We report a simulated annealing study of the morphology of block copolymer brushes in selective solvents. The investigation is carried out with a lattice model, in which the ends of A-blocks of monodisperse linear AB diblock copolymer flexible chains are grafted regularly on a flat substrate plane with an equal "spacing". The morphological dependences of the brushes on solvent selectivity, polymer grafting density, and block lengths are investigated systematically. Phase diagrams of the system are constructed. Snapshots, polymer density profiles, and average contact numbers of the blocks are used to provide detailed information about the system. It is observed that multiple morphological transitions can be induced by varying block lengths as well as polymer grafting densities. At very low polymer grafting density, B-pinned or A-legged micelles or "flowerlike" structures are observed when the solvent is selective for the A or the B-blocks, respectively. Morphological transitions as well as size and spacing of the micellar aggregates can be manipulated by varying the block lengths. These predicted phase diagrams are consistent with available experiments and theories.