Perturbation damage indicators based on complex modes

The papers focusing on dynamic identification of structural damages usually rely on the comparison of two or more responses of the structure; the measure of damage is related to the differences of the vibration signals. Almost all literature methods assume damping proportionality to mass and stiffness; however, this is acceptable for new, undamaged structures, but not for existing, potentially damaged structures, especially when localised damages occur. It is well-known that in non-proportionally damped systems the modes are no longer the same of the undamped system: thus, some authors proposed to use modal complexity as a damage indicator. This contribution presents a perturbation approach that can easily reveal such a modal complexity

Vibration and buckling of open TWBs with local weakening

Free vibration and Ljapounov stability of compressed open thin-walled beams with a cross-section reduction are studied by a in-house finite differences numerical code, based on a refined direct beam model and allowing for investigating elastic stability of non-trivial equilibrium paths in a dynamic setting. The benchmark is a beam with doubly symmetric cross-section and non-zero warping rigidity, under free, semi-, and fully restrained warping at its ends. In all cases, the results of the direct model are compared to finite element and/or experimental ones. The reduction in the cross-section rigidity induces a weakening that may model a local damage; thus, the present investigation may be useful with an outlook to damage monitoring and identification

In situ remediation of contaminated marinesediment: an overview

Sediment tends to accumulate inorganic and persistent hydrophobic organic contaminants representing one of the main sinks and sources of pollution. Generally, contaminated sediment poses medium- and long-term risks to humans and ecosystem health; dredging activities or natural resuspension phenomena (i.e., strongly adverse weather conditions) can remobilize pollution releasing it into the water column. Thus, ex situ traditional remediation activities (i.e., dredging) can be hazardous compared to in situ techniques that try to keep to a minimum sediment mobilization, unless dredging is compulsory to reach a desired bathymetric level. We reviewed in situ physico-chemical (i.e., active mixing and thin capping, solidification/stabilization, chemical oxidation, dechlorination, electrokinetic separation, and sediment flushing) and bio-assisted treatments, including hybrid solutions (i.e., nanocomposite reactive capping, bioreactive capping, microbial electrochemical technologies). We found that significant gaps still remain into the knowledge about the application of in situ contaminated sediment remediation techniques from the technical and the practical viewpoint. Only activated carbon-based technologies are well developed and currently applied with several available case studies. The environmental implication of in situ remediation technologies was only shortly investigated on a long-term basis after its application, so it is not clear how they can really perform

Adsorptive behavior, isothermal studies and kinetic modeling involved in removal of divalent lead from aqueous solutions, using Carissa carandas and Syzygium aromaticum

This study is focused on the biosorption of lead(II) ion onto surface of Carissa carandas and Syzygium aromaticum biomass from aqueous solution. The operating parameters, pH of solution, biomass dosage, contact time, initial metal ion concentration, and temperature considerably affect the biosorption efficiency of Pb(II). Biosorbent C. carandas leaf powder showed higher sorption efficiency than that of biosorbent S. aromaticum powder under identical experimental conditions. It was observed that the lead(II) removal percentage was found highest of 95.11% for C. carandas and 91.04% for S. aromaticum at contact period of 180 min. Also, it was observed that the regression coefficient (R2 = 0.99) for the pseudo-second-order kinetic model is higher in comparison with the pseudo-first-order kinetic model and the calculated value of qe for the pseudo-second-order kinetic model is very close to the experimental value, which indicates that it fits well with the equilibrium data for Pb(II) sorption from aqueous solutions on biosorbents. Also, the adsorption of Pb(II) onto C. carandas was best described by the Freundlich isotherm model

Removal of divalent nickel from aqueous solutions using Carissa carandas and Syzygium aromaticum: isothermal studies and kinetic modelling

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AVALIAÇÃO DE LIVRO DIDÁTICO: A FALTA DE ABORDAGENS SOBRE AS MATRIZES AFROBRASILEIRAS

O presente artigo busca avaliar o livro didático “PAS - UNB 2ª etapa Geografia-História” da editora exato, que é escrito em formato de apostila, com objetivo de preparar alunos de segundo ano do ensino médio para a segunda etapa do Programa de Avaliação Seriada (PAS 2) da Universidade de Brasília. Buscou-se avaliar como ou se o livro aborda conteúdos sobre as matrizes africanas e afro-brasileiras. Observou-se que o livro não aborda de forma alguma as matrizes do continente africano. Por fim, com os conhecimentos adquiridos foram feitas algumas observações sobre o livro e o que ele pode dizer sobre o sistema educacional brasileiro como um todo

Optimal sensors placement in dynamic damage detection of beams using a statistical approach

Structural monitoring plays a central role in civil engineering; in particular, optimal sensor positioning is essential for correct monitoring both in terms of usable data and for optimizing the cost of the setup sensors. In this context, we focus our attention on the identification of the dynamic response of beam-like structures with uncertain damages. In particular, the non-localized damage is described using a Gaussian distributed random damage parameter. Furthermore, a procedure for selecting an optimal number of sensor placements has been presented based on the comparison among the probability of damage occurrence and the probability to detect the damage, where the former can be evaluated from the known distribution of the random parameter, whereas the latter is evaluated exploiting the closed-form asymptotic solution provided by a perturbation approach. The presented case study shows the capability and reliability of the proposed procedure for detecting the minimum number of sensors such that the monitoring accuracy (estimated by an error function measuring the differences among the two probabilities) is not greater than a control small value

Analisi dinamica diretta e inversa di strutture danneggiate a parametri incerti

La tesi presenta un approccio perturbativo per l'identificazione dinamica di strutture a parametri incerti. Il metodo proposto, basato sulla minimizzazione di una funzione obiettivo, è indipendente dall'ordine di approssimazione raggiunto e, ereditando i vantaggi dell'approccio perturbativo, assicura un onere computazionale ridotto. Per superare le difficoltà legate alla selezione del modello fisico nel caso di parametri incerti di danno, è proposto un metodo che sfrutta la versione ortogonale dell'empirical mode decomposition, e cerca di combinare le proprietà modali della struttura con le caratteristiche dei segnali di risposta. Le due tecniche introdotte, ancorché intimamente legate per gli scopi e le applicazioni della tesi, godono di individuale validità.The thesis presents a perturbative approach for dynamic identification of structures with uncertain parameters. The proposed method, based on the minimization of an objective function, is independent of the achieved order approximation and, inheriting the advantages of the perturbation approach, ensures a low computational effort. To overcome the difficulties related to the selection of the physical model for damage like uncertain parameters, it is proposed a method that uses the orthogonal version of the empirical mode decomposition, and seeks to combine the modal properties of the structure with the response signals features. The two introduced techniques, closely related within the framework of the thesis, hold their own individual validity

Statistical analysis of risk assessment of bridges and viaducts according to recent Italian guidelines

The safety assessment of existing bridges and viaducts is nowadays a critical task. Several works have been published in recent years relying on multi-risk based approaches, then aiming to properly evaluate the various risk sources involved in the identification and evaluation processes of existing infrastructures. In Italy, after some significant collapses (the most famous case is certainly the Polcevera viaduct, also known as the Morandi’s bridge, collapsed in 2018), the Italian Higher Council of Public Works provides specific regulations, the 2020 Guidelines (updated in 2022), intended to standardize the entire risk classification procedures and monitoring activities of existing bridges and viaducts for the whole Italian road network. This work proposes two main contributions. The first concerns a conceptual analysis of the logical path that leads from the considered parameters to the risk classification (class of attention, according to the cited Guidelines). The aim is to enucleate the total amount of parameters, their role and the possible combinations. The second contribution concerns an extensive investigation on the statistics of the class of attention. Such statistics represent the “a priori” distributions of the multi-risk procedure indicated by the regulation