# force monitor flat-lining

Submitted by makau_surfboards on October 22, 2011 - 00:39

i ran a simulation of seawater flowing at a constant 20 MPH over a fin cluster in a closed volume, resulting in what looks like very reasonable pressure and Cp color maps. The Force monitor for x direction (drag) is zero everywhere though. I attached the monitor to the "group" representing my fins. Does anyone have any clue what i might be doing incorrectly here?

mahalo,

chris

## Single Flow Volume?

Did you subtract your fins from the flow volume to form a single volume for the fluid around your fins? For more details try the section "Single Volume Required" at "RANS Flow."

## moving geometry

Mahalo for the advice, you helped me figure it out. Hey, one more question related to this if you don't mind: is it possible to vary the volume geometry over time? For example, i want my fins to have 0 deg. angle of attack at t=0, and -4 deg at t=30. I cannot accomplish this by simply changing the flow direction because the fins are mirrored about XZ plane (4 fins, 2 per side). I tried making my geometry by rotating them -4 deg @ t=30, but when i subtract the volumes, i am only left with the initial state (alpha=0). Sorry if this sounds confusing... Any advice or comments will be much appreciated...!

aloha

## No moving geometry for RANS Flow

Currently Caedium does not support moving/deforming geometry for RANS Flow simulations.

I suggest constructing multiple flow volumes matching each variation. Alternatively you could simulate the full configuration (no symmetry) and just vary the flow direction.