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- Multiobjective optimization for node adaptation in the analysis of composite plates using a meshless collocation methodPublication . Roque, C. M. C.; Madeira, JFA; Ferreira, A .J. M.The bending of simply supported composite plates is analyzed using a direct collocation meshless numerical method. In order to optimize node distribution the Direct MultiSearch (DMS) for multi-objective optimization method is applied. In addition, the method optimizes the shape parameter in radial basis functions. The optimization algorithm was able to find good solutions for a large variety of nodes distribution.
- Multiobjective optimization of cold-formed steel columnsPublication . Madeira, JFA; Dias, Joaquim; Silvestre, NunoThe optimal design of cold-formed steel columns is addressed in this paper, with two objectives: maximize the local-global buckling strength and maximize the distortional buckling strength. The design variables of the problem are the angles of orientation of cross-section wall elements the thickness and width of the steel sheet that forms the cross-section are fixed. The elastic local, distortional and global buckling loads are determined using Finite Strip Method (CUFSM) and the strength of cold-formed steel columns (with given length) is calculated using the Direct Strength Method (DSM). The bi-objective optimization problem is solved using the Direct MultiSearch (DMS) method, which does not use any derivatives of the objective functions. Trade-off Pareto optimal fronts are obtained separately for symmetric and anti-symmetric cross-section shapes. The results are analyzed and further discussed, and some interesting conclusions about the individual strengths (local-global and distortional) are found.
- Optimal distribution of active piezoelectric elements for noise attenuation in sandwich panelsPublication . Madeira, JFA; Araújo, A. L.In this paper, a multiobjective optimization approach for obtaining the optimal distribution of surface-bonded piezoelectric sensors and actuators for noise attenuation in sandwich panels is presented. The noise attenuation is achieved by using negative velocity feedback control with co-located sensors and actuators. The control gains are also optimized in order to obtain the most efficient noise attenuation in a given frequency band. An in-house implementation of a viscoelastic soft core sandwich plate finite element, including surface-bonded piezoelectric sensors and actuators with active control capabilities, is used for obtaining the frequency response of the panels. The sound transmission capability of the panels is evaluated using the radiated sound power, along with the Rayleigh integral approach, which is suitable for lightly coupled structural/acoustic problems. The Direct MultiSearch (DMS) optimization algorithm is used to minimize the added weight due to the piezoelectric material, minimizing also the number of required controllers and maximizing the noise attenuation. The total length of the radiated sound power curve is shown to be an effective measure of noise attenuation in a given frequency band. Trade-off Pareto fronts and the obtained optimal configurations are presented and discussed.
- Multi-objective optimization of pultruded composite sandwich panels for building floor rehabilitationPublication . Garrido, Mário; Madeira, JFA; Proença, M.; Correia, J. R.Composite sandwich panels are being increasingly considered for civil engineering structural applications, offering high versatility in constituent materials and their geometrical arrangement. This translates to a high number of design variables, in addition to a potentially large number of design requirements and objectives related to the panels' functions. This paper presents an optimization study of a composite sandwich panel system for building floor rehabilitation, using the Direct MultiSearch (DMS) method. Pultruded multicellular panels with a polyurethane (PUR) foam core and carbon- or glass-fibre reinforced polymer (C/GFRPF) faces and ribs/webs are considered. The panel architecture was defined using 3 geometrical variables and 14 material related variables. In addition, 8 competing objective functions were studied, related to aspects such as structural serviceability and resistance, thermal insulation, acoustic performance, cost minimization, and environmental performance. The results are presented in the form of Pareto optimal sets, from which several conclusions are drawn regarding common design-related options. The influence of core material density, of the number of ribs/webs, or of the type of fibre reinforcement and its respective layup on the different objective functions are addressed. Optimal solutions for meeting different design purposes are presented, providing useful insights for structural designers and sandwich panel manufacturers.
- Multiobjective design of viscoelastic laminated composite sandwich panelsPublication . Madeira, JFA; Araújo, A. L.; Mota Soares, C. M.; Mota Soares, C. A.; Ferreira, A. J. M.The optimal design of laminated sandwich panels with viscoelastic core is addressed in this paper, with the objective of simultaneously minimizing weight and material cost and maximizing modal damping. The design variables are the number of layers in the laminated sandwich panel, the layer constituent materials and orientation angles and the viscoelastic layer thickness. The problem is solved using the Direct MultiSearch (DMS) solver for multiobjective optimization problems which does not use any derivatives of the objective functions. A finite element model for sandwich plates with transversely compressible viscoelastic core and anisotropic laminated face layers is used. Trade-off Pareto optimal fronts are obtained and the results are analyzed and discussed.
- Design of a composite crash box for a Formula Student team car: preliminary testing and model tuningPublication . Santos, André Miguel Almeida; Araújo, Aurélio Lima; Madeira, JFA; Lopes, Hernâni Miguel ReisIn this work, preliminary studies towards the development of a structural carbon fibre nose for a Formula Student team car are presented. Numerical and experimental approaches have been considered to evaluate the impact behaviour of composite tubes. Then, finite element simulations are used to determine the crush stress by fitting the numerical results to the experimental data. The crush stress is also validated using quasi-static compression tests. The obtained results are compared and discussed in the framework of the future structural nose and crashbox design. The obtained results are compared and discussed in the framework of the future structural nose and crashbox design.
- Optimal multiobjective design of a vehicle restraint system using pre-acting control: A limiting performance analysisPublication . Moita, Paulo Jorge Pires; Madeira, Jose Firmino Aguilar; Valido, Aníbal; Cardoso, João BarradasPurpose – The purpose of this paper is to perform the limiting performance analysis of a vehicle restraint system (seat belt) in order to find the optimal control force, and its pre-acting time that minimizes the risk of injury. Design/methodology/approach – A discrete model of the human thorax is used. A multiobjective optimum design problem is formulated in order to minimize the risk of injuries in case of impact. Several injury criteria are minimized and are required to remain below a safety threshold value. Findings – The authors found which of the objectives are contradictory and which are not. Several of the optimal sets of design variables are analyzed and their performance compared to one another.The results are also compared to the case of not taking in account the pre-acting time. As expected,the results in this case are worse. Research limitations/implications – As with all limiting performance analysis, the technological implementation restraints of the control force are not taken into account. As such, the solutions must be considered a benchmark to which the actual solution can be compared to. Practical implications – The limiting performance analysis concept allows us to have a theoretical benchmark to which the real control performance can be compared to. Originality/value – As far as the authors know, the pre-acting time, and it simplications on the improvement of the performance of the control system, is an original contribution to the problem the authors tried to solve.
- Damping optimization of viscoelastic laminated sandwich structures using the direct multisearch methodPublication . J.F.A. Madeira; Araújo, A. L.; Soares, C. M. Mota; Soares, C. A. MotaA multiobjective approach for optimization of passive damping for vibration reduction in sandwich structures is presented in this paper. A layerwise finite element model for sandwich plates with viscoelastic core and anisotropic laminated face layers is used along with the complex modulus approach and the dynamic problem is solved in the frequency domain. Constrained optimization is conducted for maximisation of modal loss factors and minimisation of weight of sandwich beams and plates with elastic laminated constraining layers and a viscoelastic core, with layer thickness and laminate layer ply orientation angles as design variables. The problem is solved using the Direct MultiSearch (DMS) solver for derivative-free multiobjective optimization and solutions are compared with alternative ones obtained using genetic algorithms. DMS is a solver for multiobjective optimization problems which does not use any derivatives of the objective functions. It is based on a novel technique called direct multisearch, developed by extending direct search from single to multiobjective optimisation.
- Multiobjective topology optimization of structures using genetic algorithms with chromosome repairingPublication . Madeira, JFA; Rodrigues, H. C.; Pina, H.In this work, a genetic algorithm (GA) for multiobjective topology optimization of linear elastic structures is developed. Its purpose is to evolve an evenly distributed group of solutions to determine the optimum Pareto set for a given problem. The GA determines a set of solutions to be sorted by its domination properties and a filter is defined to retain the Pareto solutions. As an equality constraint on volume has to be enforced, all chromosomes used in the genetic GA must generate individuals with the same volume value; in the coding adopted, this means that they must preserve the same number of “ones” and, implicitly, the same number of “zeros” along the evolutionary process. It is thus necessary: (1) to define chromosomes satisfying this propriety and (2) to create corresponding crossover and mutation operators which preserve volume. Optimal solutions of each of the single-objective problems are introduced in the initial population to reduce computational effort and a repairing mechanism is developed to increase the number of admissible structures in the populations. Also, as the work of the external loads can be calculated independently for each individual, parallel processing was used in its evaluation. Numerical applications involving two and three objective functions in 2D and two objective functions in3Dare employed as tests for the computational model developed. Moreover, results obtained with and without chromosome repairing are compared.
- Volcano-tectonic evolution of a linear volcanic ridge (Pico-Faial Ridge, Azores Triple Junction) assessed by paleomagnetic studiesPublication . Silva, Pedro; Henry, Bernard; Marques, Fernando Ornelas; Hildenbrand, Anthony; Lopes, Ana; Madureira, Pedro Miguel; Madeira, JFA; Nunes, João C.; Roxerová, ZuzanaThe morphology of volcanic oceanic islands results from the interplay between constructive and destructive processes, and tectonics. In this study, the analysis of the paleomagnetic directions obtained on well-dated volcanic rocks is used as a tool to assess tilting related to tectonics and large-scale volcano instability along the Pico-Faial linear volcanic ridge (Azores Triple Junction, Central-North Atlantic). For this purpose, 530 specimens from 46 lava flows and one dyke from Pico and Faial islands were submitted to thermal and alternating magnetic fields demagnetizations. Detailed rock magnetic analyses, including thermomagnetic analyses and classical high magnetic field experiments revealed titanomagnetites with different Ti-content as the primary magnetic carrier, capable of recording stable remanent magnetizations. In both islands, the paleomagnetic analysis yields a Characteristic Remanent Magnetization, which presents island mean direction with normal and reversed polarities in agreement with the islands location and the age of the studied lava flows, indicating a primary thermo-remanent magnetization. Field observations and paleomagnetic data show that lava flows were emplaced on pre-existing slopes and were later affected by significant tilting. In Faial Island, magmatic inflation and normal faults making up an island-scale graben, can be responsible for the tilting. In Pico Island, inflation related to magma intrusion during flow emplacement can be at the origin of the inferred tilting, whereas gradual downward movement of the SE flank by slumping processes appears mostly translational.