# com3Hybrid: Hybrid modeling¶

com3Hybrid is a computational module that combines the dense flow avalanche (DFA) simulation model (com1DFA) and the Alpha-Beta statistical one (com2AB), taking advantage of their strength and trying to reduce their weaknesses. The weakness of the DFA simulation lies in its required inputs, among which is the friction parameter $$\mu$$. The disadvantage of the statistical model lies in the necessary path, which is used to extract an avalanche profile and compute a runout angle. The idea here is to determine the avalanche path in an automated way by:

• first, running a DFA simulation

• computing a mass averaged path from the results

• use the path to compute the runout angle corresponding to this specific avalanche

• using a coulomb friction method, the friction parameter $$\mu$$ is extracted from the runout

• the resulting $$\mu$$ is used in the input for a new DFA simulation.

This iteration process can be repeated multiple times until “convergence”, which means until the $$\mu$$ or $$\alpha$$ value stops varying.

## Input¶

• raster of the DEM (.asc file)

• a release feature (shapefile) in Inputs/REL

• Split point (shapefile). This requirement is planned to be automated as well.

## Outputs¶

• The avalanche path specific for the input topography

• the $$\mu$$ value ($$\alpha$$ travel angle) specific for the input topography

• results from the DFA simulation for the input topography

• a combined plot showing the results of the DFA simulation and Alpha-Beta model

## To run¶

• go to AvaFrame/avaframe

• copy com3Hybrid/com3HybridCfg.ini to com3Hybrid/local_com3HybridCfg.ini and edit (if not, default values are used)

• put your com1DFA and com2AB settings in com3Hybrid/hybridModel_com1DFACfg.ini and com3Hybrid/hybridModel_com2ABCfg.ini (these files replace the local .ini files in com1DFA and com2AB)

• make sure all the required inputs are available in the avalanche directory

• enter the path to the desired dataset in local_avaframeCfg.ini

• run:

python3 runScripts/runCom3Hybrid.py


## Procedure¶

1. A first com1DFA simulation is run using the com3Hybrid/hybridModel_com1DFACfg.ini configuration and the $$\mu$$ provided in com3Hybrid/local_com3HybridCfg.ini.

2. The mass averaged path is computed from the DFA simulation using the ana5Utils.DFAPathGeneration. From this we obtain the (x,y,z) and (s,z) coordinates of the avalanche profile (the path is extended towards the relase and in the runout). This path is saved to avalancheDir/Inputs/LINES and replaces the old path. A copy is also saved to avalancheDir/Outputs/com3Hybrid.

3. com2AB module is run using the com3Hybrid/hybridModel_com2ABCfg.ini to compute the $$\mu = \tan{\alpha}$$ friction parameter corresponding to this specific avalanche and area.

4. The com3Hybrid/hybridModel_com1DFACfg.ini is updated with the new $$\mu = \tan{\alpha}$$ value and com1DFA simulation is run again.

5. Steps 2. and 3. are repeated to get the new avalanche path and $$\mu = \tan{\alpha}$$ value.

This process is repeated as long as the $$\alpha = \arctan{\mu}$$ value varies from more than alphaThreshold which you can specify in com3Hybrid/local_com3HybridCfg.ini (this is a value in degrees) and this for a maximum of nIterMax iterations.

## Configuration parameters¶

The parameters for path generation (section PATH of com3Hybrid/local_com3HybridCfg.ini) are described in Automated path generation.

The parameters for the DFA simulation are to be specified in com3Hybrid/hybridModel_com1DFACfg.ini. This file replaces the local_com1DFACfg.ini that is usually used to run a com1DFA simulation.

The parameters for the $$\alpha-\beta$$ model are to be specified in com3Hybrid/hybridModel_com2ABCfg.ini. This file replaces the local_com2ABCfg.ini that is usually used to run a com2AB simulation.