Stressstrain state of metal at the initial stage of railway rails rolling

Based on the studies of stress­strain metal formation during railway rails rolling in roughing stands of a universal rail­and­beam mill, carried out using the DEFORM­3D software package, the authors have determined the features of distribution of the Cockcroft­Latham criterion over the cross­section of the rolled stock of various shapes. An extremely uneven distribution of the Cockcroft­Latham criterion over the roll section has been established. According to the data obtained, values of the specifed criterion are minimal in the axial zone, and in the near­surface layers the greatest value of the Cockcroft­Latham criterion and, accordingly, the highest probability of defects formation occur near the gauge vertical axis. In gauges of complex shape (“trapezium”, “recumbent trapezium”, rail gauges), the authors have revealed the presence of local zones with maximum Cockcroft­Latham criterion, located in the places where the foot of the rail profle is formed. And rolling in gauge of the “trapezium” type is marked by the presence of such a zone in the near­surface area near the gauge vertical axis. Within the framework of determining formation regularities of the diagram of metal stress­strain state at the initial stage of rail rolling, direct relationship was established between the uneven temperature distribution over the section of rolling and the values (maximum and average over the section) of the Cockcroft­Latham criterion. At the same time, it was shown that uneven temperature distribution over the cross­section of the roll tends to decrease with an increase in the coefcients of extracts along the passes and increase in tilting frequency, regardless of the shape of the used gauges. For gauges of complex shape, in addition to the listed parameters, an increase in similarity of shape of the roll and gauge used also has a signifcant effect on reducing temperature inhomogeneity. Based on the results of theoretical studies, a new mode of railway rails rolling has been developed. Its pilot testing in the conditions of a universal rail­and­beam mill of JSC “EVRAZ ZSMK” has shown a decrease in rail rejection by 0.78 % compared to the previously used rolling mode.

Surface waves on the inhomogeneous interface between radiative electron–ion plasma and vacuum

The impact of temperature inhomogeneity, surface charge and surface mass densities on the stability analysis of charged surface waves at the interface between dense, incompressible, radiative, self-gravitating magnetized electron–ion plasma and vacuum is investigated. For such an incompressible plasma system, the temperature inhomogeneity is governed by an energy balance equation. Adopting the one-fluid magnetohydrodynamic (MHD) approximation, a general dispersion relation is obtained for capillary surface waves, which takes into account gravitational, radiative and magnetic field effects. The dispersion relation is analysed to obtain the conditions under which the plasma–vacuum interface may become unstable. In the absence of electromagnetic (EM) pressure, astrophysical objects undergo gravitational collapse through Jeans surface oscillations in contrast to the usual central contraction of massive objects due to enhanced gravity. EM radiation does not affect the dispersion relation much, but actually tends to stabilize the Jeans surface instability. In certain particular cases, pure gravitational radiation may propagate on the plasma vacuum interface. The growth rate of radiative dissipative instability is obtained in terms of the wavevector. Our theoretical model of the Jeans surface instability is applicable in astrophysical environments and also in laboratory plasmas.

The effect of alternating ventilation on forced air pre-cooling of cherries

Large temperature gradients caused by the traditional forced air pre-cooling method leads to the decrease of the shelf life of horticultural products. An alternating ventilation of air pre-cooling is one of the key methods to reduce the temperature inhomogeneity of cherries. The research results on the alternating ventilation change showed that the operating time of fan was not neglected in the forced air pre-cooling. It reached up to 7.70% of total pre-cooling time when the number of ventilation changes no more than five. In general, the total pre-cooling time was proportional to the number of ventilation increase. The final inhomogeneity of cherries first quickly decreased from 0.237 to 0.097 with air direction changing once and then fluctuated from 0.09 to 0.120 with the number of ventilation changing from 1 to 5. Through the comprehensive analysis of temperature inhomogeneity and pre-cooling time, the optimal alternating ventilation on forced air pre-cooling of cherries was ventilation changing once.

Influence of vertical heterogeneity of the atmosphere temperature on the propagation of acoustic-gravity waves

A new approach to the study of acoustic-gravity waves (AGW) in the Earth’s atmosphere in the presence of a vertical temperature inhomogeneity is proposed. Using this approach, the local AGW dispersion equation is obtained for an atmosphere with a small vertical temperature gradient. The modification of acoustic and gravitational regions of freely propagating AGWs on the spectral plane is studied depending on the temperature gradient. It is shown that, the acoustic and gravitational regions approach each other with a positive temperature gradient and the distance between them increases with a negative gradient. On the spectral plane, the dispersion curves of non-divergent and anelastic horizontal wave modes are the indicators of location of the acoustic and the gravitational regions of freely propagating AGWs. The possibility of overlapping the acoustic and the gravitational regions of AGWs in non-isothermal atmosphere is investigated.

Gravitating–radiative magnetohydrodynamic surface waves

Radiative-magnetohydrodynamic (RMHD) equations along with a full set of Maxwell's equations are followed to formulate the charged surface waves at the interface of an incompressible, radiative, magnetized dusty plasma and vacuum, while assuming that the characteristic wave frequency is much smaller than the ion gyrofrequency, having an equilibrium background state. It is found that the separation of charges on the surface is followed by thermal motion, which further leads to a negative pressure gradient normal to the surface, hence the plasma–vacuum interface is under tension due to two different types of oppositely directed pressures. The dusty plasma RMHD set of equations admits a linear dispersion relation of surface Jeans instability of an incompressible dusty plasma, which exhibits a strong coupling between the electron surface charge and dust surface mass densities and we conclude that the surface densities of both electrons and dust as well as the dust inertia play major roles in the gravitational collapse of the surface of astrophysical objects such as stars, galaxies etc. Further, the growth rate of radiative surface waves is found to be function of both the temperature inhomogeneity, appearing due to thermal radiation heat flux, as well as the thermal radiation pressure. The present findings of charged surface waves may seek application at the astroscales.

Influence upon temperature field distribution with straight grooves parameters of clutch friction disk

The instability of the temperature field distribution in clutch friction pair tends to increase exponentially with time when the relative velocity is greater than a certain critical value, which indicates the system enters a state of thermoelastic instability. During high-speed frictional sliding at a high temperature and high pressure, thermoelastic instability will generate local high temperature on friction pair and then cause high-frequency vibration, warping, fatigue fracture, and so on. With the aim of studying the problems arising from local hot spots and the mechanism behind the characteristics of temperature field in friction pair, a thermoelastic finite element analysis model was established for friction pair of heavy-duty vehicle clutch in this paper. The characteristics of thermoelastic stress and temperature distribution under different conditions were obtained by simulation analysis where different values were applied to groove distribution parameters such as number, angle, depth, and width. Experiments were carried out on a friction pair to test its thermoelastic instability. Results show that as the value of each groove distribution parameter increases, the fitting curves of the average temperature, range, and the temperature inhomogeneity coefficient of the temperature field are in forms of oscillation. The average temperature and range have the same trends. The paper concludes that the average temperature range and inhomogeneity coefficient of the temperature field distribute in order, so that the optimized structural parameters were obtained.