2016 Vol. 38, No. 3
Display Method:
2016, 38(3): .
Abstract:
2016, 38(3): 1-14.
doi: 10.3969/j.issn.0253-4193.2016.03.001
Abstract:
In the numerical simulation of the ocean dynamic system,data assimilation is able to use the limited observation data and numerical model to best estimate the ocean state,and effectively reduce the uncertainty from the initial conditions. Therefore,data assimilation plays an important role in the study of modern physical oceanography. The ensemble Kalman filter (EnKF) is an effective data assimilation method,which has attracted broad attention in oceanic data assimilation since it is proposed about twenty years ago. In recent years,the particle filter (PF) has become a hot research field,for it is not restricted by the linear and Gaussian assumption of the model. This paper analyzes and summarizes the current theories about the EnKF and PF,in the framework of Bayesian filtering theory. The EnKF and PF algorithms are proposed and compared. On this basis,we further discuss the major obstacle for applying the particle filter in oceanic data assimilaiton at present. Some feasible solutions are also introduced. This paper is expected to provide theoretical basis for further development and application of the ensemble-based data assimilation method in oceanic data assimilation.
In the numerical simulation of the ocean dynamic system,data assimilation is able to use the limited observation data and numerical model to best estimate the ocean state,and effectively reduce the uncertainty from the initial conditions. Therefore,data assimilation plays an important role in the study of modern physical oceanography. The ensemble Kalman filter (EnKF) is an effective data assimilation method,which has attracted broad attention in oceanic data assimilation since it is proposed about twenty years ago. In recent years,the particle filter (PF) has become a hot research field,for it is not restricted by the linear and Gaussian assumption of the model. This paper analyzes and summarizes the current theories about the EnKF and PF,in the framework of Bayesian filtering theory. The EnKF and PF algorithms are proposed and compared. On this basis,we further discuss the major obstacle for applying the particle filter in oceanic data assimilaiton at present. Some feasible solutions are also introduced. This paper is expected to provide theoretical basis for further development and application of the ensemble-based data assimilation method in oceanic data assimilation.
2016, 38(3): 15-26.
doi: 10.3969/j.issn.0253-4193.2016.03.002
Abstract:
In the near-shore wave forecasting model,the ocean buoy data assimilation method based on wave spectral decomposition and optimization is proposed. The calculated wave energy spectrum before the initial time is studied with orthogonal decomposition,and the result,combined with synchronous buoy observations of significant wave height value is used to construct a Kalman filtering system,and the initial wave energy density spectrum of wave model is revisesd by the multi-time significant wave height value. This method has been applied to 72 h wave forecast experiments with assimilation 7 buoy's significant wave height data in the Gulf of Alaska. One month experiments show that method can improve the forecasts of significant wave height at different degree of different prediction time. The mean square error for 24 h forecast of significant wave height reduces 0.13 m. Meanwhile,the effect of initial field after assimilation to forecast will extend 36 h or so,but the assimilation effect is weakened by extend the prediction time.
In the near-shore wave forecasting model,the ocean buoy data assimilation method based on wave spectral decomposition and optimization is proposed. The calculated wave energy spectrum before the initial time is studied with orthogonal decomposition,and the result,combined with synchronous buoy observations of significant wave height value is used to construct a Kalman filtering system,and the initial wave energy density spectrum of wave model is revisesd by the multi-time significant wave height value. This method has been applied to 72 h wave forecast experiments with assimilation 7 buoy's significant wave height data in the Gulf of Alaska. One month experiments show that method can improve the forecasts of significant wave height at different degree of different prediction time. The mean square error for 24 h forecast of significant wave height reduces 0.13 m. Meanwhile,the effect of initial field after assimilation to forecast will extend 36 h or so,but the assimilation effect is weakened by extend the prediction time.
2016, 38(3): 27-39.
doi: 10.3969/j.issn.0253-4193.2016.03.003
Abstract:
Monthly Sea Surface Temperature (SST) data of 6 coastal observation stations over coastal zone of circum Bohai Sea are chosen in the experimental homogeneity study. The work is expected to find a method to homogenize the monthly historical SST data in China. The coastal observation stations have the low density and it is hard to find homogeneous series for use as reference series. In light of the situation, two road maps are adopted to test the homogeneity of the SST series. Firstly, the penalized maximum F Test (PMFT) method which does not rely on reference series was chosen to detect change points. The resulting change points are then synthesized and verified by available metadata. Then, quantile-matching algorithm was used to adjust the SST series to diminish discontinuities. This method was suitable to the coastal observation stations with detailed metadata. However, for the coastal observation stations without enough metadata, penalized maximum T test (PMT) which relies on reference series was used. Here, we use air surface temperature data series from nearly meteorological stations that are highly positively correlated with the base series to construct reference series. Testing results show that some inhomogeneities exist in the whole SST series in the region. Observational system change is found to be the main cause for discontinuities, followed by station relocation. It is found that the annual mean SST trend has changed obviously and homogeneity is improved well after adjustment. Results show that the warming rate of SST series after adjustment is larger than that before adjustment. In our study, a combination of the two different methods is proved to be necessary and possible, and it shows reasonability and application values in the homogeneity study of SST data in China. The results could provide a more reliable data set of homogenized in a longer period for the climate studies over offshore areas of China.
Monthly Sea Surface Temperature (SST) data of 6 coastal observation stations over coastal zone of circum Bohai Sea are chosen in the experimental homogeneity study. The work is expected to find a method to homogenize the monthly historical SST data in China. The coastal observation stations have the low density and it is hard to find homogeneous series for use as reference series. In light of the situation, two road maps are adopted to test the homogeneity of the SST series. Firstly, the penalized maximum F Test (PMFT) method which does not rely on reference series was chosen to detect change points. The resulting change points are then synthesized and verified by available metadata. Then, quantile-matching algorithm was used to adjust the SST series to diminish discontinuities. This method was suitable to the coastal observation stations with detailed metadata. However, for the coastal observation stations without enough metadata, penalized maximum T test (PMT) which relies on reference series was used. Here, we use air surface temperature data series from nearly meteorological stations that are highly positively correlated with the base series to construct reference series. Testing results show that some inhomogeneities exist in the whole SST series in the region. Observational system change is found to be the main cause for discontinuities, followed by station relocation. It is found that the annual mean SST trend has changed obviously and homogeneity is improved well after adjustment. Results show that the warming rate of SST series after adjustment is larger than that before adjustment. In our study, a combination of the two different methods is proved to be necessary and possible, and it shows reasonability and application values in the homogeneity study of SST data in China. The results could provide a more reliable data set of homogenized in a longer period for the climate studies over offshore areas of China.
2016, 38(3): 40-48.
doi: 10.3969/j.issn.0253-4193.2016.03.004
Abstract:
By using NCEP/NCAR reanalysis data,the SST,the air temperature of 160 Chinese stations and the ice grade for Bohai Sea which indicates the ice conditions in Bohai Sea,the impacts of Barents Sea SST anomalies on the variations of the ice condition in Bohai Sea during the later period are investigated in this paper. The results indicate that the variation of the fall SST in the key region is negatively correlated to the sea-ice concentration from the preceding winter to the next summer,leading to the variations of the turbulent heat flux during the winter. During the warmer (colder) Barents Sea years,the Asian zonal circulations are evidently weakened (strengthened) accompanied by a deeper (reduced) East Asian trough and the East Asian Winter Monsoon is significantly stronger (weaker) accompany with much lower (higher) observed temperature anomalies in north China. These characteristics consistent with the increase (decrease) of the intensity and scope of the Bohai Sea Ice anomalies and the related circulation differences in the winter. Further investigation seems to suggest that in the 200 hPa wind field there is an apparent wave train from west to east related to the Barents Sea SST index and the wave train is an important way conveying the impact of the Barents Sea SST anomalies in the upstream to the East Asian area. Moreover,the circulation anomalies in the lower troposphere can be attributed to the variations of the local Hadley circulation. Therefore,the Barents Sea SST anomalies of the fall can be used as a predictor of the ice conditions in the Bohai Sea during the following winter.
By using NCEP/NCAR reanalysis data,the SST,the air temperature of 160 Chinese stations and the ice grade for Bohai Sea which indicates the ice conditions in Bohai Sea,the impacts of Barents Sea SST anomalies on the variations of the ice condition in Bohai Sea during the later period are investigated in this paper. The results indicate that the variation of the fall SST in the key region is negatively correlated to the sea-ice concentration from the preceding winter to the next summer,leading to the variations of the turbulent heat flux during the winter. During the warmer (colder) Barents Sea years,the Asian zonal circulations are evidently weakened (strengthened) accompanied by a deeper (reduced) East Asian trough and the East Asian Winter Monsoon is significantly stronger (weaker) accompany with much lower (higher) observed temperature anomalies in north China. These characteristics consistent with the increase (decrease) of the intensity and scope of the Bohai Sea Ice anomalies and the related circulation differences in the winter. Further investigation seems to suggest that in the 200 hPa wind field there is an apparent wave train from west to east related to the Barents Sea SST index and the wave train is an important way conveying the impact of the Barents Sea SST anomalies in the upstream to the East Asian area. Moreover,the circulation anomalies in the lower troposphere can be attributed to the variations of the local Hadley circulation. Therefore,the Barents Sea SST anomalies of the fall can be used as a predictor of the ice conditions in the Bohai Sea during the following winter.
2016, 38(3): 49-59.
doi: 10.3969/j.issn.0253-4193.2016.03.005
Abstract:
Subei radiation shoals consist of over 10 master sand ridges and 10 main waterways. Hydrodynamics in sand ridges dominates the shoals' birth,growth,and death,forming the unique landform of intersect tide-flats and grooves. The Yellow Sea rotational ridal wave and the East Sea forward tidal wave meet at Jianggang Port,which lies in the center of the shoals area. Affected by outer flow systems,such as the Yellow Sea coastal current,the Subei coastal current,and the Yangtze River diluted water,and with the effect of complex terrain and atmospheric force on shallow water,the shoals show 4 kinds of totally different residual circulation structure within. In this paper,quasi-synchronous survey data of 8 times and 23 sites within 2006-2012,which cover major sand ridges and waterways,the ADCP data of 4 sites at southern shoals area,continuously observed for more than 1 month,and meteorological and hydrological data from Lvsi and YangKou Port marine station were used to analyze the seasonal change of residual current transport and distribution pattern in the shoals area and to focus on the response of the southern shoals area's residuals to wind stress.
Subei radiation shoals consist of over 10 master sand ridges and 10 main waterways. Hydrodynamics in sand ridges dominates the shoals' birth,growth,and death,forming the unique landform of intersect tide-flats and grooves. The Yellow Sea rotational ridal wave and the East Sea forward tidal wave meet at Jianggang Port,which lies in the center of the shoals area. Affected by outer flow systems,such as the Yellow Sea coastal current,the Subei coastal current,and the Yangtze River diluted water,and with the effect of complex terrain and atmospheric force on shallow water,the shoals show 4 kinds of totally different residual circulation structure within. In this paper,quasi-synchronous survey data of 8 times and 23 sites within 2006-2012,which cover major sand ridges and waterways,the ADCP data of 4 sites at southern shoals area,continuously observed for more than 1 month,and meteorological and hydrological data from Lvsi and YangKou Port marine station were used to analyze the seasonal change of residual current transport and distribution pattern in the shoals area and to focus on the response of the southern shoals area's residuals to wind stress.
2016, 38(3): 60-70.
doi: 10.3969/j.issn.0253-4193.2016.03.006
Abstract:
The reasonable storm surge risk assessment is always limited by the number of the historical Tropical Cyclone (TC) samples. In this paper the influence of the data set length to the storm surge risk assessment result is studied in Lianjiang County of Fujian Province,which is based on the historical TC observations (1949-2010) and stochastic TC events (1 000 a). The two datasets were applied to force the ADCIRC model to simulate storm surges,which is used to determine the surge heights of typical return periods with the method of extreme value type I. The experiment result indicates that the surge heights of typical return periods have a close correlation with data sets length,i.e.,the longer the data sets length,the more stable of the results. As for the surge heights of 1 000 years return period,the results from 500 a length data sets can give a rather stable result,which is close to the results generated from the 1 000 a length data set. When carrying out storm surges hazards analysis,the results are more reasonable by using TC stochastic events in 1 000 years than those from historical TC events in decades of years.
The reasonable storm surge risk assessment is always limited by the number of the historical Tropical Cyclone (TC) samples. In this paper the influence of the data set length to the storm surge risk assessment result is studied in Lianjiang County of Fujian Province,which is based on the historical TC observations (1949-2010) and stochastic TC events (1 000 a). The two datasets were applied to force the ADCIRC model to simulate storm surges,which is used to determine the surge heights of typical return periods with the method of extreme value type I. The experiment result indicates that the surge heights of typical return periods have a close correlation with data sets length,i.e.,the longer the data sets length,the more stable of the results. As for the surge heights of 1 000 years return period,the results from 500 a length data sets can give a rather stable result,which is close to the results generated from the 1 000 a length data set. When carrying out storm surges hazards analysis,the results are more reasonable by using TC stochastic events in 1 000 years than those from historical TC events in decades of years.
2016, 38(3): 71-81.
doi: 10.3969/j.issn.0253-4193.2016.03.007
Abstract:
Katabatic winds are airflows that occur above a cold sloped surface. They are driven by gravity that causes colder and denser air masses to move downhill. Katabatic winds play a crucial role in the surface wind regime of Antarctica. Chinese Zhongshan Station,Antarctica,is strongly influenced by the katabatic wind all the year round. In sunny summer days,the katabatic wind at Zhongshan Station usually begins in the evening. The wind reaches its maximal speed at mid-night and then decreases before the next noon,with a significant diurnal cycle characteristics. The katabatic wind case in austral summer,January 2010,at Antarctic Zhongshan Station is analyzed with employing of conventional meteorological observations and the Polar WRF model. The results indicate that when katabatic wind emerges at nights of clear sky,the wind speed near the ground and surface air temperature trends are negatively correlated to-0.91. Simulations from Polar WRF show that the height of the maximum speed of the katabatic wind,15-21 m/s,is between 100 and 150 m from the ground. Near surface air temperature inversion always accompany with the katabatic wind. With the thickness of 200 to 300 m,the inversion has its strength of about 4-6℃. The near-ground katabatic wind at Zhongshan Station always blows from the southeast due to the ground friction. The wind direction deflects counterclockwise and eventually becomes parallel with the terrain contours while the height increasing. When there is no direct solar radiation,continuous inversion presents at Antarctica continent and enhances the katabatic air flow. With the enhancement of the inversion,windy area gradually shifts westward and the acreage increases. In the short time when inversion disappears due to solar radiation in summer times,the katabatic wind would not completely disappear,thus forming a relatively stable spatial distribution of wind direction.
Katabatic winds are airflows that occur above a cold sloped surface. They are driven by gravity that causes colder and denser air masses to move downhill. Katabatic winds play a crucial role in the surface wind regime of Antarctica. Chinese Zhongshan Station,Antarctica,is strongly influenced by the katabatic wind all the year round. In sunny summer days,the katabatic wind at Zhongshan Station usually begins in the evening. The wind reaches its maximal speed at mid-night and then decreases before the next noon,with a significant diurnal cycle characteristics. The katabatic wind case in austral summer,January 2010,at Antarctic Zhongshan Station is analyzed with employing of conventional meteorological observations and the Polar WRF model. The results indicate that when katabatic wind emerges at nights of clear sky,the wind speed near the ground and surface air temperature trends are negatively correlated to-0.91. Simulations from Polar WRF show that the height of the maximum speed of the katabatic wind,15-21 m/s,is between 100 and 150 m from the ground. Near surface air temperature inversion always accompany with the katabatic wind. With the thickness of 200 to 300 m,the inversion has its strength of about 4-6℃. The near-ground katabatic wind at Zhongshan Station always blows from the southeast due to the ground friction. The wind direction deflects counterclockwise and eventually becomes parallel with the terrain contours while the height increasing. When there is no direct solar radiation,continuous inversion presents at Antarctica continent and enhances the katabatic air flow. With the enhancement of the inversion,windy area gradually shifts westward and the acreage increases. In the short time when inversion disappears due to solar radiation in summer times,the katabatic wind would not completely disappear,thus forming a relatively stable spatial distribution of wind direction.
2016, 38(3): 82-87.
doi: 10.3969/j.issn.0253-4193.2016.03.008
Abstract:
In this paper,the objective analysis method is studied to merge the daily chlorophyll a concentration products over the northwest Pacific from three ocean color sensors:Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua platform,MODIS on the Terra platform and the Medium Resolution Imaging Spectrometer(MERIS) on the ENVISAT platform. The objective analysis method is evaluated from the spatial coverage ratio and the accuracy of the merged result. The evaluation result showed that the spatial coverage of objective analysis method products is much larger than that of the single sensor products and the GSM merged products. Through validation with the in-situ data during periods from 2002 to 2012,the matched data of the GSM merged data and the Objective Analysis method merged data is 578 and 1 432,respectively. The correlation coefficient and the root mean square error (RMSE) of the GSM merged data are -0.20 mg/m3 and 0.37 mg/m3. The same evaluation parameters of objective analysis are -0.21 mg/m3 and 0.36 mg/m3. The results show that the objective analysis is an effective method for merging chlorophyll a data and the product of this method has the similar accuracy with other products and higher spatial coverage ratio.
In this paper,the objective analysis method is studied to merge the daily chlorophyll a concentration products over the northwest Pacific from three ocean color sensors:Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua platform,MODIS on the Terra platform and the Medium Resolution Imaging Spectrometer(MERIS) on the ENVISAT platform. The objective analysis method is evaluated from the spatial coverage ratio and the accuracy of the merged result. The evaluation result showed that the spatial coverage of objective analysis method products is much larger than that of the single sensor products and the GSM merged products. Through validation with the in-situ data during periods from 2002 to 2012,the matched data of the GSM merged data and the Objective Analysis method merged data is 578 and 1 432,respectively. The correlation coefficient and the root mean square error (RMSE) of the GSM merged data are -0.20 mg/m3 and 0.37 mg/m3. The same evaluation parameters of objective analysis are -0.21 mg/m3 and 0.36 mg/m3. The results show that the objective analysis is an effective method for merging chlorophyll a data and the product of this method has the similar accuracy with other products and higher spatial coverage ratio.
Study on sediment floccules and the influence factors in the North Passage of the Changjiang Estuary
2016, 38(3): 88-97.
doi: 10.3969/j.issn.0253-4193.2016.03.009
Abstract:
Based on the field observations in April 2012 in the North Passage of the Changjiang Estuary,as well as the data measured with scanning electron microscope,the characteristics of flow and sediment,the micromorphology and size of floccules and the main influence factors in the North Passage were investigated in this paper. The results show that the tidal current velocity,the salinity,the suspended sediment concentration and the sediment particle size in the North Passage are very suitable for flocculation. There are varied forms of floccules,mainly including loose floccules,porous floccules and dense floccules. They are mainly composed of fine silts and clays,with rough surfaces,loose or dense structures. The variations of floccule size are highly related to the flood-ebb process,showing periodic features. The floccule size is big during slacks,but small during peak currents. Usually,the floccule size during high water slacks is bigger than that during low water slacks; the floccule size during neap tides is bigger than that during spring tides. Additionally,the floccule size is gradually increased from the surface to the bottom. The tidal current velocity controls the variations of floccule size. The flocculation of suspended sediment is one of the main reasons for the siltation in the navigation channel of North Passage.
Based on the field observations in April 2012 in the North Passage of the Changjiang Estuary,as well as the data measured with scanning electron microscope,the characteristics of flow and sediment,the micromorphology and size of floccules and the main influence factors in the North Passage were investigated in this paper. The results show that the tidal current velocity,the salinity,the suspended sediment concentration and the sediment particle size in the North Passage are very suitable for flocculation. There are varied forms of floccules,mainly including loose floccules,porous floccules and dense floccules. They are mainly composed of fine silts and clays,with rough surfaces,loose or dense structures. The variations of floccule size are highly related to the flood-ebb process,showing periodic features. The floccule size is big during slacks,but small during peak currents. Usually,the floccule size during high water slacks is bigger than that during low water slacks; the floccule size during neap tides is bigger than that during spring tides. Additionally,the floccule size is gradually increased from the surface to the bottom. The tidal current velocity controls the variations of floccule size. The flocculation of suspended sediment is one of the main reasons for the siltation in the navigation channel of North Passage.
2016, 38(3): 98-110.
doi: 10.3969/j.issn.0253-4193.2016.03.010
Abstract:
Coastal erosion causes great harm to islands with scarce land resources and beach of tourism value. Based on multi source data such as satellite remote sensing,aerial photography,unmanned aerial vehicle(UAV),GPS and field survey etc,the changes of coastline types,location,length and evolution of beach surface erosion in Dongshan Island was analyzed by GIS. The results show that the length of entire coastline was reduced,because of the transformation from irregular natural coastline to regular artificial coastline. UAV elevation inversion can meet precision requirements for beach surface erosion monitoring. Various breeding drainage ways on beach surface has caused different beach surface gullies in Wujiao Bay and Nanmen Bay,so the micro morphology of the beach was changed. Rising sea levels and the typhoon storm surge are representative factors of the long term and short term erosion respectively. Present human activities has become the most important factor of coastal erosion in short time scale,and is likely to turn into long term tendency factor.
Coastal erosion causes great harm to islands with scarce land resources and beach of tourism value. Based on multi source data such as satellite remote sensing,aerial photography,unmanned aerial vehicle(UAV),GPS and field survey etc,the changes of coastline types,location,length and evolution of beach surface erosion in Dongshan Island was analyzed by GIS. The results show that the length of entire coastline was reduced,because of the transformation from irregular natural coastline to regular artificial coastline. UAV elevation inversion can meet precision requirements for beach surface erosion monitoring. Various breeding drainage ways on beach surface has caused different beach surface gullies in Wujiao Bay and Nanmen Bay,so the micro morphology of the beach was changed. Rising sea levels and the typhoon storm surge are representative factors of the long term and short term erosion respectively. Present human activities has become the most important factor of coastal erosion in short time scale,and is likely to turn into long term tendency factor.
2016, 38(3): 111-122.
doi: 10.3969/j.issn.0253-4193.2016.03.011
Abstract:
Tidal flat terrain is one of the most important indexes for us to exploit intertidal mudflat legitimately. Its measure method that using water boundary of tidal flat is now widely approved as a feasible method by remote sensing. Based on this method,the paper provided a new way named hydrological station baseline to construct tidal flat terrain. The way is established in a large tidal flat of radial sand ridges in coastal area of Jiangsu Province by connecting 4 hydrological stations in a row,used the values of water level,getting from the hydrological stations,to calculate water boundaries' elevation which were extracted from remote sensing images with multi tide situations. Accordingly,completed the construction of the tidal flat terrain of radial sand ridges. The accuracy was confirmed by actual measurement terrain. Results show that the DEM can reflect the current basic form of tidal flat and the position accuracy approach 30 m and the elevation accuracy approach 20 cm.
Tidal flat terrain is one of the most important indexes for us to exploit intertidal mudflat legitimately. Its measure method that using water boundary of tidal flat is now widely approved as a feasible method by remote sensing. Based on this method,the paper provided a new way named hydrological station baseline to construct tidal flat terrain. The way is established in a large tidal flat of radial sand ridges in coastal area of Jiangsu Province by connecting 4 hydrological stations in a row,used the values of water level,getting from the hydrological stations,to calculate water boundaries' elevation which were extracted from remote sensing images with multi tide situations. Accordingly,completed the construction of the tidal flat terrain of radial sand ridges. The accuracy was confirmed by actual measurement terrain. Results show that the DEM can reflect the current basic form of tidal flat and the position accuracy approach 30 m and the elevation accuracy approach 20 cm.
2016, 38(3): 123-130.
doi: 10.3969/j.issn.0253-4193.2016.03.012
Abstract:
Silty seabed exists widely in the Yellow River Subaqueous Delta. Liquefied silt has properties similar to fluid. It has found that the behavior of liquefied silt can be simulated appropriately by modeling the liquefied silt as viscous fluid. According to the theory of Stokes Law,the test apparatus of flow characteristics of liquefied silt is developed based on the wave flume tests. A steel sphere,embedded in the wave flume,can be moved in the horizontal direction when the silt liquefaction occurs. Resistance force and velocity of the steel sphere are measured during sphere dragging,then apparent viscosity can be evaluated. Considering fully the infection of wave parameters and excess pore pressure ratio in the tests. The results indicate that this apparatus can meet the test requirements. It can be observed the processes of pressure buildup when it is forced by the cyclic loading of wave. Wave parameters have great influence on the results,apparent viscosity decreased as wave height increase. Apparent viscosity slowly enlarge with the passing of time at the same wave heights. Along with the increasing of pore pressure ratio,the apparent viscosity of the liquefied silt apparently decreases.
Silty seabed exists widely in the Yellow River Subaqueous Delta. Liquefied silt has properties similar to fluid. It has found that the behavior of liquefied silt can be simulated appropriately by modeling the liquefied silt as viscous fluid. According to the theory of Stokes Law,the test apparatus of flow characteristics of liquefied silt is developed based on the wave flume tests. A steel sphere,embedded in the wave flume,can be moved in the horizontal direction when the silt liquefaction occurs. Resistance force and velocity of the steel sphere are measured during sphere dragging,then apparent viscosity can be evaluated. Considering fully the infection of wave parameters and excess pore pressure ratio in the tests. The results indicate that this apparatus can meet the test requirements. It can be observed the processes of pressure buildup when it is forced by the cyclic loading of wave. Wave parameters have great influence on the results,apparent viscosity decreased as wave height increase. Apparent viscosity slowly enlarge with the passing of time at the same wave heights. Along with the increasing of pore pressure ratio,the apparent viscosity of the liquefied silt apparently decreases.
2016, 38(3): 131-144.
doi: 10.3969/j.issn.0253-4193.2016.03.013
Abstract:
As the permanent support seabed structures for subsea wells,pipeline manifolds and pipeline terminations,the mudmat foundations have obviously complex,nonlinear and uncertain loading,which makes the research of mudmat foundations' stability a big challenge. In this paper,the bearing capacity of mudmat foundations in rectangular,square,hexagon and circle are researched under the same steel quantity condition on the deep clay where the strength increases linearly with depth. Numerical simulation method is utilized to investigate the failure envelops and formulas of mudmat are established in V-H、V-M、V-T、Hx-Hy、Mx-My、T-H & T-M load space,when combined vertical load V,Horizontal load H,moment load M,and torque load T were applied Analysis results show that the shape of mudmat has great influence on its bearing capacity. Concretely,the circular mudmat is suitable on the condition of large V load,while the rectangular and square mudmat is better when the H is obvious among all the loads. When M is the control load,different shapes of the mudmat meet different conditions separately. But the rectangular or the square mudmat is optimal and the hexagon or the circle mudmat take second place when the influence of T load cannot be ignored.
As the permanent support seabed structures for subsea wells,pipeline manifolds and pipeline terminations,the mudmat foundations have obviously complex,nonlinear and uncertain loading,which makes the research of mudmat foundations' stability a big challenge. In this paper,the bearing capacity of mudmat foundations in rectangular,square,hexagon and circle are researched under the same steel quantity condition on the deep clay where the strength increases linearly with depth. Numerical simulation method is utilized to investigate the failure envelops and formulas of mudmat are established in V-H、V-M、V-T、Hx-Hy、Mx-My、T-H & T-M load space,when combined vertical load V,Horizontal load H,moment load M,and torque load T were applied Analysis results show that the shape of mudmat has great influence on its bearing capacity. Concretely,the circular mudmat is suitable on the condition of large V load,while the rectangular and square mudmat is better when the H is obvious among all the loads. When M is the control load,different shapes of the mudmat meet different conditions separately. But the rectangular or the square mudmat is optimal and the hexagon or the circle mudmat take second place when the influence of T load cannot be ignored.
2016, 38(3): 145-155.
doi: 10.3969/j.issn.0253-4193.2016.03.014
Abstract:
Forty eight geochemical indexs of sediment samples,including major element,trace element and rare earth element(REE) content,were analyzed by X-ray fluorescence spectrometry (XRF),ion-coupled plasma-mass spectroscopy(ICP-MS) and atomic fluorescence spectrometry (AF) for the samples of core 07 obtained in the southern coast of Laizhou Bay. Meanwhile,the elements content,changing law,the characteristic ratio and distribution patterns of REE were studied. According to research,most elements and characteristic ratios in borehole 07 changed obviously in marine-continental stratigraphic boundaries,which could be used to divide stratum. In addition,Mn,Mg,Ca,Fe,Mg/Ca and K/Na were well correlated with sedimentary environment changes; Ba,Zr,Rb,Si/A1,Ti/A1 and Rb/Sr could be utilized to trace the type of source rock,weathering degree and the transport distance. Majority elements showed multi-cycle variation,especially in the transgression layers. The stratigraphic features reflected by the changes in chemical elements were well corresponding to climatic and sea-level changes since the late Pleistocene. The Chondrite-normalized REE distribution patterns of sediments in borehole 07 with different depth were similar to that Yellow River,and the LREE content was much higher than HREE,which indicated that Yellow River was one of provenances of Mihe-WeiHe multi-source fluvial delta sedimentary system in the south of Laizhou Bay,contributing to sedimentary strata within a certain range of depth.
Forty eight geochemical indexs of sediment samples,including major element,trace element and rare earth element(REE) content,were analyzed by X-ray fluorescence spectrometry (XRF),ion-coupled plasma-mass spectroscopy(ICP-MS) and atomic fluorescence spectrometry (AF) for the samples of core 07 obtained in the southern coast of Laizhou Bay. Meanwhile,the elements content,changing law,the characteristic ratio and distribution patterns of REE were studied. According to research,most elements and characteristic ratios in borehole 07 changed obviously in marine-continental stratigraphic boundaries,which could be used to divide stratum. In addition,Mn,Mg,Ca,Fe,Mg/Ca and K/Na were well correlated with sedimentary environment changes; Ba,Zr,Rb,Si/A1,Ti/A1 and Rb/Sr could be utilized to trace the type of source rock,weathering degree and the transport distance. Majority elements showed multi-cycle variation,especially in the transgression layers. The stratigraphic features reflected by the changes in chemical elements were well corresponding to climatic and sea-level changes since the late Pleistocene. The Chondrite-normalized REE distribution patterns of sediments in borehole 07 with different depth were similar to that Yellow River,and the LREE content was much higher than HREE,which indicated that Yellow River was one of provenances of Mihe-WeiHe multi-source fluvial delta sedimentary system in the south of Laizhou Bay,contributing to sedimentary strata within a certain range of depth.
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