Sediment incipient motion is the first step in sediment resuspension.Previous studies ignored the effect of seepage flow on the mobility of sediment particles and simplified the seabed surface as a rigid boundary.A fl...Sediment incipient motion is the first step in sediment resuspension.Previous studies ignored the effect of seepage flow on the mobility of sediment particles and simplified the seabed surface as a rigid boundary.A flume experiment was designed to innovatively divide the seabed into two parts to control the dynamic response of the seabed and control the seepage conditions.In the experiment,the seabed sediments and the amplitude of internal solitary waves(ISWs)were changed to compare and analyze the impact of seepage flow on the sediment resuspension by shoaling ISWs.Moreover,parametric research and verification were carried out.Results indicate that seepage flow can greatly influence fine sand,promote sediment resuspension,and increase the amount of suspension by two times on average.However,seepage flow had a little effect on the suspension of clayey silt and sandy silt.Besides,seepage force was added to the traditional gravity,drag force,and uplift force,and the parameterization of threshold starting shear stress of coarse-grained sediments was developed.The results of this parameterization were verified,and seepage force was critical to parameterization.The threshold starting shear stress was reduced by 54.6%after increasing the seepage force.The physical mechanism of this process corresponded to the vertical reciprocating transient seepage in and out the seabed interface caused by the wave-induced transient excess pore water pressure.This quantitative study on seepage flow for shear stress of coarse-grained sediments induced by ISWs is critical to geohazard assessment.展开更多
Deep-seated gas in seabed sediments migrates upwards from effect of external factors,which easily accumulates to form gasbags at interface of shallow coarse-fine sediments.Real-time monitoring of this process is impor...Deep-seated gas in seabed sediments migrates upwards from effect of external factors,which easily accumulates to form gasbags at interface of shallow coarse-fine sediments.Real-time monitoring of this process is important to predict disaster.However,there is still a lack of effective monitoring methods,so we attempt to apply multi-points pore water pressure monitoring technology when simulating forming and dissipation of gasbags in sediments through laboratory experiment.This study focuses on discussion of sensitivity of pore water pressure monitoring data,as well as typical changing characteristics and mechanisms of excess pore water pressure corresponding to crack generation,gasbag formation and gas release.It was found that the value of excess pore water pressure in sediments is negatively correlated with vertical distance between sensors and gas source,and the evolution of gasbag forming and dissipation has a good corresponding relationship with the change of excess pore water pressure.Gasbag formation process is divided into three stages:transverse crack development,longitudinal cavity expansion,and oblique crack development.Formation of gasbag begins with the transverse crack at the interface of coarse-fine sediments while excess pore water pressure attenuates rapidly and then drops,pressure remains almost unchanged when cavity expanses longitudinally,oblique crack appeared in final stage of gasbag evolution while excess pore water pressure accumulated and dissipated again.The variation curve of excess pore water pressure in gas release stage has saw-tooth fluctuation characteristics,and the value and time of pressure accumulation are also fluctuating,indicating the uncertainty and non-uniqueness of gas migration channels in sediments.展开更多
Summary What is already known about this topic?Reports detailing the clinical presentation of coronavirus disease 2019(COVID-19)are extensive in China.However,data remains limited regarding the long-term effects of th...Summary What is already known about this topic?Reports detailing the clinical presentation of coronavirus disease 2019(COVID-19)are extensive in China.However,data remains limited regarding the long-term effects of the 2022 outbreak on the community and healthcare workers(HCWs).What is added by this report?In the follow-up study conducted with 1,069 community members and 3,309 HCWs infected with COVID-19,we observed that five months postoutbreak,39.2%of community members and 28.7%of HCWs reported experiencing at least one symptom.The symptoms most frequently reported included fatigue or muscle weakness,insomnia,cognitive dysfunction,hair loss,joint or muscle pain,and persistent cough.HCWs tended to experience fewer long-term physical consequences and their symptoms had an expedited recovery time compared to the community members.Nevertheless,HCWs displayed a higher prevalence of moderate to severe depression and anxiety.展开更多
基金Supported by the Natural Science Foundation of Jiangsu Province(No.BK20210527)the Open Research Fund of Key Laboratory of Coastal Science and Integrated Management,Ministry of Natural Resources(No.2021COSIMQ002)+1 种基金the National Natural Science Foundation of China(Nos.42107158,41831280)the Fundamental Research Funds for the Central Universities(No.2021QN1096)。
文摘Sediment incipient motion is the first step in sediment resuspension.Previous studies ignored the effect of seepage flow on the mobility of sediment particles and simplified the seabed surface as a rigid boundary.A flume experiment was designed to innovatively divide the seabed into two parts to control the dynamic response of the seabed and control the seepage conditions.In the experiment,the seabed sediments and the amplitude of internal solitary waves(ISWs)were changed to compare and analyze the impact of seepage flow on the sediment resuspension by shoaling ISWs.Moreover,parametric research and verification were carried out.Results indicate that seepage flow can greatly influence fine sand,promote sediment resuspension,and increase the amount of suspension by two times on average.However,seepage flow had a little effect on the suspension of clayey silt and sandy silt.Besides,seepage force was added to the traditional gravity,drag force,and uplift force,and the parameterization of threshold starting shear stress of coarse-grained sediments was developed.The results of this parameterization were verified,and seepage force was critical to parameterization.The threshold starting shear stress was reduced by 54.6%after increasing the seepage force.The physical mechanism of this process corresponded to the vertical reciprocating transient seepage in and out the seabed interface caused by the wave-induced transient excess pore water pressure.This quantitative study on seepage flow for shear stress of coarse-grained sediments induced by ISWs is critical to geohazard assessment.
基金The National Key Research and Development Program of China under contract No.2017YFC0307701the National Natural Science Foundation of China under contract No.41977234。
文摘Deep-seated gas in seabed sediments migrates upwards from effect of external factors,which easily accumulates to form gasbags at interface of shallow coarse-fine sediments.Real-time monitoring of this process is important to predict disaster.However,there is still a lack of effective monitoring methods,so we attempt to apply multi-points pore water pressure monitoring technology when simulating forming and dissipation of gasbags in sediments through laboratory experiment.This study focuses on discussion of sensitivity of pore water pressure monitoring data,as well as typical changing characteristics and mechanisms of excess pore water pressure corresponding to crack generation,gasbag formation and gas release.It was found that the value of excess pore water pressure in sediments is negatively correlated with vertical distance between sensors and gas source,and the evolution of gasbag forming and dissipation has a good corresponding relationship with the change of excess pore water pressure.Gasbag formation process is divided into three stages:transverse crack development,longitudinal cavity expansion,and oblique crack development.Formation of gasbag begins with the transverse crack at the interface of coarse-fine sediments while excess pore water pressure attenuates rapidly and then drops,pressure remains almost unchanged when cavity expanses longitudinally,oblique crack appeared in final stage of gasbag evolution while excess pore water pressure accumulated and dissipated again.The variation curve of excess pore water pressure in gas release stage has saw-tooth fluctuation characteristics,and the value and time of pressure accumulation are also fluctuating,indicating the uncertainty and non-uniqueness of gas migration channels in sediments.
基金funded by National Natural Science Foundation of China(82288102)Chinese Academy of Engineering(2022-XBZD-16).
文摘Summary What is already known about this topic?Reports detailing the clinical presentation of coronavirus disease 2019(COVID-19)are extensive in China.However,data remains limited regarding the long-term effects of the 2022 outbreak on the community and healthcare workers(HCWs).What is added by this report?In the follow-up study conducted with 1,069 community members and 3,309 HCWs infected with COVID-19,we observed that five months postoutbreak,39.2%of community members and 28.7%of HCWs reported experiencing at least one symptom.The symptoms most frequently reported included fatigue or muscle weakness,insomnia,cognitive dysfunction,hair loss,joint or muscle pain,and persistent cough.HCWs tended to experience fewer long-term physical consequences and their symptoms had an expedited recovery time compared to the community members.Nevertheless,HCWs displayed a higher prevalence of moderate to severe depression and anxiety.
