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| Titel |
Simulating Lahars Using A Rotating Drum |
| VerfasserIn |
Adam Neather, Gert Lube, Jim Jones, Shane Cronin |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088405
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| Publikation (Nr.) |
 EGU/EGU2014-2505.pdf |
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| Zusammenfassung |
| A large (0.5 m in diameter, 0.15 m wide) rotating drum is used to investigate the erosion and
deposition mechanics of lahars. To systematically simulate the conditions occurring in natural
mass flows our experimental setup differs from the common rotating drum employed in
industrial/engineering studies. Natural materials with their typical friction properties are used,
as opposed to the frequently employed spherical glass beads; the drum is completely
water-proof, so solid/air and solid/liquid mixtures can be investigated; the drum
velocity and acceleration can be precisely controlled using a software interface to a
micro-controller, allowing for the study of steady, unsteady and intermediate flow
regimes.
The drum has a toughened glass door, allowing high-resolution, high-speed
video recording of the material inside. Vector maps of the velocities involved in the
flows are obtained using particle image velocimetry (PIV). The changes in velocity
direction and/or magnitude are used to locate the primary internal boundaries between
layers of opposite flow direction, as well as secondary interfaces between shear
layers.
A range of variables can be measured: thickness and number of layers; the curvature of
the free surface; frequency of avalanching; position of the centre of mass of the material; and
the velocity profiles of the flowing material. Experiments to date have focussed on dry
materials, and have had a fill factor of approximately 0.3. Combining these measured
variables allows us to derive additional data of interest, such as mass and momentum flux. It
is these fluxes that we propose will allow insight into the erosion/deposition mechanics of a
lahar.
A number of conclusions can be drawn to date. A primary interface separates
flowing and passive region (this interface has been identified in previous studies).
As well as the primary interface, the flowing layer separates into individual shear
layers, with individual erosion/deposition and flow histories. This complex flow
geometry and process of erosion and deposition seen in our high speed videos is more
complicated than previously reported in the literature. We identify two layers only in
the slowest flows (< 0.5 rad s-1), while faster ones (< 4 rad s-1) include between
three and five. As the rotational velocity of the drum increases, the curvature of
the free surface increases. In the central part of the drum, the primary interfaces
occasionally merges into an elliptical zone rather than a linear shear boundary. Inside this
zone is a complete circulation of material. These zones’ size and number appears
to be a function of the rotational velocity of the drum. These "Neather cells" (as
we tentatively name these phenomena) can reach as large as 20 mm in thickness.
The centre of mass’ deflection from vertical is linearly dependent on rotational
velocity, whilst the typical flow regimes as identified by Mellmann [2001] show
no influence. The frequency of avalanches increases with velocity up to a critical
velocity (approximately 1.1 rad s-1), after which the avalanche frequency remains
constant.
1 References
J Mellmann. The transverse motion of solids in rotating cylinders—forms of motion and
transition behavior. Powder Technology, 118(3):251–270, 2001. |
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