Post on 25-Dec-2015
Dynamic Analysis of
Fan Foundation
Mahendra Madhavan
Potential Power Plant Problems Requiring Dynamic Analysis
• Machinery Vibration
• Piping Vibration
• Heavy-load drops
• Tornado missile impact
• Dry cask accidents
Need for Vibration Analysis• Meet the vendor’s performance criteria
• Industry guidelines or SCS standards
• Operation / Maintenance
• Vibration not generated or transmitted to other areas
• Foundation is free from structural resonance
• Vibration not annoying to people
Four basic components of Vibration
• Mass (m)
• Stiffness (k)
• Damping (c)
• Forcing Function (F)
Equation of motion)(tFxkxcxm
xmamF 1
xcvcF 2
xkF 3
How to quantify vibration components?
• Mass from Machine and Foundation drawings
• Stiffness and Damping from DYNA5 (pile-soil interaction)
• Force from vendor or make an estimate
F
• Mat foundation (Soil supported)
• Pile / Caisson foundations
Fan Foundation
• Modal Analysis
• Response Analysis
Types of Analysis
Forced vibration of a damped system
ω: Operating frequencyωn: Natural frequency
τ : Damping ratio
m: Mass of the system
k: Stiffness of the system DAF : Dynamic Amplification Factor
Stiffness (k) Mass (m)Damping (c)
m
kn
DAF
• Natural freq away from ± 20% of operating freq
• Bearing Housing disp ≤ 0.125 mils pk-pk for 1 oz of wheel unbalance at outer radius (Sensitivity check)
• Shaft velocity ≤ 0.1 in/sec (balancing grade)
• Dynamic stiffness of the foundation should be ≥ 11.987 x 106 lb/in per support.
Vibration Acceptance Criteria (Commonly used) (Vendor’s requirement and SCS Standards)
MODAL ANALYSIS
RESPONSE ANALYSIS
Wheel unbalance (Sensitivity check)
F = m e ω2
in
slbxm
2
386
1
16
1
m = 1 oz.
1 oz of wheel
unbalance
e=50 in
ω = 2 π f
f = 900 rpm
Hz1560
900
F = 72 lb
The resulting displacement measured at Bearing Housing ≤ 0.125 mils pk-pk
Peak to Peak
How to Prevent Vibration? • Trial sizing criteria
• Single or two degree of freedom models
• Detailed analysis using GTStrudl and Dyna5
• GTStrudl for modal analysis and estimating the natural frequency
• Dyna5 is used to estimate soil-structure spring stiffness and damping
Trial sizing criteria
Foundation Plan
Foundation/Soil Links to GTSTRUDL Combined Model
XY
ZInches Pounds
Foundation/Soil Members in GTSTRUDL Combined Model
X
Y
Z
Foundation/Soil Dynamic Properties
X
Y
Z
6 Members = 6 DOF’s for stiffness and damping
Vibration Modes • Longitudinal Sliding (Translation in X)
• Vertical (Translation in Y)
• Lateral Sliding (Translation in Z)
• Rocking (Rotation about X)
• Yawing (Rotation about Y)
• Pitching (Rotation about Z)
X
Y
Z
TYPICAL MODES
OF CONCERN
Isometric view
X
Y
Z
Longitudinal Sliding(X Translation)
X
Y
Z
Vertical(Y Translation)
Y
ZX
Lateral Sliding(Z Translation)
Z
X
Y
Rocking(X Rotation)
X
Y
Z
Yawing(Y Rotation)
X
Y
Z
Pitching(Z Rotation)
X
Y
Z
Recent Analyses • Wansley 1 and 2 (Rock Foundation )
– Single DOF, Using Hand calc
• Bowen 3 and 4 (Pile Foundation over rock) – GTStrudl and Static pile stiffness
• Bowen 1 and 2 (Pile Foundation over rock) – changing soil properties (density, shear waves, poisson etc.)
– GTStrudl and DYNA5
Vibration Testing
• In-situ testing to measure vibration for acceptance
• Use In-situ testing results to validate the math model
Thank you
Questions ?