Look at your export options in AMIRA (File>Save As or File>Export). If it includes an export to IGES format, do this, then you can import this file directly into ANSYS. Any "other" format, and you have to pay an add-on to your ANSYS licence to import. "other" can be SAT (ACIS), PARASOLID, STEP and a few others such as Solidworks, Pro/E and UG.
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