Full text
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| Author(s): |
Rafael Loureiro Tanaka
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2009-03-11 |
| Examining board members: |
Clóvis de Arruda Martins;
Enrique Casaprima Gonzalez;
Decio Crisol Donha;
Breno Pinheiro Jacob;
Celso Pupo Pesce
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| Advisor: | Clóvis de Arruda Martins |
| Abstract | |
Risers are elements that physically connect the platform to the well. They are fundamental elements in sea oil exploitation. Their project is a challenging task, due to the continuous increase in exploitation depth, which can turn infeasible the use of more traditional configurations, such as the free-hanging. To make the exploitation feasible, other configurations are possible, among them the lazy-wave, which was studied in this text. A riser must fulfill engineering criteria under several environmental conditions. Each of these environmental conditions is numerically simulated and, due to the complexity of the problem, the required computational time is high. If one considers that, in a given field, a great number of riser possibilities exists, the time required for a comprehensive search for the best configuration is too large, making the project outcome highly dependent on the designers experience. In this work a different approach was proposed, in three fronts: the use of an optimization technique to decide which configurations will be simulated; in order to reduce the number of necessary simulations, the execution of the simulations using models which are capable of reducing simulation time for each environmental condition; and the use of parallel computing, through which the computational burden is divided among several cores, leading to a faster solution. In order to apply an optimization technique, it was necessary to transform a riser design into an optimization problem, defining design variables, restrictions and objective function. Then, applicable optimization methods were studied and implemented in a computational tool. The models used for the execution of the dynamic and static analyses were generalized and tweaked, so that a better reliability and robustness could be achieved. The developed tool was applied to a real case and the results presented, through which were studied the influence of environmental conditions (top movements, currents and offsets). Two heuristic and four mathematical programming optimization algorithms were also compared, the first both in serial and parallel versions. Comparisons among different objective functions were made, with the best result being obtained by minimizing the maximum dynamic stress amplitude. Through the minimization of this function, the dynamic response of the riser is improved, with results which show that it is possible to obtain in a short time and in an automated way a configuration that fulfills the applicable engineering criteria and that is the best, according to an objective performance measure. (AU) | |