Viscoelastic Effects during Tangential Contact Analyzed by a Novel Finite Element Approach with Embedded Interface Profiles

A computational approach that is based on interface finite elements with eMbedded Profiles for Joint Roughness (MPJR) is exploited in order to study the viscoelastic contact problems with any complex shape of the indenting profiles. The MPJR finite elements, previously developed for partial slip contact problems, are herein further generalized in order to deal with finite sliding displacements. The approach is applied to a case study concerning a periodic contact problem between a sinusoidal profile and a viscoelastic layer of finite thickness. In particular, the effect of using three different rheological models that are based on Prony series (with one, two, or three arms) to approximate the viscoelastic behaviour of a real polymer is investigated. The method allows for predicting the whole transient regime during the normal contact problem and the subsequent sliding scenario from full stick to full slip, and then up to gross sliding. The effects of the viscoelastic model approximation and of the sliding velocities are carefully investigated. The proposed approach aims at tackling a class of problems that are difficult to address with other methods, which include the possibility of analysing indenters of generic profile, the capability of simulating partial slip and gross slip due to finite slidings, and, finally, the possibility of simultaneously investigating dissipative phenomena, like viscoelastic dissipation and energy losses due to interface friction

A framework for the analysis of fully coupled normal and tangential contact problems with complex interfaces

An extension to the interface finite element with eMbedded Profile for Joint Roughness (MPJR interface finite element) is herein proposed for solving the frictional contact problem between a rigid indenter of any complex shape and an elastic body under generic oblique load histories. The actual shape of the indenter is accounted for as a correction of the gap function. A regularised version of the Coulomb friction law is employed for modeling the tangential contact response, while a penalty approach is introduced in the normal contact direction. The development of the finite element (FE) formulation stemming from its variational formalism is thoroughly derived and the model is validated in relation to challenging scenarios for standard (alternative) finite element procedures and analytical methods, such as the contact with multi-scale rough profiles. The present framework enables the comprehensive investigation of the system response due to the occurrence of tangential tractions, which are at the origin of important phenomena such as wear and fretting fatigue, together with the analysis of the effects of coupling between normal and tangential contact tractions. This scenario is herein investigated in relation to challenging physical problems involving arbitrary loading histories.Comment: Final version available at https://www.sciencedirect.com/science/article/abs/pii/S0168874X2100089

A new finite element paradigm to solve contact problems with roughness

This article's main scope is the presentation of a computational method for the simulation of contact problems within the finite element method involving complex and rough surfaces. The approach relies on the MPJR (eMbedded Profile for Joint Roughness) interface finite element proposed in [arXiv:1805.07207], which is nominally flat but can embed at the nodal level any arbitrary height to reconstruct the displacement field due to contact in the presence of roughness. Here, the formulation is generalized to handle 3D surface height fields and any arbitrary nonlinear interface constitutive relation, including friction and adhesion. The methodology is herein validated with BEM solutions for linear elastic contact problems. Then, a selection of nonlinear contact problems prohibitive to be simulated by BEM and by standard contact algorithms in FEM are detailed, to highlight the promising aspects of the proposed method for tribology

Energy harvesting from bridge vibrations with piezoelectric devices - A feasibility study

We present a feasibility study on the use of piezoelectric devices to harvest the energy connected to the vibrations induced on road bridges by travelling vehicles. We have selected an existing urban bridge as case study and collected the available documentation about its original design. Furthermore, the results of a past experimental campaign on the bridge have provided experimental evidence about the natural frequencies and mode shapes of the structure. Next, we have set up a three-dimensional finite element model of the bridge, which is currently being calibrated to match the results of the experimental dynamic analysis. Besides, we have developed a mechanical model of a laminated cantilever beam with a top piezoelectric layer and a concentrated mass on its free end. Our model applies to laminated beams with general (asymmetric) stacking sequences, thus representing an extension of similar models of the literature. The partial differential equation of motion has been determined and solved in the case of free vibrations under both open- and short-circuit electrical boundary conditions. As a numerical example, a piezoelectric cantilever beam has been designed with the same first natural frequency of the case study bridge

CONTAMINANT DISPERSION SIMULATION IN A DIGITAL TWIN FRAMEWORK

Within a digital twinning process, we aim to establish a highly automated workflow to simulate air contaminant dispersion based on up-to-date urban geometries, seamlessly retrieved from open-source geo-referenced databases. The final declared scope is providing assistance and informed real time decision making processes in the context of evacuation scenarios. This entails generating an initial simulation space and refining its characteristics as needed to gain an adequate level of accuracy. In the preliminary phase of the project, high-fidelity wind flow simulations are coupled with contaminant concentration assessments based on advection-diffusion processes. A second more advanced phase aims at leveraging the workflow efficiency by introducing a Reduced Order Model (ROM) for the wind field evaluation, together with the investigation of scientific machine learning methods to merge physics with data, with the final objective of defining a reliable predictive model for a hybrid digital twin

Bryophyte, lichen, and vascular plant communities of badland grasslands show weak cross-taxon congruence but high local uniqueness in biancana pediments

Cross-taxon congruence, i.e., using certain taxonomic groups as surrogates for others, is receiving growing interest since it may allow decreasing efforts in biodiversity studies. In this work, we investigated the patterns of cross-taxon congruence in species richness and composition between communities of bryophytes, lichens, and vascular plants in different biancana grasslands of a Special Area of Conservation (SAC) of central Italy. We recorded species presence and abundance in 16 plots of 1 × 1 m size and analyzed the data using Procrustes correlation, co-correspondence analysis, and indicator species analysis. We did not highlight any correlation in species richness and composition between the three taxonomic groups. Conversely, the species composition of bryophyte communities was predictive of the species composition of lichen communities. Moreover, lichen richness was negatively correlated with the total cover of vascular plants. Indicator species analysis evidenced the presence of species from the three biotic communities being particularly related, at least at the local scale, to biancana pediments, like the bryophytes Didymodon acutus and Trichostomum crispulum, the lichens Enchylium tenax, Cladonia foliacea, and Psora decipiens, and the vascular plants Brachypodium distachyon, Parapholis strigosa, and Artemisia caerulescens subsp. cretacea. In the biancana pediments, acrocarp mosses, squamulose lichens, therophyte plants and chamaephyte plants coexisted. In spite of the weak cross-taxon congruence between the three taxonomic groups, this study could highlight a locally unique diversity of bryophytes, lichens, and vascular plants related to the extreme environment of biancana pediments, selected by high soil salinity and deposition from the upper eroded slope. Soil erosion and deposition in biancana badlands supports the increase of local multi-taxonomic plant diversity by creating unique ecosystems. Such biodiversity should be considered locally at risk of disappearance, due to the ongoing vanishing of biancana badlands in central Italy

Contributi per una flora vascolare di Toscana. XII (739-812)

Vengono presentate nuove località e/o conferme relative a 74 taxa specifici e sottospecifici di piante vascolari della flora vascolare to- scana, appartenenti a 69 generi e 28 famiglie: Bunium, Trinia (Apia- ceae), Nerium (Apocynaceae), Lemna (Araceae), Artemisia, Bidens, Centaurea, Crupina, Gazania, Hieracium, Rhagadiolus, Symphyotri- chum, Tagetes, Tripleurospermum (Asteraceae), Impatiens (Balsami- naceae), Anredera (Basellaceae), Cynoglottis, Phacelia (Boraginaceae), Cardamine, Diplotaxis, Hornungia (Brassicaceae), Campanula, Lobe- lia (Campanulaceae), Cerastium, Dianthus, Polycarpon, Spergularia, Stellaria (Caryophyllaceae), Commelina (Commelinaceae), Fallopia (Convolvulaceae), Sempervivum (Crassulaceae), Dryopteris (Dryopte- ridaceae), Euphorbia (Euphorbiaceae), Lathyrus, Medicago, Ononis, Trigonella (Fabaceae), Geranium (Geraniaceae), Lycopus, Stachys (Lamiaceae), Malva (Malvaceae), Anacamptis, Cephalanthera, Epi- pactis, Orchis (Orchidaceae), Linaria (Plantaginaceae), Ceratochloa, Eragrostis, Festuca, Gastridium, Hyparrhenia, Molineriella, Phalaris, Phyllostachys, Setaria, Sporobolus, Stipellula (Poaceae), Anogramma (Pteridaceae), Anemonoides, Ranunculus (Ranunculaceae), Reseda (Resedaceae), Alchemilla, Kerria, Pyracantha, Rosa, Rubus (Rosa- ceae), Galium, Valantia (Rubiaceae), Thesium (Santalaceae). Infine, viene discusso lo status di conservazione delle entità e gli eventuali vincoli di protezione dei biotopi segnalati

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P < .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients