Vibration Profile Question
Vibration Profile Question
(OP)
Hi...sorry for cross posting but I was advised that this section may be also help.
Can anyone help to explain a profile in Mil-STd-810.
The profile is shown in Fig 514.5C-9.
It's a vibration profile for propellor aircraft.
L0 is the g2/hz value for the first prop frequency. The profile rolls off at 6db/octave. How do I work out the g2/hz for the other frequencies (harmonics)?
f1 is twice f0 so that's an octave. Does this mean the g2/hz at f1 is L0/2 or is it L0/4 - is the g2/hz rolling off at 6db/octave or is the g rolling off at this rate and therefore g2/hz is a factor of 4 per octave lower?
Can anyone help to explain a profile in Mil-STd-810.
The profile is shown in Fig 514.5C-9.
It's a vibration profile for propellor aircraft.
L0 is the g2/hz value for the first prop frequency. The profile rolls off at 6db/octave. How do I work out the g2/hz for the other frequencies (harmonics)?
f1 is twice f0 so that's an octave. Does this mean the g2/hz at f1 is L0/2 or is it L0/4 - is the g2/hz rolling off at 6db/octave or is the g rolling off at this rate and therefore g2/hz is a factor of 4 per octave lower?





RE: Vibration Profile Question
Since I was talking about PSD then I'm almost certain that a 6dB drop is a quarter of the PSD.
RE: Vibration Profile Question
(f2/f1)=2^n
then
octaves = n=(10^(f2/f2))*log(2)
and
Db = 20*log(w2/w1)
Where "log" denotes to the base 10
The slope of -6 is in Db/octave
Divide Decibels (Db) by Octave and equate it to -6 then solve for the unknown amplitude
Since this is a log-log scale the slopes that look linear are not, they are curved, so you cannot use straight trigonometry
The plot shows that the band is between 15 and 2000 Hz.
Regards
Dave
RE: Vibration Profile Question
I thought n=(log(f2/f1))/log(2)
and since we are talking PSD (power) then
dB=10*log(w2/w1)
????
RE: Vibration Profile Question
Sorry
Regards
Dave