Modeling of the dynamic characteristics of two‐bolt‐joints

Abstract

In this paper, a method to identify the damping and stiffness properties of bolted joints from a substructure synthesis scheme is presented. The easily measured frequency response functions of substructures and the assembled structure are the only data needed in this method. A synthesis formula used to predict the frequency response functions of two‐bolt‐joint structures is proposed. The formula makes use of the extracted properties of a single‐bolt‐joint. Some experiments with two free‐free steel beams jointed with one or two bolts are made to check this method. The close correlation between predicted and measured results demonstrates that this method is acceptable.     

Process of Cooling of a High‐Temperature Two‐Phase Flow

A technique and a design of a transducer for measuring the enthalpy of twophase flows using the thinwall method have been developed. Working formulas for calculating the heat capacity and the enthalpy of a gas flow are substantiated. Results of a test of the transducer in hightemperature flows of powder gases, including those after the packing of a coolant, are presented. The results obtained show that cooling of powder gases due to an endothermic reaction makes it possible to decrease the enthalpy flux by a factor of 5 and the temperature by a factor of 2.     

Application of variable‐structure system in dc‐motor velocity‐control

Abstract

The most important characteristic of variable‐structure system (VSS) is its insensitivity to parameter variations in the sliding mode. In this paper three methods of VSS are used to implement DC‐motor velocity‐control. The conventional VSS uses only a sliding line. The adaptive VSS uses multiple switching lines. The modern method uses a sliding curve. The modern method makes a system trajectory following the sliding curve which has been set up in the controller from the initial state to the origin in the phase plane. Hence it is insensitive to parameter variations from the initial state to the steady state. If parameter variations are the most critical factors, then the modern VSS is the right method to be considered to overcome the problem of parameter variations.     

Investigation of Thermal Processes in Gas‐Thermal Spraying of Metal‐Ceramic Coatings

The features of the thermal regime of gasthermal deposition of metalceramic coatings have been studied. The procedure of calculation of the temperature field of a multicomponent coating throughout the process of formation has been developed. The quantitative dependences of the character of heating of the deposited particles and melting of the substrate on the thermophysical properties and chemical composition of the material, the intensity of heat exchange, and the technological parameters of the process have been established. The thermal conditions of spraying of powder compositions, which ensure improved strength characteristics of the coating–substrate system, have been determined.     

Quasi‐Self‐Similar Description of an Exhaust Jet

The method of construction of an analytical solution for the far field of an exhaust jet on the basis of the quasiselfsimilar solution of Prandtl equations and the turbulence model with one differential equation for the coefficient of kinematic viscosity is described. An exact numerical solution for distances to about 10¹ radii of the nozzle is constructed for the basic version. Then, a numerical solution and its analytical approximation by the quasiselfsimilar solution are constructed. Approximations of the similarity parameters of the selfsimilar problem as functions of the similarity parameters of the initial problem in the form of polynomials allow construction of analytical solutions for different situations, which are in satisfactory agreement with the exact numerical solution at distances of radii.     

Calculations of the Passage of Gamma‐Quanta through a Polymer Radiation‐Protective Composite

We have investigated the radiationprotective characteristics of a thermoplastic polystyrene composite material filled with a highdispersion modified lead oxide as well as the dependences of the energy (flux) buildup and transmission factors and albedos on the energy and protectiveshield thickness. Calculations of the integral characteristics of the radiationprotective properties of materials have been done.     

Strength development of blended blast‐furnace slag‐cement mortars

Abstract

Blast‐furnace slags cooled at different rates were used to study the effect of fineness, mixing method and content of slag on the strength development of blended‐slag mortar. Activator and curing temperature were used to activate the early strength. The microstructure of blended‐slag paste was also investigated in this study to explain the strengthen effect.     

A proof of stability of all‐pass PADé approximants TO e‐s

Abstract

This paper presents an explicit derivation of the all‐pass Routh approximants to e^‐s. It then shows that the stable all‐pass Routh approximants to e^‐s are exactly the same as the all‐pass Padé approximants. As a result, the derivation provides an alternative way of proving that the all‐pass Padé approximants to e^‐s are always asymptotically stable.     

Calculation of Chamber‐Type Pulsers

The computational relations and experimental data for deflection of rubber membranes in chambertype pulsers for the cases of independent and combined deformation of the membranes with account for initial residual deformation are presented. The results of the calculations and experiments are in satisfactory agreement.     

Hydrodynamics of Rotory‐Pulsatory Apparatuses

A kinematic and dynamic analysis of flows in a rotorypulsatory apparatus has been carried out. Based on this analysis, a method for calculating the main parameters of the apparatus with the use of minimum initial experimental information (the head at zero transit flow rate H ₀ and the flow rate at zero head Q ₀) has been developed.     

Maximum‐likelihood localization of closely‐spaced sources by MLSUM algorithm

Abstract

In this paper, we present a new scheme called the maximum log‐likelihood sum (MLSUM) algorithm to simultaneously determine the number of closely‐spaced sources and their locations by uniform linear sensor arrays. Based on the principle of the maximum likelihood (ML) estimator and a newly proposed orthogonal‐projection decomposition technique, the multivariate log‐likelihood maximization problem is transformed into a multistage one‐dimensional log‐likelihood‐sum maximization problem. The global‐optimum solution of the approximated ML localization is obtained by simply maximizing the single one‐dimensional log‐likelihood function. This algorithm is applicable to coherent sources as well as incoherent sources. The computer simulations show that the MLSUM algorithm is much superior to the MUSIC when the element SNR is low and/or the number of snapshots is small.     

High‐Temperature Radiative‐Convective Heat Exchange on the Surface of Glass‐Reinforced Plastics

The results of experimental investigations of heat exchange on the surface of a thermalprotective material — glassreinforced plastic — in the flows of hightemperature gases have been presented. It has been established that the influence of injection on the value of the heat flux does not exceed 10% in the range of variation of gas temperatures 300–2000 K and Reynolds numbers 350–9800.     

Influence of the Atomic Mass of a Plasma‐Forming Target on the Parameters of Laser‐Emission Discharge

A study has been made of the influence of the atomic mass of the material of a plasmaforming target on the characteristics of a laseremission discharge developing under the action of Ndlaser radiation on the target. It has been shown that the atomic mass substantially affects the efficiency of conversion of the energy of laser radiation to the energy of a quasistationary electric current; the behavior of the dependences of the load power on the atomic mass of the target substance is different for high vacuum and for resonance pressure and it is not related to the regime of development of the discharge.     

Mathematical Model of Vacuum‐Oscillating Drying of Lumber

A mathematical model of heat and mass transfer in vacuumoscillating drying of lumber in which the drying process is made up of alternating stages of warming up and vacuum treatment has been developed. At the stage of warming up, it has been proposed to use a superheated steam to intensify heat and masstransfer processes and to relax stresses occurring at the stage of vacuum treatment.     

Two‐Dimensional Calculation of the Parameters of a Steam‐Air Mixture in a Film‐Type Heat and Mass Exchanger

A mathematical model for twodimensional calculation of the temperature and density of the steam in a steamair mixture which rises between two water films flowing down adiabatic shields has been proposed. The parameters of the films have been calculated in a onedimensional approximation. The results of calculating the parameters of air according to the onedimensional and twodimensional models of the processes of heat and mass transfer have been compared. The range of applicability of the former to a filmtype heat and mass exchanger has been determined.     

A Model of Prediction of Forest‐Fire Hazard

A rather simple and physically substantiated deterministicprobabilistic expert system of prediction of forestfire hazard, which can be used in practice, is suggested. Results of the calculation by the verified model of drying of forest combustibles, which allows for partial pressure of water vapor, are compared with results obtained by different models and experimental data.     

Improvement of the Accuracy of the Large‐Particle Method in Calculation of Motions of Energy‐Saturated Media on Superposed Grids

A TVDmodification of the largeparticle method with the algorithm of calculation on superposed grids with a set of cells differing in shape is presented.     

Generalized Equations of One‐Dimensional Filtration with Fractional‐Power Differentiations

Based on the formalism of fractionalpower integrodifferentiation, the theory of filtration in porous media with fractal structure is generalized. Consideration is given to the cases of steady and unsteady filtration. For the steady filtration, nonlinear solutions are shown to exist. In the unsteady case, a new class of periodic solutions may exist.     

Reduced‐order modelling of linear discrete‐time systems using cauer third continued‐fraction method

Abstract

In this paper a generalization of the Cauer third continued‐fraction expansion (CFE) is introduced for the reduced‐order modelling of linear time‐invariant discrete‐time systems. First, a new algorithm is presented for obtaining the Cauer third continued‐fraction expansion about z=1 and z=8 of the z‐transfer function of a discrete‐time system from its time‐moments and Markov parameters. Next, a realization of the Cauer third continued‐fraction expansion about z=1 and z=8, and the corresponding CFE canonical state‐space model are derived. Finally, an approximate aggregation matrix is constructed for relating the state‐vector of the reduced‐order CFE canonical state‐space model to that of the original system. An example is included to illustrate the use of the method.     

High‐Temperature Deposition of Carbon Films

A mathematical model of growth of a carbon film in hightemperature deposition has been constructed in the approximation of the Stefan problem. The influence of different factors on the maximum thickness of the film has been analyzed. It has been shown that the porosity of the film is a factor of fundamental importance which determines the dynamics of its growth in terms of the effective thermal conductivity.