Sascha Eisenträger

Research Assistant

Dr.-Ing. Sascha Eisenträger

Institute of Materials, Technologies and Mechanics (IWTM)
Chair of Computational Mechanics

Gebäude 10, Universitätsplatz 2, 39106 Magdeburg, G10-013

Tel.: +49 391 67-52754 Fax: +49 391 67-12439

Homepage

Vita

seit 08/2023	Promovierter wissenschaftlicher Mitarbeiter am Institut für Werkstoffe, Technologien und Mechanik (IWTM), Otto-von-Guericke-Universität Magdeburg
08/2022 – 08/2023	Promovierter wissenschaftlicher Mitarbeiter am Institut für Mechanik, Technische Universität Darmstadt
01/2019 – 07/2022	Assistenzprofessor für Numerische Mechanik im Fachbereich Bau- und Umweltingenieurwissenschaften, Universität von Neusüdwales (UNSW Sydney), Australien
10/2014 – 01/2019	Promovierter wissenschaftlicher Mitarbeiter am Institut für Mechanik (IFME), Otto-von-Guericke-Universität Magdeburg
06/2010 – 09/2014	Wissenschaftlicher Mitarbeiter am Institut für Mechanik (IFME), Otto-von-Guericke-Universität Magdeburg (Doktorand)
09/2014	Promotion: Maschinenbau (Dr.-Ing.), Otto-von-Guericke-Universität Magdeburg, Dissertation: Higher Order Finite Elements and the Fictitious Domain Concept for Wave Propagation Analysis
05/2010	Diplom: Maschinenbau (Dipl.-Ing.), Vertiefung: Angewandte Mechanik, Otto-von-Guericke-Universität Magdeburg, Diplomarbeit: Entwicklung eines finiten 3D Schichtelementes nach der p-Methode für die Berechnung von Lambwellen in Faserverbundstrukturen
01/2008 – 06/2008	Auslandssemester an der Universität von Adelaide (University of Adelaide), Australien

Projects

Current projects

Dynamic Mesh Refinement Exploiting High-Order Transfinite Elements for the Analysis of Wave Propagation Phenomena on High-Performance Clusters
Duration: 01.08.2022 bis 31.07.2025

Adaptive mesh refinement (AMR) strategies are of interest in many branches in science and engineering. Due to the possibility to generate locally refined discretizations, large-scale problems of practical relevance become tractable. However, a review of the state of the art in AMR reveals several issues that are not sufficiently resolved yet. First, often only low-order finite elements in combination with h-extensions are applied in commercial codes resulting in a sub-optimal convergence of algebraic type. Additionally, to ensure a conformal coupling, either unstructured discretizations consisting of both simplex and tensor-product elements have to be utilized or the ansatz space of the elements has to be constrained reducing the overall accuracy of the approach. Second, high-order hp-type refinement strategies, mainly implemented in a research environment, suffer from restrictions to 1-irregular meshes to decrease the implementational complexity or are based on hierarchic shape functions that do not permit the construction of diagonal mass matrices which is essential for (explicit) transient analyses. However, these methods are at least capable of delivering exponential rates of convergence. Therefore, a novel methodology to construct dynamically refined meshes based on (nodal) high-order quadrilateral and hexahedral finite element types is proposed. Fortunately, the aforementioned drawbacks can easily be overcome by employing the so-called transfinite interpolation technique (Gordon-Coons interpolation) enabling the construction of arbitrary transition elements. In principle, it is possible to couple elements of different types, sizes, and polynomial orders without any compromise on the attainable accuracy. This unique versatility opens up a wide variety of possible applications for this element type. Additionally, highly accurate mass lumping schemes are developed to facilitate the application to transient analyses. The proposed novel family of elements constitutes the cornerstone for implementing a dynamic refinement strategy, where both refinement and coarsening steps are executed in each time step of a dynamic analysis. Hence, optimal rates of convergence can be achieved with minimal numerical effort. To increase the efficiency of the proposed framework even further, all algorithms are implemented in a high-performance computing framework. The exceptional properties of the novel methodology are showcased using different numerical examples from the area of wave propagation analysis, where dynamic mesh refinement techniques are indispensable for a numerically efficient simulation. To this end, guided waves in the context of structural health monitoring in micro-structured materials and seismic wave propagation over large regions are discussed.

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Completed projects

Development of high order fictitious domain methods for unstructured grids
Duration: 01.01.2016 bis 31.01.2019

With the advent of fast high-resolution computed tomography (CT) scanners three-dimensional information of the micro-structure is readily available. Using this data a fully automated numerical method for structural simulations is developed. Therefore, it is possible to assess the influence of a heterogeneous micro-structure on the global behavior of the component without any user intervention. The chosen approach is based on the fictitious domain concept and especially on the finite cell method (FCM) or the spectral cell method (SCM) as recently proposed by the author.The focus of the current research proposal is on the extension of the FCM and the SCM to unstructured grids. In this context, it is generally known that arbitrary geometries can be discretized by tetrahedral elements and that powerful mesh generators are available for this element type. Therefore, the first step is to develop a novel formulation of the FCM and the SCM based on tetrahedral grids. In the future also prismatic, pyramidal and polyhedral elements are included in this framework. To retain high rates of convergence as encountered in the p-FEM different high order nodal and hierarchical shape functions are implemented and tested. After developing a sound theoretical basis for the proposed approach it is evaluated in detail. Open questions including the influence of the size of the cells with respect to a typical length scale of the micro-structure and suitable time integration methods are investigated. Depending on the size of the micro-structural details a local mesh refinement might be needed to resolve the solution field. Regarding dynamical analyses, time integration schemes are responsible for the accuracy of the solution and its efficiency. Therefore, it is inevitable to test different methods in view of their suitability for high order fictitious domain methods.Finally, the proposed method is validated using two different engineering problems. The first area of application is the mechanical assessment of cast components. The second application deals with the analysis of materials used for encapsulations of engines. In both cases the numerical model is based on CT scans of the real part. Depending on the micro-structure of the used materials a local meh refinement of the tetrahedral cells might be required. The analysis of these complex practice-oriented problems demonstrates the performance of the method and its applicability to complex industrial problems.

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Granulare Medien zur Schwingungsreduktion
Duration: 01.01.2016 bis 13.07.2017

Im Rahmen der Schwingungs- und Schallreduktion können neben etablierten Systemen auch weiterführende passive Konzepte verwendet werden, die eine Füllung von Kavitäten durch granulare Medien vorsehen. Dabei werden die positiven Dämpfungseigenschaften von granularen Materialien ausgenutzt und am Beispiel einer Ölwanne gezeigt, dass deutliche Schwingungsreduktionen, ohne Erhöhung der Masse und ohne zusätzlichen Bauraum zu beanspruchen, realisiert werden können. Bedingt durch die im Betrieb unvermeidliche Verteilung des Granulates in einer großen Kavität und dem damit einhergehenden deutlichen Einfluss auf das Schwinungsverhalten der Struktur, wurde eine Struktur mit vielen kleinen Kavitäten abgeleitet. Aufgrund des vorteilhaften Steifigkeits-Gewichts-Verhältnis können in diesem Zusammenhang Honigwabenstrukturen eingesetzt werden, deren optimale Füllung abgeleitet wurde.
Im Anschluss wurden verschiedene alternative Materialien untersucht, bei denen granulares Gummi die besten Ergebnisse erzielte, da die Verformung des Materials als zusätzliche Dissipationsquelle fungiert. Die entstandenen Methoden können analog auf andere Fragestellungen angewand werden, was zur Definition einer
allgemeinen Methodik führte, die sowohl für horizontale als auch für vertikale Applikationen anwendbar ist.

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Modelling and computational analysis of ultrasonic waves in heterogeneous structures including defects
Duration: 01.01.2014 bis 31.12.2015

The project TP3 aims to develop computational methods for the simulation and analysis of guided Ultrasonic/Lamb wave propagation in typical aircraft lightweight structures, such as sandwich structures with a heterogeneous core layer (honeycomb, open foam, closed foam. For the experimental investigation of wave propagation a 3D-Laser-Scanning-Vibrometer is applied. The project TP3 aims to explain how ultrasonic guided waves propagate in such structures, how they interact with inner boundaries and failures, such as delamination between the core layer and the top layer due to impacts, damages of the core layer, and how to design an optimal structural health monitoring (SHM) system. For the simulation of ultrasonic guided waves a very fine spatial and temporal resolution is required, which exceeds the computational possibilities of today s commercial FEA software packages, operating with classical linear or quadratic finite elements, different new methods for an effective analysis of wave propagation in complex structures have to be developed. Consequently, the objective of the aims to develop and to test (a) Semi-analytical finite element methods, (b) Coupling of analytical and computational approaches,
© Simplification of models,(d) Higher order finite elements (spectral FEM, p-FEM, NURBS-FEM), (e) Extension and application of the finite cell method (FCM) to wave propagation analysis.

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Entwicklung spezieller finiter Elemente höherer Ansatzordnung für die Berechnung der Lambwellenausbreitung in Faserverbundstrukturen
Duration: 01.01.2011 bis 31.12.2012

Geführten Ultraschallwellen in dünnen Faserverbundstrukturen - derartige Wellen nennt man nach ihrem Entdecker Horaz Lamb auch Lambwellen - breiten sich über größere Entfernungen aus und interagieren wegen ihrer geringen Wellenlängen auch mit kleinen Strukturschäden. Derartige Wellen lassen sich daher vorteilhaft für die Strukturüberwachung (englisch: structural health monitoring, abgekürzt SHM) einsetzen. Um die Ausbreitung derartiger hochfrequenter Wellen berechnen zu können, benötigt man eine extrem große Anzahl von konventionellen linearen finiten Elementen (mindestens 20 Elemente pro Wellenlänge) im Rahmen einer expliziten Zeitintegration, so daß man mit derartigen Berechnungen für reale Strukturbauteile schnell an die Leistungsgrenzen der heutigen Rechentechnik stößt. Deshalb liegt der Schwerpunkt des Dissertationsprojektes auf der Entwicklung und der Untersuchung verschiedener höherwertiger finiter Elemente (Polynomgrad p ≥ 3). Im einzelnen sind das p-Elemente auf Basis der normierten Integralen der Legendre Polynomen, Spektralelemente auf der Basis von Lagrange Polynomen sowie isogeometrische finite Elemente basierend auf nicht-uniformen rationalen B-Splines (NURBS).

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Publications

2025

Peer-reviewed journal article

Implementation of isotropic hyperelastic material models - a template approach

Eisenträger, Sascha; Maurer, Lukas; Juhre, Daniel; Altenbach, Holm; Eisenträger, J.

In: Acta mechanica - Wien : Springer . - 2025, insges. 36 S. [Online first]