Marcio Martins Mourelle

Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part I — Studies on a Semisubmersible Platform

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.Copyright

A coupled approach for dynamic analysis of CALM systems

This paper presents a time domain coupled numerical model, integrating the buoy and the slender structures, for the dynamic analysis of catenary anchor leg mooring (CALM) systems under random environmental loading. The model is based on the finite element discretization of the slender structures and the buoy hydrodynamics can be represented by two approaches: one based on Morisons equation and another using the diffraction/radiation theory. The moored tanker dynamic behavior is represented in the model by the hawser dynamic tension. The numerical results of a CALM system, designed to operate in 400 m water depth, are compared to model tests data available, resulting in a very good agreement between them.

Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part II — Studies on a DICAS System

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1]. That paper describes a “basic” classic, uncoupled methodology, and comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented in the companion paper [1], and these issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The present paper proceeds describing some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.© 2002 ASME

Coupled and uncoupled solutions for the nonlinear dynamic behaviour of guyed deep water platforms

The platform presented in this work is a compliant tower in which the structural elements that produce the righting forces are guylines. The behaviour of this tower, under operating and storm conditions, is investigated by analysing the following models: a three-dimensional model for eigenvalue and nonlinear static analysis, a stick model and a coupled model, for nonlinear dynamic analysis. The equilibrium equations governing the nonlinear static analysis problem are solved using the Newton-Raphson incremental-iterative method. The eigenvalue problem is solved through the subspace iteration method. The equations of motion describing the nonlinear dynamic analysis problem are integrated using the Newmark method.

A Frequency Domain Approach for Random Fatigue Analysis of Steel Catenary Risers at Brazil’s Deep Waters

The steel catenary riser was adopted by Petrobras as a cost-effective alternative for oil and gas export and for water injection lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. The installation of the P-18 SCR was a pioneer project of a free-hanging steel catenary riser linked to a semi-submersible [1] and demonstrated the technical feasibility of the concept. Fatigue damage verification is an important issue in SCR design, demanding a high number of loading cases to be analyzed. The random time domain nonlinear analysis is considered an attractive and reliable tool for fatigue analysis as nonlinearities are properly modeled and the random behaviour of environmental loadings is considered. As time domain analysis is high computer time consuming, the frequency domain analysis has been considered as an alternative tool for the initial phases of riser design to be used mainly for fatigue damage verification. This paper presents a methodology developed to perform a linearized frequency domain analysis aiming at fatigue damage verification. Two drilling risers were analyzed with the frequency domain procedure developed. The model of a steel lazy-wave riser was analyzed both in frequency and time domain in order to compare fatigue damage results. The analyses were performed using the Petrobras’s in-house computer codes ANFLEX, ALFREQ and POSFAL developed and implemented as part of projects from CENPES/PETROBRAS with “COPPE/UFRJ -The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”.© 2004 ASME

Lazy-Wave Steel Rigid Risers for Turret-Moored FPSO

The free-hanging SCR (Steel Catenary Riser) was adopted by Petrobras as a cost-effective alternative for oil and gas export lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. It is considered an available technology for semi-submersible application. There was interest in applying SCR’s attached to FPSO (Floating, Production, Storage and Offloading) units due to the trend of using these units for exploration and production in Brazilian deep waters. This alternative has to be carefully studied due to the high offsets and heave motions imposed by the vessel on the top of the riser. This work presents the approach and methodology adopted in Petrobras to study the structural integrity and feasibility of a lazy-wave SCR attached to a bow turret-moored FPSO at a water depth of 1290 m. The analysis was performed using the Petrobras’s in-house computer codes ANFLEX and POSFAL developed and implemented as part of projects from CENPES with “COPPE/UFRJ - The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”. For VIV (Vortex Induced Vibration) fatigue damage calculation SHEAR7 was used.Copyright

NUMERICAL INVESTIGATION OF VORTEX-INDUCED VIBRATION OF A MARINE SCR

In this paper the dynamic response and fatigue analysis of a marine SCR (Steel Catenary Riser) due to vortex shedding is numerically investigated. The riser is divided in two-dimensional sections along the riser length. The discrete vortex method (DVM) is employed for the assessment of the hydrodynamic forces acting on these two-dimensional sections. The hydrodynamic sections are solved independently, and the coupling among the sections is taken into account by the solution of the structure in the time domain by the finite element method implemented in ANFLEX code [1]. Parallel processing is employed to improve the performance of the method. A master-slave approach via MPI (Message Passing Interface) is used to exploit the parallelism of the present code. The riser sections are equally divided among the nodes of the cluster. Each node solves the hydrodynamic sections assigned to it. The forces acting on the sections are then passed to the master processor, which is responsible for the calculation of the displacement of the whole structure. The time histories of stress are employed to evaluate the damage as well as the life expectancy of the structure by the rainflow method to count the cycles in the dynamic response.Copyright

RANDOM FATIGUE ANALYSIS OF A STEELCATENARY RISER IN FREQUENCY AND TIMEDOMAIN

Abstract The structural fatigue verification of a steel catenary riser model is performed by means of two random procedures of analysis. One of them is a nonlinear time-domain approach, based on simulation technique. The other one is a linearized frequency-domain approach, that considers that the structure presents a nonlinear static response and the dynamic response is almost linear around the static deformed configuration. Fatigue damage is calculated based on S-N curves and the Palmgren-Miners rule. PETROBRAS in-house software were used for the analyses. Results are compared and commented.

Titanium Stressjoint Design for the Top Connection of a SCR in HPHD

The top connection for the SCRs is one of the main critical points of their design. This situation becomes more challenging principally when there are high pressures and high deep water (HPHD) combined with extreme environmental loads — as is the case in the Gulf of Mexico. PETROBRAS became aware of this problem during the conceptual study of SCRs for ultra-deep waters, where the SWL is in the vicinity of 8200 ft, and with internal pressure of 12100 psi to 15000 psi. With this scenario in mind, a Titanium stressjoint began to be considered as the principal solution to the top connection. Due to this, PETROBRAS — in partnership with RTI ENERGY SYSTEM — developed a study to design a stressjoint model which would validate the SCR. This paper broadly discusses the search for this top connection solution. Dynamic global and local analyses were performed, which led us to the final solution of a titanium and steel mixed stressjoint.Copyright

Global Buckling of a Heated Pipeline in the Campos Basin Brazil in a Region With Free-Spans

This article presents the behavior a heated flowline in Campos Basin-Brazil that crosses an uneven seabed region with free-spans of different lengths. In that region the mean water depth is arround 900 m and the pipeline supports the highest temperatures. A regular inspection with ROV (Remote Operate Vehicle) showed that the flowline is interacting with the surrounding soil, evidencing movements due to thermal expansion. Geotechnical survey showed that the soil in the pipeline route is composed by normally consolidated clay where the strength properties were obtained by CPT interpretation. The principal question for the pipeline operator concerns the pipeline integrity despite of the evidence of thermal buckling occurrence. In order to answer this question, a 3D finite element model was generated considering lateral imperfections, free-spans and pipe-soil interaction along the pipeline route obtained by ROV. A complementary inspection was done with Side Scan Sonar Image obtained by AUV (autonomous Underwater Vehicle), mapping lateral buckles and the free-spans in the pipeline route. The bending moment and effective axial force in the pipeline obtained by 3D finite element global model were used to verify the pipeline integrity based on DNV OS-F101 standard [1]. In order to verify the vertical buckling in the free-spans, a parametric study was done with different free-spans and feed-in lengths based on geometry acquired from inspections. This study supplies the critical temperature variation that triggers thermal buckling in the free-spans, enabling the determination of the critical free-spans in the flowline route. The results obtained by finite element modeling was the definition of the maximum operating temperature and pressure that enables operate the flowline safety based on DNV OS-F101 code.Copyright