Hi,

in my latest time history analysis for a piping system subjected to surge, I noticed the "% force added" values in the 'included mass report' for some of the (force-time) spectrums have been presented with negative figures (e.g. -25%). these spectrums are acting on the pipe segments where there is an axial restriction.
I wonder to know how one should interpret that?
I am aware that the axial force spectrum acting on an axially restricted pipe segment may lead to DLF close to one (high system frequency- rigid criteria), I expected to receive highly active forces with a large amount of missing mass but, I did not expect to see negative values!

many thanks in advance,