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Reduce the pressure, go for particle velocity

Optimizing the damping treatment of a vehicle body

Car manufacturers are constantly seeking methodologies to enhance acoustic performance whilst meeting demanding weight and cost targets. Most optimisation strategies are designed via numerical simulations and later adjusted through modal and noise testing. Although traditional approaches are fairly effective, they require a very laborious and time-consuming process. Alternatively, acoustic particle velocity sensors have been proven suitable for performing non-contact vibration measurements.The direct visualisation of this information can be used to find leakage as well as problematic modes across the structure. The main purpose of this study was to design an effective damping treatment of a vehicle by means of scanning particle velocity measurements using Scan&Paint 2D.

Extracted from: Fernandez Comesana, D., Tatlow, J. (2018). Designing the damping treatment of a vehicle body based on scanning particle velocity measurements. In Proceedings of Aachen Acoustics Colloquium.

REQUIREMENTS

•Quickly identify undamped panels/areas

•Ensure existing pads are of suitable size/thickness

•Remove existing pads that are unnecessary

•Demonstrate the effectiveness

GOAL

Fulfil acoustic targets with minimal weight, cost and number of parts in a damping pack.

Measurement methodology

The acoustic signals of the sound field are acquired by manually moving a P-U probe across a measurement plane whilst filming the event with a camera. At post-processing stage, the sensor position is extracted by applying automatic colour detection to each frame of the video. The results are finally combined with a background picture of the measured environment to obtain a visual representation which allows us to “see” the sound pressure, particle velocity or sound intensity spatial distribution.

Sound visualization of a car floor

An example of the particle velocity maps obtained for a floor section are shown in this section. The direct mapping of the normal particle velocity yields large spatial variations across the evaluated area (>25 dB) even for low frequencies, revealing the critical panels with high excitation.

Applying a damping treatment

After identifying the main panel resonances and critical areas, several configurations of damping were assessed (material type, position and thickness). In practice, this implies scanning the area of interest for each configuration, obtaining direct feedback on the impact that placing several damping pads have on the structure. Figure 4 shows the spatially averaged particle velocity spectra before and after a damping treatment, along with velocity colormaps. As it can be seen, the damping treatment applied reduces significantly the acoustic output of this panels, mainly reducing the excitation of the resonance frequencies displayed above. A fairly homogenous distribution of energy across the area evaluated is obtained after applying the damping pads.

On-road noise validation

The vehicle studied in this paper was tested before and after performing modifications on the damping treatment. Sound pressure measurements were carried out at the front and rear of the cabin for multiple asphalt surfaces. Later on, the vehicle powertrain was again assembled and tested on several roads.

OUTCOME

A measurement methodology to design the damping treatment of vehicle body is hereby proposed and demonstrated for a full vehicle on the road. The acoustic performance of the modified vehicle is equal or better in all the conditions evaluated. The number of panel treatments was reduced by approximately 15 %, yielding a similar cost reduction for the total pack plus additional saving through overall costs and production time. A second vehicle model to which the proposed methodology was applied achieved a 30 % reduction in the number of panel treatments and even 10 % reduction in the damping package weight.

Reduce the pressure, go for particle velocity

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