a computational system for subsea pipelaying simulation

7/27/2019 A Computational System for Subsea Pipelaying Simulation

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Abstract. Traditional analysis methods for pipelaying

simulation consider an uncoupled model where the motions

of the barge are previously determined, without taking intoaccount the inuence of the pipeline, and are then prescribed

at the top of the pipeline.

Currently, the analyses of pipelaying operations have been

performed by commercial softwares, such as OffPipe. However,

such tools presents restrictions/limitations related to the user

interface, model generation and analysis formulations. These

limitations hinder its efcient use for analyses of installation

procedures for the scenarios considered by Petrobras, using

the BGL-1 barge or other vessels.

Therefore, the objective of this work is to present a computational

tool in which the modules follow the Petrobras users

specications. The main objective of such tool is to overcomethe limitations for specic needs and particular scenarios in

the simulation of several types of pipeline procedures. Such

tool, called SITUA-PetroPipe, presents an extremely friendly

interface with the user, for instance allowing the complete

customization of the conguration of laybarge and stinger

rollers, and includes novel analysis methods and formulations,

for instance the ability of coupling the structural behaviour of

the pipe with the hydrodynamic behaviour of the vessel motions

under environmental conditions.

Several simulations of actual operations are shown, in order to

illustrate the application of this new computational tool.

Keywords: Numerical Methods, Offshore Operations, Pipeline

Installation Procedures

1 - INTRODUCTION

Installation of pipelines and owlines constitute some

of the most challenging offshore operations. The technicalchallenges have spawned signicant research and development

efforts in a broad range of areas, not only in studies regardingdifferent installation methods, but also in the formulation andimplementation of new computational tools required to thenumerical simulation. This work addresses this latter issue.

The most common installation methods are the S-Lay, J-Lay,

and Reel-Lay methods, schematically shown in Fig. 1, andTowing methods, schematically shown in Fig. 2 (Guo, Bai,

2005; Kyriakides,2007).

Figure 1 S-Lay, J-Lay and Reel-Lay Methods.

In the S-Lay method, as the laying barge moves forward,the pipe is eased off the stern, curving downward through thewater until it reaches the touchdown point. After touchdown,as more pipe is played out, it assumes the S shaped curve. Toreduce bending stress in the pipe, a stinger is used to supportthe pipe as it leaves the barge. To avoid buckling of the pipe,

a tensioner must be used to provide appropriate tensile load tothe pipeline (Clauss,1998). This method is used for pipelineinstallations in a range of water depths from shallow to deep.

In the J-lay method, the pipe is dropped down almostvertically until it reaches touchdown; after that it assumes theJ shaped curve. J-Lay barges have a tall tower on the sternto weld and slip pre-welded pipe sections. With the simpler

pipeline shape, the J-Lay method avoids some of the difculties

of S-Laying such as tensile load forward thrust, and can be usedin deeper waters.

In the Reel-Lay method, the pipeline is installedfrom a huge reel mounted on an offshore vessel. Pipelines

are assembled at an onshore spool-base facility and spooled

INTERNATIONAL JOURNAL OF MODELING AND SIMULATION FOR THE PETROLEU M INDUSTRY, VOL. 3, NO. 1, JUNE 2009

A COMPUTATIONAL SYSTEM FOR SUBSEA PIPELAYING SIMULATION

Danilo Machado Lawinscky da Silva, Carl Horst Albrecht, Breno Pinheiro Jacob

Isaias Quaresma Masetti, Claudio Roberto Mansur Barros, Arthur Curty Saad

[email protected], [email protected], [email protected]

LAMCSO Laboratory of Computational Methods and Offshore SystemsDepartment of Civil Engineering, COPPE/UFRJ, Rio de Janeiro, RJ, Brazil

[email protected], [email protected], [email protected] Petrleo Brasileiro S.A.


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36 INTERNATIONAL JOURNAL OF MODELING AND SIMULATION FOR THE PETROLEUM INDUSTRY, VOL. 3, NO.1, JUNE 2009

onto a reel which is mounted on the deck of a pipelay barge.Horizontal reels lay pipe with an S-Lay conguration. Vertical

reels most commonly do J-Lay, but can also S-Lay.Towing methods basically consists in weld the pipeline

onshore with an onshore pipeline spread. Once the pipeline iscomplete and hydrotested, the pipeline is dewatered and movedinto the water, while being attached to a tow vessel. It is thentowed to an offshore location where each end is connected to

pre-installed facilities (Silva,2007b,2008).There are four variations of the towing method:

surface tow, mid-depth tow, off-bottom tow, and bottom tow(Fig. 2). In the surface tow approach, buoyancy modules areadded to the pipeline so that it oats at the surface. Once the

pipeline is towed on site by one or two tugboats (Silva,2008),the buoyancy modules are removed or ooded, and the pipeline

settles to the sea oor. The mid-depth tow requires fewer

buoyancy modules, and the pipeline settles to the bottom on itsown when the forward progression ceases. The off-bottom towinvolves buoyancy modules and chain weights. In the bottom

tow, primarily used for soft and at sea oor in shallow water,the pipeline is towed along the sea oor

Towing could be cheaper than other methods thatuse laybarges. However, a case-by-case analysis is required todetermine the cost-benet ratio.

Figure 2: Tow-in Methods.

2 - PIPELAYING IN OFFSHORE BRAZIL

Usual pipelaying operation in offshore Brazil areperformed by S-Lay procedures employing the BGL-1 barge(Fig. 3) owned by Petrobras. The BGL-1 is a second-generationanchor positioned laybarge that performs installation operations

by moving forward using its own mooring lines. Basically,tug boats drop anchors at some predened positions; then the

barge winches release the stern mooring cables, and collect themooring cables located at the bow.

In order to prevent the pipe from buckling in theregions of maximum bending, the bend radius is controlled bykeeping the pipe under tension, so that the pipe actually followsa lazy S shape. The tension is applied to the pipe by tensionerson the barge which are usually arrays of rubber wheels or beltswhich surround the pipe and apply an axial force to the pipethrough the friction generated between the tensioner and the

pipe external coating as shown in Fig. 4.

Figure 3 The BGL-1 Pipeline Launching Barge

The force on the pipeline is reacted at the seabed endof the pipeline by the dead weight of the pipeline and friction

between it and the seabed. Obviously the larger the force

applied by the tensioners to the pipeline, the more gradual willbe the bending radius in the S portion of the laying curve. Also,as the pipe weight increases it is necessary to apply a greaterforce to the pipe to maintain the desired bend radius and so

prevent buckling, particularly in the sag bend portion of thecurve (Torselletti,2006).

Figure 4 BGL-1 Tensioner.

As individual pipe lengths are welded onto thegrowing pipeline, the barge is winched forward and the newsection of pipeline passes over the stinger towards the seabed.As mentioned before, tugs are used to continuously repositionthe anchors ahead of the barge so that it can keep movingforward.

3 - REQUIREMENTS FOR PIPELAYING SIMULATION

Traditional analysis methods for pipeline layingconsider an uncoupled model, where the motions of the bargeare previously determined without taking into account theinuence of the pipeline, and are then prescribed at the top of

the pipeline.For oating production systems (FPS) under the

action of environmental loadings in deepwater scenarios, it

has been recognized that the use of coupled dynamic analysis


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tools is mandatory for the accurate numerical simulation, analysisand design (Ormberg,1997; Wichers,Heurtier,2001; Senra,2002).Coupled analysis formulations consider the non-linear interactionof the hydrodynamic behavior of the FPS hull with the structural/hydrodynamic behavior of the mooring lines and risers, represented

by Finite Element models. In the implementation of such analysis

tools, the 6-DOF equations of motion of the platform hull arecoupled with the equations of motion of the FEM model of thelines.

It can intuitively be seen that the use of coupledformulations is important not only for the design of production

platforms, but also for the simulation of offshore installationoperations. In the case of pipelines in S-Lay operations, even inshallow waters the motions of the laybarge can be signicantly

affected by the structural behavior of the pipeline.Also regarding pipelines in S-Lay installation operations,

it should be considered that the contact mechanism between thepipeline and the launching structure is complex, specied only in

some points of the ramp and stinger.

Traditionally, Petrobras has been performing numericalsimulations of pipelaying operations employing commercialsoftware, such as OffPipe (Malahy Jr, 1996). However, such tools

present limitations related not only to the user interface, but also tothe model generation and analysis formulations. These limitationshinder its efcient use for analyses of installation procedures for

the scenarios considered by Petrobras, using the BGL-1 bargeor other vessels, considering for instance particular types ofstingers depending on depth and pipeline, with different lengthsand geometries adapted to certain laying conditions in S-Lay

procedures.Therefore, the objective of this work is to present the

development of a in-house computational tool, referred as SITUA-PetroPipe, that overcomes the limitations for specic needs andparticular scenarios in the simulation of several types of pipelineprocedures, and addresses the requirements regarding the analysisformulations mentioned above.As will be described in the remainder of this work, such tool presentsan extremely friendly interface with the user, allowing for instancethe complete customization of the conguration of laybarge and

stinger rollers.

4 - SITUAPROSIM

The SITUA-PetroPipe tool may be seen as specializedmodules of the SITUA-Prosim system (Jacob,1997), which has

been developed since 1997, in cooperation by Petrobras andLAMCSO (Laboratory of Computer Methods and OffshoreSystems, at the Civil Engineering Department of COPPE/UFRJ,Federal University of Rio de Janeiro) . This system constitutesa computational tool that performs coupled static and dynamicnonlinear analyses of a wide range of offshore operations.

The PetroPipe modules described here are based in theSITUA graphical interface, and in the Prosim numerical solver(Jacob,2005). This numerical solver comprises a time-domainnonlinear dynamic analysis program, which has been employed byPetrobras since 1998 in several design activities related to oating

production systems.

The coupled formulation of the Prosim programincorporates, in the same computational code and data structure,a hydrodynamic model to represent the hull and a nite element

model to represent the structural hydrodynamic behavior of themooring lines, risers and pipelines. This coupled formulationallows the simultaneous determination of the motions of the hull,

and the structural response of the lines. Moreover, the results willbe more accurate since all dynamic and nonlinear interaction effectsbetween the hull and the lines are implicitly and automaticallyconsidered. Details of such coupled model are presented elsewhere(Senra,2002;Jacob,2005), and will not be reproduced here

The original Prosim code was oriented towards the analysisand design of FPS, considering their installed and operationalsituations. Later, the SITUA-Prosim system was developed byincorporating a graphical interface and adapting / specializing thecode for the analysis of installation and damage situations (henceits name, from the Portuguese SITUaes de instalao e Avaria).

The SITUA interface (Fig. 5) is designed to work as apre-processor and model generator for the Prosim nite-element

based numerical analysis modules, and to provide facilities forstatistical and graphical post-processing and visualization of results.The model generation procedures of the interface incorporate ananalytical catenary solver, able to represent complex congurations

such as lines with multiple segments and different materials,connected to other lines or to platforms, and with otation elements

such as buoys or segments with distributed oaters.

The interface allows a very simple and intuitive denition

of the model of a line. The user needs only to specify the number,length and type of segments that comprise the line. A databasewith several material types is incorporated in the system. Anotherenhanced facility for the denition of lines for actual operations of

the BGL barge consists in the denition of two of the parametersthat dene a catenary (including anchor position, horizontal force,

total top axial tension), in a variable-length procedure. The systemthen automatically adjusts the laid length of the top segment of themooring line to comply with the given parameters.

A series of adaptations and enhancements had alreadybeen incorporated in the SITUA-Prosim system, intended tospecialize its use for simulation of the BGL-1 mooring procedures.Some highlights of these tools are described in the text that follows;more details can be found in (Masetti,2004).

Figure 5 Main screen of the SITUA-Prosim System.

SILVA et al. : A COMPUTATIONAL SYSTEM FOR SUBSEA PIPELAYING


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4.1 - Interaction with Seabed

The computational tool is able to incorporate thecorrect denition of the seabed from bathymetric curves. It can

also automatically consider the position of the subsea obstacles,and determine possible interferences between the mooringlines or the pipeline with obstacles. This is performed througha specialized interface with the SGO (Obstacles ManagementSystem) database system. This system, developed by Petrobras,contains frequently updated information about the bathymetryand position of subsea obstacles, gathered by a special vesselequipped with a ROV (Remote Operated Vehicle) (2002).

The seabed is modeled by a surface mesh in which thez-coordinate represents the depth. Soil-pipe interaction effectsare modeled through nonlinear scalar elements associatedto each node that comprises the spatial discretization of the

pipeline. Such scalars act on the seabed, representing thefriction between pipe and soil, and also as contact springs onthe vertical direction (Saevik,2004; Michalopoulos,1986).

Friction effects on the seabed are represented byan elastoplastic formulation that allows the consideration ofanisotropic friction, through the denition of distinct soil-

resistance coefcients for the axial and lateral directions of the

pipeline (Silva,2006a).

4.2 - Barge Motion and Interference Management

Modules

As mentioned before, during pipelaying the barge ismoved periodically one pipe length ahead, along a predened

route. The planning of such procedure consists in the denition

and charting of a series of points on this route, specifying thepositioning of the anchors, the lines, the buoys and the hull ofthe barge.

In order to help the BGL-1 barge crew to develop safemooring procedures and to dene the sequence of mooring

operations that leads to the barge motion, the system is ableto calculate the motions of the barge due to the operations

performed with its mooring lines, leading to changes in theircatenary conguration (including placement of buoys, variation

of the onboard/released cable lengths, and relocating anchors).During the simulation of such mooring operations by

the SITUA interface, a specialized interference managementmodule can be employed to characterize interferencesituations. Such situations are detected when an obstacle fallsinto an exclusion volume dened around segments of a line

laying on the seabed, and a vertical distance below suspendedsegments, with risks of collision and damage to the line and/orthe obstacle (a manifold, another pipeline, etc.).

Figure 6 presents a 3D view where the exclusionregion around one line is graphically displayed, showing a

possible interference situation with a previously installedpipeline. A more detailed visualization, including the denition

of the types of obstacles and distances from the line, can beobserved in 2D views such as the depicted in Fig. 7. In theseviews the interferences are indicated by red arrows, with the

corresponding distances, and a tag dening the obstacle.

Once the possible interferences are identied, the

BGL-1 operator can take measures to avoid them, includingthe placement of buoys in given positions along the line. Figure8 shows a conguration of a mooring line with two buoys, to

keep the line suspended well over subsea obstacles.

Figure 6 3D View of Exclusion Region with Interference.

Figure 7 2D View Detailing Interference.

Figure 8 3D View of Mooring Lines with Buoys.

5 - SITUAPETROPIPE

As mentioned before, the PetroPipe modulesinclude new tools developed following the Petrobras usersspecications. These tools are intended to automate the

generation of numerical models for the simulation of pipelineinstallation procedures (for instance, allowing the completecustomization of the conguration of the laybarge and stinger

rollers).Moreover, the PetroPipe modules address the

requirements regarding the analysis formulations mentionedin a preceding section, including the coupling of the structural

behavior of the pipe with the hydrodynamic behavior of thevessel motions. Also, the contact of lines (mooring lines, risers,

pipelines) with the platform can be rigorously modeled during


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a nonlinear dynamic analysis, as well as the contact involvingdifferent lines or even the contact of one line with itself.

5.1 - Modeling of Contact

Traditional contact models consider for instance a

generalized scalar element, consisting of two nodes linked by anon-linear gap spring (Grealish,2005). Here, the contact modelconsists of a generalized elastic surface contact algorithm. Thecontact is modeled by augmentation of the global stiffnessmatrix, based on the orientation and contact stiffness of thecontact surfaces. Details of this algorithm are presented in(Silva,2006a,2007a).

The algorithm has been shown to be able of capturingthe detailed characteristics of the interaction between mooringlines, risers, pipelines, hulls, in a sophisticated model suchas the illustrated in Fig. 9, depicting the contact between the

pipeline and the rollers of the laybarge stinger. A more detailedexample will be presented in the application presented later.

Figure 9 Contact Model.

5.2 - Tensioner Model

As mentioned before, the tensioner (Fig. 4) is intendedto control the tension level in the pipeline during the pipelayingoperation, by keeping it within a feasible operational range.

In the PetroPipe modules, the tensioner is representedby a specialized generalized scalar element, automatically addedto the pipeline top end, which consists of two nodes linked

by a nonlinear gap spring. Force-displacement or stiffness-displacement functions associated to each local direction aredened, and the local coordinates systems can also be updated

at each simulation step.To simulate the tensioner behavior in keeping the tensionlevel at the dened range, the axial stiffness of this element

continually varies, leading to changes in the element length asthe pipeline end moves back and forth. It should be recalled thatthe pipeline end motions are induced by the tensioner behaviorand by the barge motions applied at the tensioner. The tensionermodel is schematically shown in Fig. 10.

All main characteristics of the tensioner machine areincorporated in this model, including:

Operational Range denes the range of desired tension

values; the tensioner is not activated whenever the pipeline

end tension is within this range.

Response Delay Whenever the pipe tension leaves the

operational range, the tensioner is activated but only aftera given time delay, when it effectively starts working.

Response Velocity After the tensioner effectively starts

working, it does not restore the tension level immediately,but after a certain period dened by its design response

velocity. Displacement Limit This denes the limit in which thetensioner can move the pipeline back and forth in order tocompensate its tension level.

Figure 10 Tensioner Model.

6 - MODELING OF PIPELINE INSTALLATION

PROCEDURES

In the following sections, the facilities incorporatedin the PetroPipe modules are illustrated by their application toreal-case pipeline installation scenarios.

6.1 - Lateral Deection Procedure

The Lateral Deection procedure, associated to towingmethods, may be used to move the pipeline into the sea. In thiscontext, it consists basically on deecting the pipeline to the

sea (after assembled at the coastline) using a cable connectedto a tug boat. The characterization of the deection procedure

involves the determination of the better velocity and directionof the tug boat when the pipeline is leaving the shore in orderto minimize its efforts (especially due to the curvatures).

The PetroPipe modules have been employed tomodel such a procedure for an actual scenario, as presented in(Silva,2007b). Some steps of the results of numerical simulationsfor this procedure are illustrated in Fig. 11: the pipeline ison shore (1), at the coastline, before starting towing (2), the

pipeline leaves shore (3,4) and is towed to the installation site.



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Figure 11: Lateral Deection Procedure

6.2 - Tow-in

As mentioned before, tow-in operations are performedin many situations to transport pipelines of several lengths.Usually, Petrobras performs these operations following a lateraldeection procedure such as the previously described. In the

typical conguration for surface tow, the pipe is towed using a

front and a back tugboat aligned at the transportation route, asshown in Fig. 12.

Numerical simulations of actual operations wereperformed using the SITUA-PetroPipe system, in order toassess the pipeline behavior under environmental loadings.The studies presented in (Silva, 2008) include an alternative

conguration, shown in Fig. 13, where the tugboats are notaligned. Smaller values of cable tension were obtained whenthe pipeline is nearly aligned with the direction of the resultantof the environmental loadings.

Figure 12: Tow-in Typical Conguration.

Figure 13: Tow-in Alternative Conguration.

A contingency procedure was also analyzed in(Silva,2008), for a situation in which the back tugboat isdisconnected and only the front tugboat is pulling the pipeline.This conguration simulates a situation in which one of the

tugboats loses control and its cable is disconnected. The resultsof the analyses indicated that the smaller values of cable

tensions were found in congurations where the back tugboatis disconnected, indicating that the best situation occurs whenit does not tension the pipe, or simply when it is not connectedto the pipe.

Therefore, from the results of the numericalsimulations, the actual pipeline transportation was performed

by Petrobras using only one tugboat, employing a smaller boatonly to accompany the transport operation for safety reasons,and to perform the maneuvers needed for the subsequent

pipeline launching process. During the operation, all numericalpredictions related to the pipeline behavior were conrmed.

6.3 - Shore Pull

The shore pull operation illustrated here consistsin pulling the pipe from the BGL-1 barge onto the shore bya winch. The winch needs to keep adequate pulling force toensure that the pipe is maintained under controlled tensionwithin the allowed stress/strain limits. The forces applied must

be controlled such that no damage to the pipeline anodes orcoating occurs. Buoyancy aids can be used if required to keep

pulling tension within acceptable limits.During the numerical simulation by the SITUA-

PetroPipe system, forces in the pipeline and cable are analyzedincluding any overloading, friction and dynamic effects that

may occur. Figure 14 shows snapshots from the animation ofthe numerical results, as the pipeline is pulled from the bargeand arrives on the shore.

Figure 14 Shore Pull Operation.


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7 - GENERATION OF A S-LAY MODEL

The complete generation of an S-Lay model using thespecialized interface of the SITUA-PetroPipe is described inthe following sections.

7.1 - Laybarge Characteristics

Figure 15 and Table 1 illustrate the main geometriccharacteristics of the BGL-1 barge. Detailed actual data, interms of the geometrical and hydrodynamic characteristics ofthe BGL-1 hull, were provided by Petrobras and employed togenerate the model of the barge hull, represented in Fig. 16.The geometric data are used in the denition of the contact

surface of the barge hull.

Figure 15 BGL-1 Geometry

Table 1 Main geometric characteristics of BGL-1

Propriety Values (real scale)

Drought 5.182 m

Height 9 m

Beam 30 m

Length 120 m

Figure 16 SITUA-PetroPipe BGL-1 Model

7.2 - Ramp and Stinger Data

Figure 17 illustrates the conguration of the ramp and

stinger considered for the application described here. The localramp-stinger coordinate system has its origin on the stern shoe,X-axis positive direction from bow to stern and Z-axis vertical

with positive direction upwards, as indicated in Fig. 18. Thegeometric data of ramp and stinger are summarized in Tables 2and 3, respectively.

The geometric data of the stinger structure are also usedin the denition of its contact surface. During the nite element

analysis the stinger is considered a rigid body connected to thebarge hull and all contact forces acting on it are transferredto the barge. The hydrodynamic characteristics of the stingerare incorporated at the barge hull model by its hydrodynamiccoefcients.

Figure 19 shows typical congurations for roller boxes

on the laybarge stinger and ramp, respectively.

Figure 17 BGL-1, Ramp and Stinger Geometry

Figure 18 Ramp/Stinger, Local Coordinate System.

Table 2 Ramp radius 150 m

Element X (m) Z (m) Length (m)

Tensioner -56.335 1.550 -

Roller Box 1 -38.905 1.094 2.75

Roller Box 2 -26.574 0.768 2.75

Roller Box 3 -18.078 0.034 2.75

Roller Box 4 -9.292 -1.241 2.75

Roller Box 5 -0.432 -3.157 3.00



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Table 3 Stinger radius 150 m

Element X (m) Z (m) Offset (m) Length (m)

Roller Box 1 5.277 -4.632 0.687 4.00

Roller Box 2 9.094 -5.825 0.687 4.00

Roller Box 3 12.856 -7.156 0.694 4.00

Roller Box 4 16.586 -8.555 0.714 4.00

Roller Box 5 20.275 -10.099 0.748 4.00

Roller Box 6 23.882 -11.770 0.793 4.00

Roller Box 7 27.443 -13.581 0.850 4.00

Roller Box 8a 29.361 -15.198 0.919 --

Roller Box 8 30.883 -15.835 0.950 --

Figure 19 Conguration of Rollers (Stinger and Ramp)

As mentioned before, this conguration of the laybarge

ramp and stinger roller boxes can be easily and completely

customized by the new modules of the graphical interface ofthe SITUA-PetroPipe system, as illustrated in Figs 20, 21 and22. A general view of the generated model for the BGL-1 isshown in Fig. 22.

Figure 20 Ramp Conguration.

Figure 21 Stinger Conguration.

7.3 - Mooring Lines

The BGL-1 has eleven fairleads, but in usual operationsonly nine or ten mooring lines are connected. All mooring linesare composed by two segments, with characteristics presented inTable 4. The length value for segment 2 corresponds to the totallength available on the winch drum; the released length variesduring the mooring operations, as presented in (Masetti,2004).

The catenary solver provides the results dening

the equilibrium conguration of the mooring system, and the

interference management module allows the identication of

several possible interferences with obstacles. All interferences

are successfully avoided by placing two buoys on most of thelines. Detailed tables indicating position in the line measuredfrom the anchor, and the length of the pendant for each buoy,can be found in (Masetti,2004).

Figure 22 General View of the Generated Model


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Table 4 Characteristics of Mooring Line Segments

Segment Length (m) Material

1 (anchor) 150 R3S Stub Chain 3

2 1780 (max) EEIPS Steel Wirerope 2.5

7.4 - Pipeline

All pipeline characteristics can be dened by the

user. A database with common material properties and usualpipeline characteristics, such as wall thickness and coating, isincorporated in the system. The model generated here considersa typical 16-in pipeline, with physical and geometric properties

presented in Table 5.

Table 5 16 Pipeline data

Parameter Value Unit

Outside Diameter 0.40640 m

Wall Thickness 0.011125 m

Yield Stress 414000 kN/m2

Modulus of Elasticity of steel 207000 MPa

Axial Stiffness (EA) 2859694.14 kN

Flexional Stiffness (EI) 55894.90 kN*m2

Poisson Coefcient 0.3 -

Density of steel 77 kN/m3

Corrosion Coating Thickness 0.0032 m

Corr. Coating Weight Density 9.32 kN/m3

Concrete Coating Thickness 0.0381 m

Concrete Coating Weight Density 21.974 kN/m3

Hydrodynamic Diameter 0.489 m

Tube Length 12 m

Field Joint Length 0.6 m

Joint Fill Weight Density 10.065 kN/m3

Weight in Air 2.255935 kN/m

Weight Submerged 0.368493 kN/m

7.5 - Visualization of the Complete Model

The initial equilibrium conguration of the pipeline is

generated using dynamic relaxation techniques as proposed in(Silva,2006b). The top tension in the pipeline is the parameterthat denes the S shape. The generated S-Lay conguration

is shown in the gures that follow.

The actual bathymetric data and soil properties areconsidered for the pipeline behavior on seabed. Informationabout free-spans is then available during analysis.

Figure 23 SITUA-PetroPipe S-Lay Model

7.6 - Typical Results

Besides typical results in terms of tension and VonMises stresses along the pipe length, as shown in Figs 24 and25, information about distances between the pipeline and itssupports as well as the reaction at each roller box are generated

during static and dynamic analyses.Specic reports are automatic generated for relevant

information such as distance from the laybarge stern and thepipeline touchdown point. Reports for all relevant informationabout the mooring lines are also automatic generated.

Figure 24 Von Mises Stress (static).



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Figure 25 Von Mises Stress (dynamic).

8 - FINAL REMARKS

The in-house computational system described in thiswork has already been employed by the BGL-1 crew in thesimulation and planning of actual mooring procedures for

pipeline laying operations in Campos Basin. The system hasbeen shown to be able to calculate the motions of the barge dueto the operations performed with its mooring lines (including

placement of buoys, and variation of the onboard/releasedcable lengths), taking into account general seabed data andinterferences with subsea obstacles.

Regarding the simulation of the actual pipeline

launching process, the Prosim nite-element numerical solveralready included a 3D frame element that can account for allmaterial and geometrically nonlinear effects that arise in the

pipeline behavior during the laying operation. It was also able tocouple the structural behavior of the pipe with the hydrodynamic

behavior of the vessel motions under environmental conditions,considering all mooring lines also modeled by Finite Elements,which in itself is a step further over traditional methods for thenumerical simulation of pipelaying operations.

In order to comprise an accurate and user-friendlyalternative for the analysis of pipeline installation procedures,some adaptations in the SITUA interface and in the Prosim

numerical solver were needed.Therefore, this work described some of the recentimplementations that comprise the SITUA-PetroPipe modules,including: a) Generation of initial nite-element meshes for the

S-laying conguration of the pipeline by a dynamic relaxation

procedure; b) Inclusion of generalized scalar elements torepresent the tensioner; c) Implementation of automaticcustomization facilities for the denition of the ramp and

stinger rollers; d) Development of a rigorous contact algorithmto represent the variable contact between the pipeline and therollers; e) Generation of nite-element models for other types

of laying operations that may eventually be considered for theBGL-1 or other laybarges, including J-lay and reeling methods.

Due to limitations in space, these latter facilities (regardingJ-Lay and Reeling procedures) could not be presented here, andwill be demonstrated in future works.

As the result of the recent implementations describedin this work, the SITUA-PetroPipe system now comprises acomputational tool intended to improve the applicability andaccuracy of analysis of pipeline installation operations, makingthe simulations more realistic.

Several parametric studies are currently beingperformed considering the described modeling facilities, fordifferent scenarios including shallow to deep waters, anddifferent pipeline sizes. The results of these studies will also

allow the precise assessment of the inuence of the application

of the coupled model (barge + mooring lines + pipeline) onthe dynamic pipeline-laybarge behavior in such differentscenarios, indicating where a coupled pipelay analysis, ratherthan a traditional uncoupled analysis, is required.

Acknowledgements

The authors would like to acknowledge the members of theBGL-1 crew that actively contributed with the development ofthe SITUA-PetroPipe software, with valuable comments andsuggestions.

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a computational system for subsea pipelaying simulation

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