Formulas
The damage from Deep Wounds can be calculated with the following formulas:
([(WDPS + AP/14)*WSPD]x0.16) = Rank 1
([(WDPS + AP/14)*WSPD]x0.32) = Rank 2
([(WDPS + AP/14)*WSPD]x0.48) = Rank 3
WDPS = Base main hand weapon DPS
WSPD = Base main hand weapon speed
AP = Attack Power
Deep wounds is affected by damage modifiers such as:
Enrage - 10% extra damage
Death Wish - 20% extra damage
Mangle/Trauma - 30% extra damage
Also note that abilities that affect your attack power (Battle Shout, Demoralizing Shout, etc.) will also increase/decrease the damage Deep Wounds does.