Tank you very much Mr YasserSelima for your helpnthe udfs work well in CG_MOTION UDF, The term cg_vel[1]= x-x0/dt it represent numerical velocity and it is OKnby using udf ZONE MOTION for translation the airfoil translate and deflect and evey think is fine but with Unphysical results.nby using GRID _MOTION without translation the airfoil deflectes only so it is OKnthe translation by CG MOTION is failed due to negative cell i no know why ???n