SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference

The 6th ECCOMAS Young Investigators Conference YIC2021 will take place from July 7th through 9th, 2021 at Universitat Politècnica de València, Spain. The main objective is to bring together in a relaxed environment young students, researchers and professors from all areas related with computational science and engineering, as in the previous YIC conferences series organized under the auspices of the European Community on Computational Methods in Applied Sciences (ECCOMAS). Participation of senior scientists sharing their knowledge and experience is thus critical for this event.YIC 2021 is organized at Universitat Politécnica de València by the Sociedad Española de Métodos Numéricos en Ingeniería (SEMNI) and the Sociedad Española de Matemática Aplicada (SEMA). It is promoted by the ECCOMAS.The main goal of the YIC 2021 conference is to provide a forum for presenting and discussing the current state-of-the-art achievements on Computational Methods and Applied Sciences,including theoretical models, numerical methods, algorithmic strategies and challenging engineering applications.Nadal Soriano, E.; Rodrigo Cardiel, C.; Martínez Casas, J. (2022). Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. https://doi.org/10.4995/YIC2021.2021.15320EDITORIA

Numerical simulation of the flow in model skeletal muscle ventricles

Until recently, the only realistic form of treatment available to patients in end stage heart failure was transplantation. In the last few years, the possibility of diverting skeletal muscle from its normal function to perform a cardiac assist role has emerged as a potential alternative to transplant surgery. The introduction of an Skeletal Muscle Ventricle (SMV) to the circulation is a potential long-term hazard, as the patient's blood comes into contact with the non-endothelialised surfaces of the wall of the new ventricle and the connecting conduits. This may trigger a cascade of events leading to deposition of thrombus, whose formation is dependent on the nature of the blood flow. The potential problem of haemostasis may arise in the apex of the artificial ventricle, where little mixing and large residence times may occur. There is therefore a strong need for carrying out flow analysis studies to address in detail the questions of haemostasis and thrombogenesis and in this context to evaluate possible candidate SMV configurations. Research on the dynamics of the flow inside model SMVs has been carried out on physical and numerical models with the objective of aialysing the effect of the size and shape of the ventricle and inlet/outlet orientation of the duct. Due to the physiological limit on the power available to pump the blood out of the ventricle, the efficiency of these potential assistance devices has to be maximized. It is also necessary to minimize the risks of haemolysis and thrombogenesis, which are both related, in different ways, to the level of shear stress on the wall and within the flow. A common feature of these flows is the formation of vortex rings. Vortices enhance mixing, and this is a useful process to encourage in an SMV, as it could assist in the mixing of the blood components and in the reduction of apical residence time. Being able to predict accurately the dynamics of the vortices is therefore important, as this will affect the prediction of residence times and shear stresses at the wall and within the flow. It is also very important to know whether numerical codes can predict vortex ring dynamics from both qualitative and quantitative points of view. In order to study the dynamics of the formation of these vortices, first, mathematical models were studied. The general purpose CFDS-FLOW3D code was used in all numerical simulations. Initial investigations of this research project concerned a progressive validation of the numerical solution predicted by the code when the domain where the flow is calculated had moving boundaries.Firstly, comparisons were made with the analytical solution for expanding/contracting pipes. An adapted compliant SMV model was then generated with a truncated apex using sinusoidally prescribed motion of the wall. With this model, two vortex rings could be predicted as in the experiments. The spherical-end model also gave good agreement with experimental flow patterns (ludicello et al., 1994). Frequency-dependent studies were carried out over the range of cardiac values using single- and multi-block versions of the code. A further validation exercise involved the use of sigmoidal filling curves in the in vitro models (Shortland et a!., 1994). Experimental data provided by such studies were used to drive the wall motion in the numerical simulations, and parametric studies of several simulation parameters were carried out. Flow field features and trajectories of the vortex paths were compared with the experiments for different filling curves, with reasonable agreement. However, because shear stress discontinuities occurred in the predictions a strict volume-defined analytical model was constructed for wall movement with smooth spatial and temporal behaviour reproducing experimental filling curves. Numerical predictions showed not only an improvement in the qualitative features of the flow compared with the experiments, but also a quantitative improvement in the prediction of the vortex core paths. Also the shear stress discontinuities were no longer evident. In order to be able to estimate residence times, instantaneous streamlines and particle tracks were produced. Analysis of shear stresses in the fluid and generation of particle pathlines for residence calculation in 3-D geometries will be carried out in the next feature for model candidates for the final SMV design. Some of the material published during the course of the project is included in APPENDIX 1. In this thesis, attention is paid to the SMV fluid dynamics. However, SMV behaviour is a coupled fluid-solid problem. Future work will be carried out in the muscle modelling. To this end, a careful review has been carried out, and is included in the thesis. Implications for future work are also discussed

Elektromechanische Modellierung und Simulation dünner Herzgewebekomposite

In dieser Arbeit wird ein Aufblasversuch für in vitro Herzgewebe im Rahmen der Finite Elemente Methode (FEM) modelliert und simuliert. Ziel ist dabei insbesondere die Simulation von Medikamentenwirkung auf auto-kontraktile Herzgewebe bestehend aus von human-induzierten pluripotenten Stammzellen abgeleiteten Kardiomyozyten und der Abgleich mit hausinternen experimentellen Resultaten und mit Literaturdaten. Für das sehr dünne Kompositmaterial wird ein Schalenmodell aufgestellt und mit Hodgkin-Huxley basierten Differentialgleichungssystemen gekoppelt, die die zelluläre Elektrophysiologie beschreiben. Zusätzlich wird die kanten-basiert geglättete FEM auf ihre Anwendbarkeit auf biomechanische Schalenprobleme hin untersucht. Diese Methode glättet die elementweise konstanten, kompatiblen Dehnungen über Elementgrenzen hinweg und erreicht so eine höhere Genauigkeit, als die Standard FEM. Darüberhinaus eignet sie sich in besonderem Maße für die Berechnung auf stark verzerrten Elementen, die bei automatischer Netzgenerierung für anatomische Strukturen häufig entstehen. Zunächst werden die verwendeten Schalen- und FE-Theorien, die elektromechanischen Grundlagen von Herzgeweben, sowie von Medikamentenwirkung und einschlägige Modelle vorgestellt. Im Anschluß wird das Modell auf den Aufblasversuch angewandt, an dem die Qualität und die Fähigkeit des Modellsdikamentenwirkung auf Herzgewebe vorherzusagen, validiert und beurteilt werden.This work models and simulates an inflation test for in vitro cardiac tissues in the framework of the Finite Element Method (FEM). It focuses on the simulation of drug treatment of autonomously beating cardiac tissue consisting of human-induced pluripotent stem cell-derived cardiac myocytes and the validation based on in-house experimental results and on literature data. The ultra-thin composite material is modeled as a shell that is coupled with Hodgkin-Huxley based systems of differential equations describing the cellular electrophysiology. Additionally, the edge-based smoothed FEM is investigated concerning its applicability to biomechanical plate problems. This method achieves a higher accuracy than the standard FEM by smoothing the element-wise constant compatible strains over the edges of the finite element mesh. It is especially beneficial in the computation of strongly distorted elements that are often created by automatic meshing of anatomical structures. The thesis starts by introducing the employed plate and FE theories, the electromechanical basics of cardiac tissue as well as of drug treatment and corresponding computational models. The model is then applied to the inflation test that serves as the validation basis for the quality and the ability of the model to predict drug effects on cardiac tissue

Transverse Isotropic and Orthotropic Composites: Experiments, Identification and Finite Element Analysis

Die konstitutive Modellierung und numerische Analyse des Verhaltens von Verbundwerkstoffen, insbesondere von transversal isotropen und orthotropen Werkstoffen, hat in der Industrie große Aufmerksamkeit bekommen. Dies ist vor allem durch die Verwendung von Verbundwerkstoffen für ein breites Spektrum von Anwendungen in verschiedenen Branchen erkennbar. Vorteile von Verbundwerkstoffen wie hohe Festigkeit und Flexibilität bei der Konstruktion machen diese attraktiv. Aufgrund vieler Designfaktoren bei Verbundwerkstoffen, wie zum Beispiel das Verbinden mit anderen Bauteilen, sind Löcher in Laminaten unvermeidlich. Die Fasern werden in der Regel durch Bohren eines Lochs im Laminat bzw. unterbrochen. Alternativ können die Fasern um die Löcher herum gelegt werden. Eines der Ziele dieser Arbeit ist es, herauszufinden, ob die Tendenz zum Bruch, d.h. die zugehörige Spannungsverteilung zu untersuchen. Um die beiden Fälle (Faserumlenkung versus gerader Faser) zu vergleichen und einen tieferen Einblick in den Prozess durch Simulationen zu erhalten, wird ein konstitutives Modell der transversalen Isotropie für den Fall kleiner Verzerrungen hergleitet. Das Modell ist in das in-house Finite-Elemente Programm TASAFEM implementiert worden. Eine große Herausforderung stellt die Beschreibung der räumlich verteilten Faserorientierungen für den Fall, dass die Fasern um das Loch herumgelegt werden. Zunächst wird die Verteilung der Fasern mit Hilfe der Stromlinienfunktion modelliert, um die inhomogenen Faserorientierungen für die FE-Simulationen zu erhalten. Um die Genauigkeit der Simulationen zu erhöhen, werden B-Splines verwendet, um die Faserrichtungen entsprechend den experimentellen Beobachtungen zu modellieren. Im sehr breiten Bereich der geometrischen Modellierung insbesondere bei CAD-Anwendungen (Computer-Aided Design) werden B-Splines häufig zur Beschreibung von Kurven und Flächen verwendet, vor allem aufgrund ihrer mathematischen Eigenschaften und ihrer hohen Flexibilität. Hierbei werden die Eigenschaften von Tangentenvektoren an Koordinatenflächen ausgenutzt, um die Richtungen zu bestimmen. Eine weitere Herausforderung bei den durchgeführten Simulationen ist die Identifikation der erforderlichen Materialparameter für das verwendete Materialmodell. Zu diesem Zweck werden verschiedene Experimente durchgeführt, um die Parameter eindeutig zu bestimmen. Zum Schluss wird der gesamte Prozess der Modellierung, Simulation und Identifizierung der Materialparameter durch spezielle Tests validiert. Orthotrope Laminate gehören zu den am häufigsten verwendeten Laminaten in industriellen Anwendungen. Die Untersuchungen werden daher auf orthotrope Laminate ausgeweitet. Das Ziel ist es, das Verhalten auch auf orthotrope Laminate auf der Grundlage identifizierter Parameter zu übertragen. Es wird ein konstitutives Modell der Orthotropie für den Fall kleiner Dehnungen angewandt und in den in-house-Code TASAFEM implementiert. Auch hier besteht die Herausforderung, der Materialparameter von orthotropen Laminaten bereitzustellen, die für die erforderlichen FE-Simulationen notwendig sind. Die Materialparameter werden im Rahmen eines Least-Square-Ansatzes mit Hilfe von Messdaten eines digitalen Bildkorrelationssystems identifiziert. Zu diesem Zweck sind verschiedene Versuche wie Zug-, Scher-, Druck- und Zugschertests durchgeführt worden. Diese sind zur Identifikation der neun Materialparameter der linearen, orthotropen Elastizität herangezogen worden. Im nächsten Schritt ist es notwendig, den numerischen Ansatz mit experimentellen Messungen zu validieren. Zur Validierung werden Proben verwendet, bei denen die Proben mit zwei senkrechten Faserrichtungen ausgestattet sind. Hierbei wird das Loch nach dem Herstellungsprozess der Proben gebohrt. Zum Schluss wird ein Vergleich zwischen den Ergebnissen der Finite-Elemente-Simulationen und den experimentellen Ergebnissen vorgestellt.In today’s engineering industry, constitutive modeling and numerical analysis of the behavior of composite materials, particularly transversely isotropic and orthotropic materials, have gained a lot of attention. This is mainly due to the usage of composites for a wide range of applications in different industries. Moreover, the advantages of composites such as high strength and flexibility in design make these materials attractive. Due to many factors in the design of composites, holes in laminates are unavoidable. Fibers are usually cut by drilling a hole into laminates. Alternatively, fiber can be bypassed around holes in order to reduce the fracture tendency around a hole, or to achieve different stress distributions. One of the goals of this work is to compare these cases: In one case, fibers were bypassed around the hole while fibers were cut in the other case by drilling a hole. In order to compare these cases and to get a deeper insight into the process using simulations, a constitutive model of transverse isotropic for the small strain case is applied based on large strain theory. The model is implemented in the in-house finite element program TASAFEM. One major challenge of this simulation is to determine the fiber orientations. To begin with, the circumplacement of fibers is modeled using the streamline function to obtain the inhomogeneous fiber direction for finite element simulations. In order to increase the precision of simulations, the B-spline method is used to model the fiber directions according to the experimental observations. In the broad field of geometric modeling and computer-aided design (CAD), it is common to use B-splines to describe curves and surfaces which is mainly due to their mathematical properties and their flexibility. Another challenge regarding the simulations is to identify the required parameters for the presented material model. Several different experiments are carried out in this regard. Finally, the whole process of modeling, simulation, and material parameter identification is validated by means of validation tests. Orthotropic laminates belong to the most commonly used laminates in industrial applications. The investigation is extended to orthotropy laminates, where we have fibers in two directions, and our aim is to predict the behavior of orthotropy laminates based on the calculated parameters. A constitutive model of orthotropy for the small strain case is applied and implemented in the inhouse code TASAFEM. Another challenge in this work is to calculate the material parameters of orthotropy laminates as a basis for finite element simulations. The material parameters are identified within a least-square approach with the help of optical results of a digital image correlation system. For this purpose, different experiments such as tensile, three rail shear, lap shear and compression tests are carried out. Nine material parameters of linear elastic for orthotropy case are identified. In the next step, it is necessary to validate the numerical approach with experimental observations. The validation examples are performed as theses samples have fibers in two perpendicular directions, where the hole is drilled after the production process. Finally, a comparison between the finite element simulations and the experimental results is provided

Thermo-mechanical coupling of transversely isotropic materials using high-order finite elements

Constitutive modeling and numerical analysis of the behavior of anisotropic materials, particularly transversely isotropic and orthotropic materials, attained increasing attention in the last few years. The attention is motivated by the wide range of applications of these materials in engineering industries and biomedical technologies. This work aims to develop a constitutive model for transversely isotropic materials undergoing thermo-mechanically coupled finite deformations. The model is based on the idea of multiplicative decomposition of the deformation gradient. Furthermore, making use of high-order finite elements, the capability of the model to simulate the behavior of transversely isotropic material under isothermal and thermo-mechanically coupled loadings is demonstrated by performing some numerical experiments. First of all, a constitutive model for the case of isothermal transversal isotropy is formulated. The proposed model is an extension of the volumetric/isochoric decoupling of the deformation gradient, where the isochoric part is decomposed into two parts, one part containing only the deformation along the preferred direction, while all remaining deformations are included in the other part. This formulation has the advantage that it leads to a clear split of the stress-state, i.e., the stress along the preferred direction is splitted from the remaining stresses. Additionally, the proposed model overcomes the obstacle related to the application of volumetric/isochoric decomposition to anisotropy. The formulation is, then, extended to the case of thermo-mechanically coupled problem, where a thermodynamically consistent constitutive model for transversal isotropy is developed. Moreover, a directionally dependent, i.e. transversely isotropic heat flux vector is derived, which takes into consideration the anisotropy in heat conductivity. The proposed model is implemented into a high-order finite element code, in which the p-version finite element method (p-FEM) and the high-order diagonally implicit Runge-Kutta (DIRK) methods are used for the spatial and time discretizations, respectively. In p-FEM the accuracy of the solution is improved by increasing the polynomial degree of the elements, and this makes p- FEM more convenient for the analysis of thin structures, like in the case of laminated composites. Thus, computations are carried out in order to investigate the behavior of the proposed model with different numerical examples. To this end, the influence of different factor, namely, existence of anisotropy, orientation of the preferred direction, anisotropic thermal expansion as well as anisotropic heat conductivity, on the response of transversely isotropic material under isothermal and/or thermo-mechanical loadings is discussed. Furthermore, the efficiency of the p-version implementations is demonstrated by comparing it with two different h-version finite element implementations

Large space structures and systems in the space station era: A bibliography with indexes

Bibliographies and abstracts are listed for 1219 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1990 and December 31, 1990. The purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems