A multi-level mathematical model was used to estimate the stressed-strained state of a cylindrical reservoir with a defect in the wall shape in the form of a dent; the concentration of stresses in the defect zone was studied. The proper choice of the mathematical model was verified; it has been shown that the engineering assessment of the stressed-strained state of the wall of a cylindrical tank with the variable thickness could employ ratios for a cylindrical shell with a constant wall thickness. The spread of values is 2‒10 %. This indicates the proper choice of the mathematical model, as well as the fact that it is possible, for an engineering assessment of the stressed-strained state of the wall of a cylindrical tank with variable thickness, to use the ratios for a cylindrical shell with a constant wall thickness. The stressed-strained state of the dent zone in the tank wall was numerically estimated, which proved the assumption of significant stress concentrations in the dent zone and indicated the determining effect on the concentration of stresses in the dent zone exerted by its geometric dimensions and its depth in particular. The concentration of stresses in the zone of dents in the tank wall was investigated in the ANSYS programming environment at different sizes of dents on the tank wall, for which two dimensionless parameters were introduced: the dimensionless radius of the dent and the dimensionless depth of the dent. Based on the results of a numerical study into the stressed-strained state of the dent zone in the tank wall, graphic dependences were derived of the stress concentration coefficient on the dimensionless depth of the dent for various values of the dimensionless radius of dents, which does not exceed 2 % of the indicator. Based on fitting the stress concentration curves on the dimensions of the dent and tank, a formula was derived for calculating the stress concentration coefficient as a function of the dimensionless radius ξ and the dimensionless depth ς of the dent. The resulting formula makes it possible, with known dimensionless parameters of the depth and radius of the dent, to determine the coefficients of stress concentration in the dented zone of the tank wall.

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This paper considers the structural solution for a main above-ground pipeline with a pre-stressed winding, which makes it possible to improve the efficiency of operation and reduce material consumption. The results from studying experimentally the features in the operation of prestressed pipelines under static operating loads are given. It is shown that the radial movements of the wall of a pre-stressed pipeline are constrained by the strained winding, which prevents its deformation. It was revealed that increasing the tension force of the winding wire reduces circular stresses in the pipeline wall by 1.3...1.6 times and increases meridional ones by 1.2...1.4 times. The experimental study into the models of prestressed pipelines with free vertical and horizontal oscillations has established the dependence of frequency characteristics on the operating conditions and pre-stress parameters. It was found that the envelope amplitude on the oscillogram of free attenuated oscillations takes the shape of an exponent, which indicates the damping effect of the pre-stress. Analysis of the change in the dynamic characteristics of the models depending on the pre-stress force has revealed that the frequencies of free oscillations increase by 1.5÷1.6 times while the oscillation decrement decreases by 1.2÷1.25 times. This paper reports the results of studying the influence of pre-stress parameters on the stressed-strained state of the pipeline model under forced horizontal and vertical oscillations. It is shown that the diagrams of circular dynamic stresses and deformations in the models of a prestressed pipeline are smoother compared to similar characteristics of a conventional pipeline tested at the same experimental parameters. The study results have made it possible to quantify the features in the operation of a pre-stressed pipeline under static and dynamic influences, taking into consideration the pre-stress parameters and operating conditions.

Based on the use of a multi-level mathematical model, this paper estimates the stressed-strained state of a cylindrical reservoir in the mounting joint and considers the concentration of stresses in the joint zone. The correctness of the selected mathematical model was verified to show that for an engineering assessment of the stressed-strained state of the wall of a cylindrical tank with variable thickness, it is possible to use the ratios for a cylindrical shell with a constant wall thickness. The spread of values is no more than 1 %, which indicates the proper selection of the mathematical model. A numerical assessment of the stressed-strained state in the zone of the mounting joint proved the assumption of significant stress concentrations in the zone and indicated the determining effect exerted on the concentration of stresses by its geometric dimensions. The concentration of stresses in the joint zone of the tank wall was investigated at various sizes in the ANSYS programming environment. The result of calculating the stressed-strained state of the reservoir for various values of the dent parameters f/t and  is the constructed polynomials that approximate the stress concentration coefficient Kσ. As a result of the calculations, an interpolation polynomial and an approximating stress concentration coefficient were derived, which could be used to assess the strength, durability, residual life of the tank and to normalize the limiting dimensions of the imperfection of the joint. This paper reports comparative results of the calculations of the stress concentration coefficient depending on the geometric dimensions of the imperfection of the mounting joint in the ANSYS software package, as well as using an interpolation polynomial. The results could be used to assess the strength and residual life of such structures.

An increasing demand for energy and climate change encouraged the search for new ways of using renewable energy sources, including in building structures. At present, improving energy efficiency in buildings by integrating thermal energy storage materials is an urgent task. This paper proposes a mathematical model for the thermal regime in a building with a TES building envelope. The enclosure model consists of gypsum board with 25% of phase change material (PCM). The PCM layers of different thickness reduce room temperature and heat load. The effectiveness evaluation of the proposed model involved calculating the thermal conductivity using the finite difference method. The results show that the incorporation of thermal energy storage materials can reduce temperature fluctuations in the room and maintain a comfortable temperature for a long time (up to 8 hours). With an increase in the thickness of the thermal energy storage layer, the cooling time of the exterior surface of the internal wall also increases.