Appendix B. Chapter 11. Fan Housing Vibration Caused by

Fan

Hou

sing

Vib

ratio

n C

ause

d by

Res

onan

ce

App

licat

ion

of M

odal

& V

ibra

tion

Ana

lysi

s

Ken

Sin

glet

onK

SC

Con

sulti

ng L

LC

App

endi

x B

. Cha

pter

11.

KS

C C

onsu

lting

LLC

Fou

r F

D fa

ns w

ere

inst

alle

d at

the

site

to m

eet e

nviro

nmen

tal

requ

irem

ents

of t

he p

roce

ss.

Bac

kgro

und

The

fan

desi

gn d

etai

ls w

ere

as

follo

ws:

•15

00 H

P D

irect

Driv

e A

MC

A A

rran

gem

ent

8

•In

let G

uide

Van

e C

ontr

ol

•S

pher

ical

Rol

ler

Bea

rings

, Gre

ase

Lubr

icat

ed

•P

LC M

onito

ring

and

Con

trol

11B

-1

Fig

ure

1. S

chem

atic

of F

an w

ith s

ome

Par

amet

ers

Labeled

Gas

Tem

p13

0 de

gree

s F

Win

ter

250

degr

ees

F S

umm

er

Max

. Thr

ust

Load

320

9 lb f

Flo

w 3

63,7

94 A

CF

M

8042

lbf

1888

lbf

SK

F 2

2236

C

CK

/W33

SK

F 2

2232

C

CK

/W33

1560

HP

, 119

4 R

PM

11B

-2

Bac

kgro

und

The

fans

exp

erie

nced

man

y re

liabi

lity

prob

lem

s du

ring

th

e 1

stye

ar o

f ope

ratio

n. T

hese

pro

blem

s in

clud

ed:

•B

earin

g fa

ilure

s on

eac

h fa

n

•A

cat

astr

ophi

c be

arin

g fa

ilure

on

#1 F

an r

esul

ting

in a

bro

ken

mot

or s

haft

and

dam

aged

fan

shaf

t, w

hich

requ

ired

rep

lace

men

t.

•H

igh

bear

ing

oper

atin

g te

mpe

ratu

res.

•S

ever

al lu

bric

atio

n gr

ease

s w

ere

trie

d in

clud

ing

vary

ing

quan

tity

and

inte

rval

of g

reas

ing

as w

ell a

s gr

ease

rem

oval

from

the

bear

ing

hous

ings

.

•A

sm

all o

il re

circ

ulat

ion

syst

em w

as in

stal

led

on o

ne

fan,

but

onl

y pr

ovid

ed m

ixed

res

ults

•C

ompo

nent

fatig

ue fa

ilure

s of

dis

char

ge v

ane

asse

mb

ly,

11B

-1

Initi

al A

sses

smen

tT

he in

itial

ass

essm

ent o

f the

fans

was

mad

e in

Dec

20

01.

Num

erou

s de

ficie

ncie

s w

ere

iden

tifie

d:

•T

he F

an E

nd B

earin

g w

as o

pera

ting

at 9

2% o

f max

imum

re

com

men

ded

spee

d w

ith g

reas

e lu

bric

atio

n.

•F

an h

ousi

ng h

igh

ampl

itude

vib

ratio

n (a

cces

s to

hou

sing

lim

ited

by in

sula

tion.

)

•T

he d

isch

arge

van

e ho

usin

gs e

xhib

ited

high

leve

ls o

f vi

brat

ion

and

crac

king

of w

elds

at t

he li

nkag

e/sh

aft i

nter

face

s.

•V

ibra

tion

anal

ysis

indi

cate

d lu

bric

atio

n-re

late

d hi

gh e

nerg

y vi

brat

ion

(CS

I Pea

kVue

data

) ca

used

by

bear

ing

rolle

r sk

iddi

ng(B

earin

g lo

ad le

ss th

an s

peci

fied

min

imum

load

.)

•T

he s

pher

ical

rol

ler

bear

ings

cal

cula

ted

to b

e m

arg

inal

for

grea

se lu

bric

atio

n fo

r th

e fa

n op

erat

ing

spee

d of

119

4 R

PM

. 11B

-2

Initi

al R

ecom

men

datio

ns in

clud

ed th

e fo

llow

ing:

Initi

al A

sses

smen

t

•P

erfo

rm a

mod

al te

st o

f one

fan

hous

ing.

•C

hang

e be

arin

g lu

bric

ant f

rom

gre

ase

to o

il an

d In

sta

ll an

oil

re-c

ircul

atin

g sy

stem

with

filte

ring

and

tem

pera

tur

e co

ntro

l (T

he fa

n en

d be

arin

gs w

ere

oper

atin

g at

92%

of r

ecom

mende

d m

axim

um s

peed

with

gre

ase

lubr

icat

ion

(bor

derli

ne fo

r gr

ease

; thi

s de

sign

trul

y ne

eded

oil

lubr

icat

ion)

.

11B

-2

Fig

ure

2.O

vera

llV

ibra

tion

(in/s

ec)o

fFan

#4H

ousi

ngM

easur

edP

riort

oS

tart

upof

the

Fan

and

Dur

ing

Inle

tGui

deVa

neA

djus

tmen

tsto

Ful

lOpe

n,C

lose

dand

Shu

tDow

n.

Vib

ratio

n lo

wes

t lev

el a

t 30%

to

70%

gui

de v

anes

ope

n.

Gui

de V

ane

setti

ngs

adju

sted

in 1

0% s

teps

.

Dur

ing

seco

nd v

isit

to s

ite F

eb 2

002

. B

earin

g &

fan

hous

ing

vibr

atio

n w

as m

easu

red.

A s

ingl

e ac

cele

rom

eter

was

atta

ched

to

the

fan

hous

ing

thou

gh a

hol

e dr

illed

in th

e in

sula

tion.

Min

imum

1.2

in/s

ec w

as p

rese

nt.

Inle

t Van

es 1

00%

11B

-3

Inle

t Gui

de V

anes

Clo

sed

Fan

Sta

rtup

Fig

ure

3. F

an #

4 H

ousi

ng V

ibra

tion

Spe

ctru

m. M

ost V

ibra

tion

Ene

rgy

was

at a

bout

20

Hz

(12

00 C

PM

), o

r 1

X F

an R

unni

ng S

peed

(2.

5 in/sec

).

T

he R

espo

nse

App

eare

d to

be

Cau

sed

by R

eson

ance

of

the

Hou

sing

.

Bro

ad B

ase,

Indi

cato

r of

Res

onan

ce

(at F

an S

peed

of 1

194

RP

M)

Fre

quen

cy S

pect

rum

in F

ebru

ary

2002

on

Fan

#4

Hou

sing

11B

-4

Illus

trat

ion

A. O

verv

iew

of S

crub

ber

Fan

s E

valu

ated

Fan

Insp

ectio

n A

fter

Insu

latio

n R

emov

ed•

Rec

omm

enda

tion

to p

erfo

rm fa

n ho

usin

g m

odal

test

wa

s ac

cept

ed

and

sche

dule

d fo

r S

ept 1

1-12

, 200

2.

•In

sula

tion

was

re

mov

ed to

pro

vide

ac

cess

to th

e fa

n ho

usin

g.

•T

he fa

n ho

usin

g w

as

insp

ecte

d fo

r cr

acki

ng a

s w

ell a

s ge

nera

l des

ign

and

fabr

icat

ion

met

hods

.

•N

o cr

acks

wer

e fo

und.

13 F

eet

11B-

4

•T

he h

ousi

ng w

as a

thre

e pi

ece

desi

gn

to p

erm

it sh

ippi

ng a

nd r

emov

al o

f the

fa

n w

heel

.

•T

he tw

o up

per

sect

ions

wer

e bo

lted

to

the

low

er h

alf a

t the

cen

terli

ne a

nd to

ea

ch o

ther

at a

ver

tical

flan

ge.

Fan

Insp

ectio

n A

fter

Insu

latio

n R

emov

ed

Vert

ical

Spl

it

Hor

izon

tal S

plit

Fig

ure

5. F

an H

ousi

ng S

how

ing

Vert

ical

and

Hor

izon

tal

Join

ts a

nd In

ters

ectio

n N

ear t

he F

an C

ente

rline

11B

-5

It w

as le

arne

d th

at s

ectio

ns o

f the

hou

sing

fla

nges

(4

inch

Cha

nnel

) ha

d be

en r

emov

ed

usin

g a

cutti

ng to

rch

to p

rovi

de c

lear

ance

for

th

e sh

aft.

The

rem

oval

of t

hese

stif

fene

rs in

the

ce

nter

of t

he h

ousi

ng s

igni

fican

tly r

educ

ed th

e rig

idity

of t

he h

ousi

ng.

Fig

ure

4. T

he D

raw

ing

by th

e F

an O

EM

Indi

cate

s th

e V

ertic

al an

d H

oriz

onta

l Fla

nges

wer

e D

esig

ned

to b

e V

ery

Clo

se to

the

Sha

ft.

Ext

endi

ng L

ines fo

r th

e V

ertic

al a

nd H

oriz

onta

l F

lang

es

Indi

cate

Pot

entia

l Sha

ft In

terf

eren

ce.

11B

-5

Not

e F

an H

ousi

ng S

truc

tura

l M

embe

rs o

f 4”

Cha

nnel

Cut

w

ith T

orch

to P

rovi

de F

an S

haft

Cle

aran

ce.

11B

-5

Fig

ure

6.G

roov

e W

orn

In F

an

Sha

ft C

ause

d by

Con

tinuo

us

Con

tact

With

Rub

ber

Air

Sea

l.

Mod

al T

est

•19

5 Te

st m

easu

rem

ent p

oint

s (D

OF

) w

ere

laid

out

in

a m

esh

as

show

n in

the

phot

os.

•E

xcita

tion

was

by

impa

ct u

sing

a P

CB

Inst

rum

ente

d 1

2 lb

Sle

dge

Ham

mer

. 5

Acc

eler

omet

ers

wer

e ro

ved

to e

ach

DO

F.

Mitc

h F

ranc

e -

Layi

ng O

ut

Mod

al T

est P

oint

s on

Fan

H

ousi

ng, S

haft

Inle

t Sid

e

Fig

ure

7.

11B

-6

ME

’sco

peV

ES

Mod

el

11B

-7

Illus

trat

ion

B.

Driv

ing

Poi

nt

6X/6

X

ME

’sco

peV

ES

Mod

elD

OF

’s (

195

DO

F M

easu

red) 11

B-7

DO

F 45

X

Fig

ure

9. F

requ

ency

Res

pons

e F

unct

ion

(FR

F)

of H

ousing

Iner

tanc

e M

agni

tude

Plo

t (g/

lbf)

Driv

ing

Poi

nt F

requ

ency

Res

pons

e F

unct

ion

(FR

F)

tak

en o

n th

e fa

n ho

usin

g sh

owed

man

y N

atur

al F

requ

enci

es.

Fan

2X

The

re w

as a

ver

y re

spon

sive

nat

ural

freq

uenc

y at

12

90 C

PM

(21

.5 H

z)ne

ar

Fan

1X

run

ning

spe

ed, w

hich

turn

ed o

ut to

be

the

prim

ary

prob

lem

.

©C

opyr

ight

200

5: T

ech

nica

l Ass

ocia

tes

of C

harl

otte

P.C

.

Fan

1X

11B

-8

1290

CP

M

3300

CP

M

11B

-7

Fig

ure

10 s

how

s a

Spe

ctru

m ta

ken

on D

rivin

g P

oint

6X

with

the

fan

runn

ing.

Sho

wed

hig

h vi

brat

ion

of 1

.10

in/s

ec a

t 1 X

Fan

spe

ed o

n fa

n ho

usin

g.

Als

o sh

owed

a n

otab

le le

vel o

f .38

4 in

/sec

at 3

150

CP

M (

near

the

2nd

Mod

e id

entif

ied

in F

igur

e 9)

.

11B

-8

RO

UT

E W

AV

EFO

RM

1

2-S

ep-0

2 1

7:11

:52

P

K =

1.0

6

PK

(+) =

1.7

7

P

K(-

) = 2

.08

CR

ES

TF=

2.7

7

050

100

150

200

250

300

350

400

-3-2-1012

Tim

e in

mS

ecs

Velocity in In/Sec

One

- O

FF R

OU

TE

MA

CH

INE

OFF

RO

UT

E -O

RP

O

FF R

OU

TE

ME

AS

UR

EM

EN

T P

OIN

T D

AT

A

Labe

l: P

t 6X

Ste

el A

ngle

Rem

oved

RO

UT

E S

PE

CT

RU

M

12-

Sep

-02

17:

11:5

2

OV

ER

ALL

= 1.

38 V

-DG

P

K =

1.3

7

LO

AD

= 3

0.0

R

PM

= 1

190.

R

PS

= 1

9.83

010

000

2000

030

000

0

0.3

0.6

0.9

1.2

1.5

Freq

uenc

y in

CP

M

PK Velocity in In/Sec

Freq

: O

rdr:

S

pec:

315

0.0

2.

647

.3

84

1200

CP

M 1

.1 in

/sec

3150

CP

M .3

84 in

/sec

Fig

ure

10. V

ibra

tion

at D

OF

6X

whi

ch w

as th

e M

odal

Te

st D

rivin

g P

oint

Loc

atio

n.

Mos

t Vib

ratio

n w

as F

ound

at 1

200

and

3150

CP

M (2

0.0

and

52.

5 H

z).

Hz

0.0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

10E-3

1E-3

100E-6

10E-6

(9.06E-3@

191)

(10.3E-3@

195)

M#6 <6X+: 6X+> Trace 1

Fan

Hou

sing

Mod

e S

hape

s

The

hou

sing

was

mov

ing

in a

nd o

ut

perp

endi

cula

r to

the

shaf

t axi

s due

to

cut

stif

fene

rs.

1stC

ircul

ar M

ode

Sha

pe (

near

119

4 R

PM

fan

run

ning

spe

ed).

Max

vib

ratio

n. m

easu

red

durin

g th

e te

st w

as D

OF

8X a

t 1.7

2 ip

s(nea

r th

e fa

n ho

usin

g cu

tout

whe

re th

e sh

aft p

asse

s th

roug

h th

e ho

usin

g -

see

Illus

trat

ion

B).

Fig

ure

11. D

rivin

g P

t 6X

/6X

, Cur

sor

on 1

277

CP

M (

21.2

8 H

z) M

ode.

Fig

ure

12. M

ode

Sha

pe a

t 12

77 C

PM

(21

.28

Hz)

.

11B

-10

1277

CP

M (

21.2

8 H

z)

Thi

s C

ircu

lar

Mod

e w

as th

e P

rim

ary

Con

trib

utor

to F

an

Hou

sing

Vib

ratio

n.

DO

F

8

Hz

0.0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

10E-3

1E-3

100E-6

10E-6

(9.06E-3@

191)

(10.3E-3@

195)

M#6 <6X+: 6X+> Trace 1

Fan

Hou

sing

Mod

e S

hape

s

The

hou

sing

mot

ion

is o

ut o

f pha

se

on e

ach

side

of t

he h

ousi

ng

cent

erlin

e.

Dis

char

ge n

ozzl

e pa

rtic

ipat

es in

the

mod

e – f

atig

ue fa

ilure

of w

elds

.

Max

vib

ratio

n. m

easu

red

durin

g th

e te

st w

as D

OF

45 a

t 0.1

55 ip

s(s

ee

Illus

trat

ion

B).

Fig

ure

14. M

ode

Sha

pe a

t 24

49 C

PM

(40

.8 H

z) is

nea

r 2

X F

an S

peed

.

Fig

ure

13. D

rivin

g P

t 6X

/6X

, Cur

sor

on 2

449

CP

M (

40.8

Hz)

Mod

e.

11B

-11

2449

CP

M (

40.8

Hz)

DO

F

45

Hz

0.0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

10E-3

1E-3

100E-6

10E-6

(9.06E-3@

191)

(10.3E-3@

195)

M#6 <6X+: 6X+> Trace 1

Fan

Hou

sing

Mod

e S

hape

s

The

hou

sing

mot

ion

is o

ut o

f ph

ase

each

sid

e of

the

cent

erlin

e.

Dis

char

ge n

ozzl

e do

es n

ot

part

icip

ate

in th

e m

ode.

Max

vib

ratio

n. m

easu

red

durin

g th

e te

st w

as D

OF

45 a

t 0.4

55 ip

s.

Fig

ure

16. M

ode

Sha

pe a

t 32

99 C

PM

(55

.0 H

z). T

his

was

the

2ndM

ost R

espo

nsiv

e M

ode.

Fig

ure

15. D

rivin

g P

t 6X

/6X

, Cur

sor

on 3

299

CP

M (

55.0

Hz)

Mod

e.

11B

-12

3299

CP

M (

55.0

Hz)

DO

F

45

Hz

0.0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

10E-3

1E-3

100E-6

10E-6

(9.06E-3@

191)

(10.3E-3@

195)

M#6 <6X+: 6X+> Trace 1

Fan

Hou

sing

Mod

e S

hape

s

Prim

arily

pan

el c

ircul

ar m

ode

left

side

of h

ousi

ng.

Max

vib

ratio

n m

easu

red

durin

g th

e te

st w

as D

OF

45 a

t 0.1

0 ip

s.

Fig

ure

18. M

ode

Sha

pe a

t 47

13 C

PM

(78

.65

Hz)

. Not

e M

otio

n on

Lef

t Sid

e of

B

low

er H

ousi

ng.

Fig

ure

17. D

rivin

g P

t 6X

/6X

, Cur

sor

on 4

713

CP

M (

78.5

5) H

z M

ode.

11B

-13

4713

CP

M (

78.6

5 H

z)

DO

F

45

Hz

0.0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

10E-3

1E-3

100E-6

10E-6

(9.06E-3@

191)

(10.3E-3@

195)

M#6 <6X+: 6X+> Trace 1

Fan

Hou

sing

Mod

e S

hape

s

Prim

arily

pan

el c

ircul

ar m

odes

of

the

fan

hous

ing.

Max

vib

ratio

n m

easu

red

durin

g th

e te

st w

as D

OF

45 a

t 0.1

44 ip

s.

Fig

ure

20. M

ode

Sha

pe a

t 95

80 C

PM

(15

9.7

Hz)

. P

rimar

ily P

anel

Ben

ding

M

odes

of F

an H

ousi

ng.

Fig

ure

19. D

rivin

g P

t 6X

/6X

, Cur

sor

on 9

580

CP

M (

159.

7 H

z) M

ode.

11B

-14

9580

CP

M (

159.

7 H

z)

DO

F

45

Afte

r th

e M

odal

Tes

t, a

Tem

pora

ry 4

” x

4” A

ngle

was

Cla

mpe

d to

the

Fan

Hou

sing

an

d th

e F

an w

as R

esta

rted

.

Fig

ure

21. V

ibra

tion

was

Tak

en W

ith &

With

out t

he A

ngle

Atta

ched

to

the

Hou

sing

. 11B

-15

4”X

4”

Ang

le C

-C

lam

ped

to

Fan

H

ousi

ng

Cha

nnel

One

- O

FF R

OU

TE M

ACH

INE

OFF

RO

UTE

-OR

P v

s O

FF R

OU

TE -O

RP

Labe

l: P

t 6X

Ste

el A

ngle

Rem

oved

0

0.3

0.6

0.9

1.2

1.5

Com

paris

on S

pect

rum

O

FF R

OU

TE -O

RP

1

2-S

ep-0

2 1

7:11

080

0016

000

2400

0

0

0.3

0.6

0.9

1.2

1.5

Ref

eren

ce S

pect

rum

OFF

RO

UTE

-OR

P

12-

Sep

-02

16:

58

Freq

uenc

y in

CP

M

PK Velocity in In/Sec

Freq

: O

rdr:

Sp

2:

120

0.0

1.

008

1.

105

4 X

1/2

" A

ngle

Cla

mpe

d to

Hou

sing

No

angl

e cl

ampe

d to

hou

sing

1 X Fan

Fan

Run

ning

with

Tem

pora

ry 4

x 4

Ang

le c

lam

ped

to t

he fa

n ho

usin

g. V

ibra

tion

was

pre

dom

inan

tly a

t DO

F 6

X (

Illu

stra

tion

B).

No

Ang

le C

lam

ped

to

Fan

Hou

sing

(1.

1 ip

s)

4 x

4 x

½” A

ngle

C

lam

ped

to F

an

Hou

sing

(0.

45 ip

s)

Tem

pora

ry s

tiffe

ner

did

prov

e to

be

effe

ctiv

e in

re

duci

ng v

ibra

tion

11B

-15

Scru

bber

Fan

, Com

pars

ion

of H

ousi

ng V

ibra

tion

With

/With

out 4

X4 A

ngle

Stif

fene

r Cla

mpe

d To

Hou

sin

g 12

00 C

PM F

requ

ency

0.00

0

0.20

0

0.40

0

0.60

0

0.80

0

1.00

0

1.20

0

1.40

0

1.60

0

1.80

0

2.00

0

6X7X

8X45

X43

X78

X82

X66

X9X

10X

11X

69X

85X

Mea

sure

men

t Lo

cati

on

Angl

e St

iffe

ner C

lam

ped

To H

ousin

gN

o An

gle

Stif

fene

r Cla

mpe

d To

Hou

sing

Cha

rt 1

. Vib

ratio

n at

120

0 C

PM

Fre

quen

cy w

ith T

empo

rary

Ang

le C

lam

ped

to

Hou

sing

Act

ing

as a

Stif

fene

r (B

lue)

and

the

Ang

le

Rem

oved

(Y

ello

w).

(Sep

tem

ber 2

002)

11B

-16

Rec

omm

enda

tions

1. B

olt T

wo

4” x

4” A

ngle

to

the

hous

ing

abov

e th

e be

arin

gs to

co

ntro

l the

prim

ary

mod

e. U

se b

olte

d at

tach

men

t to

perm

it re

mov

al o

f the

hou

sing

sec

tion

for

fan

whe

el a

cces

s.

2. W

eld

a 4”

x 4

” Ang

le t

o th

e ho

usin

g be

low

the

cent

erlin

e to

hel

p co

ntro

l the

prim

ary

mod

e at

127

7 C

PM

(21

.28

Hz)

.

3. W

eld

½”

x 4”

Bar

stif

fene

rs to

con

trol

pan

el m

odes

.

Stif

feni

ng th

e fa

n ho

usin

g to

con

trol

the

prim

ary

res

onan

t am

plifi

catio

n at

127

7 C

PM

(21

.28

Hz)

was

the

maj

or

focu

s.

Str

uctu

ral s

teel

stif

fene

rs b

olte

d an

d w

elde

d to

the

hous

ing

wer

e pr

opos

ed a

s fo

llow

s:

11B

-17

4” x

½”

Pla

te S

tiffe

ners

w

elde

d to

the

hous

ing

and

exis

ting

angl

e.

Fan

Hou

sing

Stif

feni

ng

Rec

omm

enda

tions

.4”

x ½

” P

late

Stif

fene

rs w

elde

d to

the

hous

ing

and

exis

ting

angl

e.

Two

4” x

4”

piec

es o

f an

gle

wel

ded

to th

e ho

usin

g an

d ex

istin

g ch

anne

l.

Fig

ure

22.

Two

4” x

4”

x 86

” an

gle

bolte

d to

the

exis

ting

vert

ical

ang

le a

nd

chan

nel.

11B

-17

4 X

4 a

ngle

Bol

ted

to

Fan

Hou

sing

A s

ite v

isit

in D

ec 2

004,

two

year

s af

ter

the

mod

al te

st, p

rovi

ded

an

oppo

rtun

ity to

rec

heck

vib

ratio

n an

d th

e st

ruct

ural

mod

ifica

tions

that

w

ere

actu

ally

mad

e to

the

fan.

Fig

ure

23.

11B

-18

One

- S

crub

ber F

an F

our

Fan

4

-F2A

Fa

n O

utbo

ard

Axia

l

Labe

l: F

an H

ousi

ng A

xial

0

0.5

1.0

1.5

2.0

Com

paris

on S

pect

rum

Fa

n 4

-F

2A

07-

Dec

-04

11:

43

010

000

2000

030

000

0

0.5

1.0

1.5

2.0

Ref

eren

ce S

pect

rum

Fan

4

-F2A

2

7-Fe

b-02

10:

03

Freq

uenc

y in

CP

M

PK Velocity in In/Sec

Fig

ure

24. C

ompa

rison

of B

efor

e an

d A

fter

Vib

ratio

n S

pect

ra M

easu

red

on

Fan

#4

Hou

sing

, D

OF

6X

at F

an H

ousi

ng S

plit

Line

Str

uctu

ral M

embe

r.

Initi

al v

ibra

tion

mea

sure

d 1.

6 in

/sec

, pk

at 4

0% in

let g

uide

van

e se

tting

.

Afte

r an

gle

was

bol

ted

to th

e ho

usin

g, v

ibra

tion

was

redu

ced

to 0

.15

in/s

ec, P

k at

1X

, sho

win

g a

10.7

:1 r

educ

tion

(91%

dec

reas

e).

11B

-18

Afte

r C

orre

ctio

n

1X F

an (

0.15

in/s

ec)

Bef

ore

Cor

rect

ion

1X F

an (

1.6

in/s

ec)

One

- S

crub

ber F

an F

our

Fan

4

-F2A

Fa

n O

utbo

ard

Axia

l

Labe

l: F

an H

ousin

g Ax

ial

Anal

yze

Spe

ctru

m

0

7-D

ec-0

4 1

1:43

:35

PK

= .

3532

L

OAD

= 1

00.0

R

PM

= 1

194.

(19.

90 H

z)

040

0080

0012

000

1600

0

0

0.05

0.10

0.15

0.20

Freq

uenc

y in

CPM

PK Velocity in In/Sec

Freq

: O

rdr:

Sp

ec:

146

2.5

1.

225

.09

321

Fig

ure

25.

The

Hou

sing

Vib

ratio

n af

ter

Ang

le B

olte

d to

Hou

sing

. S

pect

rum

Sho

ws

the

Hou

sing

Nat

ural

Fre

quen

cy h

as In

crea

sed

from

App

roxi

mat

ely

1277

CP

M to

146

2 C

PM

(20

.0 to

24

.4 H

z).

Hou

sing

Res

onan

ce

Fan

1X

Run

Spe

ed

The

res

onan

ce is

stil

l ex

cite

d by

air

flow

; B

ut th

e am

plitu

de

was

redu

ced

to o

nly

abou

t 0.1

in/s

ec, p

k (w

as 0

.32

in/s

ec, p

k).

Initi

al F

an 1

X v

ibra

tion

mea

sure

d 1.

6 in

/sec

, pk

at 4

0% in

let g

uide

van

e se

tting

.

Afte

r an

gle

was

bol

ted

to th

e ho

usin

g, v

ibra

tion

was

redu

ced

to 0

.15

in/s

ec, P

k at

1X

,sh

owin

g a

10.7

:1 r

educ

tion

(91%

decr

ease

).

11B

-19

One

- S

crub

ber F

an F

our

Fan

4

-F2A

Fa

n O

utbo

ard

Axia

l

Labe

l: F

an H

ousin

g Ax

ial

Anal

yze

Spe

ctru

m

0

7-D

ec-0

4 1

1:43

:35

PK

= .

3532

L

OAD

= 1

00.0

R

PM

= 1

194.

(19.

90 H

z)

040

0080

0012

000

1600

0

0

0.05

0.10

0.15

0.20

Freq

uenc

y in

CPM

PK Velocity in In/Sec

Freq

: O

rdr:

Sp

ec:

146

2.5

1.

225

.09

321

Fig

ure

25.

The

Hou

sing

Vib

ratio

n af

ter

Ang

le B

olte

d to

Hou

sing

. S

pect

rum

Sho

ws

the

Hou

sing

Nat

ural

Fre

quen

cy h

as S

hift

ed

from

App

roxi

mat

ely

1277

CP

M to

146

2 C

PM

(21

.3 to

24

.4 H

z).

Hou

sing

Res

onan

ce

Fan

1X

Run

Spe

ed

The

res

onan

ce is

stil

l pre

sent

but

is s

hifte

d 14

.5%

hig

her

in fr

eque

ncy

away

from

fa

n ru

nnin

g sp

eed.

Afte

r m

odifi

catio

ns, t

he M

ode

mea

sure

d 14

62 C

PM

or

22.0

% fr

om F

an 1

X. P

rior

to

mod

ifica

tions

, the

Mod

e m

easu

red

1277

CP

M o

r 6.

5% f

rom

Fan

1X

.

11B

-19

Hou

sing

Nat

ural

F

requ

ency

Shi

fted

from

12

77 to

146

2 C

PM

.

1.T

he v

ibra

tion

and

mod

al t

est d

ata

conf

irmed

the

susp

ecte

d st

ruct

ural

res

onan

ces

of th

e fa

n ho

usin

g.

2.D

urin

g or

igin

al in

stal

latio

n of

the

fans

, the

mati

ng jo

int f

lang

es a

t the

cen

ter

of

the

hous

ing

had

been

rem

oved

by

a cu

tting

torc

h to

pr

ovid

e cl

eara

nce

for

the

shaf

t. T

he r

emov

al o

f the

se s

tiffe

ners

sig

nific

antly

redu

ced

rigid

ity o

f the

sha

ft en

try

side

of t

he fa

n ho

usin

g.

3.M

ost h

ousi

ng v

ibra

tion

resp

onse

was

at f

ive

natu

ral f

requ

enci

es –

1277

, 244

9,

3299

, 471

3 an

d 96

00 C

PM

. E

xcita

tion

of th

e 12

77 C

PM

mod

e w

as th

e pr

imar

y co

ntrib

utor

to

hous

ing

vibr

atio

n. T

he 3

299

CP

M m

ode w

as th

e 2nd

mos

t re

spon

sive

.

4.D

urin

g th

e m

odal

tes

t, th

e in

abili

ty to

isol

ate

the fa

n fr

om a

ir le

akag

e ca

used

si

gnifi

cant

hou

sing

vib

ratio

n. T

his

back

grou

nd v

ibrat

ion

mad

e it

mor

e di

fficu

lt to

obt

ain

high

qua

lity

mod

al t

est d

ata.

A m

ediu

m sle

dge

mod

al h

amm

er w

as to

o sm

all t

o in

put e

noug

h fo

rce

to e

xcite

the

hous

ing

above

the

bac

kgro

und

vibr

atio

n.

An

inst

rum

ente

d sl

edge

ham

mer

was

req

uire

d to

inpu

t the

150

0 to

200

0 lb f

nece

ssar

y to

exc

ite th

e ho

usin

g.

CO

NC

LUS

ION

S:

11B

-20

5. T

he m

odal

tes

t dat

a w

ere

curv

e fit

to d

eter

min

e the

mod

e sh

apes

of t

he h

ousi

ng

natu

ral f

requ

enci

es.

Afte

r re

view

ing

the

mod

e sh

apes,

it w

as d

ecid

ed t

o at

tach

a

tem

pora

ry s

tiffe

ner

of 4

x 4

inch

ang

le to

the

vertic

al f

lang

es o

f the

hou

sing

usi

ng

heav

y du

ty C

cla

mps

. V

ibra

tion

data

tak

en w

ith th

e ang

le s

tiffe

ner

clam

ped

to

the

hous

ing

show

ed th

at v

ibra

tion

of th

e 12

77 C

PM

reson

ant

resp

onse

wou

ld b

e lo

wer

ed s

igni

fican

tly if

stif

feni

ng a

t the

pro

per

loca

tions

was

add

ed.

6. R

ecom

men

datio

ns w

ere

mad

e to

bol

t and

wel

d st

ruc

tura

l mem

bers

to

the

fan

hous

ing

base

d on

rev

iew

of t

he m

ode

shap

es (

see

Fig

ure

23).

7. A

fter

the

stiff

ener

s w

ere

inst

alle

d, th

e vi

brat

ion l

evel

s w

ere

redu

ced

from

abo

ut

1.6

in/s

ec to

0.1

5 in

/sec

, (91

% r

educ

tion)

.T

he fa

n hous

ing

1stm

ode

shift

ed f

rom

ab

out

1277

CP

M to

146

2 C

PM

pro

vidi

ng a

sep

arat

ion

marg

in o

f 22.

5% fr

om

runn

ing

spee

d (se

e F

igur

es 2

4 an

d 25

).

8. T

his

proj

ect

took

app

roxi

mat

ely

thre

e ye

ars

from

initi

al in

spec

tion

of th

e fa

ns,

reco

mm

enda

tion

to p

erfo

rm m

odal

tes

ting,

con

duct

ing t

he m

odal

tes

t, in

stal

ling

the

hous

ing

stiff

ener

s an

d re

chec

king

vib

ratio

n.

CO

NC

LUS

ION

S:

11B

-20

©C

opyr

ight

200

5: T

ech

nica

l Ass

ocia

tes

of C

harl

otte

P.C

.

Tha

nks

to M

itche

ll F

ranc

e of

Tec

hnic

al A

ssoc

iate

s of C

harlo

tte, P

C fo

r as

sist

ance

with

the

mod

al te

st, d

ata

redu

ctio

n an

d form

ulat

ing

a so

lutio

n.

Ack

now

ledg

emen

t:

11B

-20