ELFT HÍRADÓ

[StatFizSzeminar <statfiz AT glu.elte.hu>]

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                ELTE TTK Fizikai Intézet
            STATISZTIKUS FIZIKAI SZEMINÁRIUM


                     2017. június 14.
                      szerda, 11.00 


                     Gábor Drótos 

        Instituto de Física Interdisciplinar 
        y Sistemas Complejos (CSIC-UIB), 
            Palma de Mallorca, Spain

        "Non-inertial mechanisms for clustering 
                 of settling particles"


The density of settling particles accumulated on the bottom surface of
an incompressible fluid often exhibits inhomogeneities (i.e.,
clustering), which is usually supposed to be related with inertial
effects. Earlier work [1] has shown, however, that inertial effects
are negligible in the parameter range of settling biogenic particles
in relevant ocean flows, and that clustering nevertheless occurs for
such particles. Here we describe the two different non-inertial
mechanisms leading to clustering. One mechanism is dynamical: the
density varies within sheets of dimension lower than that of the
embedding fluid during the time evolution of these sheets, since
incompressibility holds only for the full-dimension volume element.
The other mechanism is a simple projection of the densities within
such moving sheets onto the bottom surface. Clustering occurs when
these sheets are inhomogeneously tilted with respect to the bottom
surface, and their non-vertical velocity also needs to be taken into
account during the projection. Foldings of the sheets and
corresponding caustics play a special role. We systematically explore
the importance of the two mechanisms in numerical examples between
limiting cases of the relevant parameters, and point out several
nontrivialities.

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