Computational analysis of the collapse behaviour of thin-walled polygonal steel beams

The present paper is focused on the development of an accurate computational method, based on the Finite Element (FE) approximation, for predicting the collapse behavior of thin-walled polygonal steel beams subject to bending. The numerical model has been created using the software ABAQUS, and has been validated with experimental data obtained from the literature, concerning rectangular hollow section (RHS) in the four-point-bending situation. The model has been improved by means of a thorough study of material hardening, imperfections and residual stresses. The computational results of the analyses have been compared with the design procedures provided by Eurocode 3 (effective cross-section method and reduced stress method), in order to check their suitability

Flutter analysis of piezoelectric beams in MEMS

Micro-electro-mechanical systems (MEMS) represent a huge class of devices characterized by the smart coupling between electronics and mechanics, in order to obtain microscopic sensors and actuators. The use of piezoelectric materials in MEMS is steadily increasing, considering both the “direct effect”, e.g. in energy harvesters, and the “indirect effect”, for the cases of resonators, micropumps and other actuators. This paper is devoted to the study of piezoelectric laminate beams in the presence of aeroelastic effects due to the interaction of the structure with a fluid flow, as it may happen if the MEMS is embedded in a fluidic system. More specifically, the analytical conditions for the onset of flutter instability are studied, with the purpose of providing a sound basis for further studies focused on energy harvesting from fluid flows

Stability of dynamic response of suspension bridges

The potential occurrence of internal parametric resonance phenomena has been recently indicated as a potential contributory cause of the appearance of critical dynamic states in long-span suspension bridges. At the same time, suspension bridges, in view of their flexibility, are prone to aeroelastic response, such as vortex shedding, torsional divergence and flutter. In this paper, a non-linear dynamic model of a suspension bridge is devised, with the purpose of providing a first attempt toward a unified framework for the study of aeroelastic and internal resonance instabilities. Inspired by the pioneering work of Herrmann and Hauger, the analyses have been based on a linearized formulation that is able to represent the main structural non-linear effects and the coupling given by aerodynamic forces. The results confirm that the interaction between aeroelastic effects and non-linear internal resonance leads to unstable conditions for wind speeds which can be lower than the critical threshold for standard aeroelastic predictions

Seismic assessment of an unconventional structure: The cryostat of "Cuore" experiment

This paper deals with the seismic assessment of a complex structure supporting the CUORE experiment (Cryogenic Underground Observatory for Rare Events). The main issues, that require a special computational treatment, are: (i) non-linear geometric behavior of the suspended vessels; (ii) multiple contacts between the nested vessels and between the cryostat and the external shields; (iii) non-linear constitutive law of the HDR bearings. The problem has been tackled by building a 3D detailed finite element model, that has been used for simulating, via an explicit step-by-step algorithm, the dynamic response to artificial spectrum-compatible accelerograms. The results of the analyses have been used for introducing some specific structural improvements

Multi-physics simulation of laminates with piezoelectric layers for energy harvesting

In this paper, a refined, yet simple, model is considered with the aim of providing fast and insightful solutions to the multi-physics problem of piezoelectric energy harvesting by means of laminate cantilevers. The main objective is to retain a simple structural model (Euler-Bernoulli beam), with the inclusion of effects connected to the actual three-dimensional shape of the device. The obtained results are validated by the comparison with 3D analysis carried out with a commercial code, and the procedure is finally applied to the case of a realistic MEMS harvester

Improved one-dimensional model of piezoelectric laminates for energy harvesters including three dimensional effects

The application of piezoelectric composites in energy harvesters is continuously increasing even at the microscale, with the immediate corollary of a fundamental need for improved computational tools for optimization of performances at the design level. In this paper, a refined, yet simple model is proposed with the aim of providing fast and insightful solutions to the multi-physics problem of energy harvesting via piezoelectric layered structures. The main objective is to retain a simple structural model (Euler–Bernoulli beam), with the inclusion of effects connected to the actual three-dimensional shape of the device. A thorough presentation of the analytical model is presented, along with its validation by comparison with the results of fully 3D computations

Electrostatic diaphragm micropump electro-fluid-mechanical simulation

In this work, a fully-silicon mechanical displacement micropump is proposed and investigated. Electrostatic actuation of a flexible diaphragm is used to generate the pressure difference required to transport the fluid at the microscale. The study is carried out by exploiting the Finite Element method in a multiphysics framework, considering simplified geometries and boundary conditions. These investigations suggest the possibility to adopt the proposed device for applications in biomedical and biological fields. Achievable stroke volumes and flow rates are computed: values are in line with those obtained for similar devices presented in the literature

Shape optimization of solid-air porous phononic crystal slabs with widest full 3D bandgap for in-plane acoustic waves

The use of Phononic Crystals (PnCs) as smart materials in structures and microstructures is growing due to their tunable dynamical properties and to the wide range of possible applications. PnCs are periodic structures that exhibit elastic wave scattering for a certain band of frequencies (called bandgap), depending on the geometric and material properties of the fundamental unit cell of the crystal. PnCs slabs can be represented by plane-extruded structures composed of a single material with periodic perforations. Such a configuration is very interesting, especially in Micro Electro-Mechanical Systems industry, due to the easy fabrication procedure. A lot of topologies can be found in the literature for PnCs with square-symmetric unit cell that exhibit complete 2D bandgaps; however, due to the application demand, it is desirable to find the best topologies in order to guarantee full bandgaps referred to in-plane wave propagation in the complete 3D structure. In this work, by means of a novel and fast implementation of the Bidirectional Evolutionary Structural Optimization technique, shape optimization is conducted on the hole shape obtaining several topologies, also with non-square-symmetric unit cell, endowed with complete 3D full bandgaps for in-plane waves. Model order reduction technique is adopted to reduce the computational time in the wave dispersion analysis. The 3D features of the PnC unit cell endowed with the widest full bandgap are then completely analyzed, paying attention to engineering design issues

BESO approach to topology optimization of GaN phononic crystals

The use of Phononic Crystals (PnC) in suspended structures and microstructures, such as plates and slabs, has gained a lot of attention in the past years for the wide range of feasible applications (acoustic waveguides, acoustic insulation, acoustic cloaking) and for the easy fabrication technique. Since the performance of the device is related to the band of frequencies reflected by the PnC and since this band (called bandgap) depends on the geometric and material properties of the fundamental unit cell of the PnC, a useful tool for the design of those structures is topology optimization. This paper is focused on a novel and fast engineering use of Bidirectional Evolutionary Structural Optimization for the definition of the optimal hole configuration in air-solid PnC. The technique adopted finds the optimal shape of the hole in less than 20 iterations, and it is easy implemented in a 2D plane strain Matlab finite element solver