Numerical solution of three-dimensional rectangular submerged jets with the evidence of the undisturbed region of flow

The evolution of turbulent rectangular submerged free jets has been investigated numerically with a two-dimensional (2D) approach by the present authors and, by using the large eddy simulations (LES) at several Reynolds numbers. The average numerical results confirmed the presence of the undisturbed region of flow (URF) located between the slot exit and the beginning of the potential core region (PCR) previously observed experimentally at the University of Rome “Tor Vergata” by Gori and coworkers. The 2D study of the present authors carried out under the conditions previously investigated in the literature, showed that the URF has a self-similar behavior, and proposed a new law for the evolution of the momentum. The present paper extends the LES to three-dimensional (3D) rectangular submerged free jets, in the range from Re =5,000 to Re =40,000, showing that the self-similar behavior of URF is also present in the 3D numerical simulations, as well as in the PCR and in the fully developed region (FDR)

Three-Dimensional Numerical Simulation of Blood Flow in Two Coronary Stents.

The aim of the present study is to carry out Computational Fluid Dynamics simulations in a realistic three dimensional geometry of two stent under physiological conditions. The two stent, similar to real coronary ones, are both made of 12 rings but are differing as far as the position of the struts is concerned. One type has parallel-connectors and the other transverse-ones. The artery is modeled as rigid cylinder and the fluid is assumed as incompressible Newtonian fluid in laminar flow with the average physical properties of blood. The commercial computational fluid dynamic code FLUENT is used with the mesh made of non-uniform tetrahedrons. The mesh independence is proved using the steady state results of the wall shear stress. The parameters correlated to neo-intimal hyperplasia, such as wall shear stress, magnitude of wall shear stress gradient, and oscillatory shear index, are investigated. Time variation of the parameters is investigated with the conclusion that the stent with parallel-connectors has a better fluid dynamic behavior

Two new differential equations of turbulent dissipation rate and apparent viscosity for non-Newtonian fluids.

A new equation for the dissipation rate of turbulent kinetic energy is derived exactly in conservative form for a Generalized Newtonian Fluid (GNF). The transport equations for mass, momentum, and turbulent kinetic energy are written along to the transport equation for the shear rate. A new transport equation for the apparent viscosity is derived assuming the viscosity as dependent only on the shear rate. The assumption is of incompressible two-dimensional GNF flow

Phase-field modelling of a miscible system in spinning droplet tensiometer

The spinning drop tensiometry is used for measurements of surface tension coefficients, especially, when interfaces are characterised by low and ultra-low interfacial stresses. A droplet of lighter liquid is introduced into a rotating capillary that was initially saturated with another heavier liquid. The tube is subject to axial rotation that results in droplet’s elongation along the tube’s axis. The equilibrium shape of the droplet is used to determine the surface tension coefficient. In this work, the evolution of a slowly miscible droplet introduced into a spinning capillary is investigated. This technique is frequently employed for studies of the dynamics of miscible systems, even despite the fact that a strict equilibrium is never achieved in a mixture of fully miscible liquids. The numerical modelling of a miscible droplet is fulfilled on the basis of the phase-field (Cahn-Hilliard) approach. The numerical results are compared against the experimental data pursuing two objectives: (i) to verify the use of the phase-field approach as a consistent physics-based approach capable of accurate tracking of the short- and long-term evolution of miscible systems, and (ii) to estimate the values of the phenomenological parameters introduced within the phase-field approach, so making this approach a practical tool for modelling of thermohydrodynamic changes in miscible systems within various configurations

Nuovo copolimero triblocco per applicazioni biomedicali a base di polilattico e contenente sequenze "PEG-like": sintesi e caratterizzazione allo stato solido

Il lavoro della presente Tesi è consistito nella preparazione e caratterizzazione di un copolimero triblocco A-B-A ad elevato peso molecolare, dove A è costituito da acido polilattico (PLLA) e B è un copolimero statistico a composizione equimolare poli(butilene/trietilene succinato), precedentemente studiato e caratterizzato da un comportamento meccanico elastomerico e da una cinetica di degradazione idrolitica lenta. Il rapporto tra i due blocchi A e B è stato fissato vicino all’equimolarità. Dai risultati ottenuti si evince come le proprietà meccaniche del copolimero triblocco siano significativamente diverse da quelle dell’omopolimero e, soprattutto, migliorative in vista di impieghi del materiale nell’ingegneria dei tessuti molli: infatti, il modulo elastico si è ridotto di due ordini di grandezza, mentre l’allungamento a rottura è aumentato di un ordine e mezzo. Per quanto concerne la cinetica di riassorbimento idrolitico, i risultati, seppure preliminari sembrano molto promettenti: la cinetica del PLLA risulta difatti rallentata per copolimerizzazione. Da ultimo, ma non meno importante, è da segnalare un miglioramento della stabilità termica (parametro importante per la processabilità di un biomateriale) del PLLA per copolimerizzazione

Passive scalar diffusion in the near field region of turbulent rectangular submerged free jets

Jets are a common way to transfer mass among fluids, or from a fluid to a surface. At moderate Reynolds numbers and low turbulent intensities the jet exhibits a Near Field Region (NFR) several diameters long. The paper presents numerical results and a theoretical model for the passive scalar diffusion of a submerged free jet in the NFR. Large Eddy Simulations (LES), in the Reynolds number range of 5000–40,000 and the Schmidt number range 1–100, are performed obtaining the passive scalar fields. Three mathematical models for the passive scalar diffusion are presented; the first one is valid in the NFR, specifically in the Undisturbed Region of Flow (URF), and the other two, obtained under the hypotheses of Tollmien and Görtler momentum spreading, are valid in the Potential Core Region (PCR). The last two models employ a turbulent Schmidt number inversely proportional to the mean velocity gradient, conclusion obtained from the LES numerical results. The self-similar solutions of the passive scalar show good agreement with the LES results. The wide range of Reynolds and Schmidt numbers investigated gives generality to the results

La comunicazione della patologia fetale. Il punto di vista della donna, del medico e dell’équipe

La comunicazione della patologia fetale riveste una serie di significati con implicazioni psicologiche e sociali importanti che richiedono al medico capacità comunicativa, attitudine alla comprensione della paziente e delle dinamiche istituzionali. La donna: la patologia ostetrica è una crisi dentro la crisi. Nella patologia ostetrica le aspettative di vivere la nuova condizione di madre e di sentirsi più compiutamente famiglia vengono frustrate e tradite. In seguito alla diagnosi di patologia, alla perdita del bambino immaginario può seguire la perdita del bambino reale. Nel caso in cui la coppia decida di proseguire la gravidanza, il sentimento di lutto può prolungarsi per tutta la vita. Il medico: dal momento della prima diagnosi per la donna inizia l’elaborazione del lutto. Anche il medico che comunica la diagnosi vive questo momento con disagio. Inoltre, il medico sente il disagio dell’incertezza: l’incertezza può essere accolta e ascoltata. Raramente in questa situazione è possibile comunicare in modo efficace le informazioni necessarie. È importante comunicare gradualmente e dedicare un secondo incontro alle richieste di spiegazioni. L’équipe: è importante che gli operatori possano condividere questa esperienza all’interno dell’equipe. L’equipe che si occupa di diagnosi prenatale dovrebbe essere composta da persone che hanno scelto liberamente di occuparsi di questo aspetto della medicina. L’equipe diviene un contenitore per le emozioni estreme delle pazienti e degli operatori

Numerical simulation of magnetic nano drug targeting in a patient-specific coeliac trunk

Magnetic nano drug targeting, through the use of an external magnetic field, is a new technique for the treatment of several diseases, which can potentially avoid the dispersion of drugs in undesired locations of the body. Nevertheless, due to the limitations on the intensity of the magnetic field applied, the hydrodynamic forces can reduce the effectiveness of the procedure. This technique is studied in this paper with the Computational Fluid Dynamics (CFD), focusing on the influence of the magnetic probe position, and the direction of the circulating electric current. A single rectangular coil is used to generate the external magnetic field. A patient-specific geometry of the coeliac trunk is reconstructed from DICOM images, with the use of VMTK. A new solver, coupling the Lagrangian dynamics of the nanoparticles with the Eulerian dynamics of the blood, is implemented in OpenFOAM to perform the simulations. The resistive pressure, the Womersley’s profile for the inlet velocity and the magnetic field of a rectangular coil are implemented in the software as boundary conditions. The results show the influence of the position of the probe, as well as the limitations associated with the rectangular coil configuration

Three-dimensional numerical simulation of a failed coronary stent implant at different degrees of residual stenosis. Part I: Fluid dynamics and shear stress on the vascular wall

The influence of the degree of residual stenosis on the hemodynamics inside coronary arteries is investigated through three-dimensional (3D) numerical simulations. The present paper, which is the first of a series of two, focuses on the influence that the degree of residual stenosis (DOR) has on the fluid dynamics and the shear stresses acting on the stent and the artery wall. The pulsatile nature of the blood flow and its non-Newtonian features are taken into account. Four models of artery are investigated. The results show that the wall shear stress (WSS) increases monotonically, but not linearly, with the DOR

Three-dimensional numerical simulation of a failed coronary stent implant at different degrees of residual stenosis. Part II: Apparent viscosity and wall permeability

The influence of the degree of residual stenosis (DOR) on the hemodynamics inside coronary arteries is investigated through three-dimensional (3D) numerical simulations. The vascular wall permeability is investigated and the effect of the non-Newtonian viscosity discussed. The results agree in predicting an abrupt increase in wall permeability above 45% DOR, indicating that the implant could lead to a massive restenosis. This behavior is considered to be due to the shift of the regions involved by low and oscillatory wall shear stress (WSS), from the zone adjacent to the struts toward the center of the stent meshes