Optimised PVDF Placement Inside an Operating Hydrodynamic Thrust Bearing

In our previous work we demonstrated the feasibility of using Polyvinylidene Fluoride (PVDF) sensors inside an operational thrust bearing and were able to measure the blade passing frequencies (BPF) due to an asymmetric flow around different propellers. In that work however the sensors were positioned inside the flat surface of the stationary portion of the bearing with the tilted pads rotated on the opposite side. Due to this configuration the output signal of the PVDF consisted of a superposition of the pad passing frequency (PPF) and the blade passing frequency (BPF) making it difficult to extract useful information from the results. Here, an improved bearing pad-film configuration is proposed in order to minimise the effects of the PPF. By embedding the films inside the pads, positioned on the stationary side of bearing, and rotating the flat surface, it was possible to eliminate the PPF and significantly increase the signal to noise ratio. The measured results give a better understanding of the fundamental vibratory components that arise from the propeller-shaft system.