TY - CHAP A1 - Klauke, Thomas A1 - Kühhorn, Arnold A1 - Liang, Luo A1 - Kober, Markus T1 - Entwicklung eines 3-Blatt-CFK-Verstellpropellers für Ultraleichtflugzeuge N2 - Internationale AVK-Tagung, 13.-14. September 2010, Essen Y1 - 2010 ER - TY - CHAP A1 - Klauke, Thomas A1 - Kühhorn, Arnold A1 - Liang, Luo A1 - Kober, Markus A1 - Sieghart, D. A1 - Führer, M. A1 - Viehweger, Bernd A1 - Fritzsche, Christoph A1 - Sarradj, Ennes T1 - Entwicklung eines 3-Blatt-CFK-Verstellpropellers für Ultraleichtflugzeuge N2 - Deutscher Luft- und Raumfahrkongress 2010, 31.08. - 02.09.2010, Hamburg Y1 - 2010 ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold T1 - Development of optimized washer-shape for damage-free load application to composites T2 - Composite Structures Y1 - 2010 SN - 0263-8223 VL - 92 IS - 9 SP - 1985 EP - 1991 ER - TY - CHAP A1 - Kober, Markus T1 - HyperWorks im Einsatz in der Lehre Y1 - 2009 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold T1 - Development of optimized washer shape for damage-free load application to composites Y1 - 2009 ER - TY - CHAP A1 - Klauke, Thomas A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Application of a Newer Inter-Fiber-Failure Criteria on CFRPs in Aero Engine Development Y1 - 2010 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold T1 - Auslegung und Optimierungsprozess einer Tragstruktur in Faserverbundbauweise unter Berücksichtigung moderner Versagenskriterien Y1 - 2009 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Klauke, Thomas T1 - Auslegung einer Flanschverbindung aus faserverstärktem Kunststoff durch Optimierung der Faserorientierungen und Schichtdicken mit Hilfe von Altair HyperStudy unter Verwendung eines Wirkebenenbruchkriteriums als Nebenbedingung Y1 - 2007 ER - TY - CHAP A1 - Kober, Markus A1 - Klauke, Thomas A1 - Kühhorn, Arnold A1 - Lenk, Olaf T1 - Einbindung eines modernen Wirkebenenbruchkriteriums für faserverstärkte Kunststoffe in eine Parameteroptimierung mit Altair HyperStudy Y1 - 2006 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Klauke, Thomas A1 - Lenk, Olaf T1 - Topology-Optimized Intermediate Casing of Aero Engine and Comparative Evaluation of Titanium and Composite Architecture in Terms of Load Capacity and Weight Reduction T2 - Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A Y1 - 2008 SN - 978-0-7918-4315-4 N1 - GT2008-50644 SP - 69 EP - 79 PB - ASME CY - New York, NY ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold T1 - Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations T2 - Composites Science and Technology KW - Failure Criteria KW - Fibre Reinforced Plastic Y1 - 2012 U6 - https://doi.org/10.1016/j.compscitech.2012.08.007 SN - 0266-3538 VL - 72 IS - 15 SP - 1941 EP - 1951 ER - TY - CHAP A1 - Zuchlinski, André A1 - Kühhorn, Arnold A1 - Kober, Markus A1 - Wehrenpfennig, Lutz T1 - Kombinierte Topologie- und Parameteroptimierung des Aufhängungssystems von heckinstallierten Turbofantriebwerken T2 - 61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin KW - Hecktriebwerksaufhängung KW - Optimierung Y1 - 2012 N1 - Beitrag DLRK 2012-281168 PB - Dt. Ges. für Luft- und Raumfahrt CY - Bonn ER - TY - THES A1 - Kober, Markus T1 - Ein Beitrag zur strukturmechanischen Optimierung realer Bauteile in metallischer und Faserverbundbauweise unter Verwendung von wirkebenenbasierten Bruchkriterien KW - Optimierung KW - Verbundbauweise KW - Bruchkriterien Y1 - 2011 SN - 978-3-86387-085-0 PB - Mensch und Buch CY - Berlin ER - TY - GEN A1 - Mahler-de Silva, Tina A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Developing a Simplified Surrogate Model for Structured Sheet Metals with Numerical and Experimental Comparisons T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - It is important to steadily refine lightweight designs with regard to saving resources and energy in common with good economic efficiency. Thin structured sheet metals offer significantly improved component stiffnesses in addition to an upgraded buckling behavior compared to flat, unstructured sheet metals. By using a distortion energy based homogenization method it is possible to develop a mechanical surrogate model which describes effective mean properties. The accurate selection of symmetric and periodic boundaries enables to determine the required parameters. The conditions are contemplated on elementary cells whose structural mechanical behavior is representative for the elastic behavior of large structures. By doing this, the amount of elements can be reduced and thus the calculating time of large components can considerably be saved. For an efficient surrogate model it is required to analyze and compare numerical with experimental investigations. Some different versions of optimization will be tested to get better approximation of the data. KW - Structured Sheet Metals Y1 - 2013 UR - http://onlinelibrary.wiley.com/doi/10.1002/pamm.201310045/abstract N1 - GAMM 2013, 84th Annual Scientific Conference, Novi Sad , 18. - 22. März 2013 VL - 13 IS - 1 SP - 99 EP - 100 ER - TY - GEN A1 - Zolochevsky, Alexander A1 - Sklepus, Sergiy A1 - Galishin, Alexander A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - A Comparison between the 3D and the Kirchhoff-Love Solutions for Cylinders under Creep-Damage Conditions T2 - Technische Mechanik KW - creep deformation Y1 - 2014 UR - http://www.ovgu.de/ifme/zeitschrift_tm/2014_Heft2/04_Zolochevsky_et_al.pdf VL - 34 IS - 2 SP - 104 EP - 113 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Kästner, Benjamin A1 - Keskin, Akin T1 - Evaluation of the Stress and Displacement Behavior of Different LS-Dyna Element Types in Combination with Different Anti-Hourglassing Formulations and Initial Element Deformations T2 - Kurzfassungen der Vorträge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg Y1 - 2014 SN - 978-3-9816215-1-8 PB - DYNAmore GmbH CY - Stuttgart ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Stelldinger, Enrico A1 - Keskin, Akin T1 - Identification of Stiffness Parameters of a Simplified Aero-Engine Mount System by Using a Higher Fidelity Model of the Mount System T2 - Kurzfassungen der Vorträge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg Y1 - 2014 SN - 978-3-9816215-1-8 PB - DYNAmore GmbH CY - Stuttgart ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Rademann, Jörg A1 - Mück, Bernhard T1 - Nonlinear topology optimization of centrifugally loaded aero-engine part with newly developed optimality-criteria based algorithm T2 - Aerospace Science and Technology N2 - In this paper a successful topology optimization of a centrifugally loaded aero-engine part is presented. For the topology optimization, which is a nonlinear problem due to several contact regions, a self-developed topology optimization algorithm in combination with a commercial FE-solver is used. The goal of the optimization was the reduction of stresses in the structure. ©2014 Rolls-Royce Deutschland Ltd & Co. KG. Published by Elsevier Masson SAS. All rights reserved. KW - Topology optimization KW - Optimality criteria KW - Aero-engine KW - Centrifugal loading Y1 - 2014 UR - http://www.sciencedirect.com/science/article/pii/S1270963814001783 U6 - https://doi.org/10.1016/j.ast.2014.09.005 VL - Vol. 39 SP - 705 EP - 711 ER - TY - GEN A1 - Stelldinger, Enrico A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Experimental evaluation of the low-velocity impact damage resistance of CFRP tubes with integrated rubber layer T2 - Composite Structures N2 - The impact performance of structural components made of fibre-reinforced plastic is often one of the limiting properties during the design process. To improve the damage resistance regarding transverse low-velocity impact loading, a rubber layer (KRAIBON®) is integrated into the composite laminate of tubular carbon/epoxy specimens. Numerous impact tests, using two different rubber compounds and three different layups, are carried out. The specimens are impacted using a modified Charpy pendulum. Force–time histories have been used to determine the damage threshold load. To visualise damage such as delaminations and inter-fibre failures, the impacted samples have been examined using microsectioning. It is shown that a significant improvement in impact damage resistance can be achieved by integrating a rubber layer into a carbon/epoxy laminate. KW - Composites KW - Tubes KW - Low-velocity impact KW - Damage resistance Y1 - 2016 U6 - https://doi.org/10.1016/j.compstruct.2015.11.069 SN - 0263-8223 IS - 139 SP - 30 EP - 35 ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Mück, Bernhard T1 - Topologieoptimierung eines fliehkraftbelasteten Triebwerkbauteils mit einfach zu implementierendem Algorithmus unter Berücksichtigung mehrerer Zielfunktionen T2 - NAFEMS-Magazin : Zeitschrift für numerische Simulationsmethoden und angrenzende Gebiete KW - Topologieoptimierung Y1 - 2015 UR - http://www.nafems.org/publications/magazin/archive/ SN - 2311-522x IS - 35 SP - 56 EP - 66 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Keskin, Akin T1 - Implicit Time Integration Schemes for the FEM Simulation of Fast Rotating Structures T2 - WCCM XII & APCOM VI (World Congress on Computational Mechanics & Asia Pacific Congress on Computational Mechanics), Seoul, South Korea, 23.-29. Juli 2016 N2 - Due to the demand of more and more detailed FEM simulation results of whole aero-engine models, the number of DOF of such models (Fig. 1) increases dramatically. Although the available computational power for the solution of such highly nonlinear, dynamic boundary value problems also increased during the last years, the overall computational time of these high-fidelity models for the simulation of a few milliseconds of the running engine is in the order of several weeks even on high performance clusters with thousands of CPU cores. Typically, for such highly dynamic FEM computations explicit time integration schemes are used in order to solve the equations of motion. To keep such a numerical integration stable, the time step size may not exceed a certain critical time step size. Unfortunately, the critical time step size of an explicit time integration algorithm for the engine models under consideration is in the order of 10-8. This means that the simulation of a running engine over a time span of a few seconds results in a computational time of several years with clusters, which are available nowadays. Therefore, implicit time integration schemes, which are unconditionally stable and allow much bigger time steps, have to be used. Since in an implicit integration, in contrast to an explicit one, an equilibrium iteration is always necessary, the computational costs for an implicit time step are much higher than for an explicit time step. Almost all commercial FE codes use the classical Newmark implicit time integration scheme. It will be shown that this algorithm fails especially for the simulation of fast rotating structures if bigger time steps are used. This is demonstrated at the example of academic examples as well as for more realistic rotor models. To overcome the problems of the Newmark integration, a 3-Point-Newmark- Euler-Backward integration scheme [1,2] has been selected, which consists of alternating Newmark and 3-Point-Euler-Backward steps. The additional interpolation information for the Euler-step is provided by the previous Newmark step. This integration procedure has been implemented and successfully applied to the FEM simulation of fast rotating structures, which will be also demonstrated during the presentation. Y1 - 2016 UR - http://wccm2016.org/data/WCCM_Proceeding_v2.1.pdf UR - http://wccm2016.org/wp/pdf/150917.pdf ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold T1 - Stable implicit time-integration of flexible rotating structures—explanation for instabilities and concepts for avoidance T2 - Applied Mathematical Modelling N2 - Instabilities occurring during the implicit time-integration are still handicapping a time-efficient solution of large FEM systems of equations. Especially the simulation of flexible rotating structures is barely mastered by implicit FEM codes. For this, the Newmark algorithm and related algorithms are used for many years. Here, we derive the reasons for the mentioned inevitable numerical issues and present concepts that lead to an efficient and stable solution. KW - Nonlinear implicit time-integration KW - Instability KW - Newmark KW - Rotating structures Y1 - 2018 U6 - https://doi.org/10.1016/j.apm.2018.03.017 SN - 0307-904X VL - 60 SP - 235 EP - 243 ER - TY - GEN A1 - Noack, Martin A1 - Kühhorn, Arnold A1 - Kober, Markus A1 - Firl, Matthias T1 - A new stress-based topology optimization approach for finding flexible structures T2 - Structural and Multidisciplinary Optimization N2 - This paper presents a new FE-based stress-related topology optimization approach for finding bending governed flexible designs. Thereby, the knowledge about an output displacement or force as well as the detailed mounting position is not necessary for the application. The newly developed objective function makes use of the varying stress distribution in the cross section of flexible structures. Hence, each element of the design space must be evaluated with respect to its stress state. Therefore, the method prefers elements experiencing a bending or shear load over elements which are mainly subjected to membrane stresses. In order to determine the stress state of the elements, we use the principal stresses at the Gauss points. For demonstrating the feasibility of the new topology optimization approach, three academic examples are presented and discussed. As a result, the developed sensitivity-based algorithm is able to find usable flexible design concepts with a nearly discrete 0 − 1 density distribution for these examples. KW - Topology optimization KW - Flexible structure KW - Stress-based KW - SIMP KW - Conceptual design Y1 - 2021 U6 - https://doi.org/10.1007/s00158-021-02960-w SN - 1615-147X SN - 1615-1488 VL - 64 IS - 4 SP - 1997 EP - 2007 ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Keskin, Akin T1 - Instability problems in implicit transient FEM simulations of fast rotating elastic structures - Description of the phenomenon and possible solutions T2 - Proceedings of NAFEMS DACH Conference 2018, Bamberg, May 14-16, 2018 Y1 - 2018 SN - 978-1-910643-14-3 SP - 48 EP - 52 PB - NAFEMS Deutschland, Österreich, Schweiz GmbH CY - Grafing ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Keskin, Akin T1 - Optimization of Newmark-Euler Time-Integration Parameters for a Stable and Efficient Implicit Simulation of Rotating Elastic Structures T2 - Proceedings of 15th German LS-DYNA Forum Y1 - 2018 SN - 978-3-9816215-5-6 SP - 235 EP - 238 PB - DYNAmore GmbH CY - Stuttgart ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Keskin, Akin A1 - Singh, Kai Navtej T1 - Challenges and opportunities of thermomechanical FEM simulations of high fidelity aero-engine models by implicit time-integration T2 - Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017 Y1 - 2017 UR - https://isabe2017.org/ PB - ISABE ER - TY - CHAP A1 - Keskin, Akin A1 - Kober, Markus A1 - Stelldinger, Enrico A1 - Kühhorn, Arnold A1 - Böhm, Holger A1 - Hornig, Andreas A1 - Hufenbach, Werner T1 - On the quantification of errors of a pre-processing effort reducing contact meshing approach : AIAA 2015-0408 T2 - 53rd AIAA Aerospace Sciences Meeting 2015, Kissimmee, Florida, USA, 5 - 9 January 2015, held at the AIAA SciTech Forum 2015, vol. 4 Y1 - 2015 SN - 978-1-5108-0117-2 U6 - https://doi.org/10.2514/6.2015-0408 SP - 3113 EP - 3124 PB - Curran CY - Red Hook, NY ER - TY - CHAP A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Stelldinger, Enrico A1 - Keskin, Akin T1 - Considerations About the Necessary Mesh Density of Bearings in Detailed Finite Element Models T2 - ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics Düsseldorf, Germany, June 16–20, 2014, Paper GT2014-25624 N2 - In order to predict properly the behavior of very complex mechanical models, much focus needs to be done on the level of model details as well as the techniques used to predict component movements based on mechanical and thermal loads. In particular bearings and joints play a significant role in big model assemblies such as aero-engines where most of the structures are modeled by solid elements rather than using traditional shell or beam elements. This approach is very complex and expensive in terms of computational effort however can lead to increased simulation accuracy when done properly. This publication will answer questions related to the modeling techniques required for detailed bearings (not only rotor bearings) and joints of an aero-engine application where these components are not idealized or simplified, i.e. the ball in a ball joint is meshed by solid elements. The investigation will discuss the question about the number of elements needed to mesh a ball joint in such a way that a correct rotation is possible. If the mesh is too coarse, a rotation would be impossible due to the faceting of the rotating parts. It will be shown that a proper rotation depends on a correct relation between the radius of the inner ball, the gap size of the bearing and the number of nodes in the circumferential direction. For this relation an analytical formula has been derived and successfully tested at some examples. Furthermore, some finite element codes offer the possibility of smoothed contact surfaces. These options improve the situation but they might cause issues too. For this reason these smoothed contact options are also considered under the aspects mentioned above. Copyright © 2014 by Rolls-Royce Deutschland Ltd & Co KG KW - Density KW - Bearings Y1 - 2014 SN - 978-0-7918-4577-6 U6 - https://doi.org/10.1115/GT2014-25624 PB - ASME ER - TY - GEN A1 - Kober, Markus A1 - Beirow, Bernd A1 - Meyer, Marcus A1 - Singh, Kai T1 - Towards the Isogeometric Aero-Engine T2 - Results in Engineering N2 - Creating very detailed finite element models of aero-engines is a very time-consuming process especially if structured meshes have to be generated for thousands of parts. Isogeometric analysis offers the possibility of an accelerated model creation process while achieving higher accuracy by using the non-uniform rational B-spline functions used for the geometry description also as basis functions for the finite element analysis. In this case, no meshing is necessary anymore. Here, we demonstrate this process by applying a self-developed tool which creates a geometry description and a computational model of a part at the same time. By the help of this tool we build up a simplified mechanical aero-engine model, which is used for transient implicit computations simulating the acceleration process of the rotor. We discuss the results as well as the computational time of isogeometric models in comparison to classical finite element models. KW - Isogeometric analysis KW - Finite element method KW - Aero-engine model generation KW - Accelerated whole-engine modeling Y1 - 2023 UR - https://www.sciencedirect.com/science/article/pii/S2590123023002621?via%3Dihub U6 - https://doi.org/10.1016/j.rineng.2023.101135 SN - 2590-1230 VL - Vol. 18 ER - TY - CHAP A1 - Stelldinger, Enrico A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Otimization of a Carbon-fiber-reinforced Plastic Composite Structure using the Example of a Wing Rigger KW - Optimization KW - Composite KW - Wing Rigger Y1 - 2011 ER - TY - GEN A1 - Kober, Markus A1 - Beirow, Bernd A1 - Singh, Kai Navtej T1 - Towards the Isogeometric Aero-Engine T2 - Proceedings of 16th German LS-DYNA Forum, 11.-12. Oktober 2022, Bamberg Y1 - 2022 UR - https://www.dynamore.it/en/training/conferences/upcoming/16th-german-ls-dyna-forum-2022/preliminary-agenda#tag-1 SN - 978-3-9816215-8-7 ER - TY - GEN A1 - Naveed, Zishan A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Contact Behaviour of Isogeometric Analysis for Rotating Structures and its Industrial Application by Coupling to the Classical Finite Element Method T2 - VII International Conference on Isogeometric Analysis, München, 18.-20. September 2019 N2 - Especially for rotating structures like bearings non-smooth contact surfaces, as they appear in classical finite element modeling, lead to various problems during the analysis involving mesh interlocking and spurious oscillations in contact forces. In order to eliminate these issues, very fine meshes and additional smoothing strategies are employed in case of the finite element method (FEM). But also Non-Uniform Rational B-splines (NURBS) based isogeometric analysis (IGA) can be very useful for the contact analysis due to the inherent higher order continuity of NURBS basis functions. In this contribution, the contact behavior using classical FEA and IGA approaches is studied by means of an example of a pendulum under gravitational load. In addition, a more practical example of a coupled IGA–FEM problem with a cylindrical roller bearing is also reported in this paper. This research study of contact analysis has been carried out for the above mentioned examples using LS-DYNA and illustrates that contact surfaces of coarsely meshed geometry lock the rotation of the parts in case of classical FEM. On the contrary, when the contact surface is represented by NURBS elements it allows the rotation of the parts and effectively alleviates the contact force oscillation. Y1 - 2019 UR - http://congress.cimne.com/iga2019/frontal/ProgramPrint.asp?t=todo ER - TY - GEN A1 - Kober, Markus A1 - Kühhorn, Arnold A1 - Keskin, Akin T1 - Instabilitätsprobleme bei der impliziten transienten FEM-Simulation schnell rotierender elastischer Strukturen – Beschreibung des Phänomens und Lösungsmöglichkeiten T2 - NAFEMS-Online-Magazin Y1 - 2018 SN - 2311-522X N1 - Download des jeweils aktuellen Hefts: https://www.nafems.org/publications/magazin/ VL - 48 IS - 4 SP - 36 EP - 49 ER - TY - GEN A1 - Naveed, Zishan A1 - Kühhorn, Arnold A1 - Kober, Markus T1 - Comparative Evaluation of Isogeometric Analysis and Classical FEM with Regard to Contact Anaylsis T2 - 12th European LS-DYNA Conference 2019, 14-16 May 2019, Koblenz N2 - Isogeometric analysis represents a newly developed technique that offers the application of Computer Aided Designs (CAD) concept of Non-uniform Rational B-Splines (NURBS) tool to describe the geometry of the computational domain. The simplified transition of CAD models into the computational domain eliminates the problems arising from the geometrical discontinuities induced by the faceted approximation of the mesh. Moreover, numerical analysis directly on NURBS objects significantly reduces the design-to-analysis time compared to traditional FEA approach. In the field of contact mechanics, when finite elements are applied to geometry with curved surfaces, the result is a non-smooth geometrical representation of interface surfaces which may lead to mesh interlocking, high jumps and spurious oscillations in contact forces. To eliminate these issues, various surface smoothening strategies are to be employed in case of FEM. Isogeometric based analysis alleviates these issues without employing any additional smoothening strategy due to inherent higher order continuity of NURBS basis functions and much more accurate results are obtained compared to conventional FE approach. In the current study, LS-DYNA is used to demonstrate the capabilities and advantage of an isogeometric analysis though an example of pendulum under gravitational load. The numerical simulation results are analytically validated and the comparison of NURBS surfaces with faceted surfaces is carried out to investigate the accuracy. Y1 - 2019 UR - https://www.dynalook.com/conferences/12th-european-ls-dyna-conference-2019/isogeometric/naveed_btu.pdf ER -