1,721,044 research outputs found
Time dependent non-Newtonian numerical study of the flow field in a realistic model of aortic arch
No full text A three-dimensional time dependent numerical simulation was performed in a geometric model of aortic arch complete with a realistic aortic root and major branches originating from the arch, for a peak Reynolds number set at 2200 and Womersley number set at 20.4. The computational fluid dynamic analysis was aimed to provide spatial and temporal distribution of the shear stress all along the entire model together with the velocity patterns, related both to the non planar geometry of the aortic system here considered and to the pulsatility imposed on the numerical model to simulate physiologic conditions. A non-Newtonian evolving fluid was considered to account for the actual rheological nature of blood; a comparison on the incidence of wall shear stress, implementing a Newtonian fluid, was also made as reference. The spatial shear stress pattern, within the cardiac cycle, was shown to have higher values in correspondence to the inner wall of the aortic arch and the sites where the major vessels originated from the arch itself. The velocity patterns, on transversal sections of the aorta, resulted in highly skewed morphology. The resulting complex fluid dynamics, established in the aortic arch and in its branches, can be related to the possible endothelium response to mechanical stimuli, induced by wall shear stress, in the promotion of inflammatory events. </jats:p
Three-dimensional numerical simulation of flow through an aortic bileaflet valve in a realistic model of aortic root
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Dielectric properties at microwave frequencies of poly(ɛ-caprolactone)/CNF films and electrospun mats
No full textThe electromagnetic (EM) properties of hybrid poly(ɛ-caprolactone)/carbon nanofiber films and electrospun mats at microwave frequencies (8.2–12.4 GHz) were assessed by means of wave guide measurements. It was found that, on equal composition, the two systems present very different permittivities, that in the case of electrospun mats is far lower than that of films. These results are explained in view of the different microstructures. In particular, the massive presence of porosity is demonstrated to be the major parameter affecting the EM properties of mats. Shielding effectiveness was evaluated and was found to be poor for both systems, despite the relative large amount of conductive nanofiller. This results was attributed, in the case of films, to the presence of multiple reflections among CNF, while in the case of mats to their porous microstructure that let the waves easily pass through
Critical aspects for a CFD simulation compared with PIV analysis of the flow field downstream a prosthetic heart valve
No full textMultiresolution analysis of the aortic blood pressure variability as investigational tool in experimental fetal cardiac surgery
No full textComputational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow
No full textVascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated comparing their pressure loss–flow rate relationships, as obtained from in vitro experiments using a monodimensional approach; this methodology neither furnish information about the local fluid dynamics nor the established flow field in specific clinical work conditions. Since the shear stress is a critical factor in the design of artificial circulatory devices, more knowledge should be necessary about the local values assumed by the haemodynamic parameters during cannulation. An alternative way to investigate the fluid dynamic as accurately as possible is given by numeric studies. A 3D model of cannula concentrically placed in a rigid wall vessel is presented, with the finite element methodology used to numerically simulate the steady-state flow field in two different venous cannulation case studies, with two cannulae having a central hole and two or four side holes, respectively, with the same boundary conditions. Lower velocity and shear stress peak values have been computed for the model with four side holes upstream of the central hole, in the region of the cannula where the inlet flows meet and towards cannula's outlet, due to the increased flow symmetry and inlet area with respect to the model with two side holes. Starting from the investigation of different cannula designs, numerically assessing the local fluid dynamics, indications can be drawn to support both the design phase and the device optimal clinical use, in order to limit risks of biomechanical origin. Thus the presence of four side holes implied, as a consequence of the greater inlet area and of the increased symmetry, a less disturbed blood flow, together with reduced shear stress values. Furthermore, results show that the numerical simulations furnished useful informations on the interaction between vessel and cannula, e.g. on the fluid dynamics establishing in the free luminal space left, in the vessel, by the inserted cannula
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