Good Evening,

I am having some issues with dynamic stability... I have a horizontal run that goes through a wall penetration then turns upwards through a LR elbow.

After my wall penetration I have a structural angle that is going to provide lateral restraint and hold the weight of the vertical pipe.

Once the pipe goes vertical I have two more structural angles that protrude from the building exterior and using a U bolt will restrain lateral movements.

So, when the first vertical support is 2'-8" away from the centerline of the horizontal support everything works out. When I lower that vertical support by 1', I get the rigid body error. Is there any way I can add a some artificial friction or snubbing to nudge the solver forward.

Unfortunately I have to move this support down...

Thank you in advance.

I'm not sure what you mean by dynamic stability.
Simply moving a node/support should not cause a problem.
Do you have nodes added between supports? Mass at your rigid restraints (in the direction of the rigid restraints) will not contribute to the response. Perhaps that is the cause.
For a better diagnosis, more information is required from you.

I think what he's trying to say is that CAESAR has popped up the error message explaining that his model is not adequately restrained and is experiencing rigid body motion.

I've only come across the error message when I know that the system shouldn't be suffering from rigid body motion, and I've never been able to reproduce the issue when the system I construct definitely should be undergoing rigid body motion.

In recent recollection, one such example included two vessels and almost nothing but spring supports in between, with really heavy wall pipe.

But to this example, you may try looking at your structural supports. If it's unlikely that your pipe will free rotate, you could plug in RX,RY,RZ to see if it makes the error go away. If your new rotational stop results in insignificant moments, then you needn't worry about it. If significant, then you may need to investigate new support schemes.

However, if this doesn't fix the problem, or I went in a completely wrong direction, help us help you by uploading some screenshots, CAESAR II file, etc.

1. Click "Switch to Full Reply Screen" Button.
2. Click "File Manager"
3. "Choose File" -> select file "Add File"
4. Repeat 3 as needed.
5. "Done adding Files"