This work was supported by NSF of China (11171203, 11201280), New Teacher's Fund for Doctor Stations, Ministry of Education (20114402120003) and NSF of Guangdong Province (10151503101000025, S20110100
Asymptotic behaviour of solutions is studied for some second order equations including the model case x(t) + γ x˙(t) + ■Φ(x(t)) = h(t) with γ > 0 and h ∈