Breno Pinheiro Jacob

Adaptive reduced integration method for nonlinear structural dynamic analysis

Abstract The development of a reduced integration method, based on a Ritz-Wilson type reduction technique, for the nonlinear dynamic analysis of large-scale structural systems is presented. Particular consideration is addressed to compliant structures for deepwater oil exploration and production, which present severe geometric nonlinear effects and thus require the use of an incremental-iterative ( i-i ) formulation. Several aspects are considered in order to improve the computational efficiency of a reduced integration method when applied to this class of problem, including: the algorithm for the generation of the Ritz basis; termination criteria for this algorithm; the formulation of the reduced equations of motion; and the calculation of the reduced matrices. The utilization of a version of an adaptive time integration strategy, which automatically calculates time step values and triggers stiffness and basis re-evaluations, is also addressed and plays an essential role in the performance of the presented method. An application of these developments on the nonlinear dynamic analysis of a compliant guyed tower is presented, and the results are discussed in order to evaluate the computational performance of the method.

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.

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

Optimization of Steel Catenary Risers for Offshore Oil Production Using Artificial Immune System

This work presents an application of Artificial Immune System (AIS) using Clonalg to the synthesis and optimization procedure of a Steel Catenary Riser (SCR) for floating oil production systems at deep and ultra-deep waters. The evaluation of the behavior of riser configurations, needed for the calculation of the fitness function in the optimization procedure by an evolutionary algorithm, requires a large number of time-consuming Finite Element analyses. Therefore, it is important to reduce the number of analyses; in this paper, the effectiveness of AIS for this purpose is assessed in this real-world industrial application. The results indicate that the AIS approach is more effective than Genetic Algorithms (GA), generating better solutions with smaller number of evaluations.

Finite Element Modeling of the Failure Behavior of Pipelines Containing Interacting Corrosion Defects

This paper describes the application of solid finite element models in the analysis of five tubular specimens containing interacting corrosion defects. Each of these specimens has been submitted to hydrotest up to failure as part of a previous research project. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. The failure pressures predicted by the solid finite element models are compared with the failure pressures of these specimens measured in the laboratory burst tests carried out previously. Also the failure behavior of each specimen is described and illustrated by contour plots of stresses.Copyright

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

Towards an adaptive `semi-implicit` solution scheme for nonlinear structural dynamic problems

Abstract This paper presents considerations regarding the search for improved computational efficiency in the solution of structural dynamic problems. Beginning with an overview of the procedures traditionally employed for the solution of such problems, it proceeds with a critical survey of ‘hybrid’ time integration schemes, that try to combine the advantages of explicit and implicit algorithms. These schemes include: ‘partitioning’ and ‘operator-splitting’ methods, ‘semi-implicit’ methods, and integration schemes employing element-by-element techniques. Next follow some remarks regarding a natural evolution of this line of research, into the study of iterative solvers for the ‘effective’ linear systems of equations that result from the application of implicit methods. An integration scheme for nonlinear dynamic problems is then proposed, based on an iterative solver and with ‘semi-implicit’ characteristics. Its potential is demonstrated by numerical studies on the finite element model of a guyed tower for offshore oil exploration and production. The following aspects are considered: the solver itself and its preconditioner; the strategy for the definition and variation of convergence tolerance values; the computational implementation (whether global or element-by-element); and the incorporation of this scheme into the adaptive time integration strategy presented in Jacob and Ebecken [ Eur.J. Mech., A / Solids 12 ,277–298 (1993)], by devising adaptive selection criteria for the identification of applications and situations where a direct or an iterative solver is more adequate.

Numerical Offshore Tank: Development of Numerical Offshore Tank for Ultra Deep Water Oil Production Systems

There are several developments concerned to simulate the behavior of floating bodies under waves in the restricted boundary conditions so called numerical wave tank. The main feature of these tanks is to calculate full Navier-Stokes equations taking account the viscosity and free surface conditions. However, the dynamic behavior of oil floating exploitation units in actual ocean environmental condition, in waves, wind and current, is more complex and very difficult to simulate using full non-linear Navier Stokes equations. In addition, in the ultra-deep water, it is the primer importance to consider the more precise mooring line and riser’s dynamics in the analysis. The present numerical simulator laboratory called Numerical Offshore Tank is a development that takes account almost all physical phenomena acting on the floating bodies and mooring and risers lines. Since full non-linear solution is not available, the several numerical, empirical and analytical models are being considered and integrated to numerical simulator. The time domain potential problem is solved to wave forces acting on the bodies and empirical models are used to simulate current and wind forces. To represent mooring & riser lines, the finite element model with more realistic hydrodynamic force models is used. Even the simulator is using the full hydrodynamic equation, the calculation time of the simulation for floating bodies with several risers & mooring lines is very high. Therefore, special cluster with 60 PC based computer was built running the code in the parallel processing. Since the preparation of all data set for numerical experiment is very tedious work, the special pre-processor PREA3D was developed for this purpose. This pre-processor allows the fast change of the environmental and system conditions to run several test conditions. Another important feature is the visualization of the results of the simulation tests. The entire 3D view of the system is presented in the Virtual Reality room with stereoscopic projection of the Numerical Tank Laboratory.Copyright

Application of Genetic Algorithms to the Synthesis of Riser Configurations

The purpose of this work is to describe the application of Genetic Algorithms in the search of the best configuration of catenary riser systems in deep waters. Particularly, an optimization methodology based on genetic algorithms is implemented on a computer program, in order to seek an optimum geometric configuration for a steel catenary riser in a lazy-wave configuration. This problem is characterized by a very large space of possible solutions; the use of traditional methods is an exhaustive work, since there is a large number of variables and parameters that define this type of system. Genetic algorithms are more robust than the more commonly used optimization techniques. They use random choice as a tool to guide a search toward regions of the search space with likely improvements. Some differences such as the coding of the parameter set, the search from a population of points, the use of objective functions and randomized operators are factors that contribute to the robustness of a genetic algorithm and result in advantages over traditional techniques. The implemented methodology has as baseline one or more criteria established by the experience of the offshore engineer. The implementation of an intelligent methodology oriented specifically to the optimization and synthesis of riser configurations will not only facilitate the work of manipulating a huge mass of data, but also assure the best alternative between all the possible ones, searching in a much larger space of possible solutions than classical methods.© 2003 ASME

Structural design of process decks for floating production, storage and offloading units

This work analyzes the influence of ship motion and deformation on the structural design of decks to support production plants in floating production, storage and offloading units (FPSOs). These decks are space frames with lengths ranging from 30 to 100 mr, with a variable number of rigid supports linked to the ship hull. The deck and ship hull are modeled together for naval and structural analysis. A global, coupled analysis is performed considering the deck and ship structures; sea loads are evaluated by means of probabilistic methods.