02 Fakultät Bau- und Umweltingenieurwissenschaften

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3

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Author: search.filters.author.Bischoff, ManfredSubject: search.filters.subject.624

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    Transverse shear parametrization in hierarchic large rotation shell formulations
    (2024) Thierer, Rebecca; Oesterle, Bastian; Ramm, Ekkehard; Bischoff, Manfred
    Consistent treatment of large rotations in common Reissner-Mindlin formulations is a complicated task. Reissner-Mindlin formulations that use a hierarchic parametrization provide an elegant way to facilitate large rotation shell analyses. This can be achieved by the assumption of linearized transverse shear strains, resulting in an additive split of strain components, which technically simplifies implementation of corresponding shell finite elements. The present study aims at validating this assumption by systematically comparing numerical solutions with those of a newly implemented hierarchic and fully nonlinear Reissner-Mindlin shell element.
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    A consistent finite element formulation of the geometrically non-linear Reissner-Mindlin shell model
    (2022) Müller, Alexander; Bischoff, Manfred
    We present an objective, singularity-free, path independent, numerically robust and efficient geometrically non-linear Reissner-Mindlin shell finite element formulation. The formulation is especially suitable for higher order ansatz spaces. The formulation utilizes geometric finite elements presented by Sander [ 47 ] and Grohs [ 34 ] for the interpolation on non-linear manifolds. The proposed method is objective and free from artificial singularities and spurious path dependence. Due to the fact that the director field lives on the unit sphere, a special linearization procedure is required to obtain the stiffness matrix. Here, we use the simple constructions of Absil et al. [ 2 , 3 ], which yields an easy way to obtain the correct tangent operator of the potential energy. Additionally, we compare three different interpolation schemes for the shell director that can be found in the literature, where one of them is applied for the first time for the Reissner-Mindlin shell model. Furthermore, we compare the exponential map to the radial return normalization as procedure to update the nodal directors and conclude the superiority of the latter, in terms of fewer load steps. We also investigate the construction of a consistent tangent base update scheme. Path independence, efficiency and objectivity of the formulation are verified via a set of numerical examples.
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    Analytical and numerical case studies on tailoring stiffness for the design of structures with displacement control
    (2023) Trautwein, Axel; Prokosch, Tamara; Senatore, Gennaro; Blandini, Lucio; Bischoff, Manfred
    This paper discusses the role that structural stiffness plays in the context of designing adaptive structures. The focus is on load-bearing structures with adaptive displacement control. A design methodology is implemented to minimize the control effort by making the structure as stiff as possible against external loads and as flexible as possible against the effect of actuation. This rationale is tested using simple analytical and numerical case studies.
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    Investigation and elimination of nonlinear Poisson stiffening in 3d and solid shell finite elements
    (2022) Willmann, Tobias; Bieber, Simon; Bischoff, Manfred
    We show that most geometrically nonlinear three‐dimensional shell elements and solid shell elements suffer from a previously unknown artificial stiffening effect that only appears in geometrically nonlinear problems, in particular in the presence of large bending deformations. It can be interpreted as a nonlinear variant of the well‐known Poisson thickness locking effect. We explain why and under which circumstances this phenomenon appears and propose concepts to avoid it.
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    Motion design with efficient actuator placement for adaptive structures that perform large deformations
    (2021) Sachse, Renate; Geiger, Florian; Scheven, Malte von; Bischoff, Manfred
    Adaptive structures have great potential to meet the growing demand for energy efficiency in buildings and engineering structures. While some structures adapt to varying loads by a small change in geometry, others need to perform an extensive change of shape to meet varying demands during service. In the latter case, it is important to predict suitable deformation paths that minimize control effort. This study is based on an existing motion design method to control a structure between two given geometric configurations through a deformation path that is optimal with respect to a measure of control efficiency. The motion design method is extended in this work with optimization procedures to obtain an optimal actuation system placement in order to control the structure using a predefined number of actuators. The actuation system might comprise internal or external actuators. The internal actuators are assumed to replace some of the elements of the structure. The external actuators are modeled as point forces that are applied to the structure nodes. Numerical examples are presented to show the potential for application of the motion design method to non-load-bearing structures.