How did Noah's descendants procreate?
From Sensus Plenior
As for Noah, one need not take the entire story literally. There may well have been more than 8 persons on the ark, as Bl. A.C. Emmerich states, and there may have been other persons who survived the flood.
A. It appears that Peter took it literally:
1Pe 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.