I am currently working on a piping system which contains one PSV valve. I have a question with regards to my results in Dynamic module. I have the reaction force and i know the opening time so I can easily extract the frequency/force spectrum of the PSV valve. I checked the spectrum and I figured out that the frequencies in which the DLF is between 2 to almost 1, are not even in the proximity of the natural frequencies of the system in the vicinity of the PSV valve.(and the valve itself) knowing this, is it really necessary to go on with this calculation or just a simple static analysis would do it?
my other question is, I had to set my frequency cut off to 5000 in order to reduce the added force percentage to almost zero. it seems a bit insane. could anyone explain why this is happening? ( the mass included however remains approximately on 90%)

regards

When you say "in the vicinity of the PSV" I trust you are refering to vicinity as in frequency rather than vicinity as in location. Modal response is not necessarily excited through a load applied at a location of high modal deflection. Your (load) participation factor is an indicator of the mpodal response to that particular load location.

Yes, it sounds like your system is responding as a rigid body so a static load should suffice. Apparently, your valve has a hard Y support under the branch connection? If so, your DLF (if any) can be calculated using the approach in B31.3 Appx. II. Or, you can find the CAESAR II mode of vibration that shows the PSV wagging back and forth and use that frequency to pick your DLF from the spectrum generated by CAESAR II.

That 90% rule falls apart when you have rigid response. Let's say you have a beam anchored at one end and you put an axial dynamic load at the other. You'll have to run out to an axial mode of vibration to get any mass participation. But the system is responding in a rigid fashion and a static load is appropriate; there is no dynamic amplification in structural response.

Dave,

thanks for your explanation. I did not know anything about 90% "rule" of the included mass. I would think the estimations and boundary limits were ok as long as the added force was less than 10% or so. could you explain it as well.

thanks