Umbilical cables are fundamental equipment used in deep and ultra-deep waters oil and gas production systems. The complexity of this kind of structure leads structural analysis to be currently performed with numerical tools. This paper presents a nonlinear three-dimensional finite element model of a typical armored Steel Tube Umbilical Cable (STU) subjected to crushing loads imposed to the umbilical cable during laying operation. The study focuses on the analysis of the stress distribution in the steel tubes at caterpillar shoes, mainly at the entry/exit transition regions. With the use of a commercial software, the finite element model is constructed, considering geometric and materials nonlinearities. Crushing loads are imposed by two rigid plates. Focus is given on the duplex tubes, with the material stress-strain curve modeled from a specific crushing experiment with a single tube and by using a classic Ramberg-Osgood fitting. Firstly, comparisons at mid-length of the three-dimensional model are made with the results from a simpler and planar finite element model. Then, the localized three-dimensional effects are analyzed. The results show a considerable increase of the stress levels in the steel tubes at these transition regions, with the occurrence of stress field redistribution after the onset of plastic deformation.
{"title":"Crushing of a Steel Tube Umbilical (STU) Cable During Laying Operation: A Finite Element Method Assessment at the Entry/Exit Regions of Tensioner Shoes","authors":"W. Guttner, C. Santos, C. Pesce","doi":"10.1115/omae2020-18950","DOIUrl":"https://doi.org/10.1115/omae2020-18950","url":null,"abstract":"\u0000 Umbilical cables are fundamental equipment used in deep and ultra-deep waters oil and gas production systems. The complexity of this kind of structure leads structural analysis to be currently performed with numerical tools. This paper presents a nonlinear three-dimensional finite element model of a typical armored Steel Tube Umbilical Cable (STU) subjected to crushing loads imposed to the umbilical cable during laying operation. The study focuses on the analysis of the stress distribution in the steel tubes at caterpillar shoes, mainly at the entry/exit transition regions. With the use of a commercial software, the finite element model is constructed, considering geometric and materials nonlinearities. Crushing loads are imposed by two rigid plates. Focus is given on the duplex tubes, with the material stress-strain curve modeled from a specific crushing experiment with a single tube and by using a classic Ramberg-Osgood fitting. Firstly, comparisons at mid-length of the three-dimensional model are made with the results from a simpler and planar finite element model. Then, the localized three-dimensional effects are analyzed. The results show a considerable increase of the stress levels in the steel tubes at these transition regions, with the occurrence of stress field redistribution after the onset of plastic deformation.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123313791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the marginal gas field development engineering, considering the low gas production with complex reservoir condition, it is difficult to develop independently because of the low economic efficiency. It is usually developed by relying on an existing offshore platform or facility nearby, in which hydrate inhibition is an important issue, and in order to inhibit hydrate formation in the subsea pipeline, hydrate inhibition method should be studied. Based on certain marginal gas field development project in South China Sea, which relies on nearby DPP platform, the paper studies methanol and MEG as inhibitor and application of double-layer insulated subsea pipeline. Finally by technical and economic comparisons, for the first time double-layer insulated pipeline is selected as the hydrate inhibition method to meet requirements of both relying on DPP and achieving better economic benefits, which is expected to provide reference for similar marginal gas field development.
{"title":"A Study on Hydrate Inhibition of Marginal Gas Field Development","authors":"Hualei Yi","doi":"10.1115/omae2020-18348","DOIUrl":"https://doi.org/10.1115/omae2020-18348","url":null,"abstract":"\u0000 In the marginal gas field development engineering, considering the low gas production with complex reservoir condition, it is difficult to develop independently because of the low economic efficiency. It is usually developed by relying on an existing offshore platform or facility nearby, in which hydrate inhibition is an important issue, and in order to inhibit hydrate formation in the subsea pipeline, hydrate inhibition method should be studied. Based on certain marginal gas field development project in South China Sea, which relies on nearby DPP platform, the paper studies methanol and MEG as inhibitor and application of double-layer insulated subsea pipeline. Finally by technical and economic comparisons, for the first time double-layer insulated pipeline is selected as the hydrate inhibition method to meet requirements of both relying on DPP and achieving better economic benefits, which is expected to provide reference for similar marginal gas field development.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130643166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High strain/stress is easy to occur in the overbend section of S-lay pipelines which are supported by stinger, leading to excessive deformation and buckling failure of the pipelines. In order to ensure the safety of pipelines and evaluate the maximum laying capacity of the pipelay vessel in 1600 meter, this paper uses the curvature radius method to automatically adjust the four angles and roller positions of the articulated stinger fixed on the pipelay vessel, then analyzes the pipeline strain and effective tension in static configuration and finally calculates the timedomain coupling response by establishing a nonlinear contact model of the pipelay vessel, stinger and pipelines. The adjustment speed, which is based on the curvature radius method using Python to call OrcFxAPI, is efficient remarkably. The results show that the stinger radius and roller locations are the major influential factors on the pipeline strain and anchor positions affect the detachment point strain of pipelines on overbend section. The static and dynamic strains of the overbend section are less than 0.25% and 0.305% respectively, which meet the DNV specifications.
{"title":"Coupling Response Analysis of Deep-Water Pipeline Based on Rapid Regulation of Stinger Radius","authors":"Gang Ma, Jie Yang, Hongwei Wang, Zizhao Zhang","doi":"10.1115/omae2020-19062","DOIUrl":"https://doi.org/10.1115/omae2020-19062","url":null,"abstract":"\u0000 High strain/stress is easy to occur in the overbend section of S-lay pipelines which are supported by stinger, leading to excessive deformation and buckling failure of the pipelines. In order to ensure the safety of pipelines and evaluate the maximum laying capacity of the pipelay vessel in 1600 meter, this paper uses the curvature radius method to automatically adjust the four angles and roller positions of the articulated stinger fixed on the pipelay vessel, then analyzes the pipeline strain and effective tension in static configuration and finally calculates the timedomain coupling response by establishing a nonlinear contact model of the pipelay vessel, stinger and pipelines. The adjustment speed, which is based on the curvature radius method using Python to call OrcFxAPI, is efficient remarkably. The results show that the stinger radius and roller locations are the major influential factors on the pipeline strain and anchor positions affect the detachment point strain of pipelines on overbend section. The static and dynamic strains of the overbend section are less than 0.25% and 0.305% respectively, which meet the DNV specifications.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121558253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The high demand for subsea transportation of corrosive wellhead produced fluids has created interest in economical mechanically lined pipes (MLP) made of external carbon steel and a thin internal layer of corrosion resistant alloy (CRA). The bending strain capacity of an MLP, where a CRA liner is adhered to a carbon steel host pipe by means of an interference fit, is often governed by the liner wrinkling limit state. Although the strain capacity of the MLP with a typical 3 mm thick liner is enough to withstand bending to strains encountered during installation with the S-lay or J-lay method, the liner is at risk of wrinkling when the MLP is subjected to higher bending strains during reel-lay. To allow reeled installation, the liner strain capacity is enhanced by either increasing the liner thickness or pressurizing the MLP during installation. In the former approach, the required liner thickness is proportional to the pipe diameter. For larger diameter MLPs, it is therefore often more economical to select a 3 mm thick liner and flood and pressurize an MLP to ensure liner stability during reeling. However, the MLP may need to be depressurized and partially drained during installation to allow welding a structure, performing reel-to-reel connection or pipeline recovery which impose bending strain on a plastically pre-strained and depressurized pipeline. Furthermore, reeled pipelines may be depressurized subsea while subjected to bending loads from operation. Although there is a history of research into the limit loads and failure modes of MLPs, there is still no comprehensive guidance on determining the risk of liner wrinkling in plastically pre-strained MLPs. In this paper, an approach is proposed for evaluating the strain capacity and assessing the risk of liner wrinkling after an MLP, subjected to plastic bending during reeled installation at elevated pressure, is depressurized and subjected to installation loads during offshore intervention or operational loading in service. The combined effect of strain history at elevated pressure, reeling-induced ovality, bending direction after depressurization, differential pressure, temperature and residual strain is discussed. The recommendations for further work are also given.
{"title":"Effect of Pre-Strain on Bending Strain Capacity of Mechanically Lined Pipe","authors":"T. Tkaczyk, Daniil Vasilikis, A. Pépin","doi":"10.1115/omae2020-18450","DOIUrl":"https://doi.org/10.1115/omae2020-18450","url":null,"abstract":"\u0000 The high demand for subsea transportation of corrosive wellhead produced fluids has created interest in economical mechanically lined pipes (MLP) made of external carbon steel and a thin internal layer of corrosion resistant alloy (CRA). The bending strain capacity of an MLP, where a CRA liner is adhered to a carbon steel host pipe by means of an interference fit, is often governed by the liner wrinkling limit state. Although the strain capacity of the MLP with a typical 3 mm thick liner is enough to withstand bending to strains encountered during installation with the S-lay or J-lay method, the liner is at risk of wrinkling when the MLP is subjected to higher bending strains during reel-lay. To allow reeled installation, the liner strain capacity is enhanced by either increasing the liner thickness or pressurizing the MLP during installation.\u0000 In the former approach, the required liner thickness is proportional to the pipe diameter. For larger diameter MLPs, it is therefore often more economical to select a 3 mm thick liner and flood and pressurize an MLP to ensure liner stability during reeling. However, the MLP may need to be depressurized and partially drained during installation to allow welding a structure, performing reel-to-reel connection or pipeline recovery which impose bending strain on a plastically pre-strained and depressurized pipeline. Furthermore, reeled pipelines may be depressurized subsea while subjected to bending loads from operation.\u0000 Although there is a history of research into the limit loads and failure modes of MLPs, there is still no comprehensive guidance on determining the risk of liner wrinkling in plastically pre-strained MLPs. In this paper, an approach is proposed for evaluating the strain capacity and assessing the risk of liner wrinkling after an MLP, subjected to plastic bending during reeled installation at elevated pressure, is depressurized and subjected to installation loads during offshore intervention or operational loading in service. The combined effect of strain history at elevated pressure, reeling-induced ovality, bending direction after depressurization, differential pressure, temperature and residual strain is discussed. The recommendations for further work are also given.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121958354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Residual curvature installation of subsea pipelines has become a popular method for lateral buckling management because of its low-cost implementation and high reliability. The method is foreseen to remain attractive due to the positive operational feedback made available to the public domain. On the design methods, previous research has predicted the behaviour of pipelines installed with residual curvature mainly via finite element analysis (FEA). These analyses include lateral buckling, installation, reeling etc. Further to this, Teigen and Ibrahim have put an effort into quantifying design uncertainties using structural reliability analysis (SRA). Analytical approaches have also been explored, such as pipeline rolling, and other effects during pipeline installation. However, there is little published work on analytical approaches for the lateral buckling behaviour. Therefore, this paper suggests analytical formulations for the lateral buckling behaviour of pipelines installed with residual curvature. For predicting the critical buckling force, the Palmer formulation was used as a basis. For predicting the pipeline integrity post buckling while accounting for non-linear effects and residual plasticity in the system, the formulation is derived using a combination of dimensional analysis, regression analysis and a modified Hobbs formulation. The resulting analytical formulation is calibrated to a database of finite element solutions. The suggested approach is assessed for a configuration that applies model parameters based on the Skuld pipeline. A validation has been performed and the errors have been assessed to verify the suitability of the proposed analytical approach.
{"title":"Analytical Formulae for the Lateral Buckling Behaviour of Pipelines Installed With Residual Curvature","authors":"M. Teigen, M. M. Ibrahim","doi":"10.1115/omae2020-18261","DOIUrl":"https://doi.org/10.1115/omae2020-18261","url":null,"abstract":"\u0000 Residual curvature installation of subsea pipelines has become a popular method for lateral buckling management because of its low-cost implementation and high reliability. The method is foreseen to remain attractive due to the positive operational feedback made available to the public domain.\u0000 On the design methods, previous research has predicted the behaviour of pipelines installed with residual curvature mainly via finite element analysis (FEA). These analyses include lateral buckling, installation, reeling etc. Further to this, Teigen and Ibrahim have put an effort into quantifying design uncertainties using structural reliability analysis (SRA). Analytical approaches have also been explored, such as pipeline rolling, and other effects during pipeline installation. However, there is little published work on analytical approaches for the lateral buckling behaviour.\u0000 Therefore, this paper suggests analytical formulations for the lateral buckling behaviour of pipelines installed with residual curvature. For predicting the critical buckling force, the Palmer formulation was used as a basis. For predicting the pipeline integrity post buckling while accounting for non-linear effects and residual plasticity in the system, the formulation is derived using a combination of dimensional analysis, regression analysis and a modified Hobbs formulation. The resulting analytical formulation is calibrated to a database of finite element solutions.\u0000 The suggested approach is assessed for a configuration that applies model parameters based on the Skuld pipeline. A validation has been performed and the errors have been assessed to verify the suitability of the proposed analytical approach.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129778966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yang Zhixun, Jun Yan, Liang Zhang, D. Shi, Qingzhen Lu
The buckling behavior and critical value are analyzed to explain the mechanism of the lateral buckling. Moreover, a 3D numerical model of four tensile armor wires with symmetrical arrangement is established with the interaction between armor wires and inner structure. The lateral buckling is discussed through a relationship between critical value and axial displacement. Then the sensitivity of critical value on friction coefficient is figured out. The results show that the lateral buckling resistance of tensile armor wires performs better with the friction coefficient in the range of 0.25 to 0.3. Finally, this research provides mechanical support for the lateral buckling resistance design of the unbonded flexible pipe.
{"title":"Research on Lateral Buckling Mechanism of Tensile Armor Wires in Unbonded Flexible Pipe","authors":"Yang Zhixun, Jun Yan, Liang Zhang, D. Shi, Qingzhen Lu","doi":"10.1115/omae2020-18204","DOIUrl":"https://doi.org/10.1115/omae2020-18204","url":null,"abstract":"\u0000 The buckling behavior and critical value are analyzed to explain the mechanism of the lateral buckling. Moreover, a 3D numerical model of four tensile armor wires with symmetrical arrangement is established with the interaction between armor wires and inner structure. The lateral buckling is discussed through a relationship between critical value and axial displacement. Then the sensitivity of critical value on friction coefficient is figured out. The results show that the lateral buckling resistance of tensile armor wires performs better with the friction coefficient in the range of 0.25 to 0.3. Finally, this research provides mechanical support for the lateral buckling resistance design of the unbonded flexible pipe.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117122708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jian Wang, C. Shi, G. Fu, Zengkai Liu, Xingxian Bao, H. Li
Subsea pipelines are prone to be damaged by the falling objects from ships or offshore platforms, which may result in economic losses and pollution. The dimensions of dent were commonly used to evaluate the impact resistance of pipes made from carbon steel. Thermoplastic composite pipes (TCPs), due to their superior properties including corrosion resistance, thermal insulation, fast installation, etc., are increasingly used as the subsea pipelines. The TCP is made from thermoplastic resins and reinforced by continuous fibers. Because of the brittle nature of carbon fibers and glass fibers, the dimensions of dent are not suitable for assessment of impact resistance of a TCP. In the present work, a procedure was proposed using the internal pressure capacity as an indicator to evaluate the lateral impact resistance of a TCP. First, the internal pressure capacity of an intact TCP was evaluated. Second, a quasi-static simulation was conducted by applying a lateral compression force on the intact TCP using a rigid ball, until one of the composite plies in the reinforcement layer failed. The quasi-static simulation provided an initial estimate of the minimum energy that causes the start of damage of the TCP. Third, the impact simulations were performed by using a rigid ball hitting the TCP and, then, the internal pressure capacity of the damaged TCP was evaluated. Finally, the internal pressure capacity of the damaged pipe, compared with that of the intact pipe, was used as an indicator to evaluate the lateral impact resistance of the TCP. In this study, a glass-fiber reinforced polyethylene (PE) pipe of an inner diameter of 150 mm was modeled by ABAQUS to illustrate the procedure. A theoretical method was proposed to calculate the impact energy of a dropped object in a shallow water. The example studied in the present work showed that the modeled TCP was not strong enough to survive the lateral impact caused by the dropped object and should be buried to a certain depth beneath the seabed if used as a subsea pipeline.
{"title":"Numerical Evaluation on Lateral Impact Resistance of Thermoplastic Composite Pipes in Terms of Internal Pressure Capacity","authors":"Jian Wang, C. Shi, G. Fu, Zengkai Liu, Xingxian Bao, H. Li","doi":"10.1115/omae2020-18047","DOIUrl":"https://doi.org/10.1115/omae2020-18047","url":null,"abstract":"\u0000 Subsea pipelines are prone to be damaged by the falling objects from ships or offshore platforms, which may result in economic losses and pollution. The dimensions of dent were commonly used to evaluate the impact resistance of pipes made from carbon steel. Thermoplastic composite pipes (TCPs), due to their superior properties including corrosion resistance, thermal insulation, fast installation, etc., are increasingly used as the subsea pipelines. The TCP is made from thermoplastic resins and reinforced by continuous fibers. Because of the brittle nature of carbon fibers and glass fibers, the dimensions of dent are not suitable for assessment of impact resistance of a TCP. In the present work, a procedure was proposed using the internal pressure capacity as an indicator to evaluate the lateral impact resistance of a TCP. First, the internal pressure capacity of an intact TCP was evaluated. Second, a quasi-static simulation was conducted by applying a lateral compression force on the intact TCP using a rigid ball, until one of the composite plies in the reinforcement layer failed. The quasi-static simulation provided an initial estimate of the minimum energy that causes the start of damage of the TCP. Third, the impact simulations were performed by using a rigid ball hitting the TCP and, then, the internal pressure capacity of the damaged TCP was evaluated. Finally, the internal pressure capacity of the damaged pipe, compared with that of the intact pipe, was used as an indicator to evaluate the lateral impact resistance of the TCP. In this study, a glass-fiber reinforced polyethylene (PE) pipe of an inner diameter of 150 mm was modeled by ABAQUS to illustrate the procedure. A theoretical method was proposed to calculate the impact energy of a dropped object in a shallow water. The example studied in the present work showed that the modeled TCP was not strong enough to survive the lateral impact caused by the dropped object and should be buried to a certain depth beneath the seabed if used as a subsea pipeline.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121352225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Hejazi, A. Grime, Mark F. Randolph, M. Efthymiou
In-service integrity management (IM) of steel lazy wave risers (SLWRs) can benefit significantly from quantitative assessment of the overall risk of system failure as it can provide an effective tool for decision making. SLWRs are prone to fatigue failure within their touchdown zone (TDZ). This failure mode needs to be evaluated rigorously in riser IM processes because fatigue is an ongoing degradation mechanism threatening the structural integrity of risers throughout their service life. However, accurately evaluating the probability of fatigue failure for riser systems within a useful time frame is challenging due to the need to run a large number of nonlinear, dynamic numerical time domain simulations. Applying the Bayesian framework for machine learning, through the use of Gaussian Processes (GP) for regression, offers an attractive solution to overcome the burden of prohibitive simulation run times. GPs are stochastic, data-driven predictive models which incorporate the underlying physics of the problem in the learning process, and facilitate rapid probabilistic assessments with limited loss in accuracy. This paper proposes an efficient framework for practical implementation of a GP to create predictive models for the estimation of fatigue responses at SLWR hotspots. Such models are able to perform stochastic response prediction within a few milliseconds, thus enabling rapid prediction of the probability of SLWR fatigue failure. A realistic North West Shelf (NWS) case study is used to demonstrate the framework, comprising a 20” SLWR connected to a representative floating facility located in 950 m water depth. A full hindcast metocean dataset with associated statistical distributions are used for the riser long-term fatigue loading conditions. Numerical simulation and sampling techniques are adopted to generate a simulation-based dataset for training the data-driven model. In addition, a recently developed dimensionality reduction technique is employed to improve efficiency and reduce complexity of the learning process. The results show that the stochastic predictive models developed by the suggested framework can predict the long-term TDZ fatigue damage of SLWRs due to vessel motions with an acceptable level of accuracy for practical purposes.
{"title":"A Bayesian Machine Learning Approach for Efficient Integrity Management of Steel Lazy Wave Risers","authors":"R. Hejazi, A. Grime, Mark F. Randolph, M. Efthymiou","doi":"10.1115/omae2020-18190","DOIUrl":"https://doi.org/10.1115/omae2020-18190","url":null,"abstract":"\u0000 In-service integrity management (IM) of steel lazy wave risers (SLWRs) can benefit significantly from quantitative assessment of the overall risk of system failure as it can provide an effective tool for decision making. SLWRs are prone to fatigue failure within their touchdown zone (TDZ). This failure mode needs to be evaluated rigorously in riser IM processes because fatigue is an ongoing degradation mechanism threatening the structural integrity of risers throughout their service life. However, accurately evaluating the probability of fatigue failure for riser systems within a useful time frame is challenging due to the need to run a large number of nonlinear, dynamic numerical time domain simulations.\u0000 Applying the Bayesian framework for machine learning, through the use of Gaussian Processes (GP) for regression, offers an attractive solution to overcome the burden of prohibitive simulation run times. GPs are stochastic, data-driven predictive models which incorporate the underlying physics of the problem in the learning process, and facilitate rapid probabilistic assessments with limited loss in accuracy.\u0000 This paper proposes an efficient framework for practical implementation of a GP to create predictive models for the estimation of fatigue responses at SLWR hotspots. Such models are able to perform stochastic response prediction within a few milliseconds, thus enabling rapid prediction of the probability of SLWR fatigue failure.\u0000 A realistic North West Shelf (NWS) case study is used to demonstrate the framework, comprising a 20” SLWR connected to a representative floating facility located in 950 m water depth. A full hindcast metocean dataset with associated statistical distributions are used for the riser long-term fatigue loading conditions. Numerical simulation and sampling techniques are adopted to generate a simulation-based dataset for training the data-driven model. In addition, a recently developed dimensionality reduction technique is employed to improve efficiency and reduce complexity of the learning process.\u0000 The results show that the stochastic predictive models developed by the suggested framework can predict the long-term TDZ fatigue damage of SLWRs due to vessel motions with an acceptable level of accuracy for practical purposes.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116303359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Leonardo Sales, C. C. O. Trigo, L. C. Sevillano, C. Morooka
Vertical pipe configuration happens in subsea well re-entry operations for wellbore drilling, subsea equipment installations, deepwater intake risers, among other scenarios, usually by hanging the marine riser at the top from a platform or ship. The simple operational configuration justifies its wide application; however, there are some drawbacks such as stress concentration, fatigue, among other issues. The purpose of this study is to contribute for the overcoming of those problems by improving the understanding of hanging risers through investigations of a vertical pipe forced to oscillate horizontally at the top. For this purpose, laboratory experiments with small diameter pipe model have been developed with oscillatory motions applied at the top termination through a mechanical device. Displacements over time and along the pipe length were measured by an optical measurement system. In the present study, a numerical scheme has been implemented for simulations to support evaluations of the experimental results. A vertical pipe response depends on several parameters, such as pipe overall length, frequency and amplitude of oscillation itself, among others. Due to existing relative velocity between the oscillating pipe and the water surrounding it, vortex shedding occurs along the pipe length which influences riser motion behaviour. The results from experiment and numerical simulations bring important insights for describing and understanding oscillatory vertical pipe behaviour, in the plane and the out of plane of the forced top oscillation. The obtained results provide a further step toward the modelling of Vortex-Induced Vibration (VIV) in marine risers, aiming to contribute to relevant technological advancements.
{"title":"Dynamic Behaviour of a Free Hanging Vertical Pipe Forced to Oscillate at the Top","authors":"Leonardo Sales, C. C. O. Trigo, L. C. Sevillano, C. Morooka","doi":"10.1115/omae2020-18458","DOIUrl":"https://doi.org/10.1115/omae2020-18458","url":null,"abstract":"\u0000 Vertical pipe configuration happens in subsea well re-entry operations for wellbore drilling, subsea equipment installations, deepwater intake risers, among other scenarios, usually by hanging the marine riser at the top from a platform or ship. The simple operational configuration justifies its wide application; however, there are some drawbacks such as stress concentration, fatigue, among other issues. The purpose of this study is to contribute for the overcoming of those problems by improving the understanding of hanging risers through investigations of a vertical pipe forced to oscillate horizontally at the top.\u0000 For this purpose, laboratory experiments with small diameter pipe model have been developed with oscillatory motions applied at the top termination through a mechanical device. Displacements over time and along the pipe length were measured by an optical measurement system. In the present study, a numerical scheme has been implemented for simulations to support evaluations of the experimental results.\u0000 A vertical pipe response depends on several parameters, such as pipe overall length, frequency and amplitude of oscillation itself, among others. Due to existing relative velocity between the oscillating pipe and the water surrounding it, vortex shedding occurs along the pipe length which influences riser motion behaviour.\u0000 The results from experiment and numerical simulations bring important insights for describing and understanding oscillatory vertical pipe behaviour, in the plane and the out of plane of the forced top oscillation. The obtained results provide a further step toward the modelling of Vortex-Induced Vibration (VIV) in marine risers, aiming to contribute to relevant technological advancements.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133761867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Prediction of internal multiphase flows in subsea pipelines is an integral part of the oil and gas production system design. High mass and pressure fluctuations are often encountered during the operation with a liquid-gas slug flow regime exhibiting a sequence of long gas bubbles and aerated liquid slugs. It is important for industry to realistically identify the slug flow occurrence and predict slug flow characteristics, depending on several multiphase flow-pipe parameters. These may be achieved using a one-dimensional, steady-state, mechanistic model accounting for a mass and momentum balance of the two liquid-gas fluids within a controlled volume often referred to as a slug unit. By reducing a 3-D flow problem to a 1-D one, several empirical or closure correlations and associated empirical coefficients have been introduced in the literature and used in commercial software predicting slug flows in subsea jumpers, pipelines and risers with variable inclinations. This study aims to investigate the influence of combined 25 closure functions on the predictions of slug flows in horizontal and inclined pipes based on a steady-state mechanistic model for a wide range of superficial liquid and gas velocities. The model with studied closures is implemented by the authors of this study as the numerical tool iSLUG. The model performance is verified with respect to the estimated film liquid holdup, film length and pressure drop per length of a slug unit for an empirically specified translational velocity, slug liquid holdup, slug liquid length and pipe wall wettability. Closure combinations are analyzed using the relative performance factors and compared against available experimental data in order to identify a set of functions suitable for upward, downward and horizontal flows, and the effect of diameter and inclination on the model prediction is considered. The present method and analysis outcomes may further contribute to the improvement of transient liquid-gas flow models to predict more practical cases.
{"title":"Influence of Combined Empirical Functions on Slug Flow Predictions of Pipelines With Variable Inclinations","authors":"H. Zanganeh, V. Kurushina, N. Srinil, O. Matar","doi":"10.1115/omae2020-18027","DOIUrl":"https://doi.org/10.1115/omae2020-18027","url":null,"abstract":"\u0000 Prediction of internal multiphase flows in subsea pipelines is an integral part of the oil and gas production system design. High mass and pressure fluctuations are often encountered during the operation with a liquid-gas slug flow regime exhibiting a sequence of long gas bubbles and aerated liquid slugs. It is important for industry to realistically identify the slug flow occurrence and predict slug flow characteristics, depending on several multiphase flow-pipe parameters. These may be achieved using a one-dimensional, steady-state, mechanistic model accounting for a mass and momentum balance of the two liquid-gas fluids within a controlled volume often referred to as a slug unit. By reducing a 3-D flow problem to a 1-D one, several empirical or closure correlations and associated empirical coefficients have been introduced in the literature and used in commercial software predicting slug flows in subsea jumpers, pipelines and risers with variable inclinations.\u0000 This study aims to investigate the influence of combined 25 closure functions on the predictions of slug flows in horizontal and inclined pipes based on a steady-state mechanistic model for a wide range of superficial liquid and gas velocities. The model with studied closures is implemented by the authors of this study as the numerical tool iSLUG. The model performance is verified with respect to the estimated film liquid holdup, film length and pressure drop per length of a slug unit for an empirically specified translational velocity, slug liquid holdup, slug liquid length and pipe wall wettability. Closure combinations are analyzed using the relative performance factors and compared against available experimental data in order to identify a set of functions suitable for upward, downward and horizontal flows, and the effect of diameter and inclination on the model prediction is considered. The present method and analysis outcomes may further contribute to the improvement of transient liquid-gas flow models to predict more practical cases.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"477 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130790440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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