Don't get things mixed up, just the z component of the force becomes Gm triple integral of delta cos phi sine phi d rho d phi d theta.

Considering the influence of the input disturbance, a mathematical description of road surface irregularity is established, which is the model of integral white noise and inspire with sine wave.

For optimal model - reduction of large scale systems, up to now, the integral-square - error method has been developed for systems with impulse, power or sine function inputs only.