how to model anti-vibration supports in CesarII to avoid vibration in dynamic modal analysis

i modeled support as a rest+holddown having 0.4 friction.

the problem is in dynamic analysis. That pipe has modal vibration <4Hz also if there is an antivibration support because dynamic doesn't know it is an antivibration support.

how can i solve the vibration "false" vibration in modal dynamic analysis?

have i to insert a virtual dampener in dynamic table to stop vibration?

note: rods are tightened by hand to stop vibrations

Use snubbers. You can add these to the model in the "dynamic input". After you have a successful solution, you can decide if you really want snubbers, or if the load is small enough perhaps "static restraints".

Of course, if you decide on "static restraints", the static analysis must be re-evaluated.

how can i insert snubbers so that they will not be shown in reports? they are virtual snubbers, they really don't exist...

If you add a snubber, it really exists. What I meant above is that if the dynamic load on the snubber is small, perhaps you can use a hard (static) restraint instead of the snubber. Naturally a hard restraint may affect the Expansion load case, which is why I said the static analysis must be reperformed.

It will be difficult to model in Caesar an antivibration support. Actually these supports have some disk springs that need to be tighten, not by hand but by wrench. This way it will not allow for vibration in vertical plan and in less amount also in the horizontal plan. It will create a grip that oppose the movement and also vibration. The Pulsation study can estimate the dynamic forces that appear at the location. If friction is bigger that the dynamic force then ok, if not then you have to place a real restraint. So this will be an iterative process. And you do not have very much control on this. The only thing you can do is to physically place rigid restraints at smaller distance in order to achieve the desired frequency. The best solution is to give the task to the manufacturer as they have all the means to solve the problem.
You can try to see if applying a force downward at the support location it will increase the frequency. I think that on your Supports Standard the value of torque should be specified.

here are some ideas
https://www.betamachinery.com/knowledge-center/pipe-stress-webinar-faq

a technical paper is available here:
https://www.betamachinery.com/knowledge-center/anti-vibration-clamp-design-guide