This paper explains the use of remote ultrasound vibration at the optimum position and frequencies to vibrate plates under welding, with the aim of initiating cavitation in the molten pool area. It has been shown in the literature that ultrasound cavitation changes microstructure morphology and refines the grain of the weld. In practice, the plates are excited through narrow-band high-power ultrasound transducers (HPUTs). Therefore, a theoretical investigation is carried out to identify the plate-mode shapes due to the ultrasound vibration aligned with the frequency bandwidth of HPUTs available in the marketplace. The effect of exciting the plate at different locations and frequencies is studied to find the optimum position and frequencies to achieve the maximum pressure at the area of the fusion zone. It was shown that applying the excitation from the side of the plate produces an order of 103 higher vibration displacement amplitude, compared with excitation from the corner. The forced vibration of cavitation and bursting time are studied to identify vibration amplitude and the time required to generate and implode cavities, hence specifying the vibration-assisted welding time. Thus, the proposed computational platform enables efficient multiparametric analysis of cavitation, initiated by remote ultrasound excitation, in the molten pool under welding.
We reported measurement results relating to non-invasive glucose sensing using a novel multiwavelength approach that combines radio frequency and near infrared signals in transmission through aqueous glucose-loaded solutions. Data were collected simultaneously in the 37–39 GHz and 900–1800 nm electromagnetic bands. We successfully detected changes in the glucose solutions with varying glucose concentrations between 80 and 5000 mg/dl. The measurements showed for the first time that, compared to single modality systems, greater accuracy on glucose level prediction can be achieved when combining transmission data from these distinct electromagnetic bands, boosted by machine learning algorithms.
This paper explains producing a novel ultrasonic system to remove/prevent biofouling growth from wind turbines’ access ladders by means of producing local ultrasound cavitation. Using bespoke hardware, an array of high-power ultrasound transducers (HPUTS) and optimally synthesized signal types to remove/prevent biofouling growth from the ladder without violating the standard noise level in the sea is explained. This is a non-toxic and non-invasive solution to detach biofouling and prevent biofilm initiation on offshore structures. It is shown that the marinisation of the HPUT slightly shifts the main resonance frequency from 28.1 to 27.5 kHz. The vibration output from the HPUTs with different mounting systems showed that the transducer with the horn could vibrate the plate at 20 cm from the excitation point, with 300 pm, six times higher than the vibration output from the marinised HPUT. A transducer array and attachment are proposed to make the ultrasound noise below the standard underwater noise limits. The produced sound pressure level (SPL) and sound equivalent level (SEL) from the proposed ultrasonic system was measured. It was specified that the SPL came below 120 dB at 25 m from the excitation point and the SEL value below the 173 dB limit. Finally, the effectiveness of the marinised HPUTS on biofouling removal has been demonstrated with an in-situ measurement, and it was indicated that local biofouling removal could be achieved.
Welding high-strength aluminium alloys is generally a delicate operation due to the degradation of mechanical properties in the thermally affected zone (TAZ) and the presence of porosities in the molten metal. Furthermore, aluminium alloys contain compounds that solidify before the rest of the base alloy, therefore acting as stress concentration points that lead to the phenomenon of hot cracking. This paper investigates the process of applying ultrasonic vibrations to the molten pool aluminium alloy AA6082 to improve both its microstructure and mechanical properties. We analysed conventional and ultrasonic-assisted laser welding processes to assess the sonication effect in the ultrasonic band 20–40 kHz. Destructive and nondestructive tests were used to compare ultrasonically processed samples to baseline samples. We achieved a 26% increase in the tensile and weld yield strengths of laser welds in the aluminium plates via the power ultrasonic irradiation of the welds under optimum ultrasonic variable values during welding. It is estimated that the ultrasound intensity in the weld melt, using a maximum power of 160 W from a pair of 28 kHz transducers, was 35.5 W/cm2 as a spatial average and 142 W/cm2 at the antinodes. Cavitation activity was significant and sometimes a main contributor to the achieved improvements in weld quality.
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