| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Feb. 2017 11.00.00.22 |
Problem:
Support span suggestions to avoid piping vibration due to Harmonic load case in AutoPIPE ?
Solution:
The following are span suggestion to avoid resonance from compressor acoustic vibration. Typically for low speed motors e.g. 300rpm use multiplier 2.4 up to 4.0, i.e. 5hz x 2.4 = 12hz. High speed compressors e.g. 1800rpm use multiplier 1.4, i.e. 30hz x 1.4 = 42hz.
Then calculate pipe span based on this fundamental frequency (1st mode) for both fixed and simply supported ends. A typical pipe behaves somewhere between these two boundary conditions. Ref Roark Table 36 case 1b, 2b
fn = Kn/2/pi *SQRT (Eig/w/L^4)
hence Span (L) = E.I.Kn2/W/f12
where :
W = weight /unit length (kg/mm)
I = moment of inertia (mm4)
f1 = frequency (Hz)
E = Youngs Modulus (Mpa)
kn = 3.55 (Fixed Ends), 1.57 (simply supported)