Designing manufacturable viscoelastic devices using a topology optimization approach within a truly-mixed fem framework

A new approach to topology optimization is presented that is based on the minimization of the input/output transfer function H∞norm. Additionally, by properly selecting input and output vector, the approach is recognized to minimize an entirely new definition of frequency-based dynamic compliance. The method is applied to viscoelastic systems in plane strain conditions that are investigated by using the Arnold-Winther finite-element resorting to a generalized solid phenomenological model. Preliminary indications on how to address the actual manufacturability of the optimal specimen are eventually outlined

Mixed variational formulations for micro-cracked continua in the multifield framework

Within the framework of multifield continua, we move from the model of elastic microcracked body introduced in (Mariano, P.M. and Stazi, F.L., Strain localization in elastic microcracked bodies, Comp. Methods Appl. Mech. Engrg. 2001, 190, 5657–5677) and propose a few novel variational formulations of mixed type along with relevant mixed FEM discretizations. To this goal, suitably extended Hellinger-Reissner principles of primal and dual type are derived. A few numerical studies are presented that include an investigation on the interaction between a single cohesive macrocrack and diffuse microcracks (Mariano, P.M. and Stazi, F.L., Strain localization due to crack–microcrack interactions: X–FEM for a multifield approach, Comp. Methods Appl. Mech. Engrg. 2004, 193, 5035–5062)

Static and dynamic topology optimization: an innovative unifying approach

This paper presents a topology optimization approach that is innovative with respect to two distinct matters. First of all the proposed formulation is capable to handle static and dynamic topology optimization with virtually no modifications. Secondly, the approach is inherently a multi-input multi-output one, i.e., multiple objectives can be pursued in the presence of multiple loads. The input-to-output transfer matrix, say G, is the key ingredient that governs the algebraic mapping between applied loads and structural response. In statics G depends on the design variables only, whereas it depends on the frequency variable as well in the dynamic case. The Singular Value Decomposition (SVD) of G represents then the core of the proposed approach. Singular values are shown to be the gains of the input/output mapping and are used to compute proper norms of G that represent the goal functions to be minimized. Singular vectors provide at no extra cost the plant directions, i.e., the load combination factors that stress the structure the most. Numerical examples are discussed in much detail and open issues object of ongoing investigations are highlighted. A full Matlab code handling the static topology optimization problem is provided as an online Appendix to the manuscript. Its extension to the dynamic case may be gathered following the formulation proposed in Sect. 5

Mixed methods for viscoelastodynamics and topology optimization

A truly-mixed approach for the analysis of viscoelastic structures and continua is presented. An additive decomposition of the stress state into a viscoelastic part and a purely elastic one is introduced along with an Hellinger-Reissner variational principle wherein the stress represents the main variable of the formulation whereas the kinematic descriptor (that in the case at hand is the velocity field) acts as Lagrange multiplier. The resulting problem is a Differential Algebraic Equation (DAE) because of the need to introduce static Lagrange multipliers to comply with the Cauchy boundary condition on the stress. The associated eigenvalue problem is known in the literature as constrained eigenvalue problem and poses several difficulties for its solution that are addressed in the paper. The second part of the paper proposes a topology optimization approach for the rationale design of viscoelastic structures and continua. Details concerning density interpolation, compliance problems and eigenvalue-based objectives are given. Worked numerical examples are presented concerning both the dynamic analysis of viscoelastic structures and their topology optimization

¿Quin tipus de preguntes fem als nostres alumnes?

Utilitzant un tipus de preguntes variat, sempre d’acord amb els objectius instructius proposats, ajudarem els nostres alumnes a pensar, més que a recordar. Hi ha molts escolars que no estan acostumats a reflexionar, menys encara a expressar al professor els seus pensaments. Variar la categoria de les preguntes que fem a la classe ens permetrà obtenir una informació més completa sobre l’evolució del procés d’aprenentatge i millorar la qualitat de l’ensenyança

Vibroacoustic modelling of orthotropic plates

The main objective of the work here presented is to extend the calculation of the radiation efficiency to plates whose characteristics differ form the simply supported isotropic rectangular plates. In this work the radiation efficiency is calculated by using the modal summation approach based on the far field sound intensity. The plate is considered isotropic or orthotropic. The orthotropy is introduced by the characteristics of the material or by the presence of ribs parallel to an edge. Different combinations of free, simply and clamped supported boundary conditions are considered for the isotropic plate, while the orthotropic plate is always considered simply supported. Free vibration of isotropic plates are calculated by using the classical Kirchoff-plates theory. The results obtained for the radiation efficiency are compared with a BEM model and show the influence of the constraints in the edges. Results show that the clamped supported plate is the the configuration for which the radiation efficiency is higher, while the freely supported configuration is the one with lower radiation efficiency. The difference between different boundary conditions is also summarized in terms of third octave bands. In this manner it has been shown that the difference between a clamped plate and a simply supported plate in the mid-frequency range in terms of radiation efficiency is not 3 dB as stated in literature by Leppington, but is variable and can reach up to 10 dB. The orthotropy has been introduced. First, a plate made of an orthotropic material is considered. Free vibration have been calculated analytically and have been compared with with a FE model, making the results a good agreement. The radiation efficiency has been calculated using the same formulae as the isotropic plate. Then the orthotropy is considered by the introduction of ribs. An analytical-numerical method is used to calculate the free vibration of a ribbed plate. Results have been compared with a FE model and make a good agreement. The radiation efficiency of a ribbed plate is calculated by modifying slightly the formulation presented for the calculation of the radiation efficiency of an isotropic plate. The formulation adopted for the radiation efficiency allows to investigate the effect of the modal damping ratio, the influence of the boundary conditions and the effect of the ratio of the stiffness along perpendicular directions.Outgoin

Parola parlata: convenzioni e tecniche di resa nella narrativa araba classica

Numero monografico: L’oralità nella scrittura. Modalità di rappresentazione della parola orale nel testo scritto”, a cura di Maria Teresa Biaso

Modal identification of storage racks for cheese wheels

During the Emilia-Romagna earthquake (2012), a great number of steel racks used to store cheese wheels collapsed, causing a non-negligible damage to the Italian economy. Therefore, for similar structures that survived and are in service, a deep investigation towards the assessment of their effective safety is required. In the seismic analysis of these frames, the mechanical constraint acting onto the racks due to the reinforced concrete sidewalls, possible nonlinearities exhibited by the base-plate joints and the in-plane restraint provided by wooden boards that connects adjacent columns should be carefully modelled to ensure realistic design results. In the paper, an experimental activity, based on suitable modal identification techniques, is presented to capture the dynamic behaviour of these peculiar structures. The scope is to collect data useful to calibrate numerical finite element models in order to accurately define the aforementioned unknown parameters. Furthermore, a few numerical models based on ideal restraints are herein discussed stressing out non-negligible differences in terms of expected seismic and static response