com1DFA: DFA-Kernel

This module is a simulation tool for dense flow (snow) avalanches (DFA). It is based on the samos-AT (Snow Avalanche Modeling and Simulation- Advanced Technologies) developed by the Austrian government in cooperation with the company AVL List GmbH in Graz. The calculation of the DFA is based on the depth integrated governing equations and solved numerically using the smoothed particle hydrodynamic (sph) method.

Dense flow avalanche simulations can be performed for different release area scenarios, with or without entrainment and/or resistance areas. There is the option to vary the internal friction parameter or the release snow thickness.

Input

The module requires an avalanche directory, that follows a specified folder structure. This avalanche directory can be created by running: runInitializeProject.py. In the directory Inputs, the following files are required:

  • digital elevation model as .asc file -> use ESRI grid format

  • release area scenario as shapefile (in Inputs/REL); multiple are possible -> the release area name should not contain an underscore, if so ‘_AF’ is added

and the following files are optional:

  • entrainment area as shapefile (in Inputs/ENT)

  • resistance area as shapefile (in Inputs/RES)

  • secondary release area as shapefile (in Inputs/SECREL)

The simulation settings area defined in the configuration file com1DFACfg.ini:

  • com1Exe - path to com1DFA executable

  • flagOut - print full model output

  • simTypeList - simulation types that shall be performed (options: null, ent, res, entres, available; if multiple, separate by ‘|’))

  • releaseScenario - name of release area scenario shapefile (with or without extension -shp, if multiple, separate by ‘|’)

  • flagVarPar - perform parameter variation

  • varPar - parameter to be varied

  • varParValues - values for parameter variation

Output

The simulation results are saved to: Outputs/com1DFA and include:

  • raster files of the peak values for pressure, flow depth and flow velocity (Outputs/com1DFA/peakFiles)

  • reports of all simulations (Outputs/com1DFA/reports)

  • log files of all simulations

  • experiment log that lists all simulations

To run

Attention

Please refer to the instructions in Com1DFA Executable on how to get the necessary C++ executable and setup the correct paths.

  • create an avalanche directory with required input files - for this task you can use Initialize Project

  • copy avaframeCfg.ini to local_avaframeCfg.ini and set your desired avalanche directory name

  • in avaframe/ run:

    python3 runCom1DFA.py

Theory

The governing equations of the dense flow avalanche are derived from the incompressible mass and momentum balance on a Lagrange control volume ([Zw2000] [ZwKlSa2003]). Assuming the avalanche is much longer and larger than thick, it is possible to integrate the governing equations over the thickness of the avalanche and operate some simplifications due to the shape of the avalanche. This leads, after some calculation steps described in details in Theory Governing Equations for the Dense Flow Avalanche to:

\[\begin{split}\begin{aligned} &\frac{\mathrm{d}V(t)}{\mathrm{d}t} = \frac{\mathrm{d}(A_b\overline{h})}{\mathrm{d}t} = \frac{\rho_{\text{ent}}}{\rho_0}\,w_f\,h_{\text{ent}}\,\left\Vert \overline{\mathbf{u}}\right\Vert\\ &\frac{\,\mathrm{d}\overline{u}_i}{\,\mathrm{d}t} = g_i + \frac{K_{(i)}}{\overline{\rho}\,A\,\overline{h}}\,\oint\limits_{\partial{A}}\left(\frac{\overline{h}\,\sigma^{(b)}}{2}\right)n_i\,\mathrm{d}l -\delta_{i1}\frac{\tau^{(b)}}{\overline{\rho}\,\overline{h}} - C_{\text{res}}\,\overline{\mathbf{u}}^2\,\frac{\overline{u_i}}{\|\overline{\mathbf{u}}\|} -\frac{\overline{u_i}}{A\,\overline{h}}\frac{\,\mathrm{d}(A\,\overline{h})}{\,\mathrm{d}t} + \frac{F_i^{\text{ent}}}{\overline{\rho}\,A\,\overline{h}}\\ &\overline{\sigma}^{(b)}_{33} = \rho\,\left(g_3-\overline{u_1}^2\,\frac{\partial^2{b}}{\partial{x_1^2}}\right)\,\overline{h} \end{aligned}\end{split}\]

Numerics

Those equations are solved numerically using a SPH method ([LL10, Sam07]). SPH is a mesh free method where the basic idea is to divide the avalanche into small mass particles. The particles interact with each other according to the equation of motion described in Theory and the chosen kernel function. This kernel function describes the domain of influence of a particle (through the smoothing length parameter). See theory Numerics for further details.