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Technical Paper

Vibro-Acoustic Simulation of Intake Air Filter Using a Hybrid Modal Physical Coupling

To assess the acoustic performance of modern automotive air filters, both the air-borne engine noise propagating through the interior air of the system (known as “pipe noise”) and the structure-borne noise radiated by the shell (“shell noise”) should be evaluated. In this paper, these different propagation paths are modeled using the finite element solver Actran on industrial test cases set-up by SOGEFI Air and Cooling Systems. The test-case is designed in such a way that the different propagation paths are assessed separately. First the engine acoustic pulsation that is transmitted through the filter's structure is considered. Second, the noise radiated by the shell excited by mechanical forces at the support location of the filter is evaluated. Finally, the acoustic transmission loss of the filter is predicted. The ingredients of the finite/infinite element models are reviewed in details in the paper.
Technical Paper

Vibro-Acoustic Simulation of Side Windows and Windshield Excited by Realistic CFD Turbulent Flows Including Car Cavity

Nowadays, the interior vehicle noise due to the exterior aerodynamic field is an emerging topic in the acoustic design of a car. In particular, the turbulent aerodynamic pressure generated by the air flow encountering the windshield and the side windows represents an important interior noise source. As a consequence PSA Peugeot Citroën is interested in the numerical prediction of this aerodynamic noise generated by the car windows with the final objective of improving the products design and reducing this noise. In the past, several joint studies have been led by PSA and Free Field Technologies on this topic. In those studies an efficient methodology to predict the noise transmission through the side window has been set up. It relies on a two steps approach: the first step involves the computation of the exterior turbulent field using an unsteady CFD solver (in this case EXA PowerFlow).
Journal Article

Evaluation of Trim Absorption to Exterior Dynamic and Acoustic Excitations Using a Hybrid Physical-Modal Approach

The NVH study of trimmed vehicle body is essential in improving the passenger comfort and optimizing the vehicle weight. Efficient modal finite-element approaches are widely used in the automotive industry for investigating the frequency response of large vibro-acoustic systems involving a body structure coupled to an acoustic cavity. In order to accurately account for the localized and frequency-dependant damping mechanism of the trim components, a direct physical approach is however preferred. Thus, a hybrid modal-physical approach combines both efficiency and accuracy for large trimmed body analysis. Dynamic loads and exterior acoustic loads can then be applied on the trimmed body model in order to evaluate the transfer functions between these loads and the acoustic response in the car compartment.
Technical Paper

Study on Sound Insulation Performance of Vehicle Dash Reinforcements

Dash panel is the most important path of structure-borne and air-borne interior noise for engine-driven vehicles. Reinforcements, which are added to dash panel, are mainly designed in order to suppress the structure-borne noise contribution from the dash panel. However, the effects of dash reinforcements do not seem clear in the viewpoint of air-borne noise. In this paper, the insulation performance of a dash structure with spot-welded reinforcements is studied through several STL (Sound Transmission Loss) tests and STL simulations. The results of this study could be utilized for increasing the sound insulation performance of vehicle body structure.
Technical Paper

Prediction and Improvement of High Frequency Road Noise of a Mid-Size Sedan

An airborne SEA model to predict high frequency interior noise is built for a mid-size sedan. The 60 KPH running condition is simulated based on this model and then the corresponding result is compared to the measured interior noise. A very similar prediction is found. Also, weak points of sound insulation and effective absorption area in this vehicle are identified using the model. It is shown that in an early design stage and when the proto vehicle is not available yet, the airborne SEA model is very useful to find out weak points of vehicle sound packages.
Technical Paper

Numerical Simulation of Noise Transmission from A-pillar Induced Turbulence into a Simplified Car Cabin

At high cruising speed, the car A-pillars generate turbulent air flow around the vehicle. The resulting aerodynamic pressure applied on the windows significantly contributes to the total cabin noise. In order to predict this particular noise contribution, the physic of both the flow and the cabin needs to be accurately modeled. This paper presents an efficient methodology to predict the turbulent noise transmission through the car windows. The method relies on a two-step approach: the first step is the computation of the exterior aero-dynamic field using an unsteady CFD solver (PowerFLOW); the second step consists in the computation of the acoustic propagation inside the cabin using a finite element vibro-acoustic solver (ACTRAN). The simplified car cabin of Hyundai Motor Company, studied in this paper, involves aluminum skin, windows, sealant, inner air cavity and acoustic treatment inside the passenger compartment (porous material, damping layer).
Technical Paper

Optimization of Trim Component and Reduction of the Road Noise Transmission Based on Finite Element Methods

The acoustic trim components play an essential role in NVH behavior by reducing both the structure borne and airborne noise transmission while participating to the absorption inside the car. Over the past years, the interest for numerical solutions to predict the noise transmission through trim packages has grown, leading to the development of dedicated CAE tools. The incrementally restrictive weight and space constraints force today CAE engineers to seek for optimized trim package solution. This paper presents a two-steps process which aims to reduce the structure borne road noise due to floor panel using a coupled simulation with MSC NASTRAN and Actran. The embossment of the supporting steel structure, the material properties of porous layers and the thickness of visco-elastic patches are the design variables of the optimization process.
Technical Paper

Extensive Correlation Study of Acoustic Trim Packages in Trimmed Body Modeling of an Automotive Vehicle

In the automotive sector, the structure borne noise generated by the engine and road-tire interactions is a major source of noise inside the passenger cavity. In order to increase the global acoustic comfort, predictive simulation models must be available in the design phase. The acoustic trims have a major impact on the noise level inside the car cavity. Although several publications for this kind of simulations can be found, an extensive correlation study with measurement is needed, in order to validate the modeling approaches. In this article, a detailed correlation study for a complete car is performed. The acoustic trim package of the measured car includes all acoustic trims, such as carpet, headliner, seats and firewall covers. The simulation methodology relies on the influence of the acoustic trim package on the car structure and acoustic cavities. The challenge lies in the definition of an efficient and accurate framework for acoustic trimmed bodies.