mathematica解微分方程组的问题

[江尹城]

data = NDSolve[{Uo[t] ==
Piecewise[{{0, V[t] <= V0 - Vb}, {D[V[t] + Vb - V0, t],
V[t] > V0 - Vb}}, 0], V'[t] == Ui - Uo[t],
T'[t] == (Ui*Th - Uo[t]*T[t] - T[t]*(Ui - Uo[t]))/V[t] -
k*(T[t] - Ta),
k == 1.5, Ta == 300, T[0] == 313, Th == 333, Vb == 0.05, V0 == 0.2,
Ui == 0.015, V[0] == 0.1},
{T[t], Uo[t]}, {t, 0, 2}]