automotive body design
simulation for system synthesis and refinement. It’s built on top of the DS V5 environment, resulting in a natural integration in the case of Catia users. However, if users are working with other meshing and simulation software, such as Ansa, Hypermesh, Ansys, Abaqus or even CFD (Fluent, Star-CD and others), they can import that data directly. Of the many areas where the software is
applied, De Langhe mentions a few that are of particular note. A manufacturer of high- end cars has studied the noise created by a door slamming because a ‘softer’ slam implies higher quality. Also considered are audio and multimedia systems, where suppliers want to design, select and mount loudspeakers in the optimum places. These studies can’t be done with FEM, says De Lange, because at 15 kHz the wavelength is 2cm, and users need at least six finite elements per wavelength, leading to a 3.5mm element size. Filling the passenger cavity with elements of this size leads to hundreds of millions of elements, meaning a far larger model that might not fit into available memory and will take a long time to solve. He feels the best solution is ray tracing, but that approach doesn’t work for low frequencies, so in that frequency range the company also turns to FEM AML (automatically matched layer) running in conjunction with ray tracing.
Covering many methods Another package that covers many of these methods is VA One from ESI, which simulates vibro-acoustics across the entire frequency spectrum using SEA, structure FE, acoustic FE, acoustic BEM and a hybrid module. The latter enables users to create fully-coupled FE/ BEM/SEA models in a single analysis. It extends existing SEA models to mid and low frequencies by adding local FE subsystems to describe junctions and stiff components, and extend existing FE/BEM models to higher frequencies. In addition, new functions being added to VA One this year include the ability to couple CFD codes for aero-acoustics, such as wind noise, and BSR (buzz/squeaks/rattle) noise studies. The design process consists of many steps:
first, import existing CAD or FE models or create one directly in VA One; second, create structural and acoustic SEA, FE and BEM subsystems and assign physical properties; third, create junctions using the AutoConnect feature; fourth, apply structural and acoustic loads directly to the subsystems; fifth, get intermediate model results for FE/BEM subsystems using built-in or external solvers, or by importing pre-computed data; and sixth, solve for the fully-coupled response of all model subsystems. Also interesting are extension modules that, for instance, interface VA One and Matlab or
www.scientific-computing.com
C/C++ programs that import CAD data from Catia, Pro/E and Step, and create advanced models of multilayer poroelastic noise control treatments using full Biot theory. As for the third company often mentioned, Free Field Technologies was founded by those responsible for the development of Sysnoise and who left the company when it was acquired by LMS. FFT now develops the Actran family. The software can be used alone to solve acoustic propagation problems like the propagation of acoustic modes in a duct with a heterogeneous temperature and flow (such as an exhaust system). In conjunction with structural dynamics tools, such as Ansys, Nastran or Abaqus, it can compute the uncoupled vibro- acoustics behaviour of systems like a powertrain or a gear box; alone it solves fully-coupled systems like a loudspeaker when the vibration of the membrane and the interior acoustics are fully coupled.
The role of general-purpose codes Commercial general-purpose codes are also finding use in this sector. ‘Our space is fairly limited, and we look at things from the air side, examining both interior and exterior flows, using fluid dynamics,’ explains Fred Mendonça, director of the Machinery Sector and a specialist in air acoustics at CD-Adapco. He gives the example of a geometry protruding into the air flow such as side mirrors, which have been a continuous standard feature of every road vehicle. Here the aerodynamics are awkward and there is considerable turbulence in the airflow in the wake of the mirror. The resulting eddies tap on the glass of the window and excite the glass panel, and the resulting vibrations can transmit noise into the passenger cabin. And while the company’s Star CCM+ simulates this airflow, there is also a migration towards adding structural analysis and coupled physics. The hybrid approach of doing aerodynamic
analysis with CFD and then sampling the information needed for vibro-acoustics is a well-proven one, and Star-CCM+ is one of the packages starting to integrate both, so there is no need to send information ‘over the fence’ from one code to another. Interestingly, Mendonça notes that one of the major challenges facing users is finding engineers who have expertise in both aerodynamics and structural mechanics; even if the software can couple them, you need people trained in both to make good use of these capabilities. General-purpose FE codes are playing an
essential and ever-increasing role, agrees Brad Heers, technical marketing automotive for Dassault Systèmes. All the specific acoustic codes mentioned earlier need a basis for their
HELPING YOU CREATE
THE FUTURE
2D/3D BEAM OPTICS & CHARGED PARTICLE TRAJECTORY ANALYSIS
Lorentz has been rewritten from the ground up. The bottom line is improved productivity.
For users familiar with Lorentz, the fl ow of the program is now quite intuitive with many new options readily available.
For new users, the speed, accuracy and ease-of-use have to be seen.
PUT OUR SOFTWARE TO THE TEST
Send us your model, whatever the level of complexity. We will show you how to get results from your exact design – no canned demos.
Contact us for an evaluation and start improving productivity today. A live demo is also available.
ANALYZE AND MODEL:
BEAMS
IONS
CHARGED PARTICLES
BEAM OPTICS
ELECTRON GUNS
BEM & FEM available in the same package
LORENTZ v9.0
Call +1 204.632.5636 email
info@integratedsoft.com or visit
www.integratedsoft.com/products/lorentz
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