A NUMERICAL ANALYSIS OF THE ELECTRICAL OUTPUT RESPONSE OF A NONLINEAR PIEZOELECTRIC OSCILLATOR SUBJECTED TO A HARMONIC AND RANDOM EXCITATION

The renewable energy is in the focus of many researches in the last decades, and the use of piezoelectric material can be used to obtain one source of this renewable energy. In this case, energy harvesting explores mainly the source of ambient motion and the piezoelectric material convert mechanical energy, present in the ambient motion, into electrical energy. In the work, we present a nonlinear bistable piezomagnetoelastic structure subjected to harmonic and random base excitation. At first, harmonic excitation is of concern and then, the system subjected to random excitation is analyzed. The goal of the numerical analysis is to present an investigation of the best electrical output response of the system given harmonic and random excitations

NONLINEAR DYNAMICS OF A VIBRATION-BASED ENERGY HARVESTING SYSTEM USING PIEZOELECTRIC AND SHAPE MEMORY ALLOY ELEMENTS

Energy harvesting is the conversion of available mechanical vibration energy into electrical energy that can be employed for different purposes. Several works have investigated the development of linear vibration energy harvesters that are efficient in a very narrow bandwidth around the fundamental resonance frequency. Nowadays, many researches have included different kinds of nonlinearities to expand the bandwidth of the energy harvesters. This paper deals with the use of smart materials for energy harvesting purposes. Basically, piezoelectric and shape memory elements are combined to build an energy harvesting system. The analysis is developed considering a one-degree of freedom mechanical system where the equation of motion is formulated by assuming the electromechanical coupling provided by a piezoelectric element and the restitution force provided by shape memory element described using a polynomial constitutive model. Numerical results indicate that the inclusion of the SMA element can dramatically change system dynamics, showing different kinds of responses including periodic and chaotic regimes

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Asymptotic homogenization model for 3D grid-reinforced composite structures with generally orthotropic reinforcements

The asymptotic homogenization method is used to develop a comprehensive micromechanical model pertaining to three-dimensional composite structures with an embedded periodic grid of generally orthotropic reinforcements. The model developed transforms the original boundary-value problem into a simpler one characterized by some effective elastic coefficients. These effective coefficients are shown to depend only on the geometric and material parameters of the unit cell and are free from the periodicity complications that characterize their original material counterparts. As a consequence they can be used to study a wide variety of boundary-value problems associated with the composite of a given microstructure. The developed model is applied to different examples of orthotropic composite structures with cubic, conical and diagonal reinforcement orientations. It is shown in these examples that the model allows for complete flexibility in designing a grid-reinforced composite structure with desirable elastic coefficients to conform to any engineering application by changing some material and/or geometric parameter of interest. It is also shown in this work that in the limiting particular case of 2D grid-reinforced structure with isotropic reinforcements our results converge to the earlier published results

Analytical and numerical analysis of 3D grid-reinforced orthotropic composite structures

A comprehensive micromechanical investigation of 3D periodic composite structures reinforced with a grid of orthotropic reinforcements is undertaken. Two different modeling techniques are presented; one is based on the asymptotic homogenization method and the other is a numerical model based on the finite element technique. The asymptotic homogenization model transforms the original boundary value problem into a simpler one characterized by effective coefficients which are shown to depend only on the geometric and material parameters of a periodicity cell. The model is applied to various 3D grid-reinforced structures with generally orthotropic constituent materials. Analytical formula for the effective elastic coefficients are derived, and it is shown that they converge to earlier published results in much simpler case of 2D grid reinforced structures with isotropic constituent materials. A finite element model is subsequently developed and used to examine the aforementioned periodic grid-reinforced orthotropic structures. The deformations from the finite element simulations are used to extract the elastic and shear moduli of the structures. The results of the asymptotic homogenization analysis are compared to those pertaining to their finite element counterparts and a very good agreement is shown between these two approaches. A comparison of the two modeling techniques readily reveals that the asymptotic homogenization model is appreciably faster in its implementation (without a significant loss of accuracy) and thus is readily amenable to preliminary design of a given 3D grid-reinforced composite structure. The finite element model however, is more accurate and predicts all of the effective elastic coefficients. Thus, the engineer facing a particular design application, could perform a preliminary design (selection of type, number and spatial orientation of the reinforcements) and then fine tune the final structure by using the finite element model

An adaptive fuzzy sliding mode controller applied to a chaotic pendulum

In this work, an intelligent controller is employed to the chaos control problem in a nonlinear pendulum. The adopted approach is based on the sliding mode control strategy and enhanced by an adaptive fuzzy algorithm to cope with modeling inaccuracies. The convergence properties of the closed-loop system are analytically proven using Lyapunov's direct method and Barbalat's lemma. Numerical results are also presented in order to demonstrate the control system performance

Nonlinear Dynamics and Chaos of a Nonsmooth Rotor-Stator System

Rotor systems have wide applications in industries, including aero engines, turbo generators, and gas turbines. Critical behaviors promoted by the system unbalance and the contact between rotor and stator lead to important nonlinearities on system dynamics. This paper investigates the complex behavior presented by a rotor-stator system’s dynamics due to intermittent contact. A four-degree-of-freedom Jeffcott nonsmooth rotor/stator system is used to describe the rotor behavior, while a viscoelastic suspended rigid cylinder represents the stator. Numerical simulations are carried out showing rich dynamics that include periodic, quasiperiodic, and chaotic responses. Special attention is dedicated to chaotic behavior and the calculation of Lyapunov exponents is employed as a diagnostic tool