THE TECHNOLOGY OF WINTER CONCRETING OF MONOLITHIC FRAME STRUCTURES WITH SUBSTANTIATION OF HEAT TREATMENT MODES BY SOLUTIONS OF THE DIFFERENTIAL EQUATION OF THERMAL CONDUCTIVITY OBTAINED BY THE METHOD OF GROUP ANALYSIS

An innovative method for calculating thermal fields inside monolithic structures has been developed, based on the use and analysis of nonlinear differential equations. The innovativeness of the method lies in the approach to the analysis of nonlinear physical processes using nonlinear differential equations. Thanks to the method of group analysis, 13 expressions are obtained from complex mathematical equations, which are easy to use and depend on several empirical coefficients. It is assumed that this calculation method is a priori more accurate than the existing ones, as well as available to people at a construction site without higher mathematical education, which makes it a priority for research. The applicability of this method must be proven by linking empirical coefficients and variables to the conditions of the experiments, while obtaining reliable data that will turn out to be more accurate than the existing calculation methods. This article demonstrates a systematic approach to establishing the suitability of using the method of group analysis of differential equations for problems of winter concreting on the basis of laboratory experiments under stationary conditions. The equations were subject to verification, which, according to the physical description, correspond to the real conditions of the course of thermal processes inside monolithic structures. Based on the obtained processing results, it was decided that it was necessary to further study the innovative method in the conditions of the construction site, but only for some expressions that showed the best results at the stage of laboratory tests.

A Fuzzy-Based Framework for Assessing Uncertainty in Drift Prediction Using Observed Currents and Winds

This paper proposes a fuzzy number—based framework for quantifying and propagating uncertainties through a model for the trajectories of objects drifting at the ocean surface. Various sources of uncertainty that should be considered are discussed. This model is used to explore the effect of parameterizing direct wind drag on the drifting object based on its geometry, and using measured winds to parameterize shear and rotational dynamics in the ocean surface currents along with wave-driven circulation and near-surface wind shear. Parameterizations are formulated in a deterministic manner that avoids the commonly required specification of empirical leeway coefficients. Observations of ocean currents and winds at Ocean Station Papa in the northeast Pacific are used to force the trajectory model in order to focus on uncertainties arising from physical processes, rather than uncertainties introduced by the use of atmospheric and hydrodynamic models. Computed trajectories are compared against observed trajectories from five different types of surface drifters, and optimal combinations of forcing parameterizations are identified for each type of drifter. The model performance is assessed using a novel skill metric that combines traditional assessment of trajectory accuracy with penalties for overestimation of uncertainty. Comparison to the more commonly used leeway method shows similar performance, without requiring the specification of empirical coefficients. When using optimal parameterizations, the model is shown to correctly identify the area in which drifters are expected to be found for the duration of a seven day simulation.

DEVELOPMENT OF METHOD TO ASSESS SEPARATION PROCESS TAKING INTO ACCOUNT RHEOLOGICAL PROPERTIES OF MINERAL SLURRY

This article considers the possibility of developing a methodology for assessing the separation process of gold-sulfide raw materials, taking into account the rheological characteristics of the mineral suspension. The object of the study is the ore of the Mayskoye deposit, which is subjected to fine crushing followed by cyanidation, so the consideration of rheological properties is the most important aspect of achieving the necessary enrichment performance. In the course of the research, using the object-oriented programming language Python 3.8, a program for calculating the empirical coefficients of the three-component rheological equation was developed. The resulting equation is the determinant for the shear stress within the suspension as a function of the velocity gradient. The developed program has been used to calculate coefficients of rheological equations for three variants of solid concentration in feed which correspond to the minimum, average and maximum for hydrocyclone used in the research (400 g/l, 500 g/l and 700 g/l respectively). Then, using the Ansys Fluent software, the multiphase classification modeling problem in the hydrocyclone was solved, resulting in shear rate profiles in the cross-section of the apparatus, from which the conditions necessary for the suspension to reach a fully dispersed state were concluded. It was determined that solid concentration 400 g/l is the optimum value that ensures maximum dispersion of the mineral slurry.

Mathematical model for assessing lateral stability of articulated tracked vehicles

The article considers the problem of increasing transport productivity, operational reliability and safety during cargo transportation by using articulated tracked vehicles and road trains with active trailers. The influence of the introduction of an electromechanical drive, the modernization of the propulsion unit and the steering control system on the lateral stability of an articulated tracked vehicle is analyzed. A mathematical model is described for calculating the lateral stability of the chassis of articulated tracked vehicles used in the regions of the Far North, Arctic and Antarctic. The model is based on developments carried out for the chassis of an articulated wheeled vehicle. The model allows calculating to determine the key geometric and kinematic parameters of the rotation, taking into account the action of external forces. The use of holonomic constraints in determining the critical speed of movement is determined by the physical picture of the beginning of overturning, which corresponds to the achievement of the critical folding angle of the sections. This approach makes it possible not to use empirical coefficients when assessing the instantaneous position of the center of gravity of the system, the center of rotation, the radius of rotation of the center of mass, and the critical speed of the chassis. The moment of the beginning of the rollover is determined by the disappearance of the normal reaction under the link caterpillar. The onset of lateral sliding is determined by the lateral force exceeding the lateral adhesion limit.

Analysis of Performance of Cavitation Models with Analytically Calculated Coefficients

Cavitation is often simulated using a mixture model, which considers the transport of an active scalar, namely the vapor fraction αv. Source and sink terms of the transport equation of αv, namely vaporization and condensation terms, rule the dynamics of the cavity and are described through different models. These models contain empirical coefficients generally calibrated through optimization processes. The purpose of this paper is to propose an analytical approach for the calculation of the coefficients, based on the time scales of vaporization and condensation processes. Four different models are compared considering as a test-case a two-dimensional flow around a cylinder. Some relevant quantities are analyzed both for standard value of coefficients, as found in the literature, and the coefficients calculated through the analytical approach. The study shows that the analytical computation of the coefficients of the model substantially improve the results, and the models considered give similar results, both in terms of cavitation regime and mean vapor fraction produced.

An Extended Entropic Model for Cohesive Sediment Flocculation in a Piecewise Varied Shear Environment

In this study, an extended model for describing the temporal evolution of a characteristic floc size of cohesive sediment particles when the flocculation system is subject to a piecewise varied turbulent shear rate was derived by the probability methods based on the Shannon entropy theory following Zhu (2018). This model only contained three important parameters: initial and steady-state values of floc size, and a parameter characterizing the maximum capacity for floc size increase (or decay), and it can be adopted to capture well a monotonic pattern in which floc size increases (or decays) with flocculation time. Comparison with 13 literature experimental data sets regarding floc size variation to a varied shear rate showed the validity of the entropic model with a high correlation coefficient and few errors. Furthermore, for the case of tapered shear flocculation, it was found that there was a power decay of the capacity parameter with the shear rate, which is similar to the dependence of the steady-state floc size on the shear rate. The entropic model was further parameterized by introducing these two empirical relations into it, and the finally obtained model was found to be more sensitive to two empirical coefficients that have been incorporated into the capacity parameter than those in the steady-state floc size. The proposed entropic model could have the potential, as an addition to existing flocculation models, to be coupled into present mature hydrodynamic models to model the cohesive sediment transport in estuarine and coastal regions.

Investigation of Operation of Coil-Flow Steam Generator of Serpentine Type in Conditions of Low Ambient Temperatures

Stationary and mobile steam generators are widely used in low ambient temperatures, for example in areas described by the Köppen world map as subarctic. Such equipment is often used in oil and gas fields. At the moment, the existing standard boiler plants are outdated. The purpose of this work is an experimental study of a coiled-type direct-flow steam generator developed by the authors in the winter period at low ambient temperatures. The tasks to be solved to achieve the goal are associated with obtaining experimental data at different operating modes of the installation, their processing and the development of empirical coefficients of gas movement inside the coaxial cylinders of the steam generator. In addition, another task is to develop a theoretical basis for the obtained experimental data. Based on the results of the work, the dependences of pressure and temperature on fuel consumption in various modes were obtained. Statistical analysis was applied to the data obtained. The authors have developed equations for calculating the convective part in the process of radiant-convective heat transfer in coaxial gas ducts, taking into account the design features of a once-through coil-type steam generator. Finally, promising directions for further improving the efficiency of steam generators of this type are proposed.

Вибір складу, параметрів робочого процесу і режиму роботи силової установки літального апарата з надзвуковою крейсерською швидкістю польоту

The issues of choosing a composition, operating process parameters and operating modes of propulsion for supersonic cruising aircraft providing transoceanic flights are considered. A condition of maximum payload relative mass is used as a criterion for choosing the composition of the propulsion. This criterion can be transformed using the aircraft mass balance equation into a condition of the minimum relative mass of fuel and propulsion. A predictor-corrector method is used to solve the task. Choosing the composition, operating process parameters and operating modes of propulsion according to the cruising segment, taking into account the remaining flight segments takeoff, climb and descent by the empirical coefficients, is used as a predictor stage. Based on the solving results of this stage, the best competing variants of propulsions are selected for the purpose of subsequent more detailed analysis at a corrector stage by numerically solving the differential equations of the aircraft motion along an entire flight profile. At the same time, on each elementary section of the path, the control parameters of the propulsion are optimized according to the criterion of the minimum required fuel consumption to overcome this section. Propulsion with turbojet engine, turbofan and mixed flows turbofan engine, turbo-ramjet engine and turbofan engines that have ramjet modes are considered. Patterns of the change in the relative mass of the fuel and propulsion for the indicated compositions of the propulsions according to cruising segment of the flight for the cruising speeds corresponding to the M = 1.5...4 are established. These dependencies make it possible to select variants of propulsion competing in terms of payload for a cruising speed or select the most advantageous cruising speed for propulsion composition which is given. These dependencies were used to determine competing variants of the power plant, providing a minimum of the relative mass of fuel and propulsion for the airplane with a cruising speed corresponding to the M = 3. At the stage of the corrector, these variants of the propulsion were evaluated according to the criterion of the relative mass of fuel and propulsion by solving the equations of the aircraft motion along the entire flight profile with the optimization of the control parameters of the propulsion on each elementary segment of the profile according to the criterion of minimum fuel consumption to overcome it. In doing so, the operating process parameters of the propulsion were optimized near of those values that were obtained at the stage of the predictor. The analysis of the obtained results indicates that, in comparison with the predictor stage at the corrector stage, the parameters of the propulsion operating process that are optimal from the point of view of the relative mass of fuel and propulsion changed by about 12.5 %, and the relative mass of fuel and propulsion by about 3...4 %.

Theoretical leakage equations towards liquid-phase flow in the straight-through labyrinth seal

Labyrinth seals are widely applied in turbomachinery for gas and liquid sealing. A series of labyrinth seal leakage equations so far have been proposed for compressible gas, but few equations for incompressible liquid. Based on the flow conserving governing equations, this paper originally presents semi-empirical analytic equations of the leakage flow rate and tooth-clearance pressure for liquid-phase flow in the straight-through labyrinth seal. The equations indicate that the leakage and pressure are closely related to the inlet pressure, outlet pressure, seal geometrical parameters and four empirical coefficients, whilst no relation to the temperature and compressibility effects compared to the common gas equations. The empirical coefficients include the velocity compensation coefficient, friction coefficient, jet contraction coefficient and resistance coefficient. Particularly, the velocity compensation coefficient is determined through an optimization by the genetic algorithm, while others are referred from previous research. Ultimately, taking the sealing of deeply subcooled liquid nitrogen within the spindle of the cryogenic cooling machine tool as a case, the accuracy of proposed equations is evaluated under various pressure ratios and geometry conditions using the numerical approach, whose numerical model has been validated by the experimental data in the literature. The results show that errors between calculation and simulation are generally within the limit of ±5%, except for the pressure values at the first two teeth. This work provides a theoretical basis for further studies on the liquid leakage equations in other labyrinth seal types.

RHEOLOGICAL BEHAVIOR OF POWDER-POLYMER MIXTURES AND MODEL DESCRIPTION OF FEEDSTOCK VISCOSITY FOR NUMERICAL SIMULATION OF INJECTION MOLDING PROCESS

The rheological behavior of the powder-polymer composition prepared for the application in the powder injection molding (PIM) technology has been studied. A review of models used to describe the rheological behavior of powder slips is presented. A viscosity study of MIM-4140 feedstock with a wax-polyolefin binder was carried out on a capillary rheometer with different capillary diameters. Empirical coefficients of viscosity models were determined. Verification of calculated viscosity values and experimental data for the studied feedstock is presented.