Juliana Souza Baioco

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

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

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.