Damping of the underground

The ROFMOD damping value is a measure of the ability of the ground to deform and allow the block to penetrate. The higher the damping value, the deeper the block penetrates into the ground and the more energy it loses during ground contact.

ROFMOD calculates various sub-steps for ground contact, in which damping is a decisive factor:

Depending on the impact velocity, the block mass and the damping, the depth and extent of an impact crater is calculated. The energy portion directed perpendicular to the terrain surface is converted into deformation work and is thus destroyed. Parts of the energy component parallel to the slope are lost through abrasion of the subsurface (see partial processes in figure).

The impact crater forms an obstacle for the fall block with regard to its direction of movement parallel to the slope and is consequently compacted on the valley side to form a bounce ramp. The direction of the potential further trajectory is calculated with the calculated buildup/degradation of the rotational energy, the remaining total energy and the geometry of the jump ramp.

The damping value is an empirical value which can vary from 10 (extremely hard) to 50 (non load-bearing).

The following table describes the damping values with underground types. Intermediate values can be defined.

Damping	Class	Description
10	extremely hard	bedrock
15	very hard	very hard surface (weathered rock)
20	hard	shallow, firm soil or loose material / talus material, large boulders
25	medium-hard	dry, medium-deep soil or loose material / talus material, scree
30	medium-soft	moist, medium-deep soil or loose material / talus material, scree
35	soft	wet, deep soil
40	very soft	very wet, deep soil
45	extremely soft	swamp
50	not load-bearing	water area / swamp

Important notes:

The damping value must be carefully defined especially for terrain sections with block debris:

Here the size ratio of the fall block to the block debris elements is decisive. If the fall block is significantly larger than the block debris elements, the above damping values can be used, but if a stone (small block) hits large block debris, it acts as a very hard rock surface and a significantly lower damping value must be used.

It should also be noted that during program development the models were calibrated with the above damping values and fall blocks with a maximum axis length of up to about 3 m. Therefore the input of the block axes is checked and limited in ROFMOD 5.0.