Issues with initial velocity

Feature Requests
1

Hi,

there are some bugs and limitations regarding the initial velocity condition, maybe they could be fixed for the next version:

  1. After selecting the part in the Part name mode, confirming and going back to the initial condition, it shows the following error message:

error

Part is set to Missing and needs to be reselected.

  1. There’s no option to select the node set for the initial velocity (even though there is such an option for the initial temperature). It would be useful in general but also for the workaround that has to be used in the case of 2D analyses - initial velocity doesn’t work there unless a dummy node-type surface is defined based on the node set used for the initial velocity condition: Can't get simple explicit dynamics impact analysis to work - #5 by Calc_em - CalculiX (official versions are on www.calculix.de, the official GitHub repository is at https://github.com/Dhondtguido/CalculiX).

  2. There’s no option to assign velocity to a reference point. This should also include rotational velocity: Simulation of rolling - #2 by FEAnalyst

2

I have fixed this bug.

  1. Looking at the code, I found out that I decided to make the InitialVelocity an element-based entry while the initial temperature is a node-based entry. Why did I decide like this? At the time, I think I could relate more to velocity being defined based on elements in order not to deform elements if different velocities are used for each node. I see this was probably a wrong decision since the keyword is node-based. So the problem is, if I change this definition, we will lose the compatibility to open older files containing Initial velocity items in the FE model tree. I am ready to make this sacrifice since not many users are using it.

  2. Adding support for a reference point will definitely require switching from element to node-based definition. Will adding additional fields in the initial velocity entry suffice, or should we have an additional entry called Initial angular velocity? The same was done for concentrated force and moment loads. This option makes more sense in the case of rotational velocity and a reference point since probably a rotation node of the reference point should have a rotational velocity assigned.

3

Great, thank you for resolving this issue. Initial velocity should indeed be a node-based entry.

Both would be fine, it’s hard to say which is better. You are right - rotational velocity has to be applied to the ROT node. One disadvantage of a separate initial rotational velocity feature would be if you wanted to assign translational and rotational velocity to a ref point at the same time - then you would have to use two separate features. But it’s not a common use case. Another benefit of the approach with additional fields is that it follows the displacement boundary condition style. However, there can be more advantages of the approach with an additional feature when it comes to the internals - implementation and CalculiX handling (e.g. situations when any initial rotational velocity is assigned to something else than a ref point).

Here’s what it looks like in Abaqus:

initial rotational vel

4

Rotational would be awsome to set up Impact test pendulums !

5

I changed the category to Feature Requests because the bug is fixed and only the two FRs are left:

  • selecting node sets for initial velocity (useful in general but also for a particular workaround needed in 2D)
  • selecting reference points for initial velocity and defining rotational velocity (from what I’ve seen on the forum, quite a few users would appreciate that, me too, of course)