**** Entered By: rlange @ 10/21/2005 04:46 PM ****
Q. I am planning to run an FSI analysis with the ANSYS/CFX MFX solver. How much flexibility do I have in the systems of units used in ANSYS and CFX.
A. The key is to recognize that the load transfer occurs in the Solver portion of CFX, and so the forces transferred will be in Solver units. These can be controlled to some degree in CFXPre. However, it must be kept in mind that the units of force are derived, not specified. That is, if you choose [lbm] for a mass unit and [in] for a length unit in CFX, the forces are in [lbm*in/sec] so pressure is [lbm/ins].
Convert the value of EX, Modulus of Elasticity, in ANSYS to the same system of units used in CFX. If the modulus in ANSYS is 30E+6 [psi], for example, multiply it by a factor of 386.04 [lbmin/lbfs2]. Also fix the units of density so that it is in terms of [lbm/in3], not [lbfs2/in4].
It is best to use the SI system of units in both ANSYS and CFX, but any system with Gc=1 will work.
**** Entered By: rlange @ 10/21/2005 04:46 PM **** Q. I am planning to run an FSI analysis with the ANSYS/CFX MFX solver. How much flexibility do I have in the systems of units used in ANSYS and CFX. A. The key is to recognize that the load transfer occurs in the Solver portion of CFX, and so the forces transferred will be in Solver units. These can be controlled to some degree in CFXPre. However, it must be kept in mind that the units of force are derived, not specified. That is, if you choose [lbm] for a mass unit and [in] for a length unit in CFX, the forces are in [lbm*in/sec] so pressure is [lbm/ins]. Convert the value of EX, Modulus of Elasticity, in ANSYS to the same system of units used in CFX. If the modulus in ANSYS is 30E+6 [psi], for example, multiply it by a factor of 386.04 [lbmin/lbfs2]. Also fix the units of density so that it is in terms of [lbm/in3], not [lbfs2/in4]. It is best to use the SI system of units in both ANSYS and CFX, but any system with Gc=1 will work. 

