Research On Lubrication Model And Structure Optimization Of Marine Large-scale Heavy-load Stern Tube Bearings

In this thesis,the lubrication model and structure optimization of marine stern tube bearing are researched through theoretical and experimental method,focusing on the problems of mixed-lubrication,surface topography,asperity contact,journal misalignment,elastic deformation of bearing liner,lubricant flow pattern and wall slip faced by marine stern tube bearing design.The work in this thesis aims to develop performance analysis methods and novel structure scheme for large-scale heavy-load stern tube bearings,and this work is significant to develop design ability for heavy-load bearings including stern tube bearings.The study of this paper can be manifested into several aspects as below:(1)A mixed-lubrication model of bearings considering journal misalignment,elastic deformation of bearing liner,surface morphology and asperity contact is presented.The model covers important issues including large deformation of hydrodynamic bearings under heavy load,inclination of journal and transition of lubrication regime.It’s applicable for both oil-lubricated and water-lubricated bearings,metal bearings and polymer bearings.This model is used to analyze the lubrication performance of large scale heavy load stern tube bearing.The accuracy of the model is verified by the experiment.The research work has a driving effect on the development of the lubrication theory of large-scale heavy-load stern tube bearing.(2)On the basis of the above model,a mixed-lubrication model considering the flow regime and wall slip is proposed.Aiming at the coexistence of local turbulence,local laminar flow and local mixed-lubrication in the large-scale heavy-load stern tube bearing and the characteristics that liquid film having ultimate shear stress on the surface of polymer materials,a generalized average Reynolds equation considering both flow regime transition and wall slip is presented.The corresponding numerical procedure is established.The influence of local turbulence and wall slip on mixed-lubrication bearings are analyzed by using this model.The relevant work makes up for the deficiencies of the existing lubrication models,and has certain guiding significance for the treatment of the flow regime and solid-liquid boundary conditions in the design of large-scale heavy-duty bearings.(3)A calculation method of misalignment bearing equivalent supporting point is proposed,and the estimation formulas of bearing equivalent supporting point and load carrying capacity are presented.The validity of the formulas is verified by typical examples.The formulas can improve the calculation efficiency of bearing equivalent supporting point and load carrying capacity of misaligned bearings.The relevant work makes up for the shortcomings of the actual design means for large-scale heavy-load bearings,and the research effectively solves the contradiction between the accuracy and efficiency of misaligned bearing performance calculation.(4)The influence of structure parameters on bearing performance is analyzed,and two optimized structures of stern tube bearings are presented.Aiming at the characteristics that the minimum liquid film thickness of polymer bearings is located at two axial ends,an improvement measure of designing trumpet-shaped opening on bearing axial ends is presented,and the effects of trumpet-shaped opening structure parameters such as length,diameter and shape on the bearing performance are analyzed.The results show that the optimum trumpet-shaped opening can effectively increase the minimum liquid film thickness,reduce friction and improve the lubrication performance.Aiming at the non-uniform distribution of bearing pressure in the axial direction due to the misaligned journal,an improvement measure of designing inclined rubber layer in bearing bush is proposed,and the effects of thickness and length of inclined rubber layer on bearing performance are analyzed.The results show that the pressure distribution of bearing with inclined rubber layer is significantly improved,and the optimal thickness of inclined rubber layer makes the pressure distribution more uniform.A fitting formula of optimum thickness of rubber layer is obtained by a large number of calculations.The formula is concise and easy to be applied to the actual bearings design.Relevant work provides new ideas for the optimization design and load-carrying capacity enhancement of stern tube bearings.(5)The non-uniform pressure distribution along the axial direction of the bearing caused by journal misalignment leads to the increase of the length-diameter ratio,which has little effect on the load-carrying capacity.Accordingly,the concepts of effective length and effective length-diameter ratio of the bearing are defined.The variation rule of effective length-diameter ratio with key structure and working parameters is summarized.The performance variation rule is verified by stern tube bearing experiment.The relevant research can provide theoretical guidance and data support for the selection of length-diameter ratio in actual bearing design.(6)The lubrication performance experiment of the stern tube bearing is carried out on a test platform.The measured data of the liquid film pressure,bearing temperature,film thickness and friction force are obtained,which have verified the theoretical analysis model presented in this thesis.The effects of structure parameters and journal misalignment on bearing performance are tested.The test results show that the grooves can reduce friction at low speed and destroy the formation of hydrodynamic lubrication film at high speed.Therefore,in bearing design,the grooves should be as far away from the main carrying area as possible.When journal is misaligned,bearing load carrying capacity decreases significantly and friction increases significantly.Proper increase of the liner thickness helps to improve the friction characteristics of misaligned bearings.The increase of bearing length when journal is misaligned has much less effect on load-carrying capacity than that of bearings without journal misalignment.The above test results are consistent with the theoretical analysis,which shows that the research work in this thesis has engineering credibility and reference value.