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Branch And Bound Mixed Nonlinear Optimization For The GRP Structure Of Galápagos Interisland Small Craft

Published in: Prospective and trends in technology and skills for sustainable social development. Leveraging emerging technologies to construct the future: Proceedings of the 19th LACCEI International Multi-Conference for Engineering, Education and Technology
Date of Conference: July 19-23, 2021
Location of Conference: Virtual
Authors: José R. Marín López (Escuela Superior Politécnica del Litoral, EC)
José M. Rodríguez (Escuela Superior Politécnica del Litoral, EC)
Miguel A. Onofre (Escuela Superior Politécnica del Litoral, EC)
Cesar H. Venegas (Escuela Superior Politécnica del Litoral, EC)
Full Paper: #474

Abstract:

The interisland transportation of passengers in Galápagos Archipelago is mainly carried out in high speed boats manufactured using Fiberglass Reinforced Plastic (GRP). The design of these boats does not commonly follow the application of construction standards and therefore there is the possibility that their structure is being oversized. In addition, these boats navigate at high speeds and therefore it is advisable to investigate ways to reduce its weight. In this work, the structure of the central module of a 12-meter-long small craft traveling at 25 knots is optimized. Mixed Integer Nonlinear Programming (MINLP) is used for the optimization process, since in the structural design there are integer and real variables. These mixed problems can be solved applying the Branching and Bounding algorithm (BB). Due to the combination of variables, the Gekko optimization library, capable of solving MINLP problems through Python programming language, is used. The process is divided into two phases, the first one optimizes the number of stiffeners and the laminate of the plates; the second one optimizes the dimensions and laminate of the stiffeners. Applied constraints correspond to the requirements of the ISO 12215 standard: flexural strength of plates and stiffeners, inter-laminar resistance to shear of plates, stiffness of stiffeners, and resistance to buckling of the web and flange of reinforcements. As a result of the structural optimization, the structural weight was reduced by 24%. Finally, the results of the optimization process are evaluated using the finite element method, to compare the current and the optimized section. The structure is modelled with plane elements with composite laminate type material; end cross sections are considered as clamped. The load is applied with a half wave distribution in the transversal direction, centered at quarter beam, and, at centreline of the bottom. It is verified that in the current design there is oversizing and that, in the case of the optimized section, stress levels do not exceed the permissible values.