A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simp...A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simply Rankine source, the resulting boundary integral equation is repeatedly solved at each time step and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A smooth technique is also adopted in order to eliminate the possible saw-tooth numerical instabilities. The incident wave at the uptank is given as theoretical wave in this paper. The outgoing waves are absorbed inside a damping zone by spatially varying artificial damping on the free surface at the wave tank end. The numerical results show that the NWT developed by these approaches has a high accuracy and good numerical stability.展开更多
A fully nonlinear numerical wave tank based on the solution of the σ-transformed Navier-Stokes equation is developed in this study. The numerical wave is generated from the inflow boundary, where the surface elevati...A fully nonlinear numerical wave tank based on the solution of the σ-transformed Navier-Stokes equation is developed in this study. The numerical wave is generated from the inflow boundary, where the surface elevation and/or velocity are specified by use of the analytical solution or the laboratory data. The Sommerfeld/Orlanski radiation condition in conjunction with an artificial damping zone is applied to reduce wave reflection from the outflow boundary. The whole numerical solution procedures are split into three steps, i.e., advection, diffusion and propagation, and a new method, the Lagrange-Euler Method, instead of the MAC or VOF method, is introduced to solve the free surface elevation at the new time step. Several typical wave cases, including solitary waves, regular waves and irregular waves, are simulated in the wave tank. The robustness and accuracy of the NWT are verified by the good agreement between the numerical results and the linear or nonlinear analytical solutions. This research will be further developed by study of wave-wave, wave-current, wave-structure or wave-jet interaction in the future.展开更多
Freak waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank. To set up the nonlinear numerical wave tank, the Boundary Element Method is used to solve potential flow equations incorpo...Freak waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank. To set up the nonlinear numerical wave tank, the Boundary Element Method is used to solve potential flow equations incorporated with fully nonlinear free surface boundary conditions. The nonlinear properties of freak waves, such as high frequency components and wave profile asymmetry, are discussed. The kinematic data, which can be useful for the evaluation of the wave forces exerted on structures to avoid underestimation of linear predictions, are obtained, and discussed, from the simulated results of freak waves.展开更多
A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra: constant amplitude spectrum, constant steepness spectrum and Pierson-M...A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra: constant amplitude spectrum, constant steepness spectrum and Pierson-Moscowitz spectrum. Numerical tests are performed to validate the model results. Then, the onset of wave breaking is discussed with geometric, kinematic, and dynamic breaking criteria. The strength of wave breaking, which is always characterized by the fractional energy loss and breaking strength coefficient, is studied for different spectra. The results show how the energy growth rate is better than the initial wave steepness on estimating the fractional energy losses as well as breaking strength coefficient.展开更多
A two-dimensional (2D) numerical model is developed for the wave sim- ulation and propagation in a wave flume. The fluid flow is assumed to be viscous and incompressible, and the Navier-Stokes and continuity equatio...A two-dimensional (2D) numerical model is developed for the wave sim- ulation and propagation in a wave flume. The fluid flow is assumed to be viscous and incompressible, and the Navier-Stokes and continuity equations are used as the governing equations. The standard k-e model is used to model the turbulent flow. The Navier- Stokes equations are discretized using the staggered grid finite difference method and solved by the simplified marker and cell (SMAC) method. Waves are generated and propagated using a piston type wave maker. An open boundary condition is used at the end of the numerical flume. Some standard tests, such as the lid-driven cavity, the constant unidirectional velocity field, the shearing flow, and the dam-break on the dry bed, are performed to valid the model. To demonstrate the capability and accuracy of the present method, the results of generated waves are compared with available wave theories. Finally, the clustering technique (CT) is used for the mesh generation, and the best condition is suggested.展开更多
The modeling of generation and subsequent propagation of irregular waves in a numerical wave flume is performed by mean of the boundary element method. Random waves are generated by a piston-type wave generator at one...The modeling of generation and subsequent propagation of irregular waves in a numerical wave flume is performed by mean of the boundary element method. Random waves are generated by a piston-type wave generator at one end of the flume with the Mitsuyasu-Bretschneider spectrum used as the target spectrum for the generation. An artificial absorbing beach is placed at the other end of the flume to minimize wave reflection. Surface fluctuations are described by use of the Lagrangian description, and finite difference is adopted for the approximation of time derivative. To monitor the developments of the waves, a number of pseudo wave gauges are installed along the tank. Through comparison of the spectra from those gauges with the target spectrum, satisfactory results can be obtained from the present numerical scheme.展开更多
A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank, which is established on Computational Fluid Dynamics (CFD) theories. The numerical ...A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank, which is established on Computational Fluid Dynamics (CFD) theories. The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out. The added mass and damping coefficients are obtained by the decomposition of the computational results, which agree well with the corresponding ones of potential theories.展开更多
A numerical wave tank with passive absorption for irregular waves is considered in this paper. Waves with spectral shapes corresponding to that of the Mitsuyasu- Bretschneider type are used as the initial condition at...A numerical wave tank with passive absorption for irregular waves is considered in this paper. Waves with spectral shapes corresponding to that of the Mitsuyasu- Bretschneider type are used as the initial condition at one end of the flume, An absorbing boundary is imposed at the other end of the wave flume to minimize reflection. By use of a Lagrangian description for the Surface elevation, and finite difference for approximation of the time derivative, the problem is then solved by the boundary element method, The effects of the absorbing boundary are investigated by varying the values of the absorption coefficient mu, and studying the time histories of the Surface elevations 'recorded' on pre-selected locations.展开更多
Recently the numerical wave tank has become a widely-used tool to study waves as well as wave-structure interactions, and the wave-absorbing method is very important as its effect on the quality of waves generated. Th...Recently the numerical wave tank has become a widely-used tool to study waves as well as wave-structure interactions, and the wave-absorbing method is very important as its effect on the quality of waves generated. The relaxation method and the derived momentum source method are often utilized, however, the damping weight is constant during calculation and repeated trials are required to obtain an acceptable wave-absorbing effect. To address the abovementioned issues, a conserved wave-absorbing method is developed. The damping weight is determined by solving the mass conservation equation of the absorbing region at every time step. Based on this method, a two-dimensional numerical wave tank is established by using the VB language to simulate various waves by which the validation of this method is evaluated.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
A 2-D numerical wave tank(NWT)is developed using the lattice Boltzmann method(LBM)and a multi-relaxation-time(MRT)collision model coupled with an algebraic volume of fluid(VOF)scheme for free surface tracking.An exter...A 2-D numerical wave tank(NWT)is developed using the lattice Boltzmann method(LBM)and a multi-relaxation-time(MRT)collision model coupled with an algebraic volume of fluid(VOF)scheme for free surface tracking.An external force based on the momentum source function is used to generate the waves,and a zone of porous media is used to absorb the waves.Numerical simulations of the progressive and standing waves show that the NWT can generate stable wave trains in agreement with the analytical solutions and eliminate the re-reflection waves.The NWT is used to simulate two problems encountered in practice,namely:the wave transformation over a submerged breakwater and the wave runup on a sea dike.The numerical predictions are in good agreement with the measured data.展开更多
A third-order KdV solution to the internal solitary wave is derived by a new method based on the weakly nonlinear assumptions in a rigid-lid two-layer system.The solution corrects an error by Mirie and Su(1984).A two-...A third-order KdV solution to the internal solitary wave is derived by a new method based on the weakly nonlinear assumptions in a rigid-lid two-layer system.The solution corrects an error by Mirie and Su(1984).A two-dimensional numerical wave tank has been established with the help of the open source CFD library OpenFOAM and the third-party software waves2Foam.Various analytical solutions,including the first-order to third-order KdV solutions,the eKdV solution and the MCC solution,have been used to initialise the flow fields in the CFD simulations of internal solitary waves.Two groups including 11 numerical cases have been carried out.In the same group,the initial wave amplitudes are the same but the implemented analytical solutions are different.The simulated wave profiles at different moments have been presented.The relative errors in terms of the wave amplitude between the last time step and the initial input have been analysed quantitatively.It is found that the third-order KdV solution results in the most stable internal solitary wave in the numerical wave tank for both small-amplitude and finite-amplitude cases.The finding is significant for the further simulations involving internal solitary waves.展开更多
Moving-particle semi-implicit(MPS) method is a new mesh-free numerical method based on Lagrangian particle. In this paper, MPS method is applied to the study on numerical wave tank. For the purpose of simulating numer...Moving-particle semi-implicit(MPS) method is a new mesh-free numerical method based on Lagrangian particle. In this paper, MPS method is applied to the study on numerical wave tank. For the purpose of simulating numerical wave, we combine the MPS method with large eddy simulation(LES) which can simulate the turbulence in the flow. The intense pressure fluctuation is a significant shortcoming in MPS method. So, we improve the original MPS method by using a new pressure Poisson equation to ease the pressure fluctuation. Divergencefree condition representing fluid incompressible is used to calculate pressure smoothly. Then, area-time average technique is used to deal with the calculation. With these improvements, the modified MPS-LES method is applied to the simulation of numerical wave. As a contrast, we also use the original MPS-LES method to simulate the wave in a numerical wave tank. The result shows that the new method is better than the original MPS-LES method.展开更多
A dynamic experiment for oil dispersion into a water column was performed with a 21 m long, 0.5 m wide, and 1 m high wind-driven wave tank. At wind velocity between 6-12 m/s and with the oil slide kept constant (about...A dynamic experiment for oil dispersion into a water column was performed with a 21 m long, 0.5 m wide, and 1 m high wind-driven wave tank. At wind velocity between 6-12 m/s and with the oil slide kept constant (about 1 um), the rate of the oil content increase in the water column could be approximated from the difference between the dispersion rate (R) of the oil slick and the coagulation rate (R’) of the dispersed oil slick. Assuming the coagulation rate is directly proportional to the concentration of the water dispersed oil slick (i. e. R’ =KC),, the integral form of the dynamic model can be expressed as C=R*[1-exp(-K*t)]/K and parameters R and K can be regressed with a computer. The relative deviation of model results from the experimental data was mainly less than 10%. The oil slick dispersion rate (R) had exponential relationship with the wind velocity (V), and can be fitted with a formula R=A*(U+1)B.The fitted constant of the coagulation rate, K(0.8-3.0* 10-3 min-1) did not have significant展开更多
The increase of wave energy in electricity production is an objective shared by many countries to meet growing demand and global warming. To analyze devices capable of converting the energy of sea waves into electrica...The increase of wave energy in electricity production is an objective shared by many countries to meet growing demand and global warming. To analyze devices capable of converting the energy of sea waves into electrical energy, it is important to master the various theories of gravity waves and generation. We will in our work consider a numerical waves tank for an amplitude A=0.5, a wavelength λ=0.25 , an average height H<sub>e</sub>=10 and a Froude number fixed at 1 × 10<sup>5</sup>. Numerical wave channel analysis is used to reproduce the natural phenomenon of wave propagation in an experimental model. Wave makers are usually used to generate waves in the channel. In theory, the influence of an incident wave can be considered, as in the case of our study. In this study, the evolution of the hydrodynamic parameters and the energy transported in one wavelength can be determined by calculation. A change of variable will be done in this work to facilitate the writing of the boundary conditions at the free surface and at the bottom. The nonlinear Stokes theory will be studied in this case in order to provide hydrodynamic solutions through the Navier-Stokes equations to finally deduce the energetic results. To do this, the finite difference method will be used for the hydrodynamic results such as the velocity potential and the free surface elevation and the trapezium method of Newton for the energetic results. Thus, we will determine the energetic potential according to the decrease in the slope of the tank. To do this, we will take as values of beta representing the inverse of the slope of the tank, β=100, β=105, β=110 and β=105. .展开更多
Oscillating Water Column (OWC) wave energy converting system is one of the most widely used facilities all over the world. The air chamber is utilized to convert the wave energy into the pneumatic energy. The numeri...Oscillating Water Column (OWC) wave energy converting system is one of the most widely used facilities all over the world. The air chamber is utilized to convert the wave energy into the pneumatic energy. The numerical wave tank based on the two-phase VOF model is established in the present study toinvestigate the operating performance of OWC air chamber. The RANS equations, standard k-ε turbulence model and dynamic mesh technology are employed in the numerical model. The effects of incident wave conditions and shape parameters on the wave energy converting efficiency are studied and the capability of the present numerical wave tank on the corresponding engineering application is validated.展开更多
In the present study, Kriebel' s method is improved to generate freak waves in laboratory. The improved method superposes a random wave train with two transient wave trains to simulate freak wave events in a wave tan...In the present study, Kriebel' s method is improved to generate freak waves in laboratory. The improved method superposes a random wave train with two transient wave trains to simulate freak wave events in a wave tank. The freak waves are more nonlinear than what generated with Kriebel' s method of the same energy. It can 'also generate freak waves to satisfy all the qualifications of the adopted definition with less energy than Kriebel' s and can hardly influence the significant wave height.展开更多
文摘A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simply Rankine source, the resulting boundary integral equation is repeatedly solved at each time step and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A smooth technique is also adopted in order to eliminate the possible saw-tooth numerical instabilities. The incident wave at the uptank is given as theoretical wave in this paper. The outgoing waves are absorbed inside a damping zone by spatially varying artificial damping on the free surface at the wave tank end. The numerical results show that the NWT developed by these approaches has a high accuracy and good numerical stability.
文摘A fully nonlinear numerical wave tank based on the solution of the σ-transformed Navier-Stokes equation is developed in this study. The numerical wave is generated from the inflow boundary, where the surface elevation and/or velocity are specified by use of the analytical solution or the laboratory data. The Sommerfeld/Orlanski radiation condition in conjunction with an artificial damping zone is applied to reduce wave reflection from the outflow boundary. The whole numerical solution procedures are split into three steps, i.e., advection, diffusion and propagation, and a new method, the Lagrange-Euler Method, instead of the MAC or VOF method, is introduced to solve the free surface elevation at the new time step. Several typical wave cases, including solitary waves, regular waves and irregular waves, are simulated in the wave tank. The robustness and accuracy of the NWT are verified by the good agreement between the numerical results and the linear or nonlinear analytical solutions. This research will be further developed by study of wave-wave, wave-current, wave-structure or wave-jet interaction in the future.
文摘Freak waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank. To set up the nonlinear numerical wave tank, the Boundary Element Method is used to solve potential flow equations incorporated with fully nonlinear free surface boundary conditions. The nonlinear properties of freak waves, such as high frequency components and wave profile asymmetry, are discussed. The kinematic data, which can be useful for the evaluation of the wave forces exerted on structures to avoid underestimation of linear predictions, are obtained, and discussed, from the simulated results of freak waves.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41106019 and 41176016)the Public Science and Technology Research Funds Projects of Ocean(Grant No.201105018)the Scientific Research Fund of the Second Institute of Oceanography,SOA(Grant No.JT1205)
文摘A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra: constant amplitude spectrum, constant steepness spectrum and Pierson-Moscowitz spectrum. Numerical tests are performed to validate the model results. Then, the onset of wave breaking is discussed with geometric, kinematic, and dynamic breaking criteria. The strength of wave breaking, which is always characterized by the fractional energy loss and breaking strength coefficient, is studied for different spectra. The results show how the energy growth rate is better than the initial wave steepness on estimating the fractional energy losses as well as breaking strength coefficient.
文摘A two-dimensional (2D) numerical model is developed for the wave sim- ulation and propagation in a wave flume. The fluid flow is assumed to be viscous and incompressible, and the Navier-Stokes and continuity equations are used as the governing equations. The standard k-e model is used to model the turbulent flow. The Navier- Stokes equations are discretized using the staggered grid finite difference method and solved by the simplified marker and cell (SMAC) method. Waves are generated and propagated using a piston type wave maker. An open boundary condition is used at the end of the numerical flume. Some standard tests, such as the lid-driven cavity, the constant unidirectional velocity field, the shearing flow, and the dam-break on the dry bed, are performed to valid the model. To demonstrate the capability and accuracy of the present method, the results of generated waves are compared with available wave theories. Finally, the clustering technique (CT) is used for the mesh generation, and the best condition is suggested.
文摘The modeling of generation and subsequent propagation of irregular waves in a numerical wave flume is performed by mean of the boundary element method. Random waves are generated by a piston-type wave generator at one end of the flume with the Mitsuyasu-Bretschneider spectrum used as the target spectrum for the generation. An artificial absorbing beach is placed at the other end of the flume to minimize wave reflection. Surface fluctuations are described by use of the Lagrangian description, and finite difference is adopted for the approximation of time derivative. To monitor the developments of the waves, a number of pseudo wave gauges are installed along the tank. Through comparison of the spectra from those gauges with the target spectrum, satisfactory results can be obtained from the present numerical scheme.
基金supported by the Key Programof the National Natural Science Foundation of China(GrantNo.50639020)the National High Technology Research and Development Program of China(863 Program,Gtant No.2006AA09Z332)the Special Fund of State Key Laboratory of Ocean Engineering of China
文摘A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank, which is established on Computational Fluid Dynamics (CFD) theories. The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out. The added mass and damping coefficients are obtained by the decomposition of the computational results, which agree well with the corresponding ones of potential theories.
基金The authors wish to express their gratitude for the financial aid of the National Science Council, China.Project Nos. NSC-89-2611-E-019-027(CRC)and NSC-89-2611-E-019-058(JZY).
文摘A numerical wave tank with passive absorption for irregular waves is considered in this paper. Waves with spectral shapes corresponding to that of the Mitsuyasu- Bretschneider type are used as the initial condition at one end of the flume, An absorbing boundary is imposed at the other end of the wave flume to minimize reflection. By use of a Lagrangian description for the Surface elevation, and finite difference for approximation of the time derivative, the problem is then solved by the boundary element method, The effects of the absorbing boundary are investigated by varying the values of the absorption coefficient mu, and studying the time histories of the Surface elevations 'recorded' on pre-selected locations.
基金financially supported by the National Natural Science Foundation of China(Grant No.51239007)
文摘Recently the numerical wave tank has become a widely-used tool to study waves as well as wave-structure interactions, and the wave-absorbing method is very important as its effect on the quality of waves generated. The relaxation method and the derived momentum source method are often utilized, however, the damping weight is constant during calculation and repeated trials are required to obtain an acceptable wave-absorbing effect. To address the abovementioned issues, a conserved wave-absorbing method is developed. The damping weight is determined by solving the mass conservation equation of the absorbing region at every time step. Based on this method, a two-dimensional numerical wave tank is established by using the VB language to simulate various waves by which the validation of this method is evaluated.
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.
基金Project supported by the National Natural Science Foundation of China(Grant No.51179122)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621092).
文摘A 2-D numerical wave tank(NWT)is developed using the lattice Boltzmann method(LBM)and a multi-relaxation-time(MRT)collision model coupled with an algebraic volume of fluid(VOF)scheme for free surface tracking.An external force based on the momentum source function is used to generate the waves,and a zone of porous media is used to absorb the waves.Numerical simulations of the progressive and standing waves show that the NWT can generate stable wave trains in agreement with the analytical solutions and eliminate the re-reflection waves.The NWT is used to simulate two problems encountered in practice,namely:the wave transformation over a submerged breakwater and the wave runup on a sea dike.The numerical predictions are in good agreement with the measured data.
基金This work is supported by Lloyd’s Register Foundation(LRF)through the joint centre involving University College London,Shanghai Jiaotong University and Harbin Engineer-ing University,to which the authors are most grateful.Lloyd’s Register Foundation helps to protect life and property by sup-porting engineering-related education,public engagement and the application of researchThe first author acknowledges the scholarship sponsored by the Erasmus Mundus Europe Asia(EMEA)scholarship pro-gramme,Faculty of Engineering of University College Lon-don and the Henry Lester Trust LtdThe second author ac-knowledges the financial support by the China Scholarship Council(CSC)(no.201206680001).
文摘A third-order KdV solution to the internal solitary wave is derived by a new method based on the weakly nonlinear assumptions in a rigid-lid two-layer system.The solution corrects an error by Mirie and Su(1984).A two-dimensional numerical wave tank has been established with the help of the open source CFD library OpenFOAM and the third-party software waves2Foam.Various analytical solutions,including the first-order to third-order KdV solutions,the eKdV solution and the MCC solution,have been used to initialise the flow fields in the CFD simulations of internal solitary waves.Two groups including 11 numerical cases have been carried out.In the same group,the initial wave amplitudes are the same but the implemented analytical solutions are different.The simulated wave profiles at different moments have been presented.The relative errors in terms of the wave amplitude between the last time step and the initial input have been analysed quantitatively.It is found that the third-order KdV solution results in the most stable internal solitary wave in the numerical wave tank for both small-amplitude and finite-amplitude cases.The finding is significant for the further simulations involving internal solitary waves.
基金the National Natural Science Foundation of China(Nos.50979059 and 11272213)
文摘Moving-particle semi-implicit(MPS) method is a new mesh-free numerical method based on Lagrangian particle. In this paper, MPS method is applied to the study on numerical wave tank. For the purpose of simulating numerical wave, we combine the MPS method with large eddy simulation(LES) which can simulate the turbulence in the flow. The intense pressure fluctuation is a significant shortcoming in MPS method. So, we improve the original MPS method by using a new pressure Poisson equation to ease the pressure fluctuation. Divergencefree condition representing fluid incompressible is used to calculate pressure smoothly. Then, area-time average technique is used to deal with the calculation. With these improvements, the modified MPS-LES method is applied to the simulation of numerical wave. As a contrast, we also use the original MPS-LES method to simulate the wave in a numerical wave tank. The result shows that the new method is better than the original MPS-LES method.
文摘A dynamic experiment for oil dispersion into a water column was performed with a 21 m long, 0.5 m wide, and 1 m high wind-driven wave tank. At wind velocity between 6-12 m/s and with the oil slide kept constant (about 1 um), the rate of the oil content increase in the water column could be approximated from the difference between the dispersion rate (R) of the oil slick and the coagulation rate (R’) of the dispersed oil slick. Assuming the coagulation rate is directly proportional to the concentration of the water dispersed oil slick (i. e. R’ =KC),, the integral form of the dynamic model can be expressed as C=R*[1-exp(-K*t)]/K and parameters R and K can be regressed with a computer. The relative deviation of model results from the experimental data was mainly less than 10%. The oil slick dispersion rate (R) had exponential relationship with the wind velocity (V), and can be fitted with a formula R=A*(U+1)B.The fitted constant of the coagulation rate, K(0.8-3.0* 10-3 min-1) did not have significant
文摘The increase of wave energy in electricity production is an objective shared by many countries to meet growing demand and global warming. To analyze devices capable of converting the energy of sea waves into electrical energy, it is important to master the various theories of gravity waves and generation. We will in our work consider a numerical waves tank for an amplitude A=0.5, a wavelength λ=0.25 , an average height H<sub>e</sub>=10 and a Froude number fixed at 1 × 10<sup>5</sup>. Numerical wave channel analysis is used to reproduce the natural phenomenon of wave propagation in an experimental model. Wave makers are usually used to generate waves in the channel. In theory, the influence of an incident wave can be considered, as in the case of our study. In this study, the evolution of the hydrodynamic parameters and the energy transported in one wavelength can be determined by calculation. A change of variable will be done in this work to facilitate the writing of the boundary conditions at the free surface and at the bottom. The nonlinear Stokes theory will be studied in this case in order to provide hydrodynamic solutions through the Navier-Stokes equations to finally deduce the energetic results. To do this, the finite difference method will be used for the hydrodynamic results such as the velocity potential and the free surface elevation and the trapezium method of Newton for the energetic results. Thus, we will determine the energetic potential according to the decrease in the slope of the tank. To do this, we will take as values of beta representing the inverse of the slope of the tank, β=100, β=105, β=110 and β=105. .
基金supported by the National Natural Science Foundation of China(Grant Nos. 50909089 and 40911140281)Qingdao S&T Development Program(09-1-3-41-jch)Korean Ministry of Land,Transport & Maritime Affairs through KORDI Program
文摘Oscillating Water Column (OWC) wave energy converting system is one of the most widely used facilities all over the world. The air chamber is utilized to convert the wave energy into the pneumatic energy. The numerical wave tank based on the two-phase VOF model is established in the present study toinvestigate the operating performance of OWC air chamber. The RANS equations, standard k-ε turbulence model and dynamic mesh technology are employed in the numerical model. The effects of incident wave conditions and shape parameters on the wave energy converting efficiency are studied and the capability of the present numerical wave tank on the corresponding engineering application is validated.
基金The project was supported by the Key Foundation of Ministry of Education of China (Grant No104061)
文摘In the present study, Kriebel' s method is improved to generate freak waves in laboratory. The improved method superposes a random wave train with two transient wave trains to simulate freak wave events in a wave tank. The freak waves are more nonlinear than what generated with Kriebel' s method of the same energy. It can 'also generate freak waves to satisfy all the qualifications of the adopted definition with less energy than Kriebel' s and can hardly influence the significant wave height.