Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly...Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly limits the accuracy of numerical analyses and finite element simulations. Therefore, this paper takes a new type of floating wind turbine as an example and performs a physical model test on the wave slamming characteristics of this floating wind turbine.Based on a 1:50 model of the Pivot Buoy floating wind turbine, an experimental study is performed under the combined effects of wind-wave loads on the peak pressure, duration, and pressure distribution of slamming. First, two sets of mooring systems, the combined scheme and the full mooring chain scheme, are designed to conduct a series of experimental studies of model slamming under different wind and wave incidence angles, wave heights, and wave periods. By doing so, the slamming characteristics of the wind turbine can be obtained. Moreover, to solve the problem of the large pitch motion response of the prototype wind turbine, a set of vertically oscillating structures is designed,and the slamming pressure characteristics of the optimized model are also investigated through model tests.展开更多
The paper presents an overview of studies of slamming on ship structures. This work focuses on the hull slamming, which is one of the most important types of slamming problems to be considered in the ship design proce...The paper presents an overview of studies of slamming on ship structures. This work focuses on the hull slamming, which is one of the most important types of slamming problems to be considered in the ship design process and the assessment of the ship safety. There are three main research aspects related to the hull slamming phenomenon, a) where and how often a slamming event occurs, b) slamming load prediction and c) structural response due to slamming loads. The approaches used in each aspect are reviewed and commented, together with the presentation of some typical results. The methodology, which combines the seakeeping analysis and slamming load prediction, is discussed for the global analysis of the hull slamming of a ship in waves. Some physical phenomena during the slamming event are discussed also. Recommendations for the future research and developments are made.展开更多
This paper presents the probability distribution of the slamming pressure from an experimental study of regular wave slamming on an elastically supported horizontal deck. The time series of the slamming pressure durin...This paper presents the probability distribution of the slamming pressure from an experimental study of regular wave slamming on an elastically supported horizontal deck. The time series of the slamming pressure during the wave impact were first obtained through statistical analyses on experimental data. The exceeding probability distribution of the maximum slamming pressure peak and distribution parameters were analyzed, and the results show that the exceeding probability distribution of the maximum slamming pressure peak accords with the three-parameter Weibull distribution. Furthermore, the range and relationships of the distribution parameters were studied. The sum of the location parameter D and the scale parameter L was approximately equal to 1.0, and the exceeding probability was more than 36.79% when the random peak was equal to the sample average during the wave impact. The variation of the distribution parameters and slamming pressure under different model conditions were comprehensively presented, and the parameter values of the Weibull distribution of wave-slamming pressure peaks were different due to different test models. The parameter values were found to decrease due to the increased stiffness of the elastic support. The damage criterion of the structure model caused by the wave impact was initially discussed, and the structure model was destroyed when the average slamming time was greater than a certain value during the duration of the wave impact. The conclusions of the experimental study were then described.展开更多
A boundary element method is developed for calculating the flare ship hull slamming problem. The nonlinear free surface elevation and the linear element assumption are employed. The method has been verified by compari...A boundary element method is developed for calculating the flare ship hull slamming problem. The nonlinear free surface elevation and the linear element assumption are employed. The method has been verified by comparisons with results for the water entry of wedges with various deadrise angles. Numerical results show that the pressure distribution varies greatly with the ship hull with different curvilinear equations, and the slamming features are also different; From the numerical simulation, the authors found that the structural damage of the flare hull might be caused by the increasing hydrodynamic pressure over an extensive area on the flare when the upper part of the flare comes into contact with water.展开更多
The sensitivity of moving particle semi-implicit(MPS)simulations to numerical parameters is investigated in this study.Although the verifcation and validation(V&V)are important to ensure accurate numerical results...The sensitivity of moving particle semi-implicit(MPS)simulations to numerical parameters is investigated in this study.Although the verifcation and validation(V&V)are important to ensure accurate numerical results,the MPS has poor perfor-mance in convergences with a time step size.Therefore,users of the MPS need to tune numerical parameters to ft results into benchmarks.However,such tuning parameters are not always valid for other simulations.We propose a practical numerical condition for the MPS simulation of a two-dimensional wedge slamming problem(i.e.,an MPS-slamming condition).The MPS-slamming condition is represented by an MPS-slamming number,which provides the optimum time step size once the MPS-slamming number,slamming velocity,deadrise angle of the wedge,and particle size are decided.The simulation study shows that the MPS results can be characterized by the proposed MPS-slamming condition,and the use of the same MPS-slamming number provides a similar fow.展开更多
The purpose of this paper is to investigate the instantaneous properties of wave slanuning on the plate structure of an open structure. The advanced instantaneous measuring technique-Particle Image Velocimetry （PIV）...The purpose of this paper is to investigate the instantaneous properties of wave slanuning on the plate structure of an open structure. The advanced instantaneous measuring technique-Particle Image Velocimetry （PIV） is applied to acquire the instantaneous velocity field of wave slamming. From the cross-correlation analysis results of the images captured by the CCD camera, the flow fields of wave impacting on the structure are displayed visually, and the instantaneous whole- field fluid velocity vectors are obtained. The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis.展开更多
In this paper,a method about the water-entry slamming of a two-dimensional(2D)bow structure has been proposed based on the experimental and simulation results.According to this method,the sensitivity analysis has been...In this paper,a method about the water-entry slamming of a two-dimensional(2D)bow structure has been proposed based on the experimental and simulation results.According to this method,the sensitivity analysis has been carried out about the effect of speed and inclination angle on the slamming pressure of the bow.Firstly,a 2D ship bow experimental model was performed to obtain the slamming pressure distribution at different measuring points under different speeds.Then,numerical simulation for the water-entry slamming of this experimental model was conducted to obtain the pressure distribution on the experimental model under different working conditions.Finally,the experimental results were compared with the numerical simulation results to evaluate the effect of speed and inclination angle on the slamming pressure of the bow.The results show that the slamming pressure is more sensitive to speed variation within the low-speed range.The effect of inclination angle on the slamming pressure is more obvious in the small angle condition.When the inclination angle is larger than 45°,the effect is limited.展开更多
Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival co...Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.展开更多
A design of offshore floating structure is mainly based on the extreme response analysis due to the forces experienced. The extreme response can induce the negative air gap response and potential impact to the deck bo...A design of offshore floating structure is mainly based on the extreme response analysis due to the forces experienced. The extreme response can induce the negative air gap response and potential impact to the deck bottom of floating structure. It is important to predict the slamming load in order to check the strength of local structures which withstand the wave slamming. In recent years, studies of the effects of wind load on air gap response and slamming load are ignored. When the platform suffers the extreme wave, the wind is also harsh.Moreover, the wind load can affect the motion response of the platform. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Though the model test results are not accurate enough for air gap and slamming load evaluation due to the loss of wind effect, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. This paper aims at presenting the sensitivity analysis results of wave slamming load with respect to the wind load for the design of semi-submersible platform. As an example of semi-submersible drilling platform design, the wind tunnel test has been carried out, and the sea-keeping model test is also performed in towing tank, while the wind load effect is ignored. According to the model test results, a numerical model is tuned and validated by ANSYS AQWA. Sensitivity analysis studies of the relative velocity between water particle and platform surface and the wave slamming load with respect to the wind load are performed in time domain by the tuned numerical model.Five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design.展开更多
Coastal wave energy resources have enormous exploitation potential due to shorter weather window,closer installation distance and lower maintenance cost.However,impact loads generated by depth variation from offshore ...Coastal wave energy resources have enormous exploitation potential due to shorter weather window,closer installation distance and lower maintenance cost.However,impact loads generated by depth variation from offshore to nearshore and wave-current interaction,may lead to a catastrophic damage or complete destruction to wave energy converters(WECs).This objective of this paper is to investigate slamming response of a coastal oscillating wave surge converter(OWSC)entering or leaving water freely.Based on fully nonlinear potential flow theory,a time-domain wave-current-structure interaction model combined with higher-order boundary element method(HOBEM),is developed to analyze the coupled hydrodynamic problem.The variable-depth seabed is considered in the model to illustrate the shallow water effect on impact loads and free surface profiles in coastal zone.A domain decomposition approach is utilized to simulate the overlapping phenomenon generated by a jet falling into water under gravity effect.Through a series of Lagrangian interpolation methods,the meshes on boundaries are rearranged to avoid the mismatch between element size on free surface and body surface.The present model is validated against the existing experimental and numerical results.Simulations are also provided for the effects of wave-current interaction and uneven local seabed on the slamming responses.It is found that the length of the splash jet increases for a following current and decreases for an opposing current,and that the slamming response of the OWSC device is sensitive to the geometric features of the uneven seabed.展开更多
A hydroelastic analysis of a rectangular plate subjected to slamming loads is presented. An analytical model based on Wagner theory is used for calculations of transient slamming load on the ship plate. A thin isotrop...A hydroelastic analysis of a rectangular plate subjected to slamming loads is presented. An analytical model based on Wagner theory is used for calculations of transient slamming load on the ship plate. A thin isotropic plate theory is considered for determining the vibration of a rectangular plate excited by an external slamming force. The forced vibration of the plate is calculated by the modal expansion method. Analytical results of the transient response of a rectangular plate induced by slamming loads are compared with numerical calculations from finite element method. The theoretical slamming pressure based on Wagner model is applied on the finite element model of a plate. Good agreement is obtained between the analytical and numerical results for the structural deflection of a rectangular plate due to slamming pressure. The effects of plate dimension and wave profile on the structural vibration are discussed as well. The results show that a low impact velocity and a small wetted radial length of wave yield negligible effects of hydroelasticity.展开更多
The water entry of large diameter cylindrical structure is studied by applying numerical simulation method. The processes of different diameter cyhndrical structures impacting water with various constant velocities ar...The water entry of large diameter cylindrical structure is studied by applying numerical simulation method. The processes of different diameter cyhndrical structures impacting water with various constant velocities are calculated numerically. Thereafter, analyzed are the distribution of slamming pressure on structure during slamming course and the influence of slamming velocity and cylindrical diameter on slamming process. Furthermore, presented herein is an equation being used to forecast the peak slamming force on a large diameter cylindrical structure.展开更多
With the development of ships towards large scale, high speed and light weight, ship hydroelastic responses and slamming strength issues are becoming increasingly important. In this paper, a time-domain nonlinear hydr...With the development of ships towards large scale, high speed and light weight, ship hydroelastic responses and slamming strength issues are becoming increasingly important. In this paper, a time-domain nonlinear hydroelasticity theory is developed to predict ship motion and load responses in harsh regular waves.Hydrostatic restoring force, wave excitation force and radiation force are calculated on the instantaneously wetted body surface to consider the nonlinear effects caused by large amplitude motions of ship in steep waves. A twodimensional(2 D) generalized Wagner model and a one-dimensional(1 D) dam-breaking model are used to estimate the impact loads caused by bow flare slamming and green water on deck, respectively;the impact loads are coupled with the hydroelastic equation in time-domain. Moreover, segmented model tests are carried out in a towing tank to investigate the wave and slamming loads acting on the hull sailing in harsh regular head waves and also validate the numerical results.展开更多
Since the research of flare slamming prediction is seldom when parametric rolling happens, we present an efficient approximation method for flare slamming analysis of large container ships in parametric rolling condit...Since the research of flare slamming prediction is seldom when parametric rolling happens, we present an efficient approximation method for flare slamming analysis of large container ships in parametric rolling conditions. We adopt a 6-DOF weakly nonlinear time domain model to predict the ship motions of parametric rolling conditions. Unlike previous flare slamming analysis, our proposed method takes roll motion into account to calculate the impact angle and relative vertical velocity between ship sections on the bow flare and wave surface. We use the Wagner model to analyze the slamming impact forces and the slamming occurrence probability. Through numerical simulations, we investigate the maximum flare slamming pressures of a container ship for different speeds and wave conditions. To further clarify the mechanism of flare slamming phenomena in parametric rolling conditions, we also conduct real-time simulations to determine the relationship between slamming pressure and 3-DOF motions, namely roll, pitch, and heave.展开更多
The paper presents an empirical method to calculate bow flare slamming pressure and the green water load. Many empirical formulae for various types of vessels have been provided by rules of ship classification societi...The paper presents an empirical method to calculate bow flare slamming pressure and the green water load. Many empirical formulae for various types of vessels have been provided by rules of ship classification societies. In the present work, attempt is made to develop generalized formulations for all types of displacement vessels. Extreme sea conditions are considered. Bow flare pressure is derived in terms of flare and waterline angles. Specific condition for limiting waterline angle is derived based on 2 D numerical simulations. Deck wetness is derived in terms of static and dynamic swell-up and the relative motion. Variation of static swell along the length is determined based on potential solution based analyses considering variation in vessels’ hull. 2 D wedge simulations are carried out to validate the formulation of dynamic swell-up. Results of the calculated bow flare and deck pressures are compared with various ship classification society formulations and the trends are found to be in good agreement in general barring at bow flare where lower pressure is found in most of the presented cases. Also IACS UR S21 A(2018) governing minimum pressure for deck scantlings is found to be conservative in few of the presented cases. Although scantlings assessment is not performed, the presented new formulations may help in realistic assessment of scantlings.展开更多
Aimed at the hydrodynamic response for marine structures slamming into water, based on the mechanism analysis to the slamming process, and by combining 3D N-S equation and k-ε turbulent kinetic equation with structur...Aimed at the hydrodynamic response for marine structures slamming into water, based on the mechanism analysis to the slamming process, and by combining 3D N-S equation and k-ε turbulent kinetic equation with structure fully 6DOF motion equation, a mathematical model for the wind-fluid-solid interaction is established in 3D marine structure slamming wave at free poses and wind-wave-flow complex environments. Compared with the results of physical model test, the numerical results from the slamming wave well correspond with the experimental results. Through the mathematical model, the wave-making issue of 3D marine structure at initial pose falls into water in different complex wind, wave and flow environments is investigated. The research results show that various kinds of natural factors and structure initial poses have different influence on the slamming wave, and there is an obvious rule in this process.展开更多
The elasto-plastic dynamic buckling and postbuckling phenomena of square plates subjected to in-plane solid-fluid slamming are investigated. According to the plate's response, the critical criteria for dynamic buc...The elasto-plastic dynamic buckling and postbuckling phenomena of square plates subjected to in-plane solid-fluid slamming are investigated. According to the plate's response, the critical criteria for dynamic buckling, dynamic plasticity and plastic collapse are defined, and the corresponding critical impulses are presented. Meanwhile, dynamic buckling modes and collapse models are observed. The effects of different boundary conditions and loading histories on the properties of buckling and postbuckling are discussed.展开更多
The present research deals with the numerical prediction of the air gap within the 6th generation of deepwater drilling floating semi-submersible platform and the experimental studies on the slamming loadings onto the...The present research deals with the numerical prediction of the air gap within the 6th generation of deepwater drilling floating semi-submersible platform and the experimental studies on the slamming loadings onto the structure. The survivability of the floating model with a mooring system was tested under extreme wave of 10-year return period. In the numerical simulation of the Gaussian method,the narrow band model was applied to obtain the first-order wave surface equation and the modified second-order wave surface equation. The hydrodynamic responses of the floating body,i.e. radiation damping,added mass,second-order wave excitation force and drifting force,were computed by using the potential flow theory based on higher order boundary element method in frequent domain. In the experimental analysis,high-frequency sensors were installed at the lower deck to measure the wave slamming loads. Equivalent truncated mooring system was applied to make sure position of the floating body in the wave tank. The comparison between the numerical and experimental results showed the numerical model underestimated the air gap of the floating body. Nevertheless,the predictions of the high risk spots underneath the floating deck that is prone to wave slamming obtained from both models were agreeable to each other. The experimental results also revealed that the wave slamming events often occurred at the connection point between the rear columns and the lower deck.展开更多
Capable and accurate predictions of some effects of strongly nonlinear interaction wave-ship associated with hydroelastic behaviors are very required for simulation tool in naval architect and ocean engineering. It ca...Capable and accurate predictions of some effects of strongly nonlinear interaction wave-ship associated with hydroelastic behaviors are very required for simulation tool in naval architect and ocean engineering. It can guarantee ship safety at the sea state by producing proper design. Therefore, we have developed a hybrid scheme based on both grid and particle method. In order to clarify hydroelastic behaviors of a ship, a dropping test of a ship with elastic motion has been performed firstly. The developed scheme has been then validated on ship dropping case under the same conditions with experiment. The comparisons showed consistently in good agreement. Furthermore, evaluation on hydroelastic behaviors of ship motion under slamming, the impact pressure tends to increase in increasing Froude number. （Fn） The bending moment and torque defined at the centre gravity due to hogging and sagging events can be predicted well, and their effects on the ship increase in increasing wave length even though the impact pressure decreases in increasing wave length after wave length λ/L, where L is ship length, is equal to 1.0. Moreover, hydroelastie behaviors affect the large heave and pitch amplitudes. Finally, the developed scheme can predict simultaneously hydrodynamic and hydroelastic with a strongly nonlinear interaction between wave and ship.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant No. 52071161)。
文摘Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly limits the accuracy of numerical analyses and finite element simulations. Therefore, this paper takes a new type of floating wind turbine as an example and performs a physical model test on the wave slamming characteristics of this floating wind turbine.Based on a 1:50 model of the Pivot Buoy floating wind turbine, an experimental study is performed under the combined effects of wind-wave loads on the peak pressure, duration, and pressure distribution of slamming. First, two sets of mooring systems, the combined scheme and the full mooring chain scheme, are designed to conduct a series of experimental studies of model slamming under different wind and wave incidence angles, wave heights, and wave periods. By doing so, the slamming characteristics of the wind turbine can be obtained. Moreover, to solve the problem of the large pitch motion response of the prototype wind turbine, a set of vertically oscillating structures is designed,and the slamming pressure characteristics of the optimized model are also investigated through model tests.
基金Supported by Portuguese Foundation for Science and Technology(Fundacao para a Ciencia e Tecnologia-FCT)
文摘The paper presents an overview of studies of slamming on ship structures. This work focuses on the hull slamming, which is one of the most important types of slamming problems to be considered in the ship design process and the assessment of the ship safety. There are three main research aspects related to the hull slamming phenomenon, a) where and how often a slamming event occurs, b) slamming load prediction and c) structural response due to slamming loads. The approaches used in each aspect are reviewed and commented, together with the presentation of some typical results. The methodology, which combines the seakeeping analysis and slamming load prediction, is discussed for the global analysis of the hull slamming of a ship in waves. Some physical phenomena during the slamming event are discussed also. Recommendations for the future research and developments are made.
基金support from the National Natural Science Foundation of China (Nos. 51579103 and 51709118)the China Postdoctoral Science Foundation (No. 2017M612669)+2 种基金the Fundamental Research Funds for the Central Universities (No. 2017BQ089)the Key Scientific Research Projects in Henan Province (No. 18B570005)the Open Research Foundation of Key Laboratory of the Pearl River Estuarine Dynamics and Associated Process Regulation, Ministry of Water Resources ([2017]KJ01)
文摘This paper presents the probability distribution of the slamming pressure from an experimental study of regular wave slamming on an elastically supported horizontal deck. The time series of the slamming pressure during the wave impact were first obtained through statistical analyses on experimental data. The exceeding probability distribution of the maximum slamming pressure peak and distribution parameters were analyzed, and the results show that the exceeding probability distribution of the maximum slamming pressure peak accords with the three-parameter Weibull distribution. Furthermore, the range and relationships of the distribution parameters were studied. The sum of the location parameter D and the scale parameter L was approximately equal to 1.0, and the exceeding probability was more than 36.79% when the random peak was equal to the sample average during the wave impact. The variation of the distribution parameters and slamming pressure under different model conditions were comprehensively presented, and the parameter values of the Weibull distribution of wave-slamming pressure peaks were different due to different test models. The parameter values were found to decrease due to the increased stiffness of the elastic support. The damage criterion of the structure model caused by the wave impact was initially discussed, and the structure model was destroyed when the average slamming time was greater than a certain value during the duration of the wave impact. The conclusions of the experimental study were then described.
文摘A boundary element method is developed for calculating the flare ship hull slamming problem. The nonlinear free surface elevation and the linear element assumption are employed. The method has been verified by comparisons with results for the water entry of wedges with various deadrise angles. Numerical results show that the pressure distribution varies greatly with the ship hull with different curvilinear equations, and the slamming features are also different; From the numerical simulation, the authors found that the structural damage of the flare hull might be caused by the increasing hydrodynamic pressure over an extensive area on the flare when the upper part of the flare comes into contact with water.
文摘The sensitivity of moving particle semi-implicit(MPS)simulations to numerical parameters is investigated in this study.Although the verifcation and validation(V&V)are important to ensure accurate numerical results,the MPS has poor perfor-mance in convergences with a time step size.Therefore,users of the MPS need to tune numerical parameters to ft results into benchmarks.However,such tuning parameters are not always valid for other simulations.We propose a practical numerical condition for the MPS simulation of a two-dimensional wedge slamming problem(i.e.,an MPS-slamming condition).The MPS-slamming condition is represented by an MPS-slamming number,which provides the optimum time step size once the MPS-slamming number,slamming velocity,deadrise angle of the wedge,and particle size are decided.The simulation study shows that the MPS results can be characterized by the proposed MPS-slamming condition,and the use of the same MPS-slamming number provides a similar fow.
基金This reseaschis supported by the National Natural Science Foundation of China (Grant No50409014) by the Science Foundation of Liaoning Province (Grant No20041075)
文摘The purpose of this paper is to investigate the instantaneous properties of wave slanuning on the plate structure of an open structure. The advanced instantaneous measuring technique-Particle Image Velocimetry （PIV） is applied to acquire the instantaneous velocity field of wave slamming. From the cross-correlation analysis results of the images captured by the CCD camera, the flow fields of wave impacting on the structure are displayed visually, and the instantaneous whole- field fluid velocity vectors are obtained. The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis.
基金the National Natural Science Foundation of China(Grant No.51979130)the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20170575 and BK20191460).
文摘In this paper,a method about the water-entry slamming of a two-dimensional(2D)bow structure has been proposed based on the experimental and simulation results.According to this method,the sensitivity analysis has been carried out about the effect of speed and inclination angle on the slamming pressure of the bow.Firstly,a 2D ship bow experimental model was performed to obtain the slamming pressure distribution at different measuring points under different speeds.Then,numerical simulation for the water-entry slamming of this experimental model was conducted to obtain the pressure distribution on the experimental model under different working conditions.Finally,the experimental results were compared with the numerical simulation results to evaluate the effect of speed and inclination angle on the slamming pressure of the bow.The results show that the slamming pressure is more sensitive to speed variation within the low-speed range.The effect of inclination angle on the slamming pressure is more obvious in the small angle condition.When the inclination angle is larger than 45°,the effect is limited.
基金financially supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20170575)University Science Research Project of Jiangsu Province(Grant No.17KJB580005)
文摘Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.
基金the National Natural Science Foundation of China(No.11072149)
文摘A design of offshore floating structure is mainly based on the extreme response analysis due to the forces experienced. The extreme response can induce the negative air gap response and potential impact to the deck bottom of floating structure. It is important to predict the slamming load in order to check the strength of local structures which withstand the wave slamming. In recent years, studies of the effects of wind load on air gap response and slamming load are ignored. When the platform suffers the extreme wave, the wind is also harsh.Moreover, the wind load can affect the motion response of the platform. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Though the model test results are not accurate enough for air gap and slamming load evaluation due to the loss of wind effect, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. This paper aims at presenting the sensitivity analysis results of wave slamming load with respect to the wind load for the design of semi-submersible platform. As an example of semi-submersible drilling platform design, the wind tunnel test has been carried out, and the sea-keeping model test is also performed in towing tank, while the wind load effect is ignored. According to the model test results, a numerical model is tuned and validated by ANSYS AQWA. Sensitivity analysis studies of the relative velocity between water particle and platform surface and the wave slamming load with respect to the wind load are performed in time domain by the tuned numerical model.Five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52025112 and 51861130358)the State Key Laboratory of Ocean Engineering+1 种基金China(Shanghai Jiao Tong University)(Grant No.1905)the Newton Advanced Fellowships(Grant No.NAF\R1\180304)by the Royal Society。
文摘Coastal wave energy resources have enormous exploitation potential due to shorter weather window,closer installation distance and lower maintenance cost.However,impact loads generated by depth variation from offshore to nearshore and wave-current interaction,may lead to a catastrophic damage or complete destruction to wave energy converters(WECs).This objective of this paper is to investigate slamming response of a coastal oscillating wave surge converter(OWSC)entering or leaving water freely.Based on fully nonlinear potential flow theory,a time-domain wave-current-structure interaction model combined with higher-order boundary element method(HOBEM),is developed to analyze the coupled hydrodynamic problem.The variable-depth seabed is considered in the model to illustrate the shallow water effect on impact loads and free surface profiles in coastal zone.A domain decomposition approach is utilized to simulate the overlapping phenomenon generated by a jet falling into water under gravity effect.Through a series of Lagrangian interpolation methods,the meshes on boundaries are rearranged to avoid the mismatch between element size on free surface and body surface.The present model is validated against the existing experimental and numerical results.Simulations are also provided for the effects of wave-current interaction and uneven local seabed on the slamming responses.It is found that the length of the splash jet increases for a following current and decreases for an opposing current,and that the slamming response of the OWSC device is sensitive to the geometric features of the uneven seabed.
基金Supported by Portuguese Foundation for Science and Technology(Fundacao para a Ciencia e Tecnologia-FCT)
文摘A hydroelastic analysis of a rectangular plate subjected to slamming loads is presented. An analytical model based on Wagner theory is used for calculations of transient slamming load on the ship plate. A thin isotropic plate theory is considered for determining the vibration of a rectangular plate excited by an external slamming force. The forced vibration of the plate is calculated by the modal expansion method. Analytical results of the transient response of a rectangular plate induced by slamming loads are compared with numerical calculations from finite element method. The theoretical slamming pressure based on Wagner model is applied on the finite element model of a plate. Good agreement is obtained between the analytical and numerical results for the structural deflection of a rectangular plate due to slamming pressure. The effects of plate dimension and wave profile on the structural vibration are discussed as well. The results show that a low impact velocity and a small wetted radial length of wave yield negligible effects of hydroelasticity.
基金the National High Technology Research and Development Programof China (863 Program,Grant No.2006AA09A109-6)the Science and Technology Commission of Shanghai Municipality (Grant No.05DJ14001)
文摘The water entry of large diameter cylindrical structure is studied by applying numerical simulation method. The processes of different diameter cyhndrical structures impacting water with various constant velocities are calculated numerically. Thereafter, analyzed are the distribution of slamming pressure on structure during slamming course and the influence of slamming velocity and cylindrical diameter on slamming process. Furthermore, presented herein is an equation being used to forecast the peak slamming force on a large diameter cylindrical structure.
基金the Foundation for Distinguished Young Talents in Higher Education of Guangdong Province(No.2017KQNCX004)the Natural Science Foundation of Guangdong Province(No.2018A030310378)
文摘With the development of ships towards large scale, high speed and light weight, ship hydroelastic responses and slamming strength issues are becoming increasingly important. In this paper, a time-domain nonlinear hydroelasticity theory is developed to predict ship motion and load responses in harsh regular waves.Hydrostatic restoring force, wave excitation force and radiation force are calculated on the instantaneously wetted body surface to consider the nonlinear effects caused by large amplitude motions of ship in steep waves. A twodimensional(2 D) generalized Wagner model and a one-dimensional(1 D) dam-breaking model are used to estimate the impact loads caused by bow flare slamming and green water on deck, respectively;the impact loads are coupled with the hydroelastic equation in time-domain. Moreover, segmented model tests are carried out in a towing tank to investigate the wave and slamming loads acting on the hull sailing in harsh regular head waves and also validate the numerical results.
基金supported by the ChinaMinistry of Education Key Research Project "KSHIP-II Project"(Knowledge-based Ship Design Hyper-Integrated Platform)No.GKZY010004the National Key Basic Research Program of China No.2014CB046804
文摘Since the research of flare slamming prediction is seldom when parametric rolling happens, we present an efficient approximation method for flare slamming analysis of large container ships in parametric rolling conditions. We adopt a 6-DOF weakly nonlinear time domain model to predict the ship motions of parametric rolling conditions. Unlike previous flare slamming analysis, our proposed method takes roll motion into account to calculate the impact angle and relative vertical velocity between ship sections on the bow flare and wave surface. We use the Wagner model to analyze the slamming impact forces and the slamming occurrence probability. Through numerical simulations, we investigate the maximum flare slamming pressures of a container ship for different speeds and wave conditions. To further clarify the mechanism of flare slamming phenomena in parametric rolling conditions, we also conduct real-time simulations to determine the relationship between slamming pressure and 3-DOF motions, namely roll, pitch, and heave.
文摘The paper presents an empirical method to calculate bow flare slamming pressure and the green water load. Many empirical formulae for various types of vessels have been provided by rules of ship classification societies. In the present work, attempt is made to develop generalized formulations for all types of displacement vessels. Extreme sea conditions are considered. Bow flare pressure is derived in terms of flare and waterline angles. Specific condition for limiting waterline angle is derived based on 2 D numerical simulations. Deck wetness is derived in terms of static and dynamic swell-up and the relative motion. Variation of static swell along the length is determined based on potential solution based analyses considering variation in vessels’ hull. 2 D wedge simulations are carried out to validate the formulation of dynamic swell-up. Results of the calculated bow flare and deck pressures are compared with various ship classification society formulations and the trends are found to be in good agreement in general barring at bow flare where lower pressure is found in most of the presented cases. Also IACS UR S21 A(2018) governing minimum pressure for deck scantlings is found to be conservative in few of the presented cases. Although scantlings assessment is not performed, the presented new formulations may help in realistic assessment of scantlings.
文摘Aimed at the hydrodynamic response for marine structures slamming into water, based on the mechanism analysis to the slamming process, and by combining 3D N-S equation and k-ε turbulent kinetic equation with structure fully 6DOF motion equation, a mathematical model for the wind-fluid-solid interaction is established in 3D marine structure slamming wave at free poses and wind-wave-flow complex environments. Compared with the results of physical model test, the numerical results from the slamming wave well correspond with the experimental results. Through the mathematical model, the wave-making issue of 3D marine structure at initial pose falls into water in different complex wind, wave and flow environments is investigated. The research results show that various kinds of natural factors and structure initial poses have different influence on the slamming wave, and there is an obvious rule in this process.
基金The project is supported by National Natural Science Foundation of China.
文摘The elasto-plastic dynamic buckling and postbuckling phenomena of square plates subjected to in-plane solid-fluid slamming are investigated. According to the plate's response, the critical criteria for dynamic buckling, dynamic plasticity and plastic collapse are defined, and the corresponding critical impulses are presented. Meanwhile, dynamic buckling modes and collapse models are observed. The effects of different boundary conditions and loading histories on the properties of buckling and postbuckling are discussed.
文摘The present research deals with the numerical prediction of the air gap within the 6th generation of deepwater drilling floating semi-submersible platform and the experimental studies on the slamming loadings onto the structure. The survivability of the floating model with a mooring system was tested under extreme wave of 10-year return period. In the numerical simulation of the Gaussian method,the narrow band model was applied to obtain the first-order wave surface equation and the modified second-order wave surface equation. The hydrodynamic responses of the floating body,i.e. radiation damping,added mass,second-order wave excitation force and drifting force,were computed by using the potential flow theory based on higher order boundary element method in frequent domain. In the experimental analysis,high-frequency sensors were installed at the lower deck to measure the wave slamming loads. Equivalent truncated mooring system was applied to make sure position of the floating body in the wave tank. The comparison between the numerical and experimental results showed the numerical model underestimated the air gap of the floating body. Nevertheless,the predictions of the high risk spots underneath the floating deck that is prone to wave slamming obtained from both models were agreeable to each other. The experimental results also revealed that the wave slamming events often occurred at the connection point between the rear columns and the lower deck.
文摘Capable and accurate predictions of some effects of strongly nonlinear interaction wave-ship associated with hydroelastic behaviors are very required for simulation tool in naval architect and ocean engineering. It can guarantee ship safety at the sea state by producing proper design. Therefore, we have developed a hybrid scheme based on both grid and particle method. In order to clarify hydroelastic behaviors of a ship, a dropping test of a ship with elastic motion has been performed firstly. The developed scheme has been then validated on ship dropping case under the same conditions with experiment. The comparisons showed consistently in good agreement. Furthermore, evaluation on hydroelastic behaviors of ship motion under slamming, the impact pressure tends to increase in increasing Froude number. （Fn） The bending moment and torque defined at the centre gravity due to hogging and sagging events can be predicted well, and their effects on the ship increase in increasing wave length even though the impact pressure decreases in increasing wave length after wave length λ/L, where L is ship length, is equal to 1.0. Moreover, hydroelastie behaviors affect the large heave and pitch amplitudes. Finally, the developed scheme can predict simultaneously hydrodynamic and hydroelastic with a strongly nonlinear interaction between wave and ship.
