s1[u_, t_, A_, 
        f_]  := (Sin[f*(t +  u)*2*Pi] + 1)/
          2+2

Plot[s1[u, -0.25, 2.0, 1.0], {u , 0, 0.5}]

Plot3D[s[u, t, 1.0, 0.5], {u , 0, 2}, {t, 0, 2}]