| Water lubricated bearing is commonly used in propeller shaft system of ship because it is cheap, structurally simple, and easy for maintenance. The use of water as working and lubricating medium in a water lubricated bearing system strategically saves a large number of resources, typically like mineral oil and rare metal. It also alleviates water resource pollution fundamentally from the possible oil leaks. Consequently, water lubricated bearing becomes a major subject in the field of studying environmental science, material science and mechanics. It has subsequently attracted a great deal of academic attention. Unfortunately, the practical use of water lubricated bearing on the basis of its basic theory is not as mature as that of oil lubricated bearing. Subsequently, there are still many relevant areas required to be further explored and systematically investigated. These areas may include:(i) the flow field distribution of water lubricated bearing, (ii) the interaction between fluid pressure and sleeve deformation, (iii) the resistance to cavitation erosion behaviors of materials, and (iv) the throughout study of tribological properties of some new polymers as water lubricated bearing materials. As a result, the advancement in the technological development of water lubricated bearing has been severely jeopardized and to certain extent badly restricted.This dissertation started with studying the fundamental key problems associated with the structural and materials designs of water lubricated bearing in ship's stern bearing, followed by systematically investigating the flow field distribution of water lubricated bearing and its interaction of fluid pressure and sleeve deformation computationally and numerically. This dissertation also focused on the study of tribological properties of water lubricated bearing materials under tap water and artificial sea water, and the behaviors of bearing resistance to cavitational erosion in water medium. It is anticipated that the results so yielded can provide theoretical and experimental data and physical understanding to guide the efficent selection and application of water lubricated bearing materials. The novelties and contributions of this research are mainly as described below:1. The study analyzed the influence of space size, grooves number, grooves shape, grooves position, and eccentricity ratio on fluid flow field distribution by two-dimensional numerical simulation. Results of the analysis show (a) an increasing trend of fluid pressure with increase in eccentricity ratio, and (b) a decrease trend with space increase. The study has revealed that: (i) the disciplinarian of fluid pressure in circle-arc space is greater than that in its rectangular counterpart which in turn is greater than that in rectangular-arc one when eccentricity ratio is 0; (ii) the disciplinarian of fluid pressure in rectangular-arc space is greater than that in rectangular one which in turn is greater than in its circle-arc counterpart when eccentricity ratio is 0.8; and (iii) fluid pressure giving an undulation decreasing trend with the increase in the size of space when eccentricity ratio is 0.8. It has also found that:(a) the capacity of bearing is lowest when the groove is of four rectangular, or six rectangular-arcs, or six rectangular-arcs; (b) When the groove is a rectangular-arc, the stability of fluid flow in the rectangular-arc groove is higher than in the rectangular groove when eccentricity ratio is 0.2. Using the fluid-structure interaction algorithm, the study thoroughly investigated the influence of eccentricity ratio and sleeve deformation on fluid flow field distribution in rectangular-arc groove water lubricated bearing. The results show two orders of magnitude increase in maximum deformation with the increase of eccentricity ratio. Although the effect of sleeve deformation on speed velocity field is very small, it becomes bigger with the increase in eccentricity ratio. Evidence of its effect on pressure field is clearly seen.3. The study performed experiments to derive the design of a new impact method for measuring the cavitation erosion properties of polymer materials by mainly considering the magnetostriction, materials cavitation erosion properties of water lubricated bearing. It went on to discuss the mechanisms of cavitation erosion through the analyses of surface morphologies and EDS investigations. Experimental results have confirmed that the viscoelasticity and amorphous characteristics of Ultra-high molecular weight polyethylene (UHMWPE) result in its best resistance to cavitation erosion. The observation of the appearance of some loosening particles and the gradual enlargement of holes which, were formed by the erosion of bubble, on the Thordon surface, suggest its inhomogeneous composition. In the cavitation erosion experiment of Tenmat (which usually has very low resistance to cavitation erosion), cracks due to some agglomerant as a result of cavitation erosion were seen. The felling off of agglomerant from the surface by the impact of bubble exposed the basketwork fiber which invited further quick erosion.4. Tribological properties of UHMWPE, Thordon and Tenmat under tap water and artificial sea water were respectively investigated. Results are summarized as follows:a. The friction coefficient, ranging between 0.069 and 0.082, of UHMWPE/GCr15 pair under artificial sea water is lower than that under tap water, and has tendency to decrease with the decrease in velocity. Its wear volume is smaller and its wear mechanism is mainly attributed to abrasive wear, plastic deformation, and materials transfer.b. The friction coefficient, ranging between 0.148 and 0.192, of Tenmat/GCrl5 pair under artificial sea water is lower than that under tap water which is in range of 0.15-0.21. It tends to firstly increase and then:(i) decrease slowly with the increase in time, (ii) decrease with the increase in velocity, and (iii) increase with the enlargement of wear volume. Its wear mechanism is mainly identified as abrasive wear and materials fatigue.c. The friction coefficient, in range of 0.345?0.425, of Thordon/GCr15 pair is much higher than that under tap water. It shows an increasing trend with the increase in time, and a decreasing trend with the increase in velocity. Its wear mechanism is identified as mainly due to abrasive wear, materials peeling off, and material fatigue and deformation. The friction coefficient, in range of 0.185?0.335, for the Thordon/GCr15 pair tends to decrease with the time and increase with the velocity under artificial sea water. The wear mechanism involved is mainly of abrasive wear, materials properties and deformation in nature.5. On the basis of correlating the capacity of bearing with the value of deformation, the wear volume, the friction coefficient, the cavitation erosion properties to rotational velocity, and the test time, etc, mathematic model which optimizes the materials properties were established and proposed. |
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