Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results ...Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results are as follows. The wave packet is a superposition of eastward travelling Kelvin waves and westward travelling Rossby waves with the slowest speed, and satisfies the boundary conditions of eastern and western coasts, respectively.The decay coefficient of this solution to the north and south sides of the equator is inversely proportional only to the phase velocity of Kelvin waves in the upper water. The oscillation frequency of the wave packet, which is also the natural frequency of the ocean, is proportional to its mode number and the phase velocity of Kelvin waves and is inversely proportional to the length of the equatorial ocean in the east-west direction. The flow anomalies of the wave packet of Mode 1 most of the time appear as zonal flows with the same direction. They reach the maximum at the center of the equatorial ocean and decay rapidly away from the equator, manifested as equatorially trapped waves. The flow anomalies of the wave packet of Mode 2 appear as the zonal flows with the same direction most of the time in half of the ocean, and are always 0 at the center of the entire ocean which indicates stagnation, while decaying away from the equator with the same speed as that of Mode 1. The spatial structure and oscillation period of the wave packet solution of Mode 1 and Mode 2 are consistent with the changing periods of the surface spatial field and time coefficient of the first and second modes of complex empirical orthogonal function(EOF)analysis of flow anomalies in the actual equatorial ocean. This indicates that the solution does exist in the real ocean, and that El Ni?o-Southern Oscillation(ENSO) and Indian Ocean dipole(IOD) are both related to Mode 2.After considering the Indonesian throughflow, we can obtain the length of bounded equatorial ocean by taking the sum of that of the t展开更多
The present paper studies the influences of the bubble size distribution on the propagation of acoustic waves in dilute polydisperse bubbly liquids theoretically.The proposed approach is validated by using available e...The present paper studies the influences of the bubble size distribution on the propagation of acoustic waves in dilute polydisperse bubbly liquids theoretically.The proposed approach is validated by using available experimental data in the literature.It is revealed that the bubble size distribution has impacts on both the wave speed and the wave attenuation.Specifically,the minimum wave speed together with the corresponding frequency could be both significantly affected by the bubble size distribution (e.g.,the standard deviation).Furthermore,the maximum wave attenuation in the frequency response curve is also sensitive to the variations of the bubble size distribution.展开更多
With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theo...With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theory lose accuracy as nonlinear effects become prominent. Because spurious harmonic waves and primary waves have different propagation velocities, waves simulated by using the first-order wave-maker theory have an unstable wave profile. In this paper, a numerical wave flume with a piston-type wave-maker based on the second-order wave-maker theory has been established. Dynamic mesh technique was developed. The boundary treatment for irregular wave simulation was specially dealt with. Comparisons of the free-surface elevations using the first-order and second-order wave-maker theory prove that second-order wave-maker theory can generate stable wave profiles in both the spatial and time domains. Harmonic analysis and spectral analysis were used to prove the superiority of the second-order wave-maker theory from other two aspects. To simulate irregular waves, the numerical flume was improved to solve the problem of the water depth variation due to low-frequency motion of the wave board. In summary, the new numerical flume using the second-order wave-maker theory can guarantee the accuracy of waves by adding an extra motion of the wave board. The boundary treatment method can provide a reference for the improvement of nonlinear numerical flume.展开更多
Based on phase focusing theory,focusing waves with different spectral types and breaking severities were generated in a wave flume.The time series of surface elevation fluctuation along the flume were obtained by util...Based on phase focusing theory,focusing waves with different spectral types and breaking severities were generated in a wave flume.The time series of surface elevation fluctuation along the flume were obtained by utilizing 22 wave probes mounted along the mid-stream of the flume.Based on the wave spectrum obtained using fast Fourier transform(FFT),the instability characteristics of the energy spectrum were reported in this paper.By analyzing the variation of total spectral energy,the total spectral energy after wave breaking was found to clearly decrease,and the loss value and ratio gradually increased and tended to stabilize with the enhancement of breaking severity for different spectral types.When wave breaking occurred,the energy loss was primarily in a high-frequency range of f/fp >1.0,and energy gain was primarily in a low-frequency range of f/fp<1.0.As the breaking severity increased,the energy gain-loss ratio decreased gradually,which demonstrates that the energy was mostly dissipated.For plunging waves,the energy gain-loss ratio reached 24%for the constant wave steepness(CWS)spectrum,and was slightly larger at approximately 30%for the constant wave amplitude(CWA)spectrum,and was the largest at approximately 42%for the Pierson-Moskowitz(PM)spectrum.展开更多
It is well known that shear wave propagates slower across than parallel to a fracture,and as a result,a travelling shear wave splits into two directions when it encounters a fracture.Shear wave splitting and permeabil...It is well known that shear wave propagates slower across than parallel to a fracture,and as a result,a travelling shear wave splits into two directions when it encounters a fracture.Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell,which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity.A single fracture was created in the samples using a modified Brazilian split test device,where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length.Based on tilt tests and fracture surface profilometry,the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies.Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch.The effective confining stress was varied from 0.5 MPa to 55 MPa,while the fractures were mismatched by 0 mm,0.45 mm and 1 mm.The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient(JMC).Shear wave splitting,as measured by the difference in the magnitudes of shear wave velocities parallel(VS1)and perpendicular(VS2)to the fracture,is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa,and decreased and approached zero as the effective stress was increased.Simple models for the stress-and JMC-dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations.The effects of the joint wall compressive strength(JCS),JMC and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response.Finally,a useful relationship between fractured rock permeability and shear wave splitting was found aft展开更多
Marmara Sea, located between Black Sea and Aegean Sea, is an important sea for ocean engineering activities. In this study, wave power potential of Marmara Sea was investigated using the third generation spectral wind...Marmara Sea, located between Black Sea and Aegean Sea, is an important sea for ocean engineering activities. In this study, wave power potential of Marmara Sea was investigated using the third generation spectral wind-wave model MIKE 21 SW with unstructured mesh. Wind data was obtained from ECMWF ERA-Interim re-analyses wind dataset at 10 m with a spatial resolution of 0.1? for the period of 1994 to 2014. The numerical model was calibrated with measured wave data from a buoy station located in Marmara Sea. Mesh optimization was also performed to obtain the most suitable mesh structure for the study area. This study is the first that dealt with the determination of wave energy potential of Marmara Sea. The numerical model results are presented in terms of monthly, seasonal and annual average of wave power flux(k W m-1). The maximum wave power flux is 1.13 kW m-1 and occurs in November. The overall annual mean wave power flux during 1994–2014 is found to be 0.27 kW m-1 in the offshore regions.展开更多
A slender cylindrical member is the fundamental component of many coastal and offshore structures.It is essential to understand the action of breaking waves on structural members since,when these members are subjected...A slender cylindrical member is the fundamental component of many coastal and offshore structures.It is essential to understand the action of breaking waves on structural members since,when these members are subjected to wave impact load,the structural damages and failures may be catastrophic.In the present study,an experimental investigation has been carried out to measure the response of the slender vertical cylinder subjected to breaking wave impact.Pressure measurements were made in order to estimate the total force acting on the structure.An empirical relation is established between total impact force and the wave steepness parameter which dictates the intensity of the breaking.Pressure rise time is an important parameter dictating the impact event.Simultaneous acceleration and strain measurements were made to evaluate the response of the cylinder.Deflection has been derived from structure acceleration.The deflection due to the moderate plunging differs by two order more than severe plunging events.Strain rate is another important consideration for the impact loading.The higher strain rate increases the resistance of the material.Under the breaking wave impact on the cylinder,the strain rate varies from 102 to 10-4.展开更多
For the inspection of large plate-like structures,the omni-directional guided wave transducer-based system has been regarded as an effective tool since only a few transducers are required to cover the entire inspectio...For the inspection of large plate-like structures,the omni-directional guided wave transducer-based system has been regarded as an effective tool since only a few transducers are required to cover the entire inspection area without blind zones.In comparison with Lamb waves,the shear horizontal(SH)wave is more promising because its fundamental mode is non-dispersive.In this work,we proposed an omni-directional SH wave piezoelec trie t ransducer(OSH-PT)based on a radially poled d24-mode PZT ring.Eoth the finite element simulations and experiments were carried out to demonstrate its performance in generating and receiving SH°wave.Results showed that the radially poled OSH-PT could generate single-mode SHo wave and receive SHo wave only over a wide frequency range from 70 to 200 kHz.The obtained signal-to-noise ratio can reach up to 26 dB in generation and 24 dB in reception.The omni-directivity of this OSH-PT is also very good with the deviation only about 6%in both generation and reception of SHo wave.Considering its easy fabrication,low cost and superior performances,this proposed OSH-PT may promote the applications of SHo wave-based inspection in structural health monitoring and nondestructive testing.展开更多
A novel numerical framework is developed for large-eddy simulation (LES) of interactions among air, water, and solid bodies. The motions of air and water are solved on a fixed block-structured mesh, with the air–wate...A novel numerical framework is developed for large-eddy simulation (LES) of interactions among air, water, and solid bodies. The motions of air and water are solved on a fixed block-structured mesh, with the air–water interface captured using the volume-of-fluid method. A new sub-grid scale stress model based on the vortex identifier is used to improve the robustness and efficiency of the simulation flows with air–water interface. The new framework is tested in the context of bow waves and Kelvin waves generated by a water-surface vehicle. Wave breaking at the bow of the vehicle is captured in LES. The LES results of wave geometry approaches the measurements progressively as the grid resolution is refined. The simulation results indicate that LES is a useful tool for studying wave dynamics of water-surface vehicles.展开更多
The two-dimensional (2D) pseudo-steady isothermal flow, which is isentropic and irrotational, around a convex corner is studied. The self-similar solutions for the supersonic flow around the convex corner are construc...The two-dimensional (2D) pseudo-steady isothermal flow, which is isentropic and irrotational, around a convex corner is studied. The self-similar solutions for the supersonic flow around the convex corner are constructed, where the properties of the centered simple wave are used for the 2D isentropic irrotational pseudo-steady Euler equations. The geometric procedures of the center simple waves are given. It is proven that the supersonic flow turns the convex corner by an incomplete centered expansion wave or an incomplete centered compression wave, depending on the conditions of the downstream state.展开更多
Using non-equilibrium molecular dynamics and the Monte Carlo method, we simulated mass transport in a onedimensional channel with dynamic external potentials. This study focuses on the influence of the dynamic externa...Using non-equilibrium molecular dynamics and the Monte Carlo method, we simulated mass transport in a onedimensional channel with dynamic external potentials. This study focuses on the influence of the dynamic external potential field on the mass transport. Traveling wave and standing wave potential fields have been employed as our dynamic potential field. We found that mass transport can be promoted by the traveling wave field when the external potential moves along the direction of the mass current. When the standing wave field is exerted on the channel, the channel is found to work like a switch. The mass current can be 'on' or 'off' by adjusting the standing wave frequency. The effects of the period number,the amplitude and the velocity of the external potential on the mass transport are also discussed. Our research provides valuable advice for the control o particle transport through one-dimensional channels.展开更多
The 1-D piston problem for the pressure gradient equations arising from the flux-splitting of the compressible Euler equations is considered.When the total variations of the initial data and the velocity of the piston...The 1-D piston problem for the pressure gradient equations arising from the flux-splitting of the compressible Euler equations is considered.When the total variations of the initial data and the velocity of the piston are both sufficiently small,the author establishes the global existence of entropy solutions including a strong rarefaction wave without restriction on the strength by employing a modified wave front tracking method.展开更多
The evolution and transition of planar wave trains propagating through defects(obstacles) in an excitable medium are studied. When the frequency of the planar wave trains is increased, three different dynamical regime...The evolution and transition of planar wave trains propagating through defects(obstacles) in an excitable medium are studied. When the frequency of the planar wave trains is increased, three different dynamical regimes,namely fusion,"V" waves, and spiral waves, are observed in turn and the underlying mechanism is discussed. The dynamics is concerned with the shapes of the defects. Circle, triangle, and rectangle defects with different sizes are considered. The increase of pacing frequency broadens the fan-shaped broken region in the behind of a rectangle defect.The increase of width of a triangle defect leads to breakup of wave trains easier while the change of height shows opposite effect, which is presented in a phase diagram. Dynamical comparison on defects with different shapes indicates that the decrease of the defect width along the propagation of wave trains makes the fan-shaped region and the minimal frequency for breakup of spiral both increased.展开更多
The integration of wave energy converters(WECs) with floating breakwaters has become common recently due to the benefits of both cost-sharing and providing offshore power supply. In this study, based on viscous comput...The integration of wave energy converters(WECs) with floating breakwaters has become common recently due to the benefits of both cost-sharing and providing offshore power supply. In this study, based on viscous computational fluid dynamics(CFD) theory, we investigated the hydrodynamic performances of the floating box and Berkeley Wedge breakwaters, both of which can also serve as WECs. A numerical wave flume model is constructed using Star-CCM+software and applied to investigate the interaction between waves and wave energy converters while completing the verification of the convergence study of time and space steps. The effects of wave length on motion response and transmission coefficient of the floating box breakwater model are studied. Comparisons of our numerical results and published experimental data indicate that Star-CCM+ is very capable of accurately modeling the nonlinear wave interaction of floating structures, while the analytical potential theory overrates the results especially around the resonant frequency. Optimal damping can be readily predicted using potential flow theory and can then be verified by CFD numerical results. Next, we investigated the relationship between wave frequencies and various coefficients using the CFD model under optimal damping, including the motion response, transmission coefficient, reflection coefficient,dissipation coefficient, and wave energy conversion efficiency. We then compared the power generation efficiencies and wave dissipation performances of the floating box and Berkeley Wedge breakwaters. The results show that the power generation efficiency of the Berkeley Wedge breakwater is always much higher than that of the floating box breakwater. Besides, the wave dissipation performance of the Berkeley Wedge breakwater is much better than that of the floating box breakwater at lower frequency.展开更多
In this paper, we first obtain a bilinear form with small perturbation u0 for a generalized(3+1)-dimensional nonlinear wave equation in liquid with gas bubbles. Based on that, a new bilinear B?cklund transformation wh...In this paper, we first obtain a bilinear form with small perturbation u0 for a generalized(3+1)-dimensional nonlinear wave equation in liquid with gas bubbles. Based on that, a new bilinear B?cklund transformation which consists of four bilinear equations and involves seven arbitrary parameters is constructed. After that, by applying a new symbolic computation method, we construct the higher order rogue waves with controllable center to the generalized(3+1)-dimensional nonlinear wave equation. The rogue waves present new structure, which contain two free parametersα and β. The dynamic properties of the higher order rogue waves are demonstrated graphically. The graphs tell that the parameters α and β can control the center of the rogue waves.展开更多
In this paper the author studies the initial boundary value problem of semilinear wave systems in exterior domain in high dimensions(n ≥ 3). Blow up result is established and what is more, the author gets the upper b...In this paper the author studies the initial boundary value problem of semilinear wave systems in exterior domain in high dimensions(n ≥ 3). Blow up result is established and what is more, the author gets the upper bound of the lifespan. For this purpose the test function method is used.展开更多
Scale effect of ISWs loads on Floating Production Storage and Offloading(FPSO)is studied in this paper.The application conditions of KdV,eKdV and MCC ISWs theories are used in the numerical method.The depthaveraged ve...Scale effect of ISWs loads on Floating Production Storage and Offloading(FPSO)is studied in this paper.The application conditions of KdV,eKdV and MCC ISWs theories are used in the numerical method.The depthaveraged velocities induced by ISWs are used for the velocity-inlet boundary.Three scale ratio numerical models λ=1,20 and 300 were selected,which the scale ratio is the size ratio of numerical models to the experimental model.The comparisons between the numerical and former experimental results are performed to verify the feasibility of numerical method.The comparisons between the numerical and simplified theoretical results are performed to discuss the applicability of the simplified theoretical model summarized from the load experiments.Firstly,the numerical results of λ=1 numerical model showed a good agreement with former experimental and simplified theoretical results.It is feasible to simulate the ISWs loads on FPSO by the numerical method.Secondly,the comparisons between the results of three scale ratio numerical models and experimental results indicated that the scale ratios have more significant influence on the experimental horizontal forces than the vertical forces.The scale effect of horizontal forces mainly results from the different viscosity effects associated with the model’s dimension.Finally,through the comparisons between the numerical and simplified theoretical results for three scale ratio models,the simplified theoretical model of the pressure difference and friction forces exerted by ISWs on FPSO is applied for large-scale or full-scale FPSO.展开更多
基金The National Major Research High Performance Computing Program of China under contract 2016YFB0200800the Strategic Priority Research Program of Chinese Academy of Sciences under contract No.XDA20060501.
文摘Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results are as follows. The wave packet is a superposition of eastward travelling Kelvin waves and westward travelling Rossby waves with the slowest speed, and satisfies the boundary conditions of eastern and western coasts, respectively.The decay coefficient of this solution to the north and south sides of the equator is inversely proportional only to the phase velocity of Kelvin waves in the upper water. The oscillation frequency of the wave packet, which is also the natural frequency of the ocean, is proportional to its mode number and the phase velocity of Kelvin waves and is inversely proportional to the length of the equatorial ocean in the east-west direction. The flow anomalies of the wave packet of Mode 1 most of the time appear as zonal flows with the same direction. They reach the maximum at the center of the equatorial ocean and decay rapidly away from the equator, manifested as equatorially trapped waves. The flow anomalies of the wave packet of Mode 2 appear as the zonal flows with the same direction most of the time in half of the ocean, and are always 0 at the center of the entire ocean which indicates stagnation, while decaying away from the equator with the same speed as that of Mode 1. The spatial structure and oscillation period of the wave packet solution of Mode 1 and Mode 2 are consistent with the changing periods of the surface spatial field and time coefficient of the first and second modes of complex empirical orthogonal function(EOF)analysis of flow anomalies in the actual equatorial ocean. This indicates that the solution does exist in the real ocean, and that El Ni?o-Southern Oscillation(ENSO) and Indian Ocean dipole(IOD) are both related to Mode 2.After considering the Indonesian throughflow, we can obtain the length of bounded equatorial ocean by taking the sum of that of the t
基金the National Natural Science Foundation of China (Project Nos.51606221,51506051).
文摘The present paper studies the influences of the bubble size distribution on the propagation of acoustic waves in dilute polydisperse bubbly liquids theoretically.The proposed approach is validated by using available experimental data in the literature.It is revealed that the bubble size distribution has impacts on both the wave speed and the wave attenuation.Specifically,the minimum wave speed together with the corresponding frequency could be both significantly affected by the bubble size distribution (e.g.,the standard deviation).Furthermore,the maximum wave attenuation in the frequency response curve is also sensitive to the variations of the bubble size distribution.
基金the National Natural Science Foundation of China(Grant Nos. 51579038, 51739010, 51490672, 51879037).
文摘With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theory lose accuracy as nonlinear effects become prominent. Because spurious harmonic waves and primary waves have different propagation velocities, waves simulated by using the first-order wave-maker theory have an unstable wave profile. In this paper, a numerical wave flume with a piston-type wave-maker based on the second-order wave-maker theory has been established. Dynamic mesh technique was developed. The boundary treatment for irregular wave simulation was specially dealt with. Comparisons of the free-surface elevations using the first-order and second-order wave-maker theory prove that second-order wave-maker theory can generate stable wave profiles in both the spatial and time domains. Harmonic analysis and spectral analysis were used to prove the superiority of the second-order wave-maker theory from other two aspects. To simulate irregular waves, the numerical flume was improved to solve the problem of the water depth variation due to low-frequency motion of the wave board. In summary, the new numerical flume using the second-order wave-maker theory can guarantee the accuracy of waves by adding an extra motion of the wave board. The boundary treatment method can provide a reference for the improvement of nonlinear numerical flume.
基金financially supported by the State Key Research and Development Program of China(Grant No.2016YFC1401405)National Natural Science Foundation of China(Grant Nos.51779038 and 51279028).
文摘Based on phase focusing theory,focusing waves with different spectral types and breaking severities were generated in a wave flume.The time series of surface elevation fluctuation along the flume were obtained by utilizing 22 wave probes mounted along the mid-stream of the flume.Based on the wave spectrum obtained using fast Fourier transform(FFT),the instability characteristics of the energy spectrum were reported in this paper.By analyzing the variation of total spectral energy,the total spectral energy after wave breaking was found to clearly decrease,and the loss value and ratio gradually increased and tended to stabilize with the enhancement of breaking severity for different spectral types.When wave breaking occurred,the energy loss was primarily in a high-frequency range of f/fp >1.0,and energy gain was primarily in a low-frequency range of f/fp<1.0.As the breaking severity increased,the energy gain-loss ratio decreased gradually,which demonstrates that the energy was mostly dissipated.For plunging waves,the energy gain-loss ratio reached 24%for the constant wave steepness(CWS)spectrum,and was slightly larger at approximately 30%for the constant wave amplitude(CWA)spectrum,and was the largest at approximately 42%for the Pierson-Moskowitz(PM)spectrum.
基金Financial support provided by the U.S. Department of Energy under grant No. DE-FE0000730
文摘It is well known that shear wave propagates slower across than parallel to a fracture,and as a result,a travelling shear wave splits into two directions when it encounters a fracture.Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell,which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity.A single fracture was created in the samples using a modified Brazilian split test device,where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length.Based on tilt tests and fracture surface profilometry,the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies.Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch.The effective confining stress was varied from 0.5 MPa to 55 MPa,while the fractures were mismatched by 0 mm,0.45 mm and 1 mm.The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient(JMC).Shear wave splitting,as measured by the difference in the magnitudes of shear wave velocities parallel(VS1)and perpendicular(VS2)to the fracture,is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa,and decreased and approached zero as the effective stress was increased.Simple models for the stress-and JMC-dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations.The effects of the joint wall compressive strength(JCS),JMC and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response.Finally,a useful relationship between fractured rock permeability and shear wave splitting was found aft
基金TüBITAK(The Scientific and Technological Research Council of Turkey)(No.112M 413).
文摘Marmara Sea, located between Black Sea and Aegean Sea, is an important sea for ocean engineering activities. In this study, wave power potential of Marmara Sea was investigated using the third generation spectral wind-wave model MIKE 21 SW with unstructured mesh. Wind data was obtained from ECMWF ERA-Interim re-analyses wind dataset at 10 m with a spatial resolution of 0.1? for the period of 1994 to 2014. The numerical model was calibrated with measured wave data from a buoy station located in Marmara Sea. Mesh optimization was also performed to obtain the most suitable mesh structure for the study area. This study is the first that dealt with the determination of wave energy potential of Marmara Sea. The numerical model results are presented in terms of monthly, seasonal and annual average of wave power flux(k W m-1). The maximum wave power flux is 1.13 kW m-1 and occurs in November. The overall annual mean wave power flux during 1994–2014 is found to be 0.27 kW m-1 in the offshore regions.
文摘A slender cylindrical member is the fundamental component of many coastal and offshore structures.It is essential to understand the action of breaking waves on structural members since,when these members are subjected to wave impact load,the structural damages and failures may be catastrophic.In the present study,an experimental investigation has been carried out to measure the response of the slender vertical cylinder subjected to breaking wave impact.Pressure measurements were made in order to estimate the total force acting on the structure.An empirical relation is established between total impact force and the wave steepness parameter which dictates the intensity of the breaking.Pressure rise time is an important parameter dictating the impact event.Simultaneous acceleration and strain measurements were made to evaluate the response of the cylinder.Deflection has been derived from structure acceleration.The deflection due to the moderate plunging differs by two order more than severe plunging events.Strain rate is another important consideration for the impact loading.The higher strain rate increases the resistance of the material.Under the breaking wave impact on the cylinder,the strain rate varies from 102 to 10-4.
基金the National Natural Science Foundation of China under Grant No.11672003.
文摘For the inspection of large plate-like structures,the omni-directional guided wave transducer-based system has been regarded as an effective tool since only a few transducers are required to cover the entire inspection area without blind zones.In comparison with Lamb waves,the shear horizontal(SH)wave is more promising because its fundamental mode is non-dispersive.In this work,we proposed an omni-directional SH wave piezoelec trie t ransducer(OSH-PT)based on a radially poled d24-mode PZT ring.Eoth the finite element simulations and experiments were carried out to demonstrate its performance in generating and receiving SH°wave.Results showed that the radially poled OSH-PT could generate single-mode SHo wave and receive SHo wave only over a wide frequency range from 70 to 200 kHz.The obtained signal-to-noise ratio can reach up to 26 dB in generation and 24 dB in reception.The omni-directivity of this OSH-PT is also very good with the deviation only about 6%in both generation and reception of SHo wave.Considering its easy fabrication,low cost and superior performances,this proposed OSH-PT may promote the applications of SHo wave-based inspection in structural health monitoring and nondestructive testing.
基金Lixing plan of Institute of Mechanics,Chinese Academy of Sciencesthe National Natural Science Foundation of China(91752119,11232011 and11572331)+1 种基金the support from the Strategic Priority Research Program(XDB22040104)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(QYZDJ-SSW-SYS002).
文摘A novel numerical framework is developed for large-eddy simulation (LES) of interactions among air, water, and solid bodies. The motions of air and water are solved on a fixed block-structured mesh, with the air–water interface captured using the volume-of-fluid method. A new sub-grid scale stress model based on the vortex identifier is used to improve the robustness and efficiency of the simulation flows with air–water interface. The new framework is tested in the context of bow waves and Kelvin waves generated by a water-surface vehicle. Wave breaking at the bow of the vehicle is captured in LES. The LES results of wave geometry approaches the measurements progressively as the grid resolution is refined. The simulation results indicate that LES is a useful tool for studying wave dynamics of water-surface vehicles.
基金the National Natural Science Foundation of China (Nos. 11371240 and 11771274).
文摘The two-dimensional (2D) pseudo-steady isothermal flow, which is isentropic and irrotational, around a convex corner is studied. The self-similar solutions for the supersonic flow around the convex corner are constructed, where the properties of the centered simple wave are used for the 2D isentropic irrotational pseudo-steady Euler equations. The geometric procedures of the center simple waves are given. It is proven that the supersonic flow turns the convex corner by an incomplete centered expansion wave or an incomplete centered compression wave, depending on the conditions of the downstream state.
基金the Natural Science Foundation of Guangdong Province,China(Grant No.2014A030313367).
文摘Using non-equilibrium molecular dynamics and the Monte Carlo method, we simulated mass transport in a onedimensional channel with dynamic external potentials. This study focuses on the influence of the dynamic external potential field on the mass transport. Traveling wave and standing wave potential fields have been employed as our dynamic potential field. We found that mass transport can be promoted by the traveling wave field when the external potential moves along the direction of the mass current. When the standing wave field is exerted on the channel, the channel is found to work like a switch. The mass current can be 'on' or 'off' by adjusting the standing wave frequency. The effects of the period number,the amplitude and the velocity of the external potential on the mass transport are also discussed. Our research provides valuable advice for the control o particle transport through one-dimensional channels.
基金the National Natural Science Foundation of China(Nos.11626176,11701435)the Fundamental Research Funds for the Central Universities of China(Nos.2018IB015,2018IVB013).
文摘The 1-D piston problem for the pressure gradient equations arising from the flux-splitting of the compressible Euler equations is considered.When the total variations of the initial data and the velocity of the piston are both sufficiently small,the author establishes the global existence of entropy solutions including a strong rarefaction wave without restriction on the strength by employing a modified wave front tracking method.
基金the Natural Science Foundation of Zhejiang Province under Grant Nos. LQ14A050003 and LR17A050001Zhejiang Province Commonweal Projects under Grant No. GK180906288001China Scholarship Council under Grant No. 201708330401.
文摘The evolution and transition of planar wave trains propagating through defects(obstacles) in an excitable medium are studied. When the frequency of the planar wave trains is increased, three different dynamical regimes,namely fusion,"V" waves, and spiral waves, are observed in turn and the underlying mechanism is discussed. The dynamics is concerned with the shapes of the defects. Circle, triangle, and rectangle defects with different sizes are considered. The increase of pacing frequency broadens the fan-shaped broken region in the behind of a rectangle defect.The increase of width of a triangle defect leads to breakup of wave trains easier while the change of height shows opposite effect, which is presented in a phase diagram. Dynamical comparison on defects with different shapes indicates that the decrease of the defect width along the propagation of wave trains makes the fan-shaped region and the minimal frequency for breakup of spiral both increased.
基金the National Natural Science Foundation of China 51409066,51761135013)High Technology Ship Scientific Research Project from the Ministry of Industry and Information Technology of the People's Republic of China-Floating Security Platform Project (the second stage,201622)the Fundamental Research Fund for the Central University (HEUCF180104, HEUCFP201809).
文摘The integration of wave energy converters(WECs) with floating breakwaters has become common recently due to the benefits of both cost-sharing and providing offshore power supply. In this study, based on viscous computational fluid dynamics(CFD) theory, we investigated the hydrodynamic performances of the floating box and Berkeley Wedge breakwaters, both of which can also serve as WECs. A numerical wave flume model is constructed using Star-CCM+software and applied to investigate the interaction between waves and wave energy converters while completing the verification of the convergence study of time and space steps. The effects of wave length on motion response and transmission coefficient of the floating box breakwater model are studied. Comparisons of our numerical results and published experimental data indicate that Star-CCM+ is very capable of accurately modeling the nonlinear wave interaction of floating structures, while the analytical potential theory overrates the results especially around the resonant frequency. Optimal damping can be readily predicted using potential flow theory and can then be verified by CFD numerical results. Next, we investigated the relationship between wave frequencies and various coefficients using the CFD model under optimal damping, including the motion response, transmission coefficient, reflection coefficient,dissipation coefficient, and wave energy conversion efficiency. We then compared the power generation efficiencies and wave dissipation performances of the floating box and Berkeley Wedge breakwaters. The results show that the power generation efficiency of the Berkeley Wedge breakwater is always much higher than that of the floating box breakwater. Besides, the wave dissipation performance of the Berkeley Wedge breakwater is much better than that of the floating box breakwater at lower frequency.
基金Supported by the National Natural Science Foundation of China(11471004,11501498)Shaanxi Key Research and Development Programs(2018SF-251)the Research Project at Yuncheng University[XK2012007].
文摘In this paper, we first obtain a bilinear form with small perturbation u0 for a generalized(3+1)-dimensional nonlinear wave equation in liquid with gas bubbles. Based on that, a new bilinear B?cklund transformation which consists of four bilinear equations and involves seven arbitrary parameters is constructed. After that, by applying a new symbolic computation method, we construct the higher order rogue waves with controllable center to the generalized(3+1)-dimensional nonlinear wave equation. The rogue waves present new structure, which contain two free parametersα and β. The dynamic properties of the higher order rogue waves are demonstrated graphically. The graphs tell that the parameters α and β can control the center of the rogue waves.
文摘In this paper the author studies the initial boundary value problem of semilinear wave systems in exterior domain in high dimensions(n ≥ 3). Blow up result is established and what is more, the author gets the upper bound of the lifespan. For this purpose the test function method is used.
基金financially supported by the National Natural Science Foundation of China(Grant No.11372184)the National Basic Research Program of China(973 Program,Grant Nos.2015CB251203-3 and 2013CB036103).
文摘Scale effect of ISWs loads on Floating Production Storage and Offloading(FPSO)is studied in this paper.The application conditions of KdV,eKdV and MCC ISWs theories are used in the numerical method.The depthaveraged velocities induced by ISWs are used for the velocity-inlet boundary.Three scale ratio numerical models λ=1,20 and 300 were selected,which the scale ratio is the size ratio of numerical models to the experimental model.The comparisons between the numerical and former experimental results are performed to verify the feasibility of numerical method.The comparisons between the numerical and simplified theoretical results are performed to discuss the applicability of the simplified theoretical model summarized from the load experiments.Firstly,the numerical results of λ=1 numerical model showed a good agreement with former experimental and simplified theoretical results.It is feasible to simulate the ISWs loads on FPSO by the numerical method.Secondly,the comparisons between the results of three scale ratio numerical models and experimental results indicated that the scale ratios have more significant influence on the experimental horizontal forces than the vertical forces.The scale effect of horizontal forces mainly results from the different viscosity effects associated with the model’s dimension.Finally,through the comparisons between the numerical and simplified theoretical results for three scale ratio models,the simplified theoretical model of the pressure difference and friction forces exerted by ISWs on FPSO is applied for large-scale or full-scale FPSO.