Técnica de otimização multiobjetivo aplicada ao projeto preliminar de navios petroleiros.

Abstract

estudo de casos para comparar os resultados obtidos com o programa implementado.Um objetivo adicional deste trabalho é expor à comunidade naval a utilidade e efetividade dos algoritmos genéticos nos problemas de projeto multiobjetivo. O enfoque desta pesquisa está na metodologia implementada e na sua recomendação para o projeto preliminar de navios. Palavras chaves: Algoritmos Genéticos. Navio Tanque (Projeto). OtimizaçãoMatemática. ABSTRACTThis paper shows the rational process of selecting the optimal dimensions and forms coefficients of tanker ships using the technique of genetic algorithm. It is proposed a procedure to balance designs in weight and useful space and assesses their feasibility so that weight and volume limited tankers can be balanced. The elaboration of a procedure and its implementation in an efficient program is so important in the preliminary dimension of a ship, so this paper is a divulgation of the genetic algorithm as robust technique for the preliminary ship design. Two objective attributes are used to evaluate each design: Total Cost and Mean Oil Outflow. This attributes are conflicting between them, that is, a low cost correspond a high outflow and vice versa. The Mean Oil Outflow is evaluated with the probabilistic methodology proposed by the INTERTANKO to IMO. The assessment of mean oil outflow, by a non dimensional parameter, supposes the event of grounding and/or collision resulting in bottom and side damage respectively. In estimating the cost two models are used performing a comparison of their effects on the final values of principal dimension. In addition, for the balance procedure, five hull weight models are tested and analyzed the impact on the form and distribution of Pareto frontier.A genetic algorithm is implemented to search the optimal design parameters and identify non-dominated frontier of Pareto. The algorithm is tested with four test functions found in the technical literature. The test functions selected are convex, non convex, discontinuing and one with four restrictions. The implementation shows similar results with those showed in others papers. A Suezmax, an Aframax, and a Panamax ships are used as case study in order to compare the gotten results by the implemented program.One additional goal of this work is to expose to naval community the usefulness and effectiveness of the genetic algorithm in the Multi-Objective design. The emphasis of this paper is on methodology of design implemented and is suggested for preliminary ship design.

Evaluation of CTOD resistance curves in clamped SE(T) specimens with weld centerline cracks

“…Note that equation 2.16 calculates the 𝐶𝑇𝑂𝐷 at the position of the original crack tip. Sarzosa et al [71] discuss the effect of extending crack on the 𝐶𝑇𝑂𝐷. Plastic hinge models is another method to measure the CTOD which assumes a constant point at distance b*rp from crack tip at crack ligament around which the specimen rotates.…”

“…As expected, though, the m-value displays a more noticeable sensitivity on material properties, ranging from ~1.2 for the UNS N06625 girth weld to 1.4-1.5 for the X80 girth weld. For reference, this plot also includes the dependence of m on crack size over the range 0.2⩽a/W ≤ 0.7 obtained from equation 14 appearing in previous work of Sarzosa et al [71], hereafter referred to as SSR, with the strain hardening exponent for the weld metal material given in table 3.1. Relative to the results of SSR, which are applicable to stationary crack analyses of plane-sided specimens made of homogeneous material, the present set of m-values derived from the V-groove weld models is in generally good agreement.…”

“…While we have not explored the source of the small deviation between both CTOD resistance curves based on the DCG method, these results suggest a potential effect of key test parameters on the measured data. For example, the 3-D numerical model has a straight, through crack whereas the crack front of the tested fracture specimen not only exhibits a certain degree of curvature but the crack front is also rather nonuniform [137].…”