Aircraft Cabin Acoustic Modeling

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Lorin Welch
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1 Penn State 2012 Center for Acoustics and Vibration Workshop Aircraft Cabin Acoustic Modeling 2012 Penn State Center for Acoustics and Vibration Workshop Adam Weston Senior Structural-Acoustics Specialist Interior Noise Technology May 2012 BOEING is a trademark of Boeing Management Company.

2 Overview Aerospace Modeling Approach Verify Simulate - Fly Cabin Noise Sources Cabin Treatments Tools SEA FEM/BEM Database Methods FEM/BEM Applications Automation Role Summary and Opportunities Adam Weston, May

3 Aerospace Modeling Approach Acoustic Simulation Role Verify State-of-the-Art Field point mesh Trim Sources Structural Components Insulation 2 Septum Air Insulation 1 Fuselage skin Treatment Acoustic Response L flight Fly Verify Processes Δ flight = L flight - L model L model Simulate Optimize Noise/Weight/Cost Adam Weston, May

4 Cabin Noise Sources Aircraft Walkaround Interior Environmental System Equipment vibration noise Galley and Lavatories Engine Noise Vibration Exhaust Shock-cells Fan Inlet Adam Weston, May

5 dba Cabin Noise Sources Flight Variation Jet Noise Buzz-Saw Turbulent Boundary Layer Shock Cell Shock-cell Turbulent Boundary Layer Turbulent Boundary Layer Thrust Reverser Jet Noise Takeoff Thrust Reverse Climb Cruise Descent Taxi Taxi Time Adam Weston, May

Cabin Acoustic Treatments Aircraft Walkaround Blankets Fiberglass Bagging materials Mass septum Foams Over blankets Trim system trim panels floors stow-bins monuments Acoustic Absorption Seats &

6 Cabin Acoustic Treatments Aircraft Walkaround Blankets Fiberglass Bagging materials Mass septum Foams Over blankets Trim system trim panels floors stow-bins monuments Acoustic Absorption Seats & surfaces Floor coverings Acoustic panels Isolation Mounts ECS/Equipment /Tie Rods Flight control actuators Engines / APU Tuned Vibration Absorbers Structural Damping Constrained layer Flow resistance Particle ECS system Inlet Lining (buzz-saw) Nozzle/Chevrons (shock-cell) Balance/Vibration (EVRN) Reactive / resistive mufflers Flow rates / pipe sizes Diffusers / flow restrictors Fans & powered equipment Air return grill ramp noise Active Noise/Vibration Control Engines / EVRN ANC zonal / headsets Smart Foams Fluidic Wall paper FEM/BEM Focus APU (ramp noise) Fluids in Pipes hydraulics Doors Hatches & Latches Adam Weston, May

7 % Tool Usage Tools Evolution 100% 90% 80% 70% 60% 50% Ray Tracing SEA CFD BEM 40% 30% 20% 10% Empirical FEM 0% Year For Project X, my preferred tools are? Adam Weston, May

Tools Structural Acoustics Design Tools System response is

frequencies Systems Cabin, Sidewall, Equipment Transfer

Low frequencies (Engine Rumble/EVRN) Small systems,

$isolation, mufflers External radiation/diffraction, e.g.$ Hybrid components (damping, mufflers) Database Close

8 Tools Structural Acoustics Design Tools System response is determined by interaction of all components SEA Mid to high frequencies Systems Cabin, Sidewall, Equipment Transfer Function, Large test articles Simple source representation FEM Low frequencies (Engine Rumble/EVRN) Small systems, components, detailed design skin pocket, insulation, damping, isolation, mufflers External radiation/diffraction, e.g. ramp Complex source representation TBL, shock cell, buzzsaw Hybrid components (damping, mufflers) Database Close derivative Quick turnaround Model verification Normalized data 10 db 2dB 3dB Adam Weston, May

9 Building Semi-empirical Source Models Scaling Uncertainty Raw data sets 3dB Normalized data 10 db 2dB The increase in the uncertainty over the measurement uncertainty is due to limitations of the scaling rules used to normalize the basic data. Physics Scaling rules are required to apply the data to new situations. 2dB Check Data / Predictions 3dB Prediction curve 5dB 1dB 2dB Engineering Measurement Uncertainty Adam Weston, May

10 Correlated Sources FEM/BEM vs. FEM-only BEM/FEM Analysis NASTRAN/Virtual Lab Coupled Structural-Acoustic Cross-spectra of Pressure Acoustic Loading FEM Analysis NASTRAN Uncoupled Structural Cross-spectra of Force No Acoustic Loading Cross-Spectra Decomposition Computational Efficiency Partition of Aero-acoustic Loading Adam Weston, May

Application Example Turbulent Boundary Layer Nastran vs. Virtual Lab Displacement PSD 1.0E-11 1.0E-12 1.

11 Application Example Turbulent Boundary Layer Nastran vs. Virtual Lab Displacement PSD 1.0E E E-13 Nastran (partition 10 x 10) Nastran (partition 15 x 15) Nastran (partition 20 x 20) sysnoise (vector=200) sysnoise (vector=100) sysnoise (vector=50) NASTRAN 1.0E-14 NASTRAN 1.0E-15 - Subdivide the structure - Smaller number of partition: overpredict 1.0E Virtual Lab - Smaller number of vector: underpredict Frequency (Hz) Virtual Lab Adam Weston, May

Frequency Band Waterline Coordinate Application Example Shock Cell Waterline Coordinate (inch) Band # Semi-Empirical Source Models 350 777-200 / Trent800 QTD1 Flight Test Data, Condition 103, Nozzle

46 Third Octave Band Spectrum Level at 1 KHz Exterior Fluctuation Pressures SEA Model SPLTOB 300 250 200 150 100 40 35 30 25 20 1600 1650 1700 1750 1800 1850 1900 (inch) 777-200 / Trent800 Axial

12 Frequency Band Waterline Coordinate Application Example Shock Cell Waterline Coordinate (inch) Band # Semi-Empirical Source Models / Trent800 QTD1 Flight Test Data, Condition 103, Nozzle Pressure Ratios 1.71 / 2.46 Third Octave Band Spectrum Level at 1 KHz Exterior Fluctuation Pressures SEA Model SPLTOB (inch) / Trent800 Axial QTD1Coordinate Flight Test Data, Condition 103, Nozzle Pressure Ratios 1.71 / 2.46 Third Octave Band Spectrum Level at angular position 75 deg. dpred SPLTOB FEM Model Axial Position (inch) Coordinate dpred06 Adam Weston, May

13 Diffuse and Aero-Acoustic Sources Generalized Complex Cross-Spectra Base Form S xy Power Spectra S xx S yy Spatial Coherence 2 xy Phase e i xy Diffuse TBL Shock Cell S12( r, ) S12( 1, 2, ) S12( 1, 2, ) S 11 ( ) S 11 S 22 S 11 S 22 e e 1 1 [( L sin kr kr e ) ( ) ] 1( ) L2 ( ) 2 2 Random No phase e i 1 / U ph w 12( 1, 2, ) e i S xx, S yy 2 xy e i r Power spectra of the pressure field Coherence of the pressure field Phase factor Separation distance between nodes 1,2 Separation distances (flow, cross-wise) 1,2 Correlation length scales (flow, cross-wise) U ph Phase velocity L 1,2 Correlation length w.r.t. engine nozzle Adam Weston, May

14 FEM Application Example Low Frequency Engine Vibration Related Noise Rotating shafts Strut Excitation (Rotor Dynamics) Structure (Entire Aircraft) Acoustic (FEM) Sidewall System (Biot Theory) Adam Weston, May

Cabin Acoustic Treatments Sidewall System Design

leaks Interior Panel mass per unit area coincidence

Fuselage Structure mass per unit area damping loss factor

focus is components Damping on a single skin pocket or

15 Cabin Acoustic Treatments Sidewall System Design Insulation flow resistance mass per unit area Thickness No leaks Interior Panel mass per unit area coincidence frequency damping loss factor Structural isolation Fuselage Structure mass per unit area damping loss factor coincidence frequency SEA entire system modeling FEM/BEM focus is components Damping on a single skin pocket or stiffener Biot sidewall/trim slice Anechoic reverb TL simulation Adam Weston, May

integration tool Includes effects of: Sources Insulation Damping

16 FEM to SEA Cross-over in Aerospace Applications Airplane Half-Ring Model 30 to 200+ subsystems Lab TL Panel Model SEA is the primary integration tool Includes effects of: Sources Insulation Damping Structure Absorption Leaks With support from FEM/BEM Adam Weston, May

FEM/BEM Application Example Transmission Loss Damping verification, Transmission Loss Don t model chambers, just panel Indirect BEM, Baffle, Diffuse Source reverberation r e v e r b e r a t i o n r o

17 FEM/BEM Application Example Transmission Loss Damping verification, Transmission Loss Don t model chambers, just panel Indirect BEM, Baffle, Diffuse Source reverberation r e v e r b e r a t i o n r o room m P Test i t e article s t a r t i c l e..... A n e c h o i anechoic a n e c h o i c c h a m b e r c c h a m b e r chamber P r isolators i s o l a t o r s G r g o r u o n u d n d Transmission Loss Test Facility Adam Weston, May

18 Transmission Loss FEM/BEM Application Example Flat Panel Transmission Loss Validation TL Comparison--SYSNOISE vs. Textbook Results Beranek Noise & Vibration Control Page 307: 5ft x 6.5 ft x 1/8 in panel (a) reference mode calc. (b) plateau calc. (c) force wave calc. (d) experimental results SYSNOISE Frequency Adam Weston, May

19 FEM/BEM Application Example Transmission Loss Validation Link Structural model Acoustic model f = 100 Hz f = 223 Hz Adam Weston, May

0 50.0 Sysnoise trim Test trim Sysnoise bare Test bare 40.

20 TL (db) FEM/BEM Application Example Transmission Loss Validation 3 3I Fiberglass Septum Lining Panel Sysnoise trim Test trim Sysnoise bare Test bare Frequency (Hz) Adam Weston, May

005 0 100 1000 10000 IRDM Analysis 0.02 0.015 Detailed FEM 0.01 0.

21 FEM/Modal/IRDM Application Example Damping Estimations Synthesized FRFs Band Average Damping System Damping (Band-Average) IRDM Analysis Detailed FEM Modal Strain Energy Material Loss Factor Modal Damping System Damping (Modal) Adam Weston, May

22 Sound Pressure Level, SPL - db re 20 m Pa Application Example - Damping Define SEA Loss Factors Through FEM 0.15 Loss Factor-1 Insulation Loss Factor-2 Insul+Add-on db Loss Factor-3 Add-On Adam Weston, May

23 FEM Application Example Automation/Components Acoustic Muffler Tool Transmission Loss Absorbent Combination GUI Frequency Perforate Reactive Adam Weston, May

Automation of the design process Physics based models Conceptual Airplane Automated model airplane creation (SEA, FEM, ECS, Ramp) Use for high pay-off, redundant

Component and Parts Specifications Sound Quality and Regulatory based Design Objectives Other (3%) TrimUpThk (36%) TrimLoThk UpperNCTL2 (40%) (51%) TrimUpThk (26%)

24 Automation of the design process Physics based models Conceptual Airplane Automated model airplane creation (SEA, FEM, ECS, Ramp) Use for high pay-off, redundant and error prone processes Muffler tool SEA Support Damping, TL test simulation Optimization EBDtrimdens (9%) Other (4%) Component Performance Confirmation Component and Parts Specifications Sound Quality and Regulatory based Design Objectives Other (3%) TrimUpThk (36%) TrimLoThk UpperNCTL2 (40%) (51%) TrimUpThk (26%) Anova information for response dbavar septsurfmass (5%) UpperNCTL2 (5%) OrthotrimDens EBDtrimdens (13%) (8%) Anova information for response weightvar Adam Weston, May

25 Summary and Challenges Summary Accurate source modeling critical for aerospace acoustic and structural-acoustic applications Future challenges Verify Lab 1. Partially correlated sources approximations 2. Improve treatment measurement techniques Lower/quantify manufacturing tolerances Component model validation Simulate Improve modeling accuracy and speed Efficient integration of all methods FEM, SEA, databases Fly Improve in-flight measurements for (1) better source representations (2) path analysis Adam Weston, May

Sonic Response Analysis (SRA) Tool Vibro-Acoustic Capabilities

Sonic Response Analysis (SRA) Tool Vibro-Acoustic Capabilities Mostafa Rassaian, Ph.D., P.E., Technical Fellow Structural Technology Boeing Research & Technology Tom Arakawa, Program Analyst, Structural