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Marcelo Caire - One of the best experts on this subject based on the ideXlab platform.
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flexible riser Bend Stiffener top connection analytical model with i tube
Marine Structures, 2020Co-Authors: Yangye He, Marcelo CaireAbstract:Abstract The flexible riser top connection to the floating unit is a critical region considering extreme loading and fatigue lifetime assessment and is generally protected by a Bend Stiffener to limit the curvature in this region. The top connection usually interface the floating unit with two main configurations: i) end-fitting and Bend Stiffener directly connected to a riser balcony or ii) riser connected to the floating unit in the end of an I-tube, which reduces the end-fitting Bending loading, and Bend Stiffener assembled to a bellmouth with a given inclination in relation to the I-tube longitudinal axis. The traditional modeling approach considers the riser/Bend Stiffener system attached to the floating unit, representative of the first configuration. A more realistic modeling approach, capturing the complex interactions of flexible riser/Bend Stiffener with I-tube interface can be employed for preliminary assessment with less conservatism. In this work, a large deflection analytical beam model is developed for the riser top connection with I-tube considering the bellmouth transition region with a straight rigid surface followed by a curved section. The riser follows a nonlinear Bending behavior described by a bilinear moment vs curvature function and the Bend Stiffener polyurethane material exhibits nonlinear elastic symmetric response represented by a power law function. It is assumed that there is no gap between the riser and the Bend Stiffener and the riser is fixed in the end-fitting position. The mathematical formulation of the statically indeterminate system results in three systems of coupled differential equations combined with the corresponding multipoint boundary conditions to be numerically solved by an iterative procedure. A case study is carried out with a 7” flexible riser protected by a Bend Stiffener connected to an inclined I-tube bellmouth. The system is subjected to extreme loading conditions and the influence of the sleeve shape and I-tube length on the riser curvature distribution, including the end-fitting position, and contact forces between the riser/sleeve and riser/Bend Stiffener sections are assessed.
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Estimation of flexible riser curvature distribution and Bend Stiffener polyurethane behavior using the Levenberg-Marquardt algorithm in full scale Bending-tension tests
Ocean Engineering, 2020Co-Authors: Irving D. Hernández, Murilo Augusto Vaz, Marcelo CaireAbstract:Abstract Long term full-scale Bending-tension tests are traditionally performed to verify the numerically estimated flexible riser lifetime. For a proper tensile armour stress calculation, the riser curvature distribution has to be accurately determined, being highly affected by the Bend Stiffener polyurethane response. The actual material response may be significantly influenced by the loading rate, environmental temperature and humidity, ageing and self-heating phenomenon, requiring an extensive experimental campaign in addition to advanced constitutive models. In this work, an inverse problem methodology is proposed to decrease riser curvature distribution estimation uncertainties by combining optical configuration measurements, a direct finite element model and the Levenberg-Marquardt algorithm to estimate a representative polyurethane response. A full-scale riser/Bend Stiffener Bending-tension test is conducted and an optical monitoring system is employed to track photoluminescence targets along the system length to estimate its deformed configuration. Five tests are performed and eight targets close to the Bend Stiffener tip selected for the inverse calculation of a representative Bend Stiffener hyperelastic response and riser top tension. The remaining target displacements and the tension measured with a load cell are employed for validation. The case study shows an excellent correlation between the numerically calculated deformed configuration and experimental measurements with the verification targets.
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Flexible Riser Top Connection Analysis With I-Tube Interface and Bending Hysteresis Effect
Volume 5A: Pipelines Risers and Subsea Systems, 2019Co-Authors: Yangye He, Hailong Lu, Marcelo CaireAbstract:Abstract The flexible riser top connection to the floating production platform is a critical region for fatigue lifetime (re)assessment. The interface with the I-tube and its curved sleeve combined with the gap between the riser and Bend Stiffener may lead to different curvature distribution when compared to the traditional modeling approach that considers the Bend Stiffener attached to the pipe. For a more accurate top connection assessment, the flexible riser Bending hysteresis can also be directly incorporated in the global dynamic analysis helping to reduce curvature amplitude and lifetime prediction conservatism. This work investigates a 7” flexible riser-Bend Stiffener top connection with I-tube interface by performing irregular wave global dynamic analyses with the OrcaFlex package and considering a nonlinear Bending moment vs curvature riser behavior obtained from a detailed cross sectional model developed in Abaqus. OrcaFlex curvature distribution results are also compared with a quasi-static finite element model that uses an elasto-plastic formulation with kinematic hardening to represent riser hysteresis through an equivalent beam model. A good curvature distribution correlation is observed for both top connection models (OrcaFlex x Abaqus) in the Bend Stiffener area with reduced amplitudes when riser Bending hysteresis is considered.
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An inverse problem methodology for multiple parameter estimation in Bend Stiffeners
Applied Ocean Research, 2019Co-Authors: Yangye He, Marcelo CaireAbstract:Abstract The flexible riser top connection is a critical region for lifetime assessment due to large tension/curvature variations and modeling uncertainties. The Bend Stiffener polyurethane mechanical response not only presents a nonlinear loading rate and temperature dependency but is also subjected to weather ageing during operation, which may affect its mechanical behavior over time. The top tension, employed for riser local cross-section stress calculation, is usually obtained from global dynamic analyses performed under selected environmental conditions, if direct measurement is not available. As a consequence, both the Bend Stiffener effect on the curvature distribution and the top tension time series present inherent uncertainties for riser lifetime (re)assessment. In the present work, a proposed monitoring approach composed by gyrometers installed along flexible riser/Bend Stiffener top connection system length combined with an inverse problem methodology is numerically investigated to estimate the following parameters: (i) polyurethane hyperelastic response and (ii) effective top tension. The top connection system is modeled using a large deflection beam Bending model and the parameters are estimated using a damped least-square minimization approach with the Levenberg–Marquardt algorithm. For the preliminary feasibility investigation, the gyrometer experimental data is numerically estimated through Monte Carlo simulations. A case study is carried out to investigate the influence that the number of sensors, sensors arrangement, loading conditions and top connection model have on the inverse parameters estimation. The results indicate that the proposed monitoring approach and inverse parameter estimation methodology may effectively reduce flexible riser lifetime calculation uncertainties.
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An Inverse Problem for Parameter Estimation in a Bend Stiffener System
Volume 5: Pipelines Risers and Subsea Systems, 2018Co-Authors: Murilo Augusto Vaz, Marcelo CaireAbstract:The top connection of the flexible pipe attached to the platform supporting structure is considered to be a critical area as it sustains the highest forces and often the maximum curvature in the riser system. Bend Stiffener, a polymeric structure with conical shape, is employed to limit the maximum curvature of the riser at the uppermost connection, and protect it against excessive Bending and accumulative fatigue damage. In this work, an inverse problem methodology is proposed for estimating unknown parameters in the Bend Stiffener system, based on a large displacement beam theoretical model combined with the Levenberg-Marquardt Method. The global mathematical formulation is used for nonlinear analysis of the riser/Bend Stiffener system considering linear elastic symmetric material. A case study is given considering simulated angle measurements in five monitoring positions to estimate two unknown parameters in the system, top tension and polyurethane Young’s modulus. Monte Carlo method is employed to analyze the statistic properties of the estimated parameters with measurement errors. The effects of sensor locations and measurement error ranges on the accuracy of parameter estimation are investigated. It is shown that the proposed procedure can estimate efficiently and accurately unknown parameters in a Bend Stiffener system. The parameter estimation procedure can also be used to assess other mechanical parameters of the Bend Stiffener system by angle measurements in certain monitoring positions in realistic production systems.
Murilo Augusto Vaz - One of the best experts on this subject based on the ideXlab platform.
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Estimation of flexible riser curvature distribution and Bend Stiffener polyurethane behavior using the Levenberg-Marquardt algorithm in full scale Bending-tension tests
Ocean Engineering, 2020Co-Authors: Irving D. Hernández, Murilo Augusto Vaz, Marcelo CaireAbstract:Abstract Long term full-scale Bending-tension tests are traditionally performed to verify the numerically estimated flexible riser lifetime. For a proper tensile armour stress calculation, the riser curvature distribution has to be accurately determined, being highly affected by the Bend Stiffener polyurethane response. The actual material response may be significantly influenced by the loading rate, environmental temperature and humidity, ageing and self-heating phenomenon, requiring an extensive experimental campaign in addition to advanced constitutive models. In this work, an inverse problem methodology is proposed to decrease riser curvature distribution estimation uncertainties by combining optical configuration measurements, a direct finite element model and the Levenberg-Marquardt algorithm to estimate a representative polyurethane response. A full-scale riser/Bend Stiffener Bending-tension test is conducted and an optical monitoring system is employed to track photoluminescence targets along the system length to estimate its deformed configuration. Five tests are performed and eight targets close to the Bend Stiffener tip selected for the inverse calculation of a representative Bend Stiffener hyperelastic response and riser top tension. The remaining target displacements and the tension measured with a load cell are employed for validation. The case study shows an excellent correlation between the numerically calculated deformed configuration and experimental measurements with the verification targets.
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An Inverse Problem for Parameter Estimation in a Bend Stiffener System
Volume 5: Pipelines Risers and Subsea Systems, 2018Co-Authors: Murilo Augusto Vaz, Marcelo CaireAbstract:The top connection of the flexible pipe attached to the platform supporting structure is considered to be a critical area as it sustains the highest forces and often the maximum curvature in the riser system. Bend Stiffener, a polymeric structure with conical shape, is employed to limit the maximum curvature of the riser at the uppermost connection, and protect it against excessive Bending and accumulative fatigue damage. In this work, an inverse problem methodology is proposed for estimating unknown parameters in the Bend Stiffener system, based on a large displacement beam theoretical model combined with the Levenberg-Marquardt Method. The global mathematical formulation is used for nonlinear analysis of the riser/Bend Stiffener system considering linear elastic symmetric material. A case study is given considering simulated angle measurements in five monitoring positions to estimate two unknown parameters in the system, top tension and polyurethane Young’s modulus. Monte Carlo method is employed to analyze the statistic properties of the estimated parameters with measurement errors. The effects of sensor locations and measurement error ranges on the accuracy of parameter estimation are investigated. It is shown that the proposed procedure can estimate efficiently and accurately unknown parameters in a Bend Stiffener system. The parameter estimation procedure can also be used to assess other mechanical parameters of the Bend Stiffener system by angle measurements in certain monitoring positions in realistic production systems.
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Characterization of seawater and weather aged polyurethane elastomer for Bend Stiffeners
Polymer Testing, 2017Co-Authors: Geovanio Lima De Oliveira, Aynor Justino Ariza Gomez, Murilo Augusto Vaz, Marcelo Caire, Marysilvia Ferreira Da CostaAbstract:A Bend Stiffener grade polyurethane (PU) elastomer was physically and mechanically characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The material was then exposed to artificial seawater and weather up to 12 months to evaluate its stability as Bend Stiffeners are exposed to this type of environment during offshore operation. The characterization of aged samples was performed comparing the ageing effects on the chemical structure, thermal stability and mechanical properties with those of the non-aged material. The mass variation of aged samples immersed in artificial seawater was also measured. A slight change in the chemical structure led to a color change from dark green to brown in the samples exposed to natural weathering for 12 months. Increases in thermal stability, stiffness and strength characteristics were also verified, which may be associated to additional crosslink formation. In contrast, a significant mechanical property drop was observed for the artificial seawater aged PU, being attributed to a plasticizer effect induced by the ageing fluid. The stress-strain curves were adjusted with the Mooney-Rivlin model allowing the crosslink density estimation. The weather aged PU presented higher crosslink density than seawater aged and non-aged samples.
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A nonlinear viscoelastic Bend Stiffener steady-state formulation
Applied Ocean Research, 2017Co-Authors: Marcelo Caire, Murilo Augusto VazAbstract:Abstract Bend Stiffeners are essential components of a flexible riser system, employed to ensure a smooth transition at the upper connection and to protect the riser against over Bending and from accumulation of fatigue damage. The highly nonlinear rate dependent behavior of these structures directly affects the integrity assessment of the riser in one of its most critical regions, the top connection. A steady-state formulation (disregarding inertial forces) and numerical solution procedure is developed in this work employing the perturbation method for a nonlinear viscoelastic Bend Stiffener large deflection beam model subjected to harmonic loading conditions. For stochastic loading conditions, the response is calculated employing the superposition principle by summing up the steady-state result of a number of individual frequency components. A time domain formulation is also derived employing the state-variable approach for the numerical solution of the resulting hereditary integral in the governing equations. A case study is presented for the top connection system of a 4″ ID flexible riser using relaxation and tensile experimental data obtained from a typical class of Bend Stiffener polyurethane. Harmonic and stochastic input loading conditions are employed for time and frequency domain model comparison/validation and to assess loading history and frequency influence in the curvature response.
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Mechanical Behavior Characterization of Polyurethane Used in Bend Stiffener
Conference Proceedings of the Society for Experimental Mechanics Series, 2016Co-Authors: Geovanio Lima De Oliveira, Marysilvia Ferreira Da Costa, Marcelo Caire, A. G. Ariza, Murilo Augusto VazAbstract:Bend Stiffeners are structures employed in the offshore oil and gas industry designed to restrict curvature of flexible lines and umbilical cables connected to floating production units. They are conically shaped and fabricated in polyurethane (PU), an elastomeric material whose properties can be largely modified by the multiplicity of resins available in the market. Therefore, detailed polyurethane characterization is important to define the properties of the materials as well as to evaluate its stability in marine environment. In this work, a Bend Stiffener grade polyurethane was exposed to synthetic sea water and to the weather for 6 months. The material was characterized by infrared spectroscopy, tensile and stress relaxation tests. It was found that the mechanical characteristics are affected by sea water with a drop in tensile strength when material is tested on the same day that the final ageing time is completed. Relaxation and stress-strain curve fittings were performed using hyperviscoelastic and hyperelastic models, respectively. Among several hyperelastic models used, Alexander, Polynomial and Yamashita-Kawabata were found to successfully describe the experimental behavior. The hyperviscoelasticity model was compared with hyperelastic models considering the same strain rate.
Marysilvia Ferreira Da Costa - One of the best experts on this subject based on the ideXlab platform.
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Characterization of seawater and weather aged polyurethane elastomer for Bend Stiffeners
Polymer Testing, 2017Co-Authors: Geovanio Lima De Oliveira, Aynor Justino Ariza Gomez, Murilo Augusto Vaz, Marcelo Caire, Marysilvia Ferreira Da CostaAbstract:A Bend Stiffener grade polyurethane (PU) elastomer was physically and mechanically characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The material was then exposed to artificial seawater and weather up to 12 months to evaluate its stability as Bend Stiffeners are exposed to this type of environment during offshore operation. The characterization of aged samples was performed comparing the ageing effects on the chemical structure, thermal stability and mechanical properties with those of the non-aged material. The mass variation of aged samples immersed in artificial seawater was also measured. A slight change in the chemical structure led to a color change from dark green to brown in the samples exposed to natural weathering for 12 months. Increases in thermal stability, stiffness and strength characteristics were also verified, which may be associated to additional crosslink formation. In contrast, a significant mechanical property drop was observed for the artificial seawater aged PU, being attributed to a plasticizer effect induced by the ageing fluid. The stress-strain curves were adjusted with the Mooney-Rivlin model allowing the crosslink density estimation. The weather aged PU presented higher crosslink density than seawater aged and non-aged samples.
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Bend Stiffener nonlinear viscoelastic time domain formulation
Marine Structures, 2016Co-Authors: Marcelo Caire, Marysilvia Ferreira Da CostaAbstract:Abstract Bend Stiffeners are conical polyurethane structures used in the offshore industry to ensure a smooth transition in the upper connection of flexible risers with the floating production unit. The polyurethane employed for Bend Stiffeners present a nonlinear viscoelastic response that is highly dependent on the loading rate and temperature. This may lead to different flexible riser response when compared to elastic or hyperelastic material modeling. In order to quantify this effect, tensile and relaxation tests are carried out to characterize the nonlinear time dependent mechanical behavior of the polyurethane. A constitutive equation based on the modified superposition method is then presented and a procedure for material identification proposed. A numerical scheme using the state variable approach is formulated for the nonlinear viscoelastic constitutive equation finite element implementation. The top connection system, consisting of a Bend Stiffener and a flexible pipe segment, is represented by a large displacement beam model accounting for geometrical and material nonlinearities. A case study is carried out to compare the system curvature response calculated for the nonlinear viscoelastic and hyperelastic (Marlow strain energy potential) Bend Stiffener subjected to harmonic loading conditions at different frequencies. The results show the importance of Bend Stiffener strain rate dependency on the riser curvature response.
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Mechanical Behavior Characterization of Polyurethane Used in Bend Stiffener
Conference Proceedings of the Society for Experimental Mechanics Series, 2016Co-Authors: Geovanio Lima De Oliveira, Marysilvia Ferreira Da Costa, Marcelo Caire, A. G. Ariza, Murilo Augusto VazAbstract:Bend Stiffeners are structures employed in the offshore oil and gas industry designed to restrict curvature of flexible lines and umbilical cables connected to floating production units. They are conically shaped and fabricated in polyurethane (PU), an elastomeric material whose properties can be largely modified by the multiplicity of resins available in the market. Therefore, detailed polyurethane characterization is important to define the properties of the materials as well as to evaluate its stability in marine environment. In this work, a Bend Stiffener grade polyurethane was exposed to synthetic sea water and to the weather for 6 months. The material was characterized by infrared spectroscopy, tensile and stress relaxation tests. It was found that the mechanical characteristics are affected by sea water with a drop in tensile strength when material is tested on the same day that the final ageing time is completed. Relaxation and stress-strain curve fittings were performed using hyperviscoelastic and hyperelastic models, respectively. Among several hyperelastic models used, Alexander, Polynomial and Yamashita-Kawabata were found to successfully describe the experimental behavior. The hyperviscoelasticity model was compared with hyperelastic models considering the same strain rate.
Mario Alfredo Vignoles - One of the best experts on this subject based on the ideXlab platform.
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Lean Global Analysis of Marine Slender Structures With Machine Learning
Volume 5A: Pipelines Risers and Subsea Systems, 2019Co-Authors: Vinícius Da Silva, Matheus Costa Dos Santos, Mario Alfredo VignolesAbstract:Abstract The new age of oil and gas industry is being driven by cost effective solutions, aiming to provide cheaper, faster and better products/services. The industry 4.0 brings an opportunity to transform systems and processes to be more efficient, making use of digitalization and new technologies, including the use of artificial intelligence algorithms applied to engineering problems. In Brazilian offshore fields, the operating conditions for flexible riser applications (deep-water, mean wave frequencies, floating units and corrosive fluids) make the metallic layer’s fatigue failure mode one of the drivers in its design. In a daily basis, nonlinear dynamic finite element analysis uses regular wave scatter diagrams as an equivalent way to model the wave elevation, avoiding the time consuming irregular wave representation. The analysis performed with regular waves are faster but carries conservatisms with it. In a deep-water scenario, the wave height and period ranges of the wave scatter diagram can be refined to improve the fatigue results obtained, leading to a considerable increase in the total amount of wave classes that need to be evaluated. Great part of the wave classes has a very low participation in the total fatigue damage, spending an unnecessary time to analyze them. Helped by a robust design of simulation experiment (DoSE) and machine learning regressors, a lean representation of the regular wave scatter can be done, where some of them are simulated and the rest of the results can be accurately predicted. This paper presents the application of supervised learners that are used to predict riser fatigue damage at different riser locations, given partial simulations of a regular wave scatter diagram. The techniques support the strategy to reduce the total amount of fatigue analysis required within a project design phase. The focus stays on the evaluation of the fatigue of metallic layers at two main critical regions, Bend Stiffener and touch down zone. Hidden patterns inside each scatter diagram are discovered, minimizing the total number of finite element analysis (FEA) required. The amount of the wave class reduction starts from 50% going up to 75%, maintaining a good level of accuracy on the predicted damage values.
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Lazy-Wave Buoyancy Length Reduction Based on Fatigue Reliability Analysis
Volume 5A: Pipelines Risers and Subsea Systems, 2017Co-Authors: Vinícius Da Silva, Luis Volnei Sudati Sagrilo, Mario Alfredo VignolesAbstract:When the profit scenario of an industry changes, the continuity of some projects can be at risk. The current downturn of the oil and gas industry force managers to take hard decisions about the continuity of projects, resulting in delays, postponements or even the cancellation of forecasted projects. In order to keep with these projects, the rush for cost reduction is a reality and the industry is pushing the involved parties to be aligned with this objective. The Brazilian Pre-Salt region, characterized by ultra-deep waters, is an example of this scenario. Subsea structures represented by flexible risers, which are responsible for the flow assurance of oil, gas and water, are forecasted to have a demand about 4.000 km in the next years. Usually, in these type of applications, lazy-wave configurations are adopted, increasing the costs of the solution with the necessity of the buoyancy modules acquisition. The smaller the buoyancy length is the cheaper the project become, reducing the necessary amount of buoys and the time spent for its installation. These type of solutions can probably carry with it a high level of conservatism, imposed by the use of standardized safety factors, and can potentially be optimized with the adoption of probabilistic approaches within the chain of analysis. The objective of this paper is to assess the possibility of buoyancy length reduction of lazy-wave configurations by using structural reliability methods of analysis. The focus stays on the evaluation of the fatigue of the armour wires located at the Bend Stiffener region, one of the most critical failure mode for the design of flexible pipes in offshore Brazilian installations. As already discussed in Ref. [1], many variables can influence on such kind of analysis. Based on this previous study, the first six random variables, identified to be the most important ones, are taken to carry out the analysis. The fatigue reliability approach considers four 6” flexible riser configurations: an original lazy-wave, a lazy-wave with less 30% of buoyance length, another one with less 50% of buoyance length and a free-hanging configuration. Failure probabilities and safety factor calibration curves are shown for each presented configuration and compared among themselves. The results indicate the possibility of defining a lazy-wave configuration with smaller buoyancy lengths, reaching 75% of reduction without changing the preconized high safety class at last year of its operational time. Safety factor curves shows to have similar behavior no matter the configuration considered. Structural reliability analysis comes as a potential method to help engineers to have a better understanding on the driving random variables of the problem, giving a support for the actual cost reduction scenario and for better decision-makings based on quantified risk.
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fatigue reliability assessment for flexible riser armour wires
ASME 2015 34th International Conference on Ocean Offshore and Arctic Engineering, 2015Co-Authors: Vinicius Ribeiro Machado Da Silva, Luis Volnei Sudati Sagrilo, Mario Alfredo VignolesAbstract:Oil and gas exploitation in regions of ultra-deep water has already been started and there is a great expectation of growth in the coming years, mainly in the region known as Pre-Salt, at Brazilian’s coast. Operators, which have the concession to exploit this region, have adopted different solutions with different configurations using rigid and flexible pipes for this initial phase. However, the last structural type mentioned shows to be much more versatile, providing attractive cost/benefit solutions to the operators, in which, only in Brazil, it is forecasted a demand about 4.000 km of flexible pipes in the next years [1]. With new challenges coming, one may ask the following question: What is the structural reliability of each failure mode of these flexible pipes? Motivated by this question, this paper has the objective to do a preliminary analysis, under the structural reliability view, of the critical failure mode for the design of flexible pipes faced in Brazil, represented by the fatigue phenomenon on metallic layers. The work assesses the fatigue reliability of the armour wires, located in the Bend Stiffener region, for two 6″ flexible risers configurations, free-hanging and lazy-wave. They are considered to be installed in ultra-deep water (2140m depth) and are submitted to the same external environmental loads. The fatigue reliability methodology used is based on that presented in Ref. [2] including new random variables. Sensitivity analyses are also performed for the variables that most contributes to the quantified probability of failure. Calibrated safety factors (SF) are obtained for different target failure probabilities.Copyright © 2015 by ASME
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Artificial Neural Networks Applied to Flexible Pipes Fatigue Calculations
Volume 5B: Pipeline and Riser Technology, 2015Co-Authors: Victor Chaves, Luis Volnei Sudati Sagrilo, Vinícius Da Silva, Mario Alfredo VignolesAbstract:Flexible pipes play an important role in offshore oil exploitation activities nowadays. However, time-domain flexible pipe irregular wave dynamic analyses are extremely computational expensive. One of the various existing methods to reduce computational costs in dynamic analyses is the hybrid methodology that combines dynamic Finite Element Analyses (FEA) and Artificial Neural Networks (ANN). This paper presents a novel application of this methodology for flexible pipes fatigue calculations. In order to decrease computational cost involved in these analyses the proposed hybrid methodology aims to predict tension and curvatures in the Bend Stiffener region. Firstly using short FEA simulations to train the ANN, and then using only the ANN and the prescribed floater motions to get the rest of the response histories. With the predicted tension and curvatures, a local analysis is applied to calculate stresses in tensile armour wires and the corresponding fatigue lives. To evaluate the optimal ANN a sensibility study is developed for some key parameters as: training time length, neurons on hidden layer and delay length. A full FEA is also performed in order to evaluate the accuracy of the proposed hybrid methodology, comparing both full FEA flexible pipe fatigue results and those obtained using the hybrid methodology.Copyright © 2015 by ASME
Geovanio Lima De Oliveira - One of the best experts on this subject based on the ideXlab platform.
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Characterization of seawater and weather aged polyurethane elastomer for Bend Stiffeners
Polymer Testing, 2017Co-Authors: Geovanio Lima De Oliveira, Aynor Justino Ariza Gomez, Murilo Augusto Vaz, Marcelo Caire, Marysilvia Ferreira Da CostaAbstract:A Bend Stiffener grade polyurethane (PU) elastomer was physically and mechanically characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The material was then exposed to artificial seawater and weather up to 12 months to evaluate its stability as Bend Stiffeners are exposed to this type of environment during offshore operation. The characterization of aged samples was performed comparing the ageing effects on the chemical structure, thermal stability and mechanical properties with those of the non-aged material. The mass variation of aged samples immersed in artificial seawater was also measured. A slight change in the chemical structure led to a color change from dark green to brown in the samples exposed to natural weathering for 12 months. Increases in thermal stability, stiffness and strength characteristics were also verified, which may be associated to additional crosslink formation. In contrast, a significant mechanical property drop was observed for the artificial seawater aged PU, being attributed to a plasticizer effect induced by the ageing fluid. The stress-strain curves were adjusted with the Mooney-Rivlin model allowing the crosslink density estimation. The weather aged PU presented higher crosslink density than seawater aged and non-aged samples.
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Mechanical Behavior Characterization of Polyurethane Used in Bend Stiffener
Conference Proceedings of the Society for Experimental Mechanics Series, 2016Co-Authors: Geovanio Lima De Oliveira, Marysilvia Ferreira Da Costa, Marcelo Caire, A. G. Ariza, Murilo Augusto VazAbstract:Bend Stiffeners are structures employed in the offshore oil and gas industry designed to restrict curvature of flexible lines and umbilical cables connected to floating production units. They are conically shaped and fabricated in polyurethane (PU), an elastomeric material whose properties can be largely modified by the multiplicity of resins available in the market. Therefore, detailed polyurethane characterization is important to define the properties of the materials as well as to evaluate its stability in marine environment. In this work, a Bend Stiffener grade polyurethane was exposed to synthetic sea water and to the weather for 6 months. The material was characterized by infrared spectroscopy, tensile and stress relaxation tests. It was found that the mechanical characteristics are affected by sea water with a drop in tensile strength when material is tested on the same day that the final ageing time is completed. Relaxation and stress-strain curve fittings were performed using hyperviscoelastic and hyperelastic models, respectively. Among several hyperelastic models used, Alexander, Polynomial and Yamashita-Kawabata were found to successfully describe the experimental behavior. The hyperviscoelasticity model was compared with hyperelastic models considering the same strain rate.