The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Gilberto Bruno Ellwanger - One of the best experts on this subject based on the ideXlab platform.
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Riser Top loads on turret moored fpso
ASME 2009 28th International Conference on Ocean Offshore and Arctic Engineering, 2009Co-Authors: Felipe De Arau Jo Castro, Carlos Magluta, Gilberto Bruno EllwangerAbstract:In the Campos Basin, offshore Brazil, catenary flexible Risers are extensively used in marine production systems. One of the most important design phases of these systems is the Riser extreme Top load analysis, which provides results for Riser and accessory designs as well as input for structural analysis of platform supports. In addition to the Riser’s characteristics (weight, diameter, structural damping, axial and bending stiffness), Riser Top loads depend on several other factors, such as platform static and dynamic behavior, including the collective effect of lines (mooring lines and Risers) drag and damping, platform motion, connection support position and environmental loading cases. This study is based on the results from a model test and numerical analysis of a typical turret moored FPSO system, with catenary Risers and mooring lines. This test was programmed to evaluate the consequence of each of the above mentioned parameters on flexible Riser Top loads. Model tests were performed in the MARIM (Maritime research Institute Netherlands) wave tank to represent the offshore system in 850 meter water depth and included loading case tests combining wind, waves and current in different relative directions (collinear, crossed and transversal). The analysis of the model tests results indicated significant variations in the platform behavior, when the drag and damping generated by the Risers and mooring lines were taken into account. Additional analyses were performed, based on numerical simulations of the Top load variations (axial, shear tension and moment), induced by movement changes (added drag and damping caused by Risers and mooring lines) and to evaluate the influence of vessel heading on Top load results.Copyright © 2009 by ASME
Bernt J Leira - One of the best experts on this subject based on the ideXlab platform.
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A reliability-based control algorithm for dynamic positioning of floating vessels
Structural Safety, 2020Co-Authors: Bernt J Leira, Asgeir J. Sørensen, Carl M. LarsenAbstract:Abstract The present paper is concerned with utilization of reliability methods in relation to on-line control of dynamic systems. The particular application is to dynamic positioning of marine vehicles in connection with reliability of mechanical subsystems. The present focus is on Top and bottom angles of marine Risers which are suspended between the seabed and the floating vessel. These angles are of crucial importance during, e.g. drilling and workover operations. The relationship between surface floater motion and angle responses is first considered. The possibility of reducing the maximum angular response levels by dynamic positioning of the floater is then investigated. Typically, and somewhat dependent of variation of current with depth, minimization of one of the Riser Top and bottom angles by adjusting the vessel position will take place at the cost of increasing the other angle. Hence, an optimum position should be defined by considering both angles but with different weight functions. An attractive approach is to determine these weights as functions of the respective reliability indices for each of the two angles. A further possibility is to apply an object function (loss function) which is purely expressed in terms of reliability indices. The viability of different schemes of this type is explored by numerical simulation for a specific Riser configuration.
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vertical position control for Top tensioned Riser with active heave compensator
ASME 2011 30th International Conference on Ocean Offshore and Arctic Engineering, 2011Co-Authors: Bernt J Leira, Shaoji Fang, Mogens BlankeAbstract:The Top and bottom angles of a marine Riser are of crucial importance during e.g. drilling and workover operations. A vertical position control with active heave compensator (AHC) is proposed to maintain the safety of the Riser when subjected to environmental excitations. The possibility of reducing the maximum angular response level by adjusting the vertical rod position by means of an active heave compensator is investigated with a positioning algorithm based on adaptive backstepping. Riser Top and bottom angles are dealt with by the algorithm in order to minimize both angles.
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Reliability-Based Schemes for Control of Riser Response and Dynamic Positioning of Floating Vessels
21st International Conference on Offshore Mechanics and Arctic Engineering Volume 2, 2002Co-Authors: Bernt J Leira, Asgeir J. Sørensen, Carl M. LarsenAbstract:Application of structural reliability methods in relation to online control of dynamic systems is considered. The particular case in focus is dynamic positioning of marine vehicles as related to mechanical limit states for the Riser system. The magnitudes of Top and bottom angles of the marine Risers are considered. These angles are of crucial importance during e.g. drilling and workover operations. The relationship between surface floater motion and angle responses is first considered. The possibility of reducing the maximum angular response levels by dynamic positioning of the floater is then investigated. Typically, minimization of one of the Riser Top and bottom angles by adjusting the vessel position can only take place at the cost of increasing the other one. Hence, an optimum position should be defined by applying different weights for the two angles. Three different alternatives are considered: (I) The relative weights are kept fixed (II) The relative weights are determined as functions of the respective reliability indices for each of the two angles. (III) A loss function which is purely expressed in terms of reliability indices is introduced. The viability of different schemes of this type is explored by numerical simulation for a specific Riser configuration.Copyright © 2002 by ASME
Carl M. Larsen - One of the best experts on this subject based on the ideXlab platform.
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Non-linear time domain analysis of cross-flow vortex-induced vibrations
Marine Structures, 2020Co-Authors: Mats Jorgen Thorsen, Svein Saevik, Carl M. LarsenAbstract:Abstract A previously proposed hydrodynamic load model for time domain simulation of cross-flow vortex-induced vibrations (VIV) is modified and combined with Morison's equation. The resulting model includes added mass, drag and a cross-flow vortex shedding force which is able to synchronize with the cylinder motion within a specified range of non-dimensional frequencies. It is demonstrated that the hydrodynamic load model provides a realistic representation of the cross-flow energy transfer and added mass for different values of the non-dimensional frequency and amplitude. Furthermore, it gives a reasonable approximation of the experimentally observed drag amplification. The load model is combined with a non-linear finite element model to predict the cross-flow VIV of a steel catenary Riser in two different conditions: VIV due to a stationary uniform flow and VIV caused by periodic oscillation of the Riser Top end. In the latter case, the prescribed motion leads to an oscillating relative flow around the Riser, causing an irregular response. The simulation results are compared to experimental measurements, and it is found that the model provides highly realistic results in terms of r.m.s. values of strains and frequency content, although some discrepancies are seen.
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A reliability-based control algorithm for dynamic positioning of floating vessels
Structural Safety, 2020Co-Authors: Bernt J Leira, Asgeir J. Sørensen, Carl M. LarsenAbstract:Abstract The present paper is concerned with utilization of reliability methods in relation to on-line control of dynamic systems. The particular application is to dynamic positioning of marine vehicles in connection with reliability of mechanical subsystems. The present focus is on Top and bottom angles of marine Risers which are suspended between the seabed and the floating vessel. These angles are of crucial importance during, e.g. drilling and workover operations. The relationship between surface floater motion and angle responses is first considered. The possibility of reducing the maximum angular response levels by dynamic positioning of the floater is then investigated. Typically, and somewhat dependent of variation of current with depth, minimization of one of the Riser Top and bottom angles by adjusting the vessel position will take place at the cost of increasing the other angle. Hence, an optimum position should be defined by considering both angles but with different weight functions. An attractive approach is to determine these weights as functions of the respective reliability indices for each of the two angles. A further possibility is to apply an object function (loss function) which is purely expressed in terms of reliability indices. The viability of different schemes of this type is explored by numerical simulation for a specific Riser configuration.
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Reliability-Based Schemes for Control of Riser Response and Dynamic Positioning of Floating Vessels
21st International Conference on Offshore Mechanics and Arctic Engineering Volume 2, 2002Co-Authors: Bernt J Leira, Asgeir J. Sørensen, Carl M. LarsenAbstract:Application of structural reliability methods in relation to online control of dynamic systems is considered. The particular case in focus is dynamic positioning of marine vehicles as related to mechanical limit states for the Riser system. The magnitudes of Top and bottom angles of the marine Risers are considered. These angles are of crucial importance during e.g. drilling and workover operations. The relationship between surface floater motion and angle responses is first considered. The possibility of reducing the maximum angular response levels by dynamic positioning of the floater is then investigated. Typically, minimization of one of the Riser Top and bottom angles by adjusting the vessel position can only take place at the cost of increasing the other one. Hence, an optimum position should be defined by applying different weights for the two angles. Three different alternatives are considered: (I) The relative weights are kept fixed (II) The relative weights are determined as functions of the respective reliability indices for each of the two angles. (III) A loss function which is purely expressed in terms of reliability indices is introduced. The viability of different schemes of this type is explored by numerical simulation for a specific Riser configuration.Copyright © 2002 by ASME
Celso Kazuyuki Morooka - One of the best experts on this subject based on the ideXlab platform.
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Model Test of a Steel Catenary Riser in a Towing Tank
Volume 3: Pipeline and Riser Technology, 2009Co-Authors: Celso Kazuyuki Morooka, Ricardo Franciss, Raphael I. Tsukada, Sergio Da Silva, Cyntia G. C. MattAbstract:The objective of the present work is the study of the dynamic behavior of steel catenary Risers (SCRs), focusing on the contribution of vortex-induced vibration (VIV), through model test in a towing tank. Nowadays, a great deal of effort is being spent in order to better understand VIV’s contribution in the dynamics of Riser structures through experiments, analytical analysis and numerical predictions. In the present work, the design of a SCR model test, along with its setup in a towing tank, will be described in detail and discussions of main results from the experiments will be presented. The experiment has been conducted under several simulated environmental condition combinations, varying the towing speed, Riser Top forced oscillation amplitudes, waves amplitudes and periods. Very promising results have been observed from the experiment. Riser oscillations due to high harmonics of vortex shedding were observed. Analysis of the experimental results, coupled with the support of numerical tools, showed the influence of the phenomena of traveling waves in the cross-flow response as is reported from the literature.Copyright © 2009 by ASME
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Experimental Study on a Self Standing Hybrid Riser System Throughout Tests on a Deep-Sea Model Basin
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 1 Parts A and B, 2005Co-Authors: Paulo S. D. Pereira, Celso Kazuyuki Morooka, Katsuya Maeda, Kenkichi Tamura, Kazuaki ItohAbstract:The present paper introduces a concept of a hybrid Riser, Self Standing Hybrid Riser (SSHR), particularly in development for ultra deepwater around 3000 meters. Main problems faced in the initial definitions for design of such Risers in the described scenario are discussed. Unique laboratory test with reduced model carried out in waves, current and Riser Top oscillation experiments in a very deepwater wave tank is shown. And, experimental results are shown and discussed, especially considering difficulties faced to carry out this experiment. Discussions are addressed in terms of vortex induced vibration (VIV) around buoyancy can, Riser line pipe and flexible jumper.Copyright © 2005 by ASME
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Dynamic Behavior of a Vertical Riser and Service Life Reduction
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 1 Parts A and B, 2005Co-Authors: Celso Kazuyuki Morooka, José Alfredo Ferrari, Elton J. B. Ribeiro, Fabio M. Coelho, Ricardo FrancissAbstract:In the last years, the most of offshore oil and gas reserves discoveries in Brazil are placed in ultra-deep water depths. Petroleum production from these offshore fields needs developments with novel solutions in terms of necessary technologies and economical viability. The use of vertical rigid Risers such as Top tensioned Risers (TTR) and others like combined systems as self standing hybrid Risers and steel catenary Risers for ultra-deep waters have shown viable from both, technical and economical aspects. However, there are needs for detailed studies on their dynamic behavior in order to improve, particularly, the understanding of influence of the environment as wave and current, and floating platform oscillations at the Riser Top. The present work presents studies on vertical Top tensioned Riser dynamic behavior through time domain simulations of its displacements and respective, bending moments and stresses. Influences of the vortex induced vibrations (VIV) and waves on the Riser service life reduction are analyzed. Maximum and minimum envelops for displacements and stresses along Riser length are shown.Copyright © 2005 by ASME
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Investigations on the Behavior of Vertical Production Risers
23rd International Conference on Offshore Mechanics and Arctic Engineering Volume 1 Parts A and B, 2004Co-Authors: Celso Kazuyuki Morooka, H. Y. Kubota, José Alfredo Ferrari, Fabio M. Coelho, Elton J. B. RibeiroAbstract:The present paper describes the behavior of a vertical Riser in waves, currents and which is excited by displacements at the Riser Top. Fundamental equations for Riser behavior are described and the Ferrari&Bearman model [4] is applied to estimate hydrodynamic load for “in-line” and transverse directions of the Riser. Solution for Riser behavior is obtained in time domain, calculations are performed for deepwater field production scenario and discussions are addressed. The influence of variation of Riser diameter and drag coefficient along its length, the presence of floaters and effect of petroleum fluid flowing in the Riser are investigated. Moreover, effects of the upper and bottom end conditions of the Riser on its behavior are also taken into account in the analysis.Copyright © 2004 by ASME
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Dynamic Behavior of a Vertical Production Riser by Quasi 3D Calculations
Volume 1: Offshore Technology; Ocean Space Utilization, 2003Co-Authors: Celso Kazuyuki Morooka, H. Y. Kubota, Kazuo Nishimoto, José Alfredo Ferrari, Elton J. B. RibeiroAbstract:A study on dynamics of a vertical production Riser under environmental loads is carried out. Current and wave loads along the Riser, and surface vessel motions due to the environment at the Riser Top are taken into account. Based on descriptions of fundamentals of the Quasi 3D model previously proposed by Ferrari&Bearman (1999), numerical simulations for Riser displacements have been performed. In line and transverse hydrodynamic current and wave loads on the Riser are estimated and Riser displacements thought Quasi 3D fashion are estimated in the time domain. Comparisons with literature results and experimental ones are carried out.Copyright © 2003 by ASME
Felipe De Arau Jo Castro - One of the best experts on this subject based on the ideXlab platform.
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Riser Top loads on turret moored fpso
ASME 2009 28th International Conference on Ocean Offshore and Arctic Engineering, 2009Co-Authors: Felipe De Arau Jo Castro, Carlos Magluta, Gilberto Bruno EllwangerAbstract:In the Campos Basin, offshore Brazil, catenary flexible Risers are extensively used in marine production systems. One of the most important design phases of these systems is the Riser extreme Top load analysis, which provides results for Riser and accessory designs as well as input for structural analysis of platform supports. In addition to the Riser’s characteristics (weight, diameter, structural damping, axial and bending stiffness), Riser Top loads depend on several other factors, such as platform static and dynamic behavior, including the collective effect of lines (mooring lines and Risers) drag and damping, platform motion, connection support position and environmental loading cases. This study is based on the results from a model test and numerical analysis of a typical turret moored FPSO system, with catenary Risers and mooring lines. This test was programmed to evaluate the consequence of each of the above mentioned parameters on flexible Riser Top loads. Model tests were performed in the MARIM (Maritime research Institute Netherlands) wave tank to represent the offshore system in 850 meter water depth and included loading case tests combining wind, waves and current in different relative directions (collinear, crossed and transversal). The analysis of the model tests results indicated significant variations in the platform behavior, when the drag and damping generated by the Risers and mooring lines were taken into account. Additional analyses were performed, based on numerical simulations of the Top load variations (axial, shear tension and moment), induced by movement changes (added drag and damping caused by Risers and mooring lines) and to evaluate the influence of vessel heading on Top load results.Copyright © 2009 by ASME
