Research On The Lubrication And Rub-impact Characteristics Between The Stern Shaft And The Stern Tube Bearing

The stern shaft is an important part of the marine propulsion shafting, the stern tube bearing not only supports its own gravity is also supporting the hull weight of the propeller. So the stern tube bearing withstands the largest load in the ship shaft bearings. Now, with the increasing tonnage of ship, the increasing gravity of stern shaft and propeller makes the stern shaft deflection phenomenon often occurs. This will give the stern tube bearing great loads, and affects or even undermines the good lubrication between the journal and bearing. Meanwhile, during the running of the ship shaft, as the ship shaft misalignment or bending, this increases the amplitude of the stern shaft. When the amplitude exceeds the gap between the bearing and the journal, it will cause the collision and friction between the bearing and the journal, and short for rub-impact. Rubbing is one common phenomenon of large-scale rotating machinery. Rubbing will wear the stern tube bearing, increase the gap between the bearing and the journal, even lead to failure of the propulsion shaft, affect the safe operation of the ship.In this paper, the stern shaft as a study. Established a Jeffcott rotor dynamics model under the oil film force, sealing force and rubbing force. Studied the rubbing behavior between the bearing and journal. Conclusions are summarized as follows:(1) According to the nonlinear dynamics theory, given the research methods of the rub-impact rotor system, related to the time-distance graph, the power spectrum, root locus diagram and poincare map and bifurcation diagram.(2) Analyzed the bearing mechanism of sliding bearing by virtue of hydrodynamic lubrication theory. In accordance with the law of Coulomb Theory, derives the mathematical expressions of rubbing. As a simple Jeffcott rotor for the study, gives the motion equation of a single disk rotor.(3) Establishs the Jeffcott rotor dynamics model which supported by the sliding bearing. Dynamic equation is given, obtained the response of the rotor system under different excitation frequency by numerical simulation. Obtained the time-distance graph, the power spectrum, orbit and Poincare map in a different excitation frequency. By numerical integration method, obtained the rotor system response bifurcation diagram within rubbing stiffness Kc at 0-2×107. When the low rubbing stiffness, a small force of local collisions, and system response is mainly affected by the non-linear oil film force and the sealing force. With the increasing rubbing stiffness kc, the rubbing force close to or more than the oil film force and the sealing force, the system gradually shows different characteristics of the nonlinear dynamics, and appears inverted bifurcation. The above nonlinear dynamics analysis of the rub-impact rotor system provides theoretical reference value for rubbing fault diagnosis of the large-scale rotating machinery such as the stern shaft.