mu=1; modell={r'[t]==(mu-r[t]^2)r[t],r[0]==r0}; r0=3; loes:=NDSolve[modell,r,{t,0,30}]; abb1=ParametricPlot[Evaluate[{Sqrt[r[t]] Cos[0.3 t], Sqrt[r[t]] Sin[0.3 t]}/.loes], {t,0,30},PlotRange->All,AxesLabel->{"x","y"}, ImageSize->{400,300},DisplayFunction->Identity]; r0=0.02; abb2=ParametricPlot[Evaluate[{Sqrt[r[t]] Cos[0.3 t], Sqrt[r[t]] Sin[0.3 t]}/.loes], {t,0,30},PlotRange->All,AxesLabel->{"x","y"}, ImageSize->{400,300},DisplayFunction->Identity]; abb=Show[abb1,abb2,DisplayFunction->$DisplayFunction];