Articles de revues : « Riserva Naturale Marina »

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Zhong, Xing Fu, Li Ming Lin, Ying Xiang Wu et Shi Ying Shi. « New Method in Suppressing Vortex-Induced Vibration of Marine Riser ». Applied Mechanics and Materials 226-228 (novembre 2012) : 9–12. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.9.

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Marine risers are key apparatus in connecting the subsea wells to the oil production platform. When the ocean current flow past a riser, the vortex shedding behind riser may induce vibration. If the frequency of vortex shedding is approaching or equal to the natural frequency of riser, the resonance will be generated. Such phenomenon leads to the potential fatigue damage of riser. Therefore, the safety and assurance of marine risers are widely arousing the interest of offshore engineering. In present paper, previous apparatus or methods in suppressing vortex-induced vibration (VIV) of risers used in marine engineering are firstly analyzed, and correspondingly the conditions in design of VIV suppressors are proposed. Based on the Bernoulli equation, the disturbance in flow around a bluff body and the relationship of vortex shedding in span-wise direction, a new method of VIV suppression is proposed. The numerical results have shown that the vibration of risers could be reduced by such disturbance.

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Bernitsas, M. M., C. J. Hoff et J. E. Kokarakis. « Nonlinear Inverse Perturbation in Structural Dynamics Redesign of Risers ». Journal of Energy Resources Technology 107, n^o 2 (1 juin 1985) : 256–63. http://dx.doi.org/10.1115/1.3231186.

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Marine risers, and offshore structures in general, may have undesirable natural frequencies and/or mode shapes. Structural redesign is mandatory in such cases. An Inverse Perturbation Redesign (IPR) method, which uses only the finite element analysis of the baseline system and was developed in previous work for general structures, is extended in this work to handle systems with geometric stiffness matrices like marine risers. The IPR method is currently applicable to undamped structural systems or systems with Rayleigh damping and is valid for large or small changes which are frequently required to change modal characteristics of offshore structures. The vibratory characteristics of risers can be altered by modifying among others, the riser top tension, the drilling mud density and the geometry of the riser tubes. The effects of their change on the riser frequencies and modes are derived and applied to two typical riser redesign problems using the IPR method.

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Kim, Y. C. « Natural Frequencies and Critical Buckling Loads of Marine Risers ». Journal of Offshore Mechanics and Arctic Engineering 110, n^o 1 (1 février 1988) : 2–8. http://dx.doi.org/10.1115/1.3257119.

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Natural frequencies, mode shapes and critical buckling loads of marine risers simply supported at both ends are given in closed form by using the WKB method. These solutions allow variable cross section, bending rigidity, tension and mass distribution along the riser length. Furthermore, a simple procedure to predict natural frequencies for other boundary conditions is described. Some special forms of these closed-form solutions are compared with existing solutions in the literature.

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VIDYA, C., J. SHEEJA et M. SEKAR. « TOWARDS REDUCING COMPUTATIONAL EFFORT IN VORTEX INDUCED VIBRATION PREDICTIONS OF A CYLINDRICAL RISER. » Periódico Tchê Química 16, n^o 33 (20 mars 2019) : 841–53. http://dx.doi.org/10.52571/ptq.v16.n33.2019.856_periodico33_pgs_841_853.pdf.

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Vibrations induced by flow, generally referred to as vortex induced vibrations, are of great importance in the design of marine risers. These flexible cylindrical risers undergo vibrations of very high amplitude when the vortex shedding frequency matches the natural frequency of the riser. Such vibrations are capable of putting the safety of crew working on offshore platforms in question. Hence the prediction of response of such structures is considered very important. Although a lot of numerical work has been done in this field treating the problem as a two-way fluid structure interaction, the fact that these works demand very high computational efforts has not made it pertinent where high end computing resources are not readily available. A quick prediction of the structural response of such slender structures needs to be handy to the engineers at times of need. This paper addresses a solution technique for such a problem through an economical method for quick and reliable prediction of riser response under vortex induced vibration utilizing minimum computational effort for moderate Reynolds number (Re = 3 x 105). Two dimensional flow simulations are carried out using RANSE based CFD followed by the uniform mapping of hydrodynamic forces on to the three dimensional riser. The grid used for the numerical simulation has been well validated against wind-tunnel experimental results for Re= 5.3 x 104. Hydrodynamic forces corresponding to the first three harmonics of natural frequency of the riser have been used as input in the structural solver to analyse the response using finite element method. Trajectories of the cylinder in the first three modes of vibration have been obtained, a typical eight figure pattern which is characteristic for lock-in vibration. It is found that the method is quite effective in the quick computation of flow induced vibration problems for low and moderate Reynolds numbers.

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Graves, Jason R., et Don W. Dareing. « Direct Method for Determining Natural Frequencies of Marine Risers in Deep Water ». Journal of Energy Resources Technology 126, n^o 1 (1 mars 2004) : 47–53. http://dx.doi.org/10.1115/1.1628677.

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This paper presents a direct method for determining natural frequencies of lateral modes of vibration for marine risers in deep water. This method applies to marine risers that are vertical, relatively straight, and attached at both ends. The method is particularly useful for determining natural frequencies of higher modes that are sometimes difficult to obtain analytically or numerically. Comparisons of numerical results with published data show that even though the method of solution is approximate, the calculation procedure gives useful engineering results. The algorithm is based on classical vibration theory and can easily be programmed on portable computers for direct use on offshore oil rigs.

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Chen, Yanfei, Juan Zhang, Hong Zhang, Xin Li et Jing Zhou. « Re-examination of natural frequencies of marine risers by variational iteration method ». Ocean Engineering 94 (janvier 2015) : 132–39. http://dx.doi.org/10.1016/j.oceaneng.2014.11.026.

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Montoya-Hernández, D. J., A. O. Vázquez-Hernández, R. Cuamatzi et M. A. Hernandez. « Natural frequency analysis of a marine riser considering multiphase internal flow behavior ». Ocean Engineering 92 (décembre 2014) : 103–13. http://dx.doi.org/10.1016/j.oceaneng.2014.09.039.

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Komachi, Younes, Said Mazaheri et Mohammadreza Tabeshpour. « The Effect of Shifting Natural Frequency on the Reduction of Vortex-Induced Vibrations of Marine Risers ». International Journal of coastal and offshore engineering 1, n^o 1 (1 mai 2017) : 9–16. http://dx.doi.org/10.18869/acadpub.ijcoe.1.1.9.

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Su, Kan Hua, Zhi Chuan Guan et Li Shi. « Dynamic Response of the Casing String in Seabed Soil for Deepwater Drilling ». Applied Mechanics and Materials 170-173 (mai 2012) : 2217–21. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.2217.

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The marine riser has transfer dynamic cyclic load to the top of casing string when deepwater drilling operating. Considering with the nonlinear characteristics of seabed soil, the variable string cross section, and the axial load on the top of string, a dynamic differential equation of casing string below mud line and its numerical solution were established. Results illustrate that, the lateral displacement, the bending moment, and the shear of the casing string are not equal when lateral dynamic cyclic loading achieves amplitude due to the soil hysteresis effect. The diameter and wall thickness of conductor have less affect to string vibration frequency, cannot adjust the string natural frequency by adjusting these parameters. The natural frequency of casing string in sand is bigger than it in clay. The undrained shear strength of soil has great effect on the natural frequency of casing string in clay. The lateral displacement amplitude is highest when the vibration frequency of casing string at its natural frequency.

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Chen, Yanfei, Y. H. Chai, Xin Li et Jing Zhou. « An extraction of the natural frequencies and mode shapes of marine risers by the method of differential transformation ». Computers & ; Structures 87, n^o 21-22 (novembre 2009) : 1384–93. http://dx.doi.org/10.1016/j.compstruc.2009.07.003.

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Wang, Wuchao, Haixia Gong, Liquan Wang et Feihong Yun. « Frequency Response Function and Design Parameter Effects of Hydro-Pneumatic Tensioner for Top-Tensioned Riser ». Processes 9, n^o 12 (13 décembre 2021) : 2239. http://dx.doi.org/10.3390/pr9122239.

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The top-tensioned riser is an important equipment in offshore oil and gas development. The hydro-pneumatic tensioner is an essential device to ensure the safety of the top-tensioned riser. To investigate the dynamic performance of the marine platform hydro-pneumatic tensioner, this paper proposed a first-order Taylor approximation method and created the frequency response function of the hydro-pneumatic tensioner. According to the frequency response function, the hydro-pneumatic tensioner is a first-order spring-mass system. With the given parameters, the system stiffness coefficient is 66.1 kN/m, the natural annular frequency is 20.99 rad/s and the damping ratio is 2.23 × 10−4. The effects of the high-pressure accumulator, low-pressure accumulator, hydraulic cylinder and pipeline design parameters on the stiffness coefficient, natural annular frequency and damping ratio are analyzed. The stiffness coefficient can be increased by (1) increasing the high-pressure accumulator pressure and reducing the high-pressure accumulator volume; (2) increasing the pressure of the low-pressure accumulator and reducing the low-pressure accumulator volume; (3) increasing the piston diameter; and vice versa. The natural annular frequency can be increased by: (1) increasing the high-pressure accumulator pressure and reducing the high-pressure accumulator volume; (2) increasing the pressure of the low-pressure accumulator and reducing the low-pressure accumulator volume; (3) increasing the piston diameter; and vice versa. The damping ratio can be increased by increasing the pipeline length and reducing the pipeline inner diameter.

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Chang, Yuanjiang, Jiayi Li, Changshuai Zhang, Guoming Chen, Xinhong Li, Shenyan Zhang, Liangbin Xu et Leixiang Sheng. « Dynamic risk assessment approach of riser recoil control failure during production test of marine natural gas hydrate ». Energy Science & ; Engineering 7, n^o 5 (21 juin 2019) : 1808–22. http://dx.doi.org/10.1002/ese3.392.

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Zeng, Song, Liangjie Mao, Qingyou Liu, Guorong Wang et Juan Li. « Study on mechanical properties of natural gas hydrate production riser considering hydrate phase transition and marine environmental loads ». Ocean Engineering 235 (septembre 2021) : 109456. http://dx.doi.org/10.1016/j.oceaneng.2021.109456.

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Bank, L. C., et C. H. Kao. « Dynamic Response of Thin-Walled Composite Material Timoshenko Beams ». Journal of Energy Resources Technology 112, n^o 2 (1 juin 1990) : 149–54. http://dx.doi.org/10.1115/1.2905723.

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Thin-walled structural members are used extensively in the offshore industry in applications ranging from marine risers to platforms and frames. Advanced fiber composite structural members may offer advantages over their conventional steel counterparts in certain situations. Use of composite members will require modifications to existing structural analysis codes. This paper presents a beam theory for thin-walled composite beams that can be incorporated into existing codes. Timoshenko beam theory is utilized to account for shear deformation effects, which cannot be neglected in composite beams, and for the variability in material properties in different walls of the beam cross section. The theory is applied to the analysis of the free vibration problem and shows the dependence of the natural frequencies and mode shapes on the in-plane properties of the laminates that form the walls of the beam. Forced periodic and forced arbitrary problems are also discussed and the deflected shapes and maximum deflections are shown as functions of wall layups.

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Su, Kan Hua, Ji Lin Liu, Cheng Wei Qi et Li Shi. « Influence Analysis of the Vibration Frequency to the Dynamic Response of Deepwater Drilling Casing String ». Advanced Materials Research 871 (décembre 2013) : 39–44. http://dx.doi.org/10.4028/www.scientific.net/amr.871.39.

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The dynamic response of the casing string under the mud line is concerned by engineer when deepwater drilling operating. Considering with the nonlinear characteristics of seabed soil, a dynamic differential equation of the casing string below mud line was established. Then the Newmark method was adapted to solving this equation by time step. Results illustrate that, the deformation and internal force of the casing string in low frequency region have little difference with the static situation. The amplitude of the string displacement increases gradually at the natural frequency. And the hysteretic phenomenon more and more obviously at this point also. In general, there are almost no influences to the dynamic lateral bearing of the casing string when not considering the wellhead vertical force. Use a static method to analyses the wellhead stability and the string bearing capacity can meet the project requirement. The dynamic analysis of casing string coupled with the marine riser is very necessary to future work.

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Oruganti, Yagna. « Technology Focus : Data Analytics (October 2021) ». Journal of Petroleum Technology 73, n^o 10 (1 octobre 2021) : 60. http://dx.doi.org/10.2118/1021-0060-jpt.

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With a moderate- to low-oil-price environment being the new normal, improving process efficiency, thereby leading to hydrocarbon recovery at reduced costs, is becoming the need of the hour. The oil and gas industry generates vast amounts of data that, if properly leveraged, can generate insights that lead to recovering hydrocarbons with reduced costs, better safety records, lower costs associated with equipment downtime, and reduced environmental footprint. Data analytics and machine-learning techniques offer tremendous potential in leveraging the data. An analysis of papers in OnePetro from 2014 to 2020 illustrates the steep increase in the number of machine-learning-related papers year after year. The analysis also reveals reservoir characterization, formation evaluation, and drilling as domains that have seen the highest number of papers on the application of machine-learning techniques. Reservoir characterization in particular is a field that has seen an explosion of papers on machine learning, with the use of convolutional neural networks for fault detection, seismic imaging and inversion, and the use of classical machine-learning algorithms such as random forests for lithofacies classification. Formation evaluation is another area that has gained a lot of traction with applications such as the use of classical machine-learning techniques such as support vector regression to predict rock mechanical properties and the use of deep-learning techniques such as long short-term memory to predict synthetic logs in unconventional reservoirs. Drilling is another domain where a tremendous amount of work has been done with papers on optimizing drilling parameters using techniques such as genetic algorithms, using automated machine-learning frameworks for bit dull grade prediction, and application of natural language processing for stuck-pipe prevention and reduction of nonproductive time. As the application of machine learning toward solving various problems in the upstream oil and gas industry proliferates, explainable artificial intelligence or machine-learning interpretability becomes critical for data scientists and business decision-makers alike. Data scientists need the ability to explain machine-learning models to executives and stakeholders to verify hypotheses and build trust in the models. One of the three highlighted papers used Shapley additive explanations, which is a game-theory-based approach to explain machine-learning outputs, to provide a layer of interpretability to their machine-learning model for identification of identification of geomechanical facies along horizontal wells. A cautionary note: While there is significant promise in applying these techniques, there remain many challenges in capitalizing on the data—lack of common data models in the industry, data silos, data stored in on-premises resources, slow migration of data to the cloud, legacy databases and systems, lack of digitization of older/legacy reports, well logs, and lack of standardization in data-collection methodologies across different facilities and geomarkets, to name a few. I would like to invite readers to review the selection of papers to get an idea of various applications in the upstream oil and gas space where machine-learning methods have been leveraged. The highlighted papers cover the topics of fatigue dam-age of marine risers and well performance optimization and identification of frackable, brittle, and producible rock along horizontal wells using drilling data. Recommended additional reading at OnePetro: www.onepetro.org. SPE 201597 - Improved Robustness in Long-Term Pressure-Data Analysis Using Wavelets and Deep Learning by Dante Orta Alemán, Stanford University, et al. SPE 202379 - A Network Data Analytics Approach to Assessing Reservoir Uncertainty and Identification of Characteristic Reservoir Models by Eugene Tan, the University of Western Australia, et al. OTC 30936 - Data-Driven Performance Optimization in Section Milling by Shantanu Neema, Chevron, et al.

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Rahmani, Masoud, et Amin Moslemi Petrudi. « Analytical Study of Nonlinear Vibrations of Marine Risers by Newton Harmonic Balance Method ». Journal of Advanced Mechanical Engineering Applications 2, n^o 1 (31 octobre 2020). http://dx.doi.org/10.30880/jamea.2020.02.01.007.

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In this paper, the nonlinear motions of marine risers are studied using the Newton's Harmonic Balance Method (NHBM). The nonlinear vibrational equations of the marine risers were obtained in the present study using the Hamilton principle and the Euler–Bernoulli beam theory. The Galerkin's decomposition technique is used to convert the partial differential governing equation (PDE) of the riser vibrations to the ordinary differential equation (ODE). By using the NHBM method, an analytical formulation has been obtained to express the natural nonlinear frequency of the riser. The effect of design parameters such as riser length and initial static displacement of high support has been investigated on riser frequency, which shows acceptable accuracy after comparing the results with previous research. The results show that fluid damping coefficient has a great effect on system instability and reducing this coefficient increases the stability range of the system. Examining the effect of nonlinear parameters shows that the effect of these parameters is greater in large amplitude of motion.

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Rahmani, Masoud, et Amin Moslemi Petrudi. « Analytical Study of Nonlinear Vibrations of Marine Risers by Newton Harmonic Balance Method ». Journal of Advanced Mechanical Engineering Applications 1, n^o 2 (30 novembre 2020). http://dx.doi.org/10.30880/jamea.2020.01.02.007.

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In this paper, the nonlinear motions of marine risers are studied using the Newton's Harmonic Balance Method (NHBM). The nonlinear vibrational equations of the marine risers were obtained in the present study using the Hamilton principle and the Euler–Bernoulli beam theory. The Galerkin's decomposition technique is used to convert the partial differential governing equation (PDE) of the riser vibrations to the ordinary differential equation (ODE). By using the NHBM method, an analytical formulation has been obtained to express the natural nonlinear frequency of the riser. The effect of design parameters such as riser length and initial static displacement of high support has been investigated on riser frequency, which shows acceptable accuracy after comparing the results with previous research. The results show that fluid damping coefficient has a great effect on system instability and reducing this coefficient increases the stability range of the system. Examining the effect of nonlinear parameters shows that the effect of these parameters is greater in large amplitude of motion.

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Zhou, Xingkun, Zhengguang Ge, Jinghao Chen et Wenhua Li. « Modal state vectors of a free-hanging drilling riser during deployment and retrieval ». Journal of Petroleum Exploration and Production Technology, 26 juillet 2022. http://dx.doi.org/10.1007/s13202-022-01549-3.

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AbstractTo prevent marine risers' resonance and eliminate potential threats, sufficient inherent dynamic characteristics such as natural frequency, modal displacement, slope, bending moment, and shear are necessary to be calculated and analyzed. However, most studies calculate the natural frequencies and modal displacements directly rather than the modal slopes and forces. The additional calculations of modal slopes and forces likely result in issue complications, time-consuming, or even errors especially when the boundaries at both ends are solved by a finite difference method. To solve the above problems, a state-vector approach is developed herein based on the precise integration method. Two traditional methods, i.e., differential transformation method and finite element method, are utilized to verify the validation of the approach. The modal state vectors of a marine drilling riser, i.e., not only modal displacements but also modal slopes, bending moments, and shears, are studied in detail under four classic cases according to the hard and soft hang-off modes and the deployment and retrieval processes. Besides, the natural frequencies versus the riser suspension lengths are investigated during the deployment and retrieval. The critical resonance suspension lengths of the riser are discussed via a double-peaked sea irregular wave spectrum. Based on the analyses presented in this study and their generic findings, powerful tools can be designed to prevent riser resonance and associated threats in operation.

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Josefsson, Per M., et Charles Dalton. « An Analytical/Computational Approach in Assessing Vortex-Induced Vibration of a Variable Tension Riser ». Journal of Offshore Mechanics and Arctic Engineering 132, n^o 3 (17 mars 2010). http://dx.doi.org/10.1115/1.4000500.

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The transverse vibratory response of a long, slender vertical top tension riser, subject to an ocean current, is studied. The problem is treated as a coupled fluid flow/vibration problem, which is solved numerically. The fluid flow part is represented by the 2D Navier–Stokes equations, with large-eddy simulation turbulence modeling and strip theory, which are solved numerically to obtain the flow field and determine the vortex-shedding behavior in the flow. The approach flow is a shear flow ranging in Reynolds number from 8000 to 10,000. Given the flow field and vortex-shedding behavior, the transverse fluid forcing function can be determined at a given instant, which becomes the input to the Euler–Bernoulli beam equation to calculate the displacement of the riser, using a technique that involves the Wentzel–Kramers–Brillouin (WKB) method and modal decomposition. The boundary conditions for the fluid flow equations are updated each time step as the cylinder moves. The natural frequency of the riser is tension dominated, not bending-stiffness dominated. With the decrease in tension with increasing depth, the natural frequency is affected. Therefore, the solution will be influenced by the depth-dependent tension. This study has indicated some interesting features regarding the vortex-induced vibration of a variable-tension riser. The vibrational response is greater for a variable-tension riser than for a constant-tension riser, when the variable-tension riser is assumed to have the same top tension as the constant-tension riser. Thus, this is one reason why it is important to take into account the variable tension when estimating fatigue failures of marine risers.

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« Influence of Frequency Ratio on the Hydroelastic Response of a Cylinder with Degrees of Freedom under Vortex Induced Vibration ». International Journal of Innovative Technology and Exploring Engineering 8, n^o 9S3 (23 août 2019) : 307–12. http://dx.doi.org/10.35940/ijitee.i3057.0789s319.

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Vortex induced vibration of cylindrical structures is an extensively researched topic. Most of the studies have concentrated on the response of the cylinder in the cross flow (CF) direction. In a realistic ocean environment, structures such as drilling and marine risers are more or less free to vibrate both in CF and in line (IL) directions. It has also been observed that the IL vibrations have significant influence on the CF response. Interaction between the responses in inline and cross flow directions has still been not fully understood. This paper addresses the same through a simplified numerical method for understanding the interaction between these two responses using two dimensional computational fluid dynamics (CFD) simulations. Here analyzes two cases have been considered; where in the cylinder is modeled with two different values of ratio of natural frequency of the cylinder in the IL direction to that in the CF direction. The trends of variation of hydrodynamic and structural parameters have been analyzed to comprehend the effect of directional natural frequency ratio on the cylinder response and hydrodynamic force coefficients. The shedding pattern has also been studied in this paper. An increase by 18% in the value of the lift coefficient and 38 % of that in the drag coefficient has been observed when the frequency ratio is increased from 1 to 2. The results show that the cylinder with frequency ratio 2 is more prone to lock in vibration. This phenomenon may be related to the shifting of shedding pattern from 2S to P + S mode when the frequency ratio is 2.

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