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Fiat uses Altair software in NVH analysis

Altair ProductDesign’s Squeak and Rattle Director (SNRD) has enabled Fiat to more accurately predict and eliminate NVH phenomena in its vehicles


Fiat’s Belo Horizonte facility in Brazil houses a team of NVH experts. For car makers, squeak and rattle phenomena represent a significant problem as many customers will interpret the noise as a general lack of quality in the product. The industry is therefore eager to better understand and predict these phenomena so interior noise can be reduced and ride quality improved.

Squeak and rattle occur when two parts of an assembly are in relative motion due to a specific excitation load. When two parts are initially separated by a gap but rapidly come into contact with each other, a rattling noise is created. On the other hand, a squeak noise might be heard when two parts are initially in contact and a sufficiently large relative displacement is caused at their interface.

Fiat has studied the potential for squeak and rattle noise in its vehicles for many years but previously this was only achieved by testing physical components that were produced using near final designs. If any noise issues were discovered, the team could only apply quick fixes to solve them which could be a time consuming and often very costly exercise. Utilizing a simulation approach, where interior noise is analyzed ahead of physical testing, can reduce the need for fixes late in the development process.

In an effort to reduce development time and minimize these additional correction costs, Fiat’s NVH department wanted to explore the potential of studying squeak and rattle during the virtual design stage. NVH experts were looking for a simulation-based methodology that was implemented inside a tool which they could build a new design process around. The solution had to enable fast, robust and flexible pre- and post-processing, with significant customization capabilities.

Marcelo Starling Braga, NVH coordinator at Fiat, and his team chose Altair ProductDesign as a partner to perform a pilot project investigating squeak and rattle. The project focused on studying issues on the Fiat UNO, a vehicle made exclusively for the South American market. To perform the project, Altair ProductDesign worked with Fiat’s NVH group to implement Altair’s Squeak and Rattle Director (SNRD).

The SNRD is a comprehensive set of services and software automations that rapidly identify and analyze design alternatives to eliminate the root causes of squeak and rattle in assemblies. With customization from the Altair ProductDesign team, the solution provides a semi-automated approach to determine relative component displacements in the time domain that can lead to undesired noise.

A four-day workshop and training sessions were held on-site at Fiat’s Belo Horizonte site by Altair domain expert, Ismail Benhayoun. These dedicated sessions facilitated a fast ramp-up of the NVH team’s knowledge of the SNRD, and helped Altair to identify Fiat specific design process that the solution could be tailored to.

SNRD enabled Fiat’s NVH specialists to import linear models for their pre-existing vehicle range, including the UNO, and correlate the simulation results with the known physical test data. Fiat’s test engineers were then able to assist the CAE analysts and design teams by performing A2B comparisons between the existing models and those evaluated with the SNRD. By understanding the performance of the new concepts and quantitatively comparing those to correlated models and/or to different variants, the engineers could be more confident in their design decisions.

Fiat’s NVH team now routinely uses the SNRD in its simulation loops with a focus on improving the performance for each system and studying the interfaces between them. The solution allows the team to identify the risk areas for squeak and rattle, and understand the effect of various deviations that could result from the manufactured parts through sensitivity studies. For example, the effect of different material properties, tolerance chains, and different road loads.

SNRD delivers valuable input for designers by enabling them to find better attachments and boundary conditions for their parts, as well as driving the choice of materials. Fiat's NVH experts are now able to quickly and accurately study the potential for squeak and rattle phenomena to occur in their vehicles earlier in the development process. Once identified, these issues can be addressed and removed from the final design before physical hardware is produced. This in turn leads to significant cost and time savings.

“Altair’s Squeak and Rattle Director is intuitive to use as a tool despite the complex computations that are performed in the background,” said Braga. “SNRD allows us to input different data, like design and manufacturing tolerances, in order to improve the output of our analysis and therefore have more valuable inputs to the project. Altair is continuously developing this solution and new features are to be implemented, which will improve our simulation capabilities and overall process.”

November 4, 2015


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