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Shixiao Fu - One of the best experts on this subject based on the ideXlab platform.
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an investigation into the hydrodynamics of a flexible Riser undergoing vortex induced vibration
Journal of Fluids and Structures, 2016Co-Authors: Leijian Song, Shixiao Fu, Jianqiao WuAbstract:Abstract In this study, a method to obtain the hydrodynamic forces of a flexible Riser undergoing vortex-induced vibration (VIV) based on measured strain is proposed. The tensioned Riser is approximated as an Euler–Bernoulli beam, and an inverse method is adopted for the calculation of the hydrodynamic forces in the cross flow (CF) and inline (IL) directions. Based on these hydrodynamic forces, and combined with the VIV velocities and accelerations of the Riser, the excitation and added-mass coefficients are obtained through a least-squares method. As an illustration example, the hydrodynamic characteristics of a flexible Riser Model undergoing VIV in a uniform flow are investigated. Results indicate that VIV leads to non-uniform distribution of the drag coefficient and amplifies the drag coefficient along the Riser. Similar distribution of the energy transfer coefficient has been found between the entire Riser and that of the CF direction. For synchronized VIV occurring in both CF and IL directions, the energy transferred from the fluid is all dissipated by the structural damping, and hence leads to the energy balance in both CF and IL directions. It further shows that the excitation coefficients on flexible Riser undergoing VIV do not agree with those of the forced oscillation tests: excitation coefficients sometimes even become negative within the normally excitation regime, and are related with not only the non-dimensional frequency and amplitude but also the phase angles between the CF and IL vibrations. The added-mass coefficient of flexible Risers does not keep a constant value of 1.0 anymore, but depends on the non-dimensional frequency and amplitude of vibration.
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experimental investigation of the response performance of viv on a flexible Riser with helical strakes
Ships and Offshore Structures, 2016Co-Authors: Shixiao Fu, Yifan ChenAbstract:Experimental investigations were conducted on a flexible Riser with and without helical strakes. A uniform current was obtained by towing a Riser Model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The experimental results indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The VIV responses in the cross-flow (CF) and in-line (IL) directions can be coupled via variations in the tensile force. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare Riser. However, for the Riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that the strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted...
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viv response of a long flexible Riser fitted with strakes in uniform and linearly sheared currents
Applied Ocean Research, 2015Co-Authors: Shixiao Fu, Youming Xiong, Leijian SongAbstract:Abstract An experimental investigation was conducted on a flexible Riser with and without various strake arrangements. The aim of the present work was to further improve the understanding of the response performance of the vortex-induced vibration (VIV) of a Riser with helical strakes. Two current profiles, including uniform and linearly sheared flows, were simulated. The uniform current was simulated by towing the Riser Model in one direction using the towing carriage, and the linearly sheared current was simulated by fixing one end of the Riser and using a driven cantilever to traverse a circular arc. Based on the modal superposition method, the displacement responses were obtained from the measured strain. Strakes with different heights and pitches were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the bare Model test show that the lock-in phenomenon displays multi-order characteristics, and the VIV displacement decreases with an increased order of the lock-in regime. The results of the straked Model test indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the response performance depends closely on the geometry of the strake configuration.
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experimental investigation on the suppression device of viv of a flexible Riser
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Shixiao Fu, Leijian Song, Tao PengAbstract:Experimental investigations were conducted on a flexible Riser with and without helical strakes. A uniform current was obtained by towing a Riser Model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare Riser show that the characteristics of the synchronization of the VIV for a flexible Riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare Riser. However, for the Riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the Riser increases with strake pitch and height.Copyright © 2014 by ASME
Guttorm Grytoyr - One of the best experts on this subject based on the ideXlab platform.
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Time Domain VIV Analysis Tool VIVANA-TD: Validations and Improvements
Volume 8: CFD and FSI, 2020Co-Authors: Jingzhe Jin, Elizabeth Passano, Michael Tognarelli, Guttorm Grytoyr, Halvor Lie, Svein Sævik, Decao Yin, Torgrim Andersen, Daniel KarunakaranAbstract:Abstract An empirical time-domain (TD) vortex-induced vibration (VIV) prediction Model has been implemented in a software called VIVANA-TD based on its earlier development by Thorsen at NTNU. It Models the synchronization of VIV loads and structural responses with a set of empirical parameters generalized from Model tests. Combining this time domain hydrodynamic load Model with a non-linear finite element structural Model makes it possible to account for structural non-linearities and time-varying flow. A joint industry project (JIP), i.e., Lazy Wave Riser JIP has been organized to improve the design basis for SLWRs. This JIP is executed by SINTEF Ocean with support from NTNU. The industry participants are Equinor, BP, Subsea7, Kongsberg Maritime and Aker Solutions. The overall objective of this JIP is to systematically validate VIVANA-TD, in order to establish it as an industrial tool for VIV prediction. It is also aimed to improve the empirical basis and methods for calculation of VIV of deep-water steel lazy wave Risers (SLWRs). In the present paper, the validation study is presented for selected Model tests in constant flow conditions with uniform and sheared profiles. The test Model includes bare pipe, pipe with partial strake coverage and Riser Model with staggered buoyancy elements. The empirical parameters have been generalized based on extensive Model test data. Limitations and improvement of the Model have been also been explored. The results show that the present TD Model can represent reasonably the VIV loads and that the prediction has good agreement with measurements in general.
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experimental and numerical study of a top tensioned Riser subjected to vessel motion
Ocean Engineering, 2019Co-Authors: Elizabeth Passano, Kristoffer H. Aronsen, Michael Tognarelli, Guttorm Grytoyr, Elizbar Buba KebadzeAbstract:Abstract Model tests of a top tensioned Riser (TTR) Model were carried out as a part of a joint industry project, with the purpose of better understanding the dynamic behaviour of drilling Riser and verifying the calculations of the Riser analysis tools. Sinusoidal motion in one direction was imposed at the top end of the Riser Model to simulate vessel motion. The tests were carried out in still water, accelerations and bending strains were measured along the Riser Model. Numerical simulations were performed using RIFLEX and the predicted global responses were compared with the Model tests. This paper discusses interesting aspects of this comparison as well as the general dynamic behaviour of the top tensioned Riser. It was found that the dynamic responses of a TTR with vessel motion can consist of not only the in-line (IL) responses due to vessel motion at the Riser top end, but also cross-flow (CF) vortex-induced vibrations (VIV) under conditions when Keulegan-Carpenter ( K C ) number is relatively small. CF VIV response is estimated using a time domain VIV prediction Model and compared to the measured response. The main conclusion is that the IL global dynamic responses and CF VIV responses are predicted sufficiently well.
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Drilling Riser Model Test for Software Verification
Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2017Co-Authors: Massimiliano Russo, Guttorm GrytoyrAbstract:Marine drilling Riser is subject to complicated environmental loads which include top motions due to mobile offshore drilling unit (MODU), wave loads, and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling Riser system, especially at the subsea wellhead (WH). Statoil and BP have carried out a comprehensive Model test program on drilling Riser in MARINTEK's Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling Riser behavior under various environmental conditions by the use of Model test data. Six drilling Riser configurations were tested, including different components such as upper flex joint (UFJ), tensioner, marine Riser, lower marine Riser package (LMRP), blow-out preventer (BOP), lower flex joint (LFJ), buoyancy elements, and seabed boundary Model. The drilling Riser Models were tested in different load conditions. Measurements were made of microbending strains and accelerations along the Riser in both in-line (IL) and crossflow (CF) directions. Video recordings were made both above and under water. In this paper, the test setup and test program are presented. Comparisons of results between Model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling Riser Model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between Model test and RIFLEX simulation is promising.
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Drilling Riser Model Tests for Software Verification
Volume 2: CFD and VIV, 2016Co-Authors: Massimiliano Russo, Guttorm GrytoyrAbstract:Marine drilling Riser is subject to complicated environmental loads which include top motions due to Mobile Offshore Drilling Unit (MODU), wave loads and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling Riser system, especially at the subsea well head (WH).Statoil and BP have carried out a comprehensive Model test program on drilling Riser in MARINTEK’s Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling Riser behaviour under various environmental conditions by use of Model test data.Six drilling Riser configurations were tested, including different components such as Upper Flex Joint (UFJ), tensioner, marine Riser, Lower Marine Riser Package (LMRP), Blow-Out Preventer (BOP), Lower Flex Joint (LFJ), buoyancy elements and seabed boundary Model.The drilling Riser Models were tested in different load conditions:1. Forced top motion tests2. Regular wave test3. Combined regular wave and towing test4. Irregular wave test5. Combined irregular wave and towing test6. Towing test (VIV)Measurements were made of micro bending strains and accelerations along the Riser in both In-Line (IL) and Cross-Flow (CF) directions. Video recordings were made both above and under water.In this paper, the test set-up and test program are presented. Comparisons of results between Model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling Riser Model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between Model test and RIFLEX simulation is promising.Copyright © 2016 by ASME
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Marine drilling Riser disconnect and recoil analysis
2011Co-Authors: Guttorm Grytoyr, Partha SharmaAbstract:A methodology is presented for the dynamic analysis of marine drilling Riser disconnect and recoil using general purpose Riser FEA programs. The methodology includes the effects of mud column discharge, which is a governing effect in the first part of the transient phase, and the effects of pressure loss in the hydraulic lines for the Riser tensioners. The global behavior of the Riser due to, e.g. elasticity and inertia, is automatically accounted for by the Riser analysis software. The presented methodology is easy to use and can be applied to any Riser system, both conventional wireline and direct acting tensioners. A typical case is selected and analyzed, with emphasis on lift height of the lower Riser package and impulsive loading due to bottoming-out of the tensioners or the telescopic joint. The effect of tension setting is studied, covering a range of settings in order to select the optimum. The methodology enables the Riser system designers to reuse Riser Models from the design analysis. No additional Riser Model has to be built for the disconnect and recoil analysis. All major physical effects are taken into account by the methodology, including detailed cross sectional properties of the Riser system, and the hydraulic and pneumatic response of the tensioner system.
Leijian Song - One of the best experts on this subject based on the ideXlab platform.
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an investigation into the hydrodynamics of a flexible Riser undergoing vortex induced vibration
Journal of Fluids and Structures, 2016Co-Authors: Leijian Song, Shixiao Fu, Jianqiao WuAbstract:Abstract In this study, a method to obtain the hydrodynamic forces of a flexible Riser undergoing vortex-induced vibration (VIV) based on measured strain is proposed. The tensioned Riser is approximated as an Euler–Bernoulli beam, and an inverse method is adopted for the calculation of the hydrodynamic forces in the cross flow (CF) and inline (IL) directions. Based on these hydrodynamic forces, and combined with the VIV velocities and accelerations of the Riser, the excitation and added-mass coefficients are obtained through a least-squares method. As an illustration example, the hydrodynamic characteristics of a flexible Riser Model undergoing VIV in a uniform flow are investigated. Results indicate that VIV leads to non-uniform distribution of the drag coefficient and amplifies the drag coefficient along the Riser. Similar distribution of the energy transfer coefficient has been found between the entire Riser and that of the CF direction. For synchronized VIV occurring in both CF and IL directions, the energy transferred from the fluid is all dissipated by the structural damping, and hence leads to the energy balance in both CF and IL directions. It further shows that the excitation coefficients on flexible Riser undergoing VIV do not agree with those of the forced oscillation tests: excitation coefficients sometimes even become negative within the normally excitation regime, and are related with not only the non-dimensional frequency and amplitude but also the phase angles between the CF and IL vibrations. The added-mass coefficient of flexible Risers does not keep a constant value of 1.0 anymore, but depends on the non-dimensional frequency and amplitude of vibration.
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viv response of a long flexible Riser fitted with strakes in uniform and linearly sheared currents
Applied Ocean Research, 2015Co-Authors: Shixiao Fu, Youming Xiong, Leijian SongAbstract:Abstract An experimental investigation was conducted on a flexible Riser with and without various strake arrangements. The aim of the present work was to further improve the understanding of the response performance of the vortex-induced vibration (VIV) of a Riser with helical strakes. Two current profiles, including uniform and linearly sheared flows, were simulated. The uniform current was simulated by towing the Riser Model in one direction using the towing carriage, and the linearly sheared current was simulated by fixing one end of the Riser and using a driven cantilever to traverse a circular arc. Based on the modal superposition method, the displacement responses were obtained from the measured strain. Strakes with different heights and pitches were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the bare Model test show that the lock-in phenomenon displays multi-order characteristics, and the VIV displacement decreases with an increased order of the lock-in regime. The results of the straked Model test indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the response performance depends closely on the geometry of the strake configuration.
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experimental investigation on the suppression device of viv of a flexible Riser
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Shixiao Fu, Leijian Song, Tao PengAbstract:Experimental investigations were conducted on a flexible Riser with and without helical strakes. A uniform current was obtained by towing a Riser Model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare Riser show that the characteristics of the synchronization of the VIV for a flexible Riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare Riser. However, for the Riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the Riser increases with strake pitch and height.Copyright © 2014 by ASME
Wenyong Tang - One of the best experts on this subject based on the ideXlab platform.
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nonlinear Riser seabed interaction response among touchdown zone of a steel catenary Riser in consideration of vortex induced vibration
Ocean Engineering, 2021Co-Authors: Yuchao Yuan, Hongxiang Xue, Mengtian Zheng, Wenyong TangAbstract:Abstract Steel catenary Riser (SCR) is a preferred solution for deepwater oil and gas exploitation under harsh marine environment. Its Riser-seabed interaction (RSI) among touchdown zone (TDZ) in consideration of the vortex-induced vibration (VIV) of sag bend is at present a research frontier in ocean engineering. This paper integrates Randolph-Quiggin Model into a published global numerical Riser Model, to investigate the nonlinear RSI response among TDZ of an SCR with VIV. The adopted numerical Model is validated against some published experimental measurements for VIV and RSI respectively. Three combined cases with top-end platform heave motion and VIV are simulated, and the trench development as well as the SCR's response characteristics among TDZ is analyzed. VIV makes the trench develop more smoothly, and the trench length as well as depth turns smaller. The VIV effect on RSI is relatively significant with violent heave excitation, under which the P-z curves present clearer interaction mode transitions. VIV enlarges the maximum bending moment visibly, and makes the sag bend of SCR dominated by higher-order modes, which are both detrimental to the structural safety. The coupling effect between RSI and VIV on the Riser's dynamic response needs to be considered for the design of full-scale SCRs.
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theoretical and numerical methods to predict the behaviour of unbonded flexible Riser with composite armour layers subjected to axial tension
Ocean Engineering, 2020Co-Authors: Wenyong Tang, Yuchao YuanAbstract:Abstract Unbonded flexible Risers are widely applied to deep-water oil and gas production field, and their complex cross-section mechanical properties have always been a challenging issue in ocean engineering. Over the recent years, the traditional steel tensile armour layers of unbonded flexible Risers are replaced by composite materials, owing to their advantages of lightweight and high strength. In this paper, a theoretical deduction based on energy method and a numerical method in consideration of detailed geometric properties are proposed to analyze the behaviour of the unbonded flexible Riser with composite armour layers. Both the theoretical and numerical methods take full consideration of the material orientation of composite, and for the numerical Model, two local coordinate systems are established to define the material properties of composite armour layers. Based on a 2.5-inches unbonded flexible Riser Model with eight-layers, some cases from theoretical and numerical methods are presented for validation. Then the effect of the fiber volume fraction of composite on the axial tensile stiffness, as well as the weight of the unbonded flexible Riser, is discussed. Furthermore, characteristics analysis of axial stiffness is carried out and the effect of the boundary condition is discussed as well.
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Cross-flow VIV-induced fatigue damage of deepwater steel catenary Riser at touch-down point
China Ocean Engineering, 2014Co-Authors: Kunpeng Wang, Wenyong Tang, Hongxiang XueAbstract:A prediction Model of the deepwater steel catenary Riser VIV is proposed based on the forced oscillation test data, taking into account the Riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point (TDP). The Model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation Model. In the present Model, the hysteretic Riser-soil interaction Model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic Riser-soil interaction. In order to validate the Model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary Riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation Riser Model and the present full Riser Model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary Riser at TDP.
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time domain prediction approach for cross flow viv induced fatigue damage of steel catenary Riser near touchdown point
Applied Ocean Research, 2013Co-Authors: Kunpeng Wang, Hongxiang Xue, Wenyong TangAbstract:Abstract Previous steel catenary Riser (SCR) Models targeted for VIV prediction are truncated at touchdown point (TDP) where simple constrain and rotation stiffness are generally applied. In this study, a time domain approach accounting for the SCR–soil interaction is proposed to predict the cross-flow (CF) VIV induced fatigue damage of a SCR near TDP. The hydrodynamic force is simulated based on the forced vibration test data as a function of the non-dimensional amplitude and frequency, and an empirical damping Model. When the non-dimensional frequency associated with the calculated frequency falls in the excitation region, the natural frequency closer to the frequency corresponding to the maximum excitation force is taken to be the dominant frequency, and applied to obtain the excitation force. The SCR–soil interaction Model takes into account the trench shape, and the mobilization and release of the soil suction. Fatigue damage is linearly accumulated by using the rain-flow counting methodology. To validate the proposed Models, simulation for a Riser Model test is carried out, and the envelopes of RMS displacement, curvature, and fatigue damage are compared. Further works focus on the sensitivity of VIV induced fatigue damage near TDP to the seabed parameters, such as mudline shear strength, shear strength gradient and soil suction, and some conclusions are obtained.
Tao Peng - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on the suppression device of viv of a flexible Riser
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Shixiao Fu, Leijian Song, Tao PengAbstract:Experimental investigations were conducted on a flexible Riser with and without helical strakes. A uniform current was obtained by towing a Riser Model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare Riser show that the characteristics of the synchronization of the VIV for a flexible Riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare Riser can be quite distinct from those of a Riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare Riser. However, for the Riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the Riser increases with strake pitch and height.Copyright © 2014 by ASME
