Manuel A. Alves

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— The objective of this study was to illustrate how different methods of obtaining the Radar Cross Section (RCS) of an object may produce different results. RCS diagrams of a metallic airplane model (length, 0.64 m) were obtained in an anechoic chamber, with a Lab-Volt RCS system, and simulated with a simulation software. The measurements and simulations(More)
financial support provided under program POCI2010 by FCT and FEDER (project POCI/EQU/59256/2004) We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden contraction-expansion. This flow configuration is typically used to generate extensional deformations and high strain rates. The excess(More)
We utilize a recently developed microfluidic device, the Optimized Shape Cross-slot Extensional Rheometer (OSCER), to study the elongational flow behavior and rheological properties of hyaluronic acid (HA) solutions representative of the synovial fluid (SF) found in the knee joint. The OSCER geometry is a stagnation point device that imposes a planar(More)
A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point(More)
Wormlike micellar surfactant solutions are encountered in a wide variety of important applications, including enhanced oil recovery and ink-jet printing, in which the fluids are subjected to high extensional strain rates. In this contribution we present an experimental investigation of the flow of a model wormlike micellar solution (cetyl pyridinium(More)
We investigate the stability of steady planar stagnation flows of a dilute polyethylene oxide (PEO) solution using T-shaped microchannels. The precise flow rate control and well-defined geometries achievable with microfluidic fabrication technologies enable us to make detailed observations of the onset of elastically-driven flow asymmetries in steady flows(More)
We study the flow of a Newtonian fluid through microfabricated hyperbolic contractions in detail. A set of planar converging geometries, with total Hencky strains ranging from 1 to 3.7, have been fabricated in order to produce a homogeneous extensional flow field within the contraction. The kinematics in the contraction region are investigated(More)
We present an experimental investigation of viscoelastic fluid flow in a cross-slot microgeometry under low Reynolds number flow conditions. By using several viscoelastic fluids, we investigate the effects of the microchannel bounding walls and the polymer solution concentration on the flow patterns. We demonstrate that for concentrated polymer solutions,(More)
In this work, we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are(More)