model mechanical command


model mechanical <b > keyword

Primary keywords:

active    dynamic    list    time-total    slave    substep    timestep

Set parameters for a mechanical analysis. The activity can be directly specified by providing b.

active b

The mechanical process is on by default. Specify active off to suppress mechanical calculations.

dynamic b

Specify the state of dynamic model in 3DEC.


Display mechanical calculation-mode information.

time-total f

f is the accumulated mechanical time for the model. This can be reset to any value, and will continue to be accumulated during cycling after that.

slave b

Specifies that mechanical mode is to be considered a slave, and cycled to equilibrium after each master step has been taken.

substep i

Specifies the maximum number of steps the mechanical process will take when solving with slave on.


The stable timestep is calculated based on the current stiffnesses and masses of all objects in the system. This is the default setting. In a static mechanical FLAC3D analysis the timestep is arbitrary, and will be set by default to 1.0.

fix f

Set the timestep to be the fixed value f. All timestep calculations are skipped, resulting in performance enhancements. In a FLAC3D static mechanical analysis the timestep can be set to any value, and inertial masses will be scaled to ensure stability. See the section ref-Mechanical Timestep Determination for Numerical Stability <mechtimestepdetermination>- for a discussion of mass scaling. CS: common trouble

increment f

Set the incremental amount that the timestep is allowed to increase from one cycle to the next in automatic mode. By default, f = 1.05. The timestep can decrease by any amount to ensure stability.

maximum f

Set the maximum allowed timestep. By default, there is no bound to the maximum timestep.

safety-factor f

Set the timestep safety factor, or the factor that is multiplied by the stable timestep calculated when auto mode. By default, f = 1.0 in FLAC3D. If the PFC module is loaded, the default value is f = 0.8. This value is not used for static mechanical FLAC3D analysis.

scale f

Enable timestep scaling in PFC. Timestep scaling is used to reach a static configuration as quickly as possible, regardless of the stress path taken. The inertial masses of each body are scaled based on the stiffnesses, so that the stable timestep is f (or 1.0 if f is not specified). Additionally, the velocity is scaled by the ratio of the old inertial mass to the new inertial mass. In this way, all degrees of freedom have an equal time response, resulting in faster convergence but a meaningless timescale. This value is not used in FLAC3D mechanical timestep calculations.

update i

Set the number of cycles between timestep calculation in PFC or 3DEC. In PFC, by default, i = 1 (i.e., the timestep is updated every cycle). The default for 3DEC is i=100. This value is not used in FLAC3D mechanical timestep calculations.