Pudasaini, Shiva Prasad (2004)
Dynamics of flow avalanches over curved and twisted channels.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication
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Item Type: | Ph.D. Thesis | ||||||
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Type of entry: | Primary publication | ||||||
Title: | Dynamics of flow avalanches over curved and twisted channels | ||||||
Language: | English | ||||||
Referees: | Noelle, Prof.Dr. Sebastian | ||||||
Advisors: | Hutter, Prof.Ph.D. Kolumban | ||||||
Date: | 19 January 2004 | ||||||
Place of Publication: | Darmstadt | ||||||
Date of oral examination: | 12 December 2003 | ||||||
Abstract: | This thesis presents a new theory and discussions about the motion of avalanches from initiation to run-out over a generally curved and twisted complicated mountain topography, its numerical simulation and comparison with well controlled, advanced laboratory experiments. It is hoped to be demonstrated that today's method of determination of the avalanche motion along its track promises to give to the avalanche practitioner a tool with the aid of which fairly reliable predictions of avalanche motion along its track can be made, from initiation to run-out. The model computations and experiments also allow inferences as to the distribution of the mass of different granulates, like gravel or snow, in the deposition zone as well as to the forces exerted on structures that are affected by the motion of the avalanche. To achieve this aim, a well known depth integrated avalanche model of Savage & Hutter is generalised to arbitrary channelised topographies, the intention being that the model would be able not only to describe the flow of snow, gravel, debris or mud, down a corrie of arbitrary curvature and twist and arbitrary cross sectional profile, but equally also the transportation of grains or pills in the agricultural and pharmaceutical industry, respectively. For the first time we were able to include the simultaneous effects of the curvature and torsion in the avalanche motion, which could not be achieved by previous models. The applicability of the present model equations is, therefore, much broader than in the previous cases. The flow down an inclined plane or within a channel with its axis in a vertical plane which may be curved can be described, as can the flow down complicated mountain valleys with arbitrarily curved and twisted talwegs and bed topographies. The new theory is ideally suited to realistic situations in connection with the use of Geographical Information and Visualisation Systems . Thus, the theory provides an entirely new direction in the field of avalanche and debris flow research. It also opens a large spectrum of applications in different industrial and geophysical problems. The emerging equations for the distribution of the avalanche thickness and the topography-parallel depth-averaged velocity components consist of non-linear hyperbolic partial differential equations with discontinuous coefficients. To avoid any spurious oscillations and include naturally induced shock phenomena we introduced shock-capturing numerical schemes. To this end, two-dimensional Non-Oscillatory Central schemes with higher order cell reconstructions and second order accurate Total Variation Diminishing limiters were implemented. One of the most interesting aspects of avalanche dynamics is the study of avalanching motion over different bed structures and the effect of topography on their motion and deposits. We performed several numerical tests for avalanching masses down curved and twisted bed topographies. Uniformly and non-uniformly curved and twisted channels as well as channels which incorporate confined and unconfined continuous transition zones with constant and variable cross-sectional topographies merging into the horizontal run-out zones are considered. They demonstrate the combined effects of curvature, torsion and the radial acceleration associated with the bed topography. Thus, we are able to quantify the intrinsic effects of the topography and, finally, disclose the unknown physics of flows of avalanches through generally curved and twisted channels. Such sophisticated studies have not been carried out before, and it was possible here only with the new model equations. In order to acquire confidence in new model equations it is vital to corroborate them by direct observation. In this spirit, we performed several laboratory experiments for different granular materials to check the validity of the theory. We used a modern measurement technique, the Particle Image Velocimetry, to measure the velocity field of the flowing particles at the free-surface and the bottom of the free-surface and unsteady motion of an unconfined avalanche over a chute that is curved in the main flow direction merging continuously into the horizontal run-out zone. We are able to demonstrate the fact that there are excellent agreements between the theoretical predictions of the model equations and the experimental measurements. This, ultimately, proves the applicability of the theory and efficiency of the numerical method and code and establishes a nice and strong correlation among the theory, numerics and the experiments. |
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Alternative Abstract: |
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Uncontrolled Keywords: | Lawinendynamik, Murgänge, Granulatströmungen, Bewegungen mit freier Obelfläche, Gekrümmte und tordierte Kanalgeometrien, Rutschströmungen, Hyperbolische Erhaltungssätze, theoretische Vorhersagen, Hoch Auflösende finite Differenzen, experimentelle Validierung, Particle Image Velocimetry | ||||||
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URN: | urn:nbn:de:tuda-tuprints-3937 | ||||||
Classification DDC: | 500 Science and mathematics > 550 Earth sciences and geology | ||||||
Divisions: | Study Areas > Study Area Mechanic | ||||||
Date Deposited: | 17 Oct 2008 09:21 | ||||||
Last Modified: | 08 Jul 2020 22:48 | ||||||
URI: | https://tuprints.ulb.tu-darmstadt.de/id/eprint/393 | ||||||
PPN: | |||||||
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