Frictional oscillations under the action of almost periodic force are studied. The modulation equations are derived by the
multiple scales method to study bifurcations behavior. Heteroclinic Melnikov function is constructed to obtain the region
of chaotic solutions of these equations. Bifurcations of almost periodic orbits are studied by Van der Pol transformation
and averaging procedure.
Keywords Frictional oscillations - Heteroclinic orbits - Multiple scales method - Heteroclinic Melnikov function