Browsing by Author "Souza, Maria Sabrina"
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- Additive manufacturing techniques for the fabrication of intracranial aneurysm biomodelsPublication . Rodrigues, D.; Souza, A.; Souza, Maria Sabrina; Ferrera, Conrado; Ribeiro, J.E.; Lima, Rui A.The hemodynamics of intracranial aneurysm (IA) involves complex phenomena that influence its growth and rupture. The advancement of additive manufacturing techniques allowed the development of biomodels suitable for in vitro experimental tests. Thus, we present in this work the process of manufacturing flow biomodels, using different additive manufacturing techniques and materials. The biomodels obtained through these methods proved to be suitable for experiments using imaging techniques and for the validation of numerical studies.
- Estudo numérico do fluxo num aneurisma intracraniano real para diferentes números de ReynoldsPublication . Souza, Maria Sabrina; Ribeiro, J.E.; Rocha, João; Santos, Luiz Alberto dosO aneurisma intracraniano (AI) é uma patologia que na maioria dos casos não apresenta sintomas no paciente e ainda não está bem compreendida em relação a interação de fatores que a desenvolvem. Atualmente, as avaliações de risco de ruptura são baseadas, principalmente, no tamanho do AI, o que não é muito confiável, visto que aneurisma pequenos também se rompem. Além disso, existem controvérsias relacionadas a valores altos ou baixos de tensão de corte na parede serem responsáveis pela ruptura de AI. Portanto, a determinação de métodos para avaliar os fatores de risco e auxiliar no diagnóstico médico é de grande importância. Com isso, o objetivo deste trabalho foi efetuar o estudo hemodinâmico do escoamento de fluidos no interior de um AI real. Para isso, foram realizadas simulações numéricas em regime estacionário e em regime transitório, utilizando o software Ansys, Fluent. Em regime estacionário foram realizadas três análises qualitativas, que são: validação do fluido análogo ao sangue utilizado no teste experimental; a validação dos resultados numéricos com o método experimental; e, em seguida, foi feita uma análise do comportamento do fluxo, classificando-o de acordo com o grau de risco de ruptura. Já em regime transitório, foi realizada uma análise quantitativa, observando parâmetros como tensão de corte e pressão na parede. Os resultados obtidos através das análises qualitativas, mostraram que: o fluido análogo possui um comportamento parecido com o do sangue para testes de visualização experimental; o comportamento do fluxo nas simulações numéricas foi semelhante ao dos testes experimentais, validando assim os resultados numéricos; e, de acordo com a classificação, pode-se dizer que o aneurisma em estudo tem uma elevada probabilidade de se romper. Os resultados da análise quantitativa obtiveram uma concordância com a análise anterior. Portanto, foi possível mostrar que o uso da ferramenta CFD apresenta grande potencial na investigação, no diagnóstico e definição de tratamentos, para patologias como o aneurisma intracraniano.
- Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloyPublication . Costa, Sharlane; Souza, Maria Sabrina; Braz-César, Manuel; Gonçalves, José; Ribeiro, J.E.One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.
- Flow visualizations in a PDMS cerebral aneurysm biomodelPublication . Souza, Andrews Victor Almeida; Ferrera, Conrado; Puga, Hélder; Lima, Rui A.; Ribeiro, J.E.; Souza, Maria SabrinaCerebral aneurysm is an abnormal dilatation of the blood vessel which affects a high percentage of the worldwide population. One way to investigate this pathology is using in vivo techniques, but these types of experiments have a high cost and low reproducibility. Thus, to understand the local hemodynamics of brain aneurysms, it is imperative to manufacture in vitro models that simulate real brain aneurysms. These biomodels are suitable for experimental testing, as well as for evaluating and validating computational models. In this work, was manufactured a biomodel of a cerebral aneurysm made by polydimethylsiloxane (PDMS), combining rapid prototyping technology with a PDMS gravity casting process. Experimental flow visualizations were performed at different flow rates. The flow visualizations results have shown that there is a transition from laminar to turbulent flow for a flow rate near 6 ml/min. The proposed PDMS biomodels have shown the ability to perform flow visualizations and have the potential to help the development and validation of computational models.
- Fluid flow and structural numerical analysis of a cerebral aneurysm modelPublication . Souza, Maria Sabrina; Souza, Andrews Victor Almeida; Carvalho, Violeta Meneses; Teixeira, Senhorinha F.C.F.; Fernandes, Carla S.; Lima, Rui A.; Ribeiro, J.E.Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several studies have been focused only on the hemodynamics of the flow within the IA. However, besides the effect of the flow, the development and rupture of the IA are also associated with a combination of other factors such as the wall mechanical behavior. Thus, the objective of this work was to analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of the fluid simulations were exported to the structural simulations in order to qualitatively observe the deformations, strains, normal stresses and shear stress generated in the channel wall. For the structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement, normal and shear stresses values.
- Manual and automatic image analysis segmentation methods for blood flow studies in microchannelsPublication . Carvalho, Violeta Meneses; Gonçalves, Inês M.; Souza, Andrews Victor Almeida; Souza, Maria Sabrina; Bento, David; Ribeiro, J.E.; Lima, Rui A.; Pinho, DianaIn blood flow studies, image analysis plays an extremely important role to examine raw data obtained by high-speed video microscopy systems. This work shows different ways to process the images which contain various blood phenomena happening in microfluidic devices and in microcirculation. For this purpose, the current methods used for tracking red blood cells (RBCs) flowing through a glass capillary and techniques to measure the cell-free layer thickness in different kinds of microchannels will be presented. Most of the past blood flow experimental data have been collected and analysed by means of manual methods, that can be extremely reliable, but they are highly time-consuming, user-intensive, repetitive, and the results can be subjective to user-induced errors. For this reason, it is crucial to develop image analysis methods able to obtain the data automatically. Concerning automatic image analysis methods for individual RBCs tracking and to measure the well know microfluidic phenomena cell-free layer thickness, two developed methods are present and discuss in order to demonstrate their feasibility for accurate data acquisition in such studies Additionally, a comparison analysis between manual and automatic methods was performed.
- Parametric optimization of the GMAW welding process in thin thickness of austenitic stainless steel by Taguchi methodPublication . Nobrega, Glauco; Souza, Maria Sabrina; Rodríguez-Martín, Manuel; Rodríguez-Gonzálvez, Pablo; Ribeiro, J.E.In the present work, an analysis of different welding parameters was carried out on the welding of stainless-steel thin thickness tubes by the Gas Metal Arc Welding (GMAW) process. The influence of three main parameters, welding voltage, movement angle, and welding current in the quality of the welds, was studied through a specifically designed experimental process based on the establishment of three different levels of values for each of these parameters. Weld quality is evaluated using destructive testing (macrographic analysis). Specifically, the width and root penetration of the weld bead were measured; however, some samples have been disregarded due to welding defects outside the permissible range or caused by excessive melting of the base metals. Data are interpreted, discussed, and analyzed using the Taguchi method and ANOVA analysis. From the analysis of variance, it was possible to identify the most influential parameter, the welding voltage, with a contribution of 43.55% for the welding penetration and 75.26% for the bead width, which should be considered in the designs of automatic welding processes to improve the quality of final welds.