| Περίληψη: | One of the most important machine elements in rotating machines is the bearing. It has been an integral part of machines since the ancient times (The Egyptians used journal bearings lubricated by animal fat in their chariots) and became even more so after the industrial revolution. The journal bearings are designed in a way that they can surround the machine shaft. The difference between the journal and bearing diameters allow the lubricant to flow through a small clearance. This is very important, since once the shaft is rotating, the hydrodynamic forces created in the lubricant can support the weight of the journal and operating loads in order to greatly reduce friction, temperature rise and most importantly prevent the shaft from coming into direct contact with the bearing which would cause wear and could prove destructive for the machine. It is therefore understandable why there is such interest in the development of journal bearings and their lubricants.
More recently, there has been an increasing need to implement the use of water as a lubricant in ships, as the need to protect the environment has never been higher and the requirements and regulations concerning such lubricants have gotten stricter. R.Pai and D.J Hargreaves et al [2] of Queensland University of technology elaborated on the increasing need for water lubricated bearings and even conducted various experiments so as to better understand the behavior of such bearings. Nevertheless, while great progress has been made in this field there is still a gap in our understanding of the flow phenomena. For example, the ability to accurately predict the equilibrium position of the journal inside the bearing is still quite limited. On the other hand, the equilibrium position of conventional journal bearings has been adequately studied and many different methods have been developed such as the twofold secant method which was used by Zhou et al [3].
In this Thesis an effort will be made to better understand how conventional lubricants and water affect the equilibrium position of the journal and a CFD (computational fluid dynamics) approach will be chosen through the software of FLUENT, in order to extract the results needed for the tribological design of each bearing respectively.
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