A finite element model of the Saab 2000 fuselage structure and interior cavity has been created in order to compute the noise level in the passenger cabin due to propeller noise. Areas covered in viewgraph format include the following: coupled acoustic/structural noise; data base creation; frequency response analysis; model validation; and planned analyses

Green, Inge S.

English

NASA Technical Reports Server

4th NASAISAE/OLR Aircraft Interior Noise Workshop 
Friedrichshafen, Germany 
May 19 - 20,1992 
Inge S. Green 
Saab Aircraft AS 
Link6ping, Sweden 
Vibro-acoustic FE analyses 
of the Saab 2000 Aircraft 
• Coupled acoustic/structural aircraft 
FE-model 
• Creation of modal database 
• BPF pressure field excitation 
• Frequency response analyses 
• Model validation analysis 
• Planned analyses 
• Model development 
44 
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https://ntrs.nasa.gov/search.jsp?R=19920023708 2020-03-17T11:22:47+00:00Z
Vibro-acoustic FE analyses 
of the Saab 2000 Aircraft 
• Coupled acoustic/structural aircraft 
FE-model 
Acoustic model 
Structural model 
- Coupled Acoustic-Structural model 
• Creation of modal database 
- Substructuring/Modal synthesis 
,- Acoustic eigenmodes 
- Structural eigenmodes 
- Coupled eigenmodes 
• BPF pressure field excitation 
- Cruise flight nearfield BPF noise 
prediction 
- Inclusion of fuselage scattering 
45 
46 
• Frequency response analyses 
- Scheme of computation 
- Modal contribution to BPF response 
- Structural response (Operating 
deflection shape) 
Cabin cavity response (Pressure < 
field in dB) 
• Model validation analysis 
- Experimental modal analysis, 
Fuselage Test Rig 
- Fuselage Rig shaker test simulation 
• Planned analyses 
- Tuned Damper installation and 
optimization 
- Structure-borne path identification 
- Active Vibration Control analyses 
• Model development 
- Fuselage sections with interior -
- Active Noise Control analyses 
4th NASNSAElDLR Aircraft Interior Noise Workshop 
Friedrichshafen, Germany 
May 19 - 20, 1992 
Inge S. Green 
Saab Aircraft AB 
Linkoping, Sweden 
VIBRO-ACOUSTIC FE ANALYSES 
OF THE SAAB 2000 AIRCRAFf 
SUMMARY 
FE-models of the Saab 2000 fuselage structure and the interior cavity have been 
created in order to compute the noise level in the passenger cabin due to propel-
ler noise (page 1). 
The FE-system ASKA was used for these analyses. The total number of degrees 
of freedom (dot) for the models is over 400000. To make the analysis possible 
substructuring was used in addition to severa1levels of "midnets" and modal 
component synthesis. This way the number of dof at each level was reduced to 
give acceptable computer times (page 2 - 6). 
Examples arc shown of Acoustic modes (page 7 - 8) and dominant structure 
modes (page 9 - 10) from the modal database. 
BPF pressure field at cruise flight was predicted and applied to the aircraft 
(page 11 - 12). 
Scheme of computations (Normal mode analysis and Frequency response 
analysis) are outlined in page 13. 
From the frequency response analysis, modal contribution (page 14), structural 
response (page 15) and cabin cavity response (page 16) are shown. 
From Fuselage Test Rig modal analysis a first validation of the FE-model is 
made (page 17). 
Validation with the Frequency Response Function method is under way 
(page 18 - 19). 
Planned analyses with the Saab 2000 AFEM model is shown in page 20 and 
proposed model development in page 21. 
47 
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48 
SAAB 2000 COUPLED STRUCTURE-CAVITY FE HODEL 
Structure model 
Sta 
Sta 399 - Sta 512 
Number of Nodal points 
Number of Elements 
Number of Substructures: 
512 
I 
Structure 
Hain Net 290 
22681 
10153 
10 
Sta625 
I 
Cavity 
62118 
3599 
10 
Database from 
Eigenvalue analysis :720 eigenvalues (11.2-342.5 Hz) 
Net (200+210) 
Net(300+310) 
Left Hand side 
Acoustic Nets y 
LH RH 
\ I 
Net (120+130) 
_____ Net (220+230) 
Net(320+330) 
/ Sta 1Hl. 3 
RH 
Right Hand side 
x 
z 
. Net (420+430) 
Net(520+530) 
.. =-~ --.,-.~,;;.-
SUB-CAVITY I Net 220 
6541 Nodal points 
0.700 T 0.700 .. ' 
0.1<40 ' -
SCALE 0.009 
OBJECT LIMITS 
X: 10.744 - 11 .Js-4 
r: -0.0770 - 1.1560 
Z: -3.6960 - -1.38-40 
Elements: 20-nodes Acoustic Volyme element 
" a-nodes Coupling element 
49 
_SMB 
""- I ACOUSnc MODEL] 
Levell Level 2 
LH RH RH 
\ 
Ne1220 
10 Subcavities 
530 
Level 3 
Net 160 
Level 4 
SI.lI 286 Su 399 Sla 62S Su 836 SI.lI 870 
; 
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. 
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f 
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§ 
I I Nel193 
I 
I I 
I Net 189 I Net 190 Net 191 Net 192 
I a ropy of net 190 I a copy of DCt 190 I 
I IT IIII I 
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e 
50 
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\ 
\ 
\ 
\ 
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SUB_STRUCTURE .Net 200 
--------~-----.-------
2386 Nodal pointS Element" QU>D8 ,8nod" quad_curved ,helll 
Bv.M3 (3nodes curved be4ll\) 
STRUCTURAL MODEL I 
Left side Right side 
Levell 
Level 2 
Level 3 
Level 4 
Level S 
SI.98 SI.286 SI.399 SU.512 
I 
St.62!1 St. U.5! 
I Nel179 Nel ISO Nel 181 
I. copy of oel 180 I copy ofoel 180 I 
Neln 
II 
~ 
Main net 290 
/1 
.. 
~ COUPLED ACOUSTIC-STRUCTURAL MODEL 
I Coupling only for the master sections Sta 399 - Sta 512 
I 
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§ Acoustic net 190 + Structure net 180 
51 
. 
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~ith rest of the rncdels M~in ~ets 300 a~j 290 ~~cc~pled . 
52 
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_SMB 
2000 AFEM. 
CREATION OF THE COUPLED ACOUSTIC-STRUCTURAL MODAL DATABASE. 
ASKA analyses on CRAY X-MP/416 
Total number of DOF's for the models > 400000 
Analyses performed with substructuring (Sub-,Mid-and Main nets) 
and modal component synthesis for reduction of the number of 
DOF's at each level. 
.. ACOUSTIC MODEL (Master section Sta 399-Sta 512) 
LEVEL TOTAL NUl\mER TOTAL Nt'MBER TOTAL CPt'· TIME 
UNCONSTRA.IND) NOR~fAL MODES IN CRA Y (SECI 
DOF 
I 30300 
-
UI 1000 
2 3100 114 5700 
J 1100 195 7800 
4 4000.- 5" 10500 
.. STRUCTURAL MODEL (Master section Sta 399-Sta 512) 
LEVEL TOTAL N1JMBER TOTALNUMBU TOTAL CPU-TIME 
UNCONSTUJNm NORMAL MODES IN CRA Y (SEeS) 
DOF 
t 117000 - 913 44000 
2 f,86O 7" 22100 
3 UtO 720 16000 
• 351-4 J02' 3700 
5 2025 +- 720 7250 
.. COUPLED ACOUSTIC-STRUCTURAL MODEL (Master sections) 
Number of Acoustic normal modes: 596 (10.9 
-
400 Hz) 
Number of Structural normal modes: 720 (11.2 342 Hz) 
After the coupled analysis, 
---------------------------
Number of coupled normal modes: 700 (9.6 - 288 Hz) 
53 
Fig 
54 
ACOUSTIC SIDE-SIDE MODE AT 8S.3 Hz 1 
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... ___ .. ~J 
PARAU.£L 
0.535 
'.21i7 
0.'02 
SCALE O. 036 
OBJECT LIMITS 
X: 10.172 - 18.0049 
V: -1.1560 - 1.1560 
Z: -3.6960 - -1.3&040 
CONTc:x.a LE'JELS 
..... T LDCS COMP OPT 
DlP1 .. 
TOP 10.:s8II1(£-1 
MOVE 9.3-4 
8.31 - 9.3-4 
7.27 - 8.31 
6.23 -7.27 
5.19 - 6.2.3 
".15 - 5.19 
3.11 - 41.15 
2.08 - ::S.l1 
1.0<4 - 2.08 
0.00 - 1.041 
-1.004 - 0.00 
-2.08 - -1.041 
-3.11 - -2.08 
-<4.15 - -::S.11 
-S.1·9 - -41.15 
-6.23 - -5.19 
-7.27 - -6.2.3 
-8.31 - -7.27 
-9.3-4 - -8.31 
_OW -9.3-4 
IOn .. -l0."'lOE-l 
Fig ACOUSTIC SIDE-SIDE MODE with LH/RH shift AT 101.6 Hz 
fWW'· 
0.535 
0.267 
0.102 
SC-..E 0.0315 
~3ECT LIMITS 
X: 10.872 - 18.0049 
V: -1.1560 - 1.1560 
Z: -3.6960 - -1.3840 
CONTQ.Il LEVELS 
R£9UL T LDCS eOl1P OPT 
OfiPl & 
'fOP 10.3SII10E-l 
MOVE 9.:U 
8.21 - 9.31 
7.2" - 8.28 
&.21 - 7.2" 
5.17 - &.21 
411.1" - 5.17 
3.10 - ".1.04 
2.07 - 3.10 
1.03 - 2.07 
-0.00 - 1.03 
-1.03 - -0.00 
-2.07 - -1.03 
-3.10 - -2.07 
-".1'" - -3.10 
-5.17 --"'.1.04 
-&.21 -. -5.17 
-7.2" - -6.21 
-1.28 - -7.2.04 
-9.l1 - -8.28 
BELOW -9.31 
IOT1aI -10 .3911 GE-l 
--- - --,.., --------------- --~~-_-_-__ i_~_. ___ . ___ -
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f Cross-sectional mode shapes ( Frames ).] 
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Fig STRUCTURE MODE No 24 / Mode shape· A4 • - 96.8 Hz 
...... ..... 
SCA( 'I.n:; 
oeJ(CT linUS 
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II: ".II~ - ZO.O 
V: -I .~.3 - 1.17 
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Fig STRUCTURE MODE No 26 / Mode shape· S3 • - 101.5 Hz 
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1'~Im-_~_~_~2~~~~~~C~~~~~[~[:::::::::::::::::::::::::::::~:~::;::~~;::::~;;:;;~:~:~;:::::::::::::::::::::::::::::::::::::==:i~ ______ __ 
• BPF pressure field excitation 
- Cruise flight nearfield BPF noise 
prediction 
- Inclusion of fuselage scattering 
• Propeller free field. prediction pro-
gram NOISEGEN developed at FFA. 
• Program code based on a linearized 
version of Ffows-Williams-Howkings 
equation. 
• Fuselage scattering and boundary 
layer effects added. 
• Complex pressures converted to 
Real and Imaginary. pressure fields (Load data). 
• Load data applied to Structure Sub-
nets. 
59 
60 
r:r:.:.-r.-=.;-';:. . 
-811 Pa 
,-: ~~;~(' 
o Pa 
---~~~ .... ------.-~-
1\0 PI 
Predicted rn:s<un: fi~ld 0~ (h::o kf!~:!'"lc <;:-: C': !l,-: s: ~~ :''''''\ c' 
different time: Steps 
'-------------- -- --.-. 
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• Scheme of computation 
Structure model Cavity model 
Coupling nets 
Main net of the coupled problem 
Figure . Natural mode flow of computation 
Coupling nets 
Figure . Frequency response flow of 
computation 61 
m 
I\) 
CONTR.FACfOR(*lO.2) - MODAL CONTRIBUTION TO BPF RESPONSE I 
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Tif'a."l".,t! :0:"' ;o:w - i Ii' iM ...... i 
STRUCTURAL BPF RESPONSE 
Oper4ting deflection sh4pe 
during one cycle. 
~ ... , 
Cu' ll •• rill bin .. 
Fig 
64 
;&I ~:{; 8(114 Dt~ 2'-! A!l. .'1. 
ACOUSTIC CABIN 
Pressure field 
CAVITY RESPONS~J 
in dB 
$:-... ... 1<'. 
ex: _ <10° 
FREQUENCY (HZ~ANAL YSIS VS EXPERIMENTAL MODAL ANAL YSIS.SAAB2000 I $4 '7'-
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2000 FUSELAGE TEST RIG 
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Acou~tic MOCkup ~haker test simulation 
* 16 shakers with simultaneou~ly sinusodial 
force ( 95 Hz ) excitation. 
* Force and phase di~tribution randomly choosen. 
Shaker' Force (H) Pha~e (deq) 
-------------------------------------
1 3.0 30 
2 5.0 105 
3 4.5 60 
4 3.5 45 
5 4.5 135 
6 3.0 75 
7 5.0 15 
8 4.0 120 
9 3.5 150 
10 4.5 120 
11 3.5 75 
a 12 5.0 45 
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I 16 4.0 105 ; 
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68 
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Damper 
coupling-
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Planned analyses . .. .... 
. '., I , A- I I.,. 
• Tuned dampers <--.t~· : '--:l: 
I ~ : 
Structure model 
CoupOng nets 
Damper net 
Maln net of the coupled problem 
. • Structure-borne path identification 
-
• Active Vibration Control 
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Model development 
- Fuselage sections with interior 
- Active Noise Control analyses 
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..... , ............. , ._ ...... _ ......... " ................. .. 
+ • 
ORIGINAL PAGE- IS " .. 
OF POOR QUALITY 69 


Vibro-Acoustic FE Analyses of the Saab 2000 Aircraft

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