35 research outputs found
A Partial Integrodifferential Equation in Granular Matter and Its Connection with a Stochastic Model
Homogenization via formal multiscale asymptotics and volume averaging: How do the two techniques compare?
A wide variety of techniques have been developed to homogenize transport equations in multiscale and multiphase systems. This has yielded a rich and diverse field, but has also resulted in the emergence of isolated scientific communities and disconnected bodies of literature. Here, our goal is to bridge the gap between formal multiscale asymptotics and the volume averaging theory. We illustrate the methodologies via a simple example application describing a parabolic transport problem and, in so doing, compare their respective advantages/disadvantages from a practical point of view. This paper is also intended as a pedagogical guide and may be viewed as a tutorial for graduate students as we provide historical context, detail subtle points with great care, and reference many fundamental works
Homogenization via formal multiscale asymptotics and volume averaging: How do the two techniques compare?
A wide variety of techniques have been developed to homogenize transport equations in multiscale and multiphase systems. This has yielded a rich and diverse field, but has also resulted in the emergence of isolated scientific communities and disconnected bodies of literature. Here, our goal is to bridge the gap between formal multiscale asymptotics and the volume averaging theory. We illustrate the methodologies via a simple example application describing a parabolic transport problem and, in so doing, compare their respective advantages/disadvantages from a practical point of view. This paper is also intended as a pedagogical guide and may be viewed as a tutorial for graduate students as we provide historical context, detail subtle points with great care, and reference many fundamental works
Rheology of frictional grains
Diese Arbeit behandelt die Beschreibung des Fließens und des Blockierens von granularer Materie. Granulare Materie kann einen Verfestigungsübergang durchlaufen. Dieser wird Jamming genannt und ist maßgeblich durch vorliegende Spannungen sowie die Packungsdichte der Körner, welche das Granulat bilden, bestimmt. Die Rheologie dichter granularer Medien ist zusätzlich zu Spannung und Packungsdichte stark durch Reibung zwischen den Körnern beeinflusst. Wir zeigen mittels numerischer Simulationen und analytischer Betrachtungen, wie Reibung Jamming qualitativ verändert. Reibungsfreies Jamming ist ein kontinuierlicher Phasenübergang mit einem kritischen Punkt bei verschwindender Spannung. Reibungsbehaftetes Jamming ist ein diskontinuierlicher Phasenübergang mit einem kritischen Punkt bei endlicher Spannung. Der kritische Punkt bei endlicher Spannung führt zu bemerkenswertem Verhalten: Oberhalb der kri- tischen Packungsdichte gibt es ein Intervall an Packungsdichten, innerhalb dessen große oder kleine Spannungen zum Fließen führen, mittlere Spannungen hingegen führen zum Blockieren des Mediums. Das Fließverhalten nahe Jamming ist stark durch die Systemgröße beeinflusst: Es gibt eine kritische Systemgröße, oberhalb derer zeitabhängiger Fluss entsteht. Dieser zeitabhängige Fluss wird durch die Ausbildung von großskaligen Strukturen im Spannungsfeld erklärt. Sowohl die großskaligen Strukuren als auch der damit einhergehende zeitabhängige Fluss sind neuartige Phänomene im Fluss von trockenen Granulaten und durch Rei- bung hervorgerufen.This thesis deals with the description of flow and arrest of granular matter.
Granular matter can undergo a rigidity transition — called jamming — that is
mainly controlled by the applied stresses and the packing fraction of the grains
that constitute the medium. In addition to stress and packing fraction, interparticle friction greatly affects the rheology of granular matter. Using numerical
simulations and analytical modeling, we show how novel behavior in dense flow
and jamming regimes arises in the presence of friction. In particular, frictionless
jamming is continuous with a critical point at zero stress. In contrast, frictional
jamming is shown to exhibit a discontinuous phase transition with a critical point
at finite stress. The fact that the critical point resides at finite stress gives rise to
remarkable flow behavior, called reentrant flow. Explicitly, there is an interval of
packing fractions above the critical packing fraction in which large or low stress
leads to flow but intermediate stress jams the medium. The behavior close to
jamming depends substantially on the system size, i.e., there is a critical system size above which unsteady flow emerges. Unsteady flow is rationalized by
large-scale structures in the stress fields. Both, the large-scale structures and
the accompanied unsteady flow, are novel phenomena regarding the flow of dry
granular matter and can be attributed to interparticle friction
Proceedings of FORM 2022. Construction The Formation of Living Environment
This study examines the integration of building information modelling (BIM) technologies in operation & maintenance stage in the system of managing real estate that helps to reduce transaction costs. The approach and method are based on Digital Twin technology and Model Based System Engineering (MBSE) approach.
The results of the development of a service for digital facility management and
digital expertise are presented. The connection between physical and digital objects is conceptualized
The 2nd International Conference on Mathematical Modelling in Applied Sciences, ICMMAS’19, Belgorod, Russia, August 20-24, 2019 : book of abstracts
The proposed Scientific Program of the conference is including plenary lectures, contributed oral talks, poster sessions and listeners. Five suggested special sessions / mini-symposium are also considered by the scientific committe
Estimation of Thalamocortical and Intracortical Network Models from Joint Thalamic Single-Electrode and Cortical Laminar-Electrode Recordings in the Rat Barrel System
A new method is presented for extraction of population firing-rate models for
both thalamocortical and intracortical signal transfer based on stimulus-evoked
data from simultaneous thalamic single-electrode and cortical recordings using
linear (laminar) multielectrodes in the rat barrel system. Time-dependent
population firing rates for granular (layer 4), supragranular (layer 2/3), and
infragranular (layer 5) populations in a barrel column and the thalamic
population in the homologous barreloid are extracted from the high-frequency
portion (multi-unit activity; MUA) of the recorded extracellular signals. These
extracted firing rates are in turn used to identify population firing-rate
models formulated as integral equations with exponentially decaying coupling
kernels, allowing for straightforward transformation to the more common
firing-rate formulation in terms of differential equations. Optimal model
structures and model parameters are identified by minimizing the deviation
between model firing rates and the experimentally extracted population firing
rates. For the thalamocortical transfer, the experimental data favor a model
with fast feedforward excitation from thalamus to the layer-4 laminar population
combined with a slower inhibitory process due to feedforward and/or recurrent
connections and mixed linear-parabolic activation functions. The extracted
firing rates of the various cortical laminar populations are found to exhibit
strong temporal correlations for the present experimental paradigm, and simple
feedforward population firing-rate models combined with linear or mixed
linear-parabolic activation function are found to provide excellent fits to the
data. The identified thalamocortical and intracortical network models are thus
found to be qualitatively very different. While the thalamocortical circuit is
optimally stimulated by rapid changes in the thalamic firing rate, the
intracortical circuits are low-pass and respond most strongly to slowly varying
inputs from the cortical layer-4 population