TY - JOUR A1 - Fischer, Jan-Thomas A1 - Kowalski, Julia A1 - Pudasaini, Shiva P. A1 - Miller, S. A. T1 - Dynamic Avalanche Modeling in Natural Terrain JF - International Snow Science Workshop, Davos 2009, Proceedings ; Proc. ISSW 2009 N2 - The powerful avalanche simulation toolbox RAMMS (Rapid Mass Movements) is based on a depth-averaged hydrodynamic system of equations with a Voellmy-Salm friction relation. The two empirical friction parameters μ and � correspond to a dry Coulomb friction and a viscous resistance, respectively. Although μ and � lack a proper physical explanation, 60 years of acquired avalanche data in the Swiss Alps made a systematic calibration possible. RAMMS can therefore successfully model avalanche flow depth, velocities, impact pressure and run out distances. Pudasaini and Hutter (2003) have proposed extended, rigorously derived model equations that account for local curvature and twist. A coordinate transformation into a reference system, applied to the actual mountain topography of the natural avalanche path, is performed. The local curvature and the twist of the avalanche path induce an additional term in the overburden pressure. This leads to a modification of the Coulomb friction, the free-surface pressure gradient, the pressure induced by the channel, and the gravity components along and normal to the curved and twisted reference surface. This eventually guides the flow dynamics and deposits of avalanches. In the present study, we investigate the influence of curvature on avalanche flow in real mountain terrain. Simulations of real avalanche paths are performed and compared for the different models approaches. An algorithm to calculate curvature in real terrain is introduced in RAMMS. This leads to a curvature dependent friction relation in an extended version of the Voellmy-Salm model equations. Our analysis provides yet another step in interpreting the physical meaning and significance of the friction parameters used in the RAMMS computational environment. KW - snow KW - avalanche Y1 - 2009 SP - 448 EP - 452 ER - TY - CHAP A1 - Knobloch, V. A1 - Kowalski, Julia A1 - Bösiger, P. A1 - Kozerke, S. T1 - Probabilistic Streamline Estimation from Accelerated Fourier Velocity Encoded Measurements T2 - Proceedings of the 19th ISMRM International Society for Magnetic Resonance in Medicine Y1 - 2011 N1 - ISMRM 19th Annual Meeting & Exhibition in Montréal, Québec, Canada SP - 1215 EP - 1215 ER - TY - CHAP A1 - Christen, Marc A1 - Bartelt, Perry A1 - Kowalski, Julia A1 - Stoffel, Lukus T1 - Calculation of dense snow avalanches in three-dimensional terrain with the numerical simulation programm RAMMS T2 - Proceedings ISSW 2008 ; International Snow Science Workshop. Whistler 2008 N2 - Numerical models have become an essential part of snow avalanche engineering. Recent advances in understanding the rheology of flowing snow and the mechanics of entrainment and deposition have made numerical models more reliable. Coupled with field observations and historical records, they are especially helpful in understanding avalanche flow in complex terrain. However, the application of numerical models poses several new challenges to avalanche engineers. A detailed understanding of the avalanche phenomena is required to specify initial conditions (release zone dimensions and snowcover entrainment rates) as well as the friction parameters, which are no longer based on empirical back-calculations, rather terrain roughness, vegetation and snow properties. In this paper we discuss these problems by presenting the computer model RAMMS, which was specially designed by the SLF as a practical tool for avalanche engineers. RAMMS solves the depth-averaged equations governing avalanche flow with first and second-order numerical solution schemes. A tremendous effort has been invested in the implementation of advanced input and output features. Simulation results are therefore clearly and easily visualized to simplify their interpretation. More importantly, RAMMS has been applied to a series of well-documented avalanches to gauge model performance. In this paper we present the governing differential equations, highlight some of the input and output features of RAMMS and then discuss the simulation of the Gatschiefer avalanche that occurred in April 2008, near Klosters/Monbiel, Switzerland. KW - snow KW - avalanche Y1 - 2008 SP - 709 EP - 716 ER - TY - JOUR A1 - McArdell, Brian W. A1 - Bartelt, Perry A1 - Kowalski, Julia T1 - Field observations of basal forces and fluid pore pressure in a debris flow JF - Geophysical Research Letters (GRL) N2 - Using results from an 8 m2 instrumented force plate we describe field measurements of normal and shear stresses, and fluid pore pressure for a debris flow. The flow depth increased from 0.1 to 1 m within the first 12 s of flow front arrival, remained relatively constant until 100 s, and then gradually decreased to 0.5 m by 600 s. Normal and shear stresses and pore fluid pressure varied in-phase with the flow depth. Calculated bulk densities are ρb = 2000–2250 kg m−3 for the bulk flow and ρf = 1600–1750 kg m−3 for the fluid phase. The ratio of effective normal stress to shear stress yields a Coulomb basal friction angle of ϕ = 26° at the flow front. We did not find a strong correlation between the degree of agitation in the flow, estimated using the signal from a geophone on the force plate, and an assumed dynamic pore fluid pressure. Our data support the idea that excess pore-fluid pressures are long lived in debris flows and therefore contribute to their unusual mobility. KW - debris flow Y1 - 2007 SN - 0094-8276 VL - 34 IS - 7 ER - TY - JOUR A1 - Heierli, Joachim A1 - Purves, Ross S. A1 - Felber, Andreas A1 - Kowalski, Julia T1 - Verification of nearest-neighbours interpretations in avalanche forecasting JF - Annals of Glaciology N2 - This paper examines the positive and negative aspects of a range of interpretations of nearest-neighbours models. Measures-oriented and distributionoriented verification methods are applied to categorial, probabilistic and descriptive interpretations of nearest neighbours used operationally in avalanche forecasting in Scotland and Switzerland. The dependence of skill and accuracy measures on base rate is illustrated. The purpose of the forecast and the definition of events are important variables in determining the quality of the forecast. A discussion of the application of different interpretations in operational avalanche forecasting is presented. KW - avalanche Y1 - 2004 SN - 1727-5644 VL - 38 IS - 1 SP - 84 EP - 88 ER - TY - GEN A1 - Baumgartner, Thomas A1 - Wunderlich, Florian A1 - Jaunich, Arthur A1 - Sato, Tomoo A1 - Bundy, Georg A1 - Grießmann, Nadine A1 - Kowalski, Julia A1 - Burghardt, Stefan A1 - Hanebrink, Jörg T1 - Lighting the way: Perspectives on the global lighting market Y1 - 2012 CY - McKinsey ET - 2nd ed. ER - TY - THES A1 - Kowalski, Julia T1 - Streamline estimation from sparsely sampled q-space Magnetic Resonance data Y1 - 2010 N1 - Master Thesis in Medical Physics, ETH Zurich ER - TY - JOUR A1 - Kowalski, Julia A1 - McElwaine, Jim N. T1 - Shallow two-component gravity-driven flows with vertical variation JF - Journal of Fluid Mechanics Y1 - 2013 SN - 0022-1120 VL - 714 SP - 434 EP - 462 PB - Cambridge Univ. Press CY - Cambridge ER - TY - JOUR A1 - Olaru, Alexandra Maria A1 - Kowalski, Julia A1 - Sethi, Vaishali A1 - Blümich, Bernhard T1 - Exchange relaxometry of flow at small Péclet numbers in a glass bead pack JF - Journal of Magnetic Resonance (JMR) N2 - In this paper we consider low Péclet number flow in bead packs. A series of relaxation exchange experiments has been conducted and evaluated by ILT analysis. In the resulting correlation maps, we observed a collapse of the signal and a translation towards smaller relaxation times with increasing flow rates, as well as a signal tilt with respect to the diagonal. In the discussion of the phenomena we present a mathematical theory for relaxation exchange experiments that considers both diffusive and advective transport. We perform simulations based on this theory and discuss them with respect to the conducted experiments. KW - NMR exchange relaxometry KW - Low-field NMR Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.jmr.2012.04.015 SN - 1096-0856 VL - 220 SP - 32 EP - 44 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Fischer, Jan-Thomas A1 - Kowalski, Julia A1 - Pudasaini, Shiva P. T1 - Topographic curvature effects in applied avalanche modelling JF - Cold Regions Science and Technology N2 - This paper describes the implementation of topographic curvature effects within the RApid Mass MovementS (RAMMS) snow avalanche simulation toolbox. RAMMS is based on a model similar to shallow water equations with a Coulomb friction relation and the velocity dependent Voellmy drag. It is used for snow avalanche risk assessment in Switzerland. The snow avalanche simulation relies on back calculation of observed avalanches. The calibration of the friction parameters depends on characteristics of the avalanche track. The topographic curvature terms are not yet included in the above mentioned classical model. Here, we fundamentally improve this model by mathematically and physically including the topographic curvature effects. By decomposing the velocity dependent friction into a topography dependent term that accounts for a curvature enhancement in the Coulomb friction, and a topography independent contribution similar to the classical Voellmy drag, we construct a general curvature dependent frictional resistance, and thus propose new extended model equations. With three site-specific examples, we compare the apparent frictional resistance of the new approach, which includes topographic curvature effects, to the classical one. Our simulation results demonstrate substantial effects of the curvature on the flow dynamics e.g., the dynamic pressure distribution along the slope. The comparison of resistance coefficients between the two models demonstrates that the physically based extension presents an improvement to the classical approach. Furthermore a practical example highlights its influence on the pressure outline in the run out zone of the avalanche. Snow avalanche dynamics modeling natural terrain curvature centrifugal force friction coefficients. KW - Snow KW - Avalanche Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.coldregions.2012.01.005 SN - 1872-7441 VL - 74-75 SP - 21 EP - 30 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Bühler, Yves A1 - Christen, Marc A1 - Kowalski, Julia A1 - Bartelt, Perry T1 - Sensitivity of snow avalanche simulations to digital elevation model quality and resolution JF - Annals of Glaciology N2 - Digital elevation models (DEMs), represent the three-dimensional terrain and are the basic input for numerical snow avalanche dynamics simulations. DEMs can be acquired using topographic maps or remote-sensing technologies, such as photogrammetry or lidar. Depending on the acquisition technique, different spatial resolutions and qualities are achieved. However, there is a lack of studies that investigate the sensitivity of snow avalanche simulation algorithms to the quality and resolution of DEMs. Here, we perform calculations using the numerical avalance dynamics model RAMMS, varying the quality and spatial resolution of the underlying DEMs, while holding the simulation parameters constant. We study both channelized and open-terrain avalanche tracks with variable roughness. To quantify the variance of these simulations, we use well-documented large-scale avalanche events from Davos, Switzerland (winter 2007/08), and from our large-scale avalanche test site, Valĺee de la Sionne (winter 2005/06). We find that the DEM resolution and quality is critical for modeled flow paths, run-out distances, deposits, velocities and impact pressures. Although a spatial resolution of ~25 m is sufficient for large-scale avalanche modeling, the DEM datasets must be checked carefully for anomalies and artifacts before using them for dynamics calculations. KW - snow KW - avalanche Y1 - 2011 SN - 1727-5644 VL - 52 IS - 58 SP - 72 EP - 80 PB - Cambridge University Press CY - Cambridge ER - TY - JOUR A1 - Kowalski, Julia T1 - Mathematische Murgangmodellierung JF - Newsletter Naturgefahren Y1 - 2008 VL - 2008 IS - 2 SP - 4 EP - 5 ER - TY - THES A1 - Kowalski, Julia T1 - Two-phase Modeling of Debris Flows Y1 - 2008 SN - 978-3-86664-524-0 N1 - Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 17827, 2008 PB - Mensch und Buch CY - Berlin ER - TY - GEN A1 - Kowalski, Julia T1 - Dynamics of Granular Material Avalanches and Numerical Approximations of Savage-Hutter Models Y1 - 2004 N1 - Diploma Thesis, University of Augsburg ER - TY - CHAP A1 - Kowalski, Julia T1 - Numerical Debris Flow Simulation T2 - Schweizer Numerik Kolloquium : Book of Abstracts 12. April 2006 Y1 - 2006 ER - TY - CHAP A1 - Kowalski, Julia A1 - McArdell, B. W. A1 - Bartelt, Perry T1 - A comparison of two approaches to modeling multiphase gravity currents T2 - Geophysical Research Abstracts Y1 - 2006 N1 - A-08738 VL - 8 ER - TY - CHAP A1 - Kowalski, Julia A1 - Bartelt, Perry A1 - McElwaine, J. T1 - Two-phase debris flow modeling T2 - Geophysical Research Abstracts Y1 - 2007 N1 - A-08119 ER - TY - CHAP A1 - Kowalski, Julia A1 - McElwaine, J. T1 - Two-phase debris flow modeling T2 - Geophysical Research Abstracts Y1 - 2008 N1 - A-01048 ER - TY - CHAP A1 - Kowalski, Julia A1 - Bugnion, Louis T1 - An extended shallow flow theory for natural debris flows Y1 - 2009 N1 - 2009 Portland GSA Annual Meeting (18-21 October 2009); Geological Society of America VL - 41 IS - 7 SP - 609 EP - 609 ER - TY - CHAP A1 - Olaru, Alexandra Maria A1 - Kowalski, Julia A1 - Sethi, Vaishali A1 - Blümich, Bernhard T1 - Fluid Transport in Porous Media probed by Relaxation-Exchange NMR T2 - 2011 Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec. Y1 - 2011 N1 - H12B-07; American Geophysical Union ER -