Numerical computation of tyre radiaion noise: a comparative study of different techniques

Increasingly stringent noise regulations concerning automotive vehicles particularly in Europe are forcing Tyre manufacturers as well as the automotive manufacturers to reduce radiated noise. With the future moving towards electric/hybrid vehicles, the ever present tyre noise will become more dominant. Even in the case of automotive engines running on fossil fuels, tyre noise dominates above speeds of 40 Km/h. Understanding the causes of tyre noise is the first step towards finding engineering solutions to reduce it. Numerical modelling can help the tyre engineer in understanding the causes of tyre-road noise with a design tool. In the present work, the noise radiated by the tyre surface is computed numerically using three different computational techniques. Both the time domain approach and the frequency domain approaches are used and the results are compared. The input structural vibrations are computed in ABAQUS (Ref. 1) and the results are then imported to LMSVirtual.Lab (Ref. 2) for further acoustic computations. As the main focus of this work is on the acoustic computations, only a brief description of the process involved in the structural vibration calculations is provided. In the present work, the “Horn effect” is inherently captured in the acoustic simulations. Two model tyres, viz., with tread pattern and with circumferential grooves is evaluated. The presence of tread leads to the phenomenon of stick slip and stick snap mechanisms contributing to the overall tyre noise. In addition, the motion of air through the grooves causes air pumping noise. It is to be noted that the structural vibration computations were performed on a rotating tyre that translated on a stationary road. In other words, the tyre underwent rotational as well as translational displacement. The acoustic computations are however performed on a stationary tyre model. One of the challenges addressed in the present work is the conversion of transient vibration results on a stationary acoustic mesh. The surface accelerations, required as boundary conditions, are converted to the frequency domain by the Fast Fourier Transformation for the Harmonic computations. The details of the structural models as well as the acoustic models and a short description of the techniques used in the computations of the radiated noise are described in the next section

Transfer path based tyre absorption tests

The development process of a tyre usually involves a combination of simulation and testing techniques focused on characterizing acoustic/aerodynamic and vibrational phenomena. One of the acoustic phenomenon of interest is the absorption of the tyre, which affects the sound radiated. This properties is mainly related to local resonant effects, which can be changed by modifying the geometry of the tyre tread. A procedure is presented to determine the attenuation achieved due to a change in tyre tread configuration. The acoustic transfer path is measured from sound produced at one side of the tyre pavement contact area to the other. A miniature microphone and a small monopole with a known output have been developed to allow measurements inside the tyre grooves. Tyre sections with a circumferential groove only, as well as sections with additional side branches, have been evaluated

Operational modal analysis of a tyre using a PU probe based scanning technique

Tyre vibration can be studied with several experimental and simulation techniques. An important goal for a tyre manufacturer is to “tune” the resonant frequency of the tyre subsystem to reduce the structure-borne noise in the car interior. In this paper, a novel measurement technique is applied to determine the operational tyre deflection shapes under different conditions; i.e. free condition, loaded condition, and rolling condition. The vibrational behaviour of a tyre is studied using a PU probe, which comprises a sound pressure and a particle velocity sensor, and a scanning technique. The relative phase information is obtained using a static reference sensor. The experimental data can be used to validate simulated mode-shapes and resonant frequencies

Measurements of 181Ta(n,2n)180Ta reaction cross-section at the neutron energy of 14.78 MeV

The cross-section of the 181Ta(n,2n)180Ta reaction has been measured with respect to the 197Au(n,2n)196Au monitor reaction at the incident neutron energy of 14.78± 0.20 MeV, using neutron activation analysis and off-line -ray spectrometric technique. The present measurement has been done at the energy where discrepant measured results are available in the EXFOR data library. The result has been compared with evaluated data libraries JEFF-3.3 and ENDF/B-VII.1. The present result has also been supported by theoretical predictions of nuclear model code TALYS1.8 and TALYS-1.9. The uncertainty and the correlations among the measured cross-section has been studied using co-variance analysis