Mid-High Frequency Vibroacoustic Modeling and Correlation of Orion Ground Test Articleand Correlation of Orion Ground Test Article

Dr. Indranil DandaroyLockheed Martin Space Systems Company

Human Space Flight Orion ProjectHuman Space Flight, Orion Project19–21 June 2012

1© The Aerospace Corporation 2012

OutlineOutline

• Motivation

• Issues with Pre-Test Model

• Post-test Hybrid Finite Element Method-Statistical Energy Analysis(FEM-SEA) Models

• Model Changes (Pre-test to Post-test) Adequate discretization of subsystems  Individual Panel CorrelationsIndividual Panel Correlations Updating System Properties Improvement of Critical Load Path Modeling Damping & Absorption Adjustments

• Results & Discussion

• Conclusions / Lessons Learned

2

• Conclusions / Lessons Learned

2012 SCLV Workshop

MotivationMotivation

• A full size Ground Test Article (GTA) of Orion Multi-Purpose Crew Vehicle (MPCV) has beentested in the Reverberant Acoustic Lab (RAL) at Lockheed Martin Space SystemsCompany.

• Various configurations of the GTA have been tested in the reverberation chamber subjected to flight-level acoustic excitations and microphone and accelerometer measurements have been taken to understand the complex dynamic load paths in this

hi lvehicle.

• Before the tests were conducted, a preliminary SEA model was built and analyzed toestimate the dynamic response of GTA. However, correlation of test data with pre-test

l i t ti f tanalysis was not satisfactory.

• This presentation describes the model refinement work that was subsequently performed on the GTA SEA vibroacoustic model to improve the correlation and reflect the power flowsth h th d l t lthrough the model more accurately.

• Development of this refined vibroacoustic model and test-analysis correlation hasestablished better modeling practices that will be used for future flight vehicle design and

ifi ti l i l

32012 SCLV Workshop

verification analysis cycles.

3

GTA AcousticGTA Acoustic TestingTesting

Test 1LAV Internal Cavity Configuration

Test 1ACrew Module (CM) only configuration

Test 2Launch Abort Vehicle Configuration

Test 3Nominal Launch Configuration

4

July 2011 August 2011 September 2011 October 2011

2012 SCLV Workshop Photos: NASA and Lockheed Martin

Orion GTA IntegrationOrion GTA Integration

CM Pressure Vessel (PV) Orion Crew Module/LAS StackHeatshield

5

( )

Photos: NASA and Lockheed Martin2012 SCLV Workshop

Issues with PreIssues with Pre--Test ModelTest Model

• Test-Analysis correlation could be better. In addition, there were largedivergences in many subsystem responses between SEA and BoundaryElement Method (BEM)* models.

• Incorrect Segmentation – Several subsystems had poor Modes-In-Band (MIB) especially towards the lower end of the frequency spectrum.

• SEA Panels did not always correlate to their FEM models.

• Significant number of beam subsystems in the model did not reflect the• Significant number of beam subsystems in the model did not reflect thecorrect properties.

• Dynamic loads paths were not modeled correctly in critical areasDynamic loads paths were not modeled correctly in critical areas.

• Structural damping and acoustic absorptions were not representative.

62012 SCLV Workshop

*BEM model is used for Orion vibroacoustic analysis below 300 Hz, SEA/Hybrid is used for > 300 Hz

GTA FEMGTA FEM--SEA Hybrid Models SEA Hybrid Models (Post(Post--test)test)( ost( ost test)test)

Represents theascent configuration

CM – Crew ModuleLAS – Launch Abort SystemSM – Service Module

CM

Backshell

Fwd Bay Cover

Abort MotorCMHeatshield

LAS Fillet

Test Fixture LAS Fairing

LAS Fillet

CM inside LAS Fairing

SM Closeout      

LAS Fairing

Configuration 1A (CM Only)

72012 SCLV Workshop

FairingConfiguration 1A (CM Only)

Configuration 3

Config 3 = Config 1A + the structure-acoustic path to CM through the LAS and SM

Figures: Lockheed Martin

Model Refinement FlowchartModel Refinement Flowchart

Refine Acoustic FFNs

Proper segmentation of SEA subsystems based on MIB / FE for stiff subsystems

Correlation of SEA Panels with FEM& Update Properties

Adequate Representation of Load Transfer Pathsi.e. connections (remodel based on FEM/test/EFM)

Tweak structural damping / acoustic absorption for best correlation

82012 SCLV Workshop Chart: Lockheed Martin

SEASEA--FEM Panel CorrelationFEM Panel Correlation

Panel –SandwichPanel Skin –

Equivalent IsotropicPanel Skin –Panel Skin –Composite

LAS Fairing Panel – FEM LAS Fairing Panel – SEALAS Fairing Panel FEM g

• From laminate (PCOMP) layup of panel skin in FEM, the equivalent isotropic representation of the skin is obtained

• The isotropic skin with the orthotropic core forms the SEA sandwich panel

• SEA panel modeled as a sandwich panel to account for transverse shear dynamics of core

92012 SCLV Workshop

• FEM panel was assessed over several boundary conditions to introduce statistics

Figures: Lockheed Martin

SEASEA--FEM Panel CorrelationFEM Panel Correlation

Radiation Efficiency ComparisonModes‐In‐Band (MIB) Comparison

Panel Response Comparison to 

102012 SCLV Workshop

DAF Excitation 

Graphs: Lockheed Martin

RefiningRefining Critical Dynamic Load Paths Critical Dynamic Load Paths

TAS-PV LAS Fairing

BSoverride

BS TAS

Pressure Vessel (PV)

BS

PV

override SEA CLFs with calculated CLFs

• Connections are representative of the FEM structural

LAS-CM BumperBS-TAS

Bulb SealBackshell

(BS)

EFM StudyConnections are representative of the FEM structuraldynamics model

• If two subsystems are not connected physically in theFEM, they have been manually disconnected in thej ti i i t hi h f ll CLF

y

junction using a script which forces null CLFs

• Test data indicated that LAS fairing was decoupled fromBS across bulb seal; bulb seal model in GTA FEM notadequate; In SEA this was turned off

112011 SCLV Workshop

q ;

• LAS-CM Bumper transmission was based on Energy Flow Method (EFM) calculations

2012 SCLV WorkshopCLF – Coupling Loss Factor

Figures and Graph: Lockheed Martin

FE SubsystemsFE Subsystems

Heatshield Shoulder (FEM)

FE subsystems in the hybrid model:

Heatshield shoulder (very stiff with tight radiusof curvature)

W-Truss beams connecting the LAS to the CM(not shown in figure)

Heatshield Center (SEA)

HS Shoulder

Drawbacks: 1. FE mesh may not be good enough for high frequencies without significant

re-meshing or using higher order elements.2. High modal count

12

g3. Hybrid FEM-SEA model takes about 2.5 hrs to run from 300 – 2500 Hz.

2012 SCLV Workshop Figure: Lockheed Martin

Config 3 TestConfig 3 Test--Analysis Correlation Analysis Correlation Results & DiscussionResults & Discussion

• PSD plots are compared between 1/3-octave for analysisand 1/6-octave for test (PSD is frequency normalized)

• SPL plots are compared between test and analysis at p p y1/3-octave

• Where multiple sensors were available, averaged datahas been compared to analysis. However, many locationsp y , yhad only one sensor for correlation

• Pre-test predictions have been shown in some plots, butnot all to avoid clutter

• Post-test predictions are run and shown only for 300 –2500 Hz

Plot guide:Solid black line – Post-test Hybrid FEM-SEA predictionDashed black line – Pre-test SEA prediction (where shown)Dashed colored lines – Various test sensor measurements for

132012 SCLV Workshop

a given subsystemSolid cyan line – Average of the various test sensor

measurements for a given subsystem

Figure: Lockheed Martin

LAS Fairing/LASLAS Fairing/LAS Fairing CavityFairing Cavity

0 deg

LAS Fairing Cavity

LAS Fairing Cavity

LAS fairing blanket was modeled as a treatment layup

0 deg. LAS Fairing PanelP t t t

g y

Post­test

Post­test

L (d

B)

g^2/

Hz)

Pre­test

Pre­test SPL

PSD

(g

142012 SCLV Workshop Figures and Graphs: Lockheed Martin

SM Fairing Cavity/HeatshieldSM Fairing Cavity/Heatshield

HeatshieldPre­test

Heatshield

PSD

(g^2

/Hz)

Post­test

GTA Crew Module (CM)

SM Closeout Cavity

B))

Load Transfer Path – Heatshield

Total PowerSM Closeout Cavity

Pow

er (d

B

SPL

(dB

) Cavity

152012 SCLV Workshop Figures and Graphs: Lockheed Martin

BackshellBackshell

Backshell F response

Backshell F

PSD

(g^2

/Hz)

Total Power

LAS Fairing Cavity ContributionBackshell

panels areprimarily drivenp yby the LASfairing cavity(acoustic path)

162012 SCLV Workshop Figure and Graphs: Lockheed Martin

PV Barrel & ConePV Barrel & Cone

PV Barrel B PV Cone B

PSD

(g^2

/Hz)

PSD

(g^2

/Hz)

SEA ribbed panel representation of orthogrid (waffle)

PV Cone

SEA ribbed panel representation of orthogrid (waffle) construction PV barrel is based on a discrete FEM model where the rib dimensions and spacing are non-uniform.

Above 1000 Hz, the SEA ribbed representation is NOT capturing the waffle construction ribbed panel dynamics

PV BarrelPV Cone B

capturing the waffle construction ribbed panel dynamics. The SEA under-prediction above 1000 Hz as seen in PV barrel is less evident on the PV Cone, but some panels still show this phenomenon (could be transmission from the PV Barrel).

This needs to be investigated through additional analysis

172012 SCLV Workshop

PV Barrel BThis needs to be investigated through additional analysis and/or test.

Figure and Graphs: Lockheed Martin

Load Transfer Path to PV BarrelLoad Transfer Path to PV Barrel

Power Input to PV Barrel B

dB)

Pow

er (d

18

Load path to PV barrel is primarily structural through the Mid & Aft Ring Beams and the Longerons (via the TAS). Acoustic path from the Backshell via the BS-PV cavities is fairly decoupled.

2012 SCLV Workshop Graph: Lockheed Martin

ConclusionsConclusions

• A refined and correlated hybrid FE-SEA model has been developed to representthe Orion Ground Test Article (GTA). Several refinements were done to the pre-test model to improve the quality of test-analysis correlation:

Avoidance of too much segmentation in SEA model to avoid poor modes-in-band. A couple subsystems which were very stiff at the lower end of the frequency range of analysis were modeled with FEM, thus making the model a hybrid FEM-SEA y , g yrepresentation.

All important SEA panels were individually correlated with their FEM representationswith the criteria of matching modes-in-band and radiation efficiency. This ensuredgood correlation between the standalone responses to the SEA and FEM versions ofgood correlation between the standalone responses to the SEA and FEM versions of the panel.

Several critical dynamic load transfer paths were remodeled. The EFM module wasused in one critical connection to ascertain the transmission characteristics using ga breakout FEM model.

Adjustments in structural damping and acoustic absorption spectra were made toachieve the best correlation as a final step.

192012 SCLV Workshop

p

ConclusionsConclusions

• Considerable improvement in the quality of correlation with test data from pre-test to post-test has been made.

• The refined vibroacoustic model is not only able to show good match with testdata, but also predicts the dynamic load transfer paths from the external acoustic excitation to the interior of the CM more accurately.

• There is some discrepancy in test-analysis correlation of the PV panel responses due to limitations of the ribbed panel SEA representation inmodeling such a non-uniform layout. Further study is needed to understand hi d fi i i h ib i d lthis deficiency in the vibroacoustic model.

• This model correlation exercise will provide valuable insight for modeling of the flight vehicle.the flight vehicle.

202012 SCLV Workshop

Questions?

21Photo Credits: NASA and Lockheed Martin