Geometry-Independent Field approximaTion (GIFT) for spline based FEM for Linear Elasticity: a Diffpack implementation

Scientific Conference (2015, June 01)

XDEM - FEM Coupling Simulations of the Interactions between a Tire Tread and Granular Terrain

E-print/Working paper (2014)

This study proposes an efficient combination of the Discrete Element Method (DEM) and the Finite Element Method (FEM) to study the tractive performance of a rubber tire in interaction with granular ... [more ▼]

This study proposes an efficient combination of the Discrete Element Method (DEM) and the Finite Element Method (FEM) to study the tractive performance of a rubber tire in interaction with granular terrain. The presented approach is relevant to all engineering devices interacting with granular matter which causes response forces. Herein, the extended discrete element method (XDEM) is used to describe the dynamics of the granular assembly. On the one hand, the discrete approach accounts for the motion and forces of each grain individually. On the other hand, the finite element method accurately predicts the deformations and stresses acting within the tire tread. Hence, the simulation domain occupied by the tire tread is efficiently described as a continuous entity. The coupling of both methods is based on the interface shared by the two spatially separated domains. Contact forces develop at the interface and propagate into each domain. The coupling method enables to capture both responses simultaneously and allows to sufficiently resolve the different length scales. Each grain in contact with the surface of the tire tread generates a contact force which it reacts on repulsively. The contact forces sum up over the tread surface and cause the tire tread to deform. The coupling method compensates quite naturally the shortages of both numerical methods. It further employs a fast contact detection algorithm to save valuable computation time. The proposed DEM-FEM Coupling technique was employed to study the tractive performance of a rubber tire with lug tread patterns in a soil bed. The contact forces at the tread surface are captured by 3D simulations for a tire slip of 5%. The simulations showed to accurately recapture the gross tractive effort, running resistance and drawbar pull of the tire tread in comparison to related measurements. Further, the traction mechanisms between the tire tread and the granular ground are studied by analysing the motion of the soil grains and the deformation of the tread. [less ▲]

An Efficient 3D FEM - DEM Coupling for Granular Matter Applications

in Coupled MBS-FE Applications: A New Trend in Simulation (2013, November)

The presented approach is relevant to almost all engineering applications that deal with granular matter such as off-road tire performance, transport on conveyor belts or displacement of granular material ... [more ▼]

The presented approach is relevant to almost all engineering applications that deal with granular matter such as off-road tire performance, transport on conveyor belts or displacement of granular material as in mixers or excavation of soil. For all these applications an engineering device is in contact with granular matter which causes responses due to the interaction forces. The proposed Extended Discrete Element Method (XDEM) as a combination of the Discrete Element Method (DEM) and the Finite Element Method (FEM) allows to sufficiently resolve the different domains involved in these engineering applications. Herein the motion of each grain is accounted for individually. Simultaneously, the finite element method accurately predicts the deformations experienced by the engineering device. Thus, the simulation domain occupied by the device is efficiently described as a continuous entity. The coupling of both methods is based on the interface shared by the two spatially separated domains. The interface coupling enables to apply a contact model suited to the particular contact behaviour between the grains and the surface material if the engineering device. In contact, forces develop at the interface and generate an responce in each domain. The coupling method enables to capture both responses simultaneously. Each grain in contact with the device surface generates a contact force to which it reacts repulsively. The contact forces sum up over the surface and cause deformations of device body. It further employs a fast contact detection algorithm to save valuable computation time. This concept is supported by the software tools of the Discrete Particle Method (DPM) and Diffpack. To exemplify the presented method, the tractive performance of different tire treads has been studied on a soil layer of the stony terrian. The simulation results are used to analyse the gross tractive effort, running resistance and drawbar pull of the different tread patterns. [less ▲]

Simulation des Traktionsverhaltens von Reifen auf granularem Untergrund durch eine Kopplung zwischen der Finiten (FEM) und der Diskreten Element Methode (DEM)

in VDI-Berichte "Reifen-Fahrwerk-Fahrbahn" (2013, October)

Kurzfassung Innerhalb dieses Beitrags wird die numerische Simulationsmethode der Extended Discrete Element Methode (XDEM) vorgestellt, mit der die Wechselwirkung zwischen Reifen und steinigem Untergrund ... [more ▼]

Kurzfassung Innerhalb dieses Beitrags wird die numerische Simulationsmethode der Extended Discrete Element Methode (XDEM) vorgestellt, mit der die Wechselwirkung zwischen Reifen und steinigem Untergrund detailliert beschrieben werden kann. Dabei wird der Reifen als ein Kontinuum betrachtet, das mit der Finiten Element Methode (FEM) abgebildet wird. Der grobkörnige Untergrund, wie beispielsweise Sand oder Kies, wird als granulares Medium betrachtet. Dieses kann sehr vorteilhaft mit der Diskreten Element Methode (DEM) behandelt werden, die eine Betrachtung der individuellen Partikel zulässt. Basierend auf den Gesetzen von Newton werden Position und Orientierung aller Partikel berechnet, wobei Kräfte zwischen den Partikeln und dem Reifen berücksichtigt werden. Kräfte zwischen Partikeln und Reifen treten als Randbedingungen in der FEM Struktur des Reifens auf, und führen damit zur Deformation und somit zu Spannungverteilung in der Reifenstrucktur. Eine Integration in der Zeit bestimmt sowohl den Zustand des Untergrunds als auch die Reaktion des Reifens. Dies wird durch eine innovative Kopplung zwischen der Discrete Particle Method (DPM) zur Beschreibung des granularen Mediums und dem Finite Element Löser DiffPACK erreicht und deshalb als Extended Discrete Element Methode bezeichnet wird. Beides sind objekt- orientierte Software-Werkzeuge, die über eine Schnittstelle die notwendigen Daten austauschen, so dass der Anwender sein Augenmerk auf die Problemlösung richten kann als sich mit Datenaustausch und Algorithmen zu befassen. Damit wurde ein vielseitiges und flexibles Werkzeug zur Lösung vielfältiger Probleme wie auch die Bewegung eines Reifens im Schnee geschaffen. Das neuartige Konzept ist sowohl auf Windows als auch auf UNIX basierenden Betriebssystemen verfügbar. Abstract The objective of this contribution is to resolve different length scales in structure analysis by an interface coupling the Discrete Element Method (DEM) with the Finite Element Method (FEM) and therefore, is labelled Extended Discrete Element Methode (XDEM). This approach distinguishes itself from other methods in so far that no overlapping domains between Finite and Discrete Elements exist. Both domains are separated in physical space and numerical simulation domain. The proposed approach is relevant to almost all engineering applications that deal with granular matter such as storage in hoppers, transport on conveyor belts or displacement of granular material as in mixers or excavation of soil. For these applications an engineering device such as mixer blades or cutting tools are in contact with granular matter. Contacts with individual particles generate contact forces that act on both the engineering device and the granular material. The latter experiences a displacement of individual particles whereby the engineering structure responds with deformation and stresses. In order to predict and optimize both the behaviour and motion of granular material and the structures in contact, numerical simulation tools are increasingly employed [1]. Simulations are popular especially because experiments which are often expensive, time- consuming and sometimes even dangerous [2]. The continuous increase in computing power is now enabling researchers to implement numerical methods that do not focus on the granular assembly as an entity, but rather deduce its global characteristics from observing the individual behaviour of each grain. An interaction between granular media and a structure relies on a transfer of forces between them. Granular media consists of an ensemble of particles of which a number of particles may be in contact with a surface e.g. walls as surfaces of solid structures. The contact is resolved similar to inter-particle contacts by a representative overlap. It defines the position of impact as well as the force acting on the particle at this position. The same force, however, into the opposite direction defines a mechanical load for the structure. In order to determine the effect of forces on the solid structure, it is discretised by finite elements. The impact of the force is transferred to the nodes of the respective surface element and appears as a load for the finite element system. Hence, integrating particle dynamics and the response of the solid structure due to particle impacts advances both new position of particles and corresponding deformation and stress of the solid structure in time. Developing flexible software which is capable of performing simulation in different applications will enable the engineers to focus entirely on their specific problem and hence save them valuable time. This concept is supported by the software tools of the Discrete Particle Method (DPM) and Diffpack. Hence, the solid structure is analysed by the Finite Element Method under load due to the impact of individual particles that changes both in time and space. For this purpose traditional formulations of the Finite Element Method are employed that are available by the commercial multi-physics software package Diffpack. It represents object-oriented hierarchy of classes that provide an excellent interface to introduce external loads from particle impact onto the finite element structure. Diffpack is an object-oriented development environment, which comes as a rich set of C++ classes, for the numerical modelling and solution of arbitrary differential equations. User applications cover a wider range of engineering areas and span from simple educational applications to major product development projects. The behaviour of granular material is represented by the advanced software package of the Discrete Particle Method (DPM), which is based on the Discrete Element Method. It is designed to relieve users from underlying mathematics and software design and allows them to focus on physics and their applications. The software uses object oriented techniques that support objects representing three-dimensional particles of various shapes such as cylinders, discs or tetrahedrons for example, size and material properties. This makes it a highly versatile tool dealing with a large variety of different applications of granular matter arising in the automotive industry, such as road tire interaction. Various force models for the inter- particle and particle-wall contacts are also available. A minimal user interface easily allows extending the software further by adding user-defined impact models or material properties to an already available selection of materials and properties. Thus, the user is relieved of the underlying mathematics or software design, and therefore, is able to direct his focus entirely onto the application. The Discrete Particle Method is written in C++ programming language and works both in Linux and Windows environments. [less ▲]

Stable extended finite element method: Convergence, Accuracy, Properties and Diffpack implementation

in International Conference on Extended Finite Element Methods - XFEM 2013, September 11 – 13, 2013, Lyon, France (2013)

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally ... [more ▼]

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally opposed approaches are attempting to simplify the CAD to Analysis pipeline: isogeometric methods on the one hand [1] aim at coupling the geometry and field approximations, whilst implicit boundary definition-based methods attempt to decouple them [3,4,5]. We examine in this paper one instance of the latter approach, and rely on partition of unity enrichment of the field variable to capture discontinuities along material interface or domain boundaries. We study in particular the stable generalized finite element method of Babuˇka and Banerjee [6] for higher order approximations in two and three dimensions and propose a generic implementation within the C++ library Diffpack from inuTech GmbH [7]. In a companion paper, the implementation of enrichment within Diffpack is presented in more detail. We will present results obtained with our 3D implementation of partition of unity enrichment within Diffpack. This implementation represents the interfaces through level-sets and palliates blending problems using various approaches. We study here the stabilisation approach proposed in [6] in more detail and pay particular attention to the global convergence rate of the approach and to the stability and the local flux converence close to the interfaces. [less ▲]

Resolution of Different Length Scales by an Efficient Combination of the Finite and the Discrete Element Method

Presentation (2012, September 04)

Loss-of-function of human PINK1 results in mitochondrial pathology and can be rescued by parkin.

in The Journal of neuroscience : the official journal of the Society for Neuroscience (2007), 27(45), 12413-8

Degeneration of dopaminergic neurons in the substantia nigra is characteristic for Parkinson's disease (PD), the second most common neurodegenerative disorder. Mitochondrial dysfunction is believed to ... [more ▼]

Degeneration of dopaminergic neurons in the substantia nigra is characteristic for Parkinson's disease (PD), the second most common neurodegenerative disorder. Mitochondrial dysfunction is believed to contribute to the etiology of PD. Although most cases are sporadic, recent evidence points to a number of genes involved in familial variants of PD. Among them, a loss-of-function of phosphatase and tensin homolog-induced kinase 1 (PINK1; PARK6) is associated with rare cases of autosomal recessive parkinsonism. In HeLa cells, RNA interference-mediated downregulation of PINK1 results in abnormal mitochondrial morphology and altered membrane potential. Morphological changes of mitochondria can be rescued by expression of wild-type PINK1 but not by PD-associated PINK1 mutants. Moreover, primary cells derived from patients with two different PINK1 mutants showed a similar defect in mitochondrial morphology. Human parkin but not PD-associated mutants could rescue mitochondrial pathology in human cells like wild-type PINK1. Our results may therefore suggest that PINK1 deficiency in humans results in mitochondrial abnormalities associated with cellular stress, a pathological phenotype, which can be ameliorated by enhanced expression of parkin. [less ▲]