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Bertrand Mareschal

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Abstract
« on: April 08, 2020, 03:05:29 PM »
Elicitation of Criteria Importance Weights through the Simos Methods – A Case Study on Decommissioning Subsea Structures
Giselle da Silva Távora, Alberto Luiz Coimbra Institute – Graduate School and Research in Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, giselletavora@oceanica.ufrj.br
Carlos Eduardo Infante, Federal University of São João del Rei, prof.eduinfante@gmail.com
Laurelena Crescencio Palhano, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, laure@sage.coppe.ufrj.br
Marcelo Igor Lourenco de Souza, Alberto Luiz Coimbra Institute – Graduate School and Research in Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, migor@lts.coppe.ufrj.br
Jean-David Caprace, Alberto Luiz Coimbra Institute – Graduate School and Research in Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, jdcaprace@oceanica.ufrj.br
With the end of life of several Brazilian oil fields, the decommissioning of submarine structures is a challenge to be faced, since there are still no consolidated methodologies to assess the general view of the problem to be found. Currently, pipelines represent a significant amount of all structures to be removed and the final disposition is one of the most important aspects to be analyzed. Decommissioning is expected to occur, once the depletion of resources or the useful life of the production units are reached.
Total removal by cutting and elevating sections of pipe, removal of the entire length of the pipe by reverse s-lay, abandonment in situ with dumping rocks at the ends of the pipe and total abandonment are several alternatives to be considered in the subsea decomissinging problem. Meawhile, the creiteria to be considered for the assessment are: Environment, Safety, Economy, Tehcnical and Social.
A significant factor pertaining to the non-compensatory multicriteria decision aiding models (MCDA), such as the outranking methods, i.e. PROMETHEE, is the criteria weighting, or the importance of the criteria. Generally, these parameters imprint the preferences of a single decision maker to the model. The existing methods, which are widely used to assess the criteria importance weights, could be classified into two categories: direct assessment procedures, where the decision maker is asked to explicitly express the criteria weights in terms of percentages, and indirect methods, inferring the weights from pairwise comparisons of the criteria.
The method proposed by Jean Simos in 1990 has gained popularity and has been applied to different types of problems to solve the weaknesses of the previous methods, due to its simplicity, and the convenience it provides to the decision makers to express his preferences.
Specifically, it requires the construction of a hierarchy on the evaluation criteria, by involving the decision maker to a “playing cards” procedure, in order to attribute numerical values to them. Nevertheless, the process recommended by Simos and its revised version proposed by Figueira and Roy (2002) have some robustness issues. In particular, they arbitrarily calculate a unique weighting vector, even though there exist infinitely more weight vectors, also satisfying the preferential statements, which have been defined by the DM during the initial arrangement of the cards.
The purpose of this paper is to expose the robustness problem of the improved Simos method observed during a large scale case study applied to decommissioning of subsea structures.
The results has been collected during a workshop held with the presence of several Oil and Gas companies, educational institutions and regulatory bodies. The participants were divided into five people per table, each participant specialized in one criterion. The people around the table and the scenarios to be analysed has been systematically varied in order to analise the influence of each decision maker teams.
In each scenario, characteristics related to distance from the oil field, water depth, presence or absence of diving, location of the country, presence or absence of Naturally-Occurring Radioactive Materials, crossings of pipes, type of seabed, type of fishing and marine life were proposed.
The main outcome of the study shows the variance between the different weights proposed by the decision making teams depending of the people around the table and the scenarios considered. The robustness problem of the Simos method has therefore been exposed and quantified for this specific situation.
« Last Edit: May 21, 2020, 01:45:22 PM by Bertrand Mareschal »
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