[bigphil]

To publicly answer a question I received via email:

Question
In the tutorial solids/elastoplasticity/impactBar, there are the following fields:

• D Displacement Vector
• D_0 ?
• DD ?
• DD_0 ?
• DD_0_0 ?
• DD_0_0_0 ?

What are all of them?

Answer

The suffix '_0' on a file/field name indicates it is an old-time field i.e. D is the displacement field at time 0 and D_0 is the displacement at the previous time-step (if it existed) assuming the current time-step size.

To set an initial velocity (or acceleration), you should appropriately set D, D_0 and D_0_0 assuming a three time-level d2dt2 time discretisation (e.g. Euler) for and also D_0_0_0 if using a four-level d2dt2 time discretisation (e.g. backward).
You can set these fields using setFields.

If the chosen solidModel solves for DD (increment of displacement) as opposed to D (total displacement) then you would need to also set DD_0, DD_0_0 (and DD_0_0_0 for a four-level time discretisation). Note: for a constant initial velocity then all the increment fields will have the same value. Note 2: DD = D - D_0 i.e. the increment of displacement is the total displacement minus the old total displacement.

Philip