Acoustic Simulations with MSC.Actran

 A few words about FFT and Actran

 Case Study: Dutch Space Solar Panels Study

. Experimental aspects, Jaap Wijker (Dutch Space / U.Twente)

. Numerical computations with Actran (FFT)

 Conclusions

2 Copyright Free Field Technologies FFT and Actran

 Free Field Technologies . Created in Belgium in 1998 . Software Development Company (Actran) . Specialists in acoustic, vibro-acoustic and aero-acoustic CAE

 Main activities . Development of the Actran software suite . Provision of related services: training, consulting, technology transfer, custom developments, CAE process automation . Research in acoustic CAE and related fields

 Over 250 industrial customers worldwide  FFT joined MSC Software Corporation in Sept.2011

4 Copyright Free Field Technologies The Actran software suite

Actran for NASTRAN Actran DGM

Actran Vibro-Acoustics Actran Aero-Acoustics Actran TM

Actran Acoustics

Actran VI Actran

5 Copyright Free Field Technologies Actran Solver

 Acoustic FEM/IFEM approach IE domain . The air is modeled with acoustic FEM . The IFEM are used for Non Reflective Boundary Conditions . Actran contains a full structural solver FE domain . Multi-layered materials (ex: glasswool-heavy-layer-steel) . Rich set of materials, loads, boundary conditions  Implementation . Multi-purpose toolbox: several computational sequences . Linux or Windows platforms . Direct & iterative solvers, multiple load & restart . Several types of parallelism available  Interfaces with many other tools

6 Copyright Free Field Technologies Ease of use

 Actran contains a pre- and post-processing tool (Actran/VI) . Nice, modern GUI with tree of objects . Based on Python + TK: Easy to automate & script . Automatic recognition of objects & their properties (ex: modal basis) . MP3 generator, waterfall, maps, dBA scale, ISO norms, animations, etc  Nastran to Actran Translator . New in R13 . Easy and fast creation of Actran vibro-acoustic model from Nastran models . Improve/update the translated model with Actran features (visco-thermal elements, porous elements, …)  Actran is compatible with most meshing tools on the market . Handling of names, comments, etc

7 Copyright Free Field Technologies How Complementary is Actran to Nastran?

 Efficient handling of the damping . Handling of physical damping, in physical coordinates! . Ex of use: put damping at a specific location, not on a mode . Foams, porous materials: Ex of use: carpets, liners, …  Loads, materials, & boundary conditions . Specific excitations: Diffuse Field, Random, … . Import loads from external CFD tools (aeroacoustics) . IFE, Modal Basis, etc . Heterogeneous media  Pre- & post-processing  The compatibility with Nastran is very high: every time it makes sense, Actran is used as a complement. It can however sometimes be better to use it alone

8 Copyright Free Field Technologies Space Applications with Actran

 At lift-off components like satellite or antennas carried on skyrockets are exposed to intense acoustic excitation that can damage their structures

TABLE 9.1. Summary of Dynamic Excitations During Various Events. Target Applications Details Event Source of Dynamic Load Basic Characteristics of Dynamic Load (Section) Transportation** Various 3.1 Pre- Seismic loads** Low frequency mechanical transient 3.2 Flight Wind on launch pad Low frequency fluctuating pressure 3.3 Motor ignition overpressure* Low frequency pressure transient 3.4 Liftoff Liftoff release* Low frequency mechanical transient 3.5 Engine/motor acoustic noise* Broadband random acoustic pressure 3.6 Wind during ascent Low freq. random fluctuating pressure 3.3 Structureborne noise Broadband random mechanical vibration 3.7 Aerodynamic noise Broadband random fluctuating pressure (including vent noise)* and possible periodic pressure 3.8 Ascent Engine/motor thrust transients Low frequency mechanical transient 3.9 Thrust vector loads Low frequency mechanical transient 3.10 Pogo** Low freq. periodic mechanical vibration 3.11 Motor resonant burning** Mid freq. periodic mechanical vibration 3.12 Fuel slosh in tanks Low freq. random fluctuating pressure 3.13 Stage and fairing separations* Low frequency mechanical transient 3.14 Staging Pyrotechnic events* High frequency mechanical transient 3.15 In-flight operations Low frequency mechanical transients 3.16 Free- Onboard equip. operations Various 3.17 flight Meteoroid impacts** High frequency mechanical transients 3.20 Wind during entry Low freq. random fluctuating pressure 3.3 Aerodynamic noise Broadband random fluctuating pressure 3.8 Entry Planetary descent and entry** Broadband random fluctuating pressure 3.18 Soil penetration** Low frequency mechanical transient 3.19 * Usually the dominant excitations for a normal flight. ** Could be the dominant excitations if they occur.

(see below NASA TECHNICAL HANDBOOK, NASA-HDBK-7005)

10 Copyright Free Field Technologies Context – Objectives

 At lift-off, components like satellites carried on launchers are exposed to intense acoustic excitation that can damage their structures

 In the frame of an ESA driven project, Dutch Space is seeking for improving the prediction of the response of a folded solar array loaded by an Acoustic Diffuse Field

 The objective of the study is to compare the vibro- acoustic response of a folded solar array loaded by an Acoustic Diffuse Field : . Measured in a reverberant chamber (Dutch Space) . Simulated with the Infinite/Finite Element solver ACTRAN (Free Field Technologies)

11 Copyright Free Field Technologies Actran Numerical Model

 Structure modeled in modal coordinates . Existing Dutch Space model . Modes extracted with NASTRAN (SOL103)

 Air layers modeled in modal coordinates . Meshed with the real thickness . Take visco-thermal effects into account (Beltmanmodel)

 Acoustic Diffuse Sound Field applied on upper and lower faces of the solar array

 Modal recombination computed with ACTRAN

12 Copyright Free Field Technologies Numerical Model

 The air layers and the surrounding air are modeled together in physical coordinates (Finite/Infinite Element domain)

 Structure modeled in modal coordinates in NASTRAN

 The exterior fluid domain is coupled to the air layers between the panels

Panels

Infinite Elements (NRBC)

FE Air Domain

13 Copyright Free Field Technologies Numerical Model

 The Acoustic Diffuse field is modeled with a large number of uncorrelated plane waves (126). 20 different samples are simulated

 As such, the effect of the presence of the structure on the excitation field is taken into account

Panels

Infinite Elements (NRBC)

FE Air Domain 126 plane waves

14 Copyright Free Field Technologies How does it work in practice?

 Step 1: do your NASTRAN computation “as before” . Compute the modes of the structure as if in vacuum . Store the results in OP2  Step 2: give the results to Actran . Import the OP2 in Actran . Import the BDF in Actran  Step 3: Create the air volume for Actran . Mesh the air around the structure . Put the infinite Elements  Step 4: launch Actran . Excite the structure with a Diffuse Sound Field . Compute the structural response (in Actran) . Compute fatigue indicators (in Actran)

15 Copyright Free Field Technologies Results on Upper Panel (1)

 Influence of the air layers and Acoustic Diffuse Field models

16 Copyright Free Field Technologies Results on Upper Panel (2)

 Influence of the air layers and Acoustic Diffuse Field models

17 Copyright Free Field Technologies Results on Inner Panel (1)

 Influence of the air layers and Acoustic Diffuse Field models

18 Copyright Free Field Technologies ACTRAN Outputs

 ACTRAN can output all the required quantities to perform a complete analysis of the system response: . Structural Results Target Applications • Displacement / Acceleration / Velocity • Mean Square Velocity • Stress (σx, σy, σz, τxy, τyz, τzx, σvon Mises) • Energy Levels (Kinetic, Potential) / Injected Power . Acoustic Results • Fluid Pressure • Mean Square Pressure • Energy Levels . FRFs and Maps . Means, envelops, standard deviations of any stochastic quantity

19 Copyright Free Field Technologies

Summary

 Starting point: an existing Nastran model

 Benefits of using Nastran+Actran . Excitation: the Diffuse Sound Field DSF corresponds exactly to the measurements at IABG . Air Gaps: viscothermal effects of the air layers between the panels . Post-processing

 Associated effort . A mesh . 1min30s per frequency

20 Copyright Free Field Technologies General Conclusions

 Actran is an acoustic simulation tool part of the MSC family . It can work alone or together with Nastran . It can solve various types of problems  Actran has been used to model a stack of (real) solar panels . Experimental measurements have been performed by Dutch Space . The numerical model corresponds to the experimental setup . The results match well . The results Actran can produce can be useful for design . The associated effort is (very) moderate  In Summa & FFT have all the expertise to help you with your acoustic challenges

22 Copyright Free Field Technologies Thank you for your attention

Jaap Wijker [email protected] Stephane Caro [email protected]