The deep‐sea ground contains a huge amount of energy and mineral resources,for example,oil,gas,and minerals.Various infrastructures such as floating structures,seabed structures,and foundations have been developed to...The deep‐sea ground contains a huge amount of energy and mineral resources,for example,oil,gas,and minerals.Various infrastructures such as floating structures,seabed structures,and foundations have been developed to exploit these resources.The seabed structures and foundations can be mainly classified into three types:subsea production structures,offshore pipelines,and anchors.This study reviewed the development,installation,and operation of these infrastructures,including their structures,design,installation,marine environment loads,and applications.On this basis,the research gaps and further research directions were explored through this literature review.First,different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations.Second,the subsea production structures,including subsea manifolds and their foundations,were reviewed and discussed.Third,the basic characteristics and design methods of deep‐sea pipelines,including subsea pipelines and risers,were analyzed and reviewed.Finally,the installation and bearing capacity of deep‐sea subsea anchors and seabed trench influence on the anchor were reviewed.Through the review,it was found that marine environment conditions are the key inputs for any offshore structure design.The fabrication,installation,and operation of infrastructures should carefully consider the marine loads and geological conditions.Different structures have their own mechanical problems.The fatigue and stability of pipelines mainly depend on the soil‐structure interaction.Anchor selection should consider soil types and possible trench formation.These focuses and research gaps can provide a helpful guide on further research,installation,and operation of deep‐sea structures and foundations.展开更多
In this paper, the buoyancy, kinetic properties and stability of air floated structures have been studied by theoretical and experimental methods. The equations for calculation of the buoyancy of the air floated buoy ...In this paper, the buoyancy, kinetic properties and stability of air floated structures have been studied by theoretical and experimental methods. The equations for calculation of the buoyancy of the air floated buoy are derived according to the Boyler law and the equilibrium equations of the air floated structure are established. Through simplification of the air floated structure as a single freedom rigid body and spring system, the natural period of heaving and some kinetic properties are discussed. In the stability analysis, the formulas for calculation of the meta centric height are presented. The theoretical results are in good agreement with the data observed from the model test and prototype test. The air buoyancy decrease coefficient presented in this paper has a large influence on the floating state, stability and dynamic properties of the air floated structure. The stability of the air floated structure can also be judged by the parameter of meta centric height, and calculations show that the air floated structure is less stable than the conventional float.展开更多
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
Analytical and numerical investigation is made of the source potential for-floating structure with forward speed in waves. A particular form is selected for numerical applications, where the double integral of the Gre...Analytical and numerical investigation is made of the source potential for-floating structure with forward speed in waves. A particular form is selected for numerical applications, where the double integral of the Green function is transformed into the single one and the oscillation characteristics for integrands in the specific computation domain are treated numerically. A comparison of calculated examples with published data is given and it shows that the numerical simulation is satisfactory and the accuracy is adequate to engineering application.展开更多
This article reviews scouring and liquefaction issues for anchor foundations of floating offshore wind farms.The review is organized in two sections:(1)the scouring issues for drag-embedment anchors(DEAs)and other sub...This article reviews scouring and liquefaction issues for anchor foundations of floating offshore wind farms.The review is organized in two sections:(1)the scouring issues for drag-embedment anchors(DEAs)and other subsea structures associated with DEAs such as tensioners,clump weights,and chains in floating offshore wind farms;and(2)the liquefaction issues for the same types of structures,particularly for DEAs.The scouring processes are described in detail,and the formulae and design guidelines for engineering predictions are included for quantities like scour depth,time scale,and sinking due to general shear failure of the bed soil caused by scoui\The latter is furnished with numerical examples.Likewise,in the second section,the liquefaction processes are described with special reference to residual liquefaction where pore-water pressure builds up in undrained soils(such as fine sand and silt)under waves,leading to liquefaction of the bed soil and precipitating failure of DEAs and their associated subsea structures.An integrated mathematical model to deal with liquefaction around and the resulted sinking failure of DEAs,introduced in a recent study,has been revisited.Implementation of the model is illustrated with a numerical example.It is believed that the present review and the existing literatures from the"neighboring"fields form a complementary source of information on scour and liquefaction around foundations of floating offshore wind farms.展开更多
A numerical model is developed by use of the boundary integral equation method to investigate the responses of a two-dimensional floating structure. The structure under consideration consisting of two pontoons, is con...A numerical model is developed by use of the boundary integral equation method to investigate the responses of a two-dimensional floating structure. The structure under consideration consisting of two pontoons, is connected by a rigid framework, and linked to the sea floor by a mooring system. The theoretical conception is based on potential theory with hnear external forces, and applied to an arbitrarily shaped body and water depth. The discussion includes the influence of draft and space between pontoons on the responses of the floating structure. Finally, the validity of the method is adequately verified by experimental results.展开更多
Transportation of floating structures for long distance has always been associated with the use of heavy semi transport vessel. The requirements of this type of vessel are always special, and its availability is limit...Transportation of floating structures for long distance has always been associated with the use of heavy semi transport vessel. The requirements of this type of vessel are always special, and its availability is limited. To prepare for the future development of the South China Sea deepwater projects, COOEC has recently built a heavy lift transport vessel - Hai Yang Shi You 278 (HYSY278). This semi-submersible vessel has displacement capacity of 50k DWT, and a breath of 42 m. Understanding the vessel's applicability and preparing its use for future deepwater projects are becoming imminent need. This paper reviews the critical issues associated with the floating structure transportation and performs detailed analysis of two designed floating structures during transportation. The newly built COOEC transportation vessel HYSY278 will be used to dry transport the floating structures from COOEC fabrication yard in Qingdao to the oil field in the South China Sea. The entire process will start with load-out/float-offthe floating structures from the construction sites, offload the platform from the vessel if needed, dry transport floating structures through a long distance, and finally offload the platform. Both hydrodynamic and struc^tral analyses are performed to evaluate transport vessel and floating structures. Critical issues associated with the transportation and offloading of platform from the vessel will be studied in detail. Detailed study is performed to evaluate the response of the system during this phase and additional work needed to make the vessel feasible for use of this purpose. The results demonstrate that with proper modifications, HYSY278 can effectively be used for transporting structures with proper arrangement and well-prepared operation. The procedure and details are presented on the basis of study results. Special attentions associated with future use will also be discussed based on the results from analysis.展开更多
With the increasing application of floating platforms in deep waters and harsh environments,a proper assessment of the reliability of floating structures is important to ensure that these structures can operate safely...With the increasing application of floating platforms in deep waters and harsh environments,a proper assessment of the reliability of floating structures is important to ensure that these structures can operate safely during their design lives.This study outlines a practical methodology for reliability analysis of a semi-submersible platform based estimating the probability distribution of the extreme response in rough sea conditions(survival conditions).The Constrained NewWave(CNW)theory combined with Monte Carlo simulations was first applied to simulate the random wave surface elevation process in the time domain.A Gumbel distribution was the best fitting to describe the dynamically sensitive extreme response statistics under extreme waves(drift and mooring tension).The derived probability distribution of the extreme response was subsequently used in estimation of the associated limit state func-tion,and a reliability analysis of the floating structure was conducted using the Monte Carlo method.A semi-submersible platform in a water depth of 1500 m subjected to extreme wave loads was used to demonstrate the efficiency of the proposed methodology.The probability of failure of the semi-submersible when considering mooring lines tension is greater than considering drift.展开更多
The present work reports a Hybrid Modular Floating Structure(HMFS)system with typical malfunction conditions.The effects of both fractured mooring lines and failed connectors on main hydrodynamic responses(mooring lin...The present work reports a Hybrid Modular Floating Structure(HMFS)system with typical malfunction conditions.The effects of both fractured mooring lines and failed connectors on main hydrodynamic responses(mooring line tensions,module motions,connector loads and wave power production)of the HMFS system under typical sea con-ditions are comparatively investigated.The results indicate that the mooring tension distribution,certain module motions(surge,sway and yaw)and connector loads(Mz)are significantly influenced by mooring line fractures.The adjacent mooring line of the fractured line on the upstream side suffers the largest tension among the remaining mooring lines,and the case with two fractured mooring lines in the same group on the upstream side is the most dangerous among all cases of two-line failures in view of mooring line tensions,module motions and connector loads.There-fore,one emergency strategy with appropriate relaxation of a proper mooring line has been proposed and proved effective to reduce the risk of more progressive mooring line fractures.In addition,connector failures substantially affect certain module motions(heave and pitch),certain connector loads(Fz and My)and wave power production.The present work can be helpful and instructive for studies on malfunction conditions of modular floating structure(MFS)systems.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
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
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
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
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
Responses of the very large floating Structures(VLFS)can be mitigated by implementing oscillating water columns(OWCs).This paper explores the fundamental mechanism of present wave interactions with both structures and...Responses of the very large floating Structures(VLFS)can be mitigated by implementing oscillating water columns(OWCs).This paper explores the fundamental mechanism of present wave interactions with both structures and examines the hydrodynamic performance of VLFS equipped with OWCs(VLFS-OWCs).Under the linear potential flow theory framework,the semi-analytical model of wave interaction with VLFS-OWCs is developed using the eigenfunction matching method.The semi-analytical model is verified using the Haskind relationship and wave energy conservation law.Results show that the system with dual-chamber OWCs has a wider frequency bandwidth in wave power extraction and hydroelastic response mitigation of VLFS.It is worth noting that the presence of Bragg resonance can be trigged due to wave interaction with the chamber walls and the VLFS,which is not beneficial for the wave power extraction performance and the protection of VLFS.展开更多
In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a t...In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a two-module semi-submersible-type VLFS.The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs.An integrated information system was set up to continuously collect and inspect the data of the encountered waves,structure responses,connector forces,mooring line forces,anti-corrosion status of the platform,the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater.In this paper,the status of the on-site measurements and validations of the key technologies are briefly described.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
An eigen-function expansion method based on a new orthogonal inner product is proposed by Sahoo et al. (2000) for the study of the hydroelastic response of mat-type VLFS in head seas. However, their main emphasis is o...An eigen-function expansion method based on a new orthogonal inner product is proposed by Sahoo et al. (2000) for the study of the hydroelastic response of mat-type VLFS in head seas. However, their main emphasis is on the effect of edge conditions and they assume that the plate is of a semi-infinite length. In reality, the plate is of finite length. For consideration of the finite length effect, the reflection and transmission from the other end must be considered. The effect of this reflection and transmission on the hydroelastic response of VLFS is of interest for practical application. Furthermore, the physical meaning of the new inner product was not given in their paper. In this paper, it is shown that the new inner product can he derived from the governing equation and the bottom boundary conditions. Then the same eigen-function expansion method is adopted for the study of the hydroelastic response of an elastic plate of finite length in surface waves. Detailed comparisons are made between the present finite length model and the semi-infinite model and between the present model predictions and the experimental results. It is found that that the finite length effect is significant and the accuracy of present model is higher than the semi-infinite model. Furthermore, a new phenomenon, which is not mentioned in Sahoo et al. (2000), is found. Taht is, for larger L/h ratios, the reflection and transmission coefficients will oscillate with the non-dimensional parameter k(0) h. Further study is needed for full understanding of this phenomenon.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
基金Key Research and Development program of Zhejiang ProvinceGrant/Award Number:2018C03031+3 种基金The Open Foundation of Key Laboratory of Offshore Geotechnical and Material Engineering of Zhejiang Province,Grant/Award Number:OGME21003Natural Science Foundation of Zhejiang Province,Grant/Award Numbers:LHZ19E090003,LY15E090002Norges Forskningsr?d,Grant/Award Number:OGME21003National Natural Science Foundation of China,Grant/Award Numbers:51209183,51779220,52101334。
文摘The deep‐sea ground contains a huge amount of energy and mineral resources,for example,oil,gas,and minerals.Various infrastructures such as floating structures,seabed structures,and foundations have been developed to exploit these resources.The seabed structures and foundations can be mainly classified into three types:subsea production structures,offshore pipelines,and anchors.This study reviewed the development,installation,and operation of these infrastructures,including their structures,design,installation,marine environment loads,and applications.On this basis,the research gaps and further research directions were explored through this literature review.First,different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations.Second,the subsea production structures,including subsea manifolds and their foundations,were reviewed and discussed.Third,the basic characteristics and design methods of deep‐sea pipelines,including subsea pipelines and risers,were analyzed and reviewed.Finally,the installation and bearing capacity of deep‐sea subsea anchors and seabed trench influence on the anchor were reviewed.Through the review,it was found that marine environment conditions are the key inputs for any offshore structure design.The fabrication,installation,and operation of infrastructures should carefully consider the marine loads and geological conditions.Different structures have their own mechanical problems.The fatigue and stability of pipelines mainly depend on the soil‐structure interaction.Anchor selection should consider soil types and possible trench formation.These focuses and research gaps can provide a helpful guide on further research,installation,and operation of deep‐sea structures and foundations.
文摘In this paper, the buoyancy, kinetic properties and stability of air floated structures have been studied by theoretical and experimental methods. The equations for calculation of the buoyancy of the air floated buoy are derived according to the Boyler law and the equilibrium equations of the air floated structure are established. Through simplification of the air floated structure as a single freedom rigid body and spring system, the natural period of heaving and some kinetic properties are discussed. In the stability analysis, the formulas for calculation of the meta centric height are presented. The theoretical results are in good agreement with the data observed from the model test and prototype test. The air buoyancy decrease coefficient presented in this paper has a large influence on the floating state, stability and dynamic properties of the air floated structure. The stability of the air floated structure can also be judged by the parameter of meta centric height, and calculations show that the air floated structure is less stable than the conventional float.
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.
文摘Analytical and numerical investigation is made of the source potential for-floating structure with forward speed in waves. A particular form is selected for numerical applications, where the double integral of the Green function is transformed into the single one and the oscillation characteristics for integrands in the specific computation domain are treated numerically. A comparison of calculated examples with published data is given and it shows that the numerical simulation is satisfactory and the accuracy is adequate to engineering application.
基金supported by the ERA-NET Cofund MarTERA Program under EU Horizon 2020 Framework(NuLIMAS,Grant No.728053)the German Federal Ministry for Economic Affairs and Energy(Grant No.03SX524A)+1 种基金the Scientific and Technological Research Council of Turkey(Grant No.TEYDEB-1509/9190068)the Polish National Centre for Research and Development.
文摘This article reviews scouring and liquefaction issues for anchor foundations of floating offshore wind farms.The review is organized in two sections:(1)the scouring issues for drag-embedment anchors(DEAs)and other subsea structures associated with DEAs such as tensioners,clump weights,and chains in floating offshore wind farms;and(2)the liquefaction issues for the same types of structures,particularly for DEAs.The scouring processes are described in detail,and the formulae and design guidelines for engineering predictions are included for quantities like scour depth,time scale,and sinking due to general shear failure of the bed soil caused by scoui\The latter is furnished with numerical examples.Likewise,in the second section,the liquefaction processes are described with special reference to residual liquefaction where pore-water pressure builds up in undrained soils(such as fine sand and silt)under waves,leading to liquefaction of the bed soil and precipitating failure of DEAs and their associated subsea structures.An integrated mathematical model to deal with liquefaction around and the resulted sinking failure of DEAs,introduced in a recent study,has been revisited.Implementation of the model is illustrated with a numerical example.It is believed that the present review and the existing literatures from the"neighboring"fields form a complementary source of information on scour and liquefaction around foundations of floating offshore wind farms.
文摘A numerical model is developed by use of the boundary integral equation method to investigate the responses of a two-dimensional floating structure. The structure under consideration consisting of two pontoons, is connected by a rigid framework, and linked to the sea floor by a mooring system. The theoretical conception is based on potential theory with hnear external forces, and applied to an arbitrarily shaped body and water depth. The discussion includes the influence of draft and space between pontoons on the responses of the floating structure. Finally, the validity of the method is adequately verified by experimental results.
基金funded by the State Key Project "Installation Technical Study for Deepwater Floating Structure"
文摘Transportation of floating structures for long distance has always been associated with the use of heavy semi transport vessel. The requirements of this type of vessel are always special, and its availability is limited. To prepare for the future development of the South China Sea deepwater projects, COOEC has recently built a heavy lift transport vessel - Hai Yang Shi You 278 (HYSY278). This semi-submersible vessel has displacement capacity of 50k DWT, and a breath of 42 m. Understanding the vessel's applicability and preparing its use for future deepwater projects are becoming imminent need. This paper reviews the critical issues associated with the floating structure transportation and performs detailed analysis of two designed floating structures during transportation. The newly built COOEC transportation vessel HYSY278 will be used to dry transport the floating structures from COOEC fabrication yard in Qingdao to the oil field in the South China Sea. The entire process will start with load-out/float-offthe floating structures from the construction sites, offload the platform from the vessel if needed, dry transport floating structures through a long distance, and finally offload the platform. Both hydrodynamic and struc^tral analyses are performed to evaluate transport vessel and floating structures. Critical issues associated with the transportation and offloading of platform from the vessel will be studied in detail. Detailed study is performed to evaluate the response of the system during this phase and additional work needed to make the vessel feasible for use of this purpose. The results demonstrate that with proper modifications, HYSY278 can effectively be used for transporting structures with proper arrangement and well-prepared operation. The procedure and details are presented on the basis of study results. Special attentions associated with future use will also be discussed based on the results from analysis.
基金supported by the National Key Research and Development Program of China(No.2016YFC0303401)the National Natural Science Foundation of China(No.51779236)the National Natural Science Foundation of China-Shandong Joint Fund(No.U1706226).
文摘With the increasing application of floating platforms in deep waters and harsh environments,a proper assessment of the reliability of floating structures is important to ensure that these structures can operate safely during their design lives.This study outlines a practical methodology for reliability analysis of a semi-submersible platform based estimating the probability distribution of the extreme response in rough sea conditions(survival conditions).The Constrained NewWave(CNW)theory combined with Monte Carlo simulations was first applied to simulate the random wave surface elevation process in the time domain.A Gumbel distribution was the best fitting to describe the dynamically sensitive extreme response statistics under extreme waves(drift and mooring tension).The derived probability distribution of the extreme response was subsequently used in estimation of the associated limit state func-tion,and a reliability analysis of the floating structure was conducted using the Monte Carlo method.A semi-submersible platform in a water depth of 1500 m subjected to extreme wave loads was used to demonstrate the efficiency of the proposed methodology.The probability of failure of the semi-submersible when considering mooring lines tension is greater than considering drift.
基金supported by Shenzhen Science and Technology Program(Grant No.KQTD20210811090112003)the National Natural Science Foundation of China(Grant No.52161041).
文摘The present work reports a Hybrid Modular Floating Structure(HMFS)system with typical malfunction conditions.The effects of both fractured mooring lines and failed connectors on main hydrodynamic responses(mooring line tensions,module motions,connector loads and wave power production)of the HMFS system under typical sea con-ditions are comparatively investigated.The results indicate that the mooring tension distribution,certain module motions(surge,sway and yaw)and connector loads(Mz)are significantly influenced by mooring line fractures.The adjacent mooring line of the fractured line on the upstream side suffers the largest tension among the remaining mooring lines,and the case with two fractured mooring lines in the same group on the upstream side is the most dangerous among all cases of two-line failures in view of mooring line tensions,module motions and connector loads.There-fore,one emergency strategy with appropriate relaxation of a proper mooring line has been proposed and proved effective to reduce the risk of more progressive mooring line fractures.In addition,connector failures substantially affect certain module motions(heave and pitch),certain connector loads(Fz and My)and wave power production.The present work can be helpful and instructive for studies on malfunction conditions of modular floating structure(MFS)systems.
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.
基金The Key Program for International Scientific and Technological Innovation Cooperation between Governments(Grant No.2019YFE0102500)National Natural Science Foundation of China(Grant No.52001086)China Postdoctoral Science Foundation Funded Project(Grant No.2019M661257).
文摘Responses of the very large floating Structures(VLFS)can be mitigated by implementing oscillating water columns(OWCs).This paper explores the fundamental mechanism of present wave interactions with both structures and examines the hydrodynamic performance of VLFS equipped with OWCs(VLFS-OWCs).Under the linear potential flow theory framework,the semi-analytical model of wave interaction with VLFS-OWCs is developed using the eigenfunction matching method.The semi-analytical model is verified using the Haskind relationship and wave energy conservation law.Results show that the system with dual-chamber OWCs has a wider frequency bandwidth in wave power extraction and hydroelastic response mitigation of VLFS.It is worth noting that the presence of Bragg resonance can be trigged due to wave interaction with the chamber walls and the VLFS,which is not beneficial for the wave power extraction performance and the protection of VLFS.
基金supported by the Ministry of Industry and Information Technology(Grant No.[2016]22)the Ministry of Science and Technology(Grant No.2013CB36100)+2 种基金supports of the High-tech Ships Research Program([2016]22 and[2019]357)of the Ministry of Industry and Information Technologythe State Key Fundamental Research Program(2013CB036100)and the National Key Research and Development Program(No.2017YFBO202701)of the Ministry of Scienceand Technologythe Jiangsu Province Science Foundation for Youths(BK20190151).
文摘In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a two-module semi-submersible-type VLFS.The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs.An integrated information system was set up to continuously collect and inspect the data of the encountered waves,structure responses,connector forces,mooring line forces,anti-corrosion status of the platform,the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater.In this paper,the status of the on-site measurements and validations of the key technologies are briefly described.
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.
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(00XD14015)
文摘An eigen-function expansion method based on a new orthogonal inner product is proposed by Sahoo et al. (2000) for the study of the hydroelastic response of mat-type VLFS in head seas. However, their main emphasis is on the effect of edge conditions and they assume that the plate is of a semi-infinite length. In reality, the plate is of finite length. For consideration of the finite length effect, the reflection and transmission from the other end must be considered. The effect of this reflection and transmission on the hydroelastic response of VLFS is of interest for practical application. Furthermore, the physical meaning of the new inner product was not given in their paper. In this paper, it is shown that the new inner product can he derived from the governing equation and the bottom boundary conditions. Then the same eigen-function expansion method is adopted for the study of the hydroelastic response of an elastic plate of finite length in surface waves. Detailed comparisons are made between the present finite length model and the semi-infinite model and between the present model predictions and the experimental results. It is found that that the finite length effect is significant and the accuracy of present model is higher than the semi-infinite model. Furthermore, a new phenomenon, which is not mentioned in Sahoo et al. (2000), is found. Taht is, for larger L/h ratios, the reflection and transmission coefficients will oscillate with the non-dimensional parameter k(0) h. Further study is needed for full understanding of this phenomenon.
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.