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.

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.

This paper presents recent advances regarding a computational tool, based in Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. Previous works by the authors have focused on some specific issues related to the development of this tool, including the incorporation of engineering criteria such as on-bottom stability (OBS), VIV-induced fatigue in free-spanning pipelines, and flow assurance. Now, this work studies the influence of different OBS criteria for particular scenarios in shallow waters, where it is expected that the environmental loads of wave and current play a more important role on the hydrodynamic stability of the pipe. Case studies are presented, to compare the influence of OBS criteria proposed by the DNV RP-F109 code (Absolute Lateral Static Stability, and Generalized Lateral Stability), both implemented into a multi-objective procedure (using specialized algorithms based on the Pareto approach) along with other engineering criteria (VIV-induced fatigue and multiphase flow).

Traditionally, the selection of a pipeline route for offshore applications has been manually performed by the engineer, by a quick inspection of the seabottom bathymetry and the available information regarding obstacles. Eventually the evaluation of a given route could be performed using analysis tools, but in any case the process is highly dependent on the expertise of the engineer. In this context, this work describes the development of a computational tool for the synthesis and optimization of submarine pipeline routes, using computational tools based in Evolutionary Algorithms. In such optimization procedures, each candidate route is randomly generated and is evaluated, in order to determine its "fitness", in terms of several criteria that are incorporated in an objective function. Such function takes into account all relevant aspects that should be considered in the selection of a route, such as total pipeline length; geophysical and geotechnical data obtained from the bathymetry and sonography, including the definition of obstacles and regions that should be avoided; number, length and location of free spans to be mitigated along the routes. Other aspects depend on the structural behavior of the pipe, under hydrostatic and environmental loadings; some of these aspects are dealt with by following recommendations established in the DNV RP-F105 and RP-F109 codes, related respectively to the on-bottom stability and free spans. This work describes the implementation of the optimization tool, beginning with the assembly of the objective function and the definition of the problem constraints, and proceeding with the association of this function and constraints in the framework of the implementation of a Genetic Algorithm-GA. Case studies are presented to illustrate the use of this optimization tool. It is expected that the application of such tool may reduce the design time needed to assess an optimal pipeline route, while reducing computational overheads and providing more accurate results (avoiding mistakes with route interpretation), ultimately minimizing costs with respect to submarine pipeline design and installation.

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.