  We investigate the tunnelling dynamics of Bose-Einstein-Condensates(BECs) in
a symmetric as well as in a tilted triple-well trap within the framework of
mean-field treatment. The eigenenergies as the functions of the zero-point
energy difference between the tilted wells show a striking entangled star
structure when the atomic interaction is large. We then achieve insight into
the oscillation solutions around the corresponding eigenstates and observe
several new types of Josephson oscillations. With increasing the atomic
interaction, the Josephson-type oscillation is blocked and the self-trapping
solution emerges. The condensates are self-trapped either in one well or in two
wells but no scaling-law is observed near transition points. In particular, we
find that the transition from the Josephson-type oscillation to the
self-trapping is accompanied with some irregular regime where tunnelling
dynamics is dominated by chaos. The above analysis is facilitated with the help
of the Poicar\'{e} section method that visualizes the motions of BECs in a
reduced phase plane.
