The flow simulation tools on Vhub

Sylvain Charbonnier

Earthcube All-Hands Meeting

24-26 June 2014

VHub cyberinfrastructure for volcanology : Modeling, data sharing, and collaboration

The Energy Line Concept

• Energy Line concept (Hsu, 1975): A density flow initiated at some elevation will move as potential energy is converted to kinetic energy minus friction.

• The energy line is the slope along which the frictional loss is balanced by conversion of potential to kinetic energy.

• If the topographic slope is greater than the energy line, the flow will decelerate. The flow comes to rest where the energy line intersects the topographic surface.

• The slope of the energy line (α) is calculated as the arc tan of the loss in height (H) divided by run-out distance (L).” (Sheridan, 1979):

The Energy Line Concept

H/L = μ = tan α

Driving acceleration = g sin α;

Retardation = μ g cos α

Δv/ Δt = a = g sin α - g μ cos α = g (sin α - μ cos α )

The Energy Cone Model• By using digital topographic models of volcanoes, the energy-line model was expanded

into a three dimensional representation called the “energy-cone” model by sweeping the energy line through a 360° arc (Malin and Sheridan, 1982; Sheridan and Malin, 1983).

• These friction models are equivalent to sliding-block models, and are thought to potentially apply to virtually all types of pyroclastic density currents (Sheridan, 1979).

• They assume straight-line flow trajectories that pass through topographic obstacles, encompass the entire cone and ignore confining topography.

• The energy cone model is the only model that can reasonably be used to simulate dilute pyroclastic density currents such as surges…

There are five input parameters:

1. DEM (in .txt format)2. H/L3. Source Altitude (always higher than

the highest point)4. Longitude (in degrees if a kmz is

desire, UTM can be used as well but only a jpg will be created)

5. Latitude (in degrees if a kmz is desire, UTM can be used as well but only a jpg will be created)

What is Titan2D? Titan2D is a freely available computer program developed by the GMFG group at SUNY

Buffalo (USA) for the purpose of simulating dry granular avalanches over digital elevation models of natural terrain.

The program is designed for simulating geological mass flows such as debris avalanches, landslides and some dense volcanic flows.

Titan2D can be run on laptops to supercomputers as a standalone version on any linux platforms and/or directly online at https://vhub.org/tools/titan2d.

2002 Pink Mountain landslide, British Columbia, Canada

2006 Merapi Block-And-Ash flow, Java,

Indonesia

1997 Mt Adams debris avalanche, Washington,

USA

Inside Titan2D…• New class of geophysical mass flow models (Savage and Hutter, 1989) → depth-averaged granular-flow model on 3D terrain (Iverson and Denlinger, 2001)

• conservation equations for mass (3) and momentum (4 and 5) → « shallow-water » model with a Mohr-Coulomb frictional resistance term

• The flowing mass → incompressible continuum with constant density

Patra, A.K., Bauer, A.C., Nichita, C.C., Pitman, E.B., Sheridan, M.F., Bursik, M.I., Rupp, B., Webber, A., Stinton, A.J., Namikawa, L.M., Renschler, C.S., 2005. Parallel adaptive simulation of dry avalanches over natural terrain. J. Volcanol. Geotherm. Res. 139, 1-22.

Model Applications• Hazard assessment:

If a mass flow were to be initiated at a particular location, what areas are most at risk from that flow?

What is the probability that flow depth at a particular location will exceed a given threshold value?

Model Verification and Validation:

Verification is a process of identifying “to what degree” a given mathematical model is numerically solved correctly.

Validation attempts to check computational results against reality (experiments and/or actual events) → back analyses

variability and frequent disparity between data sets of modeled flows and field observations.

Titan2D on VHub

Titan2D toolkit already installed and ready to use at https://vhub.org/tools/titan2d

New Java based Graphical User Interface as of June 6th 2011 including all latest stand-alone additional features (flux sources, material map, volume calc., etc…)

New adaptive visualization platform for displaying the different results over a 3D shaded relief Digital Elevation Model + Google Earth!!!

Titan2D tutorial on VHub Titan2D tutorial available to download at https://vhub.org/resources/761

During this tutorial, we will go through a stock example and:

(1) learn how to enter the different input parameters for running a Titan2D simulation;

(2) run the simulation and;

(3) visualize the results using the Titan2D Vhub viewer.

We will run a second simulation by changing only one parameter and investigate the effects on the simulated flow through a direct comparison of the results.

Load/Save Tab

Geographic Information System Tab

General Tab

Material Map Tab

The internal friction angle ϕint, is the steepest angle that the upper surface of a conical pile of dry sand can make with respect to the horizontal plane it is resting on.

The bed (also known as basal) friction angle, ϕbed, is the angle that a plane needs to be inclined so that a block of material will slide downslope at a constant speed.

Piles Tab

Minor extent

Major extent

Orientation angle

0°

0°Initial direction

Titan2D Pile geometry in map view:

Job submission Tab

Job monitor Tab 1

Job monitor Tab 2

Google Earth Outputs

Google Earth Outputs

Google Earth Outputs

PARAVIEW

• Using the Vhub workspace tool, download the entire Titan2d simulation folder from your Vhub storage into your computer

• Open Paraview and open the xdmf0000000000.xmf file from your Titan2d simulation folder and play with the options…

• Download and install on your computer the last version of Paraview software at http://www.paraview.org/paraview/resources/software.php

ArcGIS

• Using the Vhub workspace tool, download the ‘pileheightrecord’ file from the Titan2d simulation folder into your computer

• Open the file using a text editor and replace the file header to match the ArcInfo header format (ncols, nrows, xllcorner, yllcorner, cellsize, nodata_value). Save it with a new name and .asc file extension.

• Open ArcGIS, convert the ascii file into a raster, flip it and georeferenced it using the X and Y boundary coordinates from the original ‘pileheightrecord’ file header...

Titan2D Viewer

Titan2D Viewer

Titan2D Viewer

Titan2D Viewer

Titan2D Viewer

Questions?