  We study the effects of quenched disorder on the two-dimensional d-wave
superconductors (SC's) at zero temperature by Monte-Carlo simulations. The
model is defined on the three-dimesional (3D) lattice and the SC pair field is
put on each spatial link as motivated in the resonating-valence-bond theory of
the high-$T_{\rm c}$ SC's. For the nonrandom case, the model exhibits a
second-order phase transition to a SC state as density of charge carriers is
increased. It belongs to the universality class {\it different from} that of
the 3D XY model. Quenched disorders (impurities) are introduced both in the
hopping amplitude and the plaquette term of pair fields. Then the second-order
transition disappears at a critical concentration of quenched disorder,
$p_c\simeq 15%$. Implication of the results to cold atomic systems in optical
lattices is also discussed.
