Os métodos de cálculo de chumaceiras hidrodinãmicas, disponíveis para projecto, podem conduzir a previsões das condições de desempenho substancialmente diferentes das reais. Um dos principais factores responsáveis por este problema é a forma como, de uma forma geral, é tratada a questão da alimentação de lubrificante à chumaceira. Neste trabalho, apresenta-se um programa de computador para simulação do funcionamento da chumaceira radial hidrodinâmica, dotada de sulcos de alimentação axiais e sujeita a carregamento estático, capaz de entrar em linha de conta com os principais factores condicionantes do seu desempenho, nomeadamente quanto às condições de alimentação. Este programa pode ser utilizado na análise de chumaceiras já existentes, de molde a conhecer as suas reais condições de desempenho, e no estudo da influência de alterações às condições de funcionamento.

The main purpose of this work is to use the analytical mobility method to analyze journal bearings subjected to dynamic loads, with the intent to include it in a general computational program that has been developed for the dynamic analysis of general mechanical systems. A simple journal bearing subjected to a dynamic load is chosen as a demonstrative example, in order to provide the necessary results for a comprehensive discussion of the methodology presented.

Most of the mechanical systems are expected to work in different regimes. In what concerns to journal bearings, this means that variations of rotating speed and of magnitude and direction of the applied load must be accounted for in the design stage. Examples include reciprocating machinery such as internal combustion engines, compressors and other industrial processing machinery. Lubricated joints are designed so that, even in the worst conditions, journal and bearing are not expected to come into contact. Two very good reasons for designing journal bearings in this way are to reduce friction and to minimize wear and rupture risks. Furthermore, the hydrodynamic fluid film developed plays a crucial role in the stability of the mechanical systems, due to its damping characteristics, which cannot be disregarded. Lubrication theory for dynamically loaded journal bearings is mathematically complex and, over the last few decades, several analytical approaches have been proposed. However, these models are often quite complex to be used on design stage or, else, based on simplifications that constrain their application to the most common situations. Thus, the main purpose of this work is to present a general computational methodology for modelling of journal bearings subjected to dynamic loads. In the process, the fundamental aspects related to the Reynolds’ equation are reviewed and the main assumptions and simplifications discussed. The proposed methodology mathematically combines the well known infinitely short and the long journal-bearings theories.

This paper deals with a methodology to assess the influence of the lubricated revolute joints in the kinematics and dynamics of mechanisms. The existence of the clearance at revolute joints is inevitable in all mechanical systems and most of them are designed to operate with a lubricant fluid. The infinitely-short journal-bearing approach for dynamic loads is used to evaluate the resulting hydrodynamic forces of the pressure distribution in the lubricated revolute joints. These hydrodynamic forces are then introduced into the system’s equations of motion. A numerical example is presented in order to demonstrate the efficiency and accuracy of the methodology and procedures adopted.

The search for better performance in internal combustion engines and machines which use hydrodynamic journal bearings has motivated recent studies in lubrication field, with the application of computational fluid dynamics. The present study deals with the dynamics of some non-Newtonian fluids in short journal bearings, using the Newtonian, Herschel-Bulkley, and Bingham models. The main objective is to compare fluid pressure distribution, cavitation occurrence, and performance parameters, such as load-carrying capacity, friction force, and side leakage rate. The bearing equations were solved in a MATLAB program, based on the Reynolds equations, with discretization by the finite volume method and a cyclic Tri-Diagonal Matrix Algorithm solver. In all performance parameters, the Herschel-Bulkley and Bingham non-Newtonian fluids showed advantages when compared to Newtonian fluid.

Apresenta-se um método analítico simplificado para o cálculo de chumaceiras radiais hidrodinâmicas funcionando em regime estacionário. O procedimento de cálculo desenvolvido, baseado num método gráfico devido a Burke & Neale, permite uma fácil implementação em micro-computador e inclui indicações para a selecção dos valores de determinados parâmetros de partida. É analisada a correlação entre resultados obtidos usando este método e os de outro método de cálculo mais elaborado, e também com resultados experimentais. São estabelecidos limites de aplicabilidade de método.

A computer program has been developed that can be used in the analysis of steadily loaded journal bearings with a single groove at any location with respect to the load line. The program incorporates Elrod's cavitation algorithm which ensures mass conservation in both the full film and the cavitated regions enabling rupture and reformation boundaries to be located automatically. Computer results are plotted and checked against experimental measurements for the cases of a single axial groove located at the load line and at 90º to the load line. A comparison of results of this method of analysis with the performance predictions of ESDU Item No. 84031 (1984) for bearings with a single axial groove at 90º to the load line is presented.

The main purpose of this work is to present a general methodology for modeling lubricated revolute joints in constrained multibody systems. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, generated by the lubricant fluid, oppose to the journal motion. The hydrodynamic forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds’ equation written for the dynamic regime. The hydrodynamic forces built up by the lubricant fluid are evaluated from the state of variable of the system and included into the equations of motion of the mechanical system. Numerical examples are presented in order to demonstrate the efficiency and accuracy of the methodologies and procedures adopted.

This paper describes the phenomenon of negative flow rate (hot oil reflux) occurring in one of the grooves of twin axial groove hydrodynamic journal bearings. This rarely described phenomenon, which can occur under severe operating conditions, increases the risk of bearing seizure. Existing codes for predicting bearing behaviour do not seem to be suitably incorporating this phenomenon into the analysis. The present work reports some experimental observations of the phenomenon and the way it can be taken into account in theoretical modelling.