CFD Online Discussion Forums - Mesh motion with Translation & Rotation

Hello Everyone

I'm currently trying to set up a simulation of a plate translating and rotating in a 2D plane. After reading many other posts I figure using a moving mesh approach is best.

Setup:
Large Square Domain
Inside the large domain I defined a circular Subdomain (this is what I use to move the mesh)
Within the Subdomain there is a rectangular blade

The Square Domain is defined to have Regions of motion specified Mesh Deformation

Boundary Definitions:
Outside Boundary (4 sides of the square domain) has stationary mesh motion

Subdomain has specified location mesh motion using equations
X New Tran
Y Com
Z New
(see below)

Inner Interface boundary (subdomain side of interface) has a specified location mesh motion using same equations as the subdomain

Outer Interface boundary (Square domain side of interface) has a specified location mesh motion using the following equations
X Still = x - Total Mesh Displacement X
Y New Tran
Z New

All other boundaries have unspecified mesh motion.

Mesh Motion:
Case 1: Rotation Only
I started by rotating the subdomain without translation using this thread as a guideline to define the location: http://www.cfd-online.com/Forums/cfx...g-domains.html

These are the rotation equations i have used
X New Rot: ((x-X0)-Total Mesh Displacement X)*cos(alpha)+((y-Y0)-Total Mesh Displacement Y)*sin(alpha)+X0

Y New Rot: -((x-X0)-Total Mesh Displacement X)*sin(alpha)+((y-Y0)-Total Mesh Displacement Y)*cos(alpha)+Y0

Z New: z - Total Mesh Displacement Z

This rotated my subdomain and blade very nicely.

Case 2: Translation Only
Next I translated the subdomain without rotation using these equations of mesh motion
X New Tran: ((x-X0) -Total Mesh Displacement X)+ 5 [cm rad^-1] * sin(1 [rad s^-1] *pi*t)

Y New Tran: ((y-Y0) -Total Mesh Displacement Y)+ 5 [cm rad^-1] * sin(1 [rad s^-1] *pi*t)

Z New (use same as rotation)

This translated my subdomain and blade very nicely

Case 3: Rotation + Y Translation
Next I tried to combine rotation with Y translations using these equations

X New Rot (use same as rotation)
Y Com = Y New Rot + Y New Tran - y
Z New (use same as rotation)

This is where i run into issues. When i use these equations rather than translating/rotating my subdomain, it skews my circle into a oval and rotates and continues to skew the oval. I'm cirtan that its errors in my equations but i'm not sure what from. If i had to guess i'm using the x,y and z variables as well as the Total Mesh Displacement variables wrong as i'm not completely sure of what they represent.
Are x, y and z just the specific x y and z coordinate of a specific node on the mesh to be moved?
Is the Total Mesh Displacement the overall displacement of a specific node from its original point to its current point in the x, y or z direction?

Any help or advice would be greatly appreciated.

Thank You,

DM