Power spectral density of road profiles

The road profile is usually considered to be a random process x(d), where x is the road height and d is the distancealong the road. As the vehicle travels along the road with velocity v, the random process x(d) is converted to a randomprocess x(t) which is input to the vehicle suspension viathe tyre. The random process x(d) is usually described interms of its power spectral density as a function of frequency in either radiansor cycles per unit distance. However, there are several different ways ofdefining power spectral density, and this makes it difficult to compare publisheddata without knowing how the power spectral density has been defined. Theproper calculation of RMS values of vehicle response for an assumed road powerspectral density is explained by an example.B. R. DAVIS and A. G. THOMPSO