Wear monitoring method of water-lubricated polymer thrust bearing based on ultrasonic reflection coefficient amplitude spectrum

The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destructive monitoring technology,but polymer materials are characterized by viscoelasticity,heterogeneity,and large acoustic attenuation,making it challenging to extract ultrasonic echo signals.Therefore,this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient.The effects of bearing parameters,objective function,and algorithm parameters on the identification results are simulated and analyzed.Taking the correlation coefficient and root mean square error as the matching parameters,the thickness,sound velocity,density,and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm(DEA),and the wear measurement system is constructed.In order to verify the identification accuracy of this method,an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-etherketone(PEEK)fixed pad and stainless-steel thrust collar as the object.The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system,respectively.Ultimately,the results demonstrate that the thickness identification error of this method is approximately 1%,and in-situ monitoring ability will be realized in the future,which is of great significance to the life prediction of bearings.

Propagation of the Bessel-Gaussian Beams Generated by Coherent Beam Combining in Oceanic Turbulence

Coherent beam combining(CBC)is recently used to generate high power vortex beams which are strongly required in specific applications.In this paper,based on the extended Huygens-Fresnel principle,the exact theoretical forms for the intensity distribution of CBC Bessel-Gaussian beams(BGBs)in turbulent ocean are derived.To show the superiority of CBC BGBs in turbulent channels,the comparison in the intensity evolution of CBC BGBs with ideal BGBs is performed.It is found that the beam spreading of CBC BGBs is smaller than that of ideal BGBs under the same oceanic turbulence conditions.Moreover,the effect of the beam parameters and channel parameters on the quality of CBC BGBs is also analyzed.The results show that the oceanic turbulence with a higher rate of dissipation of kinetic energy per unit mass of fluid,lower dissipation rate of the mean-squared temperature,or smaller ratio of temperature and salinity contributions to the refractive index spectrum has smaller impact on CBC BGBs.Moreover,the increasing number of the beamlets,the increasing waist width of each beamlet,and the decreasing radius of the beam distribution cause the optical energy to be more concentrated,and thus leading to a longer non-diffraction propagation distance.