# com5GlideSnow: Glide snow

The com5GlideSnow computational module provides the option to add an elastic cohesion force between particles based on com1DFA. This can be used for example to simulate small glide snow avalanches.

The cohesion between particles is modeled using elastic bonds with maximum strain rate. This means that the cohesion force $$\mathbf{F}_{lk}$$ exerted by $$l$$ on $$k$$ is expressed by:

$\mathbf{F}_{lk} = -\mathbf{F}_{kl} = \frac{L-L_0}{L_0} A_{kl} E \mathbf{e_{kl}}$

Where $$L$$ and $$L_0$$ are the distances between the particles $$k$$ and $$l$$ at a time t and at rest (initial time step), $$E$$ is the elastic modulus of the material, $$A_{kl}$$ is the contact area between particles $$k$$ and $$l$$ and $$\mathbf{e_{kl}}$$ is the unit vector

$\epsilon = \frac{L-L_0}{L_0}$

represents the strain ($$\epsilon$$ is positive in the case of elongation and negative in compression). If the strain exceeds a critical value $$\epsilon_c$$ the bond between the particles $$k$$ and $$l$$ breaks.

The contact area $$A_{kl}$$ between particles $$k$$ and $$l$$ reads:

$A_{kl} = h_{kl} d_{kl} = \frac{h_k + h_l}{2} \frac{L}{\sqrt{3}}$

$$h_{kl}$$ represents the height of the contact surface and $$d_{kl}$$ represents the length of the contact surface in the horizontal plane assuming that each particle has 6 neighbours.

## Input

The standard inputs required to perform a simulation run using com1DFA can be found here: Input. There is a run script to perform a glide snow com1DFA run: runCom5GlideSnow.py, and the configuration settings can be found in com5GlideSnow/com5GlideSnowCfg.ini. The glide snow tool-specific parameters are:

• glideSnow is activated by setting glideSnow to 1

• the maximum strain before breaking of the bond cohesionMaxStrain

• the Young modulus in N/m² cohesiveSurfaceTension

However, also several other parameters, for example the particle initialization method, friction model and parameters, are changed compared to the default configuration of com1DFA and listed in the com5GlideSnow/com5GlideSnowCfg.ini in the com1DFA_override section.

## Initialization of bonds

If the elastic cohesion (glideSnow set to 1) is activated, the bonds between particles are initialized. The construction of the bonds is done by building a triangular mesh on the particles (used as a point cloud) and the Delaunay triangulation function from matplotlib. The length $$L_0$$ of the bonds at rest (initial distance between two bonded particles) is also initialized here.

Note

It is recommended to use the triangular (triangular) initialization option (Initialize particles) rather than the random or the uniform one in the case where cohesion is activated.

## To run

• first go to AvaFrame/avaframe

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

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

• copy com5GlideSnow/com5GlideSnowCfg.ini to com5GlideSnow/local_com5GlideSnowCfg.ini and if desired change configuration settings

• if you are on a develop installation, make sure you have an updated compilation, see installation:Setup AvaFrame

• run:

python3 runCom5GlideSnow.py