 He also put forward a series of new general functions for hydromechanics, and explored general theory and solution about mapping space of 3D flow reverse - cross proposition.In the last few decades, Liu has emphasized new directions, such as reverse proposition of nonsteady pneumatic mechanics, reverse proposition of multi-working condition points hydromechanics and pneumatic - thermal - elastic coupling theory.Professor Liu won the second award of national natural science in 1987, and was elected an academician of the Chinese Academy of Sciences in 1999.