error in pulsatile waveform stenosis

hii,
I am solving pulsatile waveform for velocity inlet in Steonsis. As the waveform is regular so i have to cut into 3 pieces and used interpolation to get equation for them.

I assign 3 equations of this pulsatile waveform in variable section and put them in inlet boundary conditions. These functions are

U1=(t<=0.25)*(0.02-(0.2925*t[1/s])+(3.54167*(t[1/s])^2)-(13.3333*(t[1/s])^3)-(16.6667*(t[1/s])^4)-(133.333*(t[1/s])^5))[m/s]

U2=(t>0.25 && t<=0.60)*(-274.635+(4088.24*t[1/s])-(25130.5*(t[1/s])^2)+(81457.9*(t[1/s])^3)-(146464*(t[1/s])^4)+(138300*(t[1/s])^5)-(53555.6*(t[1/s])^6))[m/s]

U3=(t>=0.65)*(-202476+(2.20729e6*t[1/s])-(1.0646e7*(t[1/s])^2)+(2.98136e7*(t[1/s])^3)-(5.34204e7*(t[1/s])^4)+(6.35088e7*(t[1/s])^5)-(.00931e7*(t[1/s])^6)+(2.52776e7*(t[1/s])^7)-(7.40476e6*(t[1/s])^8)+(959436*(t[1/s])^9))[m/s]

Time step is{ 0,0.05,1.1}

These functions run separately but I want to run them combine but Comsol give error of not convergence at 0.2499999999999

when i run like this

U=U1+U2+U3 (at inlet )


I hope someone will help me early.

Thanks