cf castro

Numerical study on the hemodynamics of patient-specific carotid bifurcation using a new mesh approach

The definition of a suitable mesh to simulate blood flow in the human carotid bifurcation has been investigated. In this research, a novel mesh generation method is proposed: hexahedral cells at the center of the vessel and a fine grid of tetrahedral cells near the artery wall, in order to correctly simulate the large blood velocity gradients associated with specific locations. The selected numerical examples to show the pertinence of the novel generation method are supported by carotid ultrasound image data of a patient-specific case. Doppler systolic blood velocities measured during ultrasound examination are compared with simulated velocities using 4 different combinations of hexahedral and tetrahedral meshes and different fluid dynamic simulators. The Lins test was applied to show the concordance of the results. Wall shear stress-based descriptors and localized normalized helicity descriptor emphasize the performance of the new method. Another feature is the reduced computation time required by the developed methodology. With the accurate combined mesh, different flow rate partitions, between the internal carotid artery and external carotid artery, were studied. The overall effect of the partitions is mainly in the blood flow patterns and in the hot-spot modulation of atherosclerosis-susceptible regions, rather than in their distribution along the bifurcation.

The design, properties and performance of shape optimized masonry blocks

The choice for a certain masonry unit depends mainly on its functional performance. The new European Directives regulations require different solutions challenging manufacturers to develop optimized systems. In particular, in south European countries where the mild winter climate justifies the use of high-thermal-performance masonry walls, the search for optimized masonry units and the design of single-leaf masonry external walls is a challenge. In this chapter, the basic requirements for enclosure walls used in the building facades are analysed. A review of innovative masonry blocks developed in recent years is presented. An example of an optimized lightweight concrete masonry unit, for single leaf enclosure walls with no external insulation, developed within a collaborative project with MAXIT group, is illustrated. The iterative problem of finding the optimal geometry and topology, namely position, size and spacing of the holes within the block that minimizes the wall thermal transmittance, is supported by a genetic algorithm constrained by the characteristics and construction practices of masonry materials. Numerical simulations and laboratory tests of two new wall solutions currently under development at the University of Porto are reported. Finally, future trends for the development of masonry systems are also introduced.