Coupled Finite Element Method Based Vibroacoustic Analysis of Orion Spacecraft

Transcription

1 Coupled Finite Element Method Based Vibroacoustic Analysis of Orion Spacecraft Lockheed Martin Space Systems Company (LMSSC) Spacecraft and Launch Vehicle Dynamic Environments Workshop June 21 23, 2016 The Aerospace Corporation, El Segundo, CA Dr. Indranil Dandaroy Human Space Flight Orion Program 2016 Lockheed Martin Corporation. All Rights Reserved

2 Introduction A coupled (structure-acoustic) Finite Element Method (FEM) method for vehicle-level vibroacoustic analysis of Orion spacecraft has been developed Aforementioned method is an alternate and comparable technique to Boundary Element Method (BEM) based vibroacoustic analysis which has traditionally been used in the Orion program for low frequency response Similar coupled FEM based technique has been used for pre/post test analyses of Orion backshell acoustic test with good correlation trends A vibroacoustic model of Orion spacecraft in Liftoff configuration has been developed using coupled FEM and results compared with a corresponding BEM based model Both models were developed in VA One; most of the modeling assumptions, properties and external loading are similar for both models; however, there are some differences in modeling practices used since they were developed by two different analysts 2

3 Outline BEM vs. FEM Talking Points VA One FEM Solution Overview Orion FEM-coupled Vibroacoustic Models Results comparison of FEM vs. BEM based Models Test-Analysis Correlation Final Summary 3

4 FEM vs. BEM Both BEM and FEM are deterministic and comparable numerical methods; For a coupled fluidstructure problem, both methods use a FEM model of the structure; the fluid (acoustics) can be modeled either w/ FEM or BEM Finite Element Method (FEM) An entire domain (volume) mesh is required Entire domain solution is calculated as part of the solution in one step Sparse symmetric (not always) matrices generated Element integrals easy to evaluate; hence computationally less intensive Better choice for interior acoustics, but not so with exterior acoustics without infinite elements Building FE volume meshes can be challenging, but solution times (modal methods) are faster Boundary Element Method (BEM) A mesh of the boundary (surface) only is required Solution on the boundary is calculated first; subsequently the solution at domain points are found as a separate step Fully populated non-symmetric matrices generated Integrals are more difficult to evaluate; requires more attention to avoid numerical inaccuracies and is computationally more intensive Works well for both interior and exterior acoustics Building BE surface meshes are easier, but solution times can be significantly long When properly executed, both methods should provide the same answer and any differences will be within the noise threshold of the numerical method implementation 4

5 Coupled system equations in modal domain VA One Solution Process FEM Coupled (Structure-Acoustic)* * courtesy of ESI US R&D, Inc Modes of FE structural and acoustic subsystems used as basis functions Modal dynamic stiffness matrices for FE structure and FE cavities at a given frequency of interest DD tttttt,ss/aa = ωω nn,ss/aa 22 ωω 22 + DD llllllll + DD iiiiii + DD FFFFFFFFFF reactive resistive impedance BC Equations in cross-spectral form (random vibroacoustics) PJI FE subsystem response 5

6 Orion EM Liftoff FEM Vibroacoustic Model FE structure FE acoustics LAS/CM/CMA/SM/MSA FE acoustic cavity meshes Figures: Lockheed Martin 6

7 Orion FEM-coupled Vibroacoustic Model Structure-Acoustic Coupling FE Area Junctions (Structure-Acoustic) orange indicates modeling of LAS acoustic blankets FE cavity and structural faces are linked individually based on the effective coupling areas Structure-acoustic modal coupling matrix Figures: Lockheed Martin 7

8 FE-coupled vs. BEM comparisons Orion EM Liftoff Model SM Fairing Panel Response SM Fairing Cavity Response Good correlation between the methods with minor spectral variances Figures: Lockheed Martin 8

9 FE-coupled vs. BEM comparisons Orion EM Liftoff Model SM Fairing Cavity (vicinity of solar array/radiator panel) SM Fairing Cavity SPL (vicinity of solar array) Close proximity of BEM surfaces SM Radiator Response Figures: Lockheed Martin 9

10 FE-coupled vs. BEM comparisons EM v7 Liftoff Model ESM Closeout Response SA-MSA Cavity Response Comparison is good with minor spectral mismatches Figures: Lockheed Martin 10

11 FE-coupled vs. BEM comparisons Orion EM Liftoff Model ESM Cavity (Water Tanks + Y) Response JM Fairing Response Good correlation between the methods with minor spectral variances Figures: Lockheed Martin 11

12 FE-coupled vs. Test Correlation Orion Backshell Acoustic Test Test article on stand inside NASA Plum Brook RATF Baffled acoustic enclosure (FE cavity) Test panel Test Vibroacoustic Model (FEM coupled) Photos / Figures: Lockheed Martin & NASA 12

13 FE-coupled vs. Test Correlation Orion Backshell Acoustic Test Test panel panel modes driving window Thermal Window response window pane drum mode 270 Hz Phased Array Antenna (PAA) response Figures: Lockheed Martin Window mode ~270 Hz 13

14 Final Summary This study has demonstrated that the FEM-coupled method is a comparable and feasible alternate technique to BEM, and can provide similar results for Orion EM vibroacoustic analyses Once the challenge of creating acoustic volume meshes is surmounted, the FEM based method is computationally more efficient For EM design cycles, use of this method has significantly shortened the model building & run time (process improvement ~10x) in VA One enabling evaluation of multiple design iterations in a time period not possible before Unless there is a change in structural geometry, the acoustic cavity meshes and FE faces can be reused over and over for future design cycles significantly reducing model building time Since the FEM acoustics is a modal representation, it provides more insight regarding the participation of structure and/or fluid on dynamic responses Use of this method has yielded good correlation with test data 14

15 Questions? 15