1、NASA CONTRACTOR REPORT 159363Analytical Prediction of the Interior Noisefor Cylindrical Models of Aircraft Fuselagesfor Prescribed Exterior Noise FieldsPHASE I : DEVELOPMENT AND VALIDATION OFPRELIMINARY ANALYTICAL MODELSL, D. POPED. C. RENNISONE. G. WILBYBOLT BERANEK AND NEWMAN INC.CANOGA PARKI CA.
2、91303CO NT RACT NAS I - 15782OCTOBER 1980N/ ANahonal Aeronaul_cs andSpace Adm=n_strat_onLangley Research CenterHampton V_rg_n_a 23665Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted
3、without license from IHS-,-,-TABLE OF CONTENTSPage1.02.03.04.05.0SUMMARY . iINTRODUCTION . 42.1 Candidate Approaches for Analytical Model 52.2 Report Organization . 8ANALYTICAL MODELS i03.1 Generalized Power Flow Approach . I03.2 Solution of a General Sound Transmission Problem. 123.3 General Result
4、s for the Noise Reduction . 173.4 Cylinder Noise Reduction . 213.5 Transmission of a Discrete Tone . 333.6 Response to Point Input Harmonic MechanicalExcitation . 523.7 Interior Response for Progressive Wave FieldExcitation . 643.8 Modifications for the Non-ideal Cylinder . 663.8.1 Cylinder Lap Join
5、t Effect . 693.8.2 Effects of End Caps and LongitudinalFlexibility 74EXPERIMENTAL INVESTIGATIONS . 794.1 Phase I Test Article . 804.1.1 Resonance Frequencies . 814.1.2 Damping 864.2 Noise Reduction Measurements . 954.3 Plane-Wave Tonal Excitation . 984.4 Point Mechanical Excitation . 1084.5 Progress
6、ive Wave Excitation . 118COMPARISONS AND VALIDATION OF ANALYTICAL MODELS 1345.1 Basics of Computer Program 1365.2 Noise Reduction of the Test Article . 137Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE OF CONTENTS (Contd).5.2.1 Calculated Resu
7、lts .5.2.2 Statistical Analysis of CylinderNoise Reduction Data .5.3 Tone Transmission Comparison .5.4 Mechanical Excitation 5.5 Excitation by a Random Progressive Wave Field .5.6 Noise Reduction for Increased InteriorAbsorption .REFERENCES APPENDICES:A: Plane Wave Tonal Transmission DataB: Mechanic
8、al Excitation DataC: Progressive Wave Field DataPage137150159164164170172iiProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure No.LIST OF FIGURES15.16.17.18.19.20.i. Cylinder Coordinates and Nomenclature 2. Cylinder/Cavity Configurations .3. Tone
9、Transmission: Incident Plane Wave at 0 = _.4. Phase I Test Article: Unpressurized, UnstiffenedCylinder 5. Cylinder Lap Joint Detail 6. Low Frequency Model .7. Interior Acoustic Response to Acoustic SourceInside 8. Cylinder Acceleration Response to InteriorAcoustic Excitation 9. Cylinder Structure Re
10、sonance Frequencies i0. Cylinder Acoustic Resonance Frequencies .ii. Typical Instrumentation for Loss Factor Measurement.12. Acoustic Loss Factors of Bare Cylinder .13. Measured Structural Loss Factors for Bare Cylinder14. Instrumentation Diagram for Cylinder Noise ReductionMeasurements with Reverbe
11、rant Field Excitation.BBN Measured Noise Reduction (Bare Cylinder) LaRC Measured Noise Reduction (Bare Cylinder) Test Layout for Plane Wave Excitation of Cylinder.Equipment Schematic for Tonal Plane Wave Excitation.Measurement Locations for Tonal Plane-WaveExcitation .(a) Ratio of Incident Pressure
12、to Interior Pressure,Tonal Plane Wave Excitation, _ = 15 20. (b) Ratio of Incident Pressure to Interior Pressure,Tonal Plane Wave Excitation, _ = 45 21. Experimental Configuration for Point MechanicalExcitation of Test Cylinder, Showing Shaker andMeasurement Locations .22. Instrumentation for Cylind
13、er Inertance and TransferFunction Measurements .Page232735676875828387889091949699i001021031041Q5106ii0iiiiiiProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-JLIST OF FIGURESFiBure No. Page23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.39.40.41.Force
14、 Output Signal for Fixed Driving Voltage toUnloaded Shaker, Showing Effect of Mass CancellationCircuit . 112Inertance Function, H(f), For Point MechanicalExcitation 114Sound Level-to-Force Input Transfer Function, H (f),for Point Mechanical Excitation . . . . . . . s. . . . 115Experimental Configura
15、tion for Progressive WaveExcitation of Cylinder 119Instrumentation Schematic for Progesssive WaveExcitation 120Variation of Mean Circumferential Level AlongCylinder Length . 124Microphone Locations for Measurement of Coherenceand Phase of Progressive Wave Field . 126Typical Axial Coherence and Phase
16、 Data for ProgressiveWave Test 128Typical Circumferential Coherence and Phase Data forProgressive Wave Test 129Ratio of Exterior Pressure to Average InteriorPressure, Progressive Wave Excitation 133Initial Noise Reduction Predictions with AnalyticalModel 139Comparison of Predicted and Measured Noise
17、Reductions 146Modal Contributions to Interior Sound Levels . 151Structure Response Contributions to ResonantAcoustic Response Only 152Measured and Predicted Noise Reduction for Cylinder. 158Predicted Tone Transmission, 15 Angle of Incidence. . 160Predicted Tone Transmission, 45 Angle of Incidence. 1
18、61Comparison of Predicted and Measured Acceleration,Point Mechanical Excitation . 165Comparison of Predicted and Measured Acceleration,Point Mechanical Excitation . 166ivProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LIST OF FIGURESFigure No. Page42
19、.45.Comparison of Predicted and Measured InteriorPressure, Point Mechanical Excitation 167Comparison of Predicted and Measured InteriorPressure, Point Mechanical Excitation 168Predictions Versus Measurements, Band-Limited Ratioof Exterior Pressure to Average Interior Pressure,Progressive Wave Excita
20、tion . 169Cylinder Noise Reduction With a 0.00635 Meter(0.25 Inch) Layer of Acoustical Foam . 171VProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Table No.LIST OF TABLESi. Acoustic Resonance Frequencies of LaRC Cylinder 2. Structural Resonance Freque
21、ncies of LaRC Cylinder.3. Band Average Loss Factors-Undamped LaRC Cylinder.4. Details of Interior Microphone Locations for848593Tone Transmission Measurements 1075. Summary of Measurement Information for PointMechanical Excitation 1166. Exterior Sound Levels for Progressive WaveExcitation 1217. Summ
22、ary of Coherence and Phase Measurements 1278. Data for Progressive Wave Field Excitation 1329. Noise Reduction Estimates from LaRC Experiments 154i0. Noise Reduction Estimates from BBN Experiments 155II. Estimated Mean Value of Noise Reduction and 99%Confidence Intervals . 1572 212. Most Significant
23、 Contributions to /,Plane Wave Excitation, _ = 45 162viProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1.0 SUMMARYDuring recent years there has been a growing interest in new air-craft propulsion systems such as powered-lift devices and high-speed pr
24、opellers (propfans) for both commercial and militaryapplications. Studies of the systems have indicated that theywill generate high noise levels, particularly at low frequencies,in the fuselage interiors. At the same time there has been anincreasing demand on the National Aeronautics and Space Admin
25、is-tration to provide technical support to the general aviationindustry, and one problem identified in this field is the reduc-tion of cabin noise levels. In an attempt to solve some of thecomplicated problems involved in the control of airplane interiornoise, NASA Langley Research Center embarked o
26、n an extensiveprogram to identify the important parameters associated withacoustic transmission (airborne and structureborne) into airplaneinteriors and to determine appropriate noise control methodswhich are acceptable with regards to weight and space. As a partof this program, an aircraft interior
27、 noise prediction model isbeing developed by Bolt Beranek and Newman Inc. (BBN), thepurpose being to undertake the required analyses and integratethe technologies and information needed to understand soundtransmission through a fuselage wall into an aircraft cabin, bothfor future development studies
28、 and for the immediate need ofaccurate prediction of interior levels (more properly stated,for prediction of the noise isolation characteristics of thefuselage structures). The effort has been divided into threephases. These are:-I-Provided by IHSNot for ResaleNo reproduction or networking permitted
29、 without license from IHS-,-,-Phase I.Analytical modeling of the transmission problem(interaction of the structures with the exteriorand interior acoustic fields) and preliminaryverification studies using, as a test article, anunpressurized unstiffened cylinder.Phase II.Development of the general ai
30、rcraft interior noisemodel and basic master computer program with appli-cation to advanced test articles (for instance, astiffened cylinder with interior partitions andsimulated trim).Phase III.Completion of the analytical models and softwarewith application to an actual aircraft fuselage,verificati
31、on tests, comparisons, refinements, anddocumentation of the finalized model and software.This report presents the results of the Phase I studies. Thebasic theoretical work required to understand sound transmissioninto an enclosed space (that is, one closed by the transmittingstructure) is developed
32、for random pressure fields and for har-monic (tonal) excitation. The analysis is used to predict thenoise reduction of the test article (i.e., the unpressurizedunstiffened cylinder) and, also, the interior response of thecylinder given a tonal (plane wave) excitation. Comparisons ofpredictions and m
33、easurements are made and a detailed analysis of-2-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-the transmission is presented. This latter study is perhaps themost informative aspect of the exercise undertaken in Phase I.In addition to the above, r
34、esults for tonal (harmonic) mechanicalexcitation are considered.The work was accomplished as a joint effort by BBN/Los Angelesand NASA Langley Research Center. L. D. Pope served as BBNprogram manager and William H. Mayes was LaRC technical monitor.The authors wish to thank Mr. Mayes and Conrad Willi
35、s of NASALaRC for their contributions to the experimental program; alsoAllan G. Piersol of BBN who performed the statistical analysisof the noise reduction data, and John F. Wilby of BBN for generalassistance.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from I
36、HS-,-,-2.0 INTRODUCTIONThe present study has the specific goal of developing an analy-tical model which can be used to predict the sound levels in acylinder for several excitation inputs and interior configura-tions. However, this objective has to be viewed in terms of theoverall objective of the pr
37、ogram of which this present studyforms only the first phase. The complete program has the objec-tive of developing an analytical model to describe the soundfield inside an airplane cabin. Consequently, the analyticalmodel resulting from the present study must not only predict thesound levels in the
38、unstiffened and unpressurized test cylinder(which is an idealized fuselage structure), but it must beadaptable to the more complicated situation present in a realis-tic airplane fuselage. Only then can this study be viewed as afirst phase in the larger program.The two main efforts of Phase I are the
39、 construction of theanalytical models and the experimental validation of thosemodels on an unstiffened cylinder. The work effort underPhase I and envisaged for Phases Ii and III of the presentprogram can be considered in terms of the interior noise re-search and development program underway at Langl
40、ey ResearchCenter. This overall program is concentrating on two areas:(i) the accumulation of experimental data which can be incor-porated into a prediction methodology, and (2) development ofthe prediction methodology itself. The work has a bias towardsgeneral aviation aircraft.Interior noise level
41、s have been measure_ by Catherines andMayes I in single- and twin-engined propeller-driven lightaircraft. These studies define to a large extent the nature of-4-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-the acoustic environment in light aircraf
42、t and establish the needfor analytical prediction methods which will eventually be use-ful in the design of quiet interiors. Sound levels in the cabinsof the aircraft were found to be dominated by propeller andengine exhaust noise, the spectra being essentially tonal innature. In 2 the measured exte
43、rior spatial distributions ofthe acoustic pressures showed the dominance of propeller noiseover the forward part of the fuselage, and exhaust noise over theaft part. Reduction of interior noise is clearly desirable sincelevels in light aircraft range from 85 to 105 dBA. Barton 3developed a method fo
44、r predicting interior noise in STOL aircraftand, utilizing a sidewall noise reduction model which likely isconservative, predicted levels of 90 - 105 dBA and 88 - 92 dBAin aircraft with USBF and EBF systems respectively.Howlett et al., 4 measured the noise reduction of a lightaircraft in a reverbera
45、nt room. Using the Cockburn and Jollymodel 5, a comparison of predicted and measured noise reduc-tion was made. Agreement was not very satisfactory.In addition to the above studies, a series of progressively morecomplicated analysis and data reduction investigations has beencompleted under LaRC spon
46、sorship. These include studies byKoval 6, 7, 8, Vaicaitis 9 and Rennison and Wilby I0,iiamong others.2.1 Candidate Approaches for Analytical ModelBefore developing an analytical model for the present study, itis useful to review the technology available and to considerits applicability to the Phase
47、I studies, and to subsequentPhase II and Phase III work. In general, it can be stated thatmuch of the technological base required for the prediction of-5-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-the test cylinder response and acoustic radiatio
48、n is availablealready. Potential analytical techniques which could be usedfor the present predictions may be generally grouped into twocategories, each of which may be broken down further, basicallyin terms of computational schemes When making predictions,such as required here, with potentially high acoustic and struc-t_re modal densities, it is important to keep in mind that thechoice of computational scheme is significant in the overallproblem solving procedure. The two types of analyses
