Research Projects

Research Projects

Our latest research projects, published papers (from fleXstructures and partners) and conference presentations are at your fingertips!

Our Latest Research Projects

Eurostars Durability and Dynamics {DDA-FleX}

Eurostars Durability and Dynamics {DDA-FleX}

Engineers need efficient simulation tools to plan the layout of slender flexible structures like cables and hoses in the virtual product development of vehicles, airplanes or medical equipment. While interactive simulation of deformed shapes of flexibles is state-of-the-art, a comparably practical simulation of mechanical loads, combined with a prediction of the impact of machine dynamics on the durability of flexible parts, is not yet available, despite of a high demand from industry. Digital tools used at early stages in product development should not only provide optimized layouts with regards to geometry, but also predict loads acting on the product during usage, as these loads have strong impacts on durability and warranty-performance. ... See more

The main scope of this project is to simulate dynamic effects of cables and hoses which are subject to motions with fast accelerations and to perform durability analysis by estimating damage values on cables and hoses subject to motions. Such simulations could be of particular interest in engine compartments, or suspension areas of a vehicle, or during the motions of an industrial robot where the dress pack is exposed to dynamic and inertial effects.

The project results show that it is possible to accurately simulate the dynamic effects of cables and hoses moving with high speeds and accelerations, as well as to estimate damage values. Therefore, it is also possible to make lifetime estimations compared to some base configuration of a cable or hose. However, for absolute lifetime predictions of cables and hoses, so-called Wöhler curves for the materials are necessary. In general, Wöhler curves for such complex materials are not simply available and probably will not be in the near future. Therefore, the comparative load data analysis is the preferred concept.

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DYMARA – A dynamic manikin with fiber-based modeling of skeletal muscles

DYMARA – A dynamic manikin with fiber-based modeling of skeletal muscles

The systematic analysis of work processes and their optimization with regard to physical load requires realistic human models. One focus of the DYMARA project is the combination of the optimum motion control of the human model and a fiber-based muscle model. The aim of this BMBF cooperative project is to develop an innovative digital human model (manikin) with a detailed modelling of the skeletal musculature in combination with efficient algorithms. The cooperative development should make it possible to integrate humans into their working environment in an optimum, ergonomic way and thus ultimately prevent symptoms of fatigue, disease and accidents. In addition to these ergonomic aspects, the developed model can also be used for the design and optimization of prostheses or orthoses. ... See more

In order to determine the dynamics of the musculoskeletal system with sufficient accuracy, a modelling approach based on the method of mechanical multi-body systems is pursued in the cooperative project. Such models are inspired by robotics and are already used in many biomechanical fields of application. However, the modelling of the musculature still poses a great challenge, especially the computing performance and the consideration of the anatomical and physiological conditions is a challenge. In this project, a one-dimensional continuum model was developed, which describes single muscle fiber bundles realistically. This model was combined with corresponding algorithms for the calculation of movement sequences and for the control of the manikin.

As a partner in this BMBF project, we focus on the validity of the results as well as on the applicability and usability of the results under industrial aspects. The performance and use should not be limited to a group of experts, but should demonstrate the greatest possible acceptance and industrial integration capabilities.

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Published Papers

Virtual design and dynamical simulation of flexible cables, hoses, and wires

Author: Annibale, E.S.; Dreßler, K.; Hermanns, O.; Linn, J.; Zemerli, C.

Source: Warrendale, Pa.: SAE, 2014, 11 S. SAE Technical Paper, 2014-36-0416

Computer simulation can provide significant help to solve practical problems concerning the optimal design and the dynamical behavior of flexible cables, hoses, and wires in vehicles and on production equipment like robots. Typical questions are the ideal cable’s length, its minimal bending radius, possible collision to surrounding parts, and designed space. To solve these problems, we developed a non-linear beam model, which accounts for large global deformations of the cable. It is based on Cosserat’s geometrically exact theory of rods and is able to represent extension, shearing, bending and torsion of the cable. With our innovative approach, one can optimize the cables design and their assembly positions in real time and with high accuracy. One can also consider a variety of material types and cross-sections profiles. Our implementation allows one to import CAD files and rigid body motions as well as the analysis of the local stress distribution within the cable volume. Important questions like finding the optimal length or the ideal assembly positions can be efficiently answered. Material and the necessary physical space can be already reduced during the design process, without the need of costly tests with hardware prototypes. We present relevant industrial examples of applicability our approach. Finally, we introduce a dynamical viscoelastic version our model, which is suitable for fast and accurate dynamical simulation of multi-body systems (MBS).

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Simulation der Nutzungsvariabilität für Betriebsfestigkeit und Energieeffizienz unter Verwendung geo-referenzierter Daten

Author: Dreßler, K; Speckert, M.

Source: 17. Kongress SIMVEC Simulation und Erprobung in der Fahrzeugentwicklung 2014

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Kabel und Schläuche simulationsgestützt optimieren und absichern

Author: Dreßler, K.; Stephan, T.

Source: Elektronik automotive (2017), Sonderausgabe Bordnetz 2017, S.14-17 ISSN: 1614-0125

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Geometrically exact Cosserat rods with Kelvin-Voigt type viscous damping

Author: Linn, J.; Lang, H.; Tuganov, A.

Source: Mechanical sciences : MS 4 (2013), No.1, pp.79-96 ISSN: 2191-9151

We present the derivation of a simple viscous damping model of Kelvin-Voigt type for geometrically exact Cosserat rods from three-dimensional continuum theory. Assuming moderate curvature of the rod in its reference configuration, strains remaining small in its deformed configurations, strain rates that vary slowly compared to internal relaxation processes, and a homogeneous and isotropic material, we obtain explicit formulas for the damping parameters of the model in terms of the well known stiffness parameters of the rod and the retardation time constants defined as the ratios of bulk and shear viscosities to the respective elastic moduli. We briefly discuss the range of validity of the Kelvin-Voigt model and illustrate its behaviour for large bending deformations with a numerical example.

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Generalized maxwell type viscoelasticity for geometrically exact Cosserat rod and shell models

Author: Linn, J.

Source: Terze, Zdravko ; European Community on Computational Methods in Applied Science -ECCOMAS-; Univ. of Zagreb

 

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Derivation of a viscoelastic constitutive model of Kelvin-Voigt type for Cosserat rods

Author: Linn, J.; Lang, H.; Tuganov, A.

Source: Kaiserslautern: Fraunhofer ITWM, 2013, 54 pp. ITWM-Berichte, 225

 

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Discrete kinematics of Cosserat rods based on the difference geometry of framed curves

Author: Linn, J.

Source: McGill University, Montreal: IMSD 2016, 4th Joint International Conference on Multibody System Dynamics. Proceedings

The theory of Cosserat rods provides versatile models for the simulation of large spatial deformations of slender flexible structures. As the strain measures of the mechanical theory are given in terms of the differential invariants of Cosserat curves, the kinematics of Cosserat rods are closely related to the differential geometry of framed curves. We utilize ideas from the difference geometry of framed curves in Euclidean space to construct the discrete kinematics of Cosserat rod models on a staggered grid, preserving the essential geometric properties independent of the coarseness of the discretization. On this basis, we also derive a vertex based model variant and discuss its relation to the discrete Cosserat rod kinematics obtained by a geodesic interpolation of the nodal variables in the Lie groups E 3 × SO(3) and SE(3).

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Kinetic aspects of discrete cosserat rods based on the difference geometry of framed curves

Author: Linn, J.; Hermansson, T.; Andersson, F.; Schneider, Fabio

Source: Valasek, M. ; Czech Technical University, Prag; European Community on Computational Methods in Applied Science -ECCOMAS-

The theory of Cosserat rods provides a self consistent framework for modeling large spatial deformations of slender flexible structures at small local strains. Discrete Cosserat rod models [1, 2] based on geometric finite differences preserve essential properties of the continuum theory. The present work investigates kinetic aspects of discrete quaternionic Cosserat rods defined on a staggered grid within the framework of Lagrangian mechanics. Assuming hyperelastic constitutive behaviour, the Euler–Lagrange equations of the model are shown to be equivalent to the (semi)discrete balance equations of forces, moments and inertial terms obtained from a direct discretization of the continuous balance equations via spatial finite differences along the centerline curve. Therefore, equilibrium configurations obtained by energy minimization correspond to solutions of the quasi-static balance equations. We illustrate this approach by two academic examples (Euler’s Elastica and Kirchhoff’s helix) and highlight its utility for practical applications with a use case from automotive industry (analysis of the layout of cooling hoses in the engine compartment of a passenger car).

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Discrete cosserat rod models based on the difference geometry of framed curves for interactive simulation of flexible cables

Author: Linn, J.; Dreßler, K.

Source: Ghezzi, L. ; European Consortium for Mathematics in Industry -ECMI-: Math for the Digital Factory

For software tools currently used in industry for computer aided design (CAD), digital mock-up and virtual assembly there is an increasing demand to handle not only rigid geometries, but to provide also capabilities for realistic simulations of large deformations of slender flexible structures in real time (i.e.: at interactive rates). The theory of Cosserat rods provides a framework to perform physically correct simulations of arbitrarily large spatial deformations of such structures by stretching, bending and twisting. The kinematics of Cosserat rods is described by the differential geometry of framed curves, with the differential invariants of rod configurations corresponding to the strain measures of the mechanical theory. We utilize ideas from the discrete differential geometry of framed curves in combination with the variational framework of Lagrangian mechanics to construct discrete Cosserat rod models that behave qualitatively correct for rather coarse discretizations, provide a fast computational performance at moderate accuracy, and thus are suitable for interactive simulations. This geometry based discretization approach for flexible 1D structures has industrial applications in design and digital validation. We illustrate this with some application examples from automotive industry.

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Discrete Cosserat Rod Kinematics Constructed on the Basis of the Difference Geometry of Framed Curves - Pt.I: Discrete Cosserat Curves on a Staggered Grid

Author: Linn, J.

Source: Journal of elasticity 139 (2020), No.2, pp.177-236

The theory of Cosserat rods provides versatile models to simulate large spatial deformations of slender flexible structures. As the strain measures of the mechanical theory are given in terms of the differential invariants of Cosserat curves, the kinematics of Cosserat rods is closely related to the differential geometry of framed curves. We utilize ideas from the difference geometry of framed curves in Euclidean space to construct the discrete kinematics of Cosserat rod models on a staggered grid, preserving the essential geometric properties independent of the coarseness of the discretization.
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Our Industrial Research Partners

SPECMA AB

SCANIA

ZF

SUBARU

TOYOTA

GM

FORD

DAIMLER

BMW

Audi

ISUZU

Get in touch with us, we do the research for you!

You need a research partner, get in touch with us. With our research competence in cables, hoses, and electrical harnesses, we will do the research for you.