Langevin simulations are preformed on the depinning dynamics of fluid monolayer on a quenched substrate.With increase in the strength of the substrate, we find for the first time a crossover from elastic crystal to smectic flowsas well as a crossover from smectic to plastic Bows above the depinning.A power-law scaling relationship can be derivedbetween the drift velocity and the driving force for both the elastic crystal and smectic Hows, but fails to be obtained forthe plastic Bow.The power-law exponents are found to be no larger than 1 for the elastic crystal Bow and larger than1 for the smectic Bow.The critical driving force and the averaged intensity of Bragg peaks remain invariant basicallyin the regime of smectic Bow.A sudden increase in the critical driving force is observed within the crossover from thesmectic to plastic Bows, and the averaged intensity of Bragg peaks shows sudden decreases within the crossovers bothfrom the elastic crystal to smectic Bows and from the smectic to plastic Bows.The results are helpful for understandingthe slip dynamics of fluids on a molecular level.
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