In this work, a simple methodology for preliminarily assessing the magnitude of potential landslide-induced impulse waves’ attenuation in mountain lakes is presented. A set of metrics is used to define the geometries of theoretical mountain lakes of different sizes and shapes and to simulate impulse waves in them using the hydrodynamic software Flow-3D. The modeling results provide the ‘wave decay potential’, a ratio between the maximum wave amplitude and the flow depth at the shoreline. Wave decay potential is highly correlated with what is defined as the ‘shape product’, a metric that represents lake geometry. The relation between these two parameters can be used to evaluate wave dissipation in a natural lake given its geometric properties, and thus estimate expected flow depth at the shoreline. This novel approach is tested by applying it to a real-world event, the 2007 landslide-generated wave in Chehalis Lake (Canada), where the results match well with those obtained using the empirical equation provided by ETH Zurich (2019 Edition). This work represents the initial stage in the development of this method, and it encourages additional research and modeling in which the influence of the impacting characteristics on the resulting waves and flow depths is investigated.
Abstract. This study aims to test the capacity of Flow-3D regarding
the simulation of a rockslide-generated impulse wave by evaluating the
influences of the extent of the computational domain, the grid
resolution, and the corresponding computation times on the accuracy of
modelling results. A detailed analysis of the Lituya Bay tsunami event
(1958, Alaska, maximum recorded run-up of 524 m a.s.l.) is presented. A
focus is put on the tsunami formation and run-up in the impact area. Several
simulations with a simplified bay geometry are performed in order to test
the concept of a “denser fluid”, compared to the seawater in the bay, for
the impacting rockslide material. Further, topographic and bathymetric
surfaces of the impact area are set up. The observed maximum run-up can be
reproduced using a uniform grid resolution of 5 m, where the wave overtops
the hill crest facing the slide source and then flows diagonally down the slope.
The model is extended along the entire bay to simulate the wave propagation.
The tsunami trimline is well recreated when using (a) a uniform mesh size of
20 m or (b) a non-uniform mesh size of 15 m × 15 m × 10 m with a relative roughness of 2 m for the topographic surface. The trimline mainly results from the primary
wave, and in some locations it also results from reflected waves. The denser fluid is a
suitable and simple concept to recreate a sliding mass impacting a waterbody,
in this case with maximum impact speed of ∼93 m s−1. The
tsunami event and the related trimline are well reproduced using the
3D modelling approach with the density evaluation model available in
Flow-3D.
The recent demand for sustainable aviation designs challenges aircraft manufacturers to reconsider existing technologies in light of the required cuts in environmental pollution. One of the key factors in addressing these green targets is represented by the integration of unconventional propulsion concepts on the airframe, exploiting electrically driven designs. Among the necessary targets to achieve, a substantial noise emission reduction is needed. Since the new aircraft designs could include existing or novel propulsion system components to address the challenge of reliably predicting noise emissions, in this work a simplified, fast and physicalprinciples-based rotor noise model is introduced, together with suitable adapted perturbation equations to represent current and possibly newly arising noise sources mechanisms. The rotor noise model is based on rotating point or line sources that represent loading noise in terms of equivalent body forces. The model is applied in a Computational Aeroacoustics (CAA) framework in the time domain. The Linearized Euler Equations (LEE) are split into two separate perturbation equation systems for the acoustic and vorticity mode, respectively. The new noise prediction model, together with the new equations, are implemented in the unstructured quadrature-free experimental Discontinuous Galerkin (DG) CAA solver DISCO++ of DLR. Acoustic Perturbation Equations (APE) describe the propagation of the acoustic mode, and can be discretized numerically very robustly in the DG-framework. The equation splitup intends to overcome numerical stability issues present in the discretization of the LEE with the DG method. The paper reports initial successful results and outlines future possible applications.
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