The Acceleration Reaction
Oscillatory flow imposes a force not observed in steady flow. In oscillatory flow, fluid constantly accelerates and decelerates around creatures attached to the substratum. It's a bit easier to think about the consequences of this acceleration by changing your frame of reference and imagining a trying to accelerate a creature through flow.
In order to accelerate an object through a fluid, you must "move" fluid out of the object's path. This requires imparting momentum to the fluid that you are pushing out of the way. The force required to accelerate the fluid in the object's path is proportional to the object's acceleration. Force due to the Acceleration Reaction = r * V * Cm * a
r = Fluid Density
Cm = Added Mass Coefficient
A = Acceleration of Fluid or Object
V = Volume of Object
© 1999 Elizabeth Nelson, Stanford University Department of Biological Sciences, Hopkins Marine Station. Educational uses permitted.