Hi everybody, I am studying the use of snubbers, I read the manuals and forum posts, I need some clarification about the use of dynamic simulation, when and where the dynamic choice is imperative? when can we choose a static simulation obtaining very similar results? I know the question is very general but I need some expert consideration on this topic or some case study. Many thanks

If the overall response of the system is dominated by a single mode of vibration, then you can typically get good results from a "static-equivalent" analysis. The problem with this statement is that unless you perform a dynamic analysis, you won't know if the overall response of the system is dominated by a single mode of vibration.

Is it correct that to know modes of vibration of a system I have to do a modal analysis?
I didn't study it yet, so I don't know, maybe in the next time I will ask here about it.
What kind of simulation I have to do to simulate a compressor nozzle?

Hai ferex,

Most probably u choose Time history analysis.

Yes.


Dynamic analysis is driven by the type of loading more so than the object (compressor nozzle) under study. What is your dynamic event?

As far ASCE 7-05 is concerned if the fundamental frequency is >16Hz , the system can be considered rigid ie there will not be any "dynamic amplification". By "dynamic amplification "we mean the response parameters ( acceleration, displacement, velocity) will be more than than when a static loading ( loading applied slowly) is applied.

A STATIC EQUIVAlENT analysis is basically use of factors to multipliply the static loads to simulate the dynamic effect.It has got its limitations, particularly if higher order modes have significant contribution, although generally this is a conservative method.

In terms of seismic analysis as per ASCE-7-05 use of ap factor takes care of the dynamic amplification ( typiclly this is a ratio between peak response acceleration and ZPA or "rigid response")and the factor {1+2zh) is used to simulate the "floor response spectrum" effect.Values prescribed are conservative values, although they may be unconservative when "sopporting" and "supported"structures have same fundamental frequencies.

Dynamic load factor or dynamic amplification factor is a function of the system natural frequencies and the Force vs time form of the apPlied loading.

To go more in depth into this subject, read the following three books:

1) Dynamics of structures by Clough and Penzien.

2) Structural dynamics by Anil K Chopra.

3) Seismic deisgn using structural dynamics publised by International code council ( you can get this from SK Ghosh associates, IL, USA)


Regards