Experimental and numerical description of rapid granular flows and some baseline constraints for simulating 3-dimensional granular flow dynamics

Accurate prediction of rapid granular flow behavior is essential to optimize protection measures from hazardous natural granular flows like snow avalanches and landslides and to design efficient production facilities for granulate processing industries. So far, most successful models for rapid granular flow descriptions employ depth-averaging, assuming an essentially constant velocity over depth. This assumption greatly reduces calculation power but can lead to incorrect predictions in regions of strong velocity shearing in the flow depth direction, e.g., during the impact on an obstacle. To overcome these limitations, this study introduces a novel type of non-depth-averaged fluid dynamics simulations for rapid granular flows of cohesionless material. A series of small scale experiments with industrial (polyvinyl chloride (PVC)) and natural (sand) granular material was performed (i) to select and refine the appropriate rheological model, (ii) to yield a better insight into velocity profiles and (iii) to obtain parameters for comparison with numerical simulations. Based on these experiments, Coulomb-type friction was selected as rheological model. A Poly(methyl methacrylate) channel set-up with variable inclination angle in combination with high-speed image recording and an open source particle image velocimetry (PIV) software developed in this study allowed detailed observation of velocity profiles during flow inception, undisturbed flows, flows encountering obstacles, and shock scenarios. The PIV measurements revealed considerable changes in velocity between layers of the granular flow and thus underpin the necessity to perform non-depth-averaged simulations in order to accurately describe the flow behavior in all aspects. Comparison of the depth-averaged simulation model of the Savage-Hutter type and the non-depth-averaged simulation method introduced here with the experiments revealed that certain quantities, like the flow height and shape could only be accurately predicted using the non-depth-averaged simulations. Furthermore, the non-depth-averaged simulations were well capable of predicting the observed velocity profiles and produce accurate predictions of associated quantities like strain rates and slip velocities for both materials in most experiments. Nevertheless, this study also revealed cases where both depth-averaged and non-depth-averaged methods generate similar predictions, e.g., the height of an undisturbed flow and deposition shapes. A detailed summary of parameters and dynamic variables in different experiments, and their predictability by both methods is provided. This serves as a guideline to decide when to employ the reduced but faster depth-averaged methods and when more calculation power intensive, but more accurate, non-depth-averaged methods must be employed. The non-depth-averaged method developed in this study was further validated to measure its predictive power in three dimensional experiments with obstacles. Also here, accurate predictions were observed. Furthermore, a method for the introduction of complex topographies into the simulation process was developed, allowing the direct integration of real mountain topographies. As pilot tests, simulations of granular flows on a complex experimental topography and a real case snow avalanche described in the literature were performed. The results demonstrated that the new method can be transferred to complex topographies and yields good predictions. These findings can serve as a basis for further refinement of the model and its expansions to describe more complex events, e.g., the entrainment of snow mass. Taken together, the novel, non-depth-averaged model and simulation technique build in this study based on the experimental observation are a suitable tool to predict important flow dynamical quantities in non-cohesive granular flows of both natural and industrial origins. Furthermore, it can serve as a basis for the development of a non-depth-averaged predictive model for real scale hazardous granular flows and is thus an important step towards the correct prediction of granular flow behavior for risk assessment in endangered regions

Diffuse retro-reflective imaging for improved mosquito tracking around human baited bednets

Robust imaging techniques for tracking insects have been essential tools in numerous laboratory and field studies on pests, beneficial insects and model systems. Recent innovations in optical imaging systems and associated signal processing have enabled detailed characterisation of nocturnal mosquito behaviour around bednets and improvements in bednet design, a global essential for protecting populations against malaria. Nonetheless, there remain challenges around ease of use for large scale in situ recordings and extracting data reliably in the critical areas of the bednet where the optical signal is attenuated. Here we introduce a retro-reflective screen at the back of the measurement volume, which can simultaneously provide diffuse illumination, and remove optical alignment issues whilst requiring only one-sided access to the measurement space. The illumination becomes significantly more uniform, although, noise removal algorithms are needed to reduce the effects of shot noise particularly across low intensity bednet regions. By systematically introducing mosquitoes in front and behind the bednet in lab experiments we are able to demonstrate robust tracking in these challenging areas. Overall, the retro-reflective imaging setup delivers mosquito segmentation rates in excess of 90% compared to less than 70% with back-lit systems

Diffuse retro-reflective imaging for improved video tracking of mosquitoes at human baited bednets

Robust imaging techniques for tracking insects have been essential tools in numerous laboratory and field studies on pests, beneficial insects and model systems. Recent innovations in optical imaging systems and associated signal processing have enabled detailed characterization of nocturnal mosquito behaviour around bednets and improvements in bednet design, a global essential for protecting populations against malaria. Nonetheless, there remain challenges around ease of use for large-scale in situ recordings and extracting data reliably in the critical areas of the bednet where the optical signal is attenuated. Here, we introduce a retro-reflective screen at the back of the measurement volume, which can simultaneously provide diffuse illumination, and remove optical alignment issues while requiring only one-sided access to the measurement space. The illumination becomes significantly more uniform, although noise removal algorithms are needed to reduce the effects of shot noise, particularly across low-intensity bednet regions. By systematically introducing mosquitoes in front of and behind the bednet in laboratory experiments, we are able to demonstrate robust tracking in these challenging areas. Overall, the retro-reflective imaging set-up delivers mosquito segmentation rates in excess of 90% compared to less than 70% with backlit systems

Adaptive modelling of coupled hydrological processes with application in water management

This paper presents recent results of a network project aiming at the modelling and simulation of coupled surface and subsurface flows. In particular, a discontinuous Galerkin method for the shallow water equations has been developed which includes a special treatment of wetting and drying. A robust solver for saturated-unsaturated groundwater flow in homogeneous soil is at hand, which, by domain decomposition techniques, can be reused as a subdomain solver for flow in heterogeneous soil. Coupling of surface and subsurface processes is implemented based on a heterogeneous nonlinear Dirichlet-Neumann method, using the dune-grid-glue module in the numerics software Dune

The Inverse Variational Problem for Autoparallels

We study the problem of the existence of a local quantum scalar field theory in a general affine metric space that in the semiclassical approximation would lead to the autoparallel motion of wave packets, thus providing a deviation of the spinless particle trajectory from the geodesics in the presence of torsion. The problem is shown to be equivalent to the inverse problem of the calculus of variations for the autoparallel motion with additional conditions that the action (if it exists) has to be invariant under time reparametrizations and general coordinate transformations, while depending analytically on the torsion tensor. The problem is proved to have no solution for a generic torsion in four-dimensional spacetime. A solution exists only if the contracted torsion tensor is a gradient of a scalar field. The corresponding field theory describes coupling of matter to the dilaton field.Comment: 13 pages, plain Latex, no figure

Wasserstoff als ein Fundament der Energiewende Teil 2: Sektorenkopplung und Wasserstoff: Zwei Seiten der gleichen Medaille

Der vorliegende zweite Teil - Sektorenkopplung und Wasserstoff: Zwei Seiten der gleichen Medaille knüpft an diesem Punkt an. Er befasst sich detailliert mit möglichen Nutzungspfaden von Wasserstoff in den Sektoren Verkehr, Industrie und Wärme sowie mit dem systemisch wichtigen Aspekt der Rückverstromung. Am Beispiel aktueller Forschungsarbeiten im DLR wird dargestellt, welche Potenziale sich durch die Kopplung der verschiedenen Energieverbrauchssektoren bei der Erzeugung und Nutzung von Wasserstoff ergeben. Diese Synergien ebnen den Weg zu einer effizienteren und flexibleren Nutzung von erneuerbarer Energie. Neben den technologischen Einsatzmöglichkeiten spielen darüber hinaus die Infrastruktur sowie dazugehörige Sicherheitsaspekte bei der Nutzung von Wasserstoff eine gewichtige Rolle. Weiterhin wird im DLR auf dem Gebiet der Energiesystemanalyse an der Einschätzung der Auswirkungen großskaliger Wasserstoffinfrastrukturen auf das bestehende und zukünftige Energiesystem geforscht. Dies beinhaltet auch die Fragestellungen, ob ein klimaneutrales Energiesystem aus heutiger Sicht überhaupt ohne Wasserstoff denkbar ist, bzw. wie groß der Wasserstoffbedarf und das -angebot in solchen Zielszenarien ausfällt. Zudem werden Umwelteinwirkungen untersucht und Lebenszyklusanalysen erstellt