Joining Two Liner Elements with Deformable Links

FLAC3D
1

I’m currently working on a problem modelling an interface (e.g. waterproofing layer) between primary and secondary tunnel linings modelled using liner elements. the modelling process i’ve tried is as follows:

  1. create primary lining on the tunnel surface using ‘structure liner create by-zone-face’ command. the primary liner has structural links on side-1 attached to zones on the ground side while side-2 has no structural links on the air side

  2. create secondary lining on the tunnel surface using ‘structure liner create by-zone-face’ command. the secondary liner is in the same position in the primary liner and has structural links on side-1 attached to zones on the ground side while side-2 has no structural links on the air side

  3. ‘structure link delete range group ‘secondary-lining’ to remove all secondary lining structural links

  4. create node-to-node structural links between primary and secondary lining using ‘structure node join side 2 range group ‘primary-lining’. the structural links are created on side 2 of the primary lining with rigid attach condition on all 6 DOF. the structural links on side-1 of the primary lining remains attached to the zones on ground side

  5. change the structural links to deformable using the following example:

structure link attach x linear range group ‘primary-permanent-lining-interface’
structure link attach y linear range group ‘primary-permanent-lining-interface’
structure link attach z linear range group ‘primary-permanent-lining-interface’
structure link attach rotation-x free range group ‘primary-permanent-lining-interface’
structure link attach rotation-y free range group ‘primary-permanent-lining-interface’
structure link attach rotation-z free range group ‘primary-permanent-lining-interface’
structure link property x stiffness 0.5 range group ‘primary-permanent-lining-interface’
structure link property y stiffness 0.5 range group ‘primary-permanent-lining-interface’
structure link property z stiffness 0.5 range group ‘primary-permanent-lining-interface’

Some questions about the above model:

  • in the itasca documentation it mentions that properties of deformable links are set automatically during a geometry update and properties that have been manually set may be overridden. if the properties of the deformable links are manually set then a fish callback would need to be implemented to maintain the link properties during model cycling? if so, at what point in the cycle sequence should the fish callback be executed? program list command — Itasca Software 9.5 documentation
  • is my understanding correct that the structural links derive their properties from the liner element they are connected i.e. spring stiffness of the link is adopted from the coupling-stiffness-normal and coupling-stiffness-shear properties of the liner element, cohesion and friction from coupling-cohesion-shear, coupling-friction-shear. the structural link properties are factored by the ‘structure link property stiffness/cohesion/friction factors provided e.g. if coupling-stiffness-normal is 10e6 then ‘structure link property stiffness 0.5’ would give spring stiffness 5e6?
2
  • If a link is reset, all properties are removed. We can re-assign its properties via commands (no need through FISH-CALL for your case).
  • For your case, since the original liner links were removed and reset to new linear links, all those original properties (coupling-stiffness-normal, coupling-stiffness-shear, cohesion, friction, et al) are removed. We just need to assign the new properties for these new linear links.
  • if you really wish to use FISH-CALL for structure property control , the sequence between -10 and 0 (e.g., -1) would be ok.
  • Refer to Fig 3 & 4 in the doc for liner: sigma_n of the x-axis in Fig 4(b) is from the y-axis of Fig 3.