101,902 research outputs found
Propagazione di fratture longitudinali in gasdotti caratterizzati da bassa duttilità
No full textIl presente lavoro propone l’analisi di propagazione di una frattura fragile longitudinale di un gasdotto interrato basata sulla valutazione dell’energy release rate. Viene illustrata l’implementazione della suddetta metodologia all’interno di un codice proprietario agli elementi finiti con formulazione esplicita, illustrando gli interventi eseguiti sul preesistente algoritmo di propagazione stazionaria, e proponendo i risultati ottenuti a seguito di simulazioni dinamiche svolte su tubi in acciaio X80 e su provini SENB in pieno spessore sottoposti a prove DWTT
La resistenza a fatica di strutture in acciaio inossidabile saldate a punti: sintesi delle analisi teoriche, numeriche e sperimentali. Parte III: Prove di fatica, evoluzione del danno ed ERS equivalente
No full textModelling of Crack Arrestors on Gas-Pipelines
No full textDesign of gas pipelines implies demanding tasks such as the definition of material requirements in terms of
ductile fracture propagation control. This task is especially challenging when high strength steels (like X100
and beyond), whose use is imposing as a result of the consolidated worldwide trend towards the realization of
long distance/high pressure gas pipelines, are considered. In fact as recent research projects clearly
demonstrated (Mannucci [1], Demofonti [2] and Papka [3]) it is not possible to rely on the self-arrestability of
such a class of high strength steel and as a consequence new solutions must be adopted, especially when
severe operating conditions (rich gas, low temperature, etc.) are envisaged. In this context, the adoption of
additional mechanical devices, such as Crack Arrestors (CA), represents a valid alternative since, if properly
designed, they can externally provide a structural positive contribution in terms of resistance opposed to
ductile fracture propagation. Optimal design of CA presupposes the knowledge of the efficiency of each
possible CA type, but also the influence of its main geometric parameters (thickness, radial clearance, axial
length…) on the constraint applied on fracturing pipe, in the specific operative condition. The use of a
specific finite element code named PICPRO, which was developed by CSM jointly with the University of Tor
Vergata and actually used in the frame of a BP project, allows to perform numerical simulations of running
shear fracture along a pressurised steel pipeline also considering the constraint applied to the running fracture
by the crack arrestor; PICPRO was used to perform a rapid comparison within all the potential CA solutions
and it allowed the successful identification of the best one for the case under consideration (Mannucci [1]). In
the present paper some new algorithms, expressly developed to simulate crack advance inside a crack
arrestor, are presented. Exploration of main CA design parameters imposes the use of algorithms different
from those based on the search and application of contact elements, in order to reduce calculation time and to
give the possibility to perform an higher number of simulations. Hence, two new algorithms are on purpose
developed and hereby presented: the first one for the evaluation of the interaction pipe-CA and the second
one for managing the fracture propagation criteria even if crack flanks cannot freely open because of crack
arrestor presence
On longitudinal propagation of a ductile fracture in a buried gas pipeline: numerical and experimental analysis
No full textAlcune considerazioni sull’implementazione numerica del modello di anneggiamento di Lemaitre-Bonora
No full textNumerical Model of the Backfill Constraint Effect During Fracture Propagation on Buried Large Diameter Gas Pipelines
No full textAnalysis of CO2 dispersion in environment, Gaussian vs CFD modelling
No full textCO2 release and dispersion to the environment, as a consequence of leakage or fracture in onshore/offshore pipelines, is a matter of great concern. This interest is due to the expected future deployment of a pipeline network as essential element in Carbon Capture and Storage (CCS) projects or EOR applications. Hazards posed by accidental or intentional releases of CO2 from pipelines are often not easy due to a complex thermodynamics in the CO2 escaping related to phase change followed by cold heavy gas dispersion. As a consequence, a risk assessment based on the study of the atmospheric dispersion should be performed in the pipeline design.
An introduction to the CO2 release and dispersion occurrence is provided as a well as a review of the numerical models for dispersion prediction in the event of CO2 pipeline failure. Indeed, different mathematical models can be used for the simulation, mainly based on Gaussian codes or Computational Fluid Dynamics (CFD).
The main features of the two different numerical approaches have been reviewed focusing on their ability to simulate possible hazard scenarios of CO2 atmospheric dispersion and to account for different parameters, such as atmospheric conditions, orography, gas release mode, etc. The comparison between Gaussian and CFD models has allowed highlighting differences that impact directly on the accuracy of the results and affect the conservatism level of a numerically-based risk assessment.
The commercial CFD code Ansys Fluent and a freely available Gaussian code, ALOHA, have been used for the simulation of dispersion caused by the release from supercritical CO2 pipelines. The impact on the dispersion to the environment of different sources releasing CO2 has been studied and the results obtained have been processed for evaluating CO2 concentration evolution with respect to time and space
Sull’identificazione del comportamento plastico di un acciaio a partire da misure a campo intero ottenute tramite correlazione digitale di immagini
No full textIn the present work a method to obtain a true stress-true strain curve of an alloy by a full field digital image correlation measurement of the specimen surface kinematics, is presented. A preliminary set of parameters of a plasticity law is obtained to start up an automatized search algorithm, that includes, for each step a FE analysis in 3D. It’s also proposed a dual approach of the same search problem
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