Re: kiai in aikido?
You should be able to find an article or two if you Google "Sansei no Kiai" or 'three purposes of kiai"....formal writings will provide better and more accurate information than I can as I have not studied the subject in some time and am just returning to training after a hiatus.
Sansei no kiai:
-To build yourself up and tear your opponent down
-to stop someone's movement
Typical kiai we are taught are as follows:
each with a specific emphasis or purpose. In advanced classes kiai is emphasized, for example creating the sound from your hara so that, despite having a deep and powerful kiai, your throat doesn't get sore.
Anyway, I think I wrote on this subject awhile back on here, back when I remembered better what my little group is taught.