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We reconstruct 2D simulation to 3D scene and integrated a fluid-solid coupling based on FLO-2D model. Furthermore we add the friction and bump. From the point of view of fluid-solid coupling, we using the flow resistance and yield stress our proposed method make the fluid behaviour and runout more realistic comparing to other fluid-solid coupling research. Besides, from the point of view of debris flow simulation, we integrate the fluid-solid coupling into the debris flow simulation. And we can handle the bump of debris flow regarding trees, stone or house compared with other debris flow simulation.

The principal objective of this investigation is to develop a nonlinear continuum based finite element formulation to examine dynamic response of flexible riser structures with large displacement and large rotation. Updated Lagrangian incremental approach together with the 2nd Piola-Kirchhoff stress tensor and the Green-Lagrange strain tensor is employed to derive the nonlinear finite element formulation. The 2nd Piola-Kirchhoff stress and the Green-Lagrange strain tensors are energy conjugates. These two Lagrangian tensors are not affected by rigid body rotations. Thus, they are used to describe the equilibrium equation of the body independent of rigid rotations. While the current configuration in Updated Lagrangian incremental approach is unknown, the resulting equation becomes strongly nonlinear and has to be modified to a linearized form. The main contribution of this work is to obtain a modified linearization method during development of incremental Updated Lagrangian formulation for large displacement and large rotation analysis of riser structures. For this purpose, the Green-Lagrange strain and the 2nd Piola-Kirchhoff stress tensors are decomposed into two second-order six termed functions of through-thethickness parameters. This decomposition makes it possible to explicitly account for the nonlinearities in the direction along the riser thickness, as well. It is noted that using this linearization scheme avoids inaccuracies normally associated with other linearization schemes. The effects of buoyancy force, riser-seabed interaction as well as steady-state current loading are considered in the finite element solution for riser structure response. An efficient riser problem fluid-solid interaction Algorithm is also developed to maintain the quality of the mesh in the vicinity of the riser surface during riser and fluid mesh movements. To avoid distortions in the fluid mesh two different approaches are proposed to modify fluid mesh movement governing elasticity equation matrices values; 1) taking the element volume into account 2) taking both element volume and distance between riser centre and element centre into account. The formulation has been implemented in a nonlinear finite element code and the results are compared with those obtained from other schemes reported in the literature.

A preliminary investigation of the added properties called added mass, added damping and added stiffness have been performed for a Kaplan turbine. The magnitude of dimensionless numbers have been used in order to classify the interaction of the fluid and the solid. The classification is done to bring clarity in which of the added properties are of importance for the system. The diameter of the runner and the hub have been calculated using the power output and the head for a Kaplan turbine. These dimensions have been used to determine the magnitude of the dimensionless numbers along with the velocity of the fluid. It turned out that all added properties affect the turbine, however, the magnitude of them are quite different. The magnitude of the added mass and the added damping are greater than the added stiffness, which often is neglected. The added mass can be determined if the natural frequencies of the structure in air and in water are known. The difference in natural frequencies can be used to determine the added mass factor and thereby the added mass of the system. The added damping can be determined by the change in damping ratio for different surrounding fluids. This was done using the simulation software ANSYS Workbench v.17.1, where two different types of simulation were used, ”acoustic coupled simulation” and ”two way coupled simulation”. The complexity of the geometry of the Kaplan turbine was simplified to a disc and a shaft. The result for the added mass was validated using results from an experiment [1]. The added damping could be determined, but not validated. The different types of simulation have been compared and it turned out that the added mass could be determined using ”acoustic coupled simulation” and ”two way coupled simulation”, but the added damping could only be determined using the ”two way coupled simulation”. / En preliminär undersökning av de adderade egenskaperna kallade, adderad massa, adderad dämpning och adderad styvhet har utförts för en Kaplan turbin. Magnituden av dimensionslösa tal har använts för att klassificera interaktionen av fluiden och soliden. Klassificeringen görs för att bringa klarhet i vilka av de adderade egenskaperna är av betydelse för systemet. Diametrarna för löphjulet och navet har beräknats utifrån effekt och fallhöjd för en Kaplan turbin. Dessa längder har använts för att bestämma magnituden av de dimensionslösa talen tillsammans med fluidens hastighet. Det visade sig att alla adderade egenskaper påverkar turbinen, men omfattningen av dem är helt annorlunda. Magnituden av den adderade massan och den adderade dämpningen är större än den adderade styvheten, som ofta försummas. Den adderade massan kan bestämmas om de naturliga frekvenserna av strukturen i luft och vatten är kända. Skillnaden i egenfrekvenser kan användas för att bestämma faktorn av den adderade massan och därigenom den adderade massan. Den adderade dämpningen kan bestämmas genom ändringen i dämpningsförhållande för olika omgivande fluider. Detta gjordes med hjälp av simuleringsprogrammet ANSYS Workbench v.17.1, där två olika typer av simulering användes, ”acoustic coupled simulation” och ”two way coupled simulation”. Komplexiteten i geometrin för en Kaplan turbin förenklades till en skiva och en axel. Resultatet för den adderade massan validerades med resultat från ett experiment [1]. Den adderade dämpningen kunde bestämmas, men inte valideras. De olika typerna av simulering har jämförts och det visade sig att den adderade massan kan bestämmas med hjälp av både ”acoustic coupled simulation” och ”two way coupled simulation”, men den adderade dämpningen kunde endast bestämmas med hjälp av ”two way coupled simulation”.

Mechanical ventilation has been a major therapy used by physicians in support of surgery as well as for treating patients with reduced lung function. Despite its many positive outcomes and ability to maintain life, in many cases, it has also led to increased injury of the lungs, further exacerbating the diseased state. Numerous studies have investigated the effects of long term ventilation with respect to lungs, however, the connection between the global deformation of the whole organ and the strains reaching the alveolar walls remains unclear. The walls of lung alveoli also called the alveolar septum are characterized as a multilayer heterogeneous biological tissue. In cases where damage to this parenchymal structure insist, alveolar overdistension occurs. Therefore, damage is most profound at the alveolar level and the deformation as a result of such mechanical forces must be investigated thoroughly. This study investigates a three-dimensional lung alveolar model from generations 22 (alveolar ducts) through 24 (alveoli sacs) in order to estimate the strain/stress levels under mechanical ventilation conditions. Additionally, a multilayer alveolar tissue model was generated to investigate localized damage at the alveolar wall. Using ANSYS, a commercial finite element software package, a fluid-structure interaction analysis (FSI) was performed on both models. Various cases were simulated that included a normal healthy lung, normal lung with structural changes to model disease and normal lung with mechanical property changes to model aging. In the alveolar tissue analysis, strains obtained from the aged lung alveolar analysis were applied as a boundary condition and used to obtain the mechanical forces exerted as a result. This work seeks to give both a qualitative and quantitative description of the stress/strain fields exerted at the alveolar region of the lungs. Regions of stress/strain concentration will be identified in order to gain perspective on where excess damage may occur. Such damage can lead to overdistension and possible collapse of a single alveolus. Furthermore, such regions of intensified stress/strain are translated to the cellular level and offset a signaling cascade. Hence, this work will provide distributions of mechanical forces across alveolar and tissue models as well as significant quantifications of damaging stresses and strains.

Nous nous intéressons à la modélisation et à la simulation numérique d'écoulements gravitaires transitoires à surface libre, pour des fluides visqueux et incompressibles. La loi de comportement est de type viscoplastique avec transition fluide/solide. Plus précisément, nous considérons la loi rhéologique de Drucker-Prager. Nous nous intéressons tout d'abord le cas unidimensionnel d'un écoulement longitudinal cisaillé. Nous étudions un modèle simplifié, avec terme source empirique, pour lequel nous concevons une méthode numérique pour le suivi de la position de l'interface entre la couche solide et la couche fluide. Nous présentons des résultats numériques, avec divers termes sources, et nous comparons ces résultats, lorsque la viscosité est petite, à la solution analytique non visqueuse. Dans le cas visqueux, nous étudions les phases de démarrage et d'arrêt de l'écoulement. Dans un second temps, nous étudions le cas bidimensionnel d'écoulement de Drucker-Prager avec surface libre. La loi de comportement du fluide est traitée par régularisation, et nous utilisons la méthode ALE pour traiter le mouvement du domaine. Nous présentons des résultats numériques pour l'étude de la mise en mouvement d'un talus / This thesis deals with the modeling and numerical simulation of transient free-surface gravity flows, for viscous and incompressible fluids. The constitutive law is viscoplastic, with fluid/solid transition. More precisely, we consider the Drucker-Prager rheological law. We first study the case of a one-dimensional shear flow. We investigate a simplified model, with an empirical source term, for which we develop a numerical method to compute the position of the solid/fluid interface. We present numerical results for various source terms, and compare, in the case of small viscosity, our results to the inviscid analytical solution. In the viscous case, we study the case of a two-dimensional Drucker--Prager flow with free surface. The constitutive law of the fluid is regularized, and the ALE method is used to treat the displacement of the domain. Numerical results are presented for the setting in motion of an embankment

The aim of this study is to investigate the fluid-structural response to pulsatile Newtonian and non-Newtonian blood flow through an axisymmetric stenosed vessel using FLOTRAN and ANSYS. This is to provide a basic understanding of atherosclerosis. The flow was set to be laminar and follows a sinusoidal waveform. The solid model was set to have isotropic elastic properties. The Fluid-Structural Interaction (FSI) coupling was two-way and iterative. Rigid and Newtonian cases were investigated to provide an understanding on the effects of incorporating FSI into the model. The wall expansion was found to decrease the axial velocity and increase the recirculation effects of the flow. To validate the models and methods used, the results were compared with the study by Lee and Xu [2002] and Ohja et al [1989]. Close comparisons were achieved, suggesting the models used were valid. Two non-Newtonian models were investigated with FSI: Carreau and Power Law models. The Carreau model fluid behaviour was very close to the Newtonian model. The Power Law model produced significant difference in viscosity, velocity and wall shear stress distributions. Pressure distribution for all models was similar. In order to quantify the changes, Importance Factor (IG) was introduced to determine the overall non-Newtonian effects at two regions: the entire flow model and about the vessel wall. The Carreau model showed reasonable values of IG whereas the Power Law model showed excessive values. Transient and geometrical effects were found to affect the Importance Factor. The stress distributions for all models were found to be similar. Highest stress occurred at the shoulders of the stenosis where a stress concentration occurred due to sharp corners of the geometry and large bending moments. The highest stresses were in the axial direction. Notable circumferential stress was found at the ends of the vessel. Carreau model produced slightly higher stresses than the other models. Wall stresses were found to be primarily influenced by internal pressure, rather than wall shear stresses.

We present a slice-based method that combined with fluid-solid interaction to render the oceans interact with the objects of the simulation. First, according to the key slices selection one can determine the initial slices simulation for reducing the computation on the number of grid and expressing the solid appearance. Second, we used 3D vector Navier-Stokes equations and combined with 3D fluid-solid coupling to comply with the laws of physics for 2D slice simulation. Third, using a volume of fluid method one can reconstruct the 2D ocean surface and further apply interpolation to extended 2D surfaces to 3D ocean surface. Finally, using the Doo-Sabin subdivision surfaces method is to be smoother for the 3D surface. From the viewpoint of ocean simulation, we can not only solve the fluid-solid coupling problem of objects floating on the sea but also achieve better result in efficiency compared with traditional ocean simulation. From the viewpoint of fluid-solid coupling, the proposed method can greatly reduce the computation in number of grid and be applied to embedded systems, games or films effectively.

Στην παρούσα Διπλωματική Εργασία μελετάται η ανάπτυξη ενός μοντέλου προσομοίωσης αλληλεπίδρασης ρευστού-στερεού για τον προσδιορισμό ρευστοδυναμικών παραμέτρων (Wall Shear Stress, Von Mises Stress κ.α.) μέσω των οποίων θα μπορεί μελλοντικά να προβλεφθεί η ρήξη ή όχι ενός ενδοκρανιακού ανευρύσματος. Αρχικά γίνεται μια σύντομη παρουσίαση του ιατρικού προβήματος ώστε να γίνει κατανοητή η σπουδαιότητα της ανάπτυξης του υπολογιστικού μοντέλου με σκοπό τον υπολογισμό παραμέτρων οι οποίες μπορούν να φανούν χρήσιμες. Κατά τη διάρκεια ανάπτυξης του μοντέλου αξιοποιήθηκαν πραγματικά δεδομένα απεικονιστικών διατάξεων ασθενών του Αττικού Πανεπιστημιακού Γενικού Νοσο- κομείου. Εν συνεχεία, η επεξεργασία των εικόνων αυτών διεξήχθει στο λογισμικό ανοιχτού κώδικα VMTK (Vascular Modeling Toolkit) από όπου προήλθε και η τρισδιάστα- τη ανακατασκευη τους. Στο επόμενο στάδιο, οι γεωμετρίες που προέκυψαν από την επεξεργασία εικόνας εισήχθησαν στο λογισμικό εμπορικού κώδικα ANSYS όπου και αναπτύχθηκε το υπολογιστικό μοντέλο το οποίο περιείχε και την αλληλεπίδραση ρευστού και στερεού (FSI). Αξίζει να αναφερθεί το γεγονός ότι το μοντέλο που αναπτύχθηκε περιείχε κινούμενα στοιχεία πλέγματος (Moving Mesh), τα οποία συμβάλλουν στον ακριβέστερο υπολογισμό και αποτύπωση παραμέτρων που υπολογίστηκαν στη συνέχεια. Τέλος αναφέρονται κάποιοι μελλοντικοί στόχοι και προοπτικές μέσω των αποτελεσ- μάτων που προέκυψαν από την ανάλυση του μοντέλου. / In the present M.Sc thesis we are studying the development of a numerical model that simulates fluid-solid interaction for determining fluid dynamics parameters (Wall Shear Stress, Von Mises Stress etc) through which through which could be predicted the rupture or not of an intracranial aneurysm. First, a brief presentation of the medical problem is being made, to understand the importance of developing the computational model in order to calculate parameters which can be useful. During the development of the model, real imaging data from CT scans taken from patients of Attikon General University Hospital were exploited. Thereafter, the processing of these images was performed in the open-source software VMTK (Vascular Modeling Toolkit) from where came the three-dimensional reconstruction. In the next step, the geometries obtained from the image processing have been introduced in the commercial software ANSYS where the computational model that contains the interaction of fluid and solid has been developed (FSI). It is worth mentioning that the model developed, contained moving mesh elements, which contribute to more accurate calculation and mapping of parameters which were calculated after. Finally, some future objectives and prospects are being referred, through the results obtained from the analysis of the model.

Incidence of abdominal aortic aneurysm (AAA) is increasing in the aging society of the western world. Development of AAA is mostly asymptomatic and is characterized by a bulge in the abdominal aorta. However, AAA may suddenly rupture, which results in an internal bleeding associated with a high mortality rate. Patients with AAA undergo regular screening until treatment indication. To date, statistical criteria are used to decide whether the risk of rupture exceeds the risk of intervention. Models of AAA development help to understand the disease progression and to yield patient-specific criterion for AAA rupture. Up to date, sophisticated models of AAA development exist. These models assume the abdominal aorta as a thin-walled structure, which saves the computational effort. This thesis aims at investigating the importance of employing a thick-walled model of the aorta. The effects on AAA development that cannot be captured with a thin-walled model are of interest. In Paper A, the thick-walled model of growth and remodeling of one layer of a AAA slice has been extended to a two-layered model. The parameter study has been performed to investigate the influence of mechanical properties and growth and remodeling (G&amp;R) parameters of two individual layers on the gross mechanical response and G&amp;R of the artery. It was concluded that the adventitia acts to protect the arterial wall against rupture even in pathological state. In Paper B, the model was extended to an organ level model of AAA development. Furthermore, the model was incorporated into a so-called Fluid-Solid-Growth (FSG) framework, where the AAA development is loosely coupled to the blood flow conditions such as wall shear stress. One patient-specific geometry of the abdominal aorta is used to illustrate the model capabilities. A transmurally non-uniform distribution of the strains of individual arterial constituents was observed. In addition, an increased aneurysm tortuosity was observed in comparison to a thin-walled approach. These findings signify the importance of a thick-walled approach to model the aneurysm development. Finally, the proposed methodology provides a realistic basis to further explore the growth and remodeling of AAA on a patient-specific basis. / <p>QC 20140311</p>