Periodic bouncing for a forced linear spring with obstacle (Q1198676)

The authors ask for \(2\pi\)-periodic solutions of \(u''+\delta u'+bu=\pm1+\varepsilon\sin t\) which satisfy \(u(t)\geq 0\) and, at the points \(t_ i\) of elastic impact, \(u(t_ i)=0\Rightarrow u'(t_ i+)=- u'(t_ i-)\). For certain parameters \(\delta\), \(b\) there exist ``large'' solutions for small \(\varepsilon\). (Physically the results are obvious and well-known.).