Investigation of the stress state of the metal frame of a ribbed-ring dome, when the number of supporting columns under it is gradually reduced. With that, the same distances or steps between the ...columns are maintained along the entire contour of the support ring. The main elements of the dome frame and columns are made of steel I-beams. Frames, the domes of which are supported by a different number of cyclically symmetrical columns, were considered as subjects of research. All the domes are characterized by the same geometric structure and size, the same cross sections of the same type of frame elements and are exposed to the same loads. The research was carried out on computer models by calculating the combined effect of the load from the weight of load-bearing and enclosing structures and an asymmetric snow load. The models with a reduced number of columns are obtained by regularly removing them from the original computer model. During the analysis, the stresses in the elements of the frames of all models were determined, which were compared with each other. Deformation graphs and comparative diagrams of the stress state relationships of the frame elements of the original and transformed models are obtained. An assessment of the change in the stress state of the ribbed-ring dome frame with a decrease in the number of columns is given. Significant changes in the stress state of the support ring were noted.
Studies of several metal ribbed-ring large-span domes on computer models have been carried out. All elements of the dome frames are made of steel I-beams. The dome frames have the same number of ribs ...and rings, but they have different size of the upper ring. The frame elements cross-sections are oriented normally to the dome surfaces, with the exception of the upper ring. The joints of the frame elements with each other are assumed to be rigid in the normal direction and hinged in the tangential direction. The frames are mounted on support nodes at the level of the lower ring pivotally. All the domes are subjected to the same nodal loads from the weight of the enclosing structures and the weight of snow. The snow load is assumed to be asymmetrical, located only on one side of the dome. Under the combined action of these loads, the dimensions of the upper ring of the domes influence the stress-strain state of their frames. As a result of the research, graphs have been generated representing the stress level in the meridional ribs and in the upper rings of the domes. The conclusion has been made that the stress state of metal dome frames depends on the size of the upper ring. The necessity of increasing the cross-section of the upper ring with an increase in its size has been noted.
The aim of current research was to establish the relationship between the stress state of the ribbed-ring dome framework and the degree of its bracing. It was assumed that the meridional ribs and ...rings of the dome framework are made of metal. The framework of the dome consists of 24 ribs and 7 rings. The study was performed for a ribbed-ring dome of spherical shape with a span of 39.3 m and a height of 11.0 m on computer models. The initial computer model of the framework of a ribbed-ring dome made of steel I-beams without bracing has been developed. On the basis of the initial model, additional models were developed for the frameworks with bracing between meridional edges in four, eight cyclically symmetric sectors and in all sectors. Both for the initial model and for all models of the dome framework with bracing, computer calculations were performed for the effect of the load from the own weight of the load-bearing and enclosing structures, and two variants of the snow load. During the calculations, deformations, internal forces and stresses in the meridional ribs, upper and intermediate rings of different models were determined, which were compared with each other. Graphs of changes in deformations of the frame, graphs and diagrams of changes in internal forces and stresses in the meridional ribs, in the upper and intermediate rings of the dome, depending on the degree of bracing in the framework, are obtained. An assessment of the influence of bracing on the stress state of the rib-ring dome frame is performed. The peculiarities of the influence of different coupling schemes on the stressed state of the dome frame are noted.
We analyze the effect of application of pulverized coal fuel (PCF) and natural gas on the parameters of blast-furnace smelting by an example of operation of blast furnaces in Ukraine (for the best ...periods of their operation). It is shown that the rational technology of blast furnace smelting performed with the use of PCF enables one to increase the productivity of blast furnaces, reduce the consumption of coke and conventional fuel, decrease the cost of power resources, preserve the ecological characteristics, decrease the consumption of the resources, improve the ecology. At the same time, this leads to an increase in the net amount of fuel required for the blast-furnace process and to a decrease in the yield of secondary energy resources to the consumers. The simultaneous injection of natural gas with PCF increases the lifetime of the furnace, decreases the heat losses, and increases the gas permeability of the charge.
Data analysis has been performed concerning the limiting values of heat losses in the cooling system and consumption of coke to compensate for them in the blast furnaces, depending on their volume, ...technical condition, and smelting technology. It was shown that the consumption of coke to compensate for heat losses may vary from 10 to 55 kg of coke or more per ton of cast iron.
Specific features of the localization of coumarin and xanthene dye molecules in ionic surfactant micelles of sodium n-dodecyl sulphate and cetyltrimethylammonium bromide have been studied by ...molecular dynamics simulation. It is shown that the change in the microenvironment of a dye molecule in a micelle after its protonation (deprotonation) depends on both the nature of such a dye and the sign of the micelle charge. It was established that the presence of a long hydrocarbon chain in a dye molecule does not prevent its movement during (de)protonation.
The aim of the research - analysis of the stress-strain state of spherical lattice dome structure during mounted assembly process. The dome has a metal frame consisting of six repeating sectors with ...triangular grid cells. The mesh dome has five tiers in height. The study is devoted to establishing the dependence of the stress-strain state of the fully assembled frame of the lattice dome on the method mounted assembly. Methods. A computer model of the frame of the lattice dome made of steel I-beams in its design configuration has been developed. On its basis, assembly models of an incomplete frame for different stages of installation are created. For all models of the lattice dome frame, computer calculations were performed for the effect of the load from the own weight of its bars. As a result of calculations deformations, internal forces and stresses in the frame bars were determined at all stages of assembly, which were compared with those for the design configuration scheme. Results. Diagrams of deformations, moments and stresses in the bars of the dome frame at all stages of mounted installation are obtained. Comparative diagrams of installation and design stresses in the bars of the lattice dome are presented. The assessment of the installation stress state of the frame is given, and their inevitability and influence on the initial stress state of the lattice dome are noted.
In Russia, boiler units at many coal-fired thermal power plants (TPPs) are being converted to operation on off-design fuel due to the introduction of more and more strict environmental regulations, ...changes in the economic situation, and also due to a decrease in design coal reserves. During the service life of the Artemovsk combined heat and power plant (TETs), the design coal deposit was exhausted. Therefore, a replacement solid fuel for BKZ-220-100F boiler units had to be found. Since conversion to off-design coals may induce negative factors, such as a decrease in the reliability of the heating surfaces and maintenance of the required superheated steam conditions, a variant analysis, including that on the basis of numerical simulation, of the processes occurring during coal burning in a combustion chamber (furnace) enjoys current interests. The objective of this study is to analyze the effect of furnace processes on operating reliability, efficiency, and environmental safety of a boiler unit when burning off-design coals. Numerical analysis was carried out using the ANSYS Fluent software package, and mathematical modeling of furnace processes was based on the Euler-Lagrange approach. The results of simulation are compared with check and zone-by-zone calculations of the furnace chamber. In the horizontal section, at the level of the burners, high-temperature zones are singled out in the near-wall region at the corners of the furnace chamber, which are formed by the waterwalls on the left side and front walls as well as the waterwalls on the right side and rear walls.
1
The numerical simulation has revealed that the tangential arrangement of the burners induces a vertical vortex in the furnace chamber; however, the direction angles of the burner jets should be corrected. Combustion of El’ginsk coal considerably changes the furnace temperature conditions, thereby increasing the risk of heating surfaces slagging.
The aim of the research. To analyze the stress state of structures of ribbed-ring domes of different heights during overhang erection. The domes have spherical metal frames and a support contour of ...the same diameter. Due to different heights, the steepness of the geometric shape of the domes changes. The study is devoted to establishing the relationship between the stress state of the frame and the steepness of the dome when mounted. It was investigated how the height of the ribbed-ring dome affects the stress state of its frame during overhang mounting process. Methods. Computer models of design frames of ribbed-ring domes of different heights made of steel I-beams were developed. Based on design models, a sequence of assembly models for incomplete frames was created for different stages of installation. Both for the design and for all installation models of dome frames of different heights, computer calculations were performed for the effect of the load from its own weight. As a result of calculations for all domes and at all stages of installation, deformations and stresses in the meridional ribs were determined, which were compared with the design diagrams. Results. Comparative graphs of deformations of dome frames and diagrams of changes in the degree of use of steel strength in meridional ribs at all stages of mounted installation are obtained. Comparative graphs of installation and design stresses in the meridional ribs on different tiers for all stages of mounted installation are also shown. The assessment of the installation stress states is given, their inevitability and the degree of influence on the stress state of the dome frames are noted.
Some characteristic features of three scenarios for the occurrence and development of turbulence are presented: the Landau–Hopf scenario, the scenario of transition to turbulence on a strange ...attractor, and the scenario followed by the solutions of the multimoment hydrodynamics equations. The analysis of the presented characteristic features allows us to draw a conclusion about the possibility of using these scenarios for the interpretation of turbulence. It is shown that only one of the scenarios satisfactorily interprets the experimental data: the scenario followed by the solutions of the multimoment hydrodynamics equations supplemented with stochastic components. The Landau–Hopf scenario leads to a system that has lost stability in the wrong direction. The scenario of the transition to turbulence on a strange attractor correctly reproduces only the initial stage of the evolution of the liquid layer in the Bénard experiment, namely, heat transfer in the resting layer and convective rolls. Analysis of the behavior of solutions of the Lorentz model leaves no hope for the ability of this scenario to interpret turbulence.
PDF
