@inproceedings{KlaukeKuehhornLiangetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Liang, Luo and Kober, Markus and Sieghart, D. and F{\"u}hrer, M. and Viehweger, Bernd and Fritzsche, Christoph and Sarradj, Ennes}, title = {Entwicklung eines 3-Blatt-CFK-Verstellpropellers f{\"u}r Ultraleichtflugzeuge}, abstract = {Deutscher Luft- und Raumfahrkongress 2010, 31.08. - 02.09.2010, Hamburg}, language = {de} } @inproceedings{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Auslegung und Optimierungsprozess einer Tragstruktur in Faserverbundbauweise unter Ber{\"u}cksichtigung moderner Versagenskriterien}, language = {de} } @inproceedings{KoberKuehhornKlauke, author = {Kober, Markus and K{\"u}hhorn, Arnold and Klauke, Thomas}, title = {Auslegung einer Flanschverbindung aus faserverst{\"a}rktem Kunststoff durch Optimierung der Faserorientierungen und Schichtdicken mit Hilfe von Altair HyperStudy unter Verwendung eines Wirkebenenbruchkriteriums als Nebenbedingung}, language = {de} } @inproceedings{KoberKlaukeKuehhornetal., author = {Kober, Markus and Klauke, Thomas and K{\"u}hhorn, Arnold and Lenk, Olaf}, title = {Einbindung eines modernen Wirkebenenbruchkriteriums f{\"u}r faserverst{\"a}rkte Kunststoffe in eine Parameteroptimierung mit Altair HyperStudy}, language = {de} } @inproceedings{KoberKuehhornKlaukeetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Klauke, Thomas and Lenk, Olaf}, title = {Topology-Optimized Intermediate Casing of Aero Engine and Comparative Evaluation of Titanium and Composite Architecture in Terms of Load Capacity and Weight Reduction}, series = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, booktitle = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4315-4}, pages = {69 -- 79}, language = {en} } @misc{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Development of optimized washer-shape for damage-free load application to composites}, series = {Composite Structures}, volume = {92}, journal = {Composite Structures}, number = {9}, issn = {0263-8223}, pages = {1985 -- 1991}, language = {de} } @inproceedings{Kober, author = {Kober, Markus}, title = {HyperWorks im Einsatz in der Lehre}, language = {de} } @inproceedings{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Development of optimized washer shape for damage-free load application to composites}, language = {en} } @inproceedings{KlaukeKuehhornKober, author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Application of a Newer Inter-Fiber-Failure Criteria on CFRPs in Aero Engine Development}, language = {en} } @inproceedings{StelldingerKuehhornKober, author = {Stelldinger, Enrico and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Otimization of a Carbon-fiber-reinforced Plastic Composite Structure using the Example of a Wing Rigger}, language = {en} } @misc{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations}, series = {Composites Science and Technology}, volume = {72}, journal = {Composites Science and Technology}, number = {15}, issn = {0266-3538}, doi = {10.1016/j.compscitech.2012.08.007}, pages = {1941 -- 1951}, language = {en} } @inproceedings{ZuchlinskiKuehhornKoberetal., author = {Zuchlinski, Andr{\´e} and K{\"u}hhorn, Arnold and Kober, Markus and Wehrenpfennig, Lutz}, title = {Kombinierte Topologie- und Parameteroptimierung des Aufh{\"a}ngungssystems von heckinstallierten Turbofantriebwerken}, series = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, booktitle = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {10}, language = {de} } @phdthesis{Kober, author = {Kober, Markus}, title = {Ein Beitrag zur strukturmechanischen Optimierung realer Bauteile in metallischer und Faserverbundbauweise unter Verwendung von wirkebenenbasierten Bruchkriterien}, publisher = {Mensch und Buch}, address = {Berlin}, isbn = {978-3-86387-085-0}, pages = {227}, language = {de} } @misc{MahlerdeSilvaKuehhornKober, author = {Mahler-de Silva, Tina and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Developing a Simplified Surrogate Model for Structured Sheet Metals with Numerical and Experimental Comparisons}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {13}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, pages = {99 -- 100}, abstract = {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.}, language = {en} } @misc{ZolochevskySklepusGalishinetal., author = {Zolochevsky, Alexander and Sklepus, Sergiy and Galishin, Alexander and K{\"u}hhorn, Arnold and Kober, Markus}, title = {A Comparison between the 3D and the Kirchhoff-Love Solutions for Cylinders under Creep-Damage Conditions}, series = {Technische Mechanik}, volume = {34}, journal = {Technische Mechanik}, number = {2}, pages = {104 -- 113}, language = {en} } @inproceedings{KoberKuehhornStelldingeretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Stelldinger, Enrico and Keskin, Akin}, title = {Considerations About the Necessary Mesh Density of Bearings in Detailed Finite Element Models}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25624}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25624}, publisher = {ASME}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-25624}, pages = {8}, abstract = {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}, language = {en} } @inproceedings{KoberKuehhornKaestneretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and K{\"a}stner, Benjamin and Keskin, Akin}, title = {Evaluation of the Stress and Displacement Behavior of Different LS-Dyna Element Types in Combination with Different Anti-Hourglassing Formulations and Initial Element Deformations}, series = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, booktitle = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, publisher = {DYNAmore GmbH}, address = {Stuttgart}, isbn = {978-3-9816215-1-8}, language = {en} } @inproceedings{KoberKuehhornStelldingeretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Stelldinger, Enrico and Keskin, Akin}, title = {Identification of Stiffness Parameters of a Simplified Aero-Engine Mount System by Using a Higher Fidelity Model of the Mount System}, series = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, booktitle = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, publisher = {DYNAmore GmbH}, address = {Stuttgart}, isbn = {978-3-9816215-1-8}, language = {en} } @misc{KoberKuehhornRademannetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Rademann, J{\"o}rg and M{\"u}ck, Bernhard}, title = {Nonlinear topology optimization of centrifugally loaded aero-engine part with newly developed optimality-criteria based algorithm}, series = {Aerospace Science and Technology}, volume = {Vol. 39}, journal = {Aerospace Science and Technology}, doi = {10.1016/j.ast.2014.09.005}, pages = {705 -- 711}, abstract = {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.}, language = {en} } @misc{StelldingerKuehhornKober, author = {Stelldinger, Enrico and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Experimental evaluation of the low-velocity impact damage resistance of CFRP tubes with integrated rubber layer}, series = {Composite Structures}, journal = {Composite Structures}, number = {139}, issn = {0263-8223}, doi = {10.1016/j.compstruct.2015.11.069}, pages = {30 -- 35}, abstract = {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.}, language = {en} } @misc{KoberKuehhornMueck, author = {Kober, Markus and K{\"u}hhorn, Arnold and M{\"u}ck, Bernhard}, title = {Topologieoptimierung eines fliehkraftbelasteten Triebwerkbauteils mit einfach zu implementierendem Algorithmus unter Ber{\"u}cksichtigung mehrerer Zielfunktionen}, series = {NAFEMS-Magazin : Zeitschrift f{\"u}r numerische Simulationsmethoden und angrenzende Gebiete}, journal = {NAFEMS-Magazin : Zeitschrift f{\"u}r numerische Simulationsmethoden und angrenzende Gebiete}, number = {35}, issn = {2311-522x}, pages = {56 -- 66}, language = {de} } @inproceedings{KeskinKoberStelldingeretal., author = {Keskin, Akin and Kober, Markus and Stelldinger, Enrico and K{\"u}hhorn, Arnold and B{\"o}hm, Holger and Hornig, Andreas and Hufenbach, Werner}, title = {On the quantification of errors of a pre-processing effort reducing contact meshing approach : AIAA 2015-0408}, series = {53rd AIAA Aerospace Sciences Meeting 2015, Kissimmee, Florida, USA, 5 - 9 January 2015, held at the AIAA SciTech Forum 2015, vol. 4}, booktitle = {53rd AIAA Aerospace Sciences Meeting 2015, Kissimmee, Florida, USA, 5 - 9 January 2015, held at the AIAA SciTech Forum 2015, vol. 4}, publisher = {Curran}, address = {Red Hook, NY}, isbn = {978-1-5108-0117-2}, doi = {10.2514/6.2015-0408}, pages = {3113 -- 3124}, language = {en} } @inproceedings{KoberKuehhornKeskin, author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin}, title = {Implicit Time Integration Schemes for the FEM Simulation of Fast Rotating Structures}, series = {WCCM XII \& APCOM VI (World Congress on Computational Mechanics \& Asia Pacific Congress on Computational Mechanics), Seoul, South Korea, 23.-29. Juli 2016}, booktitle = {WCCM XII \& APCOM VI (World Congress on Computational Mechanics \& Asia Pacific Congress on Computational Mechanics), Seoul, South Korea, 23.-29. Juli 2016}, abstract = {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.}, language = {en} } @inproceedings{KoberKuehhornKeskinetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin and Singh, Kai Navtej}, title = {Challenges and opportunities of thermomechanical FEM simulations of high fidelity aero-engine models by implicit time-integration}, series = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, booktitle = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, publisher = {ISABE}, pages = {10}, language = {en} }