To deal with the moving boundary hydrodynamic problems of the tidal flats in shallow water flow models, a new wetting and drying (WD) method is proposed. In the new method, a "predicted water depth" is evaluated e...To deal with the moving boundary hydrodynamic problems of the tidal flats in shallow water flow models, a new wetting and drying (WD) method is proposed. In the new method, a "predicted water depth" is evaluated explicitly based on the simplified shallow water equations and used to determine the status (wet or dry) together with the direction of flow. Compared with previous WD method, besides the water elevation, more factors, such as the flow velocity and the surface shear stress, are taken into account in the new method to determine the moving boundary. In addition, a formula is deduced to determine the threshold, as critical water depth, which needs to be preset before simulations. The new WD method is tested with five cases including three 1D ones and two 2D ones. The results show that the new WD method can simulate the wetting and drying process, in beth typical and practical cases, with smooth manner and achieves effective estimation of the retention volume at shallow water body.展开更多
A particular porosity method named "slot method" is implemented in a depth-integrated shallow water flow model (DIVAST) to simulate wetting and drying processes. Discussed is the relationship between the shape fac...A particular porosity method named "slot method" is implemented in a depth-integrated shallow water flow model (DIVAST) to simulate wetting and drying processes. Discussed is the relationship between the shape factors of the "slot" and the preset depth used in "wetting-drying" algorithm. Two typical tests are conducted to examine the performance of the method with the effect of the shape factors of the "slot" being checked in detail in the first test. Numerical results demonstrate that: 1 ) no additional effort to improve the finite difference scheme is needed to implement "slot method" in DIVAST, and 2) "slot method" will simulate wetting and diying processes correctly if the shape factors of the "slot" being selected properly.展开更多
In this study, we applied a two-phase flow model to simulate water and sand blowout processes when penetrating shallow water flow(SWF) formations during deepwater drilling. We define ‘sand' as a pseudo-component ...In this study, we applied a two-phase flow model to simulate water and sand blowout processes when penetrating shallow water flow(SWF) formations during deepwater drilling. We define ‘sand' as a pseudo-component with high density and viscosity, which can begin to flow with water when a critical pressure difference is attained. We calculated the water and sand blowout rates and analyzed the influencing factors from them, including overpressure of the SWF formation, as well as its zone size, porosity and permeability, and drilling speed(penetration rate). The obtained data can be used for the quantitative assessment of the potential severity of SWF hazards. The results indicate that overpressure of the SWF formation and its zone size have significant effects on SWF blowout. A 10% increase in the SWF formation overpressure can result in a more than 90% increase in the cumulative water blowout and a 150% increase in the sand blowout when a typical SWF sediment is drilled. Along with the conventional methods of well flow and pressure control, chemical plugging, and the application of multi-layer casing, water and sand blowouts can be effectively reduced by increasing the penetration rate. As such, increasing the penetration rate can be a useful measure for controlling SWF hazards during deepwater drilling.展开更多
Shallow water flow(SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shal...Shallow water flow(SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea(SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson's ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.展开更多
We develop a lattice Boltzmann method for modeling free-surface temperature dispersion in the shallow water flows.The governing equations are derived from the incompressible Navier-Stokes equations with assumptions of...We develop a lattice Boltzmann method for modeling free-surface temperature dispersion in the shallow water flows.The governing equations are derived from the incompressible Navier-Stokes equations with assumptions of shallow water flows including bed frictions,eddy viscosity,wind shear stresses and Coriolis forces.The thermal effects are incorporated in the momentum equation by using a Boussinesq approximation.The dispersion of free-surface temperature is modelled by an advection-diffusion equation.Two distribution functions are used in the lattice Boltzmann method to recover the flow and temperature variables using the same lattice structure.Neither upwind discretization procedures nor Riemann problem solvers are needed in discretizing the shallow water equations.In addition,the source terms are straightforwardly included in the model without relying on well-balanced techniques to treat flux gradients and source terms.We validate the model for a class of problems with known analytical solutions and we also present numerical results for sea-surface temperature distribution in the Strait of Gibraltar.展开更多
Based on the improved ADI method, this article proposes an improved implicit finite difference scheme for solving 3-D shallow water flows. The main objective is to design a numerical relation between the horizontal ve...Based on the improved ADI method, this article proposes an improved implicit finite difference scheme for solving 3-D shallow water flows. The main objective is to design a numerical relation between the horizontal velocity on each layer and the depth-averaged velocity for employing the improved ADI method. With the free surface elevation and the depth-averaged velocity obtained by using essentially 2-D depth-averaged mode, the velocity profiles can be obtained easily and simultaneously. The wind-induced flows, the open channel flows due to the pressure gradient and the tidal flows in coastal waters are simulated, and the results are consistent well with the analytical solution and the field data, which shows that the present implicit scheme is stable and effective, and the established model is practical. Moreover, when only one vertical layer is specified, the present 3-D numerical model is reducea to the 2-D depth-averaged model.展开更多
In this study, the performance of the extended shallow water model (ESWM) in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and pa...In this study, the performance of the extended shallow water model (ESWM) in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and particles and the Navier-Stokes equations govern the entire flow of turbidity currents. The shallow water equations governing the flow of the depositing phase of turbidity currents are derived from these equations. A case study was conducted on the flow regime of turbidity currents entering the Dez Reservoir in Iran from January 2002 to July 2003. Facing a serious sedimentation problem, the dead storage of the Dez Reservoir will be full in the coming 10 years, and the inflowing water in the hydropower conduit system is now becoming turbid. Based on the values of the dimensionless friction number ( Nf ≤1 ) and dimensionless entrainment number ( NE≤ 1 ) of turbidity currents, and the coefficient of determination between the observed and predicted deposit depths (R2 = 0.86) for the flow regime of negligible friction and negligible entrainment (NFNE), the flow regime of turbidity currents coming into the Dez Reservoir is considered to be NFNE. The results suggest that the ESWM is an appropriate approach for evaluation of the flow regime of turbidity currents in dam reservoirs where the characteristics of turbidity currents, such as the deposit depth, must be evaluated.展开更多
A simi-implicit finite element method is developed for three-dimensional shallow water flow. By using water depth to scale the vertical coordinate. the governing equation is transformed into fixed computational domain...A simi-implicit finite element method is developed for three-dimensional shallow water flow. By using water depth to scale the vertical coordinate. the governing equation is transformed into fixed computational domain. An efficient generalized conjugate gradient scheme is adopted for the solution of finite element analogy.展开更多
To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the de...To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.展开更多
The hybrid finite analytic(HFA) method is a kind of numerical scheme in rectangular element. In order to simulate the shallow circulation in irregular bathymetry by HFA scheme, the model in sigma coordinate system was...The hybrid finite analytic(HFA) method is a kind of numerical scheme in rectangular element. In order to simulate the shallow circulation in irregular bathymetry by HFA scheme, the model in sigma coordinate system was obtained. The model has been tested against three cases: 1) Wind induced circulation; 2) Density driven circulation and 3) Seiche oscillation. The results obtained in the present study compare well with those obtained from the corresponding analytical solutions under idealized for the above three cases. The hybrid finite analytic method and the circulation model in sigma coordinate system can be used calculate the flow and water quality in estuaries and coastal waters.展开更多
A semi-implicit and Eulerian - Lagrangian finite difference method for three-dimensionalshallow flow has been extended to a more complete system of equations incorporating second-moment turbulence closure model and tr...A semi-implicit and Eulerian - Lagrangian finite difference method for three-dimensionalshallow flow has been extended to a more complete system of equations incorporating second-moment turbulence closure model and transport equations of salinity and temperature. The simulation for flooding and drying of mudflats has been improved. The model is applied to Xiamen waters. Based on extensive survey data, water level elevation, temperature and salinity field along the eastern open boundary and at the Jiulong River inlets and runoffs are analyzed, specified and calibrated. The computed results show good agreement with the measured data, reproduce flooding, emergence of large and complex mudflat region.展开更多
In the paper, a numerical study on symmetrical and asymmetrical laminar jet-forced flows is carried out by using a lattice Boltzmann method (LBM) with a special boundary treatment. The simulation results are in very...In the paper, a numerical study on symmetrical and asymmetrical laminar jet-forced flows is carried out by using a lattice Boltzmann method (LBM) with a special boundary treatment. The simulation results are in very good agreement with the available numerical prediction. It is shown that the LBM is a competitive method for the laminar jet-forced flow in terms of computational efficiency and stability.展开更多
This paper presents a method for expanding horizontal flow variables in data using the free solutions to the shallow-water system as a basis set. This method for equatorial wave expansion of instantaneous flows(EWEIF...This paper presents a method for expanding horizontal flow variables in data using the free solutions to the shallow-water system as a basis set. This method for equatorial wave expansion of instantaneous flows(EWEIF) uses dynamic constraints in conjunction with projections of data onto parabolic cylinder functions to determine the amplitude of all equatorial waves.EWEIF allows us to decompose an instantaneous wave flow into individual equatorial waves with a presumed equivalent depth without using temporal or spatial filtering a priori.Three sets of EWEIF analyses are presented. The first set is to confirm that EWEIF is capable of recovering the individual waves constructed from theoretical equatorial wave solutions under various scenarios. The other two sets demonstrate the ability of the EWEIF method to derive time series of individual equatorial waves from instantaneous wave fields without knowing a priori exactly which waves exist in the data as well as their spatial and temporal scales using outputs of an equatorial β-channel shallow-water model and ERA-Interim data. The third set of demonstrations shows, for the first time, the continuous evolutions of individual equatorial waves in the stratosphere whose amplitude is synchronized with the background zonal wind as predicted by quasi-biennial oscillation theory.展开更多
The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in nature.For a better prediction of the mean flow and turbulent characteristics for this problem,a...The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in nature.For a better prediction of the mean flow and turbulent characteristics for this problem,atwo-dimensional depth-averaged numerical model is developed.The model is robust and accurate in reproducing therecirculation flow behind a groyne and turbulent flows in channels with abrupt cross-sectional changes,when com-pared to the available experimental data of mean velocities and turbulence kinetic energy.Our results reveal that theabrupt cross-sectional change of a channel can affect the flow pattern significantly and introduces the complex turbu-lence characteristics.In particular,when the channel has an abrupt expansion,the mean flow pattern is mainly in lon-gitudinal direction with rather small transverse component.Meanwhile,a recirculating region forms behind the expan-sion position and the turbulence has very strong intensity within this region.For the flow in the channel with an ab-rupt contraction,the longitudinal component of the flow is decreased by the obstruction on one side and accelerated onthe other side,whereas the transverse velocity is small.The turbulence is extraordinarily strong in the regions adja-cent to the contraction wall in the narrow channel.In both cases of abrupt cross-sectional changes,the TKE is genera-ted dominantly by the shear of the longitudinal velocities.展开更多
By solving the unsteady Reynolds averaged Navier-Stokes (RANS) equations in combination with the k- ε SST turbulence model, the unsteady viscous flow around the obliquely towed tanker KVLCC2M model in both deep and...By solving the unsteady Reynolds averaged Navier-Stokes (RANS) equations in combination with the k- ε SST turbulence model, the unsteady viscous flow around the obliquely towed tanker KVLCC2M model in both deep and shallow waters is simulated and the hydrodynamic forces, the surface pressure distribution, and the wake field are calculated. The overset grid technology is used to avoid the grid distortion in large drift angle cases. The effects of the free surface are taken into account. At the first stage, the deep water cases with five oblique angles are designed as the benchmark test cases. The predicted wake field, the surface pressure distribution and the hydrodynamic forces acting on the hull agree well with the corresponding experimental data, implying the capability of the present method in the prediction of the viscous flow around the tanker drifting in shallow water. A set of systematic computations with varying water depths and drift angles are then carried out to study the viscous flow around the model drifting in shallow water. The forces and moments, as well as the surface pressure distribution are predicted and analyzed. The most significant changes such as the increased stagnation pressure in the bow, the acceleration of the flow along the ship's sides and in the gap between ship and seabed, the lower hull pressure and finally, the stronger vortices along the bilges and weaker vortices with larger diameters in the wake are noticed.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.10872144)the Support Plan of Science and Technology of Tianjin (Grant No.07ZCGYSH01700)
文摘To deal with the moving boundary hydrodynamic problems of the tidal flats in shallow water flow models, a new wetting and drying (WD) method is proposed. In the new method, a "predicted water depth" is evaluated explicitly based on the simplified shallow water equations and used to determine the status (wet or dry) together with the direction of flow. Compared with previous WD method, besides the water elevation, more factors, such as the flow velocity and the surface shear stress, are taken into account in the new method to determine the moving boundary. In addition, a formula is deduced to determine the threshold, as critical water depth, which needs to be preset before simulations. The new WD method is tested with five cases including three 1D ones and two 2D ones. The results show that the new WD method can simulate the wetting and drying process, in beth typical and practical cases, with smooth manner and achieves effective estimation of the retention volume at shallow water body.
基金the National Natural Science Foundation of China (Grant No.10702050)the Natural Science Foundation of Tianjin (Grant No.07JCYBJC07500)the Support Plan of Science and Technology of Tianjin (Grant No.07ZCGYSH01700)
文摘A particular porosity method named "slot method" is implemented in a depth-integrated shallow water flow model (DIVAST) to simulate wetting and drying processes. Discussed is the relationship between the shape factors of the "slot" and the preset depth used in "wetting-drying" algorithm. Two typical tests are conducted to examine the performance of the method with the effect of the shape factors of the "slot" being checked in detail in the first test. Numerical results demonstrate that: 1 ) no additional effort to improve the finite difference scheme is needed to implement "slot method" in DIVAST, and 2) "slot method" will simulate wetting and diying processes correctly if the shape factors of the "slot" being selected properly.
基金Financial supports by the 973 National Research Project of China (No. 2015CB251201)the program for Changjiang Scholars and Innovative Research Team in University (‘PCSIRT’) (IRT_14R58)the Fundamental Research Funds for the Central Universities (No. 15CX0 5036A)
文摘In this study, we applied a two-phase flow model to simulate water and sand blowout processes when penetrating shallow water flow(SWF) formations during deepwater drilling. We define ‘sand' as a pseudo-component with high density and viscosity, which can begin to flow with water when a critical pressure difference is attained. We calculated the water and sand blowout rates and analyzed the influencing factors from them, including overpressure of the SWF formation, as well as its zone size, porosity and permeability, and drilling speed(penetration rate). The obtained data can be used for the quantitative assessment of the potential severity of SWF hazards. The results indicate that overpressure of the SWF formation and its zone size have significant effects on SWF blowout. A 10% increase in the SWF formation overpressure can result in a more than 90% increase in the cumulative water blowout and a 150% increase in the sand blowout when a typical SWF sediment is drilled. Along with the conventional methods of well flow and pressure control, chemical plugging, and the application of multi-layer casing, water and sand blowouts can be effectively reduced by increasing the penetration rate. As such, increasing the penetration rate can be a useful measure for controlling SWF hazards during deepwater drilling.
基金supported by the National Natural Science Foundation of China(No.41306037)the China Geo-logical Survey Project(No.DD20160213)the Strategic Research Center of Oil and Gas Resources Project(No.2017YQZYPJ0138)
文摘Shallow water flow(SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea(SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson's ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.
基金support by the DeutscheForschungsGemeinschaft(DFG)under grant No.KL 1105/9.
文摘We develop a lattice Boltzmann method for modeling free-surface temperature dispersion in the shallow water flows.The governing equations are derived from the incompressible Navier-Stokes equations with assumptions of shallow water flows including bed frictions,eddy viscosity,wind shear stresses and Coriolis forces.The thermal effects are incorporated in the momentum equation by using a Boussinesq approximation.The dispersion of free-surface temperature is modelled by an advection-diffusion equation.Two distribution functions are used in the lattice Boltzmann method to recover the flow and temperature variables using the same lattice structure.Neither upwind discretization procedures nor Riemann problem solvers are needed in discretizing the shallow water equations.In addition,the source terms are straightforwardly included in the model without relying on well-balanced techniques to treat flux gradients and source terms.We validate the model for a class of problems with known analytical solutions and we also present numerical results for sea-surface temperature distribution in the Strait of Gibraltar.
基金supported by the National Natural Science Foundation of China (Grant No.40730527)the Public Fund Project from Ministry of Water Resources (Grant No.200701026)the Open Fund of State Key Laboratory of Resource and Environment Information System,Hohai University,(Grant No.2007491211)
文摘Based on the improved ADI method, this article proposes an improved implicit finite difference scheme for solving 3-D shallow water flows. The main objective is to design a numerical relation between the horizontal velocity on each layer and the depth-averaged velocity for employing the improved ADI method. With the free surface elevation and the depth-averaged velocity obtained by using essentially 2-D depth-averaged mode, the velocity profiles can be obtained easily and simultaneously. The wind-induced flows, the open channel flows due to the pressure gradient and the tidal flows in coastal waters are simulated, and the results are consistent well with the analytical solution and the field data, which shows that the present implicit scheme is stable and effective, and the established model is practical. Moreover, when only one vertical layer is specified, the present 3-D numerical model is reducea to the 2-D depth-averaged model.
文摘In this study, the performance of the extended shallow water model (ESWM) in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and particles and the Navier-Stokes equations govern the entire flow of turbidity currents. The shallow water equations governing the flow of the depositing phase of turbidity currents are derived from these equations. A case study was conducted on the flow regime of turbidity currents entering the Dez Reservoir in Iran from January 2002 to July 2003. Facing a serious sedimentation problem, the dead storage of the Dez Reservoir will be full in the coming 10 years, and the inflowing water in the hydropower conduit system is now becoming turbid. Based on the values of the dimensionless friction number ( Nf ≤1 ) and dimensionless entrainment number ( NE≤ 1 ) of turbidity currents, and the coefficient of determination between the observed and predicted deposit depths (R2 = 0.86) for the flow regime of negligible friction and negligible entrainment (NFNE), the flow regime of turbidity currents coming into the Dez Reservoir is considered to be NFNE. The results suggest that the ESWM is an appropriate approach for evaluation of the flow regime of turbidity currents in dam reservoirs where the characteristics of turbidity currents, such as the deposit depth, must be evaluated.
文摘A simi-implicit finite element method is developed for three-dimensional shallow water flow. By using water depth to scale the vertical coordinate. the governing equation is transformed into fixed computational domain. An efficient generalized conjugate gradient scheme is adopted for the solution of finite element analogy.
基金funded by the National Key Basic Research Program of China (973 Program) (No. 2015 CB25 1201)NSFC-Shandong Joint Fund for Marine Science Research Centers (No. U1606401)Key Science & Technology Foundation of Sanya (Nos. 2017PT13 and 2017PT14)
文摘To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.
文摘The hybrid finite analytic(HFA) method is a kind of numerical scheme in rectangular element. In order to simulate the shallow circulation in irregular bathymetry by HFA scheme, the model in sigma coordinate system was obtained. The model has been tested against three cases: 1) Wind induced circulation; 2) Density driven circulation and 3) Seiche oscillation. The results obtained in the present study compare well with those obtained from the corresponding analytical solutions under idealized for the above three cases. The hybrid finite analytic method and the circulation model in sigma coordinate system can be used calculate the flow and water quality in estuaries and coastal waters.
文摘A semi-implicit and Eulerian - Lagrangian finite difference method for three-dimensionalshallow flow has been extended to a more complete system of equations incorporating second-moment turbulence closure model and transport equations of salinity and temperature. The simulation for flooding and drying of mudflats has been improved. The model is applied to Xiamen waters. Based on extensive survey data, water level elevation, temperature and salinity field along the eastern open boundary and at the Jiulong River inlets and runoffs are analyzed, specified and calibrated. The computed results show good agreement with the measured data, reproduce flooding, emergence of large and complex mudflat region.
基金supported by the National Natural Science Foundation of China (No. 10771134)the Youth Science Foundation of USTC
文摘In the paper, a numerical study on symmetrical and asymmetrical laminar jet-forced flows is carried out by using a lattice Boltzmann method (LBM) with a special boundary treatment. The simulation results are in very good agreement with the available numerical prediction. It is shown that the LBM is a competitive method for the laminar jet-forced flow in terms of computational efficiency and stability.
基金supported by grants from the National Science Foundation(Grant No.AGS-1354834)the NASA Interdisciplinary Studies Program(Grant No.NNH12ZDA001NIDS)
文摘This paper presents a method for expanding horizontal flow variables in data using the free solutions to the shallow-water system as a basis set. This method for equatorial wave expansion of instantaneous flows(EWEIF) uses dynamic constraints in conjunction with projections of data onto parabolic cylinder functions to determine the amplitude of all equatorial waves.EWEIF allows us to decompose an instantaneous wave flow into individual equatorial waves with a presumed equivalent depth without using temporal or spatial filtering a priori.Three sets of EWEIF analyses are presented. The first set is to confirm that EWEIF is capable of recovering the individual waves constructed from theoretical equatorial wave solutions under various scenarios. The other two sets demonstrate the ability of the EWEIF method to derive time series of individual equatorial waves from instantaneous wave fields without knowing a priori exactly which waves exist in the data as well as their spatial and temporal scales using outputs of an equatorial β-channel shallow-water model and ERA-Interim data. The third set of demonstrations shows, for the first time, the continuous evolutions of individual equatorial waves in the stratosphere whose amplitude is synchronized with the background zonal wind as predicted by quasi-biennial oscillation theory.
基金supported,in part,by the National Natural Science Foundation of China(51061130547 and51279120)
文摘The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in nature.For a better prediction of the mean flow and turbulent characteristics for this problem,atwo-dimensional depth-averaged numerical model is developed.The model is robust and accurate in reproducing therecirculation flow behind a groyne and turbulent flows in channels with abrupt cross-sectional changes,when com-pared to the available experimental data of mean velocities and turbulence kinetic energy.Our results reveal that theabrupt cross-sectional change of a channel can affect the flow pattern significantly and introduces the complex turbu-lence characteristics.In particular,when the channel has an abrupt expansion,the mean flow pattern is mainly in lon-gitudinal direction with rather small transverse component.Meanwhile,a recirculating region forms behind the expan-sion position and the turbulence has very strong intensity within this region.For the flow in the channel with an ab-rupt contraction,the longitudinal component of the flow is decreased by the obstruction on one side and accelerated onthe other side,whereas the transverse velocity is small.The turbulence is extraordinarily strong in the regions adja-cent to the contraction wall in the narrow channel.In both cases of abrupt cross-sectional changes,the TKE is genera-ted dominantly by the shear of the longitudinal velocities.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.51379125,51490675,11432009,51579145 and 11272120)
文摘By solving the unsteady Reynolds averaged Navier-Stokes (RANS) equations in combination with the k- ε SST turbulence model, the unsteady viscous flow around the obliquely towed tanker KVLCC2M model in both deep and shallow waters is simulated and the hydrodynamic forces, the surface pressure distribution, and the wake field are calculated. The overset grid technology is used to avoid the grid distortion in large drift angle cases. The effects of the free surface are taken into account. At the first stage, the deep water cases with five oblique angles are designed as the benchmark test cases. The predicted wake field, the surface pressure distribution and the hydrodynamic forces acting on the hull agree well with the corresponding experimental data, implying the capability of the present method in the prediction of the viscous flow around the tanker drifting in shallow water. A set of systematic computations with varying water depths and drift angles are then carried out to study the viscous flow around the model drifting in shallow water. The forces and moments, as well as the surface pressure distribution are predicted and analyzed. The most significant changes such as the increased stagnation pressure in the bow, the acceleration of the flow along the ship's sides and in the gap between ship and seabed, the lower hull pressure and finally, the stronger vortices along the bilges and weaker vortices with larger diameters in the wake are noticed.