No.2023KF-2).
文摘Accidental surcharge,a type of uncertain manmade hazard,poses a huge threat to the safe operation of shield tunnels.In this regard,a vulnerability assessment framework is proposed in this paper to evaluate the damage state of a shield tunnel subjected to sudden extreme surcharges,accounting for the effect of soil uncertainty and tunnel burial depths.A two-dimensional numerical model of the shield tunnel in soft soil under surcharge loading is established and verified by the field monitoring data.Then,joint opening and horizontal convergence of the shield tunnel are chosen as damage indices,and the corresponding fragility curves and vulnerability curves are established based on the Monte Carlo calculation.The influences of surcharge loading and buried depths on the vulnerability are discussed.Finally,the proposed vulnerability assessment framework is applied in a real case in Shanghai to make a quick judgement on the dangerous sections of shield tunnels.The research results show that the vulnerability of shield tunnels increases with the surcharge loading.Deep shield tunnels have higher initial vulnerability but are not sensitive to surcharge loading.The study sheds light on the robust design,post-hazard decision-making,and rapid risk identification for shield tunnels subjected to surcharge loads.
