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Analysis Method

In the Project Settings dialog, you can choose one of the following analysis methods for rockfall simulation:

  • Lumped Mass
  • Rigid Body

The Lumped Mass and Rigid Body analysis options use different analysis engines within the RocFall3 program.

Lumped Mass Approach

In the Lumped Mass approach:

  • Each rock is modelled as a very small spherical particle.
  • The rocks are not considered to have any size, only mass (used to calculate the kinetic energy for graphs and results).

The Lumped Mass approach is detailed in the RocFall3 Theory document. The Lumped Mass engine uses a particle analysis with three sections: the particle algorithm, the projectile algorithm, and the sliding algorithm.

The particle algorithm makes sure that the simulation parameters are valid, sets up the initial conditions, and starts the projectile algorithm. The projectile algorithm is used to calculate the movement of the rock while it is in the air. The sliding algorithm is used to calculate the movement of the rock while it is in contact with the slope.

CONSIDER ROTATIONAL VELOCITY

This option is only applicable for the Lump Mass analysis method and allows you to simulate the effect of rotational velocity on point mass rocks. If the check box (found in Project Settings - General tab) is turned off, rotational velocity will not be considered.

For Rigid Body analysis rotational velocity is always considered.

Rigid Body Approach

In the Rigid Body Approach:

  • The shape of the rocks is accounted for by selecting from a wide variety of pre-defined shapes and custom polyhedra in the RocFall3 Rock Type Library dialog.

The rigid body approach used in RocFall3 is detailed in the RocFall3 Theory document.

The Rigid Body approach considers the impulse reaction of the rock during the instantaneous contact period. The normal and tangential coefficients of restitution are used to calculate the outgoing velocities. From the change in velocity, the impulses at the contact point can be calculated and then the outgoing rotational velocities.

Comparison of Lumped Mass vs. Rigid Body Methods

The Lumped Mass and Rigid Body analysis options use completely separate analysis engines within RocFall3. A comparison of the main features of each method is summarized in the table below. For a comparison that shows that the two methods can give equivalent results if the rock shape is modelled as a very small sphere, see the RocFall3 Verification document.

Lumped MassRigid Body
RockModelled as a particleSpheres
Normal coefficient of restitutionVelocity basedVelocity based
Tangential coefficient of restitution (Rt)UsedVelocity based
Dynamic frictionEnter as an angle. Applied when rock is sliding.n/a
Rolling frictionNot used.n/a
Special OptionsConsider rotational velocity


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