1、.-. , r , .- ) , .-. I .-. , I r r ! .-. , I NASA CONTRACTOR REPORT 165869 NASA-CR-165869 19820015078 I Analytical Prediction of the Interior Noise for Cylindrical Models of Aircraft Fuselages for Prescribed Exterior Noise Fields I ) 1 PHASE II: MODELS FOR SIDEWALL TRIMI STIFFENED STRUCTURES, AND CA
2、BIN A,c6uSTICS L. D. POPE E. G. WILBY WITH FLOOR PARTITION r BOLT BERANEK AND NEWMAN INC . CANOGA PARK, CA. 91303 CONTRACT NASl-15782 APRIL 1982 NIS/ National Aeronautics and Space Admlnlslratlon Langley Research Center Hampton Virginia 23665 liBRARY COpy APR? 71982 LANGLEY RESEAR“ CnnER LIBRARY. NA
3、SA t . AM?TON. VIRGINIA Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA CONTRACTOR REPORT 165869 ANALYTICAL PREDICTION OF THE INTERIOR NOISE FOR CYLINDRICAL MODELS OF AIRCRAFT FUSELAGES FOR PRESCRIBED EXTERIOR NOISE FIELDS Phase II: Models for S
4、idewall Trim, Stiffened Structures, and Cabin Acoustics With Floor Partition L.D. Pope E. G. Wil by Bolt Beranek and Newman Inc. 21120 Vanowen Street Canoga Park, CA 91303 Contract NASI-15782 April 1982 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,
5、-!ABLE 01 CONTENTS SUMMARY . . . . . . . . . . . . . . 1 3 4 INTRODUCTION 2.1 Analyt1cal Model 2.2 Report Organization 4 2.3 Program Management. 5 3.0 ANALYTICAL MODEL 6 3.1 Trim Dynamics 6 3.7 3.8 Power Radiated 1nto Cab1n 21 A Preliminary Comparison 30 Band-L1mited Power Absorbed on Cabin Wall (wi
6、th trim) 34 Noise Reduction Calculation High Frequencies . Influence of Internal Radiation Damping Transmission of a Tone Modal Propert1es of the Cabin Space (Cy11nder w1th Floor) F1n1te D1fference in Two Dimens10ns Boundary Cond1t1ons Details of Calculation Normal1zation Fuselage Structural Model M
7、odel for a Curved Orthotropic Panel Calculation of the Structure/Acoustic Coupling Term f(n,r) (Cy11nder with Floor) Calculat10n of the Acoustic Loss Factor No1se Reduction 1n the Volume Stiffness Controlled Region End Cap Transmission 42 43 47 52 55 56 58 60 68 69 71 73 75 77 99 3.10 Status of the
8、Interior Noise Program (Phase II). 102 -1-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE OP COBTERTS (continued) EXPERIMENTS 4.1 NASA Tests . . . . . . . . . . . . . 103 . . . . . . 103 Description of Models 104 Instrumentation and Apparatus .
9、 . . . . . 105 Test Procedure . 106 Application of Tr im 108 4.2 BBN Test 109 4.3 Noise Reduction Data Analysis 109 5.0 RESULTS AND COMPARISONS 111 5.1 Cavity Modes (Cabin with Floor) 5.2 Noise Reduction Measurements, Predictions, and Comparisons . . . . 111 . . . . 113 Noise Reduction Measurements
10、114 5.2.1 Predictions for the Bare 0.020 in. Ring-Stringer Stiffened Cylinder 114 Structural Model Noise Reduction Prediction Discussion of Results . . . . . 115 117 . . . 121 5.2.2 Predictions for the 0.063 in. Unstiffened Cylinder with Floor and Insulation . . Discussion of Results Predictions for
11、 the 0.020 in. . . . . . Ring-Stringer Stiffened Cylinder with Floor and Trim . . . . Acoustic Loss Factors and Trim Transfer Coefficients 122 128 129 129 Structural Loss Factors 130 Influence of Stringer Exposure 130 Discussion of Results 136 -i1-Provided by IHSNot for ResaleNo reproduction or netw
12、orking permitted without license from IHS-,-,- fABLE OP COHTEBTS (continued) 5.3 statistical Analysis of Prediction Error 137 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . APPENDICES: A: Transfer Matrix for Trim Insulation B: Photographs of Test Articles C: Finite Difference Results - Aco
13、ustic Modal Patterns and Resonance Frequencies, e = 49, a = 1m, q = O. o FIGURES -111-141 143 148 153 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LIST OF FIGURES Figure No. 1. Trim Model - Insulation and Lining 2. Typical Wide Body Trim Installat
14、ion 3. Acoustical Parameters for Owens-Corning Fiberglas Type PF105. Fiber Diameter is 1 Micron and Bulk Density is 9.6 kg/m3 (0.6 lb/ft3) 4J 4. Comparison of Trim Transfer Coefficient Prediction with Measurement 5. 6. 7. 8. 9. 10. Fuselage Model - Cylinder with Floor Partition Finite Difference Gri
15、d Nomenclature Grid Coordinate Specification Fuselage Structural Models Cylinder Subpanel Dimensions (Skin Only) Cylinder Imperfection Model 11. -Ratio of the Integral 01 to Interval 61, versus e 12. 13. 14. 15. 16. Approximate Criteria for Relief of Membrane Stresses Status of Cylinder Noise Reduct
16、ion Program (Phase II) Unstiffened Cylinder - Model Details and Microphone Locations (Dimensions in centimeters) Stiffened Cylinder (Dimensions in cm.) Cross Section of Stiffened Cylinder with Floor and Trim Installed (Dimensions in cm.) 17. Noise Reduction Test Instrumentation 18. Arrangement of Ap
17、paratus (Dimensions in cm.) 19. Modal Pattern for the (0,0,2) Mode 20. Modal Pattern for a 150 Floor 21. Modal Pattern for a 300 Floor 22. Details of the 300 Floor Measurement 23. Finite Difference Calculation (400 Floor) 24. Equal Volume Sampling Scheme 25. Measured Noise Reduction of the Bare 0.02
18、0 in. Ring-Stringer Stiffened Cylinder -lv-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LIST OF FIGURES (continued) Figure No. 26. Measured Noise Reduction of the 0.063 in. Unstiffened Cylinder with Floor and Insulation 27. Measured Noise Reductio
19、n of the 0.020 in. Ring Stringer Stiffened Cylinder with Floor and Trim 28. Structural Loss Factors of the Stiffened Cylinder Without Floor 29. Acoustic Loss Factors of the Stiffened Cylinder Without Floor 30. Modes of the Stiffened Cylinder Computed with the Mikulas and McElman Equation 31. Respons
20、e of the Cylinder Skin to Broad Band Shaker Input 32. Comparison of Predicted and Measured Noise Reductions, 0.020 in. Stiffened Cylinder Without Floor or Trim 33. Structural Loss Factors of the Unstiffened Cylinder with Floor and Insulation 34. Acoustic Loss Factors of the Unstiffened Cylinder with
21、 Floor and Insulation 35. Trim Transfer Coefficient for the Unstiffened Cylinder with Floor and Insulation 36. Comparison of Predicted and Measured Noise Reductions, 0.063 in. Unstiffened Cylinder with Floor and Insulation 37. Acoustic Loss Factors of the Stiffened Cylinder with Floor and Trim 38. T
22、ransfer Coefficient for the Stiffened Cylinder with Floor and Trim 39. Structural Loss Factors for the Stiffened Cylinder with Floor and Trim 40. Comparison of Predicted and Measured Noise Reductions, 0.020 in. Stiffened Cylinder with Floor and Trim (Stringers Exposed) -v-Provided by IHSNot for Resa
23、leNo reproduction or networking permitted without license from IHS-,-,-LIST OP !ABLES Table No. 1. Modal Pairs Having Highest Contributions to Interior Level 118 2. Modal Pairs Having Highest Contributions to Interior Level . . . . . . . . . . . . . 125 3. Modal Pairs Having Highest Contributions to
24、 Interior Level . . . . . . . . . . . . 132 4. Effect of Stringer Exposure . . . . . . . 136 5. Predicted versus Measured Noise Reductions 138 -. -vi-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1.0 SUMMARY As a part of the NASA Langley Research C
25、enter program to identi fy the important parameters governing sound transmission into airplane interiors, and to determine noise control methods, an aircraft interior noise prediction model is being developed by Bolt Beranek and Newman Inc. (BBN) of Los Angeles. The work includes analytical modeling
26、 and integration of information and technologies needed to understand sound transmission through a fuselage wall into an aircraft cabin. A three phase program has been defined for accomplishing the goal. In the first phase (now concluded), the basic analytical modeling of the transmission problem (i
27、nteraction of the structure with the exterior and interior acoustic fields) was undertaken and preliminary validation studies were conducted using an unpressurized, unstiffened cylinder as a test article. Results of that work were presented in Reference 1. The second phase of work, reported in this
28、document, includes the development of the general aircraft interior noise model and the laying out of the basic master computer program. Validation studies are considered using more advanced test articles (one being a stiffened cylinder with a floor partition and interior trim, i.e., insulation and
29、lining). The third phase, now underway, involves completion of the analytical models (including propeller excitation) and software development with application to an actual (or simulated) aircraft fuselage, along with validation tests, comparisons, refinements, and documentation of the finalized mod
30、el and software. As stated, this report presents the results of the Phase II studies. The theoretical developments of Phase I that describe the interaction of the structure and the interior acoustic field -1-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IH
31、S-,-,-are generalized to inclune the effects of sinewll insulation and lining (trim). The new analysis leads to a transmission coefficient that multiplies the previously derived expression for the power inflow to the cavity for the case where the trim is absent and an additive term giving an increas
32、e in the damp ing of the sidewall structure by the trim. Also a more precise calculation of the power flow from a structural mode closely coupled (in frequency) to an acoustic mode is developed to account for the influence of the radiation damping of the struc tural mode by the highly receptive acou
33、stic mode. A major andition is the generalization of the geoMetry of the acoustic space to include a floor (partition). The complex cross-sections modal properties are computed using a finite difference approach. Appropriate normalizations and use of the data for calculating the acoustic/structural
34、coupling terms ann t,e cavity loss factors (using predicted wall admittances) are also detailed. Comparisons of noise reduction predictions with measurements are presented for three test articles: 1) a ring-stringer stiffened cylinder without floor or trim; wall thickness of O.000508m (0.020 inches)
35、. 2) a 0.0016m (0.064 in.) thick unstiffened cylinder (the Phase I test article) modified with a floor partition ann lined with a 0.0127m (0.50 in.) thick layer of PF-105 fiberglass that is covered with a O.0000508m (0.002 in.) vinyl film. 3) a 0.00050Rm (0.020 in.) ring-stringer stiffened cylinder
36、(same as (1) above) with floor partition lined with a simulated trim consisting of a O.0127m (0.50 in.) thick -2-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-, layer of PF-I05 fiberglass covered with a 0.00119m (0.047 in.) thick layer of lead viny
37、l weighing 2.44 kg/m2 (0.50 lb/ft2) with a 0.0127m (0.50 in.) layer of PF-105 fiberglass on the inside of each end cap and exposed directly to the interior. To our knowledge no attempt has ever previously been made to compute noise reductions for configurations as complex as cases (2) and (3) above.
38、 2.0 IR!RODUCTIOR The present study has the specific goal of developing an analyti cal model that can be used to predict the sound levels in a ring stringer stiffened cylinder that has a partition simulating a cabin floor and insulation and lining on the inside of the cylinder wall Simulating a basi
39、c cabin sidewall trim. Theoretical developments for harmonic (tonal) excitation and for excitation by a reverberant acoustic field are given. Predictions of the noise reduction for three different test articles are compared to measurements for purposes of model validation. No calculations are presen
40、ted for tonal excitation in this report (some have already been given in 1). Tone prediction capability is to be brought to a practical level in Phase III when the propeller induced exterior pressure field description is to be incorporated into the model and the modal forcing functions derived. -3-P
41、rovided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2.1 Analytical Model In Reference 1, a basic discussion of the power flow technique adopted for this project is given. To a large extent, the concepts used for the predictions of concern here have been d
42、eveloped in References 2 and 3. Rowever, in the Phase I report, results from 2 and 3 were specialized to include the case of harmonic (tonal) excitation. In this report, the concepts previously developed in 1, 2 and 3 are extended, mainly by including the trim dynamics. Also, although including such
43、 information does not represent an advance in the concepts of Phase I, much more complex structural and acoustic properties are considered. Most notable is the use of finite-difference modal data for the cavity. Also the structural (modal) properties of the orthotropic cylinder (one stiffened by rin
44、gs and stringers) are utilized. 2.2 Report Organization A brief overview of the organization of this report is included here. Basically this report presents results of (1) analytical derivations, (2) experimental tests, and (3) validation studies. In the analytical development, there is to begin wit
45、h, one funda mental goal, that being to. incorporate the trim dynamics. This has to be done for both the low and high frequency models. After that has been accomplished, consideration is given to improving the precision of calculations of power flow for certain coupled acoustic and structural modes
46、by including the effect of radia tion damping of a highly resonant structural mode when closely coupled to a highly resonant acoustic mode. Generalization of the tonal transmission calculation is then considered; however the question of exterior field for the propeller excitation remains for the Phase III study. After that the question of cavity modes for the cab
