Extreme waves,owing to their enormous impact energy,wide range of action,and strong destructive capacity,generate considerable impact forces that lead to the vibration and damage of offshore photovoltaic and other mar...Extreme waves,owing to their enormous impact energy,wide range of action,and strong destructive capacity,generate considerable impact forces that lead to the vibration and damage of offshore photovoltaic and other marine structures.The generated cracks when waves impact photovoltaic panels affect their power generation efficiency and service life,but research on wave-impacted elastic photovoltaic panels is still lacking.In this work,a two-way fluid-solid coupling numerical method was used to predict the hydroelastic response of photovoltaic panels under different wave conditions.First,an analysis of the impact loading on the photovoltaic panel was presented,including the normal impact force and peak pressure under different wave conditions.The hydroelastic response of the photovoltaic panel to impact,in terms of the displacement of the photovoltaic panel and the stress of the solar cells,was subsequently analyzed and discussed.Finally,the peak stress in the silicon panels was compared with the mechanical strength of the silicon panels,revealing the cracking risk of the PV panels under different sea states.The results showed that the impact force was the main cause of cracks in the photovoltaic panels,which can easily result in damage caused by stress concentrations at their corners,where the stress in the silicon panels was the largest.The peak stress of the photovoltaic panel under the sea state of Grade 6-1 can reach 78.93 MPa,which exceeds the mechanical strength of silicon panels;therefore,there is a larger risk of internal cracking.展开更多
A numerical study based on a two-dimensional two-phase SPH(Smoothed Particle Hydrodynamics)model to analyze the action of water waves on open-type sea access roads is presented.The study is a continuation of the analy...A numerical study based on a two-dimensional two-phase SPH(Smoothed Particle Hydrodynamics)model to analyze the action of water waves on open-type sea access roads is presented.The study is a continuation of the analyses presented by Chen et al.(2022),in which the sea access roads are semi-immersed.In this new configuration,the sea access roads are placed above the still water level,therefore the presence of the air phase becomes a relevant issue in the determination of the wave forces acting on the structures.Indeed,the comparison of wave forces on the open-type sea access roads obtained from the single and two-phase SPH models with the experimental results shows that the latter are in much better agreement.So in the numerical simulations,a two-phaseδ-SPH model is adopted to investigate the dynamical problems.Based on the numerical results,the maximum horizontal and uplifting wave forces acting on the sea access roads are analyzed by considering different wave conditions and geometries of the structures.In particular,the presence of the girder is analyzed and the differences in the wave forces due to the air cushion effects which are created below the structure are highlighted.展开更多
The interaction between solid structures and free-surface flows is investigated in this study. A Smoothed Particle Hy- drodynamics （SPH） model is used in the investigation and is verified against analytical solution...The interaction between solid structures and free-surface flows is investigated in this study. A Smoothed Particle Hy- drodynamics （SPH） model is used in the investigation and is verified against analytical solutions and experimental obser- vations. The main aim is to examine the effectiveness of a tsunami-resistant house design by predicting the wave loads on it. To achieve this, the solitary wave generation and ran-up are studied first. The solitary wave is generated by allowing a heavily weighted block to penetrate into a tank of water at one end, and the near-shore seabed is modelled by an inclined section with a constant slope. Then, the SPH model is applied to simulate the three-dimensional flows around different types of houses under the action of a solitary wave. It has been found that the tsunami-resistant house design reduces the impact force by a factor of three.展开更多
Nowadays,an increasing number of ships and marine structures are manufactured and inevitably operated in rough sea.As a result,some phenomena related to the violent fluid-elastic structure interactions(e.g.,hydrodynam...Nowadays,an increasing number of ships and marine structures are manufactured and inevitably operated in rough sea.As a result,some phenomena related to the violent fluid-elastic structure interactions(e.g.,hydrodynamic slamming on marine vessels,tsunami impact on onshore structures,and sloshing in liquid containers)have aroused huge challenges to ocean engineering fields.In this paper,the moving particle semi-implicit(MPS)method and finite element method(FEM)coupled method is proposed for use in numerical investigations of the interaction between a regular wave and a horizontal suspended structure.The fluid domain calculated by the MPS method is dispersed into fluid particles,and the structure domain solved by the FEM method is dispersed into beam elements.The generation of the 2D regular wave is firstly conducted,and convergence verification is performed to determine appropriate particle spacing for the simulation.Next,the regular wave interacting with a rigid structure is initially performed and verified through the comparison with the laboratory experiments.By verification,the MPS-FEM coupled method can be applied to fluid-structure interaction(FSI)problems with waves.On this basis,taking the flexibility of structure into consideration,the elastic dynamic response of the structure subjected to the wave slamming is investigated,including the evolutions of the free surface,the variation of the wave impact pressures,the velocity distribution,and the structural deformation response.By comparison with the rigid case,the effects of the structural flexibility on wave-elastic structure interaction can be obtained.展开更多
A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely u...A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely used in the free-surface hydrodynamic flows with good accuracy. The improvement includes the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation and a new estimation method to predict the pressure on the horizontal deck. The simulation results show a good agreement with the experiment. The present numerical model can be used to study wave impact load on the horizontal deck.展开更多
The superstructures of marine structures supported by the elastic legs and located in the splash zone will subject to violent wave slamming and vibrate consequently during storms. A series of model tests are carried o...The superstructures of marine structures supported by the elastic legs and located in the splash zone will subject to violent wave slamming and vibrate consequently during storms. A series of model tests are carried out to investigate the wave impacting on the open structures supported elastically. Three kinds of models with different natural frequencies are designed. The characteristics of the wave pressures on the three models are compared. The durations of the uplift forces and the corresponding accelerations of the structure during wave impact are analyzed simultaneously. The distributions of the peak impact pressures on the subfaces of the plates with different supporting stiffness are given. The relationship between the uplift force on the three models and the relative clearance are obtained. The spectral properties of the slamming loads on the three different structures are compared, The experimental results indicate that the behaviors of the impact pressures, the uplift forces and accelerations of the plates with small natural frequencies are obviously different from those of the plates with larger natural frequencies within the range of the experimental parameters.展开更多
Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is u...Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vibrating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the displacement of the caisson is large due to sliding, the rotation, the sliding force and the overturning moment of the caisson are significantly reduced.展开更多
An improved three-dimensional incompressible smooth particle hydrodynamics(ISPH)model is developed to simulate the impact of regular wave on a horizontal plate.The improvement is the employment of a corrective functio...An improved three-dimensional incompressible smooth particle hydrodynamics(ISPH)model is developed to simulate the impact of regular wave on a horizontal plate.The improvement is the employment of a corrective function to enhance angular momentum conservation in a particle-based calculation.And a new estimation method is proposed to predict the pressure on the horizontal plate.Then,the model simulates the variation characteristics of impact pressures generated by regular wave slamming.The main features of velocity field and pressure field near the plate are presented.The present numerical model can be used to study wave impact load on the horizontal plate.展开更多
Dam breaks are easily triggered by heavy rains due to extreme weather such as typhoons,causing serious economic losses and casualties.Through the investigation of Chaoshan coastal zone,it is found that there have been...Dam breaks are easily triggered by heavy rains due to extreme weather such as typhoons,causing serious economic losses and casualties.Through the investigation of Chaoshan coastal zone,it is found that there have been dam breaks caused by geological disasters.In the design and management of water conservancy project,it is very important to analyze the effect of disastrous flow caused by dam break on the building.In this paper,the effect of the dam break flow on the cylinder is simulated numerically by taking the water body with initial velocity as the dam break flow,and the flow characteristics around the cylinder and the water body are analyzed.Numerical model adopted the Renault Average Navier-Stokes(RANS)model and volume of fluid(VOF)method to analyze the evolution of free water surface.It is found that there are different patterns of water movement in the process of dam break resulting in the creation of several isolated convex hull forms of dam-break waves on the stationary water surface,which causes longer disturbances in the water near the cylinder and makes the cylinder more vulnerable to fatigue damage.The increase of the height of the dam breaking water will lead to the increase of the hydrodynamic force on the pipeline.This study has guiding significance for the study of dam break and dam body design in water conservancy projects.展开更多
Free surface flows are of significant interest in Computational Fluid Dynamics（CFD）. However, violent water wave impact simulation especially when free surface breaks or impacts on solid wall can be a big challenge ...Free surface flows are of significant interest in Computational Fluid Dynamics（CFD）. However, violent water wave impact simulation especially when free surface breaks or impacts on solid wall can be a big challenge for many CFD techniques. Smoothed Particle Hydrodynamics（SPH） has been reported as a robust and reliable method for simulating violent free surface flows. Weakly compressible SPH（WCSPH） uses an equation of state with a large sound speed, and the results of the WCSPH can induce a noisy pressure field and spurious oscillation of pressure in time history for wave impact problem simulation. As a remedy, the truly incompressible SPH（ISPH） technique was introduced, which uses a pressure Poisson equation to calculate the pressure. Although the pressure distribution in the whole field obtained by ISPH is smooth, the stability of the techniques is still an open discussion. In this paper, a new free surface identification scheme and solid boundary handling method are introduced to improve the accuracy of ISPH. This modified ISPH is used to study dam breaking flow and violent tank sloshing flows. On the comparative study of WCSPH and ISPH, the accuracy and efficiency are assessed and the results are compared with the experimental data.展开更多
Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments.Owing to the complex wave interactions among structural components of semi-submersibl...Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments.Owing to the complex wave interactions among structural components of semi-submersibles,in-depth analyses on the characteristics of wave impact events are of significance for both industry and academia.An experimental study was carried out to investigate the local wave impact loads on a semi-submersible,with focus on understanding the wave impacts by identifying typical impact modes.Quantitative criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two types.The results show that the classification is reasonable and provides valuable information for studying wave impacts on semi-submersibles.The incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact mode.The fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore column.However,the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore column.Energy loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave impacts.The shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave impacts.Different impact modes are also distinguished by different spatial distributions of wave impact loads.展开更多
The propagation characteristics of impact waves across a planar interface between a ceramic layer and a ceramic/metal(C/M) composite layer were investigated. Two interfacial boundary conditions were considered: one wa...The propagation characteristics of impact waves across a planar interface between a ceramic layer and a ceramic/metal(C/M) composite layer were investigated. Two interfacial boundary conditions were considered: one was a shear coupling boundary condition that simulated a perfectly bonded interface between the ceramic and composite, and the other was a slip boundary condition that only allowed a transmission of the transverse motion and normal stress at the interface. The ceramic was subjected to an incident impact wave. The ceramic and composite was assumed to be elastic during impact. The study was based on a basic method provided by Furlong, Westburg and Phillips for predicting the reflection and refraction of spherical waves across a planar interface separating two elastic solids. Emphasis was put on the effect of the metal volume fraction in the composite, ceramic thickness and interfacial boundary condition on the reflected waves. New and interesting results are obtained that provide a very useful guidance for design of a ceramic/composite armor and of a C/M functionally graded appliqué.展开更多
The wave transmission character of helical spring is applied to establish 2-DOF model of impacted vehicle on the wave impact theory. Considering the concrete structure of helical spring, corresponding responses under ...The wave transmission character of helical spring is applied to establish 2-DOF model of impacted vehicle on the wave impact theory. Considering the concrete structure of helical spring, corresponding responses under different impact frequency of the vehicle are imitated. The reason why the vehicle floor overresponds in some special frequency fields is explored based on analyzing the responses. When the impactions are in low frequency, the change of the spring has not been considered, but this does not affect the results. Because the transmission characters of velocity and acceleration are unanimous in helical spring, the responses characters of velocity and acceleration arc also unanimous, the only difference is the magnitude, which can make use of acceleration responses to analyse velocity responses.展开更多
Smoothed Particle Hydrodynamics method （SPFI） has a good adaptability for simulating of free surface flow problems. However, there are some shortcomings of SPH which are still in open discussion. This paper presents...Smoothed Particle Hydrodynamics method （SPFI） has a good adaptability for simulating of free surface flow problems. However, there are some shortcomings of SPH which are still in open discussion. This paper presents a corrected solid boundary handling method for weakly compressible SPH. This improved method is very helpful for numerical stability and pressure distribution. Compared with other solid boundary handling methods, this corrected method is simpler for virtual ghost particle interpolation and the ghost particle evaluation relationship is clearer. Several numerical tests are given, like dam breaking, solitary wave impact and sloshing tank waves. The results show that the corrected solid boundary processing method can recover the spurious oscillations of pressure distribution when simulating the problems with complex geometry boundary.展开更多
This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method...This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method （BEM）. Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes （1） vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion, （2） liquid droplets or column impact as well as wave impact on a body, （3） similarity solution of an expanding body. It covers two dimensional （2D）, axisymmetric and three dimensional （3D） cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.展开更多
The strain-rate dependent response of porcine skin oriented in the fiber direction is explored under tensile loading. Quasi-static response was obtained at strain rates in the range of 10-3s-1to 25 s-1. Characterizati...The strain-rate dependent response of porcine skin oriented in the fiber direction is explored under tensile loading. Quasi-static response was obtained at strain rates in the range of 10-3s-1to 25 s-1. Characterization of the response at even greater strain rates is accomplished by measuring the spatio-temporal evolution of the particle velocity and strain in a thin strip subjected to high speed impact loading that generates uniaxial stress conditions. These experiments indicate the formation of shock waves; the shock Hugoniot that relates particle velocity to the shock velocity and the dynamic stress to dynamic strain is obtained directly through experimental measurements, without any assumptions regarding the constitutive properties of the material.展开更多
The stress wave propagation law and dynamic buckling critical velocity are formulated and solved by considering a general axial connecting boundary for a slender elastic straight rod impacted by a rigid body. The infl...The stress wave propagation law and dynamic buckling critical velocity are formulated and solved by considering a general axial connecting boundary for a slender elastic straight rod impacted by a rigid body. The influence of connecting stiffness on the critical velocity is investigated with varied impactor mass and buckling time. The influences of rod length and rod mass on the critical velocity are also discussed. It is found that greater connecting stiffness leads to larger stress amplitude, and further results in lower critical velocity. It is particularly noteworthy that when the connecting stiffness is less than a certain value, dynamic buckling only occurs before stress wave reflects off the connecting end. It is also shown that longer rod with larger slenderness ratio is easier to buckle, and the critical velocity for a larger-mass rod is higher than that for a lighter rod with the same geometry.展开更多
Experiments are conducted to investigate the dynamic response of a plate with elastic support under a regular wave slamming. The statistical analysis results obtained in different model testing cases are presented. Th...Experiments are conducted to investigate the dynamic response of a plate with elastic support under a regular wave slamming. The statistical analysis results obtained in different model testing cases are presented. The theoretical analysis of the plate vibrations(including the forced and free vibrations) is performed. Four characteristic stages of the plate vibration accelerations between two consecutive wave impacts are identified. The submergence durations of the plate during the wave action and the hydro-elastic effects are discussed. Finally, some useful conclusions are drawn.展开更多
Using ultrasonic guided waves to assess long bone fractures and fracture healing has become a promising diagnostic issue. But the multimode overlap of the guided waves challenges the quantitative evaluation and clinic...Using ultrasonic guided waves to assess long bone fractures and fracture healing has become a promising diagnostic issue. But the multimode overlap of the guided waves challenges the quantitative evaluation and clinical application. In the preformed study, in order to simplify the signal interpretation, the low-frequency sinusoidial signals were used to only excite SO and A0 modes in fractured long bones. The amplitudes of SO and A0 modes were numerically analyzed with variation in crack width and fracture angle. Numerical simulation, based on the two-dimension finite-difference time-domain （2D-FDTD） reveals that both SO and A0 amplitudes decrease with the fracture widening. However, the increase in fracture angle gradually enhances the A0 amplitude, while with respect to the SO mode, its amplitude shows a non-monotonic trend to the variation in fracture angle with a turning point around 45°. The amplitude ratio between S0 and A0 can reflect the variations in crack width and fracture angles. The simulation illustrates that ultrasonic guided SO and A0 modes are sensitive to the degree of both vertical and oblique fractures in the long cortical bone. These findings may be helpful for fractures diagnosis and healing evaluation of the long bone.展开更多
The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircr...The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircraft ditching,together with a better understanding of the physics involved during those crucial events.Both numerical and experimental aspects are explored during this project.The present study focuses on the application of the smoothed particle hydrodynamics(SPH)method to the simulation of helicopter ditching,as this method has proved to be particularly adapted to free surface impact cases.Simulations are performed for three different impact configurations,for which the numerical solutions are compared with the experimental results(forces and kinematics)obtained at the wave basin of Ecole Centrale Nantes on a mock-up shape provided by Airbus Helicopters.Elements of sensitivity analysis are also provided when needed,to assess the role of some parameters involved in the helicopter behavior and the fluid pressure forces exerted during the impact.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.52371265).
文摘Extreme waves,owing to their enormous impact energy,wide range of action,and strong destructive capacity,generate considerable impact forces that lead to the vibration and damage of offshore photovoltaic and other marine structures.The generated cracks when waves impact photovoltaic panels affect their power generation efficiency and service life,but research on wave-impacted elastic photovoltaic panels is still lacking.In this work,a two-way fluid-solid coupling numerical method was used to predict the hydroelastic response of photovoltaic panels under different wave conditions.First,an analysis of the impact loading on the photovoltaic panel was presented,including the normal impact force and peak pressure under different wave conditions.The hydroelastic response of the photovoltaic panel to impact,in terms of the displacement of the photovoltaic panel and the stress of the solar cells,was subsequently analyzed and discussed.Finally,the peak stress in the silicon panels was compared with the mechanical strength of the silicon panels,revealing the cracking risk of the PV panels under different sea states.The results showed that the impact force was the main cause of cracks in the photovoltaic panels,which can easily result in damage caused by stress concentrations at their corners,where the stress in the silicon panels was the largest.The peak stress of the photovoltaic panel under the sea state of Grade 6-1 can reach 78.93 MPa,which exceeds the mechanical strength of silicon panels;therefore,there is a larger risk of internal cracking.
基金supported by the New Cornerstone Science Foundation through the XPLORER PRIZE and the National Natural Science Foundation of China(Grant No.52088102).
文摘A numerical study based on a two-dimensional two-phase SPH(Smoothed Particle Hydrodynamics)model to analyze the action of water waves on open-type sea access roads is presented.The study is a continuation of the analyses presented by Chen et al.(2022),in which the sea access roads are semi-immersed.In this new configuration,the sea access roads are placed above the still water level,therefore the presence of the air phase becomes a relevant issue in the determination of the wave forces acting on the structures.Indeed,the comparison of wave forces on the open-type sea access roads obtained from the single and two-phase SPH models with the experimental results shows that the latter are in much better agreement.So in the numerical simulations,a two-phaseδ-SPH model is adopted to investigate the dynamical problems.Based on the numerical results,the maximum horizontal and uplifting wave forces acting on the sea access roads are analyzed by considering different wave conditions and geometries of the structures.In particular,the presence of the girder is analyzed and the differences in the wave forces due to the air cushion effects which are created below the structure are highlighted.
基金supported by the National Natural Science Foundation of China(Grant No. 50779014)
文摘The interaction between solid structures and free-surface flows is investigated in this study. A Smoothed Particle Hy- drodynamics （SPH） model is used in the investigation and is verified against analytical solutions and experimental obser- vations. The main aim is to examine the effectiveness of a tsunami-resistant house design by predicting the wave loads on it. To achieve this, the solitary wave generation and ran-up are studied first. The solitary wave is generated by allowing a heavily weighted block to penetrate into a tank of water at one end, and the near-shore seabed is modelled by an inclined section with a constant slope. Then, the SPH model is applied to simulate the three-dimensional flows around different types of houses under the action of a solitary wave. It has been found that the tsunami-resistant house design reduces the impact force by a factor of three.
基金supported by the National Natural Science Foundation of China(51879159,51490675,11432009,and 51579145)Chang Jiang Scholars Program(T2014099)+3 种基金Shanghai Excellent Academic Leaders Program(17XD1402300)Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(2013022)Innovative Special Project of Numerical Tank of Ministry of Industry and Information Technology of China(2016-23/09)Lloyd’s Register Foundation for doctoral student
文摘Nowadays,an increasing number of ships and marine structures are manufactured and inevitably operated in rough sea.As a result,some phenomena related to the violent fluid-elastic structure interactions(e.g.,hydrodynamic slamming on marine vessels,tsunami impact on onshore structures,and sloshing in liquid containers)have aroused huge challenges to ocean engineering fields.In this paper,the moving particle semi-implicit(MPS)method and finite element method(FEM)coupled method is proposed for use in numerical investigations of the interaction between a regular wave and a horizontal suspended structure.The fluid domain calculated by the MPS method is dispersed into fluid particles,and the structure domain solved by the FEM method is dispersed into beam elements.The generation of the 2D regular wave is firstly conducted,and convergence verification is performed to determine appropriate particle spacing for the simulation.Next,the regular wave interacting with a rigid structure is initially performed and verified through the comparison with the laboratory experiments.By verification,the MPS-FEM coupled method can be applied to fluid-structure interaction(FSI)problems with waves.On this basis,taking the flexibility of structure into consideration,the elastic dynamic response of the structure subjected to the wave slamming is investigated,including the evolutions of the free surface,the variation of the wave impact pressures,the velocity distribution,and the structural deformation response.By comparison with the rigid case,the effects of the structural flexibility on wave-elastic structure interaction can be obtained.
基金the National High Technology Research and Development Program of China (863 Program,Grant No.2007AA11Z130)
文摘A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely used in the free-surface hydrodynamic flows with good accuracy. The improvement includes the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation and a new estimation method to predict the pressure on the horizontal deck. The simulation results show a good agreement with the experiment. The present numerical model can be used to study wave impact load on the horizontal deck.
基金supported by the National Natural Science Foundation of China(Grant No.51179030)the Innovative Research Group National Natural Science Foundation of China(Grant No.51309056)
文摘The superstructures of marine structures supported by the elastic legs and located in the splash zone will subject to violent wave slamming and vibrate consequently during storms. A series of model tests are carried out to investigate the wave impacting on the open structures supported elastically. Three kinds of models with different natural frequencies are designed. The characteristics of the wave pressures on the three models are compared. The durations of the uplift forces and the corresponding accelerations of the structure during wave impact are analyzed simultaneously. The distributions of the peak impact pressures on the subfaces of the plates with different supporting stiffness are given. The relationship between the uplift force on the three models and the relative clearance are obtained. The spectral properties of the slamming loads on the three different structures are compared, The experimental results indicate that the behaviors of the impact pressures, the uplift forces and accelerations of the plates with small natural frequencies are obviously different from those of the plates with larger natural frequencies within the range of the experimental parameters.
基金This project was financially supported by the National Natural Science Foundation of China(Grant No.50279027)
文摘Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vibrating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the displacement of the caisson is large due to sliding, the rotation, the sliding force and the overturning moment of the caisson are significantly reduced.
基金Supported by the National Science Foundation of China(51109022)the National Science Foundation of Liaoning Province(201202020)the Key Laboratory Foundation of Dalian University of Technoloty(LP12005)
文摘An improved three-dimensional incompressible smooth particle hydrodynamics(ISPH)model is developed to simulate the impact of regular wave on a horizontal plate.The improvement is the employment of a corrective function to enhance angular momentum conservation in a particle-based calculation.And a new estimation method is proposed to predict the pressure on the horizontal plate.Then,the model simulates the variation characteristics of impact pressures generated by regular wave slamming.The main features of velocity field and pressure field near the plate are presented.The present numerical model can be used to study wave impact load on the horizontal plate.
文摘Dam breaks are easily triggered by heavy rains due to extreme weather such as typhoons,causing serious economic losses and casualties.Through the investigation of Chaoshan coastal zone,it is found that there have been dam breaks caused by geological disasters.In the design and management of water conservancy project,it is very important to analyze the effect of disastrous flow caused by dam break on the building.In this paper,the effect of the dam break flow on the cylinder is simulated numerically by taking the water body with initial velocity as the dam break flow,and the flow characteristics around the cylinder and the water body are analyzed.Numerical model adopted the Renault Average Navier-Stokes(RANS)model and volume of fluid(VOF)method to analyze the evolution of free water surface.It is found that there are different patterns of water movement in the process of dam break resulting in the creation of several isolated convex hull forms of dam-break waves on the stationary water surface,which causes longer disturbances in the water near the cylinder and makes the cylinder more vulnerable to fatigue damage.The increase of the height of the dam breaking water will lead to the increase of the hydrodynamic force on the pipeline.This study has guiding significance for the study of dam break and dam body design in water conservancy projects.
基金supported by the National Natural Science Foundations of China(Grant Nos.51009034 and 51279041)Fundamental Research Funds for the Central Universities(Grant Nos.HEUCDZ1202 and HEUCF120113)Pre-Research Foundation of General Armament Department of China(Grant No.9140A14020712CB01158)
文摘Free surface flows are of significant interest in Computational Fluid Dynamics（CFD）. However, violent water wave impact simulation especially when free surface breaks or impacts on solid wall can be a big challenge for many CFD techniques. Smoothed Particle Hydrodynamics（SPH） has been reported as a robust and reliable method for simulating violent free surface flows. Weakly compressible SPH（WCSPH） uses an equation of state with a large sound speed, and the results of the WCSPH can induce a noisy pressure field and spurious oscillation of pressure in time history for wave impact problem simulation. As a remedy, the truly incompressible SPH（ISPH） technique was introduced, which uses a pressure Poisson equation to calculate the pressure. Although the pressure distribution in the whole field obtained by ISPH is smooth, the stability of the techniques is still an open discussion. In this paper, a new free surface identification scheme and solid boundary handling method are introduced to improve the accuracy of ISPH. This modified ISPH is used to study dam breaking flow and violent tank sloshing flows. On the comparative study of WCSPH and ISPH, the accuracy and efficiency are assessed and the results are compared with the experimental data.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51879158)the 7th Generation Ultra Deep Water Drilling Unit Innovation Project by the Ministry of Industry and Information Technology of China.
文摘Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments.Owing to the complex wave interactions among structural components of semi-submersibles,in-depth analyses on the characteristics of wave impact events are of significance for both industry and academia.An experimental study was carried out to investigate the local wave impact loads on a semi-submersible,with focus on understanding the wave impacts by identifying typical impact modes.Quantitative criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two types.The results show that the classification is reasonable and provides valuable information for studying wave impacts on semi-submersibles.The incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact mode.The fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore column.However,the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore column.Energy loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave impacts.The shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave impacts.Different impact modes are also distinguished by different spatial distributions of wave impact loads.
文摘The propagation characteristics of impact waves across a planar interface between a ceramic layer and a ceramic/metal(C/M) composite layer were investigated. Two interfacial boundary conditions were considered: one was a shear coupling boundary condition that simulated a perfectly bonded interface between the ceramic and composite, and the other was a slip boundary condition that only allowed a transmission of the transverse motion and normal stress at the interface. The ceramic was subjected to an incident impact wave. The ceramic and composite was assumed to be elastic during impact. The study was based on a basic method provided by Furlong, Westburg and Phillips for predicting the reflection and refraction of spherical waves across a planar interface separating two elastic solids. Emphasis was put on the effect of the metal volume fraction in the composite, ceramic thickness and interfacial boundary condition on the reflected waves. New and interesting results are obtained that provide a very useful guidance for design of a ceramic/composite armor and of a C/M functionally graded appliqué.
文摘The wave transmission character of helical spring is applied to establish 2-DOF model of impacted vehicle on the wave impact theory. Considering the concrete structure of helical spring, corresponding responses under different impact frequency of the vehicle are imitated. The reason why the vehicle floor overresponds in some special frequency fields is explored based on analyzing the responses. When the impactions are in low frequency, the change of the spring has not been considered, but this does not affect the results. Because the transmission characters of velocity and acceleration are unanimous in helical spring, the responses characters of velocity and acceleration arc also unanimous, the only difference is the magnitude, which can make use of acceleration responses to analyse velocity responses.
基金financially supported by the National Natural Science Foundation of China(Grant No.51279041)
文摘Smoothed Particle Hydrodynamics method （SPFI） has a good adaptability for simulating of free surface flow problems. However, there are some shortcomings of SPH which are still in open discussion. This paper presents a corrected solid boundary handling method for weakly compressible SPH. This improved method is very helpful for numerical stability and pressure distribution. Compared with other solid boundary handling methods, this corrected method is simpler for virtual ghost particle interpolation and the ghost particle evaluation relationship is clearer. Several numerical tests are given, like dam breaking, solitary wave impact and sloshing tank waves. The results show that the corrected solid boundary processing method can recover the spurious oscillations of pressure distribution when simulating the problems with complex geometry boundary.
基金Foundation item： Supported by the National Natural Science Foundation of China （Grant Nos. 11302057, 11302056）, the Fundamental Research Funds for the Central Universities （Grant No. HEUCF140115） and the Research Funds for State Key Laboratory of Ocean Engineering in Shanghai Jiao Tong University （Grant No. 1310）.
文摘This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method （BEM）. Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes （1） vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion, （2） liquid droplets or column impact as well as wave impact on a body, （3） similarity solution of an expanding body. It covers two dimensional （2D）, axisymmetric and three dimensional （3D） cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.
文摘The strain-rate dependent response of porcine skin oriented in the fiber direction is explored under tensile loading. Quasi-static response was obtained at strain rates in the range of 10-3s-1to 25 s-1. Characterization of the response at even greater strain rates is accomplished by measuring the spatio-temporal evolution of the particle velocity and strain in a thin strip subjected to high speed impact loading that generates uniaxial stress conditions. These experiments indicate the formation of shock waves; the shock Hugoniot that relates particle velocity to the shock velocity and the dynamic stress to dynamic strain is obtained directly through experimental measurements, without any assumptions regarding the constitutive properties of the material.
文摘The stress wave propagation law and dynamic buckling critical velocity are formulated and solved by considering a general axial connecting boundary for a slender elastic straight rod impacted by a rigid body. The influence of connecting stiffness on the critical velocity is investigated with varied impactor mass and buckling time. The influences of rod length and rod mass on the critical velocity are also discussed. It is found that greater connecting stiffness leads to larger stress amplitude, and further results in lower critical velocity. It is particularly noteworthy that when the connecting stiffness is less than a certain value, dynamic buckling only occurs before stress wave reflects off the connecting end. It is also shown that longer rod with larger slenderness ratio is easier to buckle, and the critical velocity for a larger-mass rod is higher than that for a lighter rod with the same geometry.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51579103,51709118)
文摘Experiments are conducted to investigate the dynamic response of a plate with elastic support under a regular wave slamming. The statistical analysis results obtained in different model testing cases are presented. The theoretical analysis of the plate vibrations(including the forced and free vibrations) is performed. Four characteristic stages of the plate vibration accelerations between two consecutive wave impacts are identified. The submergence durations of the plate during the wave action and the hydro-elastic effects are discussed. Finally, some useful conclusions are drawn.
基金supported by the National Natural Science Foundation of China(11174060,11327405,11304043)the Science and Technology Support Program of Shanghai(13441901900)+1 种基金the Ph.D.Programs Foundation of the Ministry of Education of China(20130071110020)China Postdoctoral Science Foundation(2012M520826)
文摘Using ultrasonic guided waves to assess long bone fractures and fracture healing has become a promising diagnostic issue. But the multimode overlap of the guided waves challenges the quantitative evaluation and clinical application. In the preformed study, in order to simplify the signal interpretation, the low-frequency sinusoidial signals were used to only excite SO and A0 modes in fractured long bones. The amplitudes of SO and A0 modes were numerically analyzed with variation in crack width and fracture angle. Numerical simulation, based on the two-dimension finite-difference time-domain （2D-FDTD） reveals that both SO and A0 amplitudes decrease with the fracture widening. However, the increase in fracture angle gradually enhances the A0 amplitude, while with respect to the SO mode, its amplitude shows a non-monotonic trend to the variation in fracture angle with a turning point around 45°. The amplitude ratio between S0 and A0 can reflect the variations in crack width and fracture angles. The simulation illustrates that ultrasonic guided SO and A0 modes are sensitive to the degree of both vertical and oblique fractures in the long cortical bone. These findings may be helpful for fractures diagnosis and healing evaluation of the long bone.
基金Supported by the European Union Horizon 2020 Research and Innovation Program(Grant No.724139)The authors thank the Pole de Calcul et de Donnees Marines(PCDM)for providing DATARMOR storage and computational resources(http://www.ifremer.fr/pcdm),and the Institut de Calcul Intensif(ICI)(Grant No.2018-P1804060).
文摘The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircraft ditching,together with a better understanding of the physics involved during those crucial events.Both numerical and experimental aspects are explored during this project.The present study focuses on the application of the smoothed particle hydrodynamics(SPH)method to the simulation of helicopter ditching,as this method has proved to be particularly adapted to free surface impact cases.Simulations are performed for three different impact configurations,for which the numerical solutions are compared with the experimental results(forces and kinematics)obtained at the wave basin of Ecole Centrale Nantes on a mock-up shape provided by Airbus Helicopters.Elements of sensitivity analysis are also provided when needed,to assess the role of some parameters involved in the helicopter behavior and the fluid pressure forces exerted during the impact.
