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Letícia Fleck Fadel Miguel,Otávio Augusto Peter de Souza 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.86 No.5
It is recognized that the installation of energy dissipation devices, such as the tuned mass damper (TMD), decreases the dynamic response of structures, however, the best parameters of each device persist hard to determine. Unlike many works that perform only a deterministic optimization, this work proposes a complete methodology to minimize the dynamic response of footbridges by optimizing the parameters of multiple tuned mass dampers (MTMD) taking into account uncertainties present in the parameters of the structure and also of the human excitation. For application purposes, a steel footbridge, based on a real structure, is studied. Three different scenarios for the MTMD are simulated. The proposed robust optimization problem is solved via the Circle-Inspired Optimization Algorithm (CIOA), a novel and efficient metaheuristic algorithm recently developed by the authors. The objective function is to minimize the mean maximum vertical displacement of the footbridge, whereas the design variables are the stiffness and damping constants of the MTMD. The results showed the excellent capacity of the proposed methodology, reducing the mean maximum vertical displacement by more than 36% and in a computational time about 9% less than using a classical genetic algorithm. The results obtained by the proposed methodology are also compared with results obtained through traditional TMD design methods, showing again the best performance of the proposed optimization method. Finally, an analysis of the maximum vertical acceleration showed a reduction of more than 91% for the three scenarios, leading the footbridge to acceleration values below the recommended comfort limits. Hence, the proposed methodology could be employed to optimize MTMD, improving the design of footbridges.
A controllability-based formulation for the topology optimization of smart structures
Juliano F. Gonçalves,Jun S.O. Fonseca,Otávio A.A. Silveira 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.17 No.5
This work presents a methodology to distribute piezoelectric material for structural vibration active control. The objective is to design controlled structures with actuators which maximizes the system controllability. A topology optimization was formulated in order to distribute two material phases in the domain: a passive linear elastic material and an active linear piezoelectric material. The objective is the maximization of the smallest eigenvalue of the system controllability Gramian. Analytical sensitivities for the finite element model are derived for the objective functions and constraints. Results and comparisons with previous works are presented for the vibration control of a two-dimensional short beam.
Cristiane Urcina Joanna Oliveira Lima,Cláudio Olavo de Almeida Cordova,Otávio de Tolêdo Nóbrega,Silvana Schwerz Funghetto,Margô Gomes de Oliveira Karnikowski 한국식품영양과학회 2011 Journal of medicinal food Vol.14 No.1
There has been a significant increase in the use of mushrooms for therapeutic and medicinal purposes, in particular, use of the species Agaricus blazei Murrill, a basidiomycota of Brazilian origin. The objective of this study was to identify scientific evidence regarding the influence of A. blazei Murrill on the immune system. We undertook an integrative review of indexed publications published between 2000 and 2009, using the following question as a guideline: “What evidence can be found in the literature regarding the influence of A. blazei Murrill on the immune system?” Fourteen studies verified that there is in vitro and in vivo research demonstrating this mushroom's influence on the immune system. All research was characterized as evidence level 7 (preclinical study [animals/in vitro]). The research shows that A. blazei Murrill functions through bioactive compounds via mechanisms that are not yet entirely clear, although it has been shown that they promote action on the innate and adaptive immunological response, activation of the complement system, and synthesis of pro- and anti-inflammatory cytokines and even aid in diapedesis. Despite broad scientific evidence demonstrating relevant immunomodulatory properties of A. blazei Murrill, randomized clinical trials with human subjects are still needed in order for the mushroom to be put into clinical practice.
André Santos Barros,Igor Alexsander Magno,Fabrício Andrade Souza,Carlos Alberto Mota,Antonio Luciano Moreira,Maria Adrina Silva,Otávio Lima Rocha 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.3
In this work, the effect of the growth rate (VL) and cooling rate (TR), primary dendritic arm spacing (1) and Al2Cu intermetallic phase on the microhardness was investigated during transient horizontal directional solidification of Al-3wt%Cu and Al-8wt%Cu alloys. Microstructural characterization of the investigated alloys was performed using traditional techniques of metallography, optical and SEM microscopy and X-Ray diffraction. The microhardness evolution as a function of the thermal and microstructural parameters (VL, TR, and 1) was evaluated using power and Hall-Petch type experimental laws, which were compared with other laws in the literature. In order to examine the effect of the Al2Cu intermetallic phase, microhardness measurements were performed in interdendritic regions. Finally, a comparative analysis was performed between the experimental data of this work and theoretical models from the literature that have been proposed to predict primary dendrite arm spacing, which have been tested in numerous works considering upward directional solidification.
Carolina R. Barbosa,Gabriel H. Machado,Hugo M. Azevedo,Fernando S. Rocha,José C. Filho,Arielly A. Pereira,Otávio L. Rocha 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.3
In this work, solidification and T6-heat treatment experiments were performed with the Al7Si0.3Mg alloy in order to investigatethe effect of processes parameters on the microstructure and microhardness (HV). A directional solidification devicewas used, and the solidification thermal parameters investigated were the growth and cooling rates (VL and TR). The heattreatment applied was the T6 (T6-HT), under the following conditions: solution treatment for 3 h at 520 ± 2 °C, followed byquenching in warm water (70 ± 20 °C), aging for 1, 2, 3 and 4 h at 155 ± 2 °C and air-cooling. The microstructure observedin both as-cast and T6-heat treated samples is composed of a primary phase consisting of an Al-rich dendritic network andsecondary eutectic phases, located within the interdendritic regions, formed by Si and Mg2Siparticles and Fe-intermetallicphases. The dendritic microstructure was characterized by secondary dendritic spacing (λ2) and, for both investigated samples,a single mathematical expression was proposed on the λ2 dependence with the position in the ingot. Spheroidized-likeeutectic Si particles have been found in both analyzed samples for finer microstructures. Elements quantitative and qualitativemicroanalysis by SEM/EDS as well as HV measurement at the dendritic and interdendritic regions attest to the effectivenessof the T6-heat treatment. It is highlighted in this work that mathematical expressions have been proposed to characterizethe HV dependence on aging time.
Fabricio A. Souza,Igor A. Magno,Marlo O. Costa,André S. Barros,Jacson M. Nascimento,Diego B. Carvalho,Otávio L. Rocha 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.1
Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance,high thermal and electrical conductivities, good combination of mechanical properties, good workability in machiningprocesses and mechanical forming. Currently, these alloys are produced in various systems and dozens of compositions. Inthis investigation, a mutual interaction of thermal parameters, scale of the dendritic microstructure, intermetallic compounds(IMCs), microhardness and tensile properties/fracture characteristics of a casting Al–7wt%Si–3wt%Cu–0.3wt%Fe alloywas analyzed. Solidification experiments were developed using a furnace that promoted horizontal growth under transientheat flow conditions. Then, growth rate (VL), cooling rate (CR), and local solidification time (tSL) were determined frommeasured temperature profiles. Secondary dendritic spacings (λ2), Si particles, Fe-rich and Al2Cuintermetallic phases werecharacterized by optical and SEM microscopy, as well as the area mapping and point-wise EDS microanalysis. Hence, theinterrelations involving Vickers microhardness (HV), yield strength (σYS), ultimate tensile strength (σUTS) and elongation(E%) with microstructural features were evaluated by mathematical equations. IMCs as well as morphologies of Si were alsoanalyzed in the fracture regions. In addition, the experimental growth law of λ2 = f(tSL) proposed in this study was comparedwith a predictive theoretical model reported in the literature for multicomponent alloys. It was observed that areas that tendto grow faster (lowest λ2 values) were associated with the highest σUTS and E% values, while HV and σYS properties were notaffected by the thermal and microstructural parameters (CR and λ2). In addition, less extensive cleavage planes accompaniedby small dimples in were observed in fractured samples with lower λ2 values.