Application of mathematical modeling methods to determine the effect of soil on natural vibration frequencies of pipelines

When a pipeline is subjected to an external influence that can affect the frequency of its natural vibrations, the parameters of its natural vibrations change, which increases the measurement error, and often simply distorts the results of vibration control. For pipelines, such an impact may be the influence of the soil when pipelines are laid without a channel. Different types of soil affect the change in the natural vibration frequency of the pipeline in different ways.The purpose of the article is to analyze the influence of various types of soils on the parameters of natural vibrations of the pipeline. The aim of the study was to theoretically confirm the dependence of the change in the frequency of vibration of the pipeline under the influence of soil.A modal analysis of natural oscillations of 5 polyethylene pipelines was performed. As initial data, it is assumed that the design pipeline is laid in a trench with inclined walls, with the slope laid on a flat base at a depth of 2.5 m. The calculations were performed in the ANSYS finite element analysis software package. In order to build a mathematical model, the degree of soil impact on pipelines is determined by studying the vertical and lateral pressure of the soil on the above pipelines, and the natural vibrations of pipelines are analyzed.The results of the modal analysis for polyethylene pipes with a laying scheme with inclined walls and different soils (gravel sands, coarse and medium-sized; heavy clays) are presented. The soils were chosen that are the most common on the territory of Russia.Thus, the obtained dependence of the degree of influence of different soil on the natural frequencies of pipelines significantly increases the reliability of vibration diagnostics of buried communications, can facilitate the work on its organization and allow determining long-term forecasts of pipeline operation.