Nonlinear vibrations of laminated and sandwich rectangular plates with free edges. Part 2: Experiments & comparisons

Large-amplitude (geometrically nonlinear) forced vibrations of completely free sandwich rectangular plates are investigated experimentally. Harmonic excitation is applied by using an electro-dynamic exciter and the plate vibration is measured by using laser Doppler vibrometers. A scanning laser Doppler vibrometer is used for experimental modal analysis since it provides non-contact vibration measurements with very high spatial resolution. The large-amplitude vibration experiments are carried out by using a single point laser Doppler vibrometer and a stepped-sine testing procedure. The nonlinear frequency response curves are obtained by increasing and decreasing the excitation frequency in very small steps at specific force amplitudes controlled in a closed-loop. The experimental results are compared to numerical simulations obtained by reduced-order models and show very good agreement. The nonlinear damping is experimentally obtained as a function of the vibration amplitude

Ocorrência de fungos em sementes de cevada produzidas em sistema irrigado por pivô central no cerrado brasileiro.

O objetivo desse trabalho foi determinar a ocorrência de fungos em sementes de cevada produzidas em sistema irrigado por pivô central na região do Distrito Federal e entorno.bitstream/item/38772/1/BP200418.pd

Damage detections in nonlinear vibrating thermally loaded plates

In this work, geometrically nonlinear vibrations of fully clamped rectangular plates subjected to thermal changesare used to study the sensitivity of some vibration response parameters to the presence of damage and elevated temperature. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour.Damage is represented as a stiffness reduction in a small area of the plate. The plates are subjected to harmonicloading leading to large amplitude vibrations and temperature changes. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the heated and the unheated plates and the change in the time-history diagrams and the Poincaré maps caused by damage and elevated temperature. The damage criterion formulated earlier for nonheated plates, based on analyzing the points in the Poincaré sections of the damaged and healthy plate, is modified and tested for the case of plates additionally subjected to elevated temperatures. The importance of taking into account the actual temperature in the process of damage detection is shown

Nonlinear Dynamics of Human Aortas for Material Characterization

Evaluating the nonlinear dynamics of human descending thoracic aortas is essential for building the next generation of vascular prostheses. This study characterizes the nonlinear dynamics, viscoelastic material properties, and fluid-structure interaction of 11 ex-vivo human descending thoracic aortas the full range of physiological heart rates. The aortic segments are harvested from heart-beating donors screened for transplants. A mock circulatory loop is developed to reproduce physiological pulsatile pressure and flow. The results show cyclic axisymmetric diameter changes, which are satisfactorily compared to in-vivo measurements at a resting pulse rate of 60 bpm, with an additional bending vibration. An increase of the dynamic stiffness (i.e., storage modulus) with age is also observed. This increase is accompanied by a strong reduction with age of the cyclic diameter change during the heart pulsation at 60 bpm and by a significant reduction of the loss factor (i.e., damping). Large dissipation is observed at higher pulse rates due to the combined effects of fluid-structure interaction and viscoelasticity of the aortic wall. This study presents data necessary for developing innovative grafts that better mimic the dynamics of the aorta

Improving Provenance Data Interaction for Visual Storytelling in Medical Imaging Data Exploration

Effective collaborative work in diagnostic medical imaging is not trivial due to the large amounts of complex data involved,a (non-linear) workflow involving experts in different domains, and a lack of versatility in the current tools employed inhealthcare. In this paper, we aim to introduce how the integration of visual storytelling techniques together with provenancedata in the analytic systems used in medicine can compensate for these issues, by enhancing communication of results andreproducibility of findings through diagnostic provenance data. To this end, we illustrate how we can improve the interactionwith provenance data displayed in a graph in order to facilitate authoring and the creation process of visual data storie

NONLINEAR VIBRATIONS OF FLUID-FILLED VISCOELASTIC CYLINDRICAL SHELLS

In this work the non-linear vibrations of a simply supported viscoelastic fluid-filled circular cylindrical shells subjected to lateral harmonic load is studied. Donnell's non-linear shallow shell theory is used to model the shell, assumed to be made of a Kelvin-Voigt material type, and a modal solution with six degrees of freedom is used to describe the lateral displacements. The Galerkin method is applied to derive a set of coupled non-linear ordinary differential equations of motion. The influence of shell geometry, flow velocity and dissipation parameter are studied and special attention is given to resonance curves. Obtained results show that the viscoelastic dissipation parameter, flow velocity and geometry have significant influence on the nonlinear behavior of the shells as displayed in instability loads and resonance curves