1,721,106 research outputs found
Massstabseffekte im hydraulischen modell
No full textMassstabseffekte entsprechen einer Verzerrung der Messwerte im Modell gegenüber dem Prototypen. Jedes hydraulische Modell eines Prototypen mit Modellmassstab ungleich eins weist solche Massstabseffekte auf. Wird aber das Modell genügend gross gebaut, so sind diese Effekte vernachlässigbar klein, und die Messresultate können mittels Modellgesetz auf den Prototypen übertragen werden. Nachfolgend wird in die Problematik der Massstabseffekte eingeführt unter Berücksichtigung der weiterführenden Literatur. Einige grundlegende Schwierigkeiten beim Modellieren von Naturzuständen im hydraulischen Modell werden zudem aufgezeigt. Am Beispiel rutscherzeugter Impulswellen wird die Modellähnlichkeit zwischen Modell und Prototyp verdeutlicht, und weitere Erfahrungswerte zur Vermeidung von grossen Massstabseffekten werden für verschiedene Prozesse aufgeführt. Scale effects correspond to a distortion of the measured values in the model to the prototype. Each hydraulic model of a prototype model with a scale equal to one has such scale effects. But if the model built big enough, these effects are negligible, and the measurement results can be transferred to the prototype model by means of law. Below is introduced into the problem of scale effects, taking into account the secondary literature. Some fundamental difficulties in modeling of natural conditions in the hydraulic model are also shown. The example rutscherzeugter pulse waves the model similarity between model and prototype is demonstrated, and further experiences to avoid large-scale effects are listed for different processes. <br/
Test 7. Subaerial landslide generated impulse waves in a wave channel: experimental SPH validation
No full textImpulse waves in oceans, bays, lakes, or reservoirs are generated by landslides, rock falls, shore instabilities, snow avalanches, glacier calvings, or meteorite impacts. Examples are the 1958 Lituya Bay case in Alaska where the generated impulse wave reached a maximum run-up height of 524 m on the opposite shore or the 1963 Vaiont case in North Italy where an impulse wave overtopped a dam by about 70 m and killed 2,000 people. The mainly passive methods to face such catastrophes include evacuations, water level draw-down, or freeboard control in artificial reservoirs. They require detailed knowledge of the wave features and of the wave effects on the dam or shore line. Numerical methods such as SPH may play an important role in the future in predicting the effects of impulse waves since numerical models may result in more accurate predictions for complex geometries than general physical model studies at lower costs than specific physical case studies (Heller et al. 2009). This test case is one out of three experiments presented in Heller (2007), conducted in a wave channel with a still water depth h = 0.300 m. The results include the granular slide deformation prior and during impact into the water body, the wave generation including the temporal advance of velocity vector fields measured with Particle Image Velocimetry PIV, and the wave profiles measured with seven Capacitance Wave Gages CWGs. <br/
Discussion of “Computing the Trajectory of Free Jets” by Tony L. Wahl, Kathleen H. Frizell, and Elisabeth A. Cohen
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Impulse product parameter in landslide generated impulse waves
No full textSubaerial landslide generated impulse waves were investigated in a prismatic wave channel based on Froude similitude and granular slide material. The tests included the seven governing parameters still water depth, slide impact velocity, slide thickness, bulk slide volume, bulk slide density, slide impact angle, and grain diameter. All governing parameters, except for the grain diameter with a negligible effect, are included in the impulse product parameter P allowing for a simple application. Empirical equations based on 211 experiments for all relevant wave features in practice including the maximum wave height, the maximum wave amplitude with its location and period in the slide impact zone and both the wave height and amplitude decay and the period increase in the wave propagation zone are a simple function of P. The presented equations were validated with 223 runs of Fritz (2002) and Zweifel (2004) resulting in improved goodness of fit. The limitations of the herein derived empirical equations are also highlighted. The wave height and amplitude equations based on a wave channel (2D) agree well with the 1958 Lituya Bay case
Numerical characterisation and efficient prediction of landslide-tsunami propagation over a wide range of idealised bathymetries
Full text linkLandslide-tsunamis are generated by masses, such as landslides or icebergs, impacting into water bodies. Such tsunamis resulted in major catastrophes in the recent past. Generic research into landslide-tsunamis has widely been conducted in idealised water body geometries at uniform water depths. However, varying bathymetries can significantly alter landslide-tsunamis. This article investigates this effect in a 2D flume using selected idealised bathymetries to provide methods to predict the transformed wave characteristics downwave of each feature. The selected bathymetries are: (a) linear beach bathymetries, (b) submerged positive and negative Gaussian bathymetric features and (c) submerged positive and negative step bathymetries. The hydrodynamic model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate 9 idealised landslide-tsunamis (1 approximate linear, 2 Stokes, 2 cnoidal and 4 solitary waves), for a total of 184 tests. The analysed parameters include the free water surface, wave height and amplitude. Shoaling in (a) is represented by either Green's law or the Boussinesq's adiabatic approximation up to wave breaking with an accuracy of −7% to +10% for cnoidal and solitary waves, respectively. The results are then analysed with an (i) Artificial Neural Network and (ii) a regression analysis. (i) shows a smaller Mean Square Error (MSE) of 0.0027 than (ii) (MSE =0.024) and good generalisation in predicting the transformed wave characteristics and, after defining the best dimensionless parameters, (ii) provides empirical equations to predict transformed waves. In addition, simulations were conducted in a 3D basin to investigate the combined effect of the bathymetry and geometry. The efficient use of the developed prediction methods is demonstrated with the 2014 Lake Askja landslide-tsunami where a good accuracy is achieved compared to available numerical simulations
Numerical modelling of landslide-tsunami propagation in a wide range of idealised water body geometries
Full text link© 2019 Elsevier B.V. Large landslide-tsunamis are caused by mass movements such as landslides or rock falls impacting into a water body. Research of these phenomena is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave height in 2D and 3D differs by over one order of magnitude in the far field. Further, the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The hydrodynamic numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green's law and with diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point of the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but becomes more important for Stokes-like waves in deeper water. The findings herein significantly improve the reliability of initial landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the 2014 landslide-tsunami event in Lake Askja
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