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There are numerous non-destructive methods in welded joints investigation, but the most promising, especially in applications with steady monitoring of the structure, is the vibrodiagnostic approach. In the course of the research work, the responses were obtained and detected by accelerometers, providing valuable diagnostic information, which later was mathematically processed in the field of time or frequency. The mathematical processing aimed to distinguish significant characteristics embedded in the processes typical of the investigated joints and allow an assessment of how they were made. For this purpose, two methods were proposed, based on determining the logarithmic decrement as a function of time. Due to the complicated course of the impact responses, the method of calculating the logarithmic decrement has been suggested, involving the approximation of responses with various functions. According to the research, the analysis of changes in the logarithmic decrement as a function of time applied to welded plates was proposed, as it enables the initial assessment of joint quality. [ABSTRACT FROM AUTHOR]

In some power systems, voltage subharmonics and interharmonics of significant value may occur. They exert a harmful effect on various energy receivers, including induction motors. Previous works on an induction machine supplied with voltage containing subharmonics and interharmonics generally concern currents, power losses, rotational speed, electromagnetic torque, and windings temperature. This paper reveals additional detrimental effect of voltage subharmonics and interharmonics: namely, excessive vibration of induction motors. It was found that voltage subharmonics of values a few times less than reported in real power systems may cause unacceptable levels of vibration. [ABSTRACT FROM AUTHOR]