A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is ...A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet.展开更多
Great attention has been paid to the development of very large floating structures. Owing to their extreme large size and great flexibility, the coupling between the structural deformation and fluid motion is signific...Great attention has been paid to the development of very large floating structures. Owing to their extreme large size and great flexibility, the coupling between the structural deformation and fluid motion is significant. This is a typical problem of hydroelasticity. Efficient and accurate estimation of the hydroelastic response of very large floating structures in waves is very important for design. In this paper, the plate Green function and fluid Green function are combined to analyze the hydroelastic response of very large floating structures. The plate Green function here is a new one proposed by the authors and it satisfies all boundary conditions for free-free rectangular plates on elastic foundations. The results are compared with some experimental data. It is shown that the method proposed in this paper is efficient and accurate. Finally, various factors affecting the hydroelastic response of very large floating structures are also studied.展开更多
Loads generated after an air crash, ship collision, and other accidents may destroy very large floating structures （VLFSs） and create additional connector loads. In this study, the combined effects of ship collision...Loads generated after an air crash, ship collision, and other accidents may destroy very large floating structures （VLFSs） and create additional connector loads. In this study, the combined effects of ship collision and wave loads are considered to establish motion differential equations for a multi-body VLFS. A time domain calculation method is proposed to calculate the connector load of the VLFS in waves. The Longuet-Higgins model is employed to simulate the stochastic wave load. Fluid force and hydrodynamic coefficient are obtained with DNV Sesam software. The motion differential equation is calculated by applying the time domain method when the frequency domain hydrodynamic coefficient is converted into the memory function of the motion differential equation of the time domain. As a result of the combined action of wave and impact loads, high-frequency oscillation is observed in the time history curve of the connector load. At wave directions of 0° and 75°, the regularities of the time history curves of the connector loads in different directions are similar and the connector loads of C1 and C2 in the X direction are the largest. The oscillation load is observed in the connector in the Y direction at a wave direction of 75° and not at 0° This paper presents a time domain calculation method of connector load to provide a certain reference function for the future development of Chinese VLFS展开更多
Costs and losses induced by possible future extreme environmental conditions and difficulties in repairing post yielding damage strongly suggest the need for proper consideration in design rather than just life loss ...Costs and losses induced by possible future extreme environmental conditions and difficulties in repairing post yielding damage strongly suggest the need for proper consideration in design rather than just life loss prevention. This can be addressed through the development of design methodology that balances the initial cost of the very large floating structure (VLFS) against the expected potential losses resulting from future extreme wave induced structural damage. Here, the development of a methodology for determining optimal, cost effective design will be presented and applied to a VLFS located in the Tokyo bay. Optimal design criteria are determined based on the total expected life cycle cost and acceptable damage probability and curvature of the structure, and a set of sizes of the structure are obtained. The methodology and applications require expressions of the initial cost and the expected life cycle damage cost as functions of the optimal design variables. This study includes the methodology, total life cycle cost function, structural damage modeling, and reliability analysis.展开更多
Based on the elastic foundation beam theory and the multi-floating-module hydrodynamic theory,a novel method is proposed to estimate the dynamic responses of VLFS(Very Large Floating Structure).In still water,a VLFS c...Based on the elastic foundation beam theory and the multi-floating-module hydrodynamic theory,a novel method is proposed to estimate the dynamic responses of VLFS(Very Large Floating Structure).In still water,a VLFS can be simplified as an elastic foundation beam model or a multi-floating-module model connected by elastic hinges.According to equivalent displacement of the two models in static analysis,the problem of rotation stiffness of elastic hinges can be solved.Then,based on the potential flow theory,the dynamic responding analysis of multi-floatingmodule model under wave loads can be computed in ANSYS-AQWA software.By assembling the time domain analysis results of each module,the dynamic responses of the VLFS can be obtained.Validation of the method is conducted through a series of comparison calculations,which mainly includes a continuous structure and a three-part structure connected by hinges in regular waves.The results of this paper method show a satisfactory agreement with the experiment and calculation data given in relative references.展开更多
A conceptual design of using novel telescopic piles to position a multi-modular very large floating structure(VLFS),which is supposed to be severed as a movable floating airport,is proposed.The telescopic piles can au...A conceptual design of using novel telescopic piles to position a multi-modular very large floating structure(VLFS),which is supposed to be severed as a movable floating airport,is proposed.The telescopic piles can automatically plug in the soil to resist the environmental loads and pull out from the soil to evacuate or move on to the next operational sea.The feasibility demonstration of the conceptual design includes two parts:function verification and structure design.In the latter part of the conceptual design,a time-domain structural analysis is firstly conducted by using Abaqus software.The simulation results suggest that the preliminary structure scheme is not optimum due to the insufficient structure utilization,although both structure safety of the piles and positioning accuracy are guaranteed.To realize a cost reduction of construction and installation,a Genetic Algorithm-Finite Element Analysis(GA-FEA)method is employed to perform structural optimization.After optimization,31 percent of the weight of each pile is reduced and higher structure utilization is maintained.The difference of the self-weight and allowable buoyancy of a single module(SMOD)of a semisubmersible-type VLFS is much larger than the weight of the piles.Combined with the function verification in our previous work,the conceptual design of using the novel telescopic pile to position VLFS is demonstrated to be feasible.展开更多
超大浮式结构(very large floating structure,简称VLFS)是集空港和海港为一体的大型海上多功能浮式结构,现有研究大多关注规则波下刚性模块柔性连接模型的动力响应,忽略了台风浪极端环境下海上机场自身柔性引起的非线性振动特性。针对...超大浮式结构(very large floating structure,简称VLFS)是集空港和海港为一体的大型海上多功能浮式结构,现有研究大多关注规则波下刚性模块柔性连接模型的动力响应,忽略了台风浪极端环境下海上机场自身柔性引起的非线性振动特性。针对此问题,提出了一种新型多柔-刚性混合模块建模方法,采用Jonswap谱特征参数对台风“鲇鱼”过境实测海浪谱开展了精细化仿真模拟,分析了台风浪下海上机场VLFS整体和局部非线性动态响应特性,揭示了海上机场与环境荷载之间的能量转换机理。结果表明:海上机场多柔-刚性混合模块模型可以较好地反映此类VLFS结构动力响应特性;海上机场超长柔性及台风浪场不均匀性使其结构呈现显著非线性,位移、转角和水弹性变形分别以沿波向、绕展向和沿垂向为主,极值应力主要分布于撑杆附近;环境荷载能量和结构重力势能在初始阶段主要转换为系泊势能,稳定阶段则主要转换为结构动能和弹性势能。展开更多
The wave-induced hydroelastic responses of a thin elastic plate floating on a three-layer fluid, under the assumption of linear potential flow, are investigated for two-dimensional cases. The effect of the lateral str...The wave-induced hydroelastic responses of a thin elastic plate floating on a three-layer fluid, under the assumption of linear potential flow, are investigated for two-dimensional cases. The effect of the lateral stretching or compressive stress is taken into account for plates of either semi-infinite or finite length. An explicit expression for the dispersion relation of the flexural-gravity wave in a three-layer fluid is analytically deduced. The equations for the velocity potential and the wave elevations are solved with the method of matched eigenfunction expansions. To simplify the calculation on the unknown expansion coefficients, a new inner product with orthogonality is proposed for the three-layer fluid, in which the vertical eigenfunctions in the open-water region are involved. The accuracy of the numerical results is checked with an energy conservation equation, representing the energy flux relation among three incident wave modes and the elastic plate. The effects of the lateral stresses on the hydroelastic responses are discussed in detail.展开更多
The present study aims to give general hints about hydrodynamic interactions for water wave diffraction on a super large floating structure composed of a large number of box-shaped modules with many small gaps in betw...The present study aims to give general hints about hydrodynamic interactions for water wave diffraction on a super large floating structure composed of a large number of box-shaped modules with many small gaps in between. And meanwhile, it also aims to seek for an effective way to take the gap influence into consideration without numerical difficulties existing in conventional methods. An asymptotic matching technique is exploited by virtue of the smallness of gaps. Formal potential solutions are established for the near field around the gap ends and the far field away from gap ends, respectively, and the unknowns in those solutions are uniquely determined by asymptotic matching. The eigen-function expansion method is used for the outer far field and a series of pulsating sources at each gap end is introduced to simulate the gap influence. Strong hydrodynamic interaction is observed and a new resonant phenomenon, the mechanism of which differs absolutely from any known ones, is revealed in the present study. Sharp peak responses for both vertical and horizontal wave-exciting forces on each block are found around some special resonance frequencies, which depend on the draft of the structure and the gap width. The present results are of practical significance to the design of links (connectors) of modules for super large floating structures. And the importance is also closely related to the hydro-elasticity analysis for super large floating structures, in which local loads may be as important as the integrated loads.展开更多
Very Large Floating Structures (VLFS) have received considerable attention recently. Efficient and accurate estimation of their hydroelastic responses in waves is very important for the design. The most efficient appr...Very Large Floating Structures (VLFS) have received considerable attention recently. Efficient and accurate estimation of their hydroelastic responses in waves is very important for the design. The most efficient approach would obviously be the analytical one, Within the category of analytical approaches, the simplified method proposed by Ohkusu and his colleague are of special characteristics. However, when one studies their methods, several questions arise. The purpose of this paper is to critically study the simplified methods proposed by Ohkusu and his colleague in order to answer these questions. Some problems in their original methods have been found and possible improvements are suggested. It is concluded that the improved simplified method using the same idea of Ohkusu and his colleague could provide a reasonable estimate of the hydroelastic response of mat-like VLFS in a certain range of incident angles of waves.展开更多
Very Large Floating Structures (VLFS) have drawn considerable attention recently due to their potential significance in the exploitation of ocean resources and in the utilization of ocean space. Efficient and accurate...Very Large Floating Structures (VLFS) have drawn considerable attention recently due to their potential significance in the exploitation of ocean resources and in the utilization of ocean space. Efficient and accurate estimation of their hydroelastic responses to waves is very important for the design. Recently, an efficient numerical algorithm was developed by Ertekin and Kim (1999). However, in their analysis, the linear Level I Green-Naghdi (GN) theory is employed to describe fluid dynamics instead of the conventional linear wave (LW) theory of finite water depth. They claimed that this linear level I GN theory provided better predictions of the hydroelastic responses of VLFS than the linear wave theory. In this paper, a detailed derivation is given in the conventional linear wave theory framework with the same quantity as used in the linear level I GN theory framework. This allows a critical comparison between the linear wave theory and the linear level I GN theory. It is found that the linear level I GN theory can be regarded as an approximation to the linear wave theory of finite water depth. The consequences of the differences between these two theories in the predicted hydroelastic responses are studied quantitatively. And it is found that the linear level I GN theory is not superior to the linear wave theory. Finally, various factors affecting the hydroelastic response of VLFS are studied with the implemented algorithm.展开更多
A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated bas...A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated based on the linear theory of fluid and the structural response is analyzed based on the thin plate theory. The FEM truncates the unbounded fluid domain by introducing an artificial boundary surface, thus defining a finite computational domain. At this boundary surface an impedance boundary conditions are applied so that no wave reflections occur. In the proposed scheme, all of the procedures are processed directly in time domain, which is efficient for nonlinear analyses of structure floating on unbounded fluid. Numerical results indicate acceptable accuracy of the proposed method.展开更多
Very large floating structures (VLFS) have an extremely large size of several kilometers in length, thus, the environment at one end of the platform may be different from that at the other end. The importance of such ...Very large floating structures (VLFS) have an extremely large size of several kilometers in length, thus, the environment at one end of the platform may be different from that at the other end. The importance of such an inhomogeneous environment to the hydroelastic response of a VLFS is of obvious concern for practical application. Some studies have been carried out to investigate the effects of shoreline proximity, breakwaters and harbor walls. In this paper, the impact of the variable depth on the hydroelastic responses of a VLFS is investigated. For simplicity, an ascending plane slope is taken to simulate the varying bottom although the method is capable of treating a bottom of arbitrary variation. The long wave theory and the thin plate theory are employed to model the wave field and the mat-like VLFS respectively. The finite difference method is used to numerically solve the boundary value problem. The results for the zero inclination slope are compared with experimental data and an analytical method to validate the present numerical method. Finally the effect of the inclination of the slope on reflection and transmission coefficients and plate deflections are investigated thoroughly.展开更多
This paper is concerned with the hydroelastic responses of a mat-like, rectangular very large floating structure(VLFS) edged with a pair of horizontal/inclined perforated anti-motion plates in the context of the direc...This paper is concerned with the hydroelastic responses of a mat-like, rectangular very large floating structure(VLFS) edged with a pair of horizontal/inclined perforated anti-motion plates in the context of the direct coupling method. The updated Lagrangian formulae are applied to establish the equilibrium equations of the VLFS and the total potential formula is employed for fluids in the numerical model including the viscous effect of the perforated plates through the Darcy’s law. The hybrid finite element-boundary element(FE-BE) method is implemented to determine the response reduction of VLFS with attached perforated plates under various oblique incident waves.Also, the numerical solutions are validated against a series of experimental tests. The effectiveness of the attached perforated plates in reducing the deflections of the VLFS can be significantly improved by selecting the proper design parameters such as the porous parameter, submergence depth, plate width and inclination angle for the given sea conditions.展开更多
The hydroelastic response of very large floating structures (VLFS) under the action of ocean waves is analysed considering the small amplitude wave theory. The very large floating structure is modelled as a floating t...The hydroelastic response of very large floating structures (VLFS) under the action of ocean waves is analysed considering the small amplitude wave theory. The very large floating structure is modelled as a floating thick elastic plate based on Timoshenko- Mindlin plate theory, and the analysis for the hydroelastic response is performed considering different edge boundary conditions. The numerical study is performed to analyse the wave reflection and transmission characteristics of the floating plate under the influence of different support conditions using eigenfunction expansion method along with the orthogonal mode-coupling relation in the case of finite water depth. Further, the analysis is extended for shallow water depth, and the continuity of energy and mass flux is applied along the edges of the plate to obtain the solution for the problem. The hydroelastic behaviour in terms of reflection and transmission coefficients, plate deflection, strain, bending moment and shear force of the floating thick elastic plate with support conditions is analysed and compared for finite and shallow water depth. The study reveals an interesting aspect in the analysis of thick floating elastic plate with support condition due to the presence of the rotary inertia and transverse shear deformation. The present study will be helpful for the design and analysis of the VLFS in the case of finite and shallow water depth.展开更多
The free-surface wave interaction with a pontoon-type very large floating structure(VLFS) is analyzed by utilizing a modal expansion method. The modal expansion method consists of separating the hydrodynamic analysis ...The free-surface wave interaction with a pontoon-type very large floating structure(VLFS) is analyzed by utilizing a modal expansion method. The modal expansion method consists of separating the hydrodynamic analysis and the dynamic response analysis of the structure. In the dynamic response analysis of the structure,the deflection of the structure with various edge conditions is decomposed into vibration modes that can be arbitrarily chosen. Free-free beam model, pinned-free beam model and fixed-free beam model are three different types of edge conditions considered in this study. For each of these beam models, the detailed mathematical formulations for calculating the corresponding eigenvalues and eigenmodes have been given, and the mathematical formulations corresponding to the beam models of pinned-free beam and fixed-free beam are novel. For the hydrodynamic analysis of the structure, the boundary value problem(BVP) equations in terms of plate modes have been established, and the BVP equations corresponding to the beam models of pinned-free beam and fixedfree beam are also novel. When these BVP equations are solved numerically, the structure deflections and the wave reflection and transmission coefficients can be obtained. These calculation results point out some findings valuable for engineering design.展开更多
The linearity assumption is widely used when acquiring the hydrodynamic coefficients of a floating structure.However,the linear damping is frequently underestimated,especially for the natural frequency.To investigate ...The linearity assumption is widely used when acquiring the hydrodynamic coefficients of a floating structure.However,the linear damping is frequently underestimated,especially for the natural frequency.To investigate the sloping seafloor effects on the damping terms of a single module of a semi-submersible Very Large Floating Structure(VLFS),this paper revisits the conventional formulation and further proposes the direct integration method for obtaining the linear and quadratic damping coefficients from free-decay tests.Numerical free-decay simulations of the single module over variable bathymetry are carried out by the CFD numerical tank.Corresponding model tests are also implemented to verify and validate against the numerical solutions.The effects of the sloping seafloor,as well as the water depth,on the hydrodynamic coefficients are investigated based on the validated CFD modeling.Both numerical and experimental results indicate that the acquisition of the linear and quadratic damping coefficients is sensitive to the data-processing and identification approaches.For the case studied in present paper,the identification errors introduced by the conventional method are 1.5%while they are 0.5%using the direct integration method.The quadratic damping coefficient for heave mode decreases about 10.4%when the sloping angle increases from 0 to 6 deg.展开更多
文摘A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet.
文摘Great attention has been paid to the development of very large floating structures. Owing to their extreme large size and great flexibility, the coupling between the structural deformation and fluid motion is significant. This is a typical problem of hydroelasticity. Efficient and accurate estimation of the hydroelastic response of very large floating structures in waves is very important for design. In this paper, the plate Green function and fluid Green function are combined to analyze the hydroelastic response of very large floating structures. The plate Green function here is a new one proposed by the authors and it satisfies all boundary conditions for free-free rectangular plates on elastic foundations. The results are compared with some experimental data. It is shown that the method proposed in this paper is efficient and accurate. Finally, various factors affecting the hydroelastic response of very large floating structures are also studied.
基金Foundation item： Supported by the National Natural Science Foundation of China （51309123）, National Key Basic Research and Development Plan （973 Plan, 2013CB036104）, Jiangsu Province Natural Science Research Projects in Colleges and Universities （13KJB570002）, Open Foundation of State Key Laboratory of Ocean Engineering （1407）, ＂Qing Lan Project＂ of Colleges and Universities in Jiangsu Province, Academic Program Development of Jiangsu Higher Education Institutions （PAPD）.
文摘Loads generated after an air crash, ship collision, and other accidents may destroy very large floating structures （VLFSs） and create additional connector loads. In this study, the combined effects of ship collision and wave loads are considered to establish motion differential equations for a multi-body VLFS. A time domain calculation method is proposed to calculate the connector load of the VLFS in waves. The Longuet-Higgins model is employed to simulate the stochastic wave load. Fluid force and hydrodynamic coefficient are obtained with DNV Sesam software. The motion differential equation is calculated by applying the time domain method when the frequency domain hydrodynamic coefficient is converted into the memory function of the motion differential equation of the time domain. As a result of the combined action of wave and impact loads, high-frequency oscillation is observed in the time history curve of the connector load. At wave directions of 0° and 75°, the regularities of the time history curves of the connector loads in different directions are similar and the connector loads of C1 and C2 in the X direction are the largest. The oscillation load is observed in the connector in the Y direction at a wave direction of 75° and not at 0° This paper presents a time domain calculation method of connector load to provide a certain reference function for the future development of Chinese VLFS
文摘Costs and losses induced by possible future extreme environmental conditions and difficulties in repairing post yielding damage strongly suggest the need for proper consideration in design rather than just life loss prevention. This can be addressed through the development of design methodology that balances the initial cost of the very large floating structure (VLFS) against the expected potential losses resulting from future extreme wave induced structural damage. Here, the development of a methodology for determining optimal, cost effective design will be presented and applied to a VLFS located in the Tokyo bay. Optimal design criteria are determined based on the total expected life cycle cost and acceptable damage probability and curvature of the structure, and a set of sizes of the structure are obtained. The methodology and applications require expressions of the initial cost and the expected life cycle damage cost as functions of the optimal design variables. This study includes the methodology, total life cycle cost function, structural damage modeling, and reliability analysis.
基金financially supported by the High-Tech Ship Research Projects sponsored by the Ministry of Industry and Information Technology of China(Grant No.[2019]357)China Postdoctoral Science Foundation(Grant No.2020M683755)。
文摘Based on the elastic foundation beam theory and the multi-floating-module hydrodynamic theory,a novel method is proposed to estimate the dynamic responses of VLFS(Very Large Floating Structure).In still water,a VLFS can be simplified as an elastic foundation beam model or a multi-floating-module model connected by elastic hinges.According to equivalent displacement of the two models in static analysis,the problem of rotation stiffness of elastic hinges can be solved.Then,based on the potential flow theory,the dynamic responding analysis of multi-floatingmodule model under wave loads can be computed in ANSYS-AQWA software.By assembling the time domain analysis results of each module,the dynamic responses of the VLFS can be obtained.Validation of the method is conducted through a series of comparison calculations,which mainly includes a continuous structure and a three-part structure connected by hinges in regular waves.The results of this paper method show a satisfactory agreement with the experiment and calculation data given in relative references.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51709170 and 51979167)the Ministry of Industry and Information Technology of China(Grant No.2018473)the Shanghai Sailing Program(Grant No.17YF1409700)。
文摘A conceptual design of using novel telescopic piles to position a multi-modular very large floating structure(VLFS),which is supposed to be severed as a movable floating airport,is proposed.The telescopic piles can automatically plug in the soil to resist the environmental loads and pull out from the soil to evacuate or move on to the next operational sea.The feasibility demonstration of the conceptual design includes two parts:function verification and structure design.In the latter part of the conceptual design,a time-domain structural analysis is firstly conducted by using Abaqus software.The simulation results suggest that the preliminary structure scheme is not optimum due to the insufficient structure utilization,although both structure safety of the piles and positioning accuracy are guaranteed.To realize a cost reduction of construction and installation,a Genetic Algorithm-Finite Element Analysis(GA-FEA)method is employed to perform structural optimization.After optimization,31 percent of the weight of each pile is reduced and higher structure utilization is maintained.The difference of the self-weight and allowable buoyancy of a single module(SMOD)of a semisubmersible-type VLFS is much larger than the weight of the piles.Combined with the function verification in our previous work,the conceptual design of using the novel telescopic pile to position VLFS is demonstrated to be feasible.
文摘超大浮式结构(very large floating structure,简称VLFS)是集空港和海港为一体的大型海上多功能浮式结构,现有研究大多关注规则波下刚性模块柔性连接模型的动力响应,忽略了台风浪极端环境下海上机场自身柔性引起的非线性振动特性。针对此问题,提出了一种新型多柔-刚性混合模块建模方法,采用Jonswap谱特征参数对台风“鲇鱼”过境实测海浪谱开展了精细化仿真模拟,分析了台风浪下海上机场VLFS整体和局部非线性动态响应特性,揭示了海上机场与环境荷载之间的能量转换机理。结果表明:海上机场多柔-刚性混合模块模型可以较好地反映此类VLFS结构动力响应特性;海上机场超长柔性及台风浪场不均匀性使其结构呈现显著非线性,位移、转角和水弹性变形分别以沿波向、绕展向和沿垂向为主,极值应力主要分布于撑杆附近;环境荷载能量和结构重力势能在初始阶段主要转换为系泊势能,稳定阶段则主要转换为结构动能和弹性势能。
基金Project supported by the National Basic Research Program of China(973 Programm)(No.2014CB046203)the National Natural Science Foundation of China(No.11472166)the Natural Science Foundation of Shanghai(No.14ZR1416200)
文摘The wave-induced hydroelastic responses of a thin elastic plate floating on a three-layer fluid, under the assumption of linear potential flow, are investigated for two-dimensional cases. The effect of the lateral stretching or compressive stress is taken into account for plates of either semi-infinite or finite length. An explicit expression for the dispersion relation of the flexural-gravity wave in a three-layer fluid is analytically deduced. The equations for the velocity potential and the wave elevations are solved with the method of matched eigenfunction expansions. To simplify the calculation on the unknown expansion coefficients, a new inner product with orthogonality is proposed for the three-layer fluid, in which the vertical eigenfunctions in the open-water region are involved. The accuracy of the numerical results is checked with an energy conservation equation, representing the energy flux relation among three incident wave modes and the elastic plate. The effects of the lateral stresses on the hydroelastic responses are discussed in detail.
基金Project supported by the National Natural Science Foundation of China(Grant No.59879011 and 19732004)the Foundation of the Ministry of Education of China
文摘The present study aims to give general hints about hydrodynamic interactions for water wave diffraction on a super large floating structure composed of a large number of box-shaped modules with many small gaps in between. And meanwhile, it also aims to seek for an effective way to take the gap influence into consideration without numerical difficulties existing in conventional methods. An asymptotic matching technique is exploited by virtue of the smallness of gaps. Formal potential solutions are established for the near field around the gap ends and the far field away from gap ends, respectively, and the unknowns in those solutions are uniquely determined by asymptotic matching. The eigen-function expansion method is used for the outer far field and a series of pulsating sources at each gap end is introduced to simulate the gap influence. Strong hydrodynamic interaction is observed and a new resonant phenomenon, the mechanism of which differs absolutely from any known ones, is revealed in the present study. Sharp peak responses for both vertical and horizontal wave-exciting forces on each block are found around some special resonance frequencies, which depend on the draft of the structure and the gap width. The present results are of practical significance to the design of links (connectors) of modules for super large floating structures. And the importance is also closely related to the hydro-elasticity analysis for super large floating structures, in which local loads may be as important as the integrated loads.
基金The project was supported by the National Natural Science Foundation of China (Grant No. 50039010) the Science and Technology Development Foundation of Shanghai Municipal Government (Grant No. 00XD14015).
文摘Very Large Floating Structures (VLFS) have received considerable attention recently. Efficient and accurate estimation of their hydroelastic responses in waves is very important for the design. The most efficient approach would obviously be the analytical one, Within the category of analytical approaches, the simplified method proposed by Ohkusu and his colleague are of special characteristics. However, when one studies their methods, several questions arise. The purpose of this paper is to critically study the simplified methods proposed by Ohkusu and his colleague in order to answer these questions. Some problems in their original methods have been found and possible improvements are suggested. It is concluded that the improved simplified method using the same idea of Ohkusu and his colleague could provide a reasonable estimate of the hydroelastic response of mat-like VLFS in a certain range of incident angles of waves.
基金by the National Natural Science Foundation of China(50039010)the Science and Technology Development Foundation of Shanghai Municipal Government(00XD14015)
文摘Very Large Floating Structures (VLFS) have drawn considerable attention recently due to their potential significance in the exploitation of ocean resources and in the utilization of ocean space. Efficient and accurate estimation of their hydroelastic responses to waves is very important for the design. Recently, an efficient numerical algorithm was developed by Ertekin and Kim (1999). However, in their analysis, the linear Level I Green-Naghdi (GN) theory is employed to describe fluid dynamics instead of the conventional linear wave (LW) theory of finite water depth. They claimed that this linear level I GN theory provided better predictions of the hydroelastic responses of VLFS than the linear wave theory. In this paper, a detailed derivation is given in the conventional linear wave theory framework with the same quantity as used in the linear level I GN theory framework. This allows a critical comparison between the linear wave theory and the linear level I GN theory. It is found that the linear level I GN theory can be regarded as an approximation to the linear wave theory of finite water depth. The consequences of the differences between these two theories in the predicted hydroelastic responses are studied quantitatively. And it is found that the linear level I GN theory is not superior to the linear wave theory. Finally, various factors affecting the hydroelastic response of VLFS are studied with the implemented algorithm.
文摘A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated based on the linear theory of fluid and the structural response is analyzed based on the thin plate theory. The FEM truncates the unbounded fluid domain by introducing an artificial boundary surface, thus defining a finite computational domain. At this boundary surface an impedance boundary conditions are applied so that no wave reflections occur. In the proposed scheme, all of the procedures are processed directly in time domain, which is efficient for nonlinear analyses of structure floating on unbounded fluid. Numerical results indicate acceptable accuracy of the proposed method.
文摘Very large floating structures (VLFS) have an extremely large size of several kilometers in length, thus, the environment at one end of the platform may be different from that at the other end. The importance of such an inhomogeneous environment to the hydroelastic response of a VLFS is of obvious concern for practical application. Some studies have been carried out to investigate the effects of shoreline proximity, breakwaters and harbor walls. In this paper, the impact of the variable depth on the hydroelastic responses of a VLFS is investigated. For simplicity, an ascending plane slope is taken to simulate the varying bottom although the method is capable of treating a bottom of arbitrary variation. The long wave theory and the thin plate theory are employed to model the wave field and the mat-like VLFS respectively. The finite difference method is used to numerically solve the boundary value problem. The results for the zero inclination slope are compared with experimental data and an analytical method to validate the present numerical method. Finally the effect of the inclination of the slope on reflection and transmission coefficients and plate deflections are investigated thoroughly.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51490672,51579122 and51609109)the Natural Science Foundation of Jiangsu Province(Grant No.BK20160556)+1 种基金the University Natural Science Research Project of Jiangsu Province(Grant No.16kjb70003)the Key Lab Foundation for Advanced Manufacturing Technology of Jiangsu Province(Grant No.CJ1506)
文摘This paper is concerned with the hydroelastic responses of a mat-like, rectangular very large floating structure(VLFS) edged with a pair of horizontal/inclined perforated anti-motion plates in the context of the direct coupling method. The updated Lagrangian formulae are applied to establish the equilibrium equations of the VLFS and the total potential formula is employed for fluids in the numerical model including the viscous effect of the perforated plates through the Darcy’s law. The hybrid finite element-boundary element(FE-BE) method is implemented to determine the response reduction of VLFS with attached perforated plates under various oblique incident waves.Also, the numerical solutions are validated against a series of experimental tests. The effectiveness of the attached perforated plates in reducing the deflections of the VLFS can be significantly improved by selecting the proper design parameters such as the porous parameter, submergence depth, plate width and inclination angle for the given sea conditions.
基金NITK SurathkalMHRD+2 种基金the Science and Engineering Research Board(SERB)Department of Science&Technology(DST)Government of India,for supporting financially under the Young Scientist research grant No.YSS/2014/000812
文摘The hydroelastic response of very large floating structures (VLFS) under the action of ocean waves is analysed considering the small amplitude wave theory. The very large floating structure is modelled as a floating thick elastic plate based on Timoshenko- Mindlin plate theory, and the analysis for the hydroelastic response is performed considering different edge boundary conditions. The numerical study is performed to analyse the wave reflection and transmission characteristics of the floating plate under the influence of different support conditions using eigenfunction expansion method along with the orthogonal mode-coupling relation in the case of finite water depth. Further, the analysis is extended for shallow water depth, and the continuity of energy and mass flux is applied along the edges of the plate to obtain the solution for the problem. The hydroelastic behaviour in terms of reflection and transmission coefficients, plate deflection, strain, bending moment and shear force of the floating thick elastic plate with support conditions is analysed and compared for finite and shallow water depth. The study reveals an interesting aspect in the analysis of thick floating elastic plate with support condition due to the presence of the rotary inertia and transverse shear deformation. The present study will be helpful for the design and analysis of the VLFS in the case of finite and shallow water depth.
基金the Research Project from the Chinese State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University(No.GKZD010038)
文摘The free-surface wave interaction with a pontoon-type very large floating structure(VLFS) is analyzed by utilizing a modal expansion method. The modal expansion method consists of separating the hydrodynamic analysis and the dynamic response analysis of the structure. In the dynamic response analysis of the structure,the deflection of the structure with various edge conditions is decomposed into vibration modes that can be arbitrarily chosen. Free-free beam model, pinned-free beam model and fixed-free beam model are three different types of edge conditions considered in this study. For each of these beam models, the detailed mathematical formulations for calculating the corresponding eigenvalues and eigenmodes have been given, and the mathematical formulations corresponding to the beam models of pinned-free beam and fixed-free beam are novel. For the hydrodynamic analysis of the structure, the boundary value problem(BVP) equations in terms of plate modes have been established, and the BVP equations corresponding to the beam models of pinned-free beam and fixedfree beam are also novel. When these BVP equations are solved numerically, the structure deflections and the wave reflection and transmission coefficients can be obtained. These calculation results point out some findings valuable for engineering design.
基金the support of the National Natural Science Foundation of China(Grant No.51979167,51179103)the Ministry of Industry and Information Technology(Grant No.[2018]473)+1 种基金the China Scholarship Council(Grant 201806230206)the Hainan Provincial Joint Project of Sanya Bay Science and Technology City(Grant No.520LH051).
文摘The linearity assumption is widely used when acquiring the hydrodynamic coefficients of a floating structure.However,the linear damping is frequently underestimated,especially for the natural frequency.To investigate the sloping seafloor effects on the damping terms of a single module of a semi-submersible Very Large Floating Structure(VLFS),this paper revisits the conventional formulation and further proposes the direct integration method for obtaining the linear and quadratic damping coefficients from free-decay tests.Numerical free-decay simulations of the single module over variable bathymetry are carried out by the CFD numerical tank.Corresponding model tests are also implemented to verify and validate against the numerical solutions.The effects of the sloping seafloor,as well as the water depth,on the hydrodynamic coefficients are investigated based on the validated CFD modeling.Both numerical and experimental results indicate that the acquisition of the linear and quadratic damping coefficients is sensitive to the data-processing and identification approaches.For the case studied in present paper,the identification errors introduced by the conventional method are 1.5%while they are 0.5%using the direct integration method.The quadratic damping coefficient for heave mode decreases about 10.4%when the sloping angle increases from 0 to 6 deg.
