Could you wait a few days? I have done vibration of rotating machinery recently and will answer your question with a great pleasure, but I have to finish my work with the professor of this course!

    If the shaft is lightly loaded, it will rotate by standing on the film and the journal center will operate close to the bearing center.  

    If pressure is developed in the film (BECAUSE OF IMPORTANT LOAD) when the bearing is operating under steady conditions, then the flow-in is reduced and the flow-out is increased by pressure induced flow to have continuity.  (it can be easily proven by fluid mechanic differential equations which relates pressure and velocity profiles). However, if the load is small, in the absence of pressure a small whirl velocity is induced TO MAINTAIN THE FLOW BANLANCE.

IN OTHER WORDS, THE FLOW WHICH IS CREATED AROUND THE JOURNAL WHEN IT ROTATES MAKE IT POSSIBLE TO HAVE A LOAD CAPACITY. WHEN THE FLOW-IN IS MORE, THE BEARING LOSES LOAD CARYING CAPACITY AND WHIRLS...;WHEN THE FLOW-OUT IS MORE, PRESSURE IS DEVELOPED IN THE FILM AND THE BEARING BECOMES STABLE.

BYE

Food for thought on journal bearings:
http://www.reliabilitydirect.com/appnotes/jb.html

http://www.reliabilitydirect.com/appnotes/jbfail.html