Numerical simulation of the extrusion and layer deposition processes in 3D concrete printing with the Particle Finite Element Method

3D Concrete Printing (3DCP) is a rapidly evolving technology that allows for the efficient and accurate construction of complex concrete objects. In this paper, a numerical modelling approach is presented for the simulation of the printing process of cementitious materials, based on the homogeneous fluid assumption. To cope with the large deformations of the domain and the nonlinearity resulting from the use of a non-Newtonian rheological law, the Navier–Stokes equations are solved in the framework of the Particle Finite Element Method (PFEM). Furthermore, tailored solutions have been formulated and implemented for the time-dependent moving boundary conditions at the nozzle outlet and for the efficient handling of the inter-layer contact in the same PFEM framework. The overall computational cost is decreased by the implementation of an adaptive de-refinement technique, which drastically reduces the number of degrees of freedom in time. The proposed modelling approach is finally validated by simulating the printing process of six rectilinear layers and one multi-layer “wall”. The results show good agreement with the experimental data and provide valuable insights into the printing process, paving the way for the use of numerical modelling tools for the optimization of materials and processes in the field of 3D Concrete Printing

Simulation of viscoelastic free-surface flows with the Particle Finite Element Method

Viscoelastic fluids are central in numerous applications from polymer manufacturing to the pharmaceutical industry and biological research. However, since analytical solutions are generally not available or too complex, it is common practice to study free-surface viscoelastic flows through numerical simulation techniques. This work proposes the use of the so-called particle finite element method (PFEM), a Lagrangian approach combining standard FEM techniques with a remeshing strategy. The PFEM is able to efficiently handle mesh distortion and to accurately track the free-surface evolution. Therefore, it is exploited in this work to deal with large displacements problems in the context of nonlinear viscoelasticity. An implementation of the Oldroyd-B constitutive model in the PFEM framework is here presented including details regarding how to deal with the transfer of the internal variables during remeshing events. Additionally, an innovative approach to impose unilateral Dirichlet boundary conditions ensuring optimal mass conservation is presented. The implementation is verified with two free-surface highly viscous benchmark flows: the impacting drop and the jet buckling problems. The results show perfect agreement with those obtained with other numerical techniques. The proposed framework opens the way for using PFEM in various applications, ranging from polymer extrusion to more sophisticated scenarios involving viscoelastic and viscoelasto-plastic constitutive laws

Itineraries of the Working Group for Vegetation Science of the Italian Botanical Society – 1 (2022): Excursion to the Egadi Islands, Mount San Giuliano and Mount Cofano (Trapani, western Sicily, Italy)

The results of the annual excursion of the Working Group for Vegetation Science of the Italian Botanical Society, held in the Egadi Islands, Mount San Giuliano and Mount Cofano (W Sicily) on April 23–27 2022, are presented. This paper includes: (1) general information on the visited sites; (2) geology and geomorphology; (3) climatology and bioclimatology with tables of climatic data; (4) description of the following five geobotanical itineraries – accompanied by 29 original vegetation relevés and 11 synthetic relevés, proceeding from different bibliographic references: (a) Mount San Giuliano; (b) Marettimo Island: coastal and sub-coastal stretch of the southern part, between Punta Bassana and Contrada Chiappera; (c) Marettimo Island: Case Romane, Mount Pizzo Falcone and the north-western coastal stretch; (d) Island of Levanzo; (e) Mount Cofano – with catenal pictograms of the vegetation, surveys and description of the plant communities and related syntaxonomic scheme; (5) list of the surveyed plant taxa, collected specimens and herbaria in which they are deposited. A new syntaxon is also described (Catapodio pauciflori-Moraeetum sisyrinchii ass. nova), referring to an ephemeral dry grassland located along the north-western coastal stretch of Marettimo. The new association is framed in the Plantagini-Catapodion balearici, alliance of the Stipo-Bupleuretalia semicompositi order of the class Stipo-Trachynietea distachyae (order Stipo-Bupleuretalia semicompositi, alliance Plantagini-Catapodion balearici). An original synoptic table, regarding 17 different plant communities with high frequency of Moraea sisyrinchium, provides a comparative framework of the new association with allied vegetation units so far described throughout the Mediterranean region. Syntaxonomical and nomenclatural remarks regarding the Mediterranean vegetation occurring in this territory are also given throughout the text. Some floristic updates for the study sites are also reported, including the discovery for the first time in Sicily of Lysimachia loeflingii

Autogenous and Stimulated Healing of UHPC Under Torsion Induced Cracking

Autogenous and stimulated healing capacity of UHPC is well known, though in the entirety of studies cracks induced by means of flexural or direct tension tests have been studied. In the attempt of widening the case study database and promote self-healing cement-based materials into a variety of structural applications and broaden its concept to the upkeep of the material and structural load bearing capacity, this study focuses on the effects of self-healing in UHPC under torsional behaviour. Both autogenous and stimulated, via crystalline admixture, healing capacity have been considered, investigating cylinder specimens submitted to torsional behaviour. The capacity of the material not only to heal the induced skew cracks, under wet/dry exposure conditions, but also to maintain its multiple cracking capacity and to promote, upon successive reloading after healing, the formation of new cracks instead of the simple reopening of closed ones. A validation of the experimental campaign is also proposed via fracture-mechanics based finite element analysis

Notulae to the Italian alien vascular flora: 13

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions. Nomenclatural and distribution updates published elsewhere are provided as Suppl. material 1

Notulae to the Italian alien vascular flora: 13

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions. Nomenclatural and distribution updates published elsewhere are provided as Suppl. materia

Notulae to the Italian alien vascular flora: 9

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions. Furthermore, three new combinations are proposed