Primary surface waves are present at the beginning of start-up and are caused by fabrication or assembly errors. Secondary waves are caused by: (1) nonlinear heating when the journal is eccentric in the bearing; (2) departure from cylindrical symmetry in the housing, which can cause waviness even when heat flux is uniform into the bore; and (3) mechanical constraints, which distort the bearing as it attempts to expand. None of these cause remarkable effects during start-up, but when the system is allowed to equilibrate with a strong thermal gradient in the bearing, the second and third types of waves will grow and can trigger a long delayed seizure.
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