This is probably if the other end of the spring element is not connected to a real element with mass (bar, shell, solid) as it takes its mass from that.
If this is connected just to a grounding point which is constrained or to an RBE2 (which is not a nodal rigid body FULLRIG), then you can add a dummy mass point (CONM2) to that node.
Hi Doug, thanks for the info, I managed to fix it. Although I am now having a slightly different issue and I think it is to do with my boundary conditions. I have an assembly which mounted on some vibration mounts, which I've modelled as Springs. A velocity-time input is then applied on the end nodes of the springs. When looking at the results, the whole model just slowly moves in the downwards direction, although the initial pulse is positive. Do I need to ground the springs or something similar to get it to work?
I assume you have gravity which is causing the downwards drop? I can only suggest to look at the spring stiffness to see if this is too low and absorbs the pulse. If you can send the model to me to have a look or make a small test version that does the same (spring with pulse connected to block with similar system mass?)
I do have gravity on, which is causing the dropping. The setup is effectively a mass held between two springs (one above, one below). I need to apply the velocity input below mount and so only at the bottom node of the spring element. I did manage to get it to work when I applied the velocity at both the 'free' ends of each spring, but that isn't quite what I want it to do.
Do you have an output for the 1D elements as well? I think this should show if they are just being deformed by the mass on one side and not transferring the pulse through. Since it works if you pulse both sides of the spring makes me think the stiffness is too low and that the pulse is correct as this works on its own. I've modified the workshop example with springs with end node having an initial velocity defined
