This study examined wintertime (November-April) cold wave frequency (CWF) in northern China during the last 42 years and its association with Arctic Oscillation (AO) through analysis of daily mean surface temperature ...This study examined wintertime (November-April) cold wave frequency (CWF) in northern China during the last 42 years and its association with Arctic Oscillation (AO) through analysis of daily mean surface temperature from 280 stations across northern China and European Centre for Medium-Range Weather Forecasts (ECMWF) 40-Year Re-analysis ERA-40 data. The leading empirical orthogonal function EOF mode of wintertime CWF (CWF-EOF1) indicates an identical signal over most northern China, with the characteristic trend of linear decline for the leading principal component (CWF-PC1). After the linear trend is removed, remarkable inter-annual variability is found to be the dominant feature of the CWF-PC1. The regression map for sea level pressure based on CWF-PC1 corresponds to the negative phase of AO. Correlation analysis further proves that CWF-PC1 has a significant negative correlation with AO at the inter-annual time scale. The relationship between AO and global surface air temperature is also investigated in order to understand its association with cold air activity over East Asia, and it is suggested that the anomalies of atmospheric circulation in Siberia may serve as a bridge for interaction between AO and CWF in northern China during wintertime.展开更多
A numerical wave load model based on two-phase(water-air) Reynolds-Averaged Navier Stokes(RANS) type equations is used to evaluate hydrodynamic forces exerted on flatted-bottom seafloor mining tool during its entering...A numerical wave load model based on two-phase(water-air) Reynolds-Averaged Navier Stokes(RANS) type equations is used to evaluate hydrodynamic forces exerted on flatted-bottom seafloor mining tool during its entering ocean waves of deploying process.The discretization of the RANS equations is achieved by a finite volume approach(FV).The volume of fluid method(VOF) is employed to track the complicated free surface.A numerical wave tank is built to generate the ocean waves which are suitable for deploying seafloor mining tool.A typical deploying condition is employed to reflect the process of flatted-bottom body impacting with waves,and the pressure distribution of bottom is also presented.Four different lowering velocities are applied to obtain the time histories of maximum pressure of bottom,and it can be concluded that the pressure coefficient decreases with water velocity increasing,which is similar with ordinary water entry case.The numerical results clearly demonstrate the characteristics of flatted-bottom body entering ocean waves.展开更多
In this study, hydraulic model tests are carried out to investigate the mean overtopping discharge at perforated caisson breakwaters for non-impulsive waves. Based on the experimental data, the mean overtopping discha...In this study, hydraulic model tests are carried out to investigate the mean overtopping discharge at perforated caisson breakwaters for non-impulsive waves. Based on the experimental data, the mean overtopping discharges of perforated and nonperforated caissons are compared. It is found that when the relative crest freeboard is smaller than 1.6, the mean overtopping discharge of a breakwater can be reduced by at least half by using perforated caissons with 35% porosity instead of nonperforated caissons. The effects of the relative crest freeboard, the caisson porosity and perforation shape, the relative wave chamber width and the relative water depth on the mean overtopping discharge at perforated caissons are clarified. Then,predictive formulas for the mean overtopping discharge at perforated caissons are developed. The predictive formulas based on the experimental data are valid in a wide range of the relative crest freeboard and involve the effects of the caisson porosity and the relative water depth. The predictive formulas developed in this study are of significance for the hydraulic design of perforated caissons.展开更多
基金supported by the National Basic Research Program of China (973 Program) (Grant No.2009CB421406)the National Key Technologies R&D Program of China (Grant No.2007BAC29B03)the The National Natural Science Foundation of China Project (Grant No.40821092)
文摘This study examined wintertime (November-April) cold wave frequency (CWF) in northern China during the last 42 years and its association with Arctic Oscillation (AO) through analysis of daily mean surface temperature from 280 stations across northern China and European Centre for Medium-Range Weather Forecasts (ECMWF) 40-Year Re-analysis ERA-40 data. The leading empirical orthogonal function EOF mode of wintertime CWF (CWF-EOF1) indicates an identical signal over most northern China, with the characteristic trend of linear decline for the leading principal component (CWF-PC1). After the linear trend is removed, remarkable inter-annual variability is found to be the dominant feature of the CWF-PC1. The regression map for sea level pressure based on CWF-PC1 corresponds to the negative phase of AO. Correlation analysis further proves that CWF-PC1 has a significant negative correlation with AO at the inter-annual time scale. The relationship between AO and global surface air temperature is also investigated in order to understand its association with cold air activity over East Asia, and it is suggested that the anomalies of atmospheric circulation in Siberia may serve as a bridge for interaction between AO and CWF in northern China during wintertime.
基金Project(51305463)supported by National Natural Science Foundation of ChinaProject(2012QNZT01601005125)supported by Free Exploration Plan of Central South University,ChinaProject supported by Postdoctoral Foundation of Central South university,China
文摘A numerical wave load model based on two-phase(water-air) Reynolds-Averaged Navier Stokes(RANS) type equations is used to evaluate hydrodynamic forces exerted on flatted-bottom seafloor mining tool during its entering ocean waves of deploying process.The discretization of the RANS equations is achieved by a finite volume approach(FV).The volume of fluid method(VOF) is employed to track the complicated free surface.A numerical wave tank is built to generate the ocean waves which are suitable for deploying seafloor mining tool.A typical deploying condition is employed to reflect the process of flatted-bottom body impacting with waves,and the pressure distribution of bottom is also presented.Four different lowering velocities are applied to obtain the time histories of maximum pressure of bottom,and it can be concluded that the pressure coefficient decreases with water velocity increasing,which is similar with ordinary water entry case.The numerical results clearly demonstrate the characteristics of flatted-bottom body entering ocean waves.
基金supported by the Natural Science Foundation of China(Grant Nos.51322903&51725903)
文摘In this study, hydraulic model tests are carried out to investigate the mean overtopping discharge at perforated caisson breakwaters for non-impulsive waves. Based on the experimental data, the mean overtopping discharges of perforated and nonperforated caissons are compared. It is found that when the relative crest freeboard is smaller than 1.6, the mean overtopping discharge of a breakwater can be reduced by at least half by using perforated caissons with 35% porosity instead of nonperforated caissons. The effects of the relative crest freeboard, the caisson porosity and perforation shape, the relative wave chamber width and the relative water depth on the mean overtopping discharge at perforated caissons are clarified. Then,predictive formulas for the mean overtopping discharge at perforated caissons are developed. The predictive formulas based on the experimental data are valid in a wide range of the relative crest freeboard and involve the effects of the caisson porosity and the relative water depth. The predictive formulas developed in this study are of significance for the hydraulic design of perforated caissons.
