FAQ

Question: I tried the new update, but when I try to open an old file, the following error message appears:

% Tag name _JUSTCOMPUTEDRANGE is undefined for structure IDLITVISDATASPACE.
% Execution halted at:  IDLITVISDATASPACE::GETXYZRANGE 1758
%                       _IDLITVISUALIZATION::GETXYZRANGE 1170
%                       IDLITVISNORMALIZER::COMPUTE2DPADDING  797
%                       IDLITVISNORMALIZER::ONDATACOMPLETE 1052
%                       IDLITVISNORMALIZER::SETPROPERTY  409
%                       RAMMS_GET_ID_OBJ  408
%                       RAMMS_OPENSIMULATIONNOW 1065
%                       RAMMS::CREATEROCKVIS  229
%                       RAMMS_OPENROCKOUTPUTFILE 12117
%                       RAMMS_OPENOUTPUTFILEMANYEVENT 10620
%                       IDLRTMAIN         183
%                       $MAIN$  

Can you help me?

Solution:

• close RAMMS
• remove this directory: "C:\Users\<your username>\.idl"    (if you specified Preferences in RAMMS, then you have to re-set them)
• now you should be able to start and use the new version. I strongly suggest only to use the new version (Rockfall) from now on. The speed of the handling is much improved, much easier to use RAMMS!
• if you again use the old version (Rockfall), then this problem could happen again.......

February 2^nd 2021

Problem:

I try to run a simulation, but instead of the results, I get the following error message:

Error-Messages:
% Unable to allocate memory: to make array.
Not enough space
% Execution halted at: 

What is going wrong here?

Answer:

The following issues can have an influence on the memory management of RAMMS:

• Do you use a large ortho-image that you overlay? This could be the problem here. Reduce the resolution of your ortho-image and try again.
• Calculation domain: Do you use a narrow calculation domain? If not, please have a look in the manual on how to define an ideal calculation domain (for avalanche and debris flow simulations).
• Dump Step: By increasing the dump step, you decrease the amount of memory needed to open a simulation file.
• Simulation resolution: A very good (=small) simulation resolution increases the amount of memory needed to open a simulation file.

Answer

Yes, you can make gif animations repeat. Please do the following:

• Open ‘Additional Preferences’ (button in left vertical toolbar or menu ‘Help -> Advanced… -> Additional Preferences… -> Edit’) 
• and then change the parameter GIFANIM_REPEAT_COUNT to the number of repetitions you want to have.
• Do not forget to click Save and OK.
• Create a new gif animation and import it into Powerpoint.

Answer:

Yes, you can, but this is work in progress. Please get in contact with us and we gladly help!

Answer:

Avalanches

The Voellmy model – coupled with the calibrated parameters – can be used to

• (1) predict the runout distance and
• (2) predict the maximum flow velocity of extreme, large snow avalanches.

This is one of the important research results from the Vallée de la Sionne test site. The Voellmy parameters that we recommend describe the front of a dry-snow avalanche. Because the front defines the runout distance and maximum velocity the Voellmy model will work.

However, the Voellmy model will not describe the avalanche flow behind the front, at the tail of the avalanche. Here, measurements show an increase in the friction (a rapid decrease in speed). This effect causes avalanches to elongate and eventually deposit mass. Therefore, the Voellmy model will not predict the deposition behaviour.

The Voellmy model has difficulties to predict the runout of small avalanches, which sometimes begin immediately to deposit or “to starve”. Of course, small avalanches can be modelled using higher μ and ξ values, but this is a very ad-hoc approach.

Answer:

In all RAMMS versions (Avalanche and Debrisflow) up to Version 1.5.01, an ENO (Essentially Non-Oscillatory) scheme was used to numerically solve the governing differential equations (Christen et al., 2010). However, the numerical solution was implemented on strictly orthogonal grids. This improves computational speed, but introduces numerical instabilities especially in steep terrain.
The new Version 1.6.20 uses the same second order ENO scheme, but now on general quadrilateral grid. This new scheme improves numerical stability, but slows the computational speed somewhat. The introduction of this stable ENO scheme allows us to use lower H_cutoff values minimizing mass loss during calculations. The standard value of H_cutoff is 0.000001 m.

Answer

The time required to simulate an avalanche or a debris flow is a function of the finite volume grid resolution and the size of the calculation domain. Typically we use 5m resolutions and the simulations require around 10 minutes. We usually perform the initial simulations at 10 m resolution and therefore we have results in 1 or 2 minutes. When we have a solution that we like we might take a look at the problem at 2m resolution.

Problem: My debris flow simulation takes ages to calculate. I use a 0.5m resolution. Do you have any suggestions on how to speed up my simulation? And sometimes I get this error message:

Error-Messages:
% Unable to allocate memory: to make array.
  Not enough space
% Execution halted at:  RAMMS_OPENBINARYOUTPUT 2237
%                       RAMMS_OPENOUTPUTFILE 10730
%                       RAMMS_OPENOUTPUTFILEEVENT 10590
%                       IDLRTMAIN         183
%                       $MAIN$          

Answer:

There are several important issues that affect your simulation speed and also your (RAMMS) memory management:

1. Dump Step: By increasing the dump step (when starting a simulation, e.g. 10s instead of 5s), you decrease the amount of memory needed to open a simulation file.
2. Calculation domain: Do you use a narrow calculation domain? If not, please have a look in the manual (section 3.5.4) on how to define an ideal calculation domain.
3. Simulation resolution: A very good (=small) simulation resolution increases the amount of memory needed to open a simulation file.
4. Do you use a large ortho-image that you overlay? This could also be a memory problem. Reduce the resolution of your ortho-image (do not forget to change the .tfw file too) and try again.

Answer: Erosion is explained in this article.

Answer:

Debris flow

The “best” constitutive model for debris flows is still a very open question in the scientific community. We recommend using the Voellmy model until a better model is found. Voellmy basically has only two parameters and after some calibration a useful solution can usually be found. With Voellmy one can control the flow velocity (parameter xi) and runout distance (mu).

One reason Voellmy is useful is that it only requires two parameters to calibrate. The turbulent term dominates the frictional behavior when the flow is moving rapidly and the Coulomb term is dominant when the flow is moving slowly, allowing the model to be approximately calibrated to observations of flow velocity and the stopping location of the flow front.

Finding the “right” debris flow model is more difficult than finding the “right” snow avalanche model because debris flows are two component systems (fluid, solid). Much of the behaviour of a debris flow — including the stopping process — involves the interaction between the fluid-solid components. Thus, without a two component model, it will be unlikely that we are able to model all aspects of debris flows. The Voellmy model mixes the two components and therefore models the debris flow when the components volumes are constant and well mixed. This assumes, of course, that the relative portions of solid and fluid remain the same, from head to tail of the event. This is hardly true

Answer:

There a several good reasons.

Firstly, hazard mitigation experts are often interested in the flow behaviour only near the fan. Calculating the movement of the debris flow in the torrent is a time consuming and often useless task. Therefore using a hydrograph can often cut calculation times dramatically.

Another reason is that it is impossible to describe the initial conditions of debris flows as a "block release". There are cases where block release is a good approximation of reality (e.g. dam breaks), but, in general, it does not accurately reflect the starting conditions of flows from intense precipitation.

Read this publication for more information on this issue:
Deubelbeiss, Y.; Graf, C., 2013: Two different starting conditions in numerical debris-flow models – case study at Dorfbach, Randa (Valais, Switzerland)