Dynamic Analysis

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Dynamic Analysis of Induced Draft Fan
Foundations
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Plant Bowen
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Plant Bowen
Two SCR boxes per unit
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Plant Bowen
SCR (Selective Catalytic Reduction) an
environmental control system that will reduce
Nox emissions approx. 85.
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SCR Box -- GTSTRUDL Model
Each SCR box fully loaded 2.7 million lbs.
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Plant Bowen
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I.D. Fans
Four I.D. fans per unit replaced. SCR system
requires fan output be increased to handle
additional pressure drop.
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Combined Dynamic System
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Fan Information

• Operating Speed 866 RPM
• Total Weight 210.3 kips (Weight of rotor
  66.3 kips)
• Rotor length 264, wheel diameter 147

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GTSTRUDL Rotor Model
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Rotor Support Members
Members for Stiffness Matrices

• Bearing Oil Film
• Bearing Housing
• Pedestal

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Oil Film Stiffness Matrix
MEMBER PROPERTIES STIFFNESS INBOARD BRG OIL
FILM STIFFNESS (fixed bearing) AT 900 RPM 18
MATRIX COLUMNS 1 2 3 4 5 6 ROW 1 31.66E6 ROW 2 0
10E6 ROW 3 0 0 7.56E6 ROW 4 0 0 0 0 ROW 5 0 0 0 0
10E8 ROW 6 0 0 0 0 0 10E8 OUTBOARD BRG OIL
FILM STIFFNESS (free bearing) AT 900 RPM 19
MATRIX COLUMNS 1 2 3 4 5 6 ROW 1 29.11E6 ROW 2 0
0 ROW 3 0 0 7.37E6 ROW 4 0 0 0 0 ROW 5 0 0 0 0
10E1 ROW 6 0 0 0 0 0 10E8
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Fan Vendor Information

• Shaft critical speed
• Design resonance speed
• Reqd foundation stiffness to achieve
  resonant speed ratio 9 E 106 lb/in
• Calcd response with fdn stiffns 9 E 106 lb/in
  
• 1 oz imbalance at 70 rad. 0.32 mils pk-pk at
  866 RPM
• 1000 oz-in imbalance (G2.5) 2.2 mils pk-pk at
  866 RPM

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GTSTRUDL rotor model adjusted to achieve the
results provided by the vendor.This provides
good correlated model of the rotor to combine
with the foundation for analyzing the whole
system.
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GTSTRUDL Rotor Model
SIN Forcing Fnct
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AMPL 9.321E01
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FREQ 1.443E01
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PHAS 0.000E00
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• Transient Analysis

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Combined Dynamic System
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Foundation/Soil Interaction Program

• Input
• Soil properties
• Foundation / Pile Properties
• Frequencies
• Output
• For each of 6 DOFs and for each frequency
• Damping and Stiffness Properties

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Soil PropertiesSilty clays to clayey silts
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Caisson Input

• Locations (considers pile interaction)
• Static loading
• Material properties (concrete)
• Cross-section properties
• Length
• Fixity

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Foundation Plan
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Frequencies Requested

• Operating Speed Range 339 to 866 rpm
• Soil / foundation output generated for
  frequencies every 0.5 hz over speed range.

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Foundation Plan
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Foundation/Soil Links to GTSTRUDL Combined Model
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Foundation/Soil Members in GTSTRUDL Combined Model
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Foundation/Soil Dynamic Properties
6 Members 6 DOFs for stiffness and damping
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Foundation/Soil Program Output
Freq 866.00 MEMBER PROPERTIES STIFFNESS 6000
MATRIX COLUMNS 1 ROW 1 0.1596E09 CONSTANTS M
ODAL DAMPING PROPORTIONAL TO STIFFNESS 0.032
MEM 6000 MEMBER PROPERTIES STIFFNESS 6005
MATRIX COLUMNS 2 6 ROW 6 -0.1471E10
0.2414E14 CONSTANTS MODAL DAMPING PROPORTIONAL
TO STIFFNESS 0.062 MEM 6005
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Foundation/Soil Stiffness Matrices
UNITS POUNDS INCHES RADIANS MEMBER PROPERTIES
STIFFNESS 6000 MATRIX COLUMNS 1 ROW 1
0.1596E09 MEMBER PROPERTIES STIFFNESS 6005
MATRIX COLUMNS 2 6 ROW 6 -0.1471E10
0.2414E14
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Combined Dynamic System
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Foundation
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Foundation dimensions 16 high, 58 long, 32
to 17 wide
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GTSTRUDL Combined Model Concrete Foundation
IPSL Elements
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Additional Equipment Mass Inertia of Joints
Weight
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Damping

• Rotor model
• Damping matrix values provided by vendor
• Concrete foundation steel pedestals
• Modal damping proportional to stiffness
• Foundation/Soil interaction
• Modal damping proportional to stiffness

Cannot specify damping factors using both methods
of input.
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Damping Input and Analysis
Convert all damping values to matrix input
Or...
Convert all damping values to modal damping
ratios (unable to successfully convert the oil
film damping values without losing accuracy).
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Concrete Foundation Fan Equipment Damping
Concrete 1 damping and steel 2 damping
insignificant compared to oil film and soils
damping.
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Rotor Oil Film Damping
A damping matrix for the oil film was created
for fan speeds (20 to 100 oper. speed) Fixed
bearing Free bearing
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Foundation/Soil Program Output
MODAL DAMPING PROPORTIONAL TO STIFFNESS 0.046 MEM
6000 MODAL DAMPING PROPORTIONAL TO STIFFNESS
0.200 MEM 6001 MODAL DAMPING PROPORTIONAL TO
STIFFNESS 0.200 MEM 6002 MODAL DAMPING
PROPORTIONAL TO STIFFNESS 0.200 MEM 6003 MODAL
DAMPING PROPORTIONAL TO STIFFNESS 0.094 MEM
6004 MODAL DAMPING PROPORTIONAL TO STIFFNESS
0.088 MEM 6005
Convert modal damping to damping matrix input
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Damping Matrix Input
UNITS POUNDS INCHES RADIANS CONSTANTS MATRIX
DAMPING SYMMETRIC Freq 866.00 ROW
1 0.0 ROW 2 0.0 ROW 3 0.0 ROW 13 0.0 ROW
14 4.33E05 (rotor) ROW 15 6.56E04
(rotor) ROW 16 0.0
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Which Correspondence Table ???

• PRINT DYNAMIC DAMPING MATRIX
• SYSTEM DAMPING MATRIX
• CORRESPONDENCE BETWN INT EXT DYNAMIC DEGREES OF
  FREEDOM
• CORRESPONDENCE BETWN INT EXT CONDENSED DEGREES
  OF FREEDOM
• CORRESPONDENCE BETN INT EXT DYNAMIC DEGREES OF
  FREEDOM (UNREDUCED, UNCONDENSED -- APPLIES TO
  DAMPING MATRICES)

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Direct Integration Analysis
TRANSIENT LOADING 50 'TRANSIENT _at_ 866 RPM' JOINT
10 LOADS FORCE Y FUNCTION SINE AMPL 93.21 FREQ
14.43 PHASE 0.0 JOINT 10 LOADS FORCE Z FUNCTION
SINE AMPL 93.21 FREQ 14.43 PHASE 0.25 INTEGRATE
FROM 0 TO 2 AT 0.005 END OF TRANSIENT
LOADING DYNAMIC ANALYSIS PHYSICAL NEWMARK BETA
0.25
Per ASCE 4-98 Maximum Time Step Size for
Newmark Method 1/10 Shortest Period of
Interest 1/10 1/(866/60) 0.007 sec
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Fan Vibration Criteria

• Sensitivity (displacement)
• System Resonances
• Design resonance

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Fan Vibration Displacement

• Displacement ? 0.125 mils/oz pk-pk (for
  1 oz unbalance at 70 radius) for speed
  range of 339 - 866 RPM.
• Maximum Displacement lt 0.125 mils

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866 RPM Joint 51, z-direction
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Fan Vibration Criteria

• No System Resonances in /- 20 of operating
  speed range.
• Five system resonances
• Cannot prevent system resonances in such a wide
  frequency range.

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5 Modes Between 5.65 14.43 hz
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Modes Between 5.65 hz 14.43 hz
Dynamic Mode Shape
Mode 2
Freq 7.009E00
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Modes Between 5.65 hz 14.43 hz
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Modes Between 5.65 hz 14.43 hz
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Modes Between 5.65 hz 14.43 hz
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Fan Vibration Criteria

• Fan rotor design resonance ? 1039 RPM.

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Design Resonant Mode
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Final Exam

• Bowen Fan startup
• Mid - August

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gt FINISH
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Dynamic Analysis of Induced Draft Fan
Foundations