A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing wave...A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing waves were dissipated by sponge layers and transmitted by radiation boundaries. The finite difference method was used to solve the governing equations and boundary conditions in the regular transformed domain in σ-coordinate. Satisfactory agreements between the numerical predictions and experimental results of wave force were obtained. It is concluded that the maximum wave force acting on the vertical walls is induced by the obliquely incident waves rather than the normally incident waves.展开更多
A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope...A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by it finite element method, The results of this model are compared with those from other methods and agree well with experimental data.展开更多
The model tests are performed with regular waves, and the effect of wave height, wave period, water depth, sediment size and pile diameter is evaluated. The shape and size of local scour around piles are studied. Ther...The model tests are performed with regular waves, and the effect of wave height, wave period, water depth, sediment size and pile diameter is evaluated. The shape and size of local scour around piles are studied. There are three typical scour patterns due to wave action. It is found that a relationship exists between the erosion depth and the wave number. An empirical formula of the maximum local scour is thus derived.展开更多
After the erection of the Three Gorges Dam, the water level of Yangtze River will reach 175 m, and the average wave crest will be up to 1 m. Therefore the wave action cannot be neglected for the slope stability. Throu...After the erection of the Three Gorges Dam, the water level of Yangtze River will reach 175 m, and the average wave crest will be up to 1 m. Therefore the wave action cannot be neglected for the slope stability. Through simulation tests, the wave-induced dynamic response of the slope is analyzed. The soil body is taken as linear elastic body when it has a small deformation under the small wave action. Based on tests, the excess pore pressure and slope displacement under the loading in different wave period are analyzed. The ratio of dynamic strength and static strength to the breaking process of the slope is discussed. It is demonstrated that smaller wave period gives rise to a larger strain of the slope under the same stress. At different depth of water, different weakness effect on the stability of the soil slope is observed and the slope has an adaptability to the wave action to some extent.展开更多
When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing w...When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.展开更多
In this paper the wave action balance equation in terms of frequency-direction spectrum is derived. A theoretical formulation is presented to generate an invariant frequency space to replace the varying wavenumber spa...In this paper the wave action balance equation in terms of frequency-direction spectrum is derived. A theoretical formulation is presented to generate an invariant frequency space to replace the varying wavenumber space through a Jacobian transformation in the wave action balance equation. The physical properties of the Jacobian incorporating the effects of water depths are discussed. The results provide a theoretical basis of wave action balance equations and ensure that the wave balance equations used in the SWAN or other numerical models are correct. It should be noted that the Jacobian is omitted in the wave action balance equations which are identical to a conventional action balance equation.展开更多
This study is motivated by recognition of complex sandbar evolution patterns under wave actions inside the surf zone. A series of physical model experiments were conducted in a wave flume to investigate sandbar migrat...This study is motivated by recognition of complex sandbar evolution patterns under wave actions inside the surf zone. A series of physical model experiments were conducted in a wave flume to investigate sandbar migration under various wave conditions, including wave groups, regular waves, and random waves. It was observed that under certain wave conditions sandbars move alternately shoreward and seaward rather than continuously in the same direction. The measurements show that the unstable movement of sandbars is closely related to the amplitude modulation of waves. Smaller amplitude modulation tends to produce more intense unstable bar movements. Data analysis further shows that the sandbar migration does not seem to be a passive response of the sea bed to wave forcing, but is most likely caused by the feedback interaction between waves and bed topography.展开更多
Based on the Navier-Stokes equation, an average wave energy equation and a generalized wave action conservation equation are presented in this paper. The turbulence effects on water particle velocity u i and wave s...Based on the Navier-Stokes equation, an average wave energy equation and a generalized wave action conservation equation are presented in this paper. The turbulence effects on water particle velocity u i and wave surface elavation ξ as well as energy dissipation are included. Some simplified forms are also given.展开更多
In order to build the model of the drum level wave action and sloshing, based on the method of modularization modeling, the hydrodynamic model of drum level wave action and sloshing was developed, and dynamic simulati...In order to build the model of the drum level wave action and sloshing, based on the method of modularization modeling, the hydrodynamic model of drum level wave action and sloshing was developed, and dynamic simulation researches were carried out based on the model. The results indicate that both drum level and drum length have functional relations with period of drum level wave action and sloshing. When the drum level decreases or drum length increases, the period of drum level wave action and sloshing increases, density of liquid and number of sub-module division have little influence on the period of drum level wave action and sloshing. The model was validated by the analytical solution theory of liquid’s wave action and sloshing in cuboid container, and the 3D graphics of drum level wave action and sloshing was also obtained. The model can dynamically reflect the rules of wave action and sloshing of water in the container exactly.展开更多
Based on prior investigation,this work defined a new thermodynamic shear advection parameter,which combines the vertical component of convective vorticity vector,horizontal divergence,and vertical gradient of generali...Based on prior investigation,this work defined a new thermodynamic shear advection parameter,which combines the vertical component of convective vorticity vector,horizontal divergence,and vertical gradient of generalized potential temperature.The interaction between waves and fundamental states was computed for the heavyrainfall event generated by landfalling typhoon“Morakot”.The analysis data was produced by ADAS[ARPS(Advanced Regional Prediction System)Data Analysis System]combined with the NCEP/NCAR final analysis data(1°×1°,26 vertical pressure levels and 6-hour interval)with the routine observations of surface and sounding.Because it may describe the typical vertical structure of dynamical and thermodynamic fields,the result indicates that the parameter is intimately related to precipitation systems.The parameter’s positive high-value area closely matches the reported 6-hour accumulated surface rainfall.And the statistical analysis reveals a certain correspondence between the thermodynamic shear advection parameter and the observed 6-hour accumulated surface rainfall in the summer of 2009.This implies that the parameter can predict and indicate the rainfall area,as well as the initiation and evolution of precipitation systems.展开更多
Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory an...Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory and variational principle separately. It has two kinds of expressions including the dissipation term. Model n is based on the energy conservation equation with energy flux through the wave crest lines in orthogonal curvilinear coordinates and the wave kinematic conservation equation. The analysis and comparison and special cases of these two models are also given.展开更多
A new numerical finite difference iteration method for refraction-diffraction of waves ia water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the di...A new numerical finite difference iteration method for refraction-diffraction of waves ia water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the dissipation term is briefly described, together with some analysis and comparison of computational results of the model with measurements in a hydraulic scale model (Berkhoff et al., 1982). An example of practical use of the method is given, showing that the present model is useful to engineering practice.展开更多
Two different methods for incorporating diffraction effect into wave action balance equation based coastal spectral wave models, WABED and SWAN, are discussed and evaluated with respect to their formulations, numerica...Two different methods for incorporating diffraction effect into wave action balance equation based coastal spectral wave models, WABED and SWAN, are discussed and evaluated with respect to their formulations, numerical implementations, and modeling capabilities. Both models were nm to simulate the wave transformation through a gap between two infinitely long breakwaters and that across an elliptical shoal observed in laboratory studies, with the emphasis laid on the diffraction induced by either obstacles or wave amplitude variations. Calculations of WABED were compared with Sommerfeld＇s analytical solutions, experimental observations and SWAN simulations. It is shown that both methods can predict reasonably wave diffraction for the two eases studied herein, and a fairly better performance is provided by WABED for stronger diffraction ease.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
In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves...In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves can present three types of motion, i. e. significant stratification, fragile stratification and strong mixing. The motion gf turbid;,ater presents significant stratification when (H/D)/root Delta rho/rho less than or equal to 4.5, generally this state is known as density current. The formulas of motion velocity, thickness, and discharge of density current moving on horizontal bottom are derived by use of basic equations such as momemtum equation, equation of energy conservation and continuity equation of fluid. The time-average velocity and the thickness of density current under the action of waves have a relationship with such parameters as relative density (Delta rho/rho), wave height (H), and water depth (D). When these parameters are determined, the time-average thickness and motion velocity of density current are also determined. The relative thickness of density current (D-t/D) decreases with the increase of Delta rho/rho and increases with the increase of H/D. On the other hand, the motion velocity of density current increases with the increase of Delta rho/rho and decreases with the increase of the relative thickness (D-t/D) of density current. It is shown that the calculated results are in agreement with those of the flume experiment.展开更多
A higher order boundary dement method （HOBEM） is implemented for wave-current action on structures. The freeterm coefficient and Cauchy principal value （ GPV） integrals are computed by direct methods. Numerical ex...A higher order boundary dement method （HOBEM） is implemented for wave-current action on structures. The freeterm coefficient and Cauchy principal value （ GPV） integrals are computed by direct methods. Numerical experiments are carried out to validate the computation of free-term coefficient and GPV integrals. The results show that the computation precision of free-term coefficient is very high for various bodies, even with edges and corners, and the convergence speed is fast for CPV integrals for different meshes. The comparison of the second order mean drift force due to wave-current action on a uniform cylinder is made with an analytic solution. It is found that good agreement exists between the present calculation and the analytic solutions. Finally, the numerical code is applied for computing wave-current action on Snorrc TLP.展开更多
Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied expe...Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied experimentally.The influence of various ocean environmental parameters on local scour around the cylinder is considered in physical model test.The experimental results indicate that the principal effect factors on the scour in fine-sand seabed are wave height,wavelength,current velocity,ratio of diameter to wavelength and ratio of depth to wavelength when the ratio of cylinder diameter to wavelength is from 0.2 to 0.8.In this paper,dimensional analysis theory is utilized to establish a theoretical equation for forecasting maximum scour depth around large-sized round cylinder base due to the combined action of wave and current.The results computed with the theoretical equation are compared with the experimental results,and found to be in good consistency.The results in this studies can be used to estimate the maximum sour depth around analogous structures.展开更多
A mild-slope equation for combined refraction and diffraction of random waves in the independent time current is derived using Kirby equation(1984). In the derivation, the frequency of random waves is represented base...A mild-slope equation for combined refraction and diffraction of random waves in the independent time current is derived using Kirby equation(1984). In the derivation, the frequency of random waves is represented based on the time series concept, by a typical frequency and its deviation part. Numerical results, compared with those of laboratory experiments, demonstrate that new set of irregular mild slope equation with current is of good adaptability.展开更多
The history of forecasting wind waves by wave energy conservation equation Is briefly described. Several currently used wave numerical models for shallow water based on different wave theories are discussed. Wave ener...The history of forecasting wind waves by wave energy conservation equation Is briefly described. Several currently used wave numerical models for shallow water based on different wave theories are discussed. Wave energy conservation models for the simulation of shallow water waves are introduced, with emphasis placed on the SWAN model, which takes use of the most advanced wave research achievements and has been applied to several theoretical and field conditions. The characteristics and applicability of the model, the finite difference numerical scheme of the action balance equation and its source terms computing methods are described in detail. The model has been verified with the propagation refraction numerical experiments for waves propagating in following and opposing currents; finally, the model is applied to the Haian Gulf area to simulate the wave height and wave period field there, and the results are compared with observed data.展开更多
Sediment samples with high spatial resolution （432 samples in total） and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and...Sediment samples with high spatial resolution （432 samples in total） and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and May 2007. The samples were analyzed with a particle sizer, resulting in the sediment distribution. The grain sizes and related parameters were analyzed. The results were presented in a ternary diagram. The sediment mainly consisted of sand, silty sand, sandy silt, sand-silt-clay, silt and clayey silt. And sand skeletons and clay matrices were found. At Nanhui Shoal, silt skeletons could be identified as well. Furthermore, the results were discussed per shoal. Although some depth dependencies were found per shoal, no general relation was found. The results are as follows： sediment located at these tidal flats of the Yangtze Estuary was mainly composed of sand, silty sand and silt. The median grain size in sediment was relatively complex with a range from 2.5 φ to 8 φ. The distributions of sorting coefficients ranging from 1 to 2 were in agreement with median sizes. It was suggested that sediment of the tidal flats was coarser and better sorted or finer and worse sorted. The skewness in sediment distribution varied from 0.1 to 0.8. In addition, the distributions of sorting coefficient and skewness in sediment at Chongming Eastern Shoal, Hengsha Eastern Shoal and Jiuduan Shoal were of similar characteristics because there were closely positive correlated relationships among these parameters. However, due to the location difference between Nanhui Southern Shoal and Eastern Shoal, the values of sorting coefficient and skewness had relatively large distinctions. The tracks of sediment transport could be described based on the distributions of sediment, which might reveal sediment transport controlled by two dominant hydrodynamic factors of current and wave. It was appreciable that coarser sediment with lower sorted coefficient was affected by dominant ebb current action and intense wave action resulted from rapidly dissipated wave energy. Moreover, due to the effects of obstructed branches, guided current and broken wave actions of the Deep Water Channel Project, grain-size in sediment located at two sides of the groyne was of uneven distribution characteristics.展开更多
基金supported by the National Science Foundation of China for Distinguished Young Scholars under contract No.50025925the National Natural Science Foundation of China under contract No.50079001.
文摘A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing waves were dissipated by sponge layers and transmitted by radiation boundaries. The finite difference method was used to solve the governing equations and boundary conditions in the regular transformed domain in σ-coordinate. Satisfactory agreements between the numerical predictions and experimental results of wave force were obtained. It is concluded that the maximum wave force acting on the vertical walls is induced by the obliquely incident waves rather than the normally incident waves.
基金The present work is financially supported by the National Natural Science Foundation of China (Grant No. 19732040 and No.50025924)
文摘A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by it finite element method, The results of this model are compared with those from other methods and agree well with experimental data.
文摘The model tests are performed with regular waves, and the effect of wave height, wave period, water depth, sediment size and pile diameter is evaluated. The shape and size of local scour around piles are studied. There are three typical scour patterns due to wave action. It is found that a relationship exists between the erosion depth and the wave number. An empirical formula of the maximum local scour is thus derived.
基金the National Natural Science Foundation of China (No. 50104013).
文摘After the erection of the Three Gorges Dam, the water level of Yangtze River will reach 175 m, and the average wave crest will be up to 1 m. Therefore the wave action cannot be neglected for the slope stability. Through simulation tests, the wave-induced dynamic response of the slope is analyzed. The soil body is taken as linear elastic body when it has a small deformation under the small wave action. Based on tests, the excess pore pressure and slope displacement under the loading in different wave period are analyzed. The ratio of dynamic strength and static strength to the breaking process of the slope is discussed. It is demonstrated that smaller wave period gives rise to a larger strain of the slope under the same stress. At different depth of water, different weakness effect on the stability of the soil slope is observed and the slope has an adaptability to the wave action to some extent.
文摘When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.
基金supported by the Science Council,with contract number NSC95-2221-E-006-462Research Center of Ocean Environment and Technology,under the contract NCKU-NSYSU
文摘In this paper the wave action balance equation in terms of frequency-direction spectrum is derived. A theoretical formulation is presented to generate an invariant frequency space to replace the varying wavenumber space through a Jacobian transformation in the wave action balance equation. The physical properties of the Jacobian incorporating the effects of water depths are discussed. The results provide a theoretical basis of wave action balance equations and ensure that the wave balance equations used in the SWAN or other numerical models are correct. It should be noted that the Jacobian is omitted in the wave action balance equations which are identical to a conventional action balance equation.
基金supported by the National Natural Science Foundation of China(Grant No51079024)
文摘This study is motivated by recognition of complex sandbar evolution patterns under wave actions inside the surf zone. A series of physical model experiments were conducted in a wave flume to investigate sandbar migration under various wave conditions, including wave groups, regular waves, and random waves. It was observed that under certain wave conditions sandbars move alternately shoreward and seaward rather than continuously in the same direction. The measurements show that the unstable movement of sandbars is closely related to the amplitude modulation of waves. Smaller amplitude modulation tends to produce more intense unstable bar movements. Data analysis further shows that the sandbar migration does not seem to be a passive response of the sea bed to wave forcing, but is most likely caused by the feedback interaction between waves and bed topography.
文摘Based on the Navier-Stokes equation, an average wave energy equation and a generalized wave action conservation equation are presented in this paper. The turbulence effects on water particle velocity u i and wave surface elavation ξ as well as energy dissipation are included. Some simplified forms are also given.
基金Project(200310) supported by Edison Research Foundation from General Electric (GE) in USAProject(59976022) supported by the National Natural Science Foundation of China
文摘In order to build the model of the drum level wave action and sloshing, based on the method of modularization modeling, the hydrodynamic model of drum level wave action and sloshing was developed, and dynamic simulation researches were carried out based on the model. The results indicate that both drum level and drum length have functional relations with period of drum level wave action and sloshing. When the drum level decreases or drum length increases, the period of drum level wave action and sloshing increases, density of liquid and number of sub-module division have little influence on the period of drum level wave action and sloshing. The model was validated by the analytical solution theory of liquid’s wave action and sloshing in cuboid container, and the 3D graphics of drum level wave action and sloshing was also obtained. The model can dynamically reflect the rules of wave action and sloshing of water in the container exactly.
基金National Key R&D Program of China(2017YFC1501604)Key Laboratory of South China Sea Meteorological Disaster Prevention and Mitigation of Hainan Province(SCSF202101)+1 种基金Open Grants of the State Key Laboratory of Severe Weather(2022LASW-B09)National Natural Science Foundation of China(41405049)。
文摘Based on prior investigation,this work defined a new thermodynamic shear advection parameter,which combines the vertical component of convective vorticity vector,horizontal divergence,and vertical gradient of generalized potential temperature.The interaction between waves and fundamental states was computed for the heavyrainfall event generated by landfalling typhoon“Morakot”.The analysis data was produced by ADAS[ARPS(Advanced Regional Prediction System)Data Analysis System]combined with the NCEP/NCAR final analysis data(1°×1°,26 vertical pressure levels and 6-hour interval)with the routine observations of surface and sounding.Because it may describe the typical vertical structure of dynamical and thermodynamic fields,the result indicates that the parameter is intimately related to precipitation systems.The parameter’s positive high-value area closely matches the reported 6-hour accumulated surface rainfall.And the statistical analysis reveals a certain correspondence between the thermodynamic shear advection parameter and the observed 6-hour accumulated surface rainfall in the summer of 2009.This implies that the parameter can predict and indicate the rainfall area,as well as the initiation and evolution of precipitation systems.
基金This work was financially supported by the Science Foundation of National Education Committee of China
文摘Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory and variational principle separately. It has two kinds of expressions including the dissipation term. Model n is based on the energy conservation equation with energy flux through the wave crest lines in orthogonal curvilinear coordinates and the wave kinematic conservation equation. The analysis and comparison and special cases of these two models are also given.
基金Science Foundation of National Education Committee of China
文摘A new numerical finite difference iteration method for refraction-diffraction of waves ia water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the dissipation term is briefly described, together with some analysis and comparison of computational results of the model with measurements in a hydraulic scale model (Berkhoff et al., 1982). An example of practical use of the method is given, showing that the present model is useful to engineering practice.
基金supported by the Special Fund of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(Grant No.2009585812)the National Natural Science Foundation of China(Grant No.50979033)the Programfor New Century Excellent Talentsin University of China(Grant No.NCET-07-0255)
文摘Two different methods for incorporating diffraction effect into wave action balance equation based coastal spectral wave models, WABED and SWAN, are discussed and evaluated with respect to their formulations, numerical implementations, and modeling capabilities. Both models were nm to simulate the wave transformation through a gap between two infinitely long breakwaters and that across an elliptical shoal observed in laboratory studies, with the emphasis laid on the diffraction induced by either obstacles or wave amplitude variations. Calculations of WABED were compared with Sommerfeld＇s analytical solutions, experimental observations and SWAN simulations. It is shown that both methods can predict reasonably wave diffraction for the two eases studied herein, and a fairly better performance is provided by WABED for stronger diffraction ease.
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.
文摘In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves can present three types of motion, i. e. significant stratification, fragile stratification and strong mixing. The motion gf turbid;,ater presents significant stratification when (H/D)/root Delta rho/rho less than or equal to 4.5, generally this state is known as density current. The formulas of motion velocity, thickness, and discharge of density current moving on horizontal bottom are derived by use of basic equations such as momemtum equation, equation of energy conservation and continuity equation of fluid. The time-average velocity and the thickness of density current under the action of waves have a relationship with such parameters as relative density (Delta rho/rho), wave height (H), and water depth (D). When these parameters are determined, the time-average thickness and motion velocity of density current are also determined. The relative thickness of density current (D-t/D) decreases with the increase of Delta rho/rho and increases with the increase of H/D. On the other hand, the motion velocity of density current increases with the increase of Delta rho/rho and decreases with the increase of the relative thickness (D-t/D) of density current. It is shown that the calculated results are in agreement with those of the flume experiment.
基金This researchis supported by Research Fund for Doctoral Programs of Higher Education (Grant No.20030141006) ,and a Program for Changjiang Scholars and Innovative Research Teams in Universities (Grant No.IRT0420)
文摘A higher order boundary dement method （HOBEM） is implemented for wave-current action on structures. The freeterm coefficient and Cauchy principal value （ GPV） integrals are computed by direct methods. Numerical experiments are carried out to validate the computation of free-term coefficient and GPV integrals. The results show that the computation precision of free-term coefficient is very high for various bodies, even with edges and corners, and the convergence speed is fast for CPV integrals for different meshes. The comparison of the second order mean drift force due to wave-current action on a uniform cylinder is made with an analytic solution. It is found that good agreement exists between the present calculation and the analytic solutions. Finally, the numerical code is applied for computing wave-current action on Snorrc TLP.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50409015)
文摘Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied experimentally.The influence of various ocean environmental parameters on local scour around the cylinder is considered in physical model test.The experimental results indicate that the principal effect factors on the scour in fine-sand seabed are wave height,wavelength,current velocity,ratio of diameter to wavelength and ratio of depth to wavelength when the ratio of cylinder diameter to wavelength is from 0.2 to 0.8.In this paper,dimensional analysis theory is utilized to establish a theoretical equation for forecasting maximum scour depth around large-sized round cylinder base due to the combined action of wave and current.The results computed with the theoretical equation are compared with the experimental results,and found to be in good consistency.The results in this studies can be used to estimate the maximum sour depth around analogous structures.
文摘A mild-slope equation for combined refraction and diffraction of random waves in the independent time current is derived using Kirby equation(1984). In the derivation, the frequency of random waves is represented based on the time series concept, by a typical frequency and its deviation part. Numerical results, compared with those of laboratory experiments, demonstrate that new set of irregular mild slope equation with current is of good adaptability.
基金"333"Project Scientific Research Foundation of Jiangsu ProvinceScience Fundation of Hohai University(3853)
文摘The history of forecasting wind waves by wave energy conservation equation Is briefly described. Several currently used wave numerical models for shallow water based on different wave theories are discussed. Wave energy conservation models for the simulation of shallow water waves are introduced, with emphasis placed on the SWAN model, which takes use of the most advanced wave research achievements and has been applied to several theoretical and field conditions. The characteristics and applicability of the model, the finite difference numerical scheme of the action balance equation and its source terms computing methods are described in detail. The model has been verified with the propagation refraction numerical experiments for waves propagating in following and opposing currents; finally, the model is applied to the Haian Gulf area to simulate the wave height and wave period field there, and the results are compared with observed data.
基金Key Project for the National Natural Science Foundation of China No.50939003 National Natural Science Foundation of China No.40976055 No.41076050
文摘Sediment samples with high spatial resolution （432 samples in total） and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and May 2007. The samples were analyzed with a particle sizer, resulting in the sediment distribution. The grain sizes and related parameters were analyzed. The results were presented in a ternary diagram. The sediment mainly consisted of sand, silty sand, sandy silt, sand-silt-clay, silt and clayey silt. And sand skeletons and clay matrices were found. At Nanhui Shoal, silt skeletons could be identified as well. Furthermore, the results were discussed per shoal. Although some depth dependencies were found per shoal, no general relation was found. The results are as follows： sediment located at these tidal flats of the Yangtze Estuary was mainly composed of sand, silty sand and silt. The median grain size in sediment was relatively complex with a range from 2.5 φ to 8 φ. The distributions of sorting coefficients ranging from 1 to 2 were in agreement with median sizes. It was suggested that sediment of the tidal flats was coarser and better sorted or finer and worse sorted. The skewness in sediment distribution varied from 0.1 to 0.8. In addition, the distributions of sorting coefficient and skewness in sediment at Chongming Eastern Shoal, Hengsha Eastern Shoal and Jiuduan Shoal were of similar characteristics because there were closely positive correlated relationships among these parameters. However, due to the location difference between Nanhui Southern Shoal and Eastern Shoal, the values of sorting coefficient and skewness had relatively large distinctions. The tracks of sediment transport could be described based on the distributions of sediment, which might reveal sediment transport controlled by two dominant hydrodynamic factors of current and wave. It was appreciable that coarser sediment with lower sorted coefficient was affected by dominant ebb current action and intense wave action resulted from rapidly dissipated wave energy. Moreover, due to the effects of obstructed branches, guided current and broken wave actions of the Deep Water Channel Project, grain-size in sediment located at two sides of the groyne was of uneven distribution characteristics.
