Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Functi...Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Function （UDF）, an Eulerian two-phase model, which includes an Euler-Euler coupled model for water and sediment phases, and a turbulent model for the fluid phase, is adopted to predict the scour depth around pipelines. The model is verified by observation data obtained from laboratory experiments. On the basis of the simulations, the factors affecting the scour depth, including the effects of incipient velocity, pipe diameter and sediment particle size and so on, were investigated. Meanwhile, according to formulas of incipient velocity of various sediments, approximate calculation on theoretical scour depths is developed for pipelines of seven stations in the South China Sea, where engineering application information is available.展开更多
The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during deepwater installation has drawn a great deal of attention. Extended from the model initiall...The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during deepwater installation has drawn a great deal of attention. Extended from the model initially proposed by Kyriakides and his co-workers, a 2D theoretical model which can successfully account for the case of simultaneous tension, bending, and external pressure is further developed. To confirm the accuracy of this theoretical method, numerical simulations are conducted using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. The model is then used to study the effects of several important factors such as load path, material prop-erties, and diameter-to-thickness ratio, etc., on buckling behaviors of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which aims to provide the design guidelines for deepwater pipeline with solid theoretical basis.展开更多
Drying （conditioning） is an important procedure to prevent hydrate formation during gas pipeline gas-up and to protect pipelines against corrosion. The air-drying method is preferred in offshore gas pipelines pre-co...Drying （conditioning） is an important procedure to prevent hydrate formation during gas pipeline gas-up and to protect pipelines against corrosion. The air-drying method is preferred in offshore gas pipelines pre-commissioning. The air-drying process of gas pipelines commonly includes two steps, air purging and soak test. The mass conservation and the phase equilibrium theory are applied to setting up the mathematical models of air purging, which can be used to simulate dry airflow rate and drying time. Fick diffusion law is applied to setting up the mathematical model of soak test, which can predict the water vapor concentration distribution. The results calculated from the purging model and the soak test model are in good agreement with the experimental data in the DF 1-1 offshore production pipeline conditioning. The models are verified to be available for the air-drying project design of offshore gas pipelines. Some proposals for airdrying engineering and operational procedures are put forward by analyzing the air-drying process of DFI-1 gasexporting pipelines.展开更多
In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a ...In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a weak water exchange capacity and high ecological fragility.However,at present,more than 200 oil platforms have been built in the Bohai Sea,with more than 270 offshore oil pipelines having a length exceeding 1600 km.The oil spill pollution of offshore platforms has a great impact on the marine environment and ecosystems.Therefore,a comprehensive assessment of its risks is of great practical significance.This paper systematically constructs a comprehensive oil spill risk assessment model that combines the oil spill risk probability model and the ocean hydrodynamic model.This paper uses the Bohai Sea offshore pipeline as an example to assess its oil spill risk.The high-risk-value areas of the Bohai Sea offshore pipeline are mainly distributed at the bottom of Liaodong Bay,the bottom of Bohai Bay,near the Caofeidian area,and the northern part of the Yellow River Estuary.展开更多
The significant point is the bidirectional interaction technique in FSI analysis while investigating subsea corrosion effect. By this way, pipe environment is accurately modelled and fluid effects are also considered....The significant point is the bidirectional interaction technique in FSI analysis while investigating subsea corrosion effect. By this way, pipe environment is accurately modelled and fluid effects are also considered. The effect of external corrosion defects on structural behaviour of a pipeline is studied by creating a nonlinear numerical model based on the finite element method according to ABAQUS analysis program. Corrosion losses of sections are obtained from experimental results and applied to the model. Numerical model is formed by a span of sub-sea pipeline that is subjected to environmental loads. Seismic and wind-generated irregular wave loads are considered as environmental loads. Irregular wave is represented with equivalent eight regular waves via FFT. The pipe is modelled according to two different types which are non-corroded（intact） and corroded（deteriorated） to demonstrate corrosion effects on it. The visible type of corrosion in marine environment is named ‘pitting＇ corrosion, in which the material loss is locally interpenetrated over the surface. By considering this situation, the corroded and non-corroded pipes are modelled as 3D solid elements. The main point is revealing how the subsea corrosion affects the structural behaviour of pipelines on the basis of implementation of experimental results to a model structure due to changes of stresses and displacement.展开更多
The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unste...The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×10^4.Evaluation of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2.展开更多
The buckling propagation in marine pipelines is studied by means of the cylindrical shell model in this paper. Several parameters including geometrical parameter D/ T, L/ D, physical parameter E and σy are discussed....The buckling propagation in marine pipelines is studied by means of the cylindrical shell model in this paper. Several parameters including geometrical parameter D/ T, L/ D, physical parameter E and σy are discussed. The computed results are compared with the available experimental data and other computed results, it is found that the present are closer to the experimental results than other computed results.展开更多
The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore refineries.Interactions between the pipeline and an erodible bed ...The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore refineries.Interactions between the pipeline and an erodible bed under the influence of current and waves often lead to local scouring around the structure.When this occurs, the pipeline may be suspended on the seabed resulting in the formation of a span.If the free span is long enough, the pipe may experience resonant flow-induced oscillations,leading to structural failure.This study examines the complex flow-structure-sediment interaction leading to the development of local scour holes around submarine pipelines.It reviews published literature in this area,which primarily is confined to the development of 2- dimensional scour holes.Despite the abundance of such research studies,pipeline-scour in the field essentially is 3-dimensional in nature.Hence,most of these studies have overlooked the importance of the transverse dimension of the scour hole,while emphasizing on its vertical dimension.This clearly is an issue that must be re-examined in light of the potential hazard and environmental disaster that one faces in the event of a pipeline failure.Recent studies have begun to recognize this shortcoming,and attempts have been made to overcome the deficiency.The study presents the state-of-the-art knowledge on local scour at submarine pipelines,both from a 2-dimensional as well as the 3-dimensional perspective.展开更多
To the potential oil-spill risk caused by offshore pipeline more attention has been paid after the Dalian oil spill incident from oil-pipeline explosion. Since then an issue about how to prevent and control the sudden...To the potential oil-spill risk caused by offshore pipeline more attention has been paid after the Dalian oil spill incident from oil-pipeline explosion. Since then an issue about how to prevent and control the sudden oil-spill from the offshore pipeline has been raised. In this paper, we proposed an optimized model to analyze the main causes(probability) of spill and the consequence with the fuzzy comprehensive assessment model. Considering the complicated assessment process for oil-spill, the assessment factor system involving the spill probability and consequence was established based on the operative manual and statistic leakage/damage data of offshore pipeline in order to estimate the integrated spill risk score automatically. The evaluated factors of spill probability could be grouped into five aspects: corrosion, fatigue, national damage, third party, and operational fault; the consequence evaluated factors of spill included hazard of oil and impact-controlling capability. With some modifications based on experts' opinions, each of the evaluated factors in our work was developed with a relative weight and evaluation criterion. A test example for an offshore pipeline in the Bohai waters was described to show how the model can be used for an actual case in more detail. By using the oil-spill risk assessment model, it is easy to determine the risk level associated with the ongoing activity and management level and hence to take the risk mitigation action immediately.展开更多
A system designed for a rigid and flexible pipe laying purposes is presented in the paper.Mathematical and numerical models are developed by using the rigid finite element method（RFEM）.The RFEM is an efficient solut...A system designed for a rigid and flexible pipe laying purposes is presented in the paper.Mathematical and numerical models are developed by using the rigid finite element method（RFEM）.The RFEM is an efficient solution in the time domain.Static and dynamic problems related to pipe installation are solved by taking the advantage of simple interpretation and implementation of the method.Large deformations of the pipe during spooling and when it is reeled out at sea are considered.A material model implemented is used to take into consideration nonlinear material properties.In particular,the full elasto-plastic material characteristics with hardening and Bauschinger effect are included.Dynamic analyses are performed and the results attached in this work demonstrates how the sea conditions influence the machinery and pipeline,assuming a passive reel drive system. The influence of several other operational parameters on dynamic loads is verified.An active system,implemented as a part of the mathematical model,improves the system performance.Some results are presented as well.展开更多
A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anis...A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anisotropic material characteristics in longitudinal and circumferential direction of pipeline are also considered in the proposed equations. Simplified numerical method is used to solve the generalized expressions. The comparisons of numerical results based generalized solutions and full-scale experimental results are carried out. The predicted results agree reasonably well with the experiment results. Meanwhile, the effects of corrosion shapes and locations on the ultimate load capacity are studied.展开更多
-Based on the calculation model for the floating laying of the offshore oil pipeline, this paper analyses in detail the internal force, and deformation of the pipeline under a definite structural form (pipeline and bu...-Based on the calculation model for the floating laying of the offshore oil pipeline, this paper analyses in detail the internal force, and deformation of the pipeline under a definite structural form (pipeline and buoy) and the way of pulling. The obtained results can be used for the buoy deployment, structure design, and the determination of pulling parameters (the pulling force of the cable and its length, etc.), providing an effective analysis method for floating pipeline-laying. A calculation example is given to show the related calculation process and the main results are analyzed and discussed.展开更多
Leakages in oil pipelines can cause financial losses and several environmental damages, where large-scale offshore oil and gas exploration results in large releases of oil and gas into ocean waters. In the event of oi...Leakages in oil pipelines can cause financial losses and several environmental damages, where large-scale offshore oil and gas exploration results in large releases of oil and gas into ocean waters. In the event of oil leakage, an immediate and adequate response is required to reduce environmental damage, such as containment barriers, for example, which depends on the agglomeration of oil particles, velocity and tendency to propagation. Thus, the understanding of the fluid flow behavior around of subsea pipeline at different depths is crucial. On the other hand, the knowledge of interfacial phenomena of immiscible liquids allows the process of adjective migration in submarine pipelines. Consequently, this science enables the prediction of the behavior and the geometric shape of the water-oil interface and provides a phenomenological foundation concerning the theories of perturbation, the stability criteria and mathematical modeling, as well as the flow patterns in the neighborhoods and submerged pipelines. From this perspective, this work aims to study the oil dispersion in sea water caused by leakage in a submerged pipeline. Here, a two-dimensional mathematical model based on the mass and linear momentum conservation equations and the standard k-ε turbulence model, was developed. The dynamic behavior of the oil and water phases is evaluated by pressure fields, surface velocity, volumetric fraction and velocity vectors. Simulation results show the presence of oil flux from the pipe to the marine stream and vice-versa. Further, the increase in oil velocity at the pipe inlet leads to an increase in pressure drop.展开更多
This paper studies the coupling effect of the pipeline vibration on the seabed scour. A vertical two- dimensional model is applied to numerically investigate the local scour below a vibrating pipeline with different a...This paper studies the coupling effect of the pipeline vibration on the seabed scour. A vertical two- dimensional model is applied to numerically investigate the local scour below a vibrating pipeline with different amplitudes and periods. Using the scour underneath a fixed pipeline as a reference, this paper focuses on the impact of the pipeline vibration on the equilibrium scour depth. Generic relationships are established between the non-dimensional scour depth and the non-dimensional vibrating parameters, i.e., amplitude and frequency. The normalization process takes into account the influences of such parameters as the incoming flow velocity, pipe diameter, and Shields parameter. An empirical formula is proposed to quantify these relationships.展开更多
The safety of offshore pipeline has drawn a great deal of attention during deepwater installation due to the combined actions of high external pressure, axial tension, and bending moment. Meanwhile, the pipeline confi...The safety of offshore pipeline has drawn a great deal of attention during deepwater installation due to the combined actions of high external pressure, axial tension, and bending moment. Meanwhile, the pipeline configuration has a remarkable effect on the structural behaviour of the tube. The special studies focus on the deepwater S-lay technique in the present paper. The stiffened catenary theory is applied to establish the static equilibrium governing differential equation of a pipe element, and the solution equations of the total pipeline configuration from a lay-barge over a stinger to the seabed are derived, The numerical iteration method for solving pipeline configuration is described in detail, and the corresponding program is developed to conduct the analysis of effects of various parameters such as laying water depth, pipe diameter, thickness of concrete weighted coating layer, stinger length, control strain, and axial tension on pipeline configuration. The results show that the laying water depth, the submerged weight of the pipe, and the axial tension are the critical factors influencing pipeline configuration. In addition, geometrical parameters of the stinger such as length, radius, and shape have an important effect on the pipe-laying capacity of the vessel. The validity of the program is further verified by means of a comparison with results obtained from the commercial finite element software OFFPIPE.展开更多
Pipeline spans may occur due to natural seabed irregularities or local scour of bed sediment. The pure in-line（IL）vortex-induced vibrations（VIV） analysis of the free spans is an important subject for design of pip...Pipeline spans may occur due to natural seabed irregularities or local scour of bed sediment. The pure in-line（IL）vortex-induced vibrations（VIV） analysis of the free spans is an important subject for design of pipeline in uneven seabed. The main objective of this paper is to analyze the characteristics of pure IL VIV of a free spanning pipeline under general boundary conditions. An IL wake oscillator model which can describe the coupling of pipeline structure and fluctuating drag is introduced and employed. The coupled partial differential equations of structure and wake are transformed into a set of ordinary differential equations using two-mode Galerkin method. Some case studies are presented and thoroughly discussed in order to investigate the effects of internal fluid, axial force and boundary conditions on the pure IL VIV.展开更多
A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside t...A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The oscillatory flow in this study represents the action of waves. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-ε turbulence closure, as well as the sediment transport equations, are solved with the finite difference method in a curvilinear coordinate system. Both bed and suspended loads of sediment transport are included in the morphological model. Because of the lack of experimental data on the backfilling of pipeline trenches, the numerical model is firstly verified against three closely-relevant experiments available in literature. A detailed measurement of the channel migration phenomenon under steady currents is employed for the assessment of the integral performance of the model. The two experimental results from U-tube tests are used to validate the model's ability in predicting oscillatory flows. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development.展开更多
基金Foundation item： Supported by the State Key Laboratory of Hydraulic Engineering Simulation and Safety （Grant No. HESS-1401）, the National Natural Science Foundation of China （Grant No. 51279124）, the Marine Science and Technology Foundation of South China Sea Branch, State Oceanic Administration （Grant No. 1417）, and the National High Technology Research and Development Program of China （Grant No. 2008AA09A401）. Acknowledgement We wish to thank Prof. Bai YC for stimulating discussions and reviewers for their helpful comments that led to considerable improvements to the paper.
文摘Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Function （UDF）, an Eulerian two-phase model, which includes an Euler-Euler coupled model for water and sediment phases, and a turbulent model for the fluid phase, is adopted to predict the scour depth around pipelines. The model is verified by observation data obtained from laboratory experiments. On the basis of the simulations, the factors affecting the scour depth, including the effects of incipient velocity, pipe diameter and sediment particle size and so on, were investigated. Meanwhile, according to formulas of incipient velocity of various sediments, approximate calculation on theoretical scour depths is developed for pipelines of seven stations in the South China Sea, where engineering application information is available.
基金Project supported by the National Natural Science Foundation of China (No. 51009122)Fundamental Research Funds for the Central Universities (No. 2010QNA4030)the National High-Tech R&D (863) Program of China (No. 2006AA09A105)
文摘The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during deepwater installation has drawn a great deal of attention. Extended from the model initially proposed by Kyriakides and his co-workers, a 2D theoretical model which can successfully account for the case of simultaneous tension, bending, and external pressure is further developed. To confirm the accuracy of this theoretical method, numerical simulations are conducted using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. The model is then used to study the effects of several important factors such as load path, material prop-erties, and diameter-to-thickness ratio, etc., on buckling behaviors of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which aims to provide the design guidelines for deepwater pipeline with solid theoretical basis.
文摘Drying （conditioning） is an important procedure to prevent hydrate formation during gas pipeline gas-up and to protect pipelines against corrosion. The air-drying method is preferred in offshore gas pipelines pre-commissioning. The air-drying process of gas pipelines commonly includes two steps, air purging and soak test. The mass conservation and the phase equilibrium theory are applied to setting up the mathematical models of air purging, which can be used to simulate dry airflow rate and drying time. Fick diffusion law is applied to setting up the mathematical model of soak test, which can predict the water vapor concentration distribution. The results calculated from the purging model and the soak test model are in good agreement with the experimental data in the DF 1-1 offshore production pipeline conditioning. The models are verified to be available for the air-drying project design of offshore gas pipelines. Some proposals for airdrying engineering and operational procedures are put forward by analyzing the air-drying process of DFI-1 gasexporting pipelines.
基金supported by the Special Funds for Fundamental Scientific Research Operation of Central Universities(No.202113011)the Guangxi Key Laboratory of Marine Environmental Science,Guangxi Academy of Sciences(No.GXKLHY21-04)+2 种基金the Shandong Provincial Social Science Planning Research Youth Project(No.21DSHJ2)the General Project of National Social Science Fund for Research on the Ideological and Political Courses in Colleges and Universities(No.21VSZ102)the Ministry of Natural Resources Departmental Budget Project‘Research on the Policy and Operation System of the Control System for Land and Space Use’(No.121107000000190014)。
文摘In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a weak water exchange capacity and high ecological fragility.However,at present,more than 200 oil platforms have been built in the Bohai Sea,with more than 270 offshore oil pipelines having a length exceeding 1600 km.The oil spill pollution of offshore platforms has a great impact on the marine environment and ecosystems.Therefore,a comprehensive assessment of its risks is of great practical significance.This paper systematically constructs a comprehensive oil spill risk assessment model that combines the oil spill risk probability model and the ocean hydrodynamic model.This paper uses the Bohai Sea offshore pipeline as an example to assess its oil spill risk.The high-risk-value areas of the Bohai Sea offshore pipeline are mainly distributed at the bottom of Liaodong Bay,the bottom of Bohai Bay,near the Caofeidian area,and the northern part of the Yellow River Estuary.
文摘The significant point is the bidirectional interaction technique in FSI analysis while investigating subsea corrosion effect. By this way, pipe environment is accurately modelled and fluid effects are also considered. The effect of external corrosion defects on structural behaviour of a pipeline is studied by creating a nonlinear numerical model based on the finite element method according to ABAQUS analysis program. Corrosion losses of sections are obtained from experimental results and applied to the model. Numerical model is formed by a span of sub-sea pipeline that is subjected to environmental loads. Seismic and wind-generated irregular wave loads are considered as environmental loads. Irregular wave is represented with equivalent eight regular waves via FFT. The pipe is modelled according to two different types which are non-corroded（intact） and corroded（deteriorated） to demonstrate corrosion effects on it. The visible type of corrosion in marine environment is named ‘pitting＇ corrosion, in which the material loss is locally interpenetrated over the surface. By considering this situation, the corroded and non-corroded pipes are modelled as 3D solid elements. The main point is revealing how the subsea corrosion affects the structural behaviour of pipelines on the basis of implementation of experimental results to a model structure due to changes of stresses and displacement.
基金Supported by the Technology Innovation Program(Grant number:10053121)funded by the Ministry of Trade,Industry&Energy(MI,Korea)by the Energy Efficiency&Resource of Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Ministry of Knowledge Economy of Korea(Grant number:2014301002-1870)
文摘The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×10^4.Evaluation of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2.
文摘The buckling propagation in marine pipelines is studied by means of the cylindrical shell model in this paper. Several parameters including geometrical parameter D/ T, L/ D, physical parameter E and σy are discussed. The computed results are compared with the available experimental data and other computed results, it is found that the present are closer to the experimental results than other computed results.
文摘The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore refineries.Interactions between the pipeline and an erodible bed under the influence of current and waves often lead to local scouring around the structure.When this occurs, the pipeline may be suspended on the seabed resulting in the formation of a span.If the free span is long enough, the pipe may experience resonant flow-induced oscillations,leading to structural failure.This study examines the complex flow-structure-sediment interaction leading to the development of local scour holes around submarine pipelines.It reviews published literature in this area,which primarily is confined to the development of 2- dimensional scour holes.Despite the abundance of such research studies,pipeline-scour in the field essentially is 3-dimensional in nature.Hence,most of these studies have overlooked the importance of the transverse dimension of the scour hole,while emphasizing on its vertical dimension.This clearly is an issue that must be re-examined in light of the potential hazard and environmental disaster that one faces in the event of a pipeline failure.Recent studies have begun to recognize this shortcoming,and attempts have been made to overcome the deficiency.The study presents the state-of-the-art knowledge on local scour at submarine pipelines,both from a 2-dimensional as well as the 3-dimensional perspective.
基金the Marine Public Welfare Research Project of China (No. 201205012)Preferential Funding of Tianjin
文摘To the potential oil-spill risk caused by offshore pipeline more attention has been paid after the Dalian oil spill incident from oil-pipeline explosion. Since then an issue about how to prevent and control the sudden oil-spill from the offshore pipeline has been raised. In this paper, we proposed an optimized model to analyze the main causes(probability) of spill and the consequence with the fuzzy comprehensive assessment model. Considering the complicated assessment process for oil-spill, the assessment factor system involving the spill probability and consequence was established based on the operative manual and statistic leakage/damage data of offshore pipeline in order to estimate the integrated spill risk score automatically. The evaluated factors of spill probability could be grouped into five aspects: corrosion, fatigue, national damage, third party, and operational fault; the consequence evaluated factors of spill included hazard of oil and impact-controlling capability. With some modifications based on experts' opinions, each of the evaluated factors in our work was developed with a relative weight and evaluation criterion. A test example for an offshore pipeline in the Bohai waters was described to show how the model can be used for an actual case in more detail. By using the oil-spill risk assessment model, it is easy to determine the risk level associated with the ongoing activity and management level and hence to take the risk mitigation action immediately.
基金supported by the Polish Ministry of Science and Higher Education(N N502 464934)
文摘A system designed for a rigid and flexible pipe laying purposes is presented in the paper.Mathematical and numerical models are developed by using the rigid finite element method（RFEM）.The RFEM is an efficient solution in the time domain.Static and dynamic problems related to pipe installation are solved by taking the advantage of simple interpretation and implementation of the method.Large deformations of the pipe during spooling and when it is reeled out at sea are considered.A material model implemented is used to take into consideration nonlinear material properties.In particular,the full elasto-plastic material characteristics with hardening and Bauschinger effect are included.Dynamic analyses are performed and the results attached in this work demonstrates how the sea conditions influence the machinery and pipeline,assuming a passive reel drive system. The influence of several other operational parameters on dynamic loads is verified.An active system,implemented as a part of the mathematical model,improves the system performance.Some results are presented as well.
基金financially supported by the National Natural Science Foundation of China(Grant No.51309236)Doctoral Foundation of the Ministry of Education of China(Grant No.20120007120009)+2 种基金the Opening Fund of State Key Laboratory of Ocean Engineering(Shanghai Jiao Tong University,Grant No.1314)the Opening Fund of State Key Laboratory of Hydraulic Engineering Simulation and Safety(Tianjin University,Grant No.HESS-1411)the Science Foundation of China University of Petroleum(Beijing)(Grant No.QD-2010-08)
文摘A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anisotropic material characteristics in longitudinal and circumferential direction of pipeline are also considered in the proposed equations. Simplified numerical method is used to solve the generalized expressions. The comparisons of numerical results based generalized solutions and full-scale experimental results are carried out. The predicted results agree reasonably well with the experiment results. Meanwhile, the effects of corrosion shapes and locations on the ultimate load capacity are studied.
文摘-Based on the calculation model for the floating laying of the offshore oil pipeline, this paper analyses in detail the internal force, and deformation of the pipeline under a definite structural form (pipeline and buoy) and the way of pulling. The obtained results can be used for the buoy deployment, structure design, and the determination of pulling parameters (the pulling force of the cable and its length, etc.), providing an effective analysis method for floating pipeline-laying. A calculation example is given to show the related calculation process and the main results are analyzed and discussed.
文摘Leakages in oil pipelines can cause financial losses and several environmental damages, where large-scale offshore oil and gas exploration results in large releases of oil and gas into ocean waters. In the event of oil leakage, an immediate and adequate response is required to reduce environmental damage, such as containment barriers, for example, which depends on the agglomeration of oil particles, velocity and tendency to propagation. Thus, the understanding of the fluid flow behavior around of subsea pipeline at different depths is crucial. On the other hand, the knowledge of interfacial phenomena of immiscible liquids allows the process of adjective migration in submarine pipelines. Consequently, this science enables the prediction of the behavior and the geometric shape of the water-oil interface and provides a phenomenological foundation concerning the theories of perturbation, the stability criteria and mathematical modeling, as well as the flow patterns in the neighborhoods and submerged pipelines. From this perspective, this work aims to study the oil dispersion in sea water caused by leakage in a submerged pipeline. Here, a two-dimensional mathematical model based on the mass and linear momentum conservation equations and the standard k-ε turbulence model, was developed. The dynamic behavior of the oil and water phases is evaluated by pressure fields, surface velocity, volumetric fraction and velocity vectors. Simulation results show the presence of oil flux from the pipe to the marine stream and vice-versa. Further, the increase in oil velocity at the pipe inlet leads to an increase in pressure drop.
基金supported by the National Natural Science Foundation of China(51479111) the Open Fund at the State Key Laboratory of Hydraulics and Mountain River Engineering, China(SKHL1404)
文摘This paper studies the coupling effect of the pipeline vibration on the seabed scour. A vertical two- dimensional model is applied to numerically investigate the local scour below a vibrating pipeline with different amplitudes and periods. Using the scour underneath a fixed pipeline as a reference, this paper focuses on the impact of the pipeline vibration on the equilibrium scour depth. Generic relationships are established between the non-dimensional scour depth and the non-dimensional vibrating parameters, i.e., amplitude and frequency. The normalization process takes into account the influences of such parameters as the incoming flow velocity, pipe diameter, and Shields parameter. An empirical formula is proposed to quantify these relationships.
基金supported by the National Natural Science Foundation of China (Grant No. 51009122)the Fundamental Research Funds for the Central Universities (Grant No. 2010QNA4030)the National High Technology Research and Development Program of China (863 Program, Grant No. 2006AA09A105)
文摘The safety of offshore pipeline has drawn a great deal of attention during deepwater installation due to the combined actions of high external pressure, axial tension, and bending moment. Meanwhile, the pipeline configuration has a remarkable effect on the structural behaviour of the tube. The special studies focus on the deepwater S-lay technique in the present paper. The stiffened catenary theory is applied to establish the static equilibrium governing differential equation of a pipe element, and the solution equations of the total pipeline configuration from a lay-barge over a stinger to the seabed are derived, The numerical iteration method for solving pipeline configuration is described in detail, and the corresponding program is developed to conduct the analysis of effects of various parameters such as laying water depth, pipe diameter, thickness of concrete weighted coating layer, stinger length, control strain, and axial tension on pipeline configuration. The results show that the laying water depth, the submerged weight of the pipe, and the axial tension are the critical factors influencing pipeline configuration. In addition, geometrical parameters of the stinger such as length, radius, and shape have an important effect on the pipe-laying capacity of the vessel. The validity of the program is further verified by means of a comparison with results obtained from the commercial finite element software OFFPIPE.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51479135,51525803 and51679167)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51321065)the Major State Basic Research Development Program of China(973 Program,Grant No.2014CB046801)
文摘Pipeline spans may occur due to natural seabed irregularities or local scour of bed sediment. The pure in-line（IL）vortex-induced vibrations（VIV） analysis of the free spans is an important subject for design of pipeline in uneven seabed. The main objective of this paper is to analyze the characteristics of pure IL VIV of a free spanning pipeline under general boundary conditions. An IL wake oscillator model which can describe the coupling of pipeline structure and fluctuating drag is introduced and employed. The coupled partial differential equations of structure and wake are transformed into a set of ordinary differential equations using two-mode Galerkin method. Some case studies are presented and thoroughly discussed in order to investigate the effects of internal fluid, axial force and boundary conditions on the pure IL VIV.
文摘A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The oscillatory flow in this study represents the action of waves. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-ε turbulence closure, as well as the sediment transport equations, are solved with the finite difference method in a curvilinear coordinate system. Both bed and suspended loads of sediment transport are included in the morphological model. Because of the lack of experimental data on the backfilling of pipeline trenches, the numerical model is firstly verified against three closely-relevant experiments available in literature. A detailed measurement of the channel migration phenomenon under steady currents is employed for the assessment of the integral performance of the model. The two experimental results from U-tube tests are used to validate the model's ability in predicting oscillatory flows. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development.
