Francisco de Assis das Neves

A Modulation Technique to Reduce Switching Losses in Matrix Converters

This paper presents a modulation technique based on the generalized pulsewidth-modulation strategy for matrix converters. The proposed technique uses a discontinuous modulation to clamp each output leg of the converter during 120deg of the output voltage period, achieving a reduced number of switchings compared with the traditional modulation techniques. Aside from that, the major attraction of the proposed technique is an additional algorithm that lags the clamping of each output leg of the converter to synchronize it with the peak of the corresponding output current (load current), avoiding high switching losses (switching at high currents). Therefore, this technique reduces the number of switchings as well as guarantees only medium and low current switchings. Simulation and experimental results show the efficiency of the proposed technique.

Multi-objective metaheuristic algorithms for the resource-constrained project scheduling problem with precedence relations

This study addresses the resource-constrained project scheduling problem with precedence relations, and aims at minimizing two criteria: the makespan and the total weighted start time of the activities. To solve the problem, five multi-objective metaheuristic algorithms are analyzed, based on Multi-objective GRASP (MOG), Multi-objective Variable Neighborhood Search (MOVNS) and Pareto Iterated Local Search (PILS) methods. The proposed algorithms use strategies based on the concept of Pareto Dominance to search for solutions and determine the set of non-dominated solutions. The solutions obtained by the algorithms, from a set of instances adapted from the literature, are compared using four multi-objective performance measures: distance metrics, hypervolume indicator, epsilon metric and error ratio. The computational tests have indicated an algorithm based on MOVNS as the most efficient one, compared to the distance metrics; also, a combined feature of MOG and MOVNS appears to be superior compared to the hypervolume and epsilon metrics and one based on PILS compared to the error ratio. Statistical experiments have shown a significant difference between some proposed algorithms compared to the distance metrics, epsilon metric and error ratio. However, significant difference between the proposed algorithms with respect to hypervolume indicator was not observed.

Confiabilidade estrutural utilizando o método de Monte Carlo e redes neurais.

Structural reliability analysis due to the great number of random variables or large number of simulations needed may result in a high computational cost. Two techniques largely used for structural reliability assess are Monte Carlo Simulation and the analytic methods FORM/SORM. These may present some inaccuracy in the assessment of the probability of failure. The Monte Carlo Method is easy to implement and absolutely general, but the great number of required simulations may result in high computational cost making the application impracticable. This work used a trained neural network to substitute the structural analysis needed for each Monte Carlo Simulation, in order to reduce the computational cost. The applications produced good results with low computational cost, certifying its application viability.

Acoustical vibration characterics of prefabricated panels employed in industrialized construction

With the development of industrialized steel construction, new constructive elements have been brought not only to the market, but to the everyday construction site as well and, in this way professionals and users have questioned their efficiency. In respect to vibrations in floors, what can be detected is that floor structures are thinner and a decrease of the mass in the horizontal closing panels and the utilization of new materials and systems have led them to have lower natural frequencies, and so are nearer to the frequencies produced by walking. This decrease of mass of the closing panels also lead to a considerable weakness in terms of acoustical insulation, which can cause unfavorable conditions and discomfort. Thus, it becomes necessary to do detailed studies of the efficiency of the vibration and acoustical performance of the new systems to obtain the characterization and the qualification parameters in order to optimize their use. This study does a comparative evaluation of some kinds of horizontal and vertical closing systems in respect to the vibrational and acoustical insulation performance.

Conforto humano e limites de percepção para vibrações verticais

This work presents a study on vibration levels in connection with human comfort and perception. The main objective here was to experimentally generate human-comfort and perception curves as a function of vertical sinusoidal vibrations. Thirty volunteers (15 men and 15 women) and a frequency range varying from 12 to 80 Hz were considered in the experiments. The goal of the first experiment was to determine the vibration-perception limits. Also measured was the uncertainty interval of the analysis. The second experiment was related to the determination of the relation between the perception and comfort limit, taking into account residential areas. The effects of posture on the results are also investigated. No significant differences were found between the results for men and women. Furthermore, the perception limit for seated persons is in accordance with the ISO 2631/2 (1989). On the other hand, significant differences were found for the standing posture. The results for the human-comfort limit in residential areas are found to be 2 to 4 times greater than the experimentally measured perception limit.

On the Nonlinear Transient Analysis of Planar Steel Frames with Semi-Rigid Connections: From Fundamentals to Algorithms and Numerical Studies

This paper presents the fundamentals for prediction of a more realistic behavior of planar steel frames with semi-rigid connections under dynamic loading. The majority of the research in this area concentrates on the nonlinear static analysis of frames with semi-rigid connections. Indeed, few studies have contributed to the nonlinear dynamic and vibration analyses of frames. Therefore, this article first describes the frames’ semi-rigid connection behavior under monotonic and cyclic loads, and presents the independent hardening technique adopted to simulate the joint behavior under cyclic excitation. In a finite element context, this paper presents an efficient numerical methodology that is proposed in algorithmic form to obtain the nonlinear transient response of the structural system. The paper also presents, in algorithmic form, a complete description of the adopted connection hysteretic model. Satisfying the equilibrium and compatibility conditions, and assuming only the connection’s rotational deformation due to bending as variable, this work obtains the tangent stiffness and mass matrices of the beam-column element with semi-rigid connections at the ends. The study concludes by verifying and validating the proposed numerical approach using four structural steel systems: a L-frame, a two-story frame, a six-story frame, and a four-bay five-story frame. The analyses show that the hysteresis of the semi-rigid connection has a strong effect on the frames’ responses and is an important source of damping during the structural vibration.

PARAMETRIC MODAL DYNAMIC ANALYSIS OF STEEL-CONCRETE COMPOSITE BEAMS WITH DEFORMABLE SHEAR CONNECTION

COMPOSITE STRUCTURAL ELEMENTS OF STEEL-CONCRETE BEGAN TO BE USED ONLY IN 1960 AFTER THE DEVELOPMENT OF METHODS AND CONSTRUCTIVE DISPOSITIONS THAT ENSURED THE FUNCTIONALITY OF THESE TWO MATERIALS TOGETHER. IN ORDER TO VERIFY THE IMPORTANCE OF THE PARTICIPATION OF THE AXIAL MODE IN THE FREQUENCY SPECTRUM OF THE FREE VIBRATION PROBLEM IN COMPOSITE BEAMS WITH DEFORMABLE SHEAR CONNECTION, SEVERAL ANALYSES FOR 4 DIFFERENT BOUNDARY CONDITIONS AND STIFFNESS CONNECTION VARIATION WERE PERFORMED. THE ANALYSIS OF THE PROBLEM WAS CARRIED OUT BY DEVELOPMENT AND COMPUTATIONAL IMPLEMENTATION OF A FINITE ELEMENT FOR COMPOSITE BEAMS WITH PARTIAL INTERACTION IN THE LONGITUDINAL DIRECTION AP-PLIED TO THE PROBLEM OF FREE VIBRATIONS. THE SOLUTIONS TO THIS PROBLEM IN THE LITERATURE ARE SCARCE, AND PROJECT RECOMMENDA-TIONS ARE SIMPLIFIED. THE RESULTS SHOW THAT THE FINITE ELEMENT EXHIBITS AN EXCELLENT PERFORMANCE COMPARED WITH THE ANALYTICAL RESULTS AND AS THE AXIAL MODE HAS A HIGH MODAL CONTRIBUTION, DESPITE THE BOUNDARY CONDITION AND STIFFNESS CONNECTION.

Avaliação da integridade estrutural da Ponte Marechal Hermes - rio São Francisco/MG

Its known that the degradation, which occurs in steel bridge structures, is a worldwide problem. This happens for several reasons such as the bridges advanced age, the increase of the traffic weight, environmental attacks and, sometimes, because of designs, inadequate detailment and construction of structures. In order to solve these problems, different procedures in inspection of bridges have been used in different countries. In Brazil, however, it seems there is not any concern about keeping the integrity of the structures, not being commonly used proper procedures such as inspections and maintenance of the structures that can affect its safety, causing the need of more severe and expensive repairs. This research intends to make a diagnosis and propose solutions, which aim for the least occurrence of the corrosion developed by Marechal Hermes Bridge (Sao Francisco River). Therefore visits were made in locus, in which visual inspection, screen and photo registers, the information necessary for the analysis, were collected. Some samples were also collected and than, chemical, mechanical and metalographic characterizations were made on the steel used on the bridge, besides the analysis of the corrosion. The numerical modeling was made by using the finite element method, which aimed to analyze the structural behavior of the bridge with or without damages made by corrosion in these areas. There were made tests with salt spray in different systems of painting which aims to identify the best procedure of covering in order to protect the bridge. It was verified that the use of etil silicate of zinc, with primer epoxy-amide, rich in zinc and aliphatic varnish polyurethane was the one which presented the best performance.

Mapeamento de problemas na construção industrializada em aço

Taking into consideration the greater demand of the pre-manufactured steel construction, new types of constructive elements have been often introduced in the national market and, as a consequence, users and professionals have questioned its performance levels. Moreover, its viability in the Brazilian industry is directly linked on its successful association to insulation systems. Therefore, the general performance criteria achieved by the final construction is significantly influenced by degree of association reached between both systems, in such a way that all the other construction complementary stages must be adapted to both systems mentioned. In accordance with these explanations, the goal here is to make a survey of the real problems that have appeared when the steel structures are combined with insulation panels, as well as to characterize the design and execution processes of civil construction carried out commonly in Brazil. Finally, it is worth mention that the main aspects are relating to the problems detected in prefabricated steel buildings and their solutions, in such a way their development can become in a real and viable solution in the scene of the national civil construction.