Shear Wave On Stiff Wall In Soft Soil: Dynamic Multi-Stepping


To view this project in FLAC3D, use the menu command Help ‣ Examples…. Choose “Dynamic/ ShearWaveOnStiffWallInSoftSoil” and select “ShearWaveOnStiffWallInSoftSoil. f3prj” to load. The main data file is shown at the end of this example. The remaining data files can be found in the project.

This small and simple example illustrates the effect of dynamic multi-stepping. The model consists of a “wall” of material with a modulus 150 times greater than the surrounding material. A shear wave is applied at the base of the model for a 1 s time period.

With zone dynamic multi-step on, 340 zones have a multiplier of 1, and 2660 zones have a multiplier of 8. The calculation is three times faster with dynamic multi-stepping on a 6-core CPU. The \(x\)-velocity histories monitored at the base of the model and top of the wall are identical with and without multi-stepping. Figure 1 plots the histories for the multi-stepping run.

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Figure 1: x-velocities at model base and top of wall.

Data File


model large-strain off
;              Dynamic Example 
;              Shear wave applied to a stiff wall in a soft soil
;              With dynamic multistep
model title ...
      'Shear wave applied to a stiff wall in a soft soil with dyn. multistep'
model configure dynamic
; Create zones
zone create brick size 80 20 40 ...
                  point 0 (-5,0,0) point 1 (15,0,0) ...
                  point 2 (-5,5,0) point 3 (-5,0,10)
zone face skin ; Label model boundaries
; Assign model and properties
zone cmodel assign elastic
zone cmodel assign null range position-x=-5,5 position-z=5,10
zone property young 20e4 poisson 0.2 density 2000
zone property young 30e6 range position-x=5,6 position-z=5,10
; Boundary conditions
zone face apply velocity-z 0 range group 'East' or 'West'
zone face apply velocity-normal 0 range group 'North' or 'South'
fish define wave
    wave = math.sin(math.pi * / 16.0)
zone face apply velocity-x = 1 fish wave range group 'Bottom'
zone face apply velocity-normal 0         range group 'Bottom'
; Histories
zone history name='xvelb' velocity-x position (5,2, 0)
zone history name='xvelt' velocity-x position (5,2,10)
zone history name='zvelt' velocity-z position (5,2,10)
model history name='time' dynamic time-total
; Set multi-step status, and cycle to 32, timing how long that takes
zone dynamic multi-step [multi]
[global start = time.clock] 
model solve time-total 32.0
[global time = 0.01 * (time.clock - start)]