Nonlinear water wave propagation passing a submerged shelf is studied experimentally and numerically. The applicability of the wave propagation model of higher-order Boussinesq equations derived by Zou (2000, Ocean En...Nonlinear water wave propagation passing a submerged shelf is studied experimentally and numerically. The applicability of the wave propagation model of higher-order Boussinesq equations derived by Zou (2000, Ocean Engineering, 27, 557 - 575) is investigated. Physical experiments are conducted; three different front slopes (1:10, 1 = 5 and 1:2) of the shelf are set-up in the experiment and their effects on the wave propagation are investigated. Comparisons of the numerical results with test data are made and the higher-order Boussinesq equations agree well with the measurements since the dispersion of the model is of high accuracy. The numerical results show that the good results can also be obtained for the steep-slope cases although the mild-slope assumption is employed in the derivation of the higher-order terms in the higher-order Boussinesq equations.展开更多
A fast multipole methodology (FMM) is developed as a numerical approach to reduce the computational cost andmemory requirements in solving large-scale problems. It is applied to the boundary element method (BEM) for t...A fast multipole methodology (FMM) is developed as a numerical approach to reduce the computational cost andmemory requirements in solving large-scale problems. It is applied to the boundary element method (BEM) for three-dimensional potential flow problems. The algorithm based on mixed multipole expansion and numerical integration isimplemented in combination with an iterative solver. Numerical examinations, on Dirichlet and Neumann problems,are carried out to demonstrate the capability and accuracy of the present method. It has been shown that the methodhas evident advantages in saving memory and computing time when used to solve huge-scale problems which may beprohibitive for the traditional BEM implementation.展开更多
A composite numerical model is presented for computing the wave field in a harbor. The mild slope equation is discretized by a finite element method in the domain concerned. Out of the computational domain, the water ...A composite numerical model is presented for computing the wave field in a harbor. The mild slope equation is discretized by a finite element method in the domain concerned. Out of the computational domain, the water depth is assumed to be constant. The boundary element method is applied to the outer boundary for dealing with the infinite boundary condition. Because the model satisfies strictly the infinite boundary condition, more accurate results can be obtained. The model is firstly applied to compute the wave diffraction in a narrow rectangular bay and the wave diffraction from a porous cylinder. The numerical results are compared with the analytical solution, experimental data and other numerical results. Good agreements are obtained. Then the model is applied to computing the wave diffraction in a square harbor with varying water depth. The effects of the water depth in the harbor and the incoming wave direction on the wave height distribution are discussed.展开更多
Ship-based sea ice observation data (concentrations, ice thickness, topography and overlying snow cover) were collected from Middle Weddell Sea to Prydz Bay, Antarctic during the period of 4 to 17 Jan 2003. Antarctic ...Ship-based sea ice observation data (concentrations, ice thickness, topography and overlying snow cover) were collected from Middle Weddell Sea to Prydz Bay, Antarctic during the period of 4 to 17 Jan 2003. Antarctic ice chart of first week of Jan 2003 was derived from National Ice Center (NIC). The compared analysis of sea ice concentrations and thickness distributions were conducted though in situ data and NIC chart. Results from sea ice concentration-analysis indicated the presence of large-scale open water between 2000 and 4100 km along transit route resulted from sea ice drifting. We describe the existence of mostly smooth first-year sea ice in study region ranged between 30 and 120 cm. We also display the derived overlying snow coverage. Our results reveal the strong correspondence between ship-based observations and remotely sensed ice charts whatever in ice concentrations and ice thickness distributions.展开更多
The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1) estimation of sea ice distribution by ship-based observations between the middle Wed...The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1) estimation of sea ice distribution by ship-based observations between the middle Weddell Sea and the Prydz Bay; (2) estimation of sea ice distribution by aerial photography in the Prydz Bay; (3) direct measurements of fast ice thickness and snow cover, as well as ice core sampling in Nella Fjord; (4) estimation of melting sea ice distribution near the Zhongshan Station; and (5) observation of sea ice early freeze near the Zhongshan Station. On average, sea ice covered 14.4% of the study area. The highest sea ice concentration (80%) was observed in the Weddell Sea. First-year ice was dominant (99.7%~99.8%). Sea ice distributions in the Prydz Bay were more variable due to complex inshore topography, proximity of the Larsemann Hills, and/or grounded icebergs. The average thickness of landfast ice in Nella Fjord was 169.5 cm. Wind-blown snow redistribution plays an important role in affecting the ice thickness in Nella Fjord. Preliminary freezing of sea ice near the Zhongshan Station follows the first two phases of the pancake cycle.展开更多
Some authors have developed a few methods of measuring wave slopes based on light refraction, including the measurement method via the distribution of light intensity or color under water. A new method based on light ...Some authors have developed a few methods of measuring wave slopes based on light refraction, including the measurement method via the distribution of light intensity or color under water. A new method based on light refraction is specified for the measurement of wave surface elevation in wave flume via imaging technology. A plane painted with black and white stripes is put on the flume floor as an indication plane, which can be arranged easily and cheaply. Compared with the previous methods, the present method is less sensitive to the noise and nonlinear effects of optical process, which can be taken as a digital method. The CCD camera is fixed above the flume with its optical axis arranged vertically to grab the images of stripes modulated by the wave surface. The modulated value can be calculated from the Hilbert transform, and then the wave surface elevation can be obtained. The algorithm and experimental procedure are specified in detail, and some experimental results are provided to show the validity of the present method.展开更多
The wave relative frequency in the coordinate system moving with current and the angle between the direction ofwave propagation and that of current are computed based on the wave dispersion relation. The current field...The wave relative frequency in the coordinate system moving with current and the angle between the direction ofwave propagation and that of current are computed based on the wave dispersion relation. The current field iscomputed by solving the depth averaged shallow water equations. The wave field is computed by solving the mild-slope equation which has taken the currents effect into account. A numerical model is established using a finiteelement method for simulating the wave shoaling and diffraction in current over a mild-slope, and the numericalresults are reasonable to compare with the experimental data.展开更多
A new analytical method is proposed to analyze the force acting on a rectangular oscillating buoy due to linear waves.In the method a new analytical expression for the diffraction velocity potential is obtained first ...A new analytical method is proposed to analyze the force acting on a rectangular oscillating buoy due to linear waves.In the method a new analytical expression for the diffraction velocity potential is obtained first by use of theeigenfunction expansion method and then the wave excitation force is calculated by use of the known incident wavepotential and the diffraction potential. Compared with the classical analytical method, it can be seen that the presentmethod is simpler for a two-dimensional problem due to the comparable effort needed for the computation ofdiffraction potential and for that of radiated potential. To verify the correctness of the method, a classical example inthe reference is recomputed and the obtained results are in good accordance with those by use of other methods,which shows that the present method is correct.展开更多
The experiments on pollutant movement in surf zone were conducted on the two gentle beaches(with slope of 1:100 and 1:40, respectively), for diverse wave cases. The movement contours and direction of pollutants, under...The experiments on pollutant movement in surf zone were conducted on the two gentle beaches(with slope of 1:100 and 1:40, respectively), for diverse wave cases. The movement contours and direction of pollutants, under the action of regular and random waves with diverse wave amplitudes, were provided and studied in this paper. It was shown that, due to complicated hydrodynamics in surf zone, the pollutant movement state is quite complicated and different from that in pure current zone.展开更多
The planar 2D k-ε double equations' turbulence model was adopted and transformed into non-orthogonal curvilinear coordinates. The concentration convection-diffusion was introduced to planar 2D SIMPLEC algorithm o...The planar 2D k-ε double equations' turbulence model was adopted and transformed into non-orthogonal curvilinear coordinates. The concentration convection-diffusion was introduced to planar 2D SIMPLEC algorithm of flow in non-orthogonal curvilinear coordinates. The numerical model of pollutant transportation in non-orthogonal curvilinear coordinates was constructed. The model was applied to simulate the flow and pollutant concentration fields. In the testing concentration field, two optimal operations of contamination discharging both along bank and in the centerline at the first bend of the meandering channel were adopted. Comparison with available data showed the model developed was successful, was valuable to engineering application.展开更多
An unstructured finite-volume numerical algorithm was presented for solution of the two-dimensional shallow water equations, based on triangular or arbitrary quadrilateral meshes. The Roe type approximate Riemann solv...An unstructured finite-volume numerical algorithm was presented for solution of the two-dimensional shallow water equations, based on triangular or arbitrary quadrilateral meshes. The Roe type approximate Riemann solver was used to the system. A second-order TVD scheme with the van Leer limiter was used in the space discretization and a two-step Runge-Kutta approach was used in the time discretization. An upwind, as opposed to a pointwise, treatment of the slope source terms was adopted and the semi-implicit treatment was used for the friction source terms. Verification for two-dimension dam-break problems are carried out by comparing the present results with others and very good agreement is shown.展开更多
A two-dimensional numerical irregular wave tank based on the potential wave theory was developed. A source term was used inside the domain to generate waves, and outgoing waves were dissipated by sponge layers and tra...A two-dimensional numerical irregular wave tank based on the potential wave theory was developed. A source term was used inside the domain to generate waves, and outgoing waves were dissipated by sponge layers and transmitted by radiation boundary. The σ-coordinate transformation was introduced to map the time-dependent irregular physical domain to a fixed regular computational domain, and thus the free surface and bottom boundary conditions could be implemented precisely. The model was verified by simulating the nonlinear regular and irregular wave propagation on constant-depth water, as well as regular waves reflected from a vertical wall, and satisfactory agreement between numerical results and analytical solutions was obtained. The present numerical model is proved to be an effective tool for a long-duration simulation of coastal wave dynamics where the wave reflection is significant.展开更多
The local scour around a large -scale vertical circular cylinder due tocombined wave-current action was experimentally and numerically studied in the present paper.Experiments were carried out to research the affect o...The local scour around a large -scale vertical circular cylinder due tocombined wave-current action was experimentally and numerically studied in the present paper.Experiments were carried out to research the affect of the wave height, current velocity and thediameter of the cylinder on the scour process. The topography near the cylinder in various casesduring scour was measured. The cylinder diameter affects the distribution of scour and depositionarea. The maximum scour depth increases evidently when the current velocity increases. The maximumscour depth does not increase after the wave height retains a certain value. A numerical model usinga finite element method for simulating the scour process was established. And the numerical resultsagree well with the measured, data. The numerical model is more applicable in the case oflarge-scale cylinders.展开更多
On the basis of energy and continuity equations a general threshold condition for chocking in open channels is obtained and a representation in terms of the Froude number at the upstream section and other parameters i...On the basis of energy and continuity equations a general threshold condition for chocking in open channels is obtained and a representation in terms of the Froude number at the upstream section and other parameters is given to predict whether the chocking phenomenon occurs or not at the downstream section. From the general threshold condition for chocking the limit contraction ratios of the channel width are introduced for both with and without the energy losses and a criterion for excavation of the tailrace to avoid chocking is derived. An example shows that using these criterion and the representation proposed for calculating flow depth it is very easy to determine the scheme of the excavation of the open channels.展开更多
Three-dimensional flow around a pipeline span shoulder is simulated using afractional step finite element method. The Reynolds number, based on the pipe-diameter and theapproaching flow velocity, is set at 500 and 5 x...Three-dimensional flow around a pipeline span shoulder is simulated using afractional step finite element method. The Reynolds number, based on the pipe-diameter and theapproaching flow velocity, is set at 500 and 5 x 10~5 to simulate both laminar and turbulent flow.In high Reynolds number case, Smagorinsky SGS closure is used to model the turbulent flows. The flowfield visualization by vorticity iso-surfaces shows that a spiral vortex tube is formed around thespan shoulder and extends around the span shoulder. The vortex cores defined by the eigenvalues ofthe symmetric tensor S^2 + Ω~2 (S and Ω are respectively the symmetric and antisymmetric parts ofthe velocity gradient tensor) gives more details of the flow field. It is also found that there aresignificant bed shear stress concentrations in the span shoulder area. The reasons for the shearstress concentration are discussed.展开更多
On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junc...On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junction angle, and the discharge ratio was suggestedwhich agrees well with the experimental results. The results calculated by the present formulationfor the depth ratio were compared with the results of earlier one-dimensional formulations andexperiments. It is found that the present results coincide better with experiments than those ofothers.展开更多
A numerical computation method based on B-splines is presented for thehydrodynamic interaction forces between two ships. The B-spline functions are adopted to approximatethe fully three-dimensional ship hull geometry ...A numerical computation method based on B-splines is presented for thehydrodynamic interaction forces between two ships. The B-spline functions are adopted to approximatethe fully three-dimensional ship hull geometry and unknown velocity potential in the fluid domain.The results and analysis are given in detail for the hydrodynamic interaction forces between twoships moving on parallel courses. All the computations show that the numerical results are in goodagreement with some experimental or other theoretical results.展开更多
The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to ...The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to expand velocity potentials in each domain. A phase relation is introduced for wave oscillation in each caisson, and the structure geometry is considered in constructing the models of reflection waves. The reflected waves with the present analysis include all of the waves traveling in different directions when incident wave period is short. Numerical examinations show that velocities at the inner and outer sides of the front walls of caissons ase close to each other, and reflection coefficients satisfy the energy conservation relation very well when porous effect parameter is infinite. Numerical results show that the reflection coefficients of oblique incident waves are smaller for shorter caissons at low frequency, and decrease with the increase of wave incident angle.展开更多
A new kind of open type breakwaters was proposed based on the concept of wave energy conversion. The excellent feature of the structure is that it can absorb and utilize the wave energy to dissipate waves. The effects...A new kind of open type breakwaters was proposed based on the concept of wave energy conversion. The excellent feature of the structure is that it can absorb and utilize the wave energy to dissipate waves. The effects of some factors, such as the configuration insides, the geometrical parameters and the relative width (the ratio of the width to the wave length), on the performance of the breakwater were discussed based on a series of regular wave tests in the wave flume. The hydrodynamic characteristics of the new open type breakwater were analyzed in detail, and the structure was optimized to improve the performance of the breakwater to effectively dissipate the waves with long period. The variation of the coefficients of wave transmission and reflection along with attenuation with respect to relative width was examined. The results of the physical model tests indicate that the transmission coefficient significantly decreases by about twenty percent at the range of relative width from 0.1 to 0.2, compared with the traditional open type breakwaters.展开更多
For the purpose of time-domain calculation of wave forces on moored ships ina harbor, the 2D/3D coupled numerical model was developed, in which the horizontally 2Dshallow-water wave model based on the improved Boussin...For the purpose of time-domain calculation of wave forces on moored ships ina harbor, the 2D/3D coupled numerical model was developed, in which the horizontally 2Dshallow-water wave model based on the improved Boussinesq equations was adopted for the calculationin the wide region located far from the ships while the 3D numerical model based on theReynolds-Averaged Navier-Stokes (RANS) equations was used in the limited region adjacent to theships. The domain connection technique with overlaping region between different model regions wasapplied and examined. It is shown that the present partially 3D hybrid model saves calculation timesignificantly compared to the full 3D model for the whole region and is capable of reproducing thecharacteristics of 3D and complicated flows around the ships and 3D hydrodynamic loads on them,which cannot be reproduced by the 2D model alone.展开更多
基金The project was supported by the National Natural Science Foundation of China under contracts No.59979002 and No.59839330.
文摘Nonlinear water wave propagation passing a submerged shelf is studied experimentally and numerically. The applicability of the wave propagation model of higher-order Boussinesq equations derived by Zou (2000, Ocean Engineering, 27, 557 - 575) is investigated. Physical experiments are conducted; three different front slopes (1:10, 1 = 5 and 1:2) of the shelf are set-up in the experiment and their effects on the wave propagation are investigated. Comparisons of the numerical results with test data are made and the higher-order Boussinesq equations agree well with the measurements since the dispersion of the model is of high accuracy. The numerical results show that the good results can also be obtained for the steep-slope cases although the mild-slope assumption is employed in the derivation of the higher-order terms in the higher-order Boussinesq equations.
基金This work was sponsored by the National Natural Science Foundation of China for Distinguished Young Scholars under contract No,50025924the Research Foundation for the Doctoral Program of Higher Education of China under contract No.20030141006.
文摘A fast multipole methodology (FMM) is developed as a numerical approach to reduce the computational cost andmemory requirements in solving large-scale problems. It is applied to the boundary element method (BEM) for three-dimensional potential flow problems. The algorithm based on mixed multipole expansion and numerical integration isimplemented in combination with an iterative solver. Numerical examinations, on Dirichlet and Neumann problems,are carried out to demonstrate the capability and accuracy of the present method. It has been shown that the methodhas evident advantages in saving memory and computing time when used to solve huge-scale problems which may beprohibitive for the traditional BEM implementation.
基金The present work was financially supported by the National Natural Science Foundation of China under contract No.50025924.
文摘A composite numerical model is presented for computing the wave field in a harbor. The mild slope equation is discretized by a finite element method in the domain concerned. Out of the computational domain, the water depth is assumed to be constant. The boundary element method is applied to the outer boundary for dealing with the infinite boundary condition. Because the model satisfies strictly the infinite boundary condition, more accurate results can be obtained. The model is firstly applied to compute the wave diffraction in a narrow rectangular bay and the wave diffraction from a porous cylinder. The numerical results are compared with the analytical solution, experimental data and other numerical results. Good agreements are obtained. Then the model is applied to computing the wave diffraction in a square harbor with varying water depth. The effects of the water depth in the harbor and the incoming wave direction on the wave height distribution are discussed.
文摘Ship-based sea ice observation data (concentrations, ice thickness, topography and overlying snow cover) were collected from Middle Weddell Sea to Prydz Bay, Antarctic during the period of 4 to 17 Jan 2003. Antarctic ice chart of first week of Jan 2003 was derived from National Ice Center (NIC). The compared analysis of sea ice concentrations and thickness distributions were conducted though in situ data and NIC chart. Results from sea ice concentration-analysis indicated the presence of large-scale open water between 2000 and 4100 km along transit route resulted from sea ice drifting. We describe the existence of mostly smooth first-year sea ice in study region ranged between 30 and 120 cm. We also display the derived overlying snow coverage. Our results reveal the strong correspondence between ship-based observations and remotely sensed ice charts whatever in ice concentrations and ice thickness distributions.
基金supported by the National Commonweal Research Project of China under contract No.2001DIA50040-03the National Natural Science Foundation of China under contract No.40271026.
文摘The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1) estimation of sea ice distribution by ship-based observations between the middle Weddell Sea and the Prydz Bay; (2) estimation of sea ice distribution by aerial photography in the Prydz Bay; (3) direct measurements of fast ice thickness and snow cover, as well as ice core sampling in Nella Fjord; (4) estimation of melting sea ice distribution near the Zhongshan Station; and (5) observation of sea ice early freeze near the Zhongshan Station. On average, sea ice covered 14.4% of the study area. The highest sea ice concentration (80%) was observed in the Weddell Sea. First-year ice was dominant (99.7%~99.8%). Sea ice distributions in the Prydz Bay were more variable due to complex inshore topography, proximity of the Larsemann Hills, and/or grounded icebergs. The average thickness of landfast ice in Nella Fjord was 169.5 cm. Wind-blown snow redistribution plays an important role in affecting the ice thickness in Nella Fjord. Preliminary freezing of sea ice near the Zhongshan Station follows the first two phases of the pancake cycle.
基金This research was sponsored by the National Science Foundation for Distinguished Young Scholars under contract No.50125924by the National Natural Science Foundation of China under contract Nos 50379001 and 10332050.
文摘Some authors have developed a few methods of measuring wave slopes based on light refraction, including the measurement method via the distribution of light intensity or color under water. A new method based on light refraction is specified for the measurement of wave surface elevation in wave flume via imaging technology. A plane painted with black and white stripes is put on the flume floor as an indication plane, which can be arranged easily and cheaply. Compared with the previous methods, the present method is less sensitive to the noise and nonlinear effects of optical process, which can be taken as a digital method. The CCD camera is fixed above the flume with its optical axis arranged vertically to grab the images of stripes modulated by the wave surface. The modulated value can be calculated from the Hilbert transform, and then the wave surface elevation can be obtained. The algorithm and experimental procedure are specified in detail, and some experimental results are provided to show the validity of the present method.
文摘The wave relative frequency in the coordinate system moving with current and the angle between the direction ofwave propagation and that of current are computed based on the wave dispersion relation. The current field iscomputed by solving the depth averaged shallow water equations. The wave field is computed by solving the mild-slope equation which has taken the currents effect into account. A numerical model is established using a finiteelement method for simulating the wave shoaling and diffraction in current over a mild-slope, and the numericalresults are reasonable to compare with the experimental data.
基金This work Was supported by the High Tech Research and Development(863)Program of China under Grant No.2003AA5 16010the Chinese Academy of Science Pilot Project of the National Knowledge Innovation Program under Grant No.KGCX2-SW-305Chinese National Science Fund for Distinguished Young Scholars under Grant No.50125924.
文摘A new analytical method is proposed to analyze the force acting on a rectangular oscillating buoy due to linear waves.In the method a new analytical expression for the diffraction velocity potential is obtained first by use of theeigenfunction expansion method and then the wave excitation force is calculated by use of the known incident wavepotential and the diffraction potential. Compared with the classical analytical method, it can be seen that the presentmethod is simpler for a two-dimensional problem due to the comparable effort needed for the computation ofdiffraction potential and for that of radiated potential. To verify the correctness of the method, a classical example inthe reference is recomputed and the obtained results are in good accordance with those by use of other methods,which shows that the present method is correct.
文摘The experiments on pollutant movement in surf zone were conducted on the two gentle beaches(with slope of 1:100 and 1:40, respectively), for diverse wave cases. The movement contours and direction of pollutants, under the action of regular and random waves with diverse wave amplitudes, were provided and studied in this paper. It was shown that, due to complicated hydrodynamics in surf zone, the pollutant movement state is quite complicated and different from that in pure current zone.
文摘The planar 2D k-ε double equations' turbulence model was adopted and transformed into non-orthogonal curvilinear coordinates. The concentration convection-diffusion was introduced to planar 2D SIMPLEC algorithm of flow in non-orthogonal curvilinear coordinates. The numerical model of pollutant transportation in non-orthogonal curvilinear coordinates was constructed. The model was applied to simulate the flow and pollutant concentration fields. In the testing concentration field, two optimal operations of contamination discharging both along bank and in the centerline at the first bend of the meandering channel were adopted. Comparison with available data showed the model developed was successful, was valuable to engineering application.
文摘An unstructured finite-volume numerical algorithm was presented for solution of the two-dimensional shallow water equations, based on triangular or arbitrary quadrilateral meshes. The Roe type approximate Riemann solver was used to the system. A second-order TVD scheme with the van Leer limiter was used in the space discretization and a two-step Runge-Kutta approach was used in the time discretization. An upwind, as opposed to a pointwise, treatment of the slope source terms was adopted and the semi-implicit treatment was used for the friction source terms. Verification for two-dimension dam-break problems are carried out by comparing the present results with others and very good agreement is shown.
基金the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No:50025925), the National Natural Science Foundation of China (Grant No: 50079001) and the Chinese Postdoctoral ScienceFoundation (Grant No:20040350088)
文摘A two-dimensional numerical irregular wave tank based on the potential wave theory was developed. A source term was used inside the domain to generate waves, and outgoing waves were dissipated by sponge layers and transmitted by radiation boundary. The σ-coordinate transformation was introduced to map the time-dependent irregular physical domain to a fixed regular computational domain, and thus the free surface and bottom boundary conditions could be implemented precisely. The model was verified by simulating the nonlinear regular and irregular wave propagation on constant-depth water, as well as regular waves reflected from a vertical wall, and satisfactory agreement between numerical results and analytical solutions was obtained. The present numerical model is proved to be an effective tool for a long-duration simulation of coastal wave dynamics where the wave reflection is significant.
文摘The local scour around a large -scale vertical circular cylinder due tocombined wave-current action was experimentally and numerically studied in the present paper.Experiments were carried out to research the affect of the wave height, current velocity and thediameter of the cylinder on the scour process. The topography near the cylinder in various casesduring scour was measured. The cylinder diameter affects the distribution of scour and depositionarea. The maximum scour depth increases evidently when the current velocity increases. The maximumscour depth does not increase after the wave height retains a certain value. A numerical model usinga finite element method for simulating the scour process was established. And the numerical resultsagree well with the measured, data. The numerical model is more applicable in the case oflarge-scale cylinders.
文摘On the basis of energy and continuity equations a general threshold condition for chocking in open channels is obtained and a representation in terms of the Froude number at the upstream section and other parameters is given to predict whether the chocking phenomenon occurs or not at the downstream section. From the general threshold condition for chocking the limit contraction ratios of the channel width are introduced for both with and without the energy losses and a criterion for excavation of the tailrace to avoid chocking is derived. An example shows that using these criterion and the representation proposed for calculating flow depth it is very easy to determine the scheme of the excavation of the open channels.
文摘Three-dimensional flow around a pipeline span shoulder is simulated using afractional step finite element method. The Reynolds number, based on the pipe-diameter and theapproaching flow velocity, is set at 500 and 5 x 10~5 to simulate both laminar and turbulent flow.In high Reynolds number case, Smagorinsky SGS closure is used to model the turbulent flows. The flowfield visualization by vorticity iso-surfaces shows that a spiral vortex tube is formed around thespan shoulder and extends around the span shoulder. The vortex cores defined by the eigenvalues ofthe symmetric tensor S^2 + Ω~2 (S and Ω are respectively the symmetric and antisymmetric parts ofthe velocity gradient tensor) gives more details of the flow field. It is also found that there aresignificant bed shear stress concentrations in the span shoulder area. The reasons for the shearstress concentration are discussed.
文摘On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junction angle, and the discharge ratio was suggestedwhich agrees well with the experimental results. The results calculated by the present formulationfor the depth ratio were compared with the results of earlier one-dimensional formulations andexperiments. It is found that the present results coincide better with experiments than those ofothers.
文摘A numerical computation method based on B-splines is presented for thehydrodynamic interaction forces between two ships. The B-spline functions are adopted to approximatethe fully three-dimensional ship hull geometry and unknown velocity potential in the fluid domain.The results and analysis are given in detail for the hydrodynamic interaction forces between twoships moving on parallel courses. All the computations show that the numerical results are in goodagreement with some experimental or other theoretical results.
文摘The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to expand velocity potentials in each domain. A phase relation is introduced for wave oscillation in each caisson, and the structure geometry is considered in constructing the models of reflection waves. The reflected waves with the present analysis include all of the waves traveling in different directions when incident wave period is short. Numerical examinations show that velocities at the inner and outer sides of the front walls of caissons ase close to each other, and reflection coefficients satisfy the energy conservation relation very well when porous effect parameter is infinite. Numerical results show that the reflection coefficients of oblique incident waves are smaller for shorter caissons at low frequency, and decrease with the increase of wave incident angle.
文摘A new kind of open type breakwaters was proposed based on the concept of wave energy conversion. The excellent feature of the structure is that it can absorb and utilize the wave energy to dissipate waves. The effects of some factors, such as the configuration insides, the geometrical parameters and the relative width (the ratio of the width to the wave length), on the performance of the breakwater were discussed based on a series of regular wave tests in the wave flume. The hydrodynamic characteristics of the new open type breakwater were analyzed in detail, and the structure was optimized to improve the performance of the breakwater to effectively dissipate the waves with long period. The variation of the coefficients of wave transmission and reflection along with attenuation with respect to relative width was examined. The results of the physical model tests indicate that the transmission coefficient significantly decreases by about twenty percent at the range of relative width from 0.1 to 0.2, compared with the traditional open type breakwaters.
文摘For the purpose of time-domain calculation of wave forces on moored ships ina harbor, the 2D/3D coupled numerical model was developed, in which the horizontally 2Dshallow-water wave model based on the improved Boussinesq equations was adopted for the calculationin the wide region located far from the ships while the 3D numerical model based on theReynolds-Averaged Navier-Stokes (RANS) equations was used in the limited region adjacent to theships. The domain connection technique with overlaping region between different model regions wasapplied and examined. It is shown that the present partially 3D hybrid model saves calculation timesignificantly compared to the full 3D model for the whole region and is capable of reproducing thecharacteristics of 3D and complicated flows around the ships and 3D hydrodynamic loads on them,which cannot be reproduced by the 2D model alone.
