Introduction to Actran for Acoustics Radiation Analysis

Transcription

1 Introduction to Actran for Acoustics Radiation Analysis November 21 st, 2012 Chanhee Jeong

2 Agenda Introduction to Actran Acoustic Radiation Analysis with Actran Weakly Coupled Vibro-Acoustics Computational Process Key Ingredients of the Actran Model Example of Application Live Demo in Actran VI Conclusion Q&A

3 Actran VI The Actran Software Suite Actran for Nastran Actran DGM Actran Vibro-Acoustics Actran Aero-Acoustics Actran TM Actran Acoustics

4 Actran VI Actran Acoustics Module Actran for Nastran Actran DGM Actran Vibro-Acoustics Actran Aero-Acoustics Actran TM Actran Acoustics

5 Actran Solver Acoustic FEM/IFEM approach Multi-purpose toolbox: several computational sequences Direct Frequency Response Modal Frequency Response for interior problems Hybrid Modal-Physical Response the best of both worlds Modal Extraction for undamped structure or cavity + Compressible Flow potential flow solver + Frequency response using a time domain LEE Solver + Transient solver IE domain FE domain Linux or Windows platforms Direct & iterative solvers, multiple load & restart Several types of parallelism available

6 Actran Acoustics Features Acoustics as well as weak vibro-acoustic coupling Acoustic finite elements, infinite elements Including visco-thermal loss effects Convected wave propagation (flow + temperature) Excitations imported from MSC Nastran or others Results provided (among others) Acoustic pressure, intensity and power Power distribution and radiation efficiency Applications Engine: power train and auxiliaries (oilpan, manifold, exhaust, ) Engine compartment insulation Any vibrating / radiating component Can be further extended using vibro-acoustics and aero-acoustics features

7 Few Words about Infinite Elements Infinite elements are: «finite» elements covering an unbounded domain with appropriate high order shape functions in the radial direction P P 1 3 Infinite elements: ensure there are no wave reflections at the FE/IE interface provide accurate acoustic results beyond the FE domain S P

8 Vibro-Acoustics - One-Way or Two-Way Coupling Structure Noise induces vibration One-way Two-way coupling (no (feedback) feedback) Air Vibration induces noise OK KO Engine radiating in free field Sub-marine under water

9 Computation Process 1. Structural FEA Analysis = MSC Nastran Mesh & results files 2. Acoustic computations = Actran 3. Post Processing and Analysis = Actran VI Maps FRF Waterfall

10 Acoustic Radiation Procedure An acoustic boundary condition is created from the vibration levels computed by Nastran. The MSC Nastran mesh is different than the acoustic mesh mapping is required This feature is called BC Mesh (stands for Boundary Condition Mesh) BC_MESH feature structure mesh displacement field Acoustic Radiation acoustic mesh

11 Preparation of the Acoustic Mesh A 3D finite element mesh is a requirement to support the acoustic analysis The element size must be small enough to capture the smallest acoustic wavelength and the small fluctuations very close to the structure c f use of 4 linear element per wavelength thanks to optimized integration rules The meshing process is easy Create a closed surface mesh (BC_MESH) very close around the structural model (wrapping) Create a surface mesh at a distance D (~0.3 x size of object) of the structure to support the infinite elements Automatic 3D mesh in between Infinite Elements Surface BC_MESH Surface 3D elements

12 Supported Quantities & Formats Structure Soft. Vibration Participation Factors Modes MSC Nastran OP2 / Punch Punch OP2 ANSYS RST MCF RST IDEAS UNV - - Actran OP2 / NFF - - ABAQUS ODB - - Type of vibration data compatible with Actran Acceleration, Velocity or Displacement Vector (3 directions) or Normal to the surface Can be expressed in physical quantities or under the form of mode shapes and participation factors The different realizations corresponding to the different RPMs will be automatically handled by Actran to output results for each RPM available in the structure results file

13 Results Output Specification Virtual microphones can be located anywhere in the finite and/or infinite element domain Output specifications Multiple control surfaces to compute the radiated power Maps for different frequencies on the acoustic mesh or/and on a mesh dedicated to the post-processing (named field mesh in Actran) plot acoustic pressure, acoustic intensity, etc. field points (microphones) field mesh

14 Power Evaluation from Microphones - ISO 3744 The computation of the radiated power from a set microphones is normalized through the standard ISO 3744 Actran VI has function to automatically define the field points location according to the standard ISO 3744 (sphere, hemisphere, box) Easy reproduction of experimental set-up

15 Waterfall Diagrams Waterfall are diagrams where the response is plot versus both frequencies and the engine orders (RPM) Such diagram can be obtained after a single Actran computation thanks to the multi-load case capability Some phenomena can be identified as system dependant (vertical lines on the waterfall), e.g. structure modes, Some phenomena can be identified as excitation dependant (diagonal lines on the waterfall)

16 Example Gearbox Application Case Two models are built in order to simulate: the radiation in complete free field the radiation in semi free field (reflecting floor located at -700mm in Z direction). Goal : assess the effect of the floor Actran Output specification Microphones Field Mesh BC_MESH Surface Finite Elements Infinite Element Interface

17 Floor Effect on Sound Pressure Levels Point E Point C B C E D A x z y Point A Point B

18 Floor Effect on the Directivity (3000Hz) With Floor - Without Floor = Floor effect Real part of the pressure - = SPL - =

19 Actran Demo Seat back, relax and enjoy the flight

20 Thank you!