Ground vibration due to a high-speed moving harmonic rectangular load on a poroviscoelastic half-space

AbstractThe transmission of vibrations in the ground, due to a high-speed moving vertical harmonic rectangular load, is investigated theoretically. The problem is three-dimensional and the interior of the ground is modelled as a totally or partially saturated porous viscoelastic half-space, using the complete Biot theory. The solutions in the transformed domain are obtained using a double Fourier transform on the surface spatial variables. A modified hysteretic damping model defined in the wavenumber domain is used, first presented by Lefeuve-Mesgouez et al. [Lefeuve-Mesgouez, G., Le Houédec, D., Peplow, A.T., 2000. Vibration in the vicinity of a high-speed moving harmonic strip load. Journal of Sound and Vibration 231(5) 1289–1309]. Numerical results for the displacements of the solid and fluid phases, over the surface of the ground and in depth, are presented for loads moving with speeds up to and beyond the Rayleigh wave speed of the medium

A lattice Boltzmann model for natural convection in cavities

We study a multiple relaxation time lattice Boltzmann model for natural convection with moment–based boundary conditions. The unknown primary variables of the algorithm at a boundary are found by imposing conditions directly upon hydrodynamic moments, which are then translated into conditions for the discrete velocity distribution functions. The method is formulated so that it is consistent with the second–order implementation of the discrete velocity Boltzmann equations for fluid flow and temperature. Natural convection in square cavities is studied for Rayleigh numbers ranging from 103 to 106. An excellent agreement with benchmark data is observed and the flow fields are shown to converge with second order accuracy

Experimental and numerical characterization of the viscoelastic behaviour of cartilages and soft tissues of the human nose

Dissertação de mestrado integrado em Engenharia BiomédicaThe facial plastic surgery, and particularly the area of rhinoplasty, is undoubtedly a growing up market. Surgical techniques have been evolving to respond to very specific patient desires not only for functional reasons, but also to resolve aesthetic issues. Actually, it is moving plenty of money around the world, being a great scientific and commercial opportunity among researchers. The human nose is composed of three major portions separated by two well-defined regions of transition (K-area and S-area) that are very complicated to deal with in postoperative periods. The viscoelastic behaviour of soft biological tissues, especially that of nasal cartilages and adjacent subcutaneous/fatty tissues, is barely known. There are no studies on the viscoelastic characterization of the mechanical properties of nasal septum (NS), upper lateral cartilages (ULC), and lower lateral cartilages (LLC) in creep and relaxation (basic viscoelasticity features) neither on the determination of frequency- and temperature-dependent properties of these tissues through dynamic mechanical analysis (DMA) in tension and compression. General information on thermal degradations through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) is also missing. Therefore, part of this work intends to fill this lack of the literature giving some insights into the cartilage internal composition and architecture, as well as the specificity of the activated mechanisms under constant stress or strain. Furthermore, numerical simulations were performed based on a hyper-viscoelastic mathematical formulation using a home-made open-source finite element (FE) solver (V-Biomech) in order to find a set of basic constitutive parameters that allow to replicate the experimental creep and relaxation behaviours of nasoseptal cartilage specimens from distinct regions of the quadrilateral cartilage (QLC). Thus, a complete standard biphasic poro-hyper-viscoelastic constitutive law was developed and validated. Finite Element Models (FEM) are gaining relevance to analyse soft biological components. As example, numerical simulations of the viscoelastic behaviours of the specimens harvested from anterior part of the QLC were performed to understand which of the constitutive parameters were more sensitive to achieve the best numerical-experimental agreement. The tools to reproduce these simulations in a more complex geometry (the whole nasal structure, with bony and cartilaginous components) were also developed and presented. The work still goes on it.A cirurgia plástica facial, e em particular a área da rinoplastia, é indubitavelmente um mercado em crescimento. As técnicas cirúrgicas têm evoluído no sentido de dar resposta aos desejos mais específicos de cada paciente não só por razões funcionais, mas também para resolução de problemas estéticos. Atualmente, é uma área que movimenta muito dinheiro em todo o mundo, tornando-se numa evidente oportunidade científica e comercial. O nariz humano está dividido em três regiões principais separadas por duas zonas de transição (áreas K e S) que são muito difíceis de manipular em períodos de recuperação pós-cirurgia. O comportamento viscoelástico de tecidos moles, especialmente o das cartilagens nasais e dos tecidos subcutâneo/adiposo adjacentes, é pouco conhecido. Atualmente, não existem estudos sobre a caracterização de propriedades mecânicas da cartilagem septal nem das cartilagens laterais superiores ou inferiores em fluência e relaxação (características de comportamentos viscoelásticos). A determinação de propriedades mecânicas em função da frequência de oscilação e da temperatura para estes mesmos materiais através de uma análise de DMA em tensão e compressão, assim como informações gerais sobre fenómenos de degradação térmica por DSC e TGA, também não são reportados. Assim sendo, parte desta dissertação pretende preencher esta lacuna da literatura, contribuindo para a compreensão da composição e arquitetura internas da cartilagem e da especificidade dos mecanismos ativados sob influência de uma tensão ou deformação constantes. Além disso, foram levadas a cabo simulações numéricas baseadas numa formulação matemática de híper-viscoelasticidade num software de elementos finitos desenvolvido na Instituição (V-Biomech) e foram encontrados os valores dos parâmetros que permitem replicar o comportamento experimental de fluência e relaxação de cartilagens de diferentes regiões do septo nasal. Assim, uma lei constitutiva que agrega conceitos de híper-elasticidade, viscoelasticidade e permeabilidade, acoplando o distinto comportamento de materiais sólidos e fluidos, foi desenvolvida e validada. Além das simulações do comportamento viscoelástico das amostras colhidas a partir da região anterior do septo, um conjunto de outras ferramentas para aplicação dos mesmos conceitos numa geometria mais complexa foi também desenvolvido e apresentado. Um trabalho que ainda continua

Aspects of mathematical biology : from self-organisation of the cytoskeleton to transport of migratory species

This thesis spans scales of mathematical biology, from single molecules to groups of organisms. We explore questions regarding the self-organisation of the cytoskeleton and the long distance migration of animals. Though disparate at first glance, both topics revolve around transport and self-organisation of biological particles. We first model the microtubule cytoskeleton: a self-organising dynamic scaffolding along which cellular components, e.g. proteins, are transported. Its organisation is crucial for correct cellular functions; for example, maintaining the correct distribution of E-cadherin (the epithelial cell adhesion protein) along the cell boundary to ensure tissue integrity. Using stochastic simulations, genetic manipulations of the Drosophila epithelial cells and a probabilistic model we show that microtubule cytoskeleton selforganisation principally depends on cell geometry and microtubule seed density and is robust at the tissue scale. We then extend this work. Specifically, we build and explore an analytical model and perform stochastic simulations to explain microtubule self-organisation in crowded cytoplasm, i.e. containing various highly anisotropic barriers. We consider Drosophila follicular epithelium cells, which contain actin cables throughout. We find that anisotropy in the cell interior leads to a significant increase in the number of microtubules pointing in the direction of the anisotropy. This allows us to deduce the type of interaction between microtubules and actin cables. We introduce a new measure of self-organisation of microtubules, the bundling factor, and use it to explore the persistent direction of transport created by microtubule bundles. A second research topic is subsequently discussed. Many animals navigate long distances for purposes including foraging or nesting. While often mysterious, various lines of research support the idea that navigation is aided by a combination of cues whose magnitudes change with distance from the target. Motivated by agent-based simulations from a study of green sea turtle migration, we construct an abstract model for taxis-based animal navigation. We investigate the key properties of various navigating cues and their impact on animal migration, and discuss how the starting location can affect the mean first passage time of a migratory journey

Resolving thermo-hydro-mechanical coupling: Spontaneous porous fluid and strain localisation

Localisation of deformation and flow is ubiquitously observed on Earth, spanning from sub-terraneous locations both in the deep interior and towards the shallow surface. Ductile strain localisation in tectonic processes or channelling and focusing of fluids in porous rocks are widely reported expressions of strain and flow localisation, governed by hydraulic, thermal and mechanical interactions. The intrinsic coupling of these different physical processes provides additional localisation mechanisms to well-established single-process physics. Models that address interactions between different physical processes must include non-linear feedbacks that may potentially trigger new and non-intuitive characteristic length and time scales. Accurately resolving this complex non-linear interplay resulting from coupled physics permits us to better understand the nature of multiphysics processes and to provide more accurate predictions on how, when and where to expect localisation. In many anthropogenic activities related to achieving a carbon-free energy transition, accurate predictions of mid-term to long-term behaviour for geosystems are vital. Engineered waste disposal solutions such as CO2 sequestration and nuclear waste deposits require coupled models in order to predict the complexities of the evolving system. However, there is a current lack in model capability to address the non-linear interactions resulting from multiphysics coupling. Available models often fail to reproduce major first-order field observations of localisation, mainly owing to poor coupling strategies and a lack of affordable resolution needed to resolve very local non-linear features, especially in three spatial dimensions. In this thesis, I address these issues using a supercomputing approach to resolve sufficiently high-resolution stain and flow localisation in non-linearly deforming porous media, relying on a thermodynamically consistent model formulation. The developed graphical processing unit-based parallel algorithms show close to linear weak scaling on the world’s third-largest supercomputer and are benchmarked against classical direct-iterative type solvers. The high-resolution computations are needed for the convergence of the calculations. The results confirm that a strong coupling between solid deformation, fluid flow and heat diffusion provides a viable mechanism for ‘chimney’ formation or strain localisation. Flow localisation in high-permeability chimneys provides efficient pathways for fast vertical fluid migration. By using model parameters relevant for sedimentary rocks, natural observations and their main characteristic features could be reproduced. In summary, this thesis provides an extensive study on hydro-mechanical interaction in fluid-saturated and non-linearly deforming porous rocks. Further, the predicted high-permeability pathways are vital to understand the formation of potential leakage pathways and are a prerequisite for reliable risk assessment in long-term waste storage. Finally, the developed solution strategy is successfully utilised to resolve strain localisation in thermo-mechanically coupled processes. -- La localisation de la déformation et des fluides est observée à l’échelle du Globe, allant des couches profondes jusqu’à la subsurface. Des phénomènes géologiques tels que la localisation de la déformation ductile ou la chenalisation des fluides dans les roches poreuses témoignent d’amplifications locales de la déformation et de la porosité et résultent d’interactions entre des processus hydrauliques, thermiques et mécaniques. Le couplage de ces divers processus physiques génère des rétroactions non-linéaires et aboutit à des nouvelles grandeurs caractéristiques non-triviales. Une résolution précise de ces interactions complexes permet de mieux comprendre la nature des processus multi-physiques et permet d’établir de meilleures prédictions quant à de possibles occurrences de localisation. Passablement d’activités anthropogéniques liées à la transition énergétique reposent sur des prédictions précises de l’évolution à long terme des géo-systèmes. La séquestration du CO2 ainsi que le stockage des déchets nucléaires requièrent l’utilisation de modèles couplés afin de prédire l’évolution des systèmes de confinement. Toutefois, les modèles actuels peinent à reproduire les observations de premier ordre, notamment les évidences de localisation des fluides et de la déformation. Les principales raisons sont le traitement des problèmes trop souvent effectué en deux dimensions, le manque de rigueur dans les stratégies de couplage entre les différents processus ainsi que l’utilisation de résolutions insuffisantes dans les modèles. Dans cette thèse, je propose une approche basée sur le calcul à haute performance permettant de résoudre avec des résolutions élevées les processus de localisation dans des milieux poreux déformables en utilisant des modèles thermodynamiquement consistants. Les algorithmes parallèles développés utilisent des processeurs graphiques disponibles entre autres sur le troisième plus performant superordinateur du monde et reportent un temps de calcul identique lorsque la taille du problème à résoudre grandi proportionnellement avec le nombre de ressources disponibles. Les résultats attestent de la convergence de la méthode et confirment le fait qu’un couplage important entre déformation, écoulement des fluides et diffusion de la chaleur permet la formation de chenaux à perméabilité élevée ainsi que la localisation de la déformation. Ces chenaux, ou drains, permettent l’écoulement focalisé ainsi qu’une migration verticale rapide des fluides. En prenant en compte les paramètres pétrophysiques caractéristiques des roches situées dans des bassins sédimentaires, ces écoulements préférentiels reproduisent les observations naturelles. La prédiction d’occurrence de chenaux à perméabilité élevée est vitale afin de mieux prévenir de potentiels risques de fuites et de fournir des solutions suˆres pour les générations futures en termes de stockage de déchets à risque. Pour conclure, cette thèse propose une étude extensive sur les interactions hydromécaniques dans des roches poreuses saturées avec des fluides. De manière analogue, la stratégie de solution développée a été appliquée pour étudier la localisation de la déformation ductile résultant d’un couplage thermomécanique

Towards patient-specific modelling as a pre-operative planning strategy and follow up assessment for the treatment of advanced heart failure with rotary blood pumps

Background: Ventricular Assist Devices (VADs) insertion is an established treatment for patients with end-stage heart failure waiting for a heart transplant or in need for long-term circulatory support (destination therapy). Rotary blood pumps (RBP) are the most popular devices in view of their size and performance. Pre-operative planning strategy for the insertion of a left ventricular assist device (LVAD) requires a timely discussion at a Multi-Disciplinary Team Meeting (MDT). Clinical-decision making is based according to the needs of the patient and must be processed without delays. Nevertheless, thrombus formation remains a feared complication which affects outcome. VADs operate in a flow regime which is difficult to simulate: the transitional region at the boundary of laminar and turbulent flow (low Reynolds number). Different methods have been used but the best approach remains debatable. Computational Fluid Dynamics (CFD) is an attractive and invaluable tool for the study of the interactions between VADs and the cardiovascular system. The aim of this thesis is three-fold: a) to investigate the use of pressure-volume analysis in a clinical setting through the review of six heart failure patients previously discussed at a MDT meeting with a view to predict or guide further management; b) to review the theory behind modelling approaches to VADs and their interactions with the cardiovascular system for better understanding of their clinical use. Then, an overview of computational fluid dynamics (CFD) is considered as a prelude to its application to the analysis of VADs performance. Additionally, the development of a simplified model of centrifugal pump will be used in initial simulations as preliminary analysis; c) to examine an example of a proof-of-concept pilot patient-specific model of an axial flow pump (HeartMate II) as pre-operative planning strategy in a patient-specific model with a view to identify potential critical areas that may affect pump function and outcome in a clinical setting. Material and Methods: 3D reconstruction from CT-scan images of patients who underwent the insertion of rotary blood pumps, namely HeartWare HVAD and HeartMate II. Ansys Fluent has been used for CFD analysis based on the fundamental governing equations of motion. Blood has been modelled as incompressible, Newtonian fluid with density = 1060 and viscosity = 0.0035 kg/m-s. The laminar and SST models have been used for comparison purposes. The rotational motion of the impeller has been implemented using the moving reference frame (MRF) approach. The sliding mesh method has also been used to account for unsteady interaction between stationary and moving part. The no-slip condition has been applied to all walls, which were assumed to be rigid. Boundary conditions consisting of velocity inlet and pressure outlet of the pump based on different settings and constant rotational speed for the impeller. Pressure-velocity coupling has been based on the coupled scheme. Spatial discretisation consisted of the “least square cell based” gradient for velocity and “PRESTO” or second order for pressure. Second order upwind has been set for the momentum, turbulent kinetic energy and specific dissipation rate. First order implicit has been set for transient formulation. The pseudo transient algorithm (steady state), the high order relaxation term and the warped-face gradient correction have been used to add an unsteady term to the solution equations with the aim to improve stability and enhance convergence. Specific settings have been considered for comparison purposes. Results: Pressure-volume simulation analysis in six advanced heart failure patients showed that an integrated model of the cardiovascular system based on lumped-parameter representation, modified time-varying elastance and pressure-volume analysis of ventricular function seems a feasible and suitable approach yielding a sufficiently accurate quantitative analysis in real time, therefore applicable within the time-constraints of a clinical setting. Lumped-parameter models consist of simultaneous ordinary differential equations complemented by an algebraic balance equation and are suitable for examination of global distribution of pressure, flow and volume over a range of physiological conditions with inclusion of the interaction between modelled components. Higher level lumped-parameter modelling is needed to address the interaction between the circulation and other systems based on a compromise between complexity and ability to set the required parameters to personalise an integrated lumped-parameter model for a patient-specific approach. CARDIOSIM© fulfils these requirements and does address the systems interaction with its modular approach and assembly of models with varying degree of complexity although 0-D and 1-D coupling may be required for the evaluation of long-term VAD support. The challenge remains the ability to predict outcome over a longer period of time. The preliminary CFD simulations with the HeartWare HVAD centrifugal pump demonstrated that it is possible to obtain an accurate analysis in a timely manner to complement the clinical review process. The simulations with the pilot patient-specific model of the HeartMate II axial flow pump revealed that a complex 3D reconstruction is feasible in a timely manner and can be used to generate sufficiently accurate results to be used in the context of a MDT meeting for the purposes of clinical decision-making. Overall, these three studies demonstrate that the time frame of the simulations was within hours which may fit the time constraints of the clinical environment in the context of a MDT meeting. More specifically, it was shown that the laminar model may be used for an initial evaluation of the flow development within the pump. Nonetheless, the k- model offers higher accuracy if the timeline of the clinical setting allows for a longer simulation. Conclusion: This thesis aimed at the understanding of the use of computational modelling as a pre-operative planning strategy and follow up assessment for the treatment of advanced heart failure with rotary blood pumps. The novelty lays in the use of both pressure-volume simulation analysis and 3D flow dynamics studies in VADs with a view to treatment optimisation and outcome prediction within the time constraints of a clinical setting in the context of a MDT meeting. The clinical significance and the contribution to the field is a more targeted approach for different groups of patients and a more quantitative evaluation in the clinical decision process based on a pro-active co-operation between clinicians and scientists reducing the potential for “guess work”. The results of this thesis are a proof-of-concept as a prelude to a potential future implementation of patient-specific modelling within a clinical setting on a daily basis demonstrating a clear clinical significance and contribution to the field. The proposed approach does not consider modelling and simulation as a substitute for clinical experience but an additional tool to guide therapeutic intervention and complement the clinical decision process in which the clinician remains the ultimate decision-maker. Such an approach may well add a different dimension to the problem of heart failure with potential for high return in terms of patient’s outcome and long-term surveillance. The same principles would be applicable to other cardiovascular problems in line with the current concept of “Team Approach” such as the Heart Team, the Structural Heart Team or the Aortic Team. The present work has taken this concept closer to clinical delivery and has highlighted its potential but further work remains to be done in refining the technique.Background: Ventricular Assist Devices (VADs) insertion is an established treatment for patients with end-stage heart failure waiting for a heart transplant or in need for long-term circulatory support (destination therapy). Rotary blood pumps (RBP) are the most popular devices in view of their size and performance. Pre-operative planning strategy for the insertion of a left ventricular assist device (LVAD) requires a timely discussion at a Multi-Disciplinary Team Meeting (MDT). Clinical-decision making is based according to the needs of the patient and must be processed without delays. Nevertheless, thrombus formation remains a feared complication which affects outcome. VADs operate in a flow regime which is difficult to simulate: the transitional region at the boundary of laminar and turbulent flow (low Reynolds number). Different methods have been used but the best approach remains debatable. Computational Fluid Dynamics (CFD) is an attractive and invaluable tool for the study of the interactions between VADs and the cardiovascular system. The aim of this thesis is three-fold: a) to investigate the use of pressure-volume analysis in a clinical setting through the review of six heart failure patients previously discussed at a MDT meeting with a view to predict or guide further management; b) to review the theory behind modelling approaches to VADs and their interactions with the cardiovascular system for better understanding of their clinical use. Then, an overview of computational fluid dynamics (CFD) is considered as a prelude to its application to the analysis of VADs performance. Additionally, the development of a simplified model of centrifugal pump will be used in initial simulations as preliminary analysis; c) to examine an example of a proof-of-concept pilot patient-specific model of an axial flow pump (HeartMate II) as pre-operative planning strategy in a patient-specific model with a view to identify potential critical areas that may affect pump function and outcome in a clinical setting. Material and Methods: 3D reconstruction from CT-scan images of patients who underwent the insertion of rotary blood pumps, namely HeartWare HVAD and HeartMate II. Ansys Fluent has been used for CFD analysis based on the fundamental governing equations of motion. Blood has been modelled as incompressible, Newtonian fluid with density = 1060 and viscosity = 0.0035 kg/m-s. The laminar and SST models have been used for comparison purposes. The rotational motion of the impeller has been implemented using the moving reference frame (MRF) approach. The sliding mesh method has also been used to account for unsteady interaction between stationary and moving part. The no-slip condition has been applied to all walls, which were assumed to be rigid. Boundary conditions consisting of velocity inlet and pressure outlet of the pump based on different settings and constant rotational speed for the impeller. Pressure-velocity coupling has been based on the coupled scheme. Spatial discretisation consisted of the “least square cell based” gradient for velocity and “PRESTO” or second order for pressure. Second order upwind has been set for the momentum, turbulent kinetic energy and specific dissipation rate. First order implicit has been set for transient formulation. The pseudo transient algorithm (steady state), the high order relaxation term and the warped-face gradient correction have been used to add an unsteady term to the solution equations with the aim to improve stability and enhance convergence. Specific settings have been considered for comparison purposes. Results: Pressure-volume simulation analysis in six advanced heart failure patients showed that an integrated model of the cardiovascular system based on lumped-parameter representation, modified time-varying elastance and pressure-volume analysis of ventricular function seems a feasible and suitable approach yielding a sufficiently accurate quantitative analysis in real time, therefore applicable within the time-constraints of a clinical setting. Lumped-parameter models consist of simultaneous ordinary differential equations complemented by an algebraic balance equation and are suitable for examination of global distribution of pressure, flow and volume over a range of physiological conditions with inclusion of the interaction between modelled components. Higher level lumped-parameter modelling is needed to address the interaction between the circulation and other systems based on a compromise between complexity and ability to set the required parameters to personalise an integrated lumped-parameter model for a patient-specific approach. CARDIOSIM© fulfils these requirements and does address the systems interaction with its modular approach and assembly of models with varying degree of complexity although 0-D and 1-D coupling may be required for the evaluation of long-term VAD support. The challenge remains the ability to predict outcome over a longer period of time. The preliminary CFD simulations with the HeartWare HVAD centrifugal pump demonstrated that it is possible to obtain an accurate analysis in a timely manner to complement the clinical review process. The simulations with the pilot patient-specific model of the HeartMate II axial flow pump revealed that a complex 3D reconstruction is feasible in a timely manner and can be used to generate sufficiently accurate results to be used in the context of a MDT meeting for the purposes of clinical decision-making. Overall, these three studies demonstrate that the time frame of the simulations was within hours which may fit the time constraints of the clinical environment in the context of a MDT meeting. More specifically, it was shown that the laminar model may be used for an initial evaluation of the flow development within the pump. Nonetheless, the k- model offers higher accuracy if the timeline of the clinical setting allows for a longer simulation. Conclusion: This thesis aimed at the understanding of the use of computational modelling as a pre-operative planning strategy and follow up assessment for the treatment of advanced heart failure with rotary blood pumps. The novelty lays in the use of both pressure-volume simulation analysis and 3D flow dynamics studies in VADs with a view to treatment optimisation and outcome prediction within the time constraints of a clinical setting in the context of a MDT meeting. The clinical significance and the contribution to the field is a more targeted approach for different groups of patients and a more quantitative evaluation in the clinical decision process based on a pro-active co-operation between clinicians and scientists reducing the potential for “guess work”. The results of this thesis are a proof-of-concept as a prelude to a potential future implementation of patient-specific modelling within a clinical setting on a daily basis demonstrating a clear clinical significance and contribution to the field. The proposed approach does not consider modelling and simulation as a substitute for clinical experience but an additional tool to guide therapeutic intervention and complement the clinical decision process in which the clinician remains the ultimate decision-maker. Such an approach may well add a different dimension to the problem of heart failure with potential for high return in terms of patient’s outcome and long-term surveillance. The same principles would be applicable to other cardiovascular problems in line with the current concept of “Team Approach” such as the Heart Team, the Structural Heart Team or the Aortic Team. The present work has taken this concept closer to clinical delivery and has highlighted its potential but further work remains to be done in refining the technique

Development of a biomimetic finite element model of the intervertebral disc diseases and regeneration

Tese de doutoramento do Programa Doutoral em Engenharia BiomédicaDegenerative Disc Disease is one of the largest health problems faced worldwide, based on lost working time and associated costs. This is the driving force for the development of a biomimetic Finite Element (FE) model of the Intervertebral Disc (IVD), which is a multiphasic and highly inhomogeneous structure. A great amount of experimental and numerical works have studied the IVD and proven that it presents osmo-poro-hyper-visco-elastic behavior, with high influence of the anisotropic behavior of collagen fibers. Poroelastic models of the IVD are mostly implemented in commercial FE-packages, which means that the accessibility to the source algorithm is often circumscribed. In order to approach to the biomechanical behavior of the IVD in the Human spine with higher flexibility and accuracy, an innovative poroelastic formulation implemented on a home-developed open-source FE solver is addressed and validated throughout this work. Numerical simulations were mostly devoted to the analysis of the non-degenerated Human IVD time-dependent behavior, using a geometrically accurate FE model of a full motion segment (MS), constructed with quadratic 27 nodes hexaedral elements. The results of the tests performed for creep assessment were inside the scope of the experimental and numerical literature data, with remarkable improvements of the numerical accuracy when compared with some previously published results obtained with the commercial FE-package ABAQUS®. Previously unpublished experimental data from the research partners at VUmc (Amsterdam, The Netherlands) were also analyzed and compared with the MS FE model, which proved to reproduce satisfactorily to the physiological and non-physiological conditions of those experimental tests. The IVD biomechanical behavioral is complex and dependent on multiple factors. The numerical simulations with the present MS FE model, using the home-developed open-source FE solver, demonstrated potential to biomimitize the IVD and thus contribute to the advance of the knowledge on its biomechanics.A Doença Degenerativa dos Discos é um dos maiores problemas de saúde enfrentados a nível mundial, a nível de tempo de trabalho perdido e custos associados. Esta é a motivação para o desenvolvimento de um modelo biomimético de Elementos Finitos (EF) do Disco Intervertebral (DIV), que é uma estrutura multifásica e altamente heterogénea. Um grande número de trabalhos, experimentais e numéricos, estudou o DIV e provou que este apresenta comportamento osmo-poro-hiper-visco-elástico, com influência significativa do comportamento anisotrópico das fibras de colagénio. Os modelos poroelásticos do DIV têm sido frequentemente implementados em programas comerciais de EF, o que significa que o acesso ao algoritmo-fonte é circunscrito. Para obter uma aproximação mais flexível e rigorosa ao comportamento biomecânico do DIV, uma formulação poroelástica inovadora foi implementada num programa de EF de acesso livre, desenvolvido internamente. Esta formulação é descrita e validada ao longo do presente trabalho. As simulações numéricas foram quase totalmente dedicadas à análise do comportamento do DIV Humano não-degenerado, que se sabe ser fortemente dependente do factor tempo. Para esse feito, foi utilizado um modelo de EF geométrico correcto de um segmento móvel (SM) completo, construído com elementos quadráticos hexaédricos de 27 nós. Os resultados dos testes levados a cabo para análise do comportamento do DIV em termos de fluência ficaram dentro do espectro dos resultados experimentais e numéricos disponíveis na literatura. Foram, inclusivé, registadas melhorias notáveis em relação a alguns trabalhos que utilizaram ABAQUS®, um programa de EF comericalmente disponível. Foram também analisados dados experimentais não publicados dos parceiros de investigação da VUmc (Amesterdão, Holanda). A comparação com o modelo EF do SM demonstrou que este modelo reproduz satisfactoriamente as condições dos testes experimentais, sejam elas condições fisiológicas ou não-fisiológicas. O comportamento biomecânico do DIV é complexo e dependente de múltiplos factores. As simulações numéricas levadas a cabo com o modelo EF do SM, utilizando o programa de EF de acesso livre desenvolvido internamente, demonstraram potencial para biomimetizar o DIV e assim contribuir para o avanço do conhecimento da sua biomecânica