Webinars

“Dynamics of programmable and multifunctional piezoelectric metamaterials and metastructures”

Speaker: Alper Erturk (Georgia Institute of Technology, EUA)

Abstract: This talk reviews our efforts on the development of piezoelectric metamaterials to enable programmable and multifunctional concepts in next-generation smart structures. First, we summarize the theoretical and experimental work on passive metamaterials and phononic crystals for the problems of locally resonant bandgap formation and Lamb wave guiding, respectively, with applications to low-frequency vibration attenuation and enhanced energy harvesting. Then, the fully coupled problem of 1D and 2D piezoelectric metamaterials is discussed with a focus on electromechanical bandgap formation via inductive shunted unit cells. Specifically, finite piezoelectric beam and plate type structures with specified boundary conditions (i.e. metamaterial-based finite metastructures) are considered to quantify the effects of various system parameters. Piezoelectric bandgap tailoring and bandwidth enhancement, as well as formation of multiple bandgaps, are discussed. Synthetic impedance circuit representation of the unit cell shunts is then presented, along with experimental validations, to enable negative capacitance shunts combined with inductive loading. Such digitally programmable transfer functions in shunt circuits of piezoelectric metamaterials paves the way for next generation smart structures with on-demand, tunable bandgap formation capabilities. With this approach, the problem is then extended to spatial and temporal modulation of shunt capacitance and inductance for nonreciprocal wave propagation to achieve elastic wave diode behavior. Further examples of programmable piezoelectric metamaterials are given for spatially reversible elastic wave mode conversion (Rayleigh wave to shear wave) and gradient/graded concepts such as elastic wave rainbow and black hole devices as well as multifunctional counterparts that combine vibration attenuation and energy harvesting.

Mediator: José Roberto de França Arruda (Unicamp, Brazil)

“On the Lagrange’s equation for variable mass systems”

Speaker: Celso P. Pesce (USP, Brazil)

Abstract: This webinar brings a summary of the analytical dynamics of mechanical systems with mass varying
with time and position. The extended Lagrange’s equations for such systems are readdressed and simpler forms
are de-rived. Examples are given for nonlinear oscillators with variable mass and a one-degree of freedom
model of an oscillating water column driven by free surface waves is discussed.

Mediator: Paulo J. Paupitz Gonçalves (UNESP, Brazil)

“Impacts of model reduction and dynamic matrices extraction applied to rotating machines”

Speaker: Katia Lucchesi Cavalca (Unicamp, Brazil)

Abstract: Model reduction is a relevant subject within the field of rotor dynamics since low order models are fundamental for control strategies design and implementation, health monitoring, behavior prediction, Fault Detection and Identification (FDI) and stochastic analyses. In this context, this talk proposes a review of three widely used reduction methods: static or Guyan technique, the System Equivalent Reduction Expansion Process (SEREP) and the modified SEREP. Regarding SEREP, a new approach is presented in which right and left eigenvectors from the undamped original system (with mass and stiffness matrices not symmetric) are used to transform all original system dynamic matrices. To modified SEREP (that contemplates all original system characteristics, including frequency dependent damping and gyroscopic effect) an extraction from the reduced state-space representation is achieved to build rotor and bearings reduced dynamic matrices with physical interpretability. A set of practical recommendations is presented and discussed, highlighting key aspects to increase reduction success chances. The methods are applied to two different rotors and the results are properly shown regarding the agreement between reduced and complete model responses when analyzing Frequency Response Functions (FRFs) and Campbell diagrams. The computational costs of processing each reduced model and running common rotor dynamic analyses with reduced and complete models are also compared and discussed.

Mediator: Ilmar Santos (DTU, Denmark)

“Mathematical models to predict the spread of an epidemic”

Speaker: Americo Barbosa da Cunha Junior (UERJ, Brazil)
Abstract: Infectious diseases are a historic reality, with violent epidemics affecting people’s lives from time to time. In an epidemic, so that public managers and health professionals can better respond to the demands of the affected population, it is necessary to obtain a detailed understanding of the underlying mechanism of spread of the infectious disease. Mathematical models are a fundamental tool in this context, as they are able to provide rational explanations for the spread of the disease and, consequently, predict the intensity of its progress and test the effectiveness of different control strategies. In the context of the COVID epidemic19, these models can be used as decision aid tools, guiding public agents on how to respond optimally to the challenges imposed on civil society by the advancement of the new corona virus. In this presentation we will expose some of the fundamentals of mathematical modeling in epidemics, indicating possible approaches, the respective domains of applicability and limitations, as well as their use to guide decision making.

“Data-driven modeling for COVID-19 pandemics in Brazil”

Speaker: Silvio da Costa Ferreira Junior (UFV, Brazil)

Abstract: Mathematical and computational modelling constitutes a powerful tool for drawing hypothetical

Mediator: Marcelo Amorim Savi (COPPE/UFRJ, Brazil)

Tema: Passive Vibration Control
Abstract: This short course is devoted to techniques intended for passive vibration control, understood as those which do not require direct input of energy to counteract vibration excitations. After the presentation of the general principles underlying vibration control, along with practical needs and constraints, three control techniques are addressed, namely those based on dynamic vibration absorbers, viscoelastic materials and shunted piezoelectric transducers. For each of them, the underlying formulation, modelling strategies and experimental investigations are presented.
Professor: Domingos Rade (ITA, Brasil)
Dias: 24 Fev. at 8 – 10hs
25 Fev. at 8 – 12hs

Tema: Dinâmica e Vibrações
Abstract: The short course, which will be presented in the Portuguese language is aimed at young students and researchers that are interested in techniques of modelling and simulation of dynamic systems. Analysis of vibrating dynamic systems, in particular, will be presented with examples of application of such knowledge

Professor: Paulo Roberto Gardel Kurka (Unicamp, Brasil)
Dias: 24 Fev. at 16 – 18hs
25 Fev. at 14 – 18hs