No abstract

No abstract

Abstract. The paper presents a design of squeeze film air journal bearing based on the design rules derived from CFX and FEA simulation study of an air film in between two flat plates, one of which was driven in a sinusoidal manner. The rules are that the oscillation frequency should be at least 15 kHz and that the oscillation amplitude be as large as possible to ensure a greater film thickness and to allow the bearing to reach its stable equilibrium quickly. The proposed journal bearing is made from AL2024-T3, of 20.02 mm outer diameter, 600 mm length and 2 mm thickness. Three 20-mm long fins are on the outer surface of the bearing tube and are spaced 120• apart; three longitudinal flats are milled equi-spaced between the fins and two piezoelectric actuators are mounted lengthwise on each flat. Such a design produces a modal shape on the bearing tube which resembles a triangle. When excited in this mode at the frequency of 16.37 kHz, and a voltage of 75 V AC with 75 V DC offset acting on the piezoelectric actuators, the air gap underneath of the bearing tube behaves as a squeeze air film with a response amplitude of 3.22 µm. The three design rules were validated by experiments.

Two tubular squeeze film journal bearings, made from Al 2024 T3 and Cu C101, were excited by driving the single-layer piezoelectric actuators at a 75-V AC with a 75-V DC offset. The input excitation frequencies were coincident with the 13th modal frequency, at 16.32 and 12.18 kHz for the respective Al and Cu bearings, in order to produce a 'triangular' modal shape. The paper also provided a CFX model, used to solve the Reynolds equation and the equation of motion, to explain the squeeze film effect of an oscillating plate with pressure end leakage. The dynamic characteristics of both bearings were studied in ANSYS and then validated by experiments with respect to their squeeze film thickness and loadcarrying capacity. It was observed that whilst both bearings did levitate a load when excited at mode 13, the Al bearing showed a better floating performance than Cu bearing. This is due to the fact that the Al bearing had a higher modal frequency and a greater amplitude response than the Cu bearing.

Bearings are important machine parts and their condition is often critical to success of an operation or process, hence there is a great need for periodic knowledge of their performance. According to reported research works in the past several years, it is believed that the extracted information from acoustic emission (AE) signals can be used for bearing condition monitoring. In this work, a novel parameter based on using the ratio of AE mean (μ) and AE standard deviation (σ), formulated as μ/σ is proposed to distinguish between lubricated and dry bearings. A heavy duty test rig was used in experimental work. Various levels of radial loads and rotational speed (ω) were applied to rotating shaft, which is connected to rolling element bearings. It was found that, except few cases, regardless of various levels of radial loads used, at higher levels of rotational speed, dry and lubricated bearings can be clearly distinguished when using proposed parameter.

A tubular squeeze-film journal bearing was designed such that it flexed its shell at its normal modes producing a triangular modal shape. The shell motion was created by a single-layer piezoelectric actuator powered at 75 V AC with a 75 V DC offset and the driving frequency coincided with the modal frequency of the bearing. The paper provided a theory that shows the existence of a positive pressure in a squeeze film responsible for the levitation phenomenon. The various modes of vibration of the tubular bearing, made from AL2024-T3, were obtained from a finite element model implemented in ANSYS. Two normal modes, the 13th and 23rd, at the respective theoretical frequencies of 16.37 and 25.64 kHz, were identified for further investigation by experiments with respect to the squeeze-film thickness and its load-carrying capacity. While the bearing at both modes could cause levitation, the 13th mode has a greater load-carrying capacity because its modal shape produced a much lower end leakage.

No abstract

The present work shows how the equations of motion for a Lanchester damper can be modified to include the effects of a damper slug rolling inside a cavity within the parent body, and of the kinetic energy of the damping fluid. The effect of the slug rolling is to reduce the performance of the damper below that predicted by the standard theory and to require a different value for damping at the optimum condition. These effects are significant when the build-up of self-excited type of vibrations are to be prevented, and when small forced vibrations are to be controlled. Fluid kinetic energy effects can be neglected when the damping fluid is gaseous, but not necessarily so when it is a liquid.