The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGH...The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGHF)is the main gas-producing formation and is composed of various sedimentary types;however,a clear understanding of the sedimentary types and development patterns is lacking.Here,typical lithofacies,logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling,logging,analysis and testing data.Based on 3D seismic interpretation and attribute analysis,the origin of high-amplitude reflections is clarified,and the main types and evolution characteristics of sedimentary facies are identified.Taking gas formation upper II(IIU)as an example,the plane distribution of the delta front and bottom current channel is determined;finally,a comprehensive sedimentary model of the YGHF second member is established.This second member is a shallowly buried“bright spot”gas reservoir with weak compaction.The velocity of sandstone is slightly lower than that of mudstone,and the reflection has medium amplitude when there is no gas.The velocity of sandstone decreases considerably after gas accumulation,resulting in an increase in the wave impedance difference and high-amplitude(bright spot)reflection between sandstone and mudstone;the range of high amplitudes is consistent with that of gas-bearing traps.The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps,and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps.The study area is a delta front deposit developed on a shallow sea shelf.The lithologies of the reservoir are mainly composed of very fine sand and coarse silt,and a variety of sedimentary structural types reflect a shallow sea delta environment;upward thickening funnel type,strong toothed bell type and toothed funnel type logging facies are developed.In total,4 stages of delta front sand bodies(corresponding to progradational reflection seismic facies)derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF;these sand bodies are dated to 1.5 Ma and correspond to four gas formations.During sedimentation,many bottom current channels(corresponding to channel fill seismic facies)formed,which interacted with the superposed progradational reflections.When the provenance supply was strong in the northwest,the area was dominated by a large set of delta front deposits.In the period of relative sea level rise,surface bottom currents parallel to the coastline were dominant,and undercutting erosion was obvious,forming multistage superimposed erosion troughs.Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.展开更多
Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal c...Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation.展开更多
There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,...There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,extending from the NE to the SW,leading to accumulation of discontinuous drifts with higher sedimentation rates on the eastern side of the channel. The stacking pattern of the layers sug-gests that these drifts propagated southwestward,following the direction of the bottom currents. One sedimentary drift to the southeast of the Dongsha Islands has the highest sedimentation rate of 97cm/ka in the last 12 ka. The sedimentary characteristics of the sediment layers indicate that these bottom currents are most likley caused by the water movement of a branch of the West Pacific Ocean Current,which enters the northern SCS via the Bashi Strait. Once formed,the bottom currents trans-port sediments along the northern slope of SCS southwestward and finally disappear into the central basin of the SCS. Due to the bottom current activity,the deep-sea sedimentary process in the northern SCS is complex.展开更多
On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating botto...On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.展开更多
A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Ha...A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.展开更多
The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be ...The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be extended and applicated to the study of the mechanism. Considering the effects of moving bottoms and starting from the Navier-Stokes equation of motion of a vinous fluid including the Coriolis force, a generalized mean-flow medel theory for the nearshore region, that is, a set of mean-flow equations and their generalized wave action equation involving the three new kinds of actions termed respectively as the current wave action, the bottom wave action and the dissipative wave action which can be applied to arbitrary depth over moving bottoms and ambient currents with a typical vertical structure, is developed by vertical integration and time-averaglng over a wave peried, thus extending the classical concept, wave action, from the ideal averaged flow conservative system to the real averaged flow dissipative dynamical system, and having a large range of application.展开更多
This paper proposes a new method for data assimilation of the surface radial current observed by High Frequency ground wave radar and optimization of the bottom friction coefficient.In this method,the shallow water wa...This paper proposes a new method for data assimilation of the surface radial current observed by High Frequency ground wave radar and optimization of the bottom friction coefficient.In this method,the shallow water wave equation is introduced into the cost function of the multigrid three-dimensional variation data assimilation method as the weak constraint term,the surface current and the bottom friction coefficient are defined as the analytical variables,and the high spatiotemporal resolution surface radial flow observed by the high-frequency ground wave radar is used to optimize the surface current and bottom friction coefficient.This method can effectively consider the spatiotemporal correlation of radar data and extract multiscale information from surface radial flow data from long waves to short waves.Introducing the shallow water wave equation into the cost function as a weak constraint condition can adjust both the momentum and mass fields simultaneously to obtain more reasonable analysis information.The optimized bottom friction coefficient is introduced into the regional ocean numerical model to carry out numerical experiments.The test results show that the bottom friction coefficient obtained by this method can effectively improve the accuracy of the numerical simulation of sea surface height in the offshore area and reduce the simulation error.展开更多
Based on an inverted one-and-one-half inviscid reduced gravity shallow water model with bottom topography representing an abyssal layer under a stagnant upper layer on the equatorial β-Plane, a set of field equations...Based on an inverted one-and-one-half inviscid reduced gravity shallow water model with bottom topography representing an abyssal layer under a stagnant upper layer on the equatorial β-Plane, a set of field equations governing the wave-induced Lagrangian residual currents is developed. The equations show that the wave-induced Lagrangian residual ot satisfies generalized geostrophic dynamics. The relation of meridional residual current to vertical residual current resulted from the varied bottom is similar to the Sverdrup transport relation. The tranport process of potential vorticity for zeroth order approximation is determined by the advection whose velocity is equal to that of the weve-induced Lagrangian residual current.A Kelvin wave solution and the reated solution of Kelvin wave-induced Lagrangian residual current for the case of slowly varying topography are obtained anaytically. The wave solution shows that a shoaling eastward bottom can decrease the propagation speed of the Kelvin wave and cause it to take a longer time to transmit the energy from the west to the central and easterm parts of the basin, and can also shorten the wavelength and enhance the wave amplitude. The wave-induced residual current solution reveals that the existence of a sloping bottom can result in a onier meridional component of wave-induced mesidual current and that Kelvin wave-induced Lagrangian currents’s responses to bottom variation are greater than those of Kelvin wave orbital currents.展开更多
This paper reports study focusing on the effects of sloping bottom on the deep cross-equatorial boundary current, and discusses model and laboratory experiment results showing that the southward that the southward int...This paper reports study focusing on the effects of sloping bottom on the deep cross-equatorial boundary current, and discusses model and laboratory experiment results showing that the southward that the southward intrusion distance and flow speed of the western boundary current depend on the bottom slope variation rate,the difference between and and are the current thickness at eastward edge and westward edge, respectively), and the net mass transport.展开更多
Interaction between current and underwater bottom topography leads to roughness of the sea surface, which in turn yields variation of the radar scattering echo. By using the continuity equation and weak hydrodynamic i...Interaction between current and underwater bottom topography leads to roughness of the sea surface, which in turn yields variation of the radar scattering echo. By using the continuity equation and weak hydrodynamic interaction theory in the relaxation time approximation, the spatial variation of the radar scattering cross-section has been proved as proportional to the gradient of current velocity. The current direction is first determined by using two-dimensional (2-D) correlation of spatial variation of backscattering measured by the SAR imagery, as the priori knowledge of the current direction is not available. The inverse algorithm to successively derive 2 - D underwater bottom topography from the SAR imagery is developed. As an application, the SAR SIR- C image over the sea area of Hong Kong, China is studied.展开更多
In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom bound...In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom boundary layer （BBL）. Field observations were carried out in the northwest Caofeidian sea area in the Bohai Bay. Near 2 m isobath （under the lowest tidal level）, a tripod system was installed with AWAC （Acoustic Wave And Current）, ADCP （Acoustic Doppler Current Profilers）, OBS-3A （Optical Backscatter Point Sensor）, ADV （Acoustic Doppler Velocimeters）, etc. The accurate measurement of the bottom boundary layer during a single tidal period was carried out, together with a long-term sediment concentration measurement under different hydrological conditions. All the measured data were used to analyze the characteristics of wave-current-sediment movement and the BBL. Analysis was performed on flow structure, shear stress, roughness, eddy viscosity and other parameters of the BBL. Two major findings were made. Firstly, from the measured data, the three-layer distribution model of the velocity profiles and eddy viscosities in the wave-current BBL are proposed in the observed sea area; secondly, the sediment movement is related closely to wind-waves in the muddy coast area where sediment is clayey silt： 1） The observed suspended sediment concentration under light wind conditions is very low, with the peak value generally smaller than 0.1 kg/m^3 and the average value being 0.03 kg/m^3; 2） The sediment concentration increases continuously under the gales over 6-7 in Beaufort scale, under a sustained wind action. The measured peak sediment concentration at 0.4 m above the seabed is 0.15-0.32 kg/m^3, and the average sediment concentration during wind-wave action is 0.08-0.18 kg/m^3, which is about 3-6 times the value under light wind conditions. The critical wave height signaling remarkable changes of sediment concentration is 0.5 m. The results show that the suspended load sediment concentration is mainly influenced by wave-induced sediment suspension.展开更多
Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain...Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain. The free surface velocities and the bottom velocities were connected by the exact solution of the Laplace equation. Taking the velocities on half relative water depth as the fundamental unknowns, terms relating to the gradient of the water depth were retained in the inverse series expansion of the exact solution, with which the problem was closed. With enhancements of the finite order Taylor expansion for the velocity field, the application range of the present model was extended to the slope bottom which is not so mild. For linear properties, some validation computations of linear shoaling and Booij' s tests were carried out. The problems of wave-current interactions were also studied numerically to test the performance of the enhanced Boussinesq equations associated with the effect of currents. All these computational results confirm perfectly to the theoretical solution as well as other numerical solutions of the full potential problem available.展开更多
基金The National Natural Science Foundation of China’s Major Project“Research on Geophysical Theories and Methods of Unconventional Oil and Gas Exploration and Development”,Task I:“China’s Tight Oil and Gas Reservoir Geological Characteristics,Classification and Typical Geological Model Establishment”under contract No.41390451。
文摘The Dongfang1-1 gas field(DF1-1)in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources.The second member of the Pliocene Yinggehai Formation(YGHF)is the main gas-producing formation and is composed of various sedimentary types;however,a clear understanding of the sedimentary types and development patterns is lacking.Here,typical lithofacies,logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling,logging,analysis and testing data.Based on 3D seismic interpretation and attribute analysis,the origin of high-amplitude reflections is clarified,and the main types and evolution characteristics of sedimentary facies are identified.Taking gas formation upper II(IIU)as an example,the plane distribution of the delta front and bottom current channel is determined;finally,a comprehensive sedimentary model of the YGHF second member is established.This second member is a shallowly buried“bright spot”gas reservoir with weak compaction.The velocity of sandstone is slightly lower than that of mudstone,and the reflection has medium amplitude when there is no gas.The velocity of sandstone decreases considerably after gas accumulation,resulting in an increase in the wave impedance difference and high-amplitude(bright spot)reflection between sandstone and mudstone;the range of high amplitudes is consistent with that of gas-bearing traps.The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps,and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps.The study area is a delta front deposit developed on a shallow sea shelf.The lithologies of the reservoir are mainly composed of very fine sand and coarse silt,and a variety of sedimentary structural types reflect a shallow sea delta environment;upward thickening funnel type,strong toothed bell type and toothed funnel type logging facies are developed.In total,4 stages of delta front sand bodies(corresponding to progradational reflection seismic facies)derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF;these sand bodies are dated to 1.5 Ma and correspond to four gas formations.During sedimentation,many bottom current channels(corresponding to channel fill seismic facies)formed,which interacted with the superposed progradational reflections.When the provenance supply was strong in the northwest,the area was dominated by a large set of delta front deposits.In the period of relative sea level rise,surface bottom currents parallel to the coastline were dominant,and undercutting erosion was obvious,forming multistage superimposed erosion troughs.Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.
基金The National Key Research and Development Program of China under contract No.2017YFC1404201the National Natural Science Foundation of China under contract Nos 41706035 and 41876029+2 种基金the NSFC-Shandong Joint Fund for Marine Science Research Centers under contract No.U1606405the Laboratory for Regional Oceanography and Numerical Modeling,Qingdao National Laboratory for Marine Science and Technology under contract No.2017A01the China Postdoctoral Science Foundation under contract No.2017M622111
文摘Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40276019 and 40238060)the National Key Basic Research Special Foundation Project of China (Grant No. G2000078500)
文摘There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,extending from the NE to the SW,leading to accumulation of discontinuous drifts with higher sedimentation rates on the eastern side of the channel. The stacking pattern of the layers sug-gests that these drifts propagated southwestward,following the direction of the bottom currents. One sedimentary drift to the southeast of the Dongsha Islands has the highest sedimentation rate of 97cm/ka in the last 12 ka. The sedimentary characteristics of the sediment layers indicate that these bottom currents are most likley caused by the water movement of a branch of the West Pacific Ocean Current,which enters the northern SCS via the Bashi Strait. Once formed,the bottom currents trans-port sediments along the northern slope of SCS southwestward and finally disappear into the central basin of the SCS. Due to the bottom current activity,the deep-sea sedimentary process in the northern SCS is complex.
基金The Program of International S&T Cooperation under contract No.2010DFA24470the National Science Foundation of China under contract No.41376101the Guangdong Provincial Science and Technology Planning Project under contract Nos 2012A030200002 and 2011B031100008
文摘On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.
基金This project was supported by the National Outstanding Youth Science Foundation of China under contract! No. 49825161.
文摘A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.
基金This paper was supported bythe Foundationforthe Author of National Excellent Doctoral Dissertation of P.R.China(Grant No.200428) the National Natural Science Foundation of China (Grant Nos .10272072 and 50424913) +1 种基金theShanghai Natural Science Foundation (Grant No.05ZR14048) the Shanghai Leading Academic Discipline Pro-ject (Grant No. Y0103)
文摘The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be extended and applicated to the study of the mechanism. Considering the effects of moving bottoms and starting from the Navier-Stokes equation of motion of a vinous fluid including the Coriolis force, a generalized mean-flow medel theory for the nearshore region, that is, a set of mean-flow equations and their generalized wave action equation involving the three new kinds of actions termed respectively as the current wave action, the bottom wave action and the dissipative wave action which can be applied to arbitrary depth over moving bottoms and ambient currents with a typical vertical structure, is developed by vertical integration and time-averaglng over a wave peried, thus extending the classical concept, wave action, from the ideal averaged flow conservative system to the real averaged flow dissipative dynamical system, and having a large range of application.
基金supported by the National Natural Science Foundation of China (Nos. 41506039, 41776004, 41775100 and 41606039)the National Key Research and Development Program of China (No. 2016YFC1401800)+1 种基金the Fundamental Research Funds for the Central Universities (No. 2016B12514)the National Programme on Global Change and Air-Sea Interaction of China (No. GASI-IPO VAI-04)
文摘This paper proposes a new method for data assimilation of the surface radial current observed by High Frequency ground wave radar and optimization of the bottom friction coefficient.In this method,the shallow water wave equation is introduced into the cost function of the multigrid three-dimensional variation data assimilation method as the weak constraint term,the surface current and the bottom friction coefficient are defined as the analytical variables,and the high spatiotemporal resolution surface radial flow observed by the high-frequency ground wave radar is used to optimize the surface current and bottom friction coefficient.This method can effectively consider the spatiotemporal correlation of radar data and extract multiscale information from surface radial flow data from long waves to short waves.Introducing the shallow water wave equation into the cost function as a weak constraint condition can adjust both the momentum and mass fields simultaneously to obtain more reasonable analysis information.The optimized bottom friction coefficient is introduced into the regional ocean numerical model to carry out numerical experiments.The test results show that the bottom friction coefficient obtained by this method can effectively improve the accuracy of the numerical simulation of sea surface height in the offshore area and reduce the simulation error.
文摘Based on an inverted one-and-one-half inviscid reduced gravity shallow water model with bottom topography representing an abyssal layer under a stagnant upper layer on the equatorial β-Plane, a set of field equations governing the wave-induced Lagrangian residual currents is developed. The equations show that the wave-induced Lagrangian residual ot satisfies generalized geostrophic dynamics. The relation of meridional residual current to vertical residual current resulted from the varied bottom is similar to the Sverdrup transport relation. The tranport process of potential vorticity for zeroth order approximation is determined by the advection whose velocity is equal to that of the weve-induced Lagrangian residual current.A Kelvin wave solution and the reated solution of Kelvin wave-induced Lagrangian residual current for the case of slowly varying topography are obtained anaytically. The wave solution shows that a shoaling eastward bottom can decrease the propagation speed of the Kelvin wave and cause it to take a longer time to transmit the energy from the west to the central and easterm parts of the basin, and can also shorten the wavelength and enhance the wave amplitude. The wave-induced residual current solution reveals that the existence of a sloping bottom can result in a onier meridional component of wave-induced mesidual current and that Kelvin wave-induced Lagrangian currents’s responses to bottom variation are greater than those of Kelvin wave orbital currents.
文摘This paper reports study focusing on the effects of sloping bottom on the deep cross-equatorial boundary current, and discusses model and laboratory experiment results showing that the southward that the southward intrusion distance and flow speed of the western boundary current depend on the bottom slope variation rate,the difference between and and are the current thickness at eastward edge and westward edge, respectively), and the net mass transport.
基金National Natural Science Foundation of China Under contract Nos 49831060, 69771007,and National 863 - 818 - 06 - 05.
文摘Interaction between current and underwater bottom topography leads to roughness of the sea surface, which in turn yields variation of the radar scattering echo. By using the continuity equation and weak hydrodynamic interaction theory in the relaxation time approximation, the spatial variation of the radar scattering cross-section has been proved as proportional to the gradient of current velocity. The current direction is first determined by using two-dimensional (2-D) correlation of spatial variation of backscattering measured by the SAR imagery, as the priori knowledge of the current direction is not available. The inverse algorithm to successively derive 2 - D underwater bottom topography from the SAR imagery is developed. As an application, the SAR SIR- C image over the sea area of Hong Kong, China is studied.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51061130546 and 51379127)the Key Projects in the National Science&Technology Pillar Program(Grant No.2012BAC07B02)
文摘In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom boundary layer （BBL）. Field observations were carried out in the northwest Caofeidian sea area in the Bohai Bay. Near 2 m isobath （under the lowest tidal level）, a tripod system was installed with AWAC （Acoustic Wave And Current）, ADCP （Acoustic Doppler Current Profilers）, OBS-3A （Optical Backscatter Point Sensor）, ADV （Acoustic Doppler Velocimeters）, etc. The accurate measurement of the bottom boundary layer during a single tidal period was carried out, together with a long-term sediment concentration measurement under different hydrological conditions. All the measured data were used to analyze the characteristics of wave-current-sediment movement and the BBL. Analysis was performed on flow structure, shear stress, roughness, eddy viscosity and other parameters of the BBL. Two major findings were made. Firstly, from the measured data, the three-layer distribution model of the velocity profiles and eddy viscosities in the wave-current BBL are proposed in the observed sea area; secondly, the sediment movement is related closely to wind-waves in the muddy coast area where sediment is clayey silt： 1） The observed suspended sediment concentration under light wind conditions is very low, with the peak value generally smaller than 0.1 kg/m^3 and the average value being 0.03 kg/m^3; 2） The sediment concentration increases continuously under the gales over 6-7 in Beaufort scale, under a sustained wind action. The measured peak sediment concentration at 0.4 m above the seabed is 0.15-0.32 kg/m^3, and the average sediment concentration during wind-wave action is 0.08-0.18 kg/m^3, which is about 3-6 times the value under light wind conditions. The critical wave height signaling remarkable changes of sediment concentration is 0.5 m. The results show that the suspended load sediment concentration is mainly influenced by wave-induced sediment suspension.
基金Project supported by the National Natural Science Foundation of China (No. 10172058)the Special Fund for PhD Program of Education Ministry of China (No.2000024817)
文摘Higher order Boussinesq-type equations for wave propagation over variable bathymetry were derived. The time dependent free surface boundary conditions were used to compute the change of the free surface in time domain. The free surface velocities and the bottom velocities were connected by the exact solution of the Laplace equation. Taking the velocities on half relative water depth as the fundamental unknowns, terms relating to the gradient of the water depth were retained in the inverse series expansion of the exact solution, with which the problem was closed. With enhancements of the finite order Taylor expansion for the velocity field, the application range of the present model was extended to the slope bottom which is not so mild. For linear properties, some validation computations of linear shoaling and Booij' s tests were carried out. The problems of wave-current interactions were also studied numerically to test the performance of the enhanced Boussinesq equations associated with the effect of currents. All these computational results confirm perfectly to the theoretical solution as well as other numerical solutions of the full potential problem available.
