The procedure proposed and examined in this paper for diagnosis of possible damage in aged large concrete dams can be outlined as follows. Zone-wise uniform Young’s moduli of concrete are ...traditionally the parameters to identify as representative of structural damage due to past physico-chemical processes or/and extreme loads. Change of reservoir level with annual periodicity in plant service is considered as inexpensive significant external action for nondestructive diagnostic experiments. Many displacements, concomitant with the transition from highest to lowest level, are measured on the downstream surface of the dam by radar instruments, which at present are promising innovations in dam engineering. Clearly nonnegligible contributions to measurable displacements due to seasonal thermal effects are taken into account by temperature measurements at time intervals through thermometers inside the dam, identification by them of parameters governing simplified thermal boundary conditions, time-dependence expressed by truncated Fourier series over a one-year period. Finally, damage diagnosis is carried out by minimization, with respect to the sought Young’s moduli, of a batch discrepancy function between measured and computed displacements, as inverse analysis in a linear thermoelasticity context. The proposed method is computationally validated also through its stochastic extension.
In this paper a complete multiphysics modelling via the finite element method (FEM) of an air-coupled array of piezoelectric micromachined ultrasonic transducers (PMUT) and its experimental ...validation are presented. Two numerical models are described for the single transducer, axisymmetric and 3D, with the following features: the presence of fabrication induced residual stresses, which determine a non-linear initial deformed configuration of the diaphragm and a substantial fundamental mode frequency shift; the multiple coupling between different physics, namely electro-mechanical coupling for the piezo-electric model, thermo-acoustic-structural interaction and thermo-acoustic-pressure interaction for the waves propagation in the surrounding fluid. The model for the single transducer is enhanced considering the full set of PMUTs belonging to the silicon dye in a 4×4 array configuration. The results of the numerical multiphysics models are compared with experimental ones in terms of the initial static pre-deflection, of the diaphragm central point spectrum and of the sound intensity at 3.5 cm on the vertical direction along the axis of the diaphragm.
•Short-range effects across small gaps in a high-aspect-ratio electrostatic-capacitive MEMS device are investigated.•The influence of surface separations and residual potential on MEMS behaviour ...including electrostatic pull-in are studied.•Comprehensive electro‑mechanical models for both static and dynamic regimes are developed and validated.•An extensive experimental characterization of the MEMS device is reported.•The extraction of mechanical and electrical parameters from the experimental data using the model is presented.
As the typical surface separations in Micro Electro-Mechanical Systems (MEMS) are reduced to below one micrometer, detailed knowledge of the interaction forces down to this scale is required. In this context, we have developed a dedicated experimental platform to directly investigate electrostatic and physical effects in a high-aspect-ratio electrostatic-capacitive MEMS device based on commercial technology. In the present work, we report on an extensive experimental characterization, focused on the influence of the surface separations, electric surface potentials, and pressure on the static and dynamical behaviour of the device under precisely controlled conditions. For the proper analysis of the bias position and small‑displacement response of the device, we have developed a comprehensive electro‑mechanical model capable of describing the aforementioned effects, and allowing to extract the mechanical and electrical device parameters from the experimental data. Based on the developed model, a strong experimental evidence is found for significant variations in device characteristics upon reduction of surface separation to below one micrometer.
This paper investigates the evolution of adhesion forces during dynamic contacts, which simulate realistic shocks. The developed method accounts for the differences in offset, resonance, and quality ...factor among the devices under test to precisely predict (and monitor) the kinetic impact energy during shocks. The results clearly show that adhesion force grows and stabilizes at an increasing amplitude with the applied impact energy. This dynamic adhesion is also dependent on the contact area, while the native adhesion on the same specimens was independent of it. Finally, a relaxation of the adhesion force with a very long time constant is observed after the end of the tests.
The safety assessment of structures by the maximization of a load factor up to a critical threshold is considered in this paper and a procedure is developed which generalizes limit analysis by the ...static approach. The following issues are dealt with: (a) piecewise linear approximation of material models is adopted as a unifying framework; (b) a procedure is developed apt to reduce the computing effort by means of yield mode selection or “sifting”; (c) a method which combines limit and deformation analysis is presented, based on mathematical optimization under linear and complementarity constraints and apt to compute, also in the presence of nonassociativity and softening, the safety factor with respect to either plastic collapse or local fracture or unserviceability because of excessive deformations, alternatively. Classical limit analysis rooted in associative perfect plasticity has well-known limitations, which are substantially mitigated in its generalization represented by method (c) proposed herein.
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