Strength of Materials and Theory of Structures

Didactic aspects of the transformation of clip thinking in the context of teaching of construction mechanics

2024-01-04T15:00:03+02:00

The relevance of the problem of transforming the clip-based thinking of higher education students in the conditions of teaching construction mechanics and its solution taking into account the didactic capabilities of educational and digital technologies is undeniable in view of the dynamics of the growth of the volume of educational information, which requires the subjects of the educational process to flexibly adapt scientific approaches, teaching technologies , ways of thinking to modern educational needs. It was determined that clip thinking, which is characterized by speed and superficial consideration of information, lack of attention and its concentration, fragmentation and mosaicism of the world picture, loss of desire for knowledge, reduced need and ability for productive activity, can be both an advantage and a disadvantage in the conditions of digital era, modern system requirements for the training of professionals with a formed system of value orientations, innovative thinking, a culture of cognitive activity. It was established that the essence of the transformation of clip thinking of higher education students in the context of teaching construction mechanics is the integration of educational innovations with the aim of improving the quality of learning and teaching, developing students' critical thinking, and changes in the ways of perceiving and processing information. It was found that didactic mechanisms for the transformation of clip thinking - effective use of data analytics, interactive educational platforms, data visualization, joint platforms and exchange of opinions, automation of processes for data collection and processing, stimulation of critical thinking - contribute to the balanced use of educational tools to improve the perception of information , the development of cognitive competence and contribute to the creation of an educational environment that meets the needs of today. It was concluded that the properties of "clip thinking" can be transformed under the condition of the appropriate construction of the organization of the study of construction mechanics in the direction of the logical presentation of educational material; compliance of training with practical goals; implementation of learning technologies aimed at educational interaction; ensuring an individual approach to the organization of students' educational and cognitive activities.

Selection of the optimal design for a vibro-impact nonlinear energy sink

2024-01-04T15:44:57+02:00

The efficiency of a vibro-impact nonlinear energy sink (VI NES), that is, a vibro-impact damper, is largely determined by its design. The optimal damper design can be found through optimization procedures. However, the result of their work is ambiguous, their various options show different values of the optimal damper parameters. A thorough analysis of the obtained parameters values allow you to select the best option according to a certain criterion. While carrying out this analysis, we observe many interesting phenomena, namely, the synergistic effect of multiple parameters, rich complex dynamics of the VI NES, the presence of direct impacts between the damper and the main body, the dependence of the total energy on the exciting force parameters.The analysis also allows us to formulate the limitations of the VI NES. All these problems are reflected in this article.

Features of the methods of the slope stability evaluation

2024-01-04T16:26:40+02:00

Solving slope stability problems and selecting optimal calculation methods remains an urgent problem. A significant variety of engineering and geological conditions, and a large number of factors that can affect the stability of the slope, lead to the need to select a calculation method in each specific case.

The article examines the features of the two most common methods of calculating the stability of slopes and slopes in geotechnical practice. The first group - limit equilibrium methods, has been widely tested and is the basis of simple engineering calculations of slope stability. Within the framework of the article, the circular cylindrical sliding surface method based on the method of moments, the method of horizontal forces, the methods of tangential forces based on the analytical method of H.M. Shakhunyanets, with the introduction of calculation schemes and the mathematical apparatus of these methods, are considered. The method of L. P. Yasyunas was also noted due to the idea he highlighted of simplifying calculations using unit shear pressure, which is generally an interesting idea but has certain difficulties in practical implementation. The key advantages and disadvantages of the finite element method for solving slope stability problems are given. The question of combining MSE with the method of reducing strength to determine the coefficient of stability of slopes is highlighted.

Several software complexes are presented that allow us to automatically determine the coefficient of stability of slopes based on different groups of methods. A comparative calculation of the imaginary slope of PC "Plaxis 2D" and "Ukis" was performed. Two formulations of the problem are considered: for a free slope and with an additional load in the upper part of the slope. The received coefficients of stability and the shape of the sliding surface were analyzed and a generalized table of results was formed. The displayed results demonstrate sufficient convergence, which confirms the possibility of using the specified methods in engineering practice to determine the stability coefficient of slopes.

Іnfluence of explosive loads on buildings and structures of the population civil protection

2024-01-04T16:49:34+02:00

The article substantiates the relevance of the design and construction of buildings and structures of the Ukraine population civil protection in the conditions of possible shock-explosive influences. The aim of the work is to systematize information about the impact of explosive loads on building structures and develop recommendations for improving the stability of buildings and civil protection structures.The influence of shock wave during the detonation of explosives on the structures of buildings is considered and systematized. The features of distribution of pressure of blast wave on the structures of buildings in time, depending on magnitude of their distances to the epicenter of the explosion, are analyzed. The features of the influence of blast wave, which expands from the source of detonation, on low-rise buildings with flat roofs and the sequence of development of deformations and destruction of their structures at three stages of wave propagation are revealed. The nature of the influence of blast wave on multi-storey and high-rise buildings and the sequence of development of deformations and destruction of their structures are analyzed. Examples of destruction of structures of buildings of various structural systems from explosions are given.The paper gives recommendations for design of blast-resistant buildings with built-in bomb shelters that are able to resist explosive loads without progressive collapse, which leads to a cascading sequence of damage to adjacent building structures. The ways of redistribution of gravitational loads on the structural systems of buildings and structures are analyzed, recommendations are made for design of explosion-proof buildings.Conclusions are drawn about the feasibility of using monolithic reinforced concrete frames, which are able to plastically deform, redistribute loads and resist the onset of progressive collapse, which leads to appearance of a cascading sequence of damage to adjacent building structures.

Comparative analysis of the stability and natural vibrations of shallow panels under the action of thermomechanical loads

2024-01-04T17:34:01+02:00

The work is a continuation of research devoted to substantiating the reliability of solutions obtained by the finite element method for the analysis of nonlinear deformation, buckling and vibrations of thin elastic shells under the action of thermomechanical loads. The method is based on geometrically nonlinear relations of the three-dimensional theory of thermoelasticity and the principles of the moment finite element scheme. A thin elastic shell of an inhomogeneous structure is modeled by a universal spatial isoparametric finite element. The modal analysis of the shell is implemented at each step of the static thermomechanical load. The subspace iteration method is used to determine the spectrum of the lowest frequencies of natural vibrations of shells. A shallow spherical panel with a square plan is considered. The effect of preheating on the loss of stability and vibrations of an elastic isotropic shell under uniform pressure loading is investigated. The behavior of the shell weakened by two pairs of cross-channels is analyzed. The weakening of the panel by narrow and wide channels, which can be eccentrically located relative to the middle surface of the shell, is considered. The effectiveness and adequacy of the method is confirmed by a comparative analysis of solutions with results obtained using modern multifunctional software systems LIRA-SAPR and SCAD. The features of using the systems for solving the problems under consideration are given. Analysis of the results made it possible to evaluate the possibilities of using these software systems to substantiate the reliability of solutions to certain classes of problems of geometrically nonlinear deformation, buckling and vibrations of elastic shells.

Choice of the shape imperfections model in dynamics problems of a long flexible cylindrical shell subjected to force couples

2024-01-04T18:04:06+02:00

The issue of modeling geometrical imperfections in the dynamics problems of thin-walled shells was little researched. In cases when the natural modes of shell coincided with its buckling modes, the issue of choosing a dangerous imperfection model did not arise. When these shell modes did not coincide, it was important to investigate and compare the effect of different imperfections models on the static and dynamic characteristics of such shells. The choosing the shape imperfections model of a long flexible cylindrical shell subjected to force couples, the natural and buckling modes of which did not coincide, was studied using procedures of the finite element analysis software NASTRAN. The shell wall as a set of plat rectangular elements with six degrees of freedom at the node in the cylindrical coordinate system was modeled. The action of force couples as the concentrated forces were distributed at the nodes of the shell edges in accordance to the presentation of A.S. Volmir. The linear buckling problem and the geometrical nonlinear static analysis of the perfect shell by the Lanzosh method and the Newton-Raphson one were performed, respectively. The long half-waves buckling mode was taken as the first shell imperfections model. The modeling of the second shape imperfections as the first natural mode of the perfect shell using the natural vibration analysis by the Lanzosh method was performed. The different amplitudes of geometrical imperfections in proportion to the shell thickness using a program adapted to this software were set. The results of the geometrical nonlinear static analysis of the imperfect shell by the Newton-Raphson method showed that the shape imperfection model in the form of long half-waves more reduced the values of critical buckling loads. Investigations of natural shell vibrations by the Lanzosh method revealed the same influence of different imperfections models on the natural frequencies and natural forms. We think that the shape imperfections model in the form of long half-waves in studies of forced vibrations and dynamic stability of a long flexible cylindrical shell subjected to force couples will be more effective.

Stability of cylindrical anisotropic composite shells under torsion in a three-dimensional formulation

2024-01-04T18:25:22+02:00

The article presents a calculation of the stability of non-thin cylindrical anisotropic layered shells under the action of end torsional moments in a spatial formulation. The anisotropy of the used material is characterized by one plane of elastic symmetry of characteristics. This is caused by the mismatch between the main elastic directions of the composite fibrous orthotropic material and the axes of the curvilinear cylindrical coordinate system.

A three-dimensional inhomogeneous system of partial differential equations describing the subcritical stress-strain state within the linear theory of elasticity is derived using the Hu-Washizu variational principle. Reducing the dimension of the problem under consideration from three-dimensional to one-dimensional is carried out by taking into account the axial symmetry of the deformation of the cylindrical shell and using the method of straight lines along the generatrix.

Based on the modified Hu-Washizu variational principle, a three-dimensional system of homogeneous partial differential stability equations is derived within the framework of the spatial theory of elasticity. The reduction of a three-dimensional system to a one-dimensional one is carried out along the generatrix and in the circular direction - by expanding the components of stresses and displacements into double trigonometric series when applying the procedure of the Bubnov-Galorkin method, as well as taking into account the periodicity of the resolving functions.

An algorithm has been developed, implemented in the form of application software packages for PCs. In it, in a single computational process using the numerical method of discrete orthogonalization in the direction normal to the middle surface of the shell, the establishment of the parameters of the subcritical stress-strain state and the solution on this basis of stability problems for non-thin anisotropic cylindrical shells under the influence of torsion are combined.

The problem of the influence on the stability of an anisotropic cylindrical non-thin shell of an increase in the number of cross-reinforced layers depending on the angle of rotation of the main directions of elasticity of the material and the direction of application of torque is considered. The obtained results of stability calculations according to the proposed approach were compared with critical torsion loads calculated using an orthotropic model for calculating anisotropic shells. It is shown that for single-layer cylindrical shells the difference between the compared results reaches 69%. An increase in the number of cross-reinforced layers leads to a decrease in this discrepancy, and with seven to eight layers, the difference between the critical loads obtained using the described approach and the orthotropic model is within 5%. This result is consistent with those obtained using classical or refined theories of calculations of both thin and non-thin anisotropic cylindrical shells.

Simulation of flood inflammation due to destruction of hydrotechnical structures

2024-01-05T15:13:15+02:00

The article presents the new results of scientific researches of technical aspects of forecasting the consequences of emergencies related to hydraulic accidents.Based on the analysis of statistical data, the relevance of the raised issue of the need to improve the existing scientific and methodological apparatus to justify the parameters of the breakthrough wave and the flood zone in the event of destruction of hydraulic structures is substantiated. The attention is focused on the need to take into account the condition of ensuring the consumption of bulk mass of water before the restoration of its domestic level in the lower reaches of the water barrier.This condition is the basis of an improved method for determining the parameters of active and passive flooding of the area, based on a three-dimensional model of the longitudinal section of the breakthrough of the hydraulic structure and the parameters of the breakthrough wave.Based on the results of verification of the proposed methodology, calculations and modeling according to the initial data in accordance with the developed situation of destruction of the hydro unit, a conclusion about the feasibility of its use for forecasting emergencies during hydraulic accidents was made.

A numerical study of the multicriteria parametric optimization of the displacement and weight of a two-connected conical shell of minimal surface under thermal and power loading

2024-01-05T16:13:45+02:00

Various methods and approaches are used to solve the problem of optimal design. Problems of this type are used for the optimal design of spatial coverings, which in modern architecture are progressive structures that are of interest to the whole world. Spatial coatings allow to give the building architectural expressiveness, cover large spans and combine load-bearing and enclosing functions.

The hulls of minimal surfaces are the hulls of negative Gaussian curvature. In general, the geometry of minimal surfaces cannot be described analytically. To solve this problem, which is associated with solving the differential equation that describes the minimal surface in general, under appropriate boundary conditions, one has to use methods of numerical analysis. This approach allows us to build a point frame of the shell, which is a matrix of discrete solutions of functions that searches for a given minimum surface. In view of this, its geometric characteristics can be obtained only in numerical form.

The basic relations of the linear theory of thin elastic shells of minimal surface are highlighted in the numerical study of parametric optimization. The mathematical justifications of how the external load is perceived and the process of creating the stress-strain state of the shells of minimal surfaces are highlighted.

For the numerical implementation of the multicriteria parametric optimization of a double-connected conical shell of minimal surface, a finite element model was built from plate finite elements in the amount of 4824 pieces and 4896 nodes. The perimeter is rigidly clamped to the ground disk. The thermal force load is set, which consists of a combination of static and temperature loads.

The developed methodology shows quite good results that coincide with the works of other authors and makes it possible to use two types of optimization for one research object simultaneously. The first stage is shape optimization, and the second stage is multicriteria parametric optimization.

This methodology makes it possible to perform optimization processes in an automated mode, which is an important applied task for construction and applied mechanics.

Safety assessment of the steel structures of nuclear power plants units considering special operation conditions

2024-01-08T13:26:31+02:00

Special operation conditions of steel structures nuclear power plants units (elevated temperature of the surrounding environment, the need to consider the simultaneous action of several episodic impacts etc.) require using of special approaches to their safety assessment. Among the wide variety of steel structures at nuclear power plantsunits, the supporting structures of equipment and pipelines play an essential role in ensuring its safety. At the same time, state building codes oriented towards traditional steel structures that are subjected to standard loads and impacts, and do not consider mensioned special operating conditions. Regulatory acts on nuclear and radiation safety in this aspect contain general regulatory requirements, which is due to the modern concept of the development of the regulatory-legal framework of Ukraine for ensuring the safety of nuclear plants. Therefore, the existing regulatory and methodological support does not sufficiently cover the aspects of safety assessment of supporting structures, taking into account the special operation conditions. The article proposes approaches to assessing the safety of equipment and pipelines supporting structures nuclear power plants units, which consider both the special operation conditions and the degree of responsibility for ensuring safety during and after seismic hazards.

Methods of assessing the seismic resistance of building structures and nuclear power plant structures in Lira-SAPR program

2024-01-08T14:29:55+02:00

This article proposes a methodology for assessing seismic resistance and determining the reserve of seismic resistance, taking into account the interaction of the structure with the foundation for buildings and structures of power units, strength and deformation criterion of workability, etc. During verification calculation, three criteria of strength of workability, compiled according to the General principles of ensuring reliability and structural safety of buildings and structures, were considered. The seismic calculation was performed according to the linear-spectral theory of seismic resistance. In LIRA-SAPR program, considerationoftheinfluenceofthebaseisimplementedaccordingtoBuildingnorm DBN B.1.1-12-2014. Building Construction in seismic areas of Ukraine.

The method of calculating the value of the ultimate seismic resistance of HCLPF and the method of constructing damage curves are proposed. To determine the integral parameter HCLPF, which characterizes the level of seismic resistance of this element, a calculation analysis of the seismic resistance of elements of operating nuclear power plants was carried out within the framework of the method of ultimate seismic resistance. The methodology and verification examples for determining the values of FS and HCLPF parameters for reinforced concrete structuresin LIRA-SAPR programare proposed.

Analysis of structures with arbitrary kinematic boundary conditions by the semi-analytical finite element method

2024-01-08T16:05:20+02:00

The successful application of FEM to the analysis of structures is largely due to the efficiency of the use of modern software packages, in connection with which the role of program systems that implement the solution process increases. The correct organization of the computing complex, the choice of optimal algorithms for solving systems of linear and nonlinear equations largely determine the possibilities of the method in terms of the structural complexity of the objects under consideration, the accuracy of the results obtained, and the complexity of setting nonlinear problems. Therefore, there is an increased interest in the development of fairly universal computing complexes based on FEM. One of the effective software complexes is the "Strength" system, designed to conduct comprehensive research in the field of mechanics of a deformable solid, the basic principles of construction of which are used in this work in the implementation of a semi-analytical version of the FEM.

In this work, solutions of a significant number of control problems of deformation of massive and thin-walled prismatic bodies under different boundary conditions and loads are obtained. In the process of solving new problems, the estimation of the convergence of results was carried out on the basis of a sequential increase in finite elements and contained terms of decomposition, an increase in the accuracy of systems of linear and nonlinear equations, and the accuracy of satisfaction with natural boundary conditions was checked. The developed effective method for solving new complex problems of deformation of prismatic bodies is implemented in the form of complex programs and can be used in design and construction practice in construction, mechanical engineering and other fields of technology.

Investigation of the dynamics of a three-layer shell structure of an elliptical cross-section under non-stationary dynamic loading

2024-01-08T16:47:31+02:00

The dynamic behavior of a three-layer cylindrical structure of normal elliptical cross-section with a discrete polymer filler under the action of an internal non-stationary load was studied. Finite element models of the structure were created and deformations and normal stresses of its bearing layers were calculated. Variants of structures without polymer aggregate and with aggregate of different stiffness, reinforced with ribs, were considered. A comparative analysis of the deformations and stresses of the bearing layers at the ratio of the modulus of elasticity of the material of the bearing layers and the aggregate E_1.2/E_t=500 and E_1.2/E_t=50 is given. Finite elements of the Solid and Laminate types are used in the finite-element models. The calculations were carried out by the software and calculation complex Nastran using the direct transient dynamic process algorithm.

Methods of calculation and engineering protection of critical infrastructure objects and other strategic facilities against long-range projectiles

2024-01-08T17:11:30+02:00

Relevance. One of the key areas of russia's military operations against Ukraine is the destruction of critical infrastructure objects (CIO) of strategic importance. The main types of enemy means for air strikes on CIO are air-launched, ground-launched and water-launched missiles, as well as barrage munitions. The vast majority of the CIO were built in Ukraine above ground, without any engineering structural protection systems to counter air threats, explosions or other impacts related to military operations. The importance of developing the most effective methods of engineering structural protection of the CIO from various types of projectiles as soon as possible was demonstrated by the experience of Ukraine's war with russia, in particular, the analysis of the significant impact of damage to the CIO in the energy sector. At present, Ukraine has a certain lack of regulatory data for designing reliable protective structures for CIO. The aim of this work is to develop a regulatory base for making calculations for the possible impact of various types of forceful effects from air strikes, terrorist attacks, etc. when designing the CIO and other strategic facilities. Currently, the issue of organising the defence of critical infrastructure and other strategic objects is being systematically addressed on the basis of the "Country-Fortress" principle, which provides for the organisation of echeloned air defence combined with comprehensive civil and engineering defence measures. In addition, it is necessary to provide for the reliable protection of existing facilities, taking into account the hazards and threats of today. The process of reducing the risks of damage to the CIO involves identifying threats, their comprehensive assessment, developing measures to reduce threats and their prompt implementation, followed by an assessment of the measures effectiveness. Results. The presented methods of risk assessment of critical infrastructure damage, methods of their engineering and analytical calculations and methods of engineering structural protection against ammunition of various types allow developing an effective integrated system of protection of strategically important objects. The article deals with both the protection of existing facilities and the design of new ones, taking into account the requirements for engineering protection and civil defence.

Analysis of the influence of different soil types on the natural frequencies of multi-storey reinforced concrete buildings

2024-01-08T17:40:31+02:00

According to current concepts, the construction of multi-storey and high-rise buildings is quite topical. Increasing the number of storeys and building density provokes an increase in loads and forces on the structural elements of the building, as well as on the soil base. It is necessary to take into account the mechanical characteristics of the soils underlying multi-storey buildings to improve the design models of objects when determining the forces and deformations in their elements. A vital indicator in monitoring the structural characteristics of buildings is global stiffness. Natural frequencies determined by modal analysis are used to detect its change. The purpose of this study is a numerical analysis of the effect of changes in the parameters of the soil base on the natural frequencies and values of vibrations of multi-storey reinforced concrete frame buildings using software systems. In this study, four variants of design models with rigidly fixed foundations and elastic foundations with different types of soils were developed.In the models with elastic foundations, stable soils were used, such as sandy, moderately stable, represented by loams and sandy loams, and weak soils containing a layer of peat. The building scheme was developed using the SCAD software package with the application of the finite element method. Taking into account that 90% of the territory of Ukraine is located in complex engineering and geological conditions, the use of the finite element method allows to effectively solve complex problems of interaction of heterogeneous elements, including in a nonlinear approach. As a result, it was found that the type of soil foundation affects the change in the natural vibration frequencies of a building. In the model with a rigidly fixed foundation, the frequencies are the highest, and the eigenvalues of oscillations are the lowest. A point that should be mentioned is that in the variants with an elastic foundation, the lowest frequencies are observed in the model on weak soils, and the highest values are typical for sandy foundation soils.

Methodical approach to determining the resistance of field fortification coating structures built to the shock-explosive impact of modern missile weapons

2024-01-09T12:02:11+02:00

The purpose of the article is to publicize a methodical approach to determining the stability of cover structures of field fortifications to the shock-explosive action of modern missile weapons, in particular cruise and ballistic missiles.

The purpose of this article is to present a methodological approach for determining the resistance of the cover structures of field fortifications to the impact and explosive effects of modern missile weapons, in particular cruise and ballistic missiles.The analysis shows that currently, the most dangerous means of fire destruction for troops are long-range cruise and ballistic missiles with high explosive effect. Under such conditions, the most effective way to protect troops is to shelter them in field fortifications, the cover structures of which are resistant to the impact and explosive effects of these missiles.The article presents a methodological approach to determining the resistance of the cover structures of field fortifications to the impact and explosive effects of cruise and ballistic missiles and the results of determining the required thickness of the cover of these structures, which are made of the most readily available building materials in the field – soil, sand, clay, stone, concrete and reinforced concrete. The scientific novelty of the proposed methodological approach lies in the comprehensive consideration of a set of indicators quantifying the main tactical and technical characteristics of modern cruise and ballistic missiles, their flight and trajectory parameters, as well as indicators taking into account the most important properties of materials for the construction of a penetration and emission protection cover of a field fortification.

Determination of the stress-deformed state of the grinding circle adjustment pencil

2024-01-09T16:40:30+02:00

Using the Ery stress function in a linear formulation, using the methods of the classical theory of elasticity, an algorithm for analytically determining the stress-strain state of the working part of the abrasive wheel straightening tool as a two-layer composite material was developed. The algorithm allows considering arbitrarily distributed normal and tangential loads of the working surface of the abrasive grain of the tool. It considers the mandrel's limitation of deformations of the grain and the material that attaches it to it, the compatibility of the deformation of the grain and the material of its attachment to the mandrel, and their mechanical properties.

Calculations performed according to the obtained algorithm allowed the following to be established. The maximum standard stresses on the working face of the grain exceed the corresponding stresses on the opposite face due to their more uniform distribution. The tangential stresses are almost uniformly distributed along the specified face. The material connecting the grain to the tool mandrel deforms almost uniformly due to its lower modulus of elasticity and smaller thickness than the abrasive grain's modulus of elasticity and thickness. Determining the stress-deformed state of the executive part of the pencil for correcting the working surfaces of grinding wheels for abrasive processing of materials makes it possible to specify the known mechanism of their interaction and increase the efficiency of the technological process of restoring the working surfaces of the tool for abrasive processing of metals.

Taking into account the simultaneous deformation of the abrasive grain and the material that attaches it to the pencil mandrel, determining their stress-strain states using the methods of the classical theory of elasticity allows us to consider the results obtained by the given algorithm as sufficiently reliable within the limits of linear deformation. It is advisable to direct further research to determine the durability of the "abrasive grain-bond" system under variable cyclic loads.

Determination of internal efforts in the base finite elements of SAFEM

2024-01-09T17:25:27+02:00

The principles of calculating the internal efforts of a circular finite element in the semi-analytical finite element method (FEM) based on the obtained components of the stress tensor and the peculiarities of the approach associated with the use of the moment scheme of the finite element (FEM) are considered. Formulas for determining longitudinal, shear forces, bending and torque moments have been obtained.

A special place, among the variety of objects considered with the help of analytical and numerical methods, is occupied by bodies of revolution of complex shape and cross-sectional structure, formed by the movement of some creative surface along a closed or opened line without breaks. The selected geometric class is used as natural structures of nodes and details in construction of mechanical engineering. The sufficiently wide distribution of the specified forms in the construction and machine-building industries, on the one hand, and the possibility of significantly simplifying the solving relationships by taking into account their geometric features, on the other hand, provide a basis for the development and use of various modifications of the finite element method (FEM). The semi-analytical finite element method (SAFEM) is one such approach that has gained widespread use for solving problems whose objects are prismatic bodies and bodies of revolution of complex shape and cross-sectional structure. Due to the introduction of additional hypotheses that do not reduce the accuracy of the approximation, the representation of deformations and stresses in physical terms and in accordance with the moment scheme of the finite element (MSFE), on the one hand, it is possible to avoid the time-consuming procedure of numerical integration over the cross-sectional area of the finite element (FE), on the other hand - maintain the high efficiency of 3D discretization.

Despite the large number of publications devoted to the semi-analytical method of finite elements, the question of determining internal forces, which are often component factors of the strength criteria laid down in state building codes, is inappropriately neglected. The use of SAFEM in combination with МSFЕ creates some mathematical features of calculating internal longitudinal, shearing forces and moments.

Computer modelling of thin-walled shell structures with geometric imperfections

2024-01-10T13:08:29+02:00

The study presented in the article focuses on modelling of thin-walled cylindrical shell structures with initial geometrical imperfections under external radial pressure. The critical pressure of the perfect shell obtained using linear analysis significantly exceeded that calculated by the Papkovich formula. This discrepancy can be attributed to the shell displacement constraints and the fact that linear analysis provides non-conservative estimates. Initially, the geometric imperfections were assumed to follow an eigenmode-affine pattern with varying amplitudes. Critical pressure values iteratively determined using the modified Ricks method were found to be lower than the critical pressure of the first buckling mode. Importantly, all these values remained notably higher than the normative value. Subsequently, the initial imperfections were modelled as combinations of sinusoidal deviations with different amplitudes and varying numbers of waves along the perimeter. Short-wavelength eigenmode-affine imperfections were superimposed on longer-wavelength deviations. The research indicated that while the long-wavelength imperfections had a marginal impact on the critical pressure values, they notably altered the post-buckling behaviour of the shell, as depicted in load-deflection figures in the form of loops. These processes occurred at pressure levels considerably higher than the normative value. The simulation results are in good agreement with established theories regarding the pre- and post-buckling behaviour of thin-walled shells. Nonlinear analysis revealed that the actual critical pressure values exceeded the normative value by 30-45%, and the post-buckling pressure values exhibited a gradual decrease without posing a threat to abrupt changes in the geometry of the shells. This outcome provides a basis for a more accurate estimation of the load-carrying capacity of the shell structures.

The influence of noncannonical form of boundary and contact surfaces close to spherical, on the stress state of thick shells of rotation under pressure

2024-01-10T14:59:24+02:00

On the basis of the general solution of the equilibrium equations for an isotropic medium in a spherical coordinate system within the framework of the second variant of the method of perturbation of the shape of the boundary (MZFG), it is obtained taking into account the first three approximations of the solution of the problem of the stress-strain state (SST) of thick layered shells of rotation, limited surfaces with a small amplitude of deviation from spherical ones. According to the analytical solutions, numerical data were obtained, which made it possible to analyze the stress-strain state of the shells under the action of constant or variable axisymmetric (internal and external) pressure. Depending on the geometric parameters of the equations of the non-canonical surfaces of the shells, the effect of the conditions of ideal and non-ideal contact between the layers on the redistribution of stresses is shown compared to the case of a spherical shell with a layered structure (canonical form – zero approximation).

Optimization of the mode of movement of the boom system of the loader crane

2024-01-11T12:59:28+02:00

The article presents a method for solving the problem of eliminating vibrations of the load, which is fixed on a rigid articulated suspension at the time of simultaneous movement of two links of the boom system. The essence of the method is to optimize the mode of simultaneous movement of two links of the boom system of the loader crane with horizontal movement of the load during the start-up period. The problem is solved according to two optimization criteria, namely: according to the optimization criterion of the root-mean-square value of the generalized force and the optimization criterion of the root-mean-square value of the power of drive mechanisms. The developed criteria reflect the undesirable properties of the links of the boom system and drive mechanisms, so their value was minimized.

The solution of the optimization problem is presented in a discrete form. For this purpose, the particle swarm optimization (ME-PSO) method was used. This helped to obtain discrete values of the kinematic and power characteristics of the boom system of the loader crane.

Since the optimization criterion is an integral functional, the methods of the calculus of variations are used for its optimization. The solution of the variational optimization problem is presented in the form of many parametric functions that satisfy the boundary conditions of motion and minimize the obtained dimensionless criteria. For this purpose, the particle swarm optimization (ME-PSO) method was used. This made it possible to obtain the dependence of the optimal energy and power characteristics of the boom system and the drive mechanisms of the loader crane. The mode of movement of the boom system links obtained as a result of optimization improved the power and energy characteristics of the loader crane, which made it possible to increase its reliability and productivity.

Speed of metal deformation of welded pipe sections in the process of natural tests

2024-01-11T16:23:59+02:00

It is clear that testing on Menage Charpey samples and other materials, which may not match the durability of pipe walls, does not reflect the real picture of visco-plastic failures, which does not allow the development of a methodology or model for predicting the residual life (failure-free) gas pipelines have a three-year term of operation. At the same time, theoretical and laboratory studies do not always provide sufficient evidence for nutrition, directly related to the reliability and trouble-free operation of pipelines. It is likely that in the laboratory minds of enterprises and scientific foundations, it is important to create and identify all the factors that characterize the growing and widespread use of metal in gas pipelines to represent nature. and testing of cutting gas pipelines with a length of 150-250 m. However, due to the technical complexity of their implementation, in the field Our minds will never again be faced with the need to identify a new set of registration parameters. In addition, the testing of highly labor-intensive procedures, including ensuring the safety of their implementation, requires large material and hourly costs. Serial testing of enclosed pipes in the drains of a specially lined landfill and cutting on this basis is quite consistent with the results of field testing of gas pipelines. Field testing of pipes allows for consistently inexpensive research when testing new types of steel and pipe designs. Therefore, laboratory data need to be verified and necessarily clarified based on the results of pneumatic testing of long-life pipe sections, so that at the present time there is an urgent need to combine laboratory and field tests pipes of the gas pipeline. Such testing is not widespread, but as a result of their experimentation, important information is taken away from the behavior and power of metal in the minds of vantagement and exploitation, those closest to exploitation. Full-scale testing was carried out at a specially trained test site for cutting pipes intended for the construction of main gas pipelines, which made it possible to determine the kinematic and dynamic parameters of the alignment of the model gas pipeline under operating conditions. importance and in minds as close as possible to the operational ones. Analysis of the results of the field (natural) tests is to confirm that from the moment of initiation of the collapse in the central pipe, the fluidity of the main crack (on both sides of the initiator) increases and increases distance approximately 2-3 diameters from the cut, reaching a maximum. Changing the fluidity after tightening the central pipe can be either symmetrical or asymmetrical to the cut in the middle pipe. This is due to the technique of carrying out the experiment and the formation of cracks, including displacements of the cutting edge in the middle of the pipe and various influences on the metal of the pipes in the zone of local tearing. The underlying regularity is that the maximum fluidity is not evident at the crack acceleration stage. It is necessary to note that in order to carry out the experiment, so that the achieved high fluidity of the structure is preserved when the top of the crack enters the final plot. This is ensured by consistent selection of the viscosity of the metal of the central pipe.

The dynamic analysis of fixed deep-water platform

2024-01-11T17:31:31+02:00

The industrial progress is closely related with active using of hydrocarbons more than half of reserves of which lie in rock formations beneath seabed or ocean floor. For oil production at the great depth of immersion oil production fixed platforms are used most often. But using of such technological structures is not limited only to interest of oil and natural gas industry whereas they are important for navigation and military purposes. Offshore fixed platforms are exposed to effects of a high seismicity, wind, waves, strong undercurrents and an impulse impact during the movement of ice fields especially when exploitation in northern seas. The impact of different factors on the value of the period of natural oscillations ofthe offshore fixed deep-water ice-resistant platform with the depth of immersion 120 m that rests on the pile foundation was researched. Two discrete idealized models of the platform were used for the analysis: the first model that was implemented without taking into account the flexibility of the foundation and the second model where the flexibility of the pile foundation and the action of ground foundation were taking into account by the addition of elastic links that simulate the elastic connection between joints. Also, impacts of the connected mass of water media that was modeled in the form of additional distributed joints mass and the impact of the ice field that was modeled by the addition of additional links were investigated. The analysis showsthat values of periods of natural oscillations form increase by 8-20% when the flexibility of the pile foundation was taken into account; increase by 9-100% when the impact of the connected mass of water media was taken into account; decrease by 9-100% when the impact of the ice field and water media were taken into accountthat is significant when analyzing of stress-strain state of members of the structure.

Monitoring of structures with bearing elements in the form of long vertical rods

2024-01-15T16:12:12+02:00

A building structure is considered, which in the design form consists of two vertical rectilinear interacting elements. One of them is loading, the other is carrying. The bearing element is presented in the form of a long thin rod loaded with an external axial vertical force. Due to the errors of geodetic verification and installation work, the bearing rod will be installed with some inclination and displacement relative to the coordinate axes. The external load on the bearing element is represented by the force vector, which is equivalent to the loading rod. Errors of geodetic verification and installation work will change the design direction of the force line and its design position on the supporting element. An inclined force vector will have a vertical and horizontal force component. Thus, the line of action of the loading force and the longitudinal axis of the supporting rod will be located at an angle to each other, which will cause bending momentsand transverse forces in the sections of the rod. A design "changed" in relation to the project is created. Bending moments and horizontal forces in this design will contribute to premature bending of the rod. An unevenly heated rod also acquires the ability to distort. The influence of the specified factors can be increased, and the stability of the rod significantly weakened due to uneven subsidence, horizontal displacement or tilting of the supporting structure due to dangerous exogenous geological processes. Therefore, errors in the position of elements, changes in temperature, geological processes disrupt the linear form of equilibrium of the bearing rod and its position in space. The change in shape and relative position contributes to the premature emergence of an unstable state under an increasing external load. In the changed design, the bearing rod may suddenly find itself in a critical stress-deformed state. The task of monitoring is to sense and properly record changes and dynamics of the stress-strain state. For this purpose, measuring complexes with a certain configuration are designed, which provide with the necessary specified accuracy the measurement of changes in the physical state of the elements of building structures.

Development of a parametric model of the spatially oriented knife on the bulldozer blade

2024-01-15T16:45:51+02:00

The paper considers the results of the study of resistances arising during the operation of a bulldozer in the soil environment and processes in the drawing prism. What affects the stability and productivity of the bulldozer during excavation works. The geological map of the "Ukrainian crystalline shield" was studied, where the most common soils on the territory of Ukraine were found. Using the proposed hypothesis of the movement of spatially oriented knives on a bulldozer blade, it was shown that when excavating soil at different speed ratios, there is a deviation of the cutting force application vector by an angle (α), which in turn affects the geometric interaction of the spatially oriented knife with the working environment. Changing the geometric interaction of the spatially oriented knife with the soil affects the cutting force, which led to the creation of a parametric model of the interaction of spatially oriented knives with the working environment. The model was developed for different knife configurations and different ratios of the bulldozer speed to the spatially oriented knife movement speed. The total, normal, and orthogonal cutting forces for the working, subcritical, and critical depths of soil cutting were calculated, according to changes in the parametric model of the spatially oriented knife. A comparative calculation of the cutting force by a bulldozer without and with spatially oriented knives was carried out.

Comprehensive analysis of the performance of welding joints of gas pipelines with different viscosities

2024-01-15T17:02:37+02:00

Full-scale tests of gas pipelines with different viscosities were carried out in landfill conditions, which are as close as possible to the natural conditions of operation of gas pipelines. The kinetics of crack propagation along welded joints - their trajectory, the transition from the weld seam to the base metal of the pipe and vice versa, the speed of movement of cracks in viscous and brittle metal and defined zones of plastic deformation - were experimentally investigated. It is known that tests on Menaget, Charpy and other samples, which have thicknesses that do not correspond to the thickness of the pipe walls, do not reflect the real picture of visco-plastic and brittle fractures, which does not allow to develop a methodology or model for predicting the final resource (non-accident) of long-term gas pipelines period of operation. At the same time, theoretical and laboratory researches do not always adequately answer the questions directly related to ensuring the durability and trouble-free operation of pipelines. It is likely that in the laboratory conditions of enterprises or scientific institutions it is difficult to reproduce and take into account all the factors that characterize the growth and spread of destruction in a real operating gas pipeline. Therefore, the data of laboratory studies must be checked and necessarily clarified according to the results of pneumatic tests of long pipe sections, i.e., at present, the need to combine laboratory and field tests of pipes of the gas pipeline network is urgently needed. Such tests are not massive, but as a result of their performance, important information is obtained regarding the behavior and properties of the metal in the conditions of loading and operation, which are closest to operational conditions. In field tests, pipes with a diameter of 1000x18 mm were used, which underwent controlled rolling (steel class X70 - grade 06G2BA) at a working pressure of RR = 9.7 MPa (in the northern - low-temperature version). Tensile tests, studies of impact toughness, strength and plasticity of the weld metal were carried out according to standard methods described in works [2-5]. During the experiments, a large number of sensors of temperature, pressure, strain, stress, crack propagation speed, etc. were used. The obtained results regarding the kinetics of the destruction of natural pipes in landfill conditions lay the groundwork for the development of a mathematical model of the engineering forecast of the residual (non-accident) resource of pipelines operating in oil and gas fields.

Design calculations and study of the assembly and technological indicators of coating's consolidated structural blocks

2024-01-29T17:54:27+02:00

The article considers and implements the calculation model of the system using the design and calculation complex LIRA. The features of load perception and their rational distribution between structural elements are analyzed. The stress-strain state is calculated, taking into account the subsequent installation of the structure. The approach to determining the labor-intensiveness and duration of consolidation processes during the installation of structural blocks of the covering, which is caused by atypical structural and technological solutions, is considered.

Modern approaches to the process of consolidation of structural blocks of coatings are analyzed. The use of load-lifting assembly modules is proposed to reduce the specific share of the use of heavy crane equipment at the construction site. The method of installation of a structural coating with the use of heavy crane equipment and load-lifting installation modules is compared.