Riser Top Loads on Turret Moored FPSO

2009 ◽  
Author(s):  
Felipe de Arau´jo Castro ◽  
Carlos Magluta ◽  
Gilberto Bruno Ellwanger
Keyword(s):  
Production Systems ◽  
Wind Waves ◽  
Model Tests ◽  
Structural Damping ◽  
Mooring Lines ◽  
Load Variations ◽  
Campos Basin ◽  
Loading Case ◽  
Flexible Risers ◽  
Important Design

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.

Flexible Riser Fatigue Procedure Using a Long Term Distribution of FPSO’s Heading Direction

2002 ◽  
Author(s):  
Carlos Alberto Duarte de Lemos ◽  
Murilo Augusto Vaz
Keyword(s):  
Environmental Conditions ◽  
Environmental Data ◽  
Mooring Lines ◽  
Fatigue Design ◽  
Beam Seas ◽  
Heading Direction ◽  
Campos Basin ◽  
Directional Waves ◽  
Flexible Risers

The intensive use of FPSOs in Campos Basin, offshore Brazil, has demanded more attention on the fatigue design of flexible risers. Field experience and a new set of environmental data collected in the last years have shown a large number of swell waves reaching the floating units in quartering and beam seas, which has amplified the motions at the risers’ top connections. Hence, it is necessary to evaluate the occurrence probability of wave heading direction relative to the vessel, especially for beam seas, but also noting the probability increase of quartering seas considering the existence of bi-modal and bi-directional wave spectra. The simultaneous environmental conditions — wind, current and bi-directional waves (sea and swell) — registered in Campos Basin, were condensed in a few hundreds environmental conditions to enable its utilization on a simulation program, where the FPSO, mooring lines and risers were modeled to obtain the mean heading and offsets. This new set of FPSO headings were then used to define a new proposal of load conditions to evaluate the fatigue life of flexible risers. This new procedure was then applied to a case study for the FPSO P-33 employing the tools available at PETROBRAS research center. The results have confirmed the importance of beam and quarter seas, which respectively cause heavy roll and vertical motions at the turret and then, affecting the fatigue of the risers.

Flexible Riser Fatigue Evaluation for FPSO’s in Bi-Directional Sea Spectra

2003 ◽  
Author(s):  
Carlos Alberto Duarte de Lemos ◽  
Murilo Augusto Vaz ◽  
Marcos Queija de Siqueira
Keyword(s):  
Operational Experience ◽  
Flexible Riser ◽  
Mooring Lines ◽  
Directional Spectrum ◽  
Campos Basin ◽  
Calculation Methodology ◽  
Flexible Risers ◽  
Fatigue Evaluation ◽  
Simplified Procedure ◽  
The Impact

The fatigue calculation methodology applied to flexible risers connected to FPSOs, offshore Brazil, is based on a simplified procedure considering a deterministic regular wave approach and a wave heading distribution supported by past operational experience with semi-submersible platforms. However the utilization of deterministic waves approach does not necessarites guarantee the consideration of the worst sea conditions, and the weathervaning capability of those systems are usually not accounted for when non-collinear wave, wind and current are present. A new procedure is being evaluated considering an integrated model for ship, mooring lines and risers to define the distribution of ship headings for fatigue analysis using an irregular bi-directional sea approach. The impact on a flexible riser’s fatigue life will be evaluated when a new ship heading distribution with irregular bi-directional spectrum is presented for the case of a FPSO with bow turret in operation at the Marlin Field offshore Campos Basin.

FPU Mooring Footprint Reduction in Buzios Field: Key Driver to its Successful Subsea Layout

2021 ◽  
Author(s):  
Gabriel Rodrigues Cabral ◽  
Helvio Ferreira da Silva ◽  
Anderson Takehiro Oshiro ◽  
Leandro Cerqueira Trovoado ◽  
Thierry Hernalsteens ◽  
...  
Keyword(s):  
Production Systems ◽  
Economic Feasibility ◽  
Horizontal Projection ◽  
Mooring Lines ◽  
Large Reservoir ◽  
Field Development ◽  
Well Design ◽  
Production Wells ◽  
High Production ◽  
Flexible Risers

Abstract Buzios field development has the potential to implement several production systems due to large reservoir volumes. Considering the oil specification, the drive to use standard solutions already in place in Pre-salt area, associated with the high production indexes of the wells, Petrobras decided to tie back all production wells in satellite configuration. These facts, together with geological hazards in the area, lead to a potentially congested seabed scenario. Hence, FPU positioning has been challenging and demanding innovative engineering solutions to optimize FPU mooring as to overcome these challenges and enable FPU positioning close to wells. This optimization gave birth to new issues, such as risk of clashing between mooring lines and lazy-wave flexible risers. Integrated riser and mooring lines dynamic analysis, together with subsea layout assessment were performed to ensure technical and economic feasibility. Furthermore, due to the Buzios reservoir, well design requirements and subsea layout specificities, all FPU were located on the edge of the reservoir and flexible risers were tied back mainly from only one board of each FPU. Hence, enhancing clearance between bow and stern mooring clusters and the optimization of the risers’ configuration were of paramount importance for enabling most of the risers’ connections on the desirable board. FPU mooring optimization led to up to 30% of mooring lines’ radius reduction (horizontal projection), and an average of up to 500m per flowline reduction, saving CAPEX, OPEX and increasing the return on investment.

On the Model Scaling of Polyester Mooring Lines for Offshore Applications

2002 ◽  
Author(s):  
Antonio Carlos Fernandes ◽  
Ronaldo Rosa Rossi
Keyword(s):  
Steel Wire ◽  
Random Excitation ◽  
Model Tests ◽  
Early Model ◽  
Random Waves ◽  
Mooring Lines ◽  
New Approach ◽  
Linear Behavior ◽  
Non Linear ◽  
Similarity Laws

With the introduction of the polyester ropes as mooring lines of large systems such as semi-submersibles, the need to simulate these lines in model tests became a necessity. Although the non-linear behavior is clear, depending on the type of cycling, the polyester rope responds in ways that may be considered linear as a steel wire rope. Because of that, the early model tests have been performed using a linear restoring capability, with different restoring coefficients. The use of equivalent springs seemed the proper way. However, with the help of fundamental investigation on the similarity laws, the present work shows that the use of very thin polyester lines in model scaling is feasible and will indeed allow a closer physical representation. By avoid using springs, but using the same material as in full scale, the same non-linear behavior is present during the tests and even the response to random excitation due to random waves is better represented. The paper closely describes the application of these ideas in a model test of a FPSO (Floating Production Storage and Offloading) comparing both the linear springs and new approach with the model scale equivalent polyester line.

Challenges Faced in the Design of SLWR Configuration for the Pre-Salt Area

2011 ◽  
Author(s):  
Stael Ferreira Senra ◽  
Marcio Martins Mourelle ◽  
Edmundo Queiroz de Andrade ◽  
Ana Lu´cia Fernandes Lima Torres
Keyword(s):  
Storage Capacity ◽  
Production Systems ◽  
Gas Injection ◽  
Brazilian Coast ◽  
Production Frontier ◽  
New Production ◽  
Campos Basin ◽  
Key Points ◽  
High Level ◽  
Selection Of

With the recent discoveries of the pre-salt reservoir, new areas of the Brazilian coast rose to prominence, especially for the Santos Basin. This area is adjacent to the Campos Basin, which now accounts for around 80% of Brazilian production. In this new area, in addition to the difficulties of drilling in salt rock, the deployment of subsea production systems have also to overcome new challenges, since environmental conditions are more severe than those in the Campos Basin. Other important issues are: the water depth of about 2200 meters; the high pressure for gas injection riser; and the high CO2 content, requiring special attention to the materials that will be in contact with the production fluid. At this new production frontier, priority was given to the use of floating units with storage capacity like VLCC hulls, in order to export oil production through shuttle tankers, as no pipeline grid is available. Depending on the motions level of these VLCC vessels, the selection of a viable configuration of riser becomes crucial. Thus, some alternatives have been studied and the Steel Lazy Wave Riser (SLWR) configuration was one of the options considered to be used for production and gas injection riser functions, besides being possibly used for risers with large diameters. As this area of the Santos Basin presents more severe conditions, the free-hanging configuration (SCR) was not feasible, even with the use of VLCCs with optimized motions. In this case, the SLWR configuration was better suited to overcome the problems faced by free-hanging configuration. This paper aims to present a set of variables and its right combination involved in SLWR configuration to make it feasible, considering some key points in the design of SLWRs, for example: motions level of the floating unit, thermal insulation required for the flow assurance of production risers; difficulties faced during the installation process and the need of using clad pipes or lined pipes due to the high level of corrosion imposed by CO2 fluid content.

Truss Spar Vortex Induced Motions: Benchmarking of CFD and Model Tests

2006 ◽  
Author(s):  
John Halkyard ◽  
Sampath Atluri ◽  
Senu Sirnivas
Keyword(s):  
Fluid Dynamics ◽  
Best Practices ◽  
Turbulence Modeling ◽  
Production Systems ◽  
Model Tests ◽  
The Past ◽  
Helical Strakes ◽  
Truss Spar ◽  
Computational Fluid Dynamics Cfd ◽  
Riser Design

Spar production systems are subject to Vortex Induced Motions (VIM) which may impact mooring and riser design. Helical strakes are employed to mitigate VIM. Model tests are typically required to validate the performance of the strakes. This paper will report on the results of benchmarking studies that have been conducted over the past few years to compare model tests with computational fluid dynamics (CFD). The paper discusses comparisons of CFD with model tests, “best practices” for the use of CFD for these classes of problems and issues related to turbulence modeling and meshing of problems at large Reynold’s numbers. This work is ongoing.

An enhanced semi-coupled methodology for the analysis and design of floating production systems

2020 ◽  
pp. 1-33
Author(s):  
Aldo Roberto Cruces Giron ◽  
William Steven Mendez Rodriguez ◽  
Fabrício Nogueira Correa ◽  
Breno P Jacob
Keyword(s):  
Equilibrium Position ◽  
Production Systems ◽  
Equations Of Motion ◽  
Coupled Analysis ◽  
Mooring Lines ◽  
Analysis And Design ◽  
Stiffness Matrices ◽  
Linear Effects ◽  
The Mean ◽  
Nonlinear Static

Abstract This work presents an enhanced hybrid methodology for the analysis and design of floating production systems (FPS). The semi-coupled (S-C) procedure exploits advantages of coupled and uncoupled models, incorporated into a three-stage sequence of analyses that can be fully automated within a single analysis program, presenting striking reductions of computational costs. The procedure begins by determining, through a full nonlinear static coupled analysis, the mean equilibrium position of the FPS with its mooring lines and risers. Then, it automatically evaluates equivalent 6-DOF stiffness matrices and force vectors representing the whole array of lines. Finally, these matrices/vectors are transferred to the dynamic analysis, solving the global 6-DOF equations of motion restarted from the static equilibrium position. This way, the S-C methodology represents all non-linear effects associated to the lines and consider their influence on the dynamic behavior of the hull. However, in some situations it could still overestimate dynamic amplitudes of LF motions, and/or underestimate amplitudes of line tensions. Thus, to improve the overall accuracy, enhanced procedures are incorporated to better represent damping and inertial contribution of the lines. Results of case studies confirm that this methodology provides results adequate for preliminary or intermediary design stages.

Calibration of Mooring Line Damping for Taut-Leg FPSOs Model Testing

2008 ◽  
Author(s):  
Antonio C. Fernandes ◽  
Allan Carre´ de Oliveira ◽  
Fabio P. S. Mineiro ◽  
Joel S. Sales ◽  
Andre´ Luis Rosa ◽  
...  
Keyword(s):  
Numerical Experiments ◽  
Model Testing ◽  
Model Tests ◽  
Reduced Model ◽  
Mooring Line ◽  
Mooring Lines ◽  
Stiffness And Damping

The paper discusses alternatives to represent the MLD (Mooring Line Damping) in models tests with truncated mooring lines. The work has performed both numerical experiments and reduced model tests. The results for stiffness and damping have been compared. This allows further considerations for future designs.

Coupled Dynamic Analyses of Deep-Water Semi-Submersible With New Spread Mooring System

2020 ◽  
Author(s):  
S. Chandrasekaran ◽  
Arvind Kumar Jain ◽  
Syed Azeem Uddin
Keyword(s):  
Fatigue Life ◽  
Deep Water ◽  
Production Systems ◽  
Irregular Waves ◽  
Mooring System ◽  
Mooring Lines ◽  
Dynamic Positioning System ◽  
Exploration And Production ◽  
Ocean Environment ◽  
Offshore Oil

Abstract Offshore complaint structures dominate the deepwater oil exploration and production due to their adaptive geometric form and well-established construction practices. Semi-submersible is one of the widely preferred, floating production systems due to its form-dominant ability, better stability characteristics, and best constructional features. It is usually position-restrained using a dynamic-positioning system (active-restraining) or mooring system (passive-restraining); being less-sensitive to freak ocean environment is an added advantage. The Semi-submersible, chosen for the present study is based on a similar configuration of a 6th generation deep-water Hai Yang Shi You (HYSY) – 981 platforms, commissioned by the China National Offshore Oil Corporation (CNOOC) in 2012. A sixteen-point, spread catenary-mooring without submerged buoy (case-1) in the form of chain-wire-chain type configuration is used for position-restraining. Response behavior of the semi-submersible with a conventional spread catenary-mooring system with a submerged buoy (case-2) is compared. API spectrum is used for computing wind loads, while the JONSWAP spectrum is used to represent irregular waves for various directions of wave heading. The effect of non-linearly varying current is considered up to 10% of water depth. Numerical analyses of the semi-submersible are carried out under 10-years, and 100-years return period events using Ansys Aqwa. Under wind, wave, and current loads, motion responses of the Semi-submersible at 1500 m and 2000 m water depths are investigated for both the cases in time-domain. Dynamic mooring tension variations arise from the environmental loads are further investigated for a fatigue failure using the S-N curve approach. It is found that the fatigue life of the mooring lines after the inclusion of the buoy is enhanced. It was also observed that, during failure of mooring lines there is an increase in tension of the mooring lines which are adjacent to the failed mooring lines and this is due to the transfer of mooring load and hence reducing their fatigue life.

Experimental Study on the Effects of Mooring System on Air Gap Response of Semi-Submersible Platform

2020 ◽  
Author(s):  
Xu Li ◽  
Longfei Xiao ◽  
Handi Wei ◽  
Mingyue Liu
Keyword(s):  
Model Tests ◽  
Air Gap ◽  
Mooring System ◽  
Complex Task ◽  
Ocean Engineering ◽  
Free Surface Elevation ◽  
Mooring Lines ◽  
Scaled Model ◽  
Air Gap Responses ◽  
Floating Platforms

Abstract The air gap response is crucial for the safe design and operation of large-volume floating platforms such as semi-submersible and tension leg platforms. It is a complex task to perform numerical simulation on the air gap response considering the wave free surface elevation and the motions of the floating vessel. Therefore, the prediction of air gap response still relies heavily on model tests. This paper attempts to investigate the effects of the mooring system, especially the effects of the length of mooring lines, on the air gap response of semi-submersible platform based on model tests results. The scaled model of the semi-submersible platform is supported by a symmetric mooring system composed of 8 mooring lines. A set of model tests with different length of mooring lines was performed in the State Key Laboratory of Ocean Engineering basin at Shanghai Jiao Tong University, and the air gap responses of 15 locations were measured using wave probes. The results indicate that the mooring system plays an important role in the air gap response of semi-submersible platform.

Sign in / Sign up

Export Citation Format

Share Document