Showing papers by "Volga State University of Water Transport published in 2018"

Simulation of Patterned Glass Film Formation in the Evaporating Colloidal Liquid under IR Heating

Abstract: The paper theoretically studies the method of evaporative lithography in combination with external infrared heating. This method makes it possible to form solid microstructures of the required relief shape as a result of evaporation of the liquid film of the colloidal solution under the mask. The heated particles are sintered easier, so there are no cracks in the obtained structure, unlike the structure obtained employing the standard method of evaporative lithography. The paper puts forward a modification of the mathematical model which allows to describe not only heat and mass transfer at the initial stage of the process, but also the phase transition of colloidal solution into glass. Aqueous latex is taken as an example. The resulting final form of solid film is in good agreement with the experimental data of other authors.

Dynamics of acousto-convective drying of sunflower cake compared with drying by a traditional thermo-convective method

Abstract: The article is devoted to the dynamics of sunflower cake drying in a fundamentally new acousto-convective way. Unlike the traditional (thermo-convective) method, the method proposed allows extracting moisture from porous materials without supplying heat to the sample. Thermo-vacuum drying helped to determine the absolute and relative initial moisture for the analysed samples of the sunflower cake, which equaled 313.1% and 75.8%, respectively. The kinetic curves for drying by thermo- and acousto-convective methods were obtained and analysed. A study of the acousto-convective drying of sunflower cake showed that the rate of moisture extraction depended on the resonating frequency, while there is an optimal mode in which drying proceeds from two to three times more intensively. In thermo-convective drying of sunflower cake, increasing the temperature of the drying stream twice (from 74.2°C to 127°C) reduces the duration of drying to a final absolute humidity of 40% three times. Comparing the thermo-convective and acousto-convective drying methods showed that twice as much moisture was removed from the samples dried by the (ACDP) with a flow frequency of 790 Hz and at room temperature for a 30-minute interval as with thermal convective drying with a working flow temperature of 127°C. The relaxation mathematical model used to describe the drying phenomenon and the experimental data for sunflower cake drying allows obtaining the quantitative parameters characterizing different modes and methods of drying the samples under study. The article analyses a discrete drying regime that contributes to increasing the efficiency of the acousto-convective mode of moisture extraction.

Synchronization Thresholds in an Ensemble of Kuramoto Phase Oscillators with Randomly Blinking Couplings

Abstract: We consider a network of Kuramoto phase oscillators with randomly blinking couplings. Applicability of the averaging method for small switching intervals is rigorously substantiated. Using this method, we analytically estimate the threshold coupling force for synchronizing the ensemble oscillators. The threshold synchronization is studied as a function of the switching interval for various network sizes. The effect of preserving synchronization for a significant increase in the switching interval is found, which is the key feature of the system since a slight increase in this interval usually leads to the synchronization failure. The intermittent-synchronization possibility for small network sizes and large switching intervals is shown. An increase in the network size is shown to result in a stability increase due to the decreasing probability of appearance of uncoupled configurations. The regions corresponding to the global synchronization of oscillators are singled out in the system-parameter space.

Mathematical model of the vessel with wheeled propulsion-steering complex "golden ring"

Abstract: A mathematical model of a large cruise ship "Golden ring" under construction (PKS-180 project) with a wheeled propulsion and steering complex equipped with azimuth thruster has been developed. Ships with such a set of propellers (two propellers in the stern and an azimuthal thruster) have never been built before. The model is based on the basic equations of mechanics. While creating the model there were used the calculated data and data from the design documentation of the company "Gama" (Nizhny Novgorod) obtained from the tests in the experimental pool. There was derived the formula for total thrust force of the propeller wheels with split slabs with displacement, for resistance of the hull depending on the speed of the vessel, for the traction characteristics of the water-bearing azimuth thruster. Due to the design features of the vessel (low draft, flat bottom, large sail), much attention is paid to the consideration of wind impact on its dynamic characteristics. There were also obtained expressions for the longitudinal and transverse forces of the wind impact on the hull and their torques, as well as for calculating the direction and strength of the "apparent" wind. As a result, a system of ten differential equations describing the vessel with wheeled propulsion and steering complex "Golden ring" has been produced, in which two propeller wheels and an azimuthal thruster are used as propulsion unit, taking into consideration the wind load. The paper also presents the results of checking the adequacy of the given mathematical model of the vessel with wheeled propulsion and steering complex, results of analysis of the vessel acceleration characteristics at different speeds of propeller wheels rotation, as well as dynamic characteristics of the vessel during the circulation. The data calculated with the mathematical model coincide with the design data.

Quality of Rolled Steel for Cold Bulk Stamping

Abstract: Metal products obtained from rolled blanks by cold upsetting are used in every branch of manufacturing. The quality of such components is assessed in terms of the required chemical composition and the plasticity, the consistency of the mechanical characteristics over the whole length, and the lack of internal and surface defects. If such metal components are to be competitive, all the steps in the production chain must be optimized: from smelting of the steel to cold upsetting of the product. In attempting to minimize costs and ensure the required quality, it is important to ensure safety and to decrease energy and labor costs in manufacturing. In this chain, the preparation of the material for cold bulk stamping is a key step. The high-strength fasteners obtained by cold upsetting are most often made of chrome steel. Recently, alternative boron-bearing steels have been actively introduced. However, their thermal hardening in quenching is unstable because boron oxides and nitrides may be formed, with decrease in their hardenability. In addition, chrome steels are 12–16% cheaper, as a rule. Also, since foreign supplies of boron steels are associated with additional costs, fasteners made of boron steels are even more expensive. That is a further impetus to using chrome steels. In the present work, we obtain standard mechanical characteristics and failure criteria for 40Kh steel components patented in a saltpeter bath at different temperatures, with subsequent drawing. The optimal preparation of the rolled steel in terms of its structural and mechanical characteristics after cold bulk stamping is determined: patenting (in a saltpeter bath at 400°C) and drawing (with 5–10% reduction). Such treatment yields products of the required quality and is preferable to the existing technology.

Electrodynamic Characteristics of Dipole Antennas Made of Graphene-Containing Carbon Fiber Composite Materials

Abstract: The electrodynamic characteristics of dipole antennas made of carbon fiber composites with a graphene-containing binder have been investigated at 200 and 600 MHz. It is shown that main characteristics of antennas, including the standing wave ratio, radiation pattern, and gain factor, coincide with characteristics of their metal analogs. The effect of conductive properties of the metal–carbon fiber composite contact in the dipole radiating elements on the parameters of the antennas is estimated.

State Equations of Unsteady Creep under Complex Loading

Abstract: A mathematical model describing the unsteady creep of metals under complex loading is proposed. The results of numerical simulation of creep of St.304 steel in complex regimes of block multiaxial cyclic deformation are given. The numerical calculation results obtained are compared with the data of full-scale experiments. Creep is simulated in complex deformation processes accompanied by the rotation of main regions of stress, strain, and creep strain tensors.

Characteristics of heat transfer in fire tube of marine gas turbine engine in starting mode

Abstract: The paper presents the results of experimental studies of heat transfer in a cylindrical tube, which is a simulation model of a fire tube. The experiments were performed on a gas-dynamic pipe of open type. The starting mode during operation of the gas turbine engine is one of the main modes in which failures sometimes occur. The failure may occur due to external heat transfer mode, when the thermal parameters of the gas flow exceed the calculated values and there takes place intense local heating of the streamlined surface of the structural element(s) of the engine. Experimental studies were carried out at different intensity of the increasing temperature of the working fluid, which allowed to fix the phenomenon of laminarization of the thermal turbulent boundary layer at the heat flow directed from the gas flow to the channel wall. In the event of laminarization phenomenon, the values of local heat transfer coefficients are reduced by 2.5-3 times. Since the discovery of this phenomenon, it has also been observed in various situations of accelerating the gas flow and even at high degrees of heating of the cylindrical pipe wall under stationary flow conditions. This phenomenon has been recorded for the first time in the non-stationary mode and the specified direction of the heat flow. The temperature head or temperature factor is proposed as a laminarization parameter of a turbulent boundary layer, and the boundary of the laminarization area of a turbulent boundary layer is Δ T ≥ 700 K.