Fernando Geremias Toni, C. Martins, Rodrigo Provasi, R. Morini
Armor pots are mechanical devices employed in the offshore oil production to anchor armor wires/steel tubes of an umbilical cable. In epoxy-based armor pots, this anchoring is obtained through the interaction between the resin and the tensile armors/steel tubes and also through the capstan effect from geometric variations, such as radius and lay angle changes. In this context, friction plays a fundamental role in the anchoring capacity and is mainly affected, among other factors, by the intensity of resin thermal contraction, which generates positive pressure at the contact interfaces, and also by the friction coefficient. Therefore, this works presents an extensive parametric analysis of the resin thermal contraction and of the friction coefficient performed through the finite element method with the objective of understanding their qualitative and quantitative influence at the anchoring capacity of a steel-tube umbilical armor pot. In recent years, the authors published fully three-dimensional finite element models of armor pots. In order to accomplish the present work, several enhancements were performed in the aforementioned models. The main development is an innovative methodology for the resin mesh generation, ensuring mapped elements at the interfaces with steel tubes, resulting in a smoother contact representation. At the same time, this methodology is computationally advantageous by allowing larger element sizes at the remaining resin volume without loss of quality in the representation.
{"title":"Parametric Analysis of Steel-Tube Umbilical Armor Pots","authors":"Fernando Geremias Toni, C. Martins, Rodrigo Provasi, R. Morini","doi":"10.1115/omae2020-18011","DOIUrl":"https://doi.org/10.1115/omae2020-18011","url":null,"abstract":"\u0000 Armor pots are mechanical devices employed in the offshore oil production to anchor armor wires/steel tubes of an umbilical cable. In epoxy-based armor pots, this anchoring is obtained through the interaction between the resin and the tensile armors/steel tubes and also through the capstan effect from geometric variations, such as radius and lay angle changes. In this context, friction plays a fundamental role in the anchoring capacity and is mainly affected, among other factors, by the intensity of resin thermal contraction, which generates positive pressure at the contact interfaces, and also by the friction coefficient. Therefore, this works presents an extensive parametric analysis of the resin thermal contraction and of the friction coefficient performed through the finite element method with the objective of understanding their qualitative and quantitative influence at the anchoring capacity of a steel-tube umbilical armor pot. In recent years, the authors published fully three-dimensional finite element models of armor pots. In order to accomplish the present work, several enhancements were performed in the aforementioned models. The main development is an innovative methodology for the resin mesh generation, ensuring mapped elements at the interfaces with steel tubes, resulting in a smoother contact representation. At the same time, this methodology is computationally advantageous by allowing larger element sizes at the remaining resin volume without loss of quality in the representation.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"10 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":"124879854","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}
Deepwater steel catenary risers (SCRs) are designed considering strength under extreme loads and long-term fatigue of the riser from installation through the full range of conditions anticipated over the service life of the riser. Short-term single event fatigue is also checked to ensure that a single extreme storm or current event does not consume an excessive amount of fatigue capacity. For Gulf of Mexico SCRs, single event fatigue can be a governing case for the riser hang-off. The requirement imposes a relatively modest number of higher stress range cycles and may bias the selection of the hang-off option (titanium, steel, and flex joints) since the three common choices have widely different sensitivity to this case. Assessing a single event hurricane is problematic because the evolution of storms which generate an extreme 100-year significant wave height at a site can vary considerably from storm-to-storm. Simplistic representations of the extreme hurricane event could lead to either non-optimal hang-off option or a unconservative design. This study documents a response-based analysis simulating fatigue damage accumulated in differing risers over a broad set of extreme hurricanes. The extreme hurricanes are gathered from hundreds of years of hindcast storms to develop a statistical assessment of the amount of damage accumulated per event. Since the response-based analysis would be cumbersome in the design process, a simplified method benchmarked to the response-based analysis is proposed for design. The simplified method consists of accumulating fatigue damage from multiple seastate cases that are already developed to assess riser strength.
{"title":"Gulf of Mexico Hurricane Single Event Fatigue Method for Riser Analysis","authors":"J. Mesa, M. Santala","doi":"10.1115/omae2020-19057","DOIUrl":"https://doi.org/10.1115/omae2020-19057","url":null,"abstract":"\u0000 Deepwater steel catenary risers (SCRs) are designed considering strength under extreme loads and long-term fatigue of the riser from installation through the full range of conditions anticipated over the service life of the riser. Short-term single event fatigue is also checked to ensure that a single extreme storm or current event does not consume an excessive amount of fatigue capacity. For Gulf of Mexico SCRs, single event fatigue can be a governing case for the riser hang-off. The requirement imposes a relatively modest number of higher stress range cycles and may bias the selection of the hang-off option (titanium, steel, and flex joints) since the three common choices have widely different sensitivity to this case.\u0000 Assessing a single event hurricane is problematic because the evolution of storms which generate an extreme 100-year significant wave height at a site can vary considerably from storm-to-storm. Simplistic representations of the extreme hurricane event could lead to either non-optimal hang-off option or a unconservative design. This study documents a response-based analysis simulating fatigue damage accumulated in differing risers over a broad set of extreme hurricanes. The extreme hurricanes are gathered from hundreds of years of hindcast storms to develop a statistical assessment of the amount of damage accumulated per event. Since the response-based analysis would be cumbersome in the design process, a simplified method benchmarked to the response-based analysis is proposed for design. The simplified method consists of accumulating fatigue damage from multiple seastate cases that are already developed to assess riser strength.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"301 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":"122012675","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}
Steel catenary risers (SCRs) offer a cost-effective solution to deep water deployments. Hanging from a floater, an SCR is commonly subjected to large tension at hangoff location and large bending moments at touchdown zone (TDZ) which lead to fatigue damage. Field observations showed that the depth of a seabed trench might reach to a depth of four to five times of the diameter of a riser, however, a flat seabed was often assumed for the modeling of SCRs which surely affects simulations of fatigue behavior of the SCR at the touchdown zone. Studies on the effects of seabed trench on TDZ fatigue conducted by different researchers led to contradictory conclusions, i.e., some studies suggested that considering seabed trench reduced fatigue damage at TDZ of SCRs, while, others drew opposing conclusions. The contradiction may be explained by factors including inappropriate trench profiles and different sea states assumed in the analysis model. An iterative procedure initially developed by Wang and Low and further improved in the present work was used to estimate the position and the length of a seabed trench beneath an SCR and, then, an improved empirical formulation was generated to approximate the profile of the seabed trench. Additionally, dynamic simulations were conducted to study the effects of seabed trench on fatigue behaviors of SCRs encountering variant directional waves.
{"title":"Improved Empirical Formulation for Seabed Trench Profile at Touchdown Zone and its Effects on Fatigue of Steel Catenary Risers","authors":"S. Zhuang, C. Shi, M. Lou, Y. Liu, X. Bao, H. Li","doi":"10.1115/omae2020-19281","DOIUrl":"https://doi.org/10.1115/omae2020-19281","url":null,"abstract":"\u0000 Steel catenary risers (SCRs) offer a cost-effective solution to deep water deployments. Hanging from a floater, an SCR is commonly subjected to large tension at hangoff location and large bending moments at touchdown zone (TDZ) which lead to fatigue damage. Field observations showed that the depth of a seabed trench might reach to a depth of four to five times of the diameter of a riser, however, a flat seabed was often assumed for the modeling of SCRs which surely affects simulations of fatigue behavior of the SCR at the touchdown zone. Studies on the effects of seabed trench on TDZ fatigue conducted by different researchers led to contradictory conclusions, i.e., some studies suggested that considering seabed trench reduced fatigue damage at TDZ of SCRs, while, others drew opposing conclusions. The contradiction may be explained by factors including inappropriate trench profiles and different sea states assumed in the analysis model. An iterative procedure initially developed by Wang and Low and further improved in the present work was used to estimate the position and the length of a seabed trench beneath an SCR and, then, an improved empirical formulation was generated to approximate the profile of the seabed trench. Additionally, dynamic simulations were conducted to study the effects of seabed trench on fatigue behaviors of SCRs encountering variant directional waves.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"10 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":"132159602","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}
D. Yan, Shuang‐Xi Guo, Yilun Li, Jixiang Song, Min Li, Weimin Chen
As oil and gas industry is developing towards deeper ocean area, the length and flexibility of ocean risers become larger, which may induce larger-amplitude displacement of flexible riser response due to lower structural stiffness against environmental and operational loads. Moreover, suffering not only the external fluid loads coming from environmental ocean wave and current, these risers also convey internal flow. In other words, the dynamic characteristics and response of the flow-conveying riser face great challenge, such as bucking, divergence and flutter, because of the fluid-solid coupling of the internal hydrodynamics and riser structural dynamics. In this study the dynamic characteristics and stability of a flexible riser, under consideration of its internal flow and, particularly, non-uniform axial tension, are examined through our FEM numerical simulations. First, the governing equations and FEM models of a flexible riser with axially-varying tension and internal flow are developed. Then the dynamic characteristics, including the coupled frequency and modal shape, are presented, as considering the speed of internal speed changes. At last, the dynamic response and corresponding stability behaviors are discussed and compared with the cases of riser with uniform tension. Our FEM results show that the stability and response are quite different from riser with uniform tension. And, the time-spatial evolution of riser displacement exhibit a strong wave propagation phenomenon where travelling wave are observed.
{"title":"Dynamic Characteristics and Stability of Flexible Riser Under Consideration of Non-Uniform Tension and Internal Flow","authors":"D. Yan, Shuang‐Xi Guo, Yilun Li, Jixiang Song, Min Li, Weimin Chen","doi":"10.1115/omae2020-18347","DOIUrl":"https://doi.org/10.1115/omae2020-18347","url":null,"abstract":"\u0000 As oil and gas industry is developing towards deeper ocean area, the length and flexibility of ocean risers become larger, which may induce larger-amplitude displacement of flexible riser response due to lower structural stiffness against environmental and operational loads. Moreover, suffering not only the external fluid loads coming from environmental ocean wave and current, these risers also convey internal flow. In other words, the dynamic characteristics and response of the flow-conveying riser face great challenge, such as bucking, divergence and flutter, because of the fluid-solid coupling of the internal hydrodynamics and riser structural dynamics.\u0000 In this study the dynamic characteristics and stability of a flexible riser, under consideration of its internal flow and, particularly, non-uniform axial tension, are examined through our FEM numerical simulations. First, the governing equations and FEM models of a flexible riser with axially-varying tension and internal flow are developed. Then the dynamic characteristics, including the coupled frequency and modal shape, are presented, as considering the speed of internal speed changes. At last, the dynamic response and corresponding stability behaviors are discussed and compared with the cases of riser with uniform tension. Our FEM results show that the stability and response are quite different from riser with uniform tension. And, the time-spatial evolution of riser displacement exhibit a strong wave propagation phenomenon where travelling wave are observed.","PeriodicalId":240325,"journal":{"name":"Volume 4: Pipelines, Risers, and Subsea Systems","volume":"64 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":"132555533","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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