Abaqus Multiphysics / Structural-Acoustic Simulation / Structural-Acoustic Simulation Example

Acoustic Resonance of the Tire-Air Cavity

The coupled vibration of the tire-air system is an important factor in automotive N&V. Spindle forces, and therefore noise and vibration, are observed at the resonances of the tire-air system.

Tire rotation has a significant effect on the behavior of the tire-air modes. For a stationary tire, the fundamental acoustic cavity resonance consists of two acoustic modes; the fore/aft acoustic mode and the vertical acoustic mode. For a tire with no load, all these modes occur at the same frequency. For a tire under footprint loading, the difference in frequency depends primarily on the tire construction and the load magnitude.

When a tire undergoes rotation, the air inside a tire rotates with the same velocity as the tire. This rotation gives rise to two rotating modes, one rotating with the tire and one rotating against the tire. The difference in frequency of these modes is approximately equal to twice the rotational frequency of the tire; the mode that rotates with the tire increases in frequency while the one that rotates against the tire decreases in frequency.

This behavior is illustrated by simulating a tire-wheel-air cavity model in Abaqus/Standard. The cross-section of this model is shown to the right. The tire is inflated with a prescribed inflation pressure. For simplicity, no footprint load is applied to the tire. For the stationary case, both the fore/aft and vertical modes of the tire are observed at 241 Hz. An animation showing the pressure distribution in the cavity for these modes is given below.

The tire is analyzed under two different rotational velocities, corresponding roughly to ground speeds of 40 km/h and 100 km/h. A mixed Eulerian-Lagrangian scheme is used in Abaqus to analyze the steady state rotation of the tire. The modes of the cavity for the 40 km/h case are located around 235 Hz and 247 Hz. For the 100 km/h case, the modes are located around 226 Hz and 255 Hz. The pressure distribution for the rotating modes is shown in the following animation.

A frequency response analysis, conducted for all three cases, illustrates the effect of these modes on the spindle forces. A vertical excitation in the form of a concentrated load is applied to the bottom of the tread. The effect of the mode-split can be observed on the spindle forces.