Linear simulations of acoustic wave propagation in a sun-like spherical shell
Helioseismology is the study of the variations in the internal structure and properties of the dynamics of the sun from measurements of its surface oscillations. We are interested in validating and determining the efficacy of the helioseismic measurement procedure. To this end, we simulate acoustic wave propagation in a solar-like spherical shell that extends from 0.2R to about 1.0004 R, where R is the radius of the sun. In order to render the calculation tractable, wave propagation is treated as a linear phenomenon. In this article, I will discuss the difficulties that are consequent to the assumption of linearity and the methods to resolve them thereof.
The paper presents research results referring to the development of a non-invasive method of assessment of the power transformer core technical condition based on the analysis of the mechanical vibrations registered. It characterizes the power object under study, the measuring system used and the developed methodology of assessment of the core pressing degree using the vibroacoustic method. The original results of the time–frequency analysis of the vibroacoustic signals presented in the paper were obtained during switching on a real 800 kVA dry type power transformer in laboratory conditions. The analysis of the signals registered was carried out for three states of its operation: the core pressed by the manufacturer, the core with loose screws fixing the upper yoke and the core with separated upper yoke beams.