Boundary element method for the Peridynamics theory

openUna recente teoria del continuo per la meccanica dei solidi e` la teoria introdotta da Silling [34] nota come Bond-Based Peridynamics. Questa teoria risulta di particolare interesse per problemi riguardanti il danneggiamento e la propagazione di cricche [42] [43] [23]. Le discontinuita` nel dominio possono essere studiate con le stesse relazioni che si utilizzano nelle zone integre grazie all’utilizzo di una formulazione integrale, a differenza di quella differenziale della meccanica classica. La Bond-Based Peridynamics utilizza un approccio non-locale quindi prevede l’interazione a distanza tra coppie di punti materiali nel dominio continuo. A causa di questo i metodi numerici che la utilizzano sono computazionalmente molto piu` onerosi rispetto ai metodi agli elementi finiti tradizionali. Per la risolvere la Peridynamics esistono tre categorie di metodi. La prima categoria prevede di risolvere le equazioni integro-differenziali peridinamiche discretizzandole rispetto al tempo e alle coordinate spaziali [35] [18] [3] [9]. Nella seconda categoria si vogliono risolvere le equazioni della Peridynamics attraverso i metodi numerici tradizionali come elementi finiti e volumi finiti [24] [17] [5]. Con tutti questi metodi, pero`,si riscontrano quattro problematiche: l’indebolimento ai bordi a causa di un orizzonte non completo [20], il problema con domini infiniti [40], l’imposizione di condizioni al contorno [10] e l’elevato costo computazionale. A causa di questi problemi si e` introdotta la terza categoria di algoritmi risolutivi in cui si prevede l’accoppiamento tra metodi numerici locali, nel dominio intatto, e metodi non-locali nelle zone con discontinuita` [19] [22] [14] [44]. Con quest’ultima categoria di metodi numerici si hanno dei problemi di connessione nelle zone di accoppiamento e delle riflessioni spurie delle onde elastiche [30]. Come lavoro di tesi si vuole sviluppare il Boundary Element Method per la Peridynamics [21], quindi calcolando le soluzioni dell’equazione che governano la Peridynamics tramite la discretizzazione dei bordi del dominio. I vantaggi presentati da questo metodo sono quelli di risolvere le problematiche di accoppiamento precedentemente elencate. Il primo e il terzo problema vengono risolti tramite la discretizzazione dei bordi

MODELING THE EFFECT OF EXCESS PORE-WATER PRESSURE ON THE BEARING CAPACITY OF FULL DISPLACEMENT PILES IN GROUP: A CASE-STUDY IN PARMA (ITALY)

Excess pore-water pressure development during installation of piles into saturated clays is of primary importance and strongly affects pile bearing capacity and settlements. Such a problem is well known in literature, but excess pore-water pressure magnitude prediction, and then that of the bearing capacity, is an open research topic. In addition, excess pore-water pressure may increase greatly when numerous piles are installed in a relatively small area - as in the case of a pile group foundation - thus leading to a non-negligible modification of stress conditions at the soil-pile interface and, as a consequence, to a temporary reduction of ultimate load-bearing capacity. The paper focuses on the interpretation of load-test data performed on several auger-screw piles (full displacement), part of an important soil improvement intervention in Parma (Italy). The analysis of load test showed low values of ultimate load bearing capacity of the tested piles. Hence, the need to investigate the evolution of excess pore-water pressure with time and its relationship with the ultimate pile bearing capacity. In addition, special attention is dedicated to the study of possible mechanisms standing beneath the superposition of excess pore-water pressure effects among adjacent piles. Eventually, in order to give a consistent theoretical explanation of the recorded data, a simplified model is introduced. Such a model could be applied to similar case studies

Fatal varicella in immigrants from tropical countries: case reports and forensic perspectives

The primary Varicella Zoster Virus (VZV) infection results in varicella, a generally benign, self-limiting disease in immunocompetent children. Despite the usual course a possible fatal evolution of the primary infection is observed predominantly in immunocompromised subjects and in adults, especially emigrating from tropical regions. Two cases of fatal varicella have been investigated and discussed. Death occurred in two patients over 40years of age, coming from South Asia and receiving chronic immunosuppressive therapy. The forensic expert must be cautious and consider all clinical records in managing fatal varicella cases, bearing in mind risk factors and pre-existing conditions such as age, geographical provenance and pathological comorbidity, which may lead to a bad prognosis irrespective of therapies. Based on the severe and fatal course observed in the reported cases, an extension of the immunization program appears advisable for immigrants from tropical countries, especially before scheduled immunotherap

Measurement of the Planck’s constant in the framework of the Lab2Go project

Aiming at exposing high school students to experimental Physics, Sapienza Universita`a di Roma and INFN participate to the Lab2Go project in the context of PCTO and supported by PLS. In a webinar offered in the framework of the Lab2Go@home initiative (on- line version of Lab2Go), tutors from INFN Roma 2 proposed a method for measuring the Planck’s constant by reconstructing the characteristic curve of a LED, acquiring voltage and intensity of current by using a voltmeter and an ammeter, respectively. A similar experiment, but replacing the voltmeter and the ammeter with an Arduino board, was proposed by tutors from Universit`a Sapienza and INFN Roma to students of Liceo Scientifico “L. Trafelli” in Nettuno. The employ of LEDs allows for a simple, but functional, approach to measure the Planck’s constant making it accessible to the high school level; moreover, using Arduino for the acquisition of voltage and current enables a fast execution of the experiment and allows students to acquire additional competences, as for example coding and programming. In this report, we will show the two measurement methods and the obtained results