Carl Horst Albrecht

Optimal design of submarine pipeline routes by genetic algorithm with different constraint handling techniques

Abstract This work deals with optimization methods for the selection of submarine pipeline routes, employed to carry the oil & gas from offshore platforms. The main motives are related to the assessment of constraint-handling techniques, an important issue in the application of genetic algorithms and other nature-inspired algorithms to such complex, real-world engineering problems. Several methods associated to the modeling and solution of the optimization problem are addressed, including: the geometrical parameterization of candidate routes; their encoding in the context of the genetic algorithm; and, especially, the incorporation into the objective function of the several design criteria involved in the route evaluation. Initially, we propose grouping the design criteria as either “soft” or “hard”, according to the practical consequences of their violation. Then, the latter criteria are associated to different constraint-handling techniques: the classical static penalty function method, and more advanced techniques such as the Adaptive Penalty Method, the e-Constrained method, and the Ho-Shimizu technique. Case studies are presented to compare the performance of these methods, applied to actual offshore scenarios. The results indicate the importance of clearly characterizing feasible and infeasible solutions, according to the classification of design criteria as “soft” or “hard” respectively. They also indicate that the static penalty approach is not adequate, while the other techniques performed better, especially the e-Constrained and the Ho-Shimizu methods. Finally, it is seen that the optimization tool may reduce the design time to assess an optimal route, providing accurate results, and minimizing the costs of installation and operation of submarine pipelines.

Synthesis and Optimization of Submarine Pipeline Routes Considering On-Bottom Stability Criteria

Researchers from Petrobras and LAMCSO/COPPE/UFRJ are currently involved in the development and implementation of a computational tool, based in Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. In this tool, randomly generated candidate routes are evaluated in terms of several criteria, incorporated in an objective (or fitness) function to take into account the relevant aspects that should be considered in the design of a route. A previous work [1] described the initial steps taken towards the development of such tool. In that work, attention was dedicated to the geometrical representation of a route, and to some of the terms of the objective function associated with a preliminary, global step of the optimization process (such as total pipeline length, and geographical-topographical issues associated with the route geometry and to the seabottom bathymetry and obstacles). Now, this work focuses in other aspects related to the structural behavior of the pipe, under hydrostatic and environmental loadings; more specifically, special attention is dedicated to the implementation of On-Bottom Stability (OBS) criteria such as the proposed in the RP-F109 code [2]. Case studies are presented to illustrate the use of the optimization tool and to assess the influence of the OBS criteria.Copyright

Numerical Simulation of the Mooring Procedures of the BGL-1 Pipeline Launching Barge

The objective of this paper is to present the application of a computational tool intended to help the crew of the BGL-1 pipeline launching barge to develop safe mooring procedures. This tool is able to calculate the deformed catenary configuration of all mooring lines, regarding the subsea layout and the local environmental conditions, and taking into account one or more buoys attached to the mooring lines in order to avoid interference and accidents with subsea obstacles. One of the main characteristics of this computational tool is the fact that it is able to incorporate the correct definition of the seabed from bathymetric curves, and to automatically consider the position of the subsea obstacles, and possible interferences between the mooring lines and the obstacles. This is performed through a specialized interface with the SGO (Obstacles Management System) database system. This system, developed by Petrobras, contains frequently updated information about the bathymetry and position of subsea obstacles, gathered by a special vessel equipped with a ROV (Remote Operated Vehicle). Case studies will be presented, in order to illustrate the application of the system to the design of actual mooring procedures.Copyright

Mooring Optimization of Offshore Floating Systems Using an Improved Particle Swarm Optimization Method

The offshore oil production industry is currently expanding its activities in even deeper waters, using moored floating platforms submitted to extreme environmental conditions. Therefore, the design of mooring systems to keep the position of such platforms is of vital importance to assure safety and economical feasibility for offshore oil production.In this context, this work presents optimization procedures to find the minimum offsets for floating platforms under environmental loads, taking radius, azimuth, pre-tension and material of the mooring lines as design variables.Considering that such optimization procedures require high computational costs, due to the need of nonlinear static and dynamic analyses with Finite Element models for each candidate solution, among the various meta-heuristic algorithms the Particle Swarm Optimization method (PSO) was chosen due to its simplicity, efficiency and parallel capability.Results of typical systems are presented, which indicate that the method is effective.Copyright

Synthesis and Optimization of Submarine Pipeline Routes Considering VIV-Induced Fatigue on Free Spans

Researchers from Petrobras and LAMCSO/COPPE have been involved in the development and implementation of a computational tool, based on Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. In this tool, randomly generated candidate routes are evaluated in terms of several criteria, incorporated in an objective (or fitness) function to take into account the relevant aspects that should be considered in the design of a route.Previous works described the initial steps taken towards the development of such tool, including the geometrical representation of a route, and some of the terms of the objective function associated with a preliminary, global step of the optimization process (such as total pipeline length, and geographical-topographical issues associated with the route geometry and to the seabed bathymetry and obstacles). Special attention was dedicated to the implementation of On-Bottom Stability (OBS) criteria such as the proposed in the DNV-RP-F109 code.This work is focused on another aspect related to the structural behavior of the pipe under hydrostatic and environmental loadings; more specifically, fatigue induced by vortex induced vibrations (VIV) on free spans along the candidate routes. Special attention is dedicated to the implementation of the screening criteria proposed in the DNV-RP-F105 code. Case studies are presented to assess the influence of the VIV criteria on the results of the optimization tool.Copyright

Incorporating Engineering Criteria to the Synthesis and Optimization of Submarine Pipeline Routes: On-Bottom Stability, VIV-Induced Fatigue and Multiphase Flow

In offshore field development it is extremely important to plan the submarine pipeline route for the hydrocarbons transportation. To ensure an expedited project, researchers from Petrobras and LAMCSO/COPPE/UFRJ have been involved in the development and implementation of a computational tool, based on Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. In this tool, each candidate route is evaluated in terms of several criteria that are incorporated in an objective function, to take into account the relevant aspects that should be considered in the design of a route, such as the pipeline length, bathymetry data, obstacles, number and length of free spans and others.Previous works described the incorporation of engineering criteria related to on-bottom stability and VIV-induced fatigue in free spans for pipes under the action of hydrostatic and hydrodynamic environmental loads of current and waves. Now, this work presents more examples of applications related to this latter criterion, and focus on the incorporation of a production criterion related to the pressure drop due to multiphase fluid flow, according to correlations for inclined pipelines.The goal is to obtain a robust tool to reduce the design time and minimize the cost of the pipeline route, leading to an optimal route configuration complying with various engineering criteria that, on a traditional design procedure, would be checked separately only after the definition of the route.Copyright

Numerical Simulation of the ‘Floating Spiral’ Pipeline Installation Procedure: First Stage, Spiral Assembly

The underlying concept for the Floating Spiral pipeline installation method is to wind the pipeline into a huge floating spiral, and then tow this assembly to the installation site, where the spiral is then unwound and lowered to the seabed in a single operation. In this method the pipes are fabricated on shore, which allows for optimal control of costs and quality in pipeline manufacturing. The first stage of the installation process by this method consists in setting the pipeline afloat and winding it elastically to form a large flat spiral, which is then ready to be towed to the installation site by standard tugboats. The objective of this work is to present results of studies for a long pipeline length at this first stage of the Floating Spiral method. The focus here is the process of moving the pipeline around a fixed structure to wind it and form the floating spiral. Problems related to modeling of contact between pipeline and its guides at the first spiral cycle, as well as contact between further pipeline cycles, are rigorously analyzed. Several numerical simulations are performed; the results are presented and discussed. Other stages of this installation method have also been studied, and are presented in a companion paper [1].Copyright

Numerical Simulation of the “Floating Spiral” Pipeline Installation Procedure: Second Stage, Spiral Transportation, Behavior Under Waves

The Floating Spiral pipeline installation method consists basically in winding the pipeline into a huge floating spiral, and towing this assembly to the installation site, where the spiral is then unwound and lowered to the seabed. In this method the pipeline is fabricated onshore, as the spiral is created, under well controlled conditions and relatively relaxed time constraints. Therefore the welds can be better inspected, which allows for optimal control of quality in pipeline manufacturing. The first stage of the installation process by this method consists in setting the pipeline afloat and winding it elastically to form a large flat spiral. This stage is studied in a companion paper [1], to be also presented at IPC2008. The second stage consists in towing the floating spiral pipeline employing standard tugboats before laying it at the installation site. The objective of this work is, therefore, to present results of parametric studies for a large length pipeline at this second stage of the Floating Spiral method. The focus now is in the pipeline behavior under wave environmental conditions during transportation. Several numerical simulations are performed and the results are discussed and compared.© 2008 ASME

Optimal Design of Submarine Pipelines by a Genetic Algorithm with Embedded On-Bottom Stability Criteria

This work describes a computational tool, based on an evolutionary algorithm, for the synthesis and optimization of submarine pipeline routes considering the incorporation of on-bottom stability criteria (OBS). This comprises a breakthrough in the traditional pipeline design methodology, where the definition of a route and the stability calculations had been performed independently: firstly, the route is defined according to geographical-topographical issues (including manual/visual inspection of seabed bathymetry and obstacles); afterwards, stability is verified, and mitigating procedures (such as ballast weight) are specified. This might require several design spirals until a final configuration is reached, or (most commonly) has led to excessive costs for the mitigation of instability problems. The optimization tool evaluates each candidate route by incorporating, as soft and hard constraints, several criteria usually considered in the manual design (pipeline length, bathymetry data, obstacles); also, with the incorporation of OBS criteria into the objective function, stability becomes an integral part of the optimization process, simultaneously handling minimization of length and cost of mitigating procedures. Case studies representative of actual applications are presented. The results show that OBS criteria significantly influences the best route, indicating that the tool can reduce the design time of a pipeline and minimize installation/operational costs.

Development of Operational Limit Diagrams for Offshore Lifting Procedures

Lifting operations with offshore cranes are fundamental for proper functioning of a platform. Despite the great technological development, offshore cranes load charts only consider the significant wave height as parameter of environmental load, neglecting wave period, which may lead to unsafe or overestimated lifting operations. This paper aims to develop a method to design offshore crane operational limit diagrams for lifting of personnel and usual loads, in function of significant wave height and wave peak period, using time domain dynamic analysis, for a crane installed on a floating unit. The lifting of personnel with crane to transfer between a floating unit and a support vessel is a very used option in offshore operations, and this is in many cases, the only alternative beyond the helicopter. Due to recent fatal accidents with lifting operations in offshore platforms, it is essential the study about this subject, contributing to the increase of safety. The sea states for analysis were chosen covering usual significant wave heights and peak periods limits for lifting operations. The methodology used the SITUA / Prosim software to obtain the dynamic responses of the personnel transfer basket lifting and container loads on a typical FPSO. Through program developed by the author, it was implemented the automatic generation of diagrams as a function of operational limits. It is concluded that using this methodology, it is possible to achieve greater efficiency in the design and execution of personnel and routine load lifting, increasing safety and a wider weather window available.Copyright