The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmara...The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmaras(SA)turbulence model and Schnerr-Sauer cavitation model,to simulate the cavitating flow around a three-dimension twisted hydrofoil.The accuracy of simulation is accessed by examining the power spectral density of pressure fluctuations and the percentage of resolved turbulent kinetic energy.The simulated cavitation behavior is compared with experimental observation in terms of shedding patterns and frequencies.The cavitation-radiated noise,computed via the porous Ffowcs-Williams and Hawkings(PFWH)method,is subsequently calculated.Strategies for setting different integral surfaces are discussed.An analysis of sound pressure and cavity evolution patterns for a typical cycle elucidates the correlation between the dynamic characteristics of the cavity and the noise properties.The simulation addresses the lack of experimental data,which poses challenges due to the need for numerous hydrophones and the elimination of tunnel wall effects.The combination of the PFWH source surface and the original FW-H source surface facilitates the investigation of various noise sources.The results indicate that the pseudo-thickness term approximates a monopole noise associated with cavity volume acceleration,the loading term resembles a dipole,and the quadrupole term can be obtained by subtracting from the total sound pressure.The sound pressure levels at the monitoring points reveal that the monopole term predominates,followed by the quadrupole term,with the dipole term registering the lowest values.展开更多
Wind turbines(WTs)face a high risk of failure due to environmental factors like erosion,particularly in high-precipitation areas and offshore scenarios.In this paper we introduce a novel computational tool for the fas...Wind turbines(WTs)face a high risk of failure due to environmental factors like erosion,particularly in high-precipitation areas and offshore scenarios.In this paper we introduce a novel computational tool for the fast prediction of rain erosion damage on WT blades that is useful in operation and maintenance decision making tasks.The approach is as follows:Pseudo-Direct Numerical Simulation(P-DNS)simulations of the droplet-laden flow around the blade section profile are employed to build a high-fidelity data set of impact statistics for potential operating conditions.Using this database as training data,a machine learning-based surrogate model provides the feature of the impact pattern over the 2-D section for given wind and rain conditions.With this information,a fatigue-based model estimates the remaining lifetime and erosion damage for both homogeneous and coating-substrate blade materials.This prediction is done by quantifying the accumulated droplet impact energy and evaluating operative conditions over time periods for which the weather at the installation site is known.In this work,we describe the modules that compose the prediction method,namely the database creation,the training of the surrogate model and their coupling to build the prediction tool.Then,the method is applied to predict the remaining lifetime and erosion damage to the blade sections of a reference WT.To evaluate the reliability of the tool,several site locations(offshore,coastal,and inland),the coating material and the coating thickness of the blade are investigated.In few minutes we are able to estimate erosion after many years of operation.The results are in good agreement with field observations,showing the promise of the new rain erosion prediction approach.展开更多
Either potential flow or viscous flow based model may be flawed for numerical wave simulations.The two-way coupling of potential and viscous flow models with the domain decomposition utilizing respective strengths has...Either potential flow or viscous flow based model may be flawed for numerical wave simulations.The two-way coupling of potential and viscous flow models with the domain decomposition utilizing respective strengths has been a trending research topic.In contrast to existing literatures in which closed source potential models were used,the widely used open source OceanWave3D,OpenFOAM-v2012 are used in the present research.An innovative overlapping two-way coupling strategy is developed utilizing the ghost points in OceanWave3D.To guarantee computational stability,a relaxation zone used both for outlet damping and data transfer is built over the overlapping region in OceanWave3D.The free surface elevation in the relaxation zone is directly probed in OpenFOAM while the velocity potential is indirectly built upon its temporal variation which is calculated by the free surface boundary condition using the probed velocity.Strong coupling is achieved based on the fourth-order Runge-Kutta(RK)algorithm.Both two-and three-dimensional tests including linear,nonlinear,irregular,and multi-directional irregular waves,are conducted.The effectiveness of the coupling procedure in bidirectional data transfer is fully demonstrated,and the model is validated to be accurate and efficient,thus providing a competitive alternative for ocean wave simulations.展开更多
The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river.So far,few studies have been conducted to investigate the suspended se...The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river.So far,few studies have been conducted to investigate the suspended sediment transport capacity in the vegetated sediment-laden flow.In this study,a new formula is derived to predict the sediment transport capacity in a vegetated flow by considering the absolute value of the energy loss between the sediment-laden flow and the clear water flow.Finally,the formula is expressed in a practical form by using the logarithmic matching method.展开更多
In this paper, the large eddy simulation (LES) method in conjunction with the Zwart cavitation model is adopted for the assessment of the erosion risk on a hydrofoil surface. The numerical results are in good agreemen...In this paper, the large eddy simulation (LES) method in conjunction with the Zwart cavitation model is adopted for the assessment of the erosion risk on a hydrofoil surface. The numerical results are in good agreement with the experiments. On this basis, three methods, namely the intensity function method (IFM), the time-averaged aggressiveness indicators (TAIs) and the gray level method (GLM), are applied for the assessment of the erosion risk. It is shown that the erosion intensity index of the IFM is extremely sensitive to the artificially selected thresholds, which greatly limits the application of the method. The erosion risk predicted by four indicators in the TAIs does not agree well with the experimental results. Further analysis demonstrates that the GLM using the instantaneous pressure field is relatively satisfactory, which can provide a reasonable assessment of the erosion and is not very sensitive to the artificially selected thresholds. To further improve the accuracy of the GLM for the erosion risk prediction, the time-average pressure field is adopted in the GLM for the erosion evaluation. It is suggested that the erosion assessment by using the time-averaged pressure field is in better agreement with the experimental results when compared with that by using the instantaneous pressure field.展开更多
Wash waves produced by ships disintegrate river banks and coastal lines. This phenomenon of bank erosion is mainly due to the height of the waves. Various factors govern the formation of these waves and their amplitud...Wash waves produced by ships disintegrate river banks and coastal lines. This phenomenon of bank erosion is mainly due to the height of the waves. Various factors govern the formation of these waves and their amplitudes: the geometry of the water channel, the shape and the speed of the boat, etc.. These factors play an important role on the wave generation, in addition on the resistance of the ship and so on its fuel consumption. Whether to study the impact of wash waves on the ship's environment or its resistance, the analysis of the generated wake is essential. Hence a fine characterization of the wave field is necessary. This study proposes a comparison of wakes generated by two generic ships based on a Wigley hull with block coefficients 0.67 and 0.89 respectively representative of maritime and fluvial ships. The wakes generated in deep water and confined water configurations have been measured for different Froude numbers by a non-intrusive optical stereo-correlation method, giving access to a detailed and complete definition of the generated wave fields. The resistance of the ship hulls has been measured in deep and confined water configurations with a hydrodynamic balance. The results permit one to study the influence of both hull and water channel geometries on the ship wake, on the amplitude of the far-field generated waves and on the near-field hydrodynamic response. Moreover, resistance curves are obtained for both configurations and highlight the effect of both hull and water channel geometries on the resistance coefficient of the ship. A comparison of the resistance curves with or without the ship trim is conducted and shows the influence of the trim on the resistance coefficient in the different ship speed regimes.展开更多
The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut ...The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut on pressure pulsations of a low specific speed centrifugal pump,three volute tongues are obtained through twice cuts,named cases 1,2,3.Twenty measuring points are evenly mounted on periphery of the volute casing to obtain unsteady pressure signals using high response transducers.Pressure amplitudes at the blade passing frequency fBPF and root mean square(rms)values in 0 Hz-500 Hz frequency band are applied to evaluate the cutting effect.Results show that pressure spectrum is significantly affected by the volute tongue cut,especially for the component at fBPF.For different measuring points,influences of the volute tongue cut on three cases are not identical.From nns values,it is evident that cutting the volute tongue will lead to pressure energy increasing for most of the concerned measuring points,especially for the points at the far away region from the volute tongue.Finally,from comparison with the original shape case 1,the averaged increment of the twenty points is more than 20%.So it is concluded that for this type centrifugal pump,cutting the volute tongue is not reasonable considering low pressure pulsation requirement.展开更多
The fundamental solutions of the Stokes/Oseen equations due to a point force in an unbounded viscous fluid are referred to as the Stokeslet/Oseenlet,for which a systematic derivation are analytically presented here in...The fundamental solutions of the Stokes/Oseen equations due to a point force in an unbounded viscous fluid are referred to as the Stokeslet/Oseenlet,for which a systematic derivation are analytically presented here in terms of a uniform expression.By means of integral transforms,the closed-form solutions are explicitly deduced in a formula which involves the Hamiltonian,Hessian,and Laplacian operators,and elementary functions.Secondly,interfacial viscous capillary-gravity waves between two semi-infinite fluids due to oscillating singularities,including a simple source in the upper inviscid fluid and a Stokeslet in the low viscous fluid,were analytically studied by the Laplace-Fourier integral transform and asymptotic analysis.The dynamics responses consist of the transient and steady-state components,which are dealt with by the method of stationary phase and the Cauchy residue theorem,respectively.The transient response is made up of one short capillarity・dominated and one long gravity-dominated wave with the former riding on the latter.The steady-state wave has the same frequency as that of oscillating singularities.Asymptotic solutions for the wave profiles and the exact solution for the wave number are analytically derived,which show the combined effects of fluid viscosity,surface capillarity and an upper layer fluid.展开更多
To control the shedding of cavitation, an obstacle is placed on the surface of a flat hydrofoil. Both experimental and numerical studies are carried out. Images of cavitation evolution are recorded by a high-speed cam...To control the shedding of cavitation, an obstacle is placed on the surface of a flat hydrofoil. Both experimental and numerical studies are carried out. Images of cavitation evolution are recorded by a high-speed camera. 3-D simulations are performed to investigate the cavitating flows around the hydrofoil. The results show that the re-entrant jet plays an important role during the process of cavitation shedding. A kind of U-type shedding is identified during the evolution of the cloud cavitation. The length of the cavity is apparently reduced due to the placement of the obstacle. It is interesting to find that the cavitation shedding changes from the large-scale mode to a small-scale mode, as an obstacle is placed on the hydrofoil surface. As we can observe from both experimental and numerical results, the small-scale cavitation shedding dominates the cavitating flow dynamics, we thereby conclude that the placement of an obstacle is favorable for the inhibition of cavitation shedding.展开更多
Almost everything I have done in the last twenty years is based on what I have discovered from studying ocean phenomena.Specifically,the waves on the surface of the ocean and their dynamics.Two items stand out:The fir...Almost everything I have done in the last twenty years is based on what I have discovered from studying ocean phenomena.Specifically,the waves on the surface of the ocean and their dynamics.Two items stand out:The first one is from studying the evolution of the waves from ripples to fully developed giant ocean waves.To quantify the changes,I found that frequency is very different from what had been defined traditionally through Fourier analysis.Ture frequency should be determined by difterentiation of the phase function defined by an adaptive method rather than by any form of integral transform.Therefore,it should have ever changing instantaneous values.The second discovery is from studying wave turbulence interactions.To reveal the detailed dynamics,I found that spectral representation should not be a single line on the frequency and energy plane.True spectrum should be a high dimensional manifold to cover all the possible dynamic interactions:additive and multiplicative ones.These discoveries have enabled me to develop a set of nonlinear and nonstationary data analysis tools to study many other phenomena,from turbulence to brain waves.They have led me to new wonders I have never even contemplated before.展开更多
As a classical topic,the hydrodynamic forces on a submerged horizontal cylinder undergoing forced oscillation have been widely studied based on potential flow theory.However,the fluid viscosity and the flow rotation m...As a classical topic,the hydrodynamic forces on a submerged horizontal cylinder undergoing forced oscillation have been widely studied based on potential flow theory.However,the fluid viscosity and the flow rotation may play an important role when the oscillation amplitude of the circular cylinder is large,and large discrepancy will occur between the potential flow simulation and the experimental results.This study focuses on the study of hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation by means of a viscous fluid numerical wave tank(NWT)model.The accuracy of the numerical model is validated against available experimental data.The comparisons between the hydrodynamic forces on the circular cylinder predicted by the viscous fluid model and the potential flow model are conducted to show the viscous effects on the hydrodynamic forces.By the study on the flow fields,the mechanism of the viscous effects is explained by the vortex effect.The basic reason for the difference between the results based on the viscous fluid theory and the potential flow theory is revealed by analyzing the force components.展开更多
This paper studies the dynamics of a multi-module floating airport with flexible connectors using the network theory. A mathematical model for a chain-type topology structure is developed by using the wave theory, and...This paper studies the dynamics of a multi-module floating airport with flexible connectors using the network theory. A mathematical model for a chain-type topology structure is developed by using the wave theory, and the models of a single floating module and the connector and mooring system. The nonlinear dynamics of the floating airport and the connector force are studied. A remarkable phenomenon of amplitude death is observed, as a weak oscillation state of all floating modules, an important state for the system global dynamic stability. The parametric domain for the onset of amplitude death is identified, and the effects of the wave height and the number of the floating modules on the dynamic stability are discussed. An application of the network theory in the marine engineering is illustrated with the introduction of a new concept for global dynamic stability for the floating airport.展开更多
This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or t...This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or the ice jam release events.The flume model experimental and numerical simulation methods are both applied to analyze the stability of submerged ice blocks.The flume model experiment is first conducted,and the experimental results indicate that the influencing factors of the stability of a submerged ice block include the relative length,the relative water depth and the relative width.It was shown that the effect of the relative width on the stability of submerged ice blocks was not well studied.Based on the experimental results,the k-eturbulence model is applied to establish a 3-D numerical model for studying the pressure distribution beneath submerged ice blocks.The effects of the relative width on the Venturi pressure and the leading edge pressure are evaluated.Finally,according to the force balance equation and the moment balance equation,this paper proposes a computational formula for the sliding and underturning critical conditions of submerged ice blocks,and the results are in good agreement with the experimental results.展开更多
The previous model for the boundary layer nanofluid flow past a stretching surface with a specified nanoparticle volume fraction on the surface is revisited.The major limitation of the previous model is the active con...The previous model for the boundary layer nanofluid flow past a stretching surface with a specified nanoparticle volume fraction on the surface is revisited.The major limitation of the previous model is the active control of the nanoparticle volume fraction on the surface.In a revised model proposed in this paper,the nanoparticle volume fraction on the surface is passively controlled,which accounts for the effects of both the Brownian motion and the thermophoresis under the boundary condition,whereas the Buongiorno＇s model considers both effects in the governing equations.The assumption of zero nanoparticle flux on the surface makes the model physically more realistic.In the revised model,the dimensionless heat transfer rates are found to be higher whereas the dimensionless mass transfer rates are identically zero due to the passive boundary condition.It is also found that the Brownian motion parameter has a negligible effect on the Nusselt number.展开更多
In this paper, we investigate the implications of electro-osmosis on electrohydrodynamic transport of a non-Newtonian fluid on a hydrophobic micro-channel by developing a suitable analytical method. Velocity-slip and ...In this paper, we investigate the implications of electro-osmosis on electrohydrodynamic transport of a non-Newtonian fluid on a hydrophobic micro-channel by developing a suitable analytical method. Velocity-slip and temperature-jump conditions are paid due attention. An attempt has been made to examine the effects of rheological and electro-osmotic parameters on the kinematics of the fluid. The nonlinear Poisson-Boltzmann equation governing the formation of the electrical double layer and the body force that is generated by the applied potential are accounted for in the study. Perturbation solutions are presented. In order to exhibit the applicability of the analysis, the problem of electro-osmotic flow and heat transfer of blood in an arteriole has been taken up as an illustrative example of a real-life problem. An intensive quantitative study has been made through numerical computation of the physical variables involved in the analysis, which are of special interest in the study. The computational results are presented graphically. The study reveals that the temperature of blood can be controlled by increasing/decreasing the Joule heating parameter.展开更多
Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of t...Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of the evolution of the flow pattern at places far from the outlet. The relationship between the hydraulic gradient and the flow velocity at different points, and the proportion evolution of the linear and nonlinear portions in the Forchheimer formula are then discussed. Three major conclusions are obtained. First, the non-Darcian flow exists in a single fracture in different laboratory tests. Better fitting accuracy is obtained by using the Forchheimer formula than by using the Darcy law. Second, the proportion of the Darcy flow increases with the increase of the observation scale. In places far enough, the Darcy flow prevails, and the critical velocity between the non-Darcian flow and the Darcy flow decreases as the fracture aperture increases. Third, when the fracture aperture increases, the critical Reynolds number between the non-Darcian flow and the Darcy flow decreases.展开更多
The contribution of the vortex Rossby wave （VRW） to framework of a barotropic non-divergent TC-like vortex model. the spiral rainband in the tropical cyclones （TCs） is studied in the The spectral function expandin...The contribution of the vortex Rossby wave （VRW） to framework of a barotropic non-divergent TC-like vortex model. the spiral rainband in the tropical cyclones （TCs） is studied in the The spectral function expanding method is used to analyze the disturbance evolution of a defined basic state vortex. The results show that the numerical solution of the model is a superposition of the continuous spectrum component （non-normal modes） and the discrete spectrum component （normal modes）. Only the eyewall and the rainbands in the inner core-region in a TC are related to the VRW normal modes, whereas the continuous spectrum wave components play an important role in the formation of secondary-, principal-, and distant- rainbands, especially the outer rainband, through an indirect way. The continuous spectrum can promote the development of the TC circulation for the occurrence of a mesoscale instability. The convection under a favorable moisture condition will trigger the inertial-gravitational wave to cause the formation of unstable spiral bandliked-disturbances outside of the eyewall. The complicated interaction between the basic state-vortex and the VRW disturbances will cause a positive feedback between the TC circulation and the rainband.展开更多
The wind-induced vibration of the front windshield concerns the traffic safety and the aerodynamic characteristics of cars. In this paper, the numerical simulation and the experiment are combined to study the wind-ind...The wind-induced vibration of the front windshield concerns the traffic safety and the aerodynamic characteristics of cars. In this paper, the numerical simulation and the experiment are combined to study the wind-induced vibrations of the front windshield at different speeds of a van-body model bus. The Fluid-Structure Interaction （FSI） model is used for the finite element analysis of the vibration characteristics of the front windshield glass in the travelling process, and the wind-induced vibration response characteristics of the glass is obtained. A wind-tunnel experiment with an eddy current displacement sensor is carried out to study the deformation of the windshield at different wind speeds, and to verify the numerical simulation results. It is shown that the windshield of the model bus windshield undergoes a noticeable deformation as the speed changes, and from the deformation curve obtained, it is seen that in the accelerating process, the deformation of the glass increases as the speed increases, and with the speed being stablized, it also tends to a certain value. The results of this study can provide a scientific basis for the safety design of the windshield and the body.展开更多
Hydrodynamic effects play a very important role in the contaminants release from sediments. Experiments were performed to study contaminants releasing characteristics due to resuspension. The time-dependent variation ...Hydrodynamic effects play a very important role in the contaminants release from sediments. Experiments were performed to study contaminants releasing characteristics due to resuspension. The time-dependent variation of COD concentration and relative roles under static and dynamic state of the overlying water were analyzed. Experimental results showed that COD concen- tration in the water column got a striking increment on the dynamic conditions, mainly by reducing the thickness of concentration boundary layer near sediment-water interface and destructing the surface structure of sediment. Hydrodynamics increased contamina- nts release rates and flux in unit time. Before reaching an equilibrium stage, the dynamic release caused by the resuspension was more effective than static one due to molecular diffusion. The release rate of COD increased with flow velocity and decreased with water depth. But at a shallow water depth, wave effects would dominate the causing resuspension, resulting in contaminants release in large quantity. The intensity of pollutant release increased with time in a rather circuitous process. The diffusion of pollutant from internal sediment to the sediment-water interface would maintain the endogenous release effects.展开更多
基金Project supported by the Fundamental Research Project(Grant No.909120103),the National Natural Science Foundation of China(Grant Nos.92252205,11802275 and 12172219).
文摘The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations.In the present work,we employ the improved delayed detached eddy simulation(IDDES),coupled with Spalart-Allmaras(SA)turbulence model and Schnerr-Sauer cavitation model,to simulate the cavitating flow around a three-dimension twisted hydrofoil.The accuracy of simulation is accessed by examining the power spectral density of pressure fluctuations and the percentage of resolved turbulent kinetic energy.The simulated cavitation behavior is compared with experimental observation in terms of shedding patterns and frequencies.The cavitation-radiated noise,computed via the porous Ffowcs-Williams and Hawkings(PFWH)method,is subsequently calculated.Strategies for setting different integral surfaces are discussed.An analysis of sound pressure and cavity evolution patterns for a typical cycle elucidates the correlation between the dynamic characteristics of the cavity and the noise properties.The simulation addresses the lack of experimental data,which poses challenges due to the need for numerous hydrophones and the elimination of tunnel wall effects.The combination of the PFWH source surface and the original FW-H source surface facilitates the investigation of various noise sources.The results indicate that the pseudo-thickness term approximates a monopole noise associated with cavity volume acceleration,the loading term resembles a dipole,and the quadrupole term can be obtained by subtracting from the total sound pressure.The sound pressure levels at the monitoring points reveal that the monopole term predominates,followed by the quadrupole term,with the dipole term registering the lowest values.
基金supported by the CERCA programme of the Generalitat de Catalunya,and the Spanish Ministry of Economy and Competitiveness through the“Severo Ochoa Programme for Centres of Excellence in Research and Development”(Grant No.CEX2018-000797-S)Also,the authors acknowledge MCIN/AEI and FEDER Una manera de hacer Europa for funding this work via(Grant No.PID2021-122676NB-I00)。
文摘Wind turbines(WTs)face a high risk of failure due to environmental factors like erosion,particularly in high-precipitation areas and offshore scenarios.In this paper we introduce a novel computational tool for the fast prediction of rain erosion damage on WT blades that is useful in operation and maintenance decision making tasks.The approach is as follows:Pseudo-Direct Numerical Simulation(P-DNS)simulations of the droplet-laden flow around the blade section profile are employed to build a high-fidelity data set of impact statistics for potential operating conditions.Using this database as training data,a machine learning-based surrogate model provides the feature of the impact pattern over the 2-D section for given wind and rain conditions.With this information,a fatigue-based model estimates the remaining lifetime and erosion damage for both homogeneous and coating-substrate blade materials.This prediction is done by quantifying the accumulated droplet impact energy and evaluating operative conditions over time periods for which the weather at the installation site is known.In this work,we describe the modules that compose the prediction method,namely the database creation,the training of the surrogate model and their coupling to build the prediction tool.Then,the method is applied to predict the remaining lifetime and erosion damage to the blade sections of a reference WT.To evaluate the reliability of the tool,several site locations(offshore,coastal,and inland),the coating material and the coating thickness of the blade are investigated.In few minutes we are able to estimate erosion after many years of operation.The results are in good agreement with field observations,showing the promise of the new rain erosion prediction approach.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52101324,52131102,51879159 and 52131102)the National Key Research and Development Program of China(Grant No.2019YFB1704200).
文摘Either potential flow or viscous flow based model may be flawed for numerical wave simulations.The two-way coupling of potential and viscous flow models with the domain decomposition utilizing respective strengths has been a trending research topic.In contrast to existing literatures in which closed source potential models were used,the widely used open source OceanWave3D,OpenFOAM-v2012 are used in the present research.An innovative overlapping two-way coupling strategy is developed utilizing the ghost points in OceanWave3D.To guarantee computational stability,a relaxation zone used both for outlet damping and data transfer is built over the overlapping region in OceanWave3D.The free surface elevation in the relaxation zone is directly probed in OpenFOAM while the velocity potential is indirectly built upon its temporal variation which is calculated by the free surface boundary condition using the probed velocity.Strong coupling is achieved based on the fourth-order Runge-Kutta(RK)algorithm.Both two-and three-dimensional tests including linear,nonlinear,irregular,and multi-directional irregular waves,are conducted.The effectiveness of the coupling procedure in bidirectional data transfer is fully demonstrated,and the model is validated to be accurate and efficient,thus providing a competitive alternative for ocean wave simulations.
基金the Natural Science Foundation of China(Grant Nos.52020105006,11872285)the UK Royal Society-International Exchanges Program(Grant No.IESIR2\181122)the Open Funding of the State Key Laboratory of Water Resources and Hydropower Engineering Science(WRHES)and the Wuhan University(Grant No.2018HLG01).
文摘The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river.So far,few studies have been conducted to investigate the suspended sediment transport capacity in the vegetated sediment-laden flow.In this study,a new formula is derived to predict the sediment transport capacity in a vegetated flow by considering the absolute value of the energy loss between the sediment-laden flow and the clear water flow.Finally,the formula is expressed in a practical form by using the logarithmic matching method.
基金Projects supported by the National Natural Science Foundation of China (Grant Nos.51822903, 11772239 and 11772305).
文摘In this paper, the large eddy simulation (LES) method in conjunction with the Zwart cavitation model is adopted for the assessment of the erosion risk on a hydrofoil surface. The numerical results are in good agreement with the experiments. On this basis, three methods, namely the intensity function method (IFM), the time-averaged aggressiveness indicators (TAIs) and the gray level method (GLM), are applied for the assessment of the erosion risk. It is shown that the erosion intensity index of the IFM is extremely sensitive to the artificially selected thresholds, which greatly limits the application of the method. The erosion risk predicted by four indicators in the TAIs does not agree well with the experimental results. Further analysis demonstrates that the GLM using the instantaneous pressure field is relatively satisfactory, which can provide a reasonable assessment of the erosion and is not very sensitive to the artificially selected thresholds. To further improve the accuracy of the GLM for the erosion risk prediction, the time-average pressure field is adopted in the GLM for the erosion evaluation. It is suggested that the erosion assessment by using the time-averaged pressure field is in better agreement with the experimental results when compared with that by using the instantaneous pressure field.
文摘Wash waves produced by ships disintegrate river banks and coastal lines. This phenomenon of bank erosion is mainly due to the height of the waves. Various factors govern the formation of these waves and their amplitudes: the geometry of the water channel, the shape and the speed of the boat, etc.. These factors play an important role on the wave generation, in addition on the resistance of the ship and so on its fuel consumption. Whether to study the impact of wash waves on the ship's environment or its resistance, the analysis of the generated wake is essential. Hence a fine characterization of the wave field is necessary. This study proposes a comparison of wakes generated by two generic ships based on a Wigley hull with block coefficients 0.67 and 0.89 respectively representative of maritime and fluvial ships. The wakes generated in deep water and confined water configurations have been measured for different Froude numbers by a non-intrusive optical stereo-correlation method, giving access to a detailed and complete definition of the generated wave fields. The resistance of the ship hulls has been measured in deep and confined water configurations with a hydrodynamic balance. The results permit one to study the influence of both hull and water channel geometries on the ship wake, on the amplitude of the far-field generated waves and on the near-field hydrodynamic response. Moreover, resistance curves are obtained for both configurations and highlight the effect of both hull and water channel geometries on the resistance coefficient of the ship. A comparison of the resistance curves with or without the ship trim is conducted and shows the influence of the trim on the resistance coefficient in the different ship speed regimes.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51706086,51576090).
文摘The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut on pressure pulsations of a low specific speed centrifugal pump,three volute tongues are obtained through twice cuts,named cases 1,2,3.Twenty measuring points are evenly mounted on periphery of the volute casing to obtain unsteady pressure signals using high response transducers.Pressure amplitudes at the blade passing frequency fBPF and root mean square(rms)values in 0 Hz-500 Hz frequency band are applied to evaluate the cutting effect.Results show that pressure spectrum is significantly affected by the volute tongue cut,especially for the component at fBPF.For different measuring points,influences of the volute tongue cut on three cases are not identical.From nns values,it is evident that cutting the volute tongue will lead to pressure energy increasing for most of the concerned measuring points,especially for the points at the far away region from the volute tongue.Finally,from comparison with the original shape case 1,the averaged increment of the twenty points is more than 20%.So it is concluded that for this type centrifugal pump,cutting the volute tongue is not reasonable considering low pressure pulsation requirement.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11872239,10602032).
文摘The fundamental solutions of the Stokes/Oseen equations due to a point force in an unbounded viscous fluid are referred to as the Stokeslet/Oseenlet,for which a systematic derivation are analytically presented here in terms of a uniform expression.By means of integral transforms,the closed-form solutions are explicitly deduced in a formula which involves the Hamiltonian,Hessian,and Laplacian operators,and elementary functions.Secondly,interfacial viscous capillary-gravity waves between two semi-infinite fluids due to oscillating singularities,including a simple source in the upper inviscid fluid and a Stokeslet in the low viscous fluid,were analytically studied by the Laplace-Fourier integral transform and asymptotic analysis.The dynamics responses consist of the transient and steady-state components,which are dealt with by the method of stationary phase and the Cauchy residue theorem,respectively.The transient response is made up of one short capillarity・dominated and one long gravity-dominated wave with the former riding on the latter.The steady-state wave has the same frequency as that of oscillating singularities.Asymptotic solutions for the wave profiles and the exact solution for the wave number are analytically derived,which show the combined effects of fluid viscosity,surface capillarity and an upper layer fluid.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11772298).
文摘To control the shedding of cavitation, an obstacle is placed on the surface of a flat hydrofoil. Both experimental and numerical studies are carried out. Images of cavitation evolution are recorded by a high-speed camera. 3-D simulations are performed to investigate the cavitating flows around the hydrofoil. The results show that the re-entrant jet plays an important role during the process of cavitation shedding. A kind of U-type shedding is identified during the evolution of the cloud cavitation. The length of the cavity is apparently reduced due to the placement of the obstacle. It is interesting to find that the cavitation shedding changes from the large-scale mode to a small-scale mode, as an obstacle is placed on the hydrofoil surface. As we can observe from both experimental and numerical results, the small-scale cavitation shedding dominates the cavitating flow dynamics, we thereby conclude that the placement of an obstacle is favorable for the inhibition of cavitation shedding.
文摘Almost everything I have done in the last twenty years is based on what I have discovered from studying ocean phenomena.Specifically,the waves on the surface of the ocean and their dynamics.Two items stand out:The first one is from studying the evolution of the waves from ripples to fully developed giant ocean waves.To quantify the changes,I found that frequency is very different from what had been defined traditionally through Fourier analysis.Ture frequency should be determined by difterentiation of the phase function defined by an adaptive method rather than by any form of integral transform.Therefore,it should have ever changing instantaneous values.The second discovery is from studying wave turbulence interactions.To reveal the detailed dynamics,I found that spectral representation should not be a single line on the frequency and energy plane.True spectrum should be a high dimensional manifold to cover all the possible dynamic interactions:additive and multiplicative ones.These discoveries have enabled me to develop a set of nonlinear and nonstationary data analysis tools to study many other phenomena,from turbulence to brain waves.They have led me to new wonders I have never even contemplated before.
基金Project supported by the Natural Science Foundation of China(Grant Nos.51490672,51761135011,51679036 and 51709038).
文摘As a classical topic,the hydrodynamic forces on a submerged horizontal cylinder undergoing forced oscillation have been widely studied based on potential flow theory.However,the fluid viscosity and the flow rotation may play an important role when the oscillation amplitude of the circular cylinder is large,and large discrepancy will occur between the potential flow simulation and the experimental results.This study focuses on the study of hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation by means of a viscous fluid numerical wave tank(NWT)model.The accuracy of the numerical model is validated against available experimental data.The comparisons between the hydrodynamic forces on the circular cylinder predicted by the viscous fluid model and the potential flow model are conducted to show the viscous effects on the hydrodynamic forces.By the study on the flow fields,the mechanism of the viscous effects is explained by the vortex effect.The basic reason for the difference between the results based on the viscous fluid theory and the potential flow theory is revealed by analyzing the force components.
基金Project supported by the National Basic Research Development Program of China(973 Program,Grant No.2013CB036104)the National Natural Science Foundation of China(Grant Nos.11472100,11702088)the High-Technology Ship Research Projects Sponsored by MIIT
文摘This paper studies the dynamics of a multi-module floating airport with flexible connectors using the network theory. A mathematical model for a chain-type topology structure is developed by using the wave theory, and the models of a single floating module and the connector and mooring system. The nonlinear dynamics of the floating airport and the connector force are studied. A remarkable phenomenon of amplitude death is observed, as a weak oscillation state of all floating modules, an important state for the system global dynamic stability. The parametric domain for the onset of amplitude death is identified, and the effects of the wave height and the number of the floating modules on the dynamic stability are discussed. An application of the network theory in the marine engineering is illustrated with the introduction of a new concept for global dynamic stability for the floating airport.
基金supported by the Funds for Creative Research Groups of China(Grant No.51321065)the Tianjin Municipal Science and Technology Project(Grant No.13JCZDJC35100)
文摘This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or the ice jam release events.The flume model experimental and numerical simulation methods are both applied to analyze the stability of submerged ice blocks.The flume model experiment is first conducted,and the experimental results indicate that the influencing factors of the stability of a submerged ice block include the relative length,the relative water depth and the relative width.It was shown that the effect of the relative width on the stability of submerged ice blocks was not well studied.Based on the experimental results,the k-eturbulence model is applied to establish a 3-D numerical model for studying the pressure distribution beneath submerged ice blocks.The effects of the relative width on the Venturi pressure and the leading edge pressure are evaluated.Finally,according to the force balance equation and the moment balance equation,this paper proposes a computational formula for the sliding and underturning critical conditions of submerged ice blocks,and the results are in good agreement with the experimental results.
基金supported by the National Natural Science Foun-dation of China(Grant No.11271023)
文摘The previous model for the boundary layer nanofluid flow past a stretching surface with a specified nanoparticle volume fraction on the surface is revisited.The major limitation of the previous model is the active control of the nanoparticle volume fraction on the surface.In a revised model proposed in this paper,the nanoparticle volume fraction on the surface is passively controlled,which accounts for the effects of both the Brownian motion and the thermophoresis under the boundary condition,whereas the Buongiorno＇s model considers both effects in the governing equations.The assumption of zero nanoparticle flux on the surface makes the model physically more realistic.In the revised model,the dimensionless heat transfer rates are found to be higher whereas the dimensionless mass transfer rates are identically zero due to the passive boundary condition.It is also found that the Brownian motion parameter has a negligible effect on the Nusselt number.
基金Science and Engineering Research Board, Department of Science and Technology, Government of India, New Delhi for the financial support of this investigation through (Grant No. SB/S4/MS: 864/14)
文摘In this paper, we investigate the implications of electro-osmosis on electrohydrodynamic transport of a non-Newtonian fluid on a hydrophobic micro-channel by developing a suitable analytical method. Velocity-slip and temperature-jump conditions are paid due attention. An attempt has been made to examine the effects of rheological and electro-osmotic parameters on the kinematics of the fluid. The nonlinear Poisson-Boltzmann equation governing the formation of the electrical double layer and the body force that is generated by the applied potential are accounted for in the study. Perturbation solutions are presented. In order to exhibit the applicability of the analysis, the problem of electro-osmotic flow and heat transfer of blood in an arteriole has been taken up as an illustrative example of a real-life problem. An intensive quantitative study has been made through numerical computation of the physical variables involved in the analysis, which are of special interest in the study. The computational results are presented graphically. The study reveals that the temperature of blood can be controlled by increasing/decreasing the Joule heating parameter.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.41272251,41372245)
文摘Laboratory experiments are designed in this paper using single fractures made of cement and coarse sand for a series of hydraulic tests under the conditions of different fracture apertures, and for the simulation of the evolution of the flow pattern at places far from the outlet. The relationship between the hydraulic gradient and the flow velocity at different points, and the proportion evolution of the linear and nonlinear portions in the Forchheimer formula are then discussed. Three major conclusions are obtained. First, the non-Darcian flow exists in a single fracture in different laboratory tests. Better fitting accuracy is obtained by using the Forchheimer formula than by using the Darcy law. Second, the proportion of the Darcy flow increases with the increase of the observation scale. In places far enough, the Darcy flow prevails, and the critical velocity between the non-Darcian flow and the Darcy flow decreases as the fracture aperture increases. Third, when the fracture aperture increases, the critical Reynolds number between the non-Darcian flow and the Darcy flow decreases.
基金supported by the National Nature Science Foundation of China(Grant No.40905021)the Chinese Postdoctoral Science Foundation(Grant No.2011M500894)
文摘The contribution of the vortex Rossby wave （VRW） to framework of a barotropic non-divergent TC-like vortex model. the spiral rainband in the tropical cyclones （TCs） is studied in the The spectral function expanding method is used to analyze the disturbance evolution of a defined basic state vortex. The results show that the numerical solution of the model is a superposition of the continuous spectrum component （non-normal modes） and the discrete spectrum component （normal modes）. Only the eyewall and the rainbands in the inner core-region in a TC are related to the VRW normal modes, whereas the continuous spectrum wave components play an important role in the formation of secondary-, principal-, and distant- rainbands, especially the outer rainband, through an indirect way. The continuous spectrum can promote the development of the TC circulation for the occurrence of a mesoscale instability. The convection under a favorable moisture condition will trigger the inertial-gravitational wave to cause the formation of unstable spiral bandliked-disturbances outside of the eyewall. The complicated interaction between the basic state-vortex and the VRW disturbances will cause a positive feedback between the TC circulation and the rainband.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10972123,10802042)the Natural Science Foundation of Shandong Province(Grant No.Y2007A04)
文摘The wind-induced vibration of the front windshield concerns the traffic safety and the aerodynamic characteristics of cars. In this paper, the numerical simulation and the experiment are combined to study the wind-induced vibrations of the front windshield at different speeds of a van-body model bus. The Fluid-Structure Interaction （FSI） model is used for the finite element analysis of the vibration characteristics of the front windshield glass in the travelling process, and the wind-induced vibration response characteristics of the glass is obtained. A wind-tunnel experiment with an eddy current displacement sensor is carried out to study the deformation of the windshield at different wind speeds, and to verify the numerical simulation results. It is shown that the windshield of the model bus windshield undergoes a noticeable deformation as the speed changes, and from the deformation curve obtained, it is seen that in the accelerating process, the deformation of the glass increases as the speed increases, and with the speed being stablized, it also tends to a certain value. The results of this study can provide a scientific basis for the safety design of the windshield and the body.
基金Project supported by the National Natural Science Foundation of China(Grant No.10972134)the National Key Program of National Natural Science Foundation of China(GrantNo.11032007)the Shanghai Program for Innovative Research Team in Universities
文摘Hydrodynamic effects play a very important role in the contaminants release from sediments. Experiments were performed to study contaminants releasing characteristics due to resuspension. The time-dependent variation of COD concentration and relative roles under static and dynamic state of the overlying water were analyzed. Experimental results showed that COD concen- tration in the water column got a striking increment on the dynamic conditions, mainly by reducing the thickness of concentration boundary layer near sediment-water interface and destructing the surface structure of sediment. Hydrodynamics increased contamina- nts release rates and flux in unit time. Before reaching an equilibrium stage, the dynamic release caused by the resuspension was more effective than static one due to molecular diffusion. The release rate of COD increased with flow velocity and decreased with water depth. But at a shallow water depth, wave effects would dominate the causing resuspension, resulting in contaminants release in large quantity. The intensity of pollutant release increased with time in a rather circuitous process. The diffusion of pollutant from internal sediment to the sediment-water interface would maintain the endogenous release effects.
