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This work presents a novel application of the Shifted Boundary Method (SBM) within the Isogeometric Analysis (IGA) framework, applying it to two-dimensional and three-dimensional Poisson problems with Dirichlet and Neumann boundary conditions. The SBM boundary condition imposition is achieved by means of a fully penalty-free formulation, eliminating the need for penalty calibration. The numerical experiments demonstrate how order elevation, coupled with SBM through higher-order Taylor expansions, consistently achieves optimal convergence rates. Additionally, analyzing the condition number of the problem matrix reveals that SBM, when integrated with IGA, effectively circumvents the small cut-cell problem, a common issue in numerical methods with unfitted boundaries., Peer Reviewed, Postprint (published version)

In this work we present a novel methodology for the numerical simulation of patient-specific aortic dissections. Our proposal, which targets the seamless virtual prototyping of customized scenarios, combines an innovative two-step segmentation procedure with a CutFEM technique capable of dealing with thin-walled bodies such as the intimal flap. First, we generate the fluid mesh from the outer aortic wall disregarding the intimal flap, similarly to what would be done in a healthy aorta. Second, we create a surface mesh from the approximate midline of the intimal flap. This approach allows us to decouple the segmentation of the fluid volume from that of the intimal flap, thereby bypassing the need to create a volumetric mesh around a thin-walled body, an operation widely known to be complex and error-prone. Once the two meshes are obtained, the original configuration of the dissection into true and false lumen is recovered by embedding the surface mesh into the volumetric one and calculating a level set function that implicitly represents the intimal flap in terms of the volumetric mesh entities. We then leverage the capabilities of unfitted mesh methods, specifically relying on a CutFEM technique tailored for thin-walled bodies, to impose the wall boundary conditions over the embedded intimal flap. We tested the method by simulating the flow in four patient-specific aortic dissections, all involving intricate geometrical patterns. In all cases, the preprocess is greatly simplified with no impact on the computational times. Additionally, the obtained results are consistent with clinical evidence and previous research., The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S). Eduardo Soudah acknowledges the support of “Proyecto CPP2021-008546 financiado por MCIN/AEI/10.13039/501100011033 por la Unión Europea NextGenerationEU/ PRTR” and “Proyecto PID2021-122518OB-I00 financiado por MCIN/AEI/ 10.13039/501100011033 por FEDER Una manera de hacer Europa ”. Finally, the authors gratefully thank Aortyx and Mr. Yago Trias for the collaboration in the segmentation of the four patient-specific scenarios., Peer Reviewed, Postprint (published version)

This paper presents a dynamic formulation for the simulation of nearly incompressible structures using a mixed finite element method with equal-order interpolation pairs. Specifically, the nodal unknowns are the displacement and the volumetric strain component, something that makes possible the reconstruction of the complete stain at the integration point level and thus enables the use of strain-driven constitutive laws. Furthermore, we also discuss the resulting eigenvalue problem and how it can be applied for the modal analysis of linear elastic solids. The article puts special emphasis on the stabilisation technique used, which becomes crucial in the resolution of the generalised eigenvalue problem. In particular, we prove that using a variational multiscale method assuming the sub-grid scales to lie in the finite element space orthogonal to that of the approximation, namely the Orthogonal Sub-Grid Scales (OSGS), results in a convenient linear and symmetric generalised eigenvalue problem. The correctness, convergence and performance of the method are proven by solving a series of two- and three-dimensional examples., Peer Reviewed, Postprint (published version)

In this work, we present a novel unfitted mesh boundary strategy in the context of the Particle Finite Flement Method (PFEM) aiming to improve endemic limitations of the PFEM relative to boundary conditions treatment and mass conservation. In this new methodology, which we called Cut-PFEM, the fluid–wall interaction is not performed by adding interface elements, as is done in the standard PFEM boundaries. Instead, we use an implicit representation of (all or some of) the boundaries by introducing the use of a level set function. Such distance function detects the elements trespassing the (virtual) contours of the domain to equip them with opportunely boundary conditions, which are variationally enforced using Nitsche’s method. The proposed Cut-PFEM circumvents important issues associated with the standard PFEM contact detection algorithm, such as the artificial addition of mass to the computational domain and the anticipation of contact time. Furthermore, the Cut-PFEM represents a natural ground for the imposition of alternative wall boundary conditions (e.g., pure slip) which pose significant difficulties in a standard PFEM framework. Several numerical examples, featuring both no-slip and slip boundary conditions, are presented to prove the accuracy and robustness of the method in two-dimensional and three-dimensional scenarios., Peer Reviewed, Postprint (published version)

We consider formulations of the Shifted Boundary Method based on extrapolation operators other than the Taylor expansion. In the specific case of the Poisson equation, we prove that this approach is stable, provided some basic properties of well-posedness of the extrapolation operator are verified., This research is partly supported by the European High-Performance Computing Joint Undertaking (JU) through the project eFlows4HPC (grant agreement No 955558). The JU receives support from the European Union Horizon 2020 research and innovation program and Spain, Germany, France, Italy, Poland, Switzerland, Norway. This publication is also part of the R&D project PCI2021-121944, financed by MCIN/AEI/10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S). Guglielmo Scovazzi was supported by the Army Research Office, United States (ARO) under Grant W911NF-18-1-0308, the National Science Foundation, United States under Grant 2207164 (Division of Mathematical Sciences – DMS), and by Lawrence Livermore National Laboratory, United States under an LDRD Grant. Claudio Canuto performed this research with the support of the Italian MIUR PRIN Project 201752HKH8-003. He is a member of the Italian INdAM-GNCS research group. Antonio Rodríguez-Ferran was supported by the Spanish Ministry of Science and Innovation (grant PID2020-116141GB-I00)., Peer Reviewed, Postprint (published version)

Este trabajo consiste en analizar cómo interactúan las cubiertas esbeltas frente a las fuerzas del viento mediante el ejemplo de un estadio de fútbol: Anoeta. El mayor problema que presentan las cubiertas formadas por materiales ligeros y esbeltos es que son propensas a sufrir accidentes relacionados con la aeroelasticidad, por ejemplo, el flameo. Por ello, en este trabajo se estudiarán las frecuencias propias de la estructura que sujeta la cubierta y las frecuencias que obtiene el viento tras encontrarse con el estadio, y finalmente, se compararán. En cuanto al viento, cuando debe atravesar algún obstáculo como puede ser un estadio de fútbol suelen producirse oscilaciones del flujo que convergen en pequeños vórtices de aire. Estos vórtices tienen una cierta frecuencia y hay que asegurarse de que no se acople a la frecuencia propia de la estructura. Para conocer la frecuencia del flujo, se hará uso de dos modelos computacionales de dinámica de fluidos: el primero, un modelo simplificado en 2D para validar que la metodología a utilizar es correcta mediante la comparación de los resultados obtenidos respecto a unos resultados conocidos de una referencia; el segundo, el modelo real del estadio en 2D, una vez sabido que la metodología es correcta, para conocer las frecuencias reales del fluido. En la simulación numérica se calcularán las presiones y velocidades de todos los puntos del dominio y mediante la Transformada Rápida de Fourier estos datos pasarán de estar en el dominio del tiempo a estar en el dominio de las frecuencias, obteniéndose así estas. Por otro lado, cada estructura tiene sus propias frecuencias naturales, las cuales tienen asociado un modo de vibración que muestra la deformada que obtiene la estructura en caso de acoplarse con esta frecuencia. Entonces, si las frecuencias del viento coinciden o se parecen a las frecuencias del estadio existe un gran riesgo de producirse algún problema de aeroelasticidad, que puede resultar en un accidente catastrófic

El presente Trabajo de Final de Máster se enfoca principalmente en la implementación de un sistema de acoplamiento multiescalar utilizando la metodología Pseudo-DNS, con el objetivo de reducir la complejidad de los modelos de simulación de dinámica de fluidos. El sistema involucra la confección y simulación de modelos de Elementos Volumétricos Representativos (RVE), que permiten la obtención de los efectos o patrones de las turbulencias de pequeña escala que no pueden resolver las mallas gruesas. A través de esta información, en el proyecto se ha confeccionado una nueva ley constitutiva modifica la viscosidad en cada caso para que se puedan insertar de forma adecuada estos efectos capturados previamente. A partir de aquí, se han verificado los resultados obtenidos a través de la creación de un modelo de una tubería, el cual se poseen los resultados de referencia. Por último, se ha utilizado la nueva ley constitutiva para la simulación del paso de un flujo de agua por una de las fundamentaciones que sustentan el Puente de la Bahía de Hangzhou para poder comprender la aplicabilidad real que tiene el sistema confeccionado dentro del campo de la ingeniería civil., This Master's thesis focuses mainly on the implementation of a multiscale coupling system using the Pseudo-DNS methodology, with the aim of reducing the complexity of fluid dynamics simulation models. The system involves the creation and simulation of Representative Volume Element (RVE) models, which allow the effects or patterns of small-scale turbulence that cannot be resolved by coarse meshes to be obtained. Using this information, the project has created a new constitutive law that modifies the viscosity in each case so that these previously captured effects can be inserted appropriately. From here, the results obtained have been verified by making a model of a pipe, which has the reference results. Finally, the new constitutive law has been used to simulate the passage of a water flow through one of the foundations supporting the Hangzhou Bay Bridge in order to understand the real applicability of the system created within the field of civil engineering., Aquest Treball de Final de Màster s'enfoca principalment a la implementació d'un sistema d'acoblament multiescalar utilitzant la metodologia Pseudo-DNS, amb l'objectiu de reduir la complexitat dels models de simulació de dinàmica de fluids. El sistema involucra la confecció i simulació de models d'Elements Volumètrics Representatius (RVE), que permeten l'obtenció dels efectes o els patrons de les turbulències de petita escala que no poden resoldre les malles més grosses. A través d'aquesta informació, al projecte ha confeccionat una nova llei constitutiva modifica la viscositat en cada cas perquè es puguin inserir de forma adequada aquests efectes capturats prèviament. A partir d'aquí, s'han verificat els resultats obtinguts a través de la creació d'un model d'una canonada, el qual es posseeixen els resultats de referència. Finalment, s'ha utilitzat la nova llei constitutiva per a la simulació del pas d'un flux d'aigua per una de les fonamentacions que sustenten el pont de la badia de Hangzhou per poder comprendre l'aplicabilitat real que té el sistema confeccionat dins del camp de l'enginyeria civil.

In this work we present a novel Quasi-Newton technique for the black-box partitioned coupling of interface coupled problems. The new RandomiZed Multi-Vector Quasi-Newton method stems from the combination of the original Multi-Vector Quasi-Newton technique with the randomized Singular Value Decomposition algorithm, avoiding thus any dense DOFs-sized square matrix operation. This results in a reduction from quadratic to linear complexity in terms of the number of DOFs. Besides this, the need of storing the old inverse Jacobian is also avoided. Instead, only two very “thin” matrices are required to be saved, thus implying a much smaller memory footprint. Furthermore, our proposal can be used free of any user-defined parameter. The article describes the application of the method to the FSI interface residual equations in both Interface Quasi-Newton and Interface Block Quasi-Newton forms. For the latter, we also derive a closed form expression for the update, thus avoiding any linear system of equations resolution, by applying the Woodbury matrix identity to the inverse Jacobian decomposition matrices., This research is partly supported by the European High-Performance Computing Joint Undertaking (JU) through the project eFlows4HPC (grant agreement No 955558). The JU receives support from the European Union’s Horizon 2020 research and innovation program and Spain, Germany, France, Italy, Poland, Switzerland, Norway. The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S)., Peer Reviewed, Postprint (published version)

Projection-based Reduced Order Models are based on the idea of minimizing the discrete residual of a “full order model” (FOM) while at the same time constraining the unknowns to live in a space of reduced dimension. For problems with symmetric positive definite (SPD) Jacobians, this minimization can be achieved optimally by projecting the full order residual onto the approximation basis (Galerkin Projection). This approach is sub-optimal for problems with non-SPD Jacobians since it only guarantees that the projection of the residual onto the chosen basis is minimized and not the residual itself. One possible alternative in such cases is to directly minimize the 2-norm of the residual. This minimization can be achieved either by using QR factorization to solve the resulting least-squares problem or by employing the method of the normal equations (LSPG) to the same end. The first approach involves constructing and factorizing a rectangular tall and skinny matrix of size proportional to the number of unknowns of the FOM. The LSPG method avoids the use of the large matrix by directly constructing the product by its transpose. Unfortunately, constructing such a product element by element is not feasible and requires the use of a complementary mesh, which adds an extra layer of complexity to the hyper-reduction process when performing mesh sampling. The main idea of this work is to propose an alternative technique based on the idea of Petrov–Galerkin minimization. Essentially, we choose a left basis so that a least-squares minimization procedure can be carried out on a reduced problem while guaranteeing that the discrete full order residual is minimized. The resulting procedure is applicable to problems with both SPD and non-SPD Jacobians. Additionally, the resulting minimization problem can be assembled element by element, avoiding the use of the complementary mesh and simplifying implementation in the context of finite elements. The resulting technique is amenable to hy, The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S)”. We acknowledge financial support from the Generalitat de Catalunya through the FI_SDUR-2021 grant, which provided funding for the predoctoral training of Sebastian Ares de Parga Regalado. This project has received funding from the European High-Performance Computing Joint Undertaking (JU) under grant agreement Nos 955558 and 956104. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and from Spain, Germany, France, Italy, Poland, Switzerland, and Norway. Spanish Ministry of Science and Innovation (MICINN) supports the project through the project PCI2021-121945. This publication is part of the R&D project PCI2021-121944, financed by MCIN/AEI/10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR ”., Peer Reviewed, Postprint (author's final draft)

We propose a stabilized linear tetrahedral finite element method for static, finite elasticity problems involving compressible and nearly incompressible materials. Our approach relies on a mixed formulation, in which the nodal displacement unknown filed is complemented by a nodal Jacobian determinant unknown field. This approach is simple to implement in practical applications (e.g., in commercial software), since it only requires information already available when computing the Newton–Raphson tangent matrix associated with irreducible (i.e., displacement-based) finite element formulations. By nature, the proposed method is easily extensible to nonlinear models involving visco-plastic flow. An extensive suite of numerical tests in two and three dimensions is presented, to demonstrate the performance of the method., This research is partly supported by the European High-Performance Computing Joint Undertaking (JU) through the project eFlows4HPC (grant agreement number 955558). The JU receives support from the European Union Horizon 2020 research and innovation program and Spain, Germany, France, Italy, Poland, Switzerland, Norway. This publication is also part of the R&D project PCI2021-121944, financed by MCIN/AEI/10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness , through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S)., Peer Reviewed, Postprint (author's final draft)

This work comprises the start of what will be a fully operational P-DNS algorithm within the Kratos Multiphysics framework. As the methodology followed requires an offline computation the algorithm that runs it ought to be fast. In that spirit a modification was proposed through implementing the fine scale simulation with the main-secondary multi-point-constraints method. This implementation proved to be faster while yielding the same results than the previous one.

A potential transonic solver with an embedded wake is presented. The flow outside of attached boundary layers of streamlined bodies flying at high Reynold numbers can be assumed to be irrotational and isentropic. This assumption reduces the Navier-Stokes equations to a single scalar nonlinear partial differential equation, namely the full-potential equation (FPE). The FPE expresses the conservation of mass in terms of the velocity potential. In this work, the FPE is discretized using a standard Galerkin finite element method, and the nonlinear system of equations stemming from the discretization is solved using Newton's method. An artificial compressibility method is used to stabilize the problem in supersonic flow regions. This method prevents the Jacobian from becoming singular and allows capturing shock waves. To include the viscosity effects in the lift generation, a model for the trailing wake needs to be introduced. In the presented method, the wake is modeled as a straight surface in the free-stream direction. This assumption is relaxed allowing mass flux across the wake. To capture the discontinuity in the velocity potential across the wake, a multivalued element method is employed. This implicit description of the wake within the mesh presents an effective approach to perform fluid-structure interaction computations and apply aeroelastic optimization methods, where the position of the wake changes during consecutive iterations. The solver is implemented in Kratos Multi-Physics and verified for different angles of attack and free-stream conditions. Since the pressure does not change in the transverse direction of the boundary layer, the FPE yields accurate lift, induced drag, and moment computations., Postprint (published version)

This is the peer reviewed version of the following article: [Zorrilla, R, Larese de Tetto, A, Rossi, R. A discontinuous Nitsche-based finite element formulation for the imposition of the Navier-slip condition over embedded volumeless geometries. Int J Numer Meth Fluids. 2021; 93: 2968– 3003. https://doi.org/10.1002/fld.5018], which has been published in final form at https://doi.org/10.1002/fld.5018. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving, This work describes a novel formulation for the simulation of incompressible Navier–Stokes problems involving nonconforming discretizations of membrane-like bodies. The new proposal relies on the use of a modified finite element space within the elements intersected by the embedded geometry, which is represented by a discontinuous (or element-by-element) level set function. This is combined with a Nitsche-based imposition of the general Navier-slip boundary condition, to be intended as a wall law model. Thanks to the use of an alternative finite element space, the formulation is capable of reproducing exactly discontinuities across the embedded interface, while preserving the structure of the graph of the discrete matrix. The performance, accuracy and convergence of the new proposal is compared with analytical solutions as well as with a body fitted reference technique. Moreover, the proposal is tested against another similar embedded approach. Finally, a realistic application showcasing the possibilities of the method is also presented., European Commission, H2020-FETHPC-2016-2017-800898; International Graduate School of Science and Engineering (IGSSE)), ATMOPACE; Istituto Nazionale di Alta Matematica “Francesco Severi”, Ministero dell'Università e della Ricerca, Programma per Giovani Ricercatori “Rita Levi Mon; Secretaría de Estado de Investigación, Desarrollo e Innovación, CEX2018-000797-S, Peer Reviewed, Postprint (author's final draft)

The simulation of structural problems involving the deformations of volumetric bodies is of paramount importance in many areas of engineering. Although the use of tetrahedral elements is extremely appealing, tetrahedral discretisations are generally known as very stiff and are hence often avoided in typical simulation workflows. The development of mixed displacement–pressure approaches has allowed to effectively overcome this problem leading to a class of locking-free elements which can effectively compete with hexahedral discretisations while retaining obvious advantages in the mesh generation step. Despite such advantages the adoption of the technology within commercial codes is not yet pervasive. This can be attributed to two different reasons: the difficulty in making use of standard constitutive libraries and the implied continuity of the pressure, which makes the application of the method questionable in the context of multi-material problems. Current paper proposes the adoption of the volumetric strain instead of the pressure as a nodal value. Such choice leads to the definition of a modified strain making the use of standard strain-driven constitutive laws straightforward. At the same time, the continuity of the volumetric strain across multimaterial interfaces can be understood as a sort of kinematic constraint (stresses can still remain discontinuous across material interfaces). The new element also opens the door to the use of anisotropic constitutive laws, which are typically problematic in the context of mixed elements., This research has been partly supported by the European Commission (EC) through the project ExaQUte (H2020-FETHPC-2016-2017-800898). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R& D” (CEX2018-000797-S). R. Codina acknowledges the support received from the ICREA Acadèmia Research Program, from the Catalan Government ., Peer Reviewed, Postprint (author's final draft)

El sector dels transformadors elèctrics està afectat per possibles explosions en l’interior dels tancs plens d’oli que aïllen els components elèctrics a causa de malfuncionaments elèctrics que generen un gas inflamable a mesure que l’oli que envolta l’arc elèctric es vaporitza. En questió de mili-segons, el volum de gas és pressuritzat donat que la inèrcia del fluid que l’envolta prevé la bombolla d’incrementar el seu volum i reduir- ne la pressió. Aquest fenòmen comporta la formació d’ones de pressió a causa del fort gradient de pressió a la interfície entre el gas i el líquid, que es propaguen i interaccionen amb l’estructura del transformador. Les parets del tanc poden suportar el primer pic de pressió, de caràcter dinàmic, que tendeix a ser el més gran en magnitud però de curt període. Tot i això, la pressió estàtica que es genera en el tanc a mesura que les ones de pressió interaccionen amb les ones emergents de la bombolla és la més perillosa i la que pot generar explosions, trencament del tanc, contaminació i costs tant materials com humans. En aquesta tesis, una formulació multi-fluid i quasi-incompressible simula a través de la implementació de les equacions de Navier-Stokes amb el mètode d’Elements Finits el fenòmen detallat per tal de tenir coneixement i entendre les condicions físiques dins del tanc i implementar estratègies de depressurització adequades., The transformer manufacturing sector often suffers explosions originated in the oil- filled tanks due to arcing faults that generate flammable gas as the oil surrounding the electrical arc vaporizes. In a matter of milliseconds, the volume containing the gas is pressurized as the oil inertia prevents it from growing and reducing its pressure. This phenomena leads to the formation of pressure waves due to the strong pressure gradient at the oil-gas interface, which propagate and interact with the transformer structure. The tank walls may sustain the first pressure peak, of dynamic nature, which tends to be the highest in magnitude, but has a short period. On the contrary, the static pressure which builds up in the tank as the reflecting pressure waves interact with the incoming waves may generate the highest hazard and lead to explosions, tank rupture, pollution and expensive human and material costs. In this work, a weakly-compressible multi-fluid flow formulation simulates with the Finite Element implementation of the Navier-Stokes equations the phenomena detailed above in order to have a proper understanding of the physical conditions in the tank and devise adequate depressurization strategies.

This work derives an incompressible Variational Multiscales time-averaged Navier-Stokes formulation that aims at obtaining accurate steady state solutions. Rather than using the standard time instantaneous velocity and pressure, the new formulation devises a time averaging procedure based on rewriting and solving the Navier-Stokes equations in terms of the newly defined time-averaged velocity and pressure. Hence, the method could be understood as a convenient change of variable so that the problem is rewritten directly in terms of the steady state quantities. The important advantage of such a point of view is that it can in principle be applied to any other formulation. Such time averaging procedure is complemented by two time step modification strategies in order to accelerate the convergence to the steady state. The guidelines of an integrated framework are presented in the paper, starting with the description of the proposed numerical technique applied to general incompressible flows. The explanation is enhanced with a 1D non-linear oscillator example. Several results are presented concerning analytical benchmarks, simulation of flows in laminar, transitional and turbulent regimes with and without an inherently steady solution., This research has been partly supported by the International Graduate School of Science and Engineering (IGSSE) and the European Commission (EC) through the projects ATMOPACE and ExaQUte (H2020FETHPC-2016-2017-800898). Rubén Zorrilla gratefully acknowledges the support of the Spanish Government for his FPU Grant (FPU15/03796)., Peer Reviewed, Postprint (published version)

Tesi per compendi de publicacions, This thesis develops a numerical tool (the Virtual Wind Tunnel, VWT) for the resolution of problems involving fluid flow around structures. Due to the limitations that traditional methods may have in this context, the VWT is based on the use of fixed mesh technologies (CutFEM-type) combined with an implicit representation of the embedded bodies. One of the main contributions of the thesis is the use of such fixed mesh methods to solve lightweight thin-walled structures problems. Hence, two embedded formulations capable of representing the flow around bodies with and without internal volume are proposed. The first one results in a simpler implementation and lower computational effort but can only represent a slip behavior of the wall. The second one gets rid of such limitation by including a Nitsche imposition of the Navier-slip condition, thus allowing modelling any wall behavior as a wall law would do. The applicability range of the VWT includes the fluid–structure interaction problem (FSI). To that purpose an improvement for the boundary condition imposition of the FM-ALE algorithm mesh motion problem is also proposed. Moreover, the implementation, which has been conceived to be easily extended to any other coupled problem, is also treated. The validation of the technologies within the VWT includes multiple theoretical test cases as well as feasible industrial applications. Among these, the FSI analysis of a 4-point tent during a strong wind episode deserves to be highlighted as it showcases the achievement of the initial objective of the thesis., En esta tesis se desarrolla una herramienta numérica (el Virtual Wind Tunnel, VWT) para la resolución de problemas que involucran el flujo de un fluido alrededor de una estructura. Debido a las limitaciones que los métodos tradicionales pueden tener en este contexto, el VWT se basa en el empleo de técnicas de malla fija (tipo CutFEM) combinadas con una descripción implícita de los cuerpos embebidos. Una de las principales contribuciones de la tesis es el empleo de dichos métodos de malla fija para resolver problemas de estructuras ligeras de pared delgada. Así pues, se proponen dos formulaciones embebidas capaces de representar el flujo alrededor de un cuerpo con o sin volumen interno. La primera de ellas resulta en una implementación más sencilla así como en un menor coste computacional pero únicamente puede reprentar un comportamiento deslizante de la pared. La segunda elimina esta limitación incluyendo una imposición mediante el método de Nitsche de la condición de Navier-slip, permitiendo así modelar cualquier comportamiento del mismo modo que lo haría una ley de pared. El rango de aplicabilidad del VWT incluye el problema de interacción fluido¿estructura (FSI). A tal propósito se plantea una mejora para la imposición de las condiciones de contorno del problema de movimiento de la malla del algoritmo FM-ALE. Asimismo, también se hace especial hincapié en la implementación, que ha sido concebida para ser fácilmente extensible a cualquier otro problema acoplado. La validación de las tecnologías implementadas en el VWT incluyen múltiples casos teóricos así como posibles aplicaciones industriales. Entre éstas se destaca el análisis FSI de una 4-point tent durante un episodio de viento severo ya que demuestra la consecución del objetivo inicial de la tesis., Postprint (published version)

The final publication is available at Springer via http://dx.doi.org/10.1007/s10237-020-01291-x, This work explores the use of an embedded computational fluid dynamics method to study the type B aortic dissection. The use of the proposed technique makes it possible to easily test different intimal flap configurations without any need of remeshing. To validate the presented methodology, we take as reference test case an in vitro experiment present in the literature. This experiment, which considers several intimal flap tear configurations (number, size and location), mimics the blood flow in a real type B aortic dissection. We prove the correctness and suitability of the presented approach by comparing the pressure values and waveform. The obtained results exhibit a remarkable similarity with the experimental reference data. Complementary, we present a feasible surgical application of the presented computer method. The aim is to help the clinicians in the decision making before the type B aortic dissection surgical fenestration. The capabilities of the proposed technique are exploited to efficiently create artificial reentry tear configurations. We highlight that only the radius and center of the reentry tear need to be specified by the clinicians, without any need to modify neither the model geometry nor the mesh. The obtained computational surgical fenestration results are in line with the medical observations in similar clinical studies., Peer Reviewed, Postprint (author's final draft)

This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements and rotations. We focus on the application of the proposed tool to lightweight membrane-like structures. Nonetheless, all the techniques we present in this work can be applied to both volumetric and volumeless bodies. To achieve this, we rely on the use of embedded mesh methods in the fluid solver to conveniently handle the extremely large deflections and eventual topology changes of the structure. The coupling between the embedded fluid and mechanical solvers is based on an interface residual black-box strategy. We validate our proposal by solving reference benchmarking examples that consider both volumetric and volumeless geometries. Whenever it is possible, we also compare the embedded solution with the one obtained with our reference body fitted solver. Finally we present a real-life application of the presented embedded Fluid–Structure Interaction solver., This research has been partly supported by the International Graduate School of Science and Engineering, Germany (IGSSE) and the European Commission (EC) through the projects ATMOPACE and ExaQUte (H2020-FETHPC-2016-2017-800898). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness , through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S). Rubén Zorrilla gratefully acknowledges the support of the Spanish ministry of Science, Innovation and Universities for his FPU grant (FPU15/03796)., Peer Reviewed, Postprint (author's final draft)

Cuando se realiza un estudio del flujo sanguíneo en el sistema cardiovascular, la mayoría de autores, tratan la sangre como si fuese un caso ideal en estado estacionario y el fluido como newtoniano, si bien esta aproximación permite obtener buenos resultados, en la realidad el flujo sanguíneo se comporta de esta manera, ya que este es pulsátil debido al impulso del corazón. Los efectos de dicho impulso tienen mayor importancia en los vasos sanguíneos grandes y cercanos al corazón (arterias), disminuyendo así hasta llegar a los vasos más alejados y pequeños (capilares), donde el efecto de la onda de presión es prácticamente imperceptible. Otra discrepancia entre autores es la diferencia entre tratar el fluido como newtoniano o no newtoniano, pues es sabido que la sangre para bajas tasas de cizalladura presenta comportamiento no newtoniano, sin embargo, a partir de 100 s-1 la viscosidad se vuelve constante. En este documento vamos a comparar los resultados obtenidos del Wall Shear Stress (WSS) o esfuerzo cortante, obtenidos modelando la sangre como fluido newtoniano contra los obtenidos si se modeliza como no newtoniano con el fin de poder observar la diferencia existente dependiendo del modelo que escojamos. Los resultados serán valorados en 4 geometrías diferentes de arterias coronarias con estenosis, con el fin de poder observar de manera gráfica la distribución de WSS, el perfil de velocidad en ciertas secciones, así como el gradiente de presión existente. Con los datos analizados, se puede observar que el modelo Newtoniano obtiene valores de mayor magnitud.

The idea is to work on the developement of an explicit solver using B-Bar type elements on structured meshes. The idea is to begin with a completely structured mesh, to employ immersed-type techniques in the application of BCs, and later to pass to an octree like structure

This work describes a novel formulation for the simulation of Navier–Stokes problems including embedded objects. The new proposal is based on the use of a modified finite element space, which replaces the standard one within the elements intersected by the immersed geometry. The modified space is able to exactly reproduce the jumps happening at the embedded boundary while preserving the conformity across the faces intersected by the embedded object. The paper focuses particularly on the imposition of a slip boundary condition on the surface of the embedded geometry, proposing a new technique for the application of such constraint. The new proposal is carefully benchmarked using the results of a body fitted technique and of an alternative embedded approach. Potential applications of interest are also presented., Peer Reviewed, Postprint (author's final draft)

The main advantage of embedded formulations in front of body-fitted ones is to get rid of the ALE mesh problem and its complexities. Besides, they suppress the model clean up tasks, since the problem is not solved for the real geometry but for a distance function that represents it. In this context, two different embedded formulations have been developed in Kratos Multiphysics. The first one is suitable for bodies with well defined internal volume (e.g. airfoils) while the second one is intended to be used in bodies with no internal volume (e.g. boat sails).

The maturity of numerical techniques both in Computational Structural and Fluid Dynamics, accompanied by the availability of affordable high-performance hardware, allows the use of virtual rapid-prototyping facilities as realistic alternatives to traditional wind tunnel experiments. This work aims to present a virtual wind tunnel tool that combines both “standard” body-fitted approaches and innovative embedded techniques. Two are the distinctive features of the work. Firstly, it allows the simulation of membrane structures subjected to large displacements. This is typically challenging both for embedded solvers, due to the need of modelling a strong discontinuity of the flow field in correspondence of the structural position, and for body-fitted techniques, due to the large displacement regime. Secondly, it allows combining body fitted and embedded structures within the same simulation. All the presented strategies are developed both in Open MP and MPI., Postprint (published version)

Implementation of a FSI procedure involving the interaction of shell structures and fluids.

This paper describes trends concerning the analysis of steel structures using FEM and Big Data from two perspectives: i) the increase of the computing capacity and ii) the de-sign guidelines. For the former, computers allow performing considerably vast studies for frames, members or cross-section verification. For the latter, guidelines follow a particularly careful pace when it comes to standardizing new methodologies related to the use of FE in the analysis of steel structures. Both trends move at a rather different speed, with consequences in steel design in a broad sense. The paper presents emphasis of the discussions in the frame of TC8 encompassing “Numerical Modeling”- “Structural Design”- “Statistics” and “Big Data” ., Postprint (published version)

In this paper, a realistic nonlinear 3D simulation of an incrementally launched steel bridge girder is presented. The numerical simulation accounts for three sources of nonlinearity: geometry, material and boundary conditions. For the sake of depicting the capabilities of the presented numerical model in structural verifications, the study is focused on the patch loading field, a structurally complex phenomenon. Patch loading (or concentrated loading) is one of the most typically encountered structural verifications on incrementally launched steel 1-girders. The presented realistic simulation is based upon an experimentally calibrated numerical model and may provide relevant information at both design and construction stages. For the former, the predictive capabilities of the model for inferring the potential failure due to patch loading are depicted. For the latter, the results obtained are displayed in a way that may be useful for planning a Structural Health Monitoring (SHM) deployment aimed at controlling the patch loading-related phenomena in incrementally launched steel plate girders., Peer Reviewed, Postprint (author’s final draft)

El método de lanzamiento incremental (ILM) ha sido ampliamente utilizado desde la década de los 60 para la construcción de puentes en localizaciones inaccesibles, o donde es imposible la afectación del entorno de la obra, ya que este método no requiere del empleo de una cimbra. En el método de construcción de puentes por empuje, la superestructura es construida por tramos en un parque de prefabricación una vez se ha finalizado la ejecución de estribos y pilas. El parque de prefabricación implica un elevado nivel de industrialización, que mejora la calidad, acelera el ritmo de ejecución y reduce la siniestralidad. Una vez finalizado un tramo del tablero, se empuja éste hacia delante, para iniciar seguidamente la construcción de un nuevo segmento, repitiendo el ciclo hasta completar la totalidad del tablero. Según la descripción del método, se puede intuir que el esquema estructural varía continuamente hasta que el puente está finalizado. Esta es una de las principales desventajas de este método constructivo puesto que una misma sección puede estar sometida a esfuerzos totalmente distintos durante la construcción a los que sufrirá durante su vida útil. Este comportamiento requiere también calcular múltiples problemas estructurales para cada uno de los instantes del lanzamiento. En el presente trabajo se ha realizado un modelo numérico realista no lineal a escala real con elementos tipo shell, que tiene la ventaja de que simular el lanzamiento desde su inicio hasta el final, por lo que se evita la necesidad de usar un modelo para cada instante. Se ha planteado el lanzamiento de la parte metálica de un puente de vigas armadas tipo I. Este modelo está basado en otro modelo numérico unidimensional, contrastado previamente con experimentos a escala reducida realizados en laboratorio. Una vez se juzgó la convergencia del modelo como satisfactoria, se trató de explotar las capacidades del mismo desde dos vertientes distintas. La primera de ellas es más cercana a la fase de d

III Premi del CAATEEB al millor Projecte Fi de Carrera del curs 2011/12., El presente documento contiene un análisis y optimización bajo criterios energéticos y sostenibles de un instituto en Corró d’Avall (Les Franqueses del Vallès), que cuenta con una superficie construida de 4.232 m², repartida en seis edificios de diferente configuración y uso . Para el modelado digital en 3D del instituto se ha utilizado la aplicación Google SketchUp 8, para el análisis y planteamiento de mejoras en la iluminación natural y comportamiento térmico se ha utilizado Autodesk Ecotect 2011. En primer lugar se ha realizado un estudio de la localización del instituto, que comprende la climatología y el entorno cercano e inmediato del mismo, se ha comprobado que la localización del instituto no repercute negativamente sobre el mismo. A continuación, se ha analizado el uso de la iluminación natural y el comportamiento térmico, sin tener en cuenta ningún tipo de climatización artificial. Con los datos obtenidos del análisis de la iluminación se han planteado una serie de modificaciones en las aberturas originales para incrementar el FLD (Factor luz diurna) incrementando la calidad y cantidad de luz natural en los diferentes espacios. Con el objetivo de optimizar el comportamiento térmico sin usar equipos de climatización artificial, se han propuesto una serie de modificaciones, enfocadas principalmente hacia los programas de ventilación de los espacios, materiales y color de acabado de la envolvente, prestando atención a la inercia térmica de las soluciones y tratándola como una herramienta para favorecer la climatización. Gracias a las modificaciones se ha conseguido reducir aproximadamente un 28% la demanda energética de iluminación, incrementando a su vez la calidad de la iluminación, y un 50% la demanda energética para climatización. También se ha estudiado el correcto posicionamiento de las placas solares originales mediante un estudio del asoleo y radiación solar de las cubiertas del instituto. Para evaluar el impacto energético de la construcción de este