Doklady Physics最新文献

A numerical simulation of a turbulent boundary layer on a permeable plate with helium injection into a supersonic xenon flow in the presence of a positive longitudinal pressure gradient has been carried out. The injection regimes in which the temperature of the injected gas is lower than the temperature of the adiabatic impermeable wall and the stagnation temperature of the oncoming flow are considered. The existence of a minimum temperature of the permeable wall is confirmed, at which the wall temperature is lower than the temperature of the injected gas, while there are two sections along the length of the permeable plate in which the adiabatic conditions are satisfied. The results of calculations of a supersonic flow with a longitudinal pressure gradient differ significantly from the results obtained for a gradientless flow around a plate, for both subcritical and critical injection.

Experiments on the propagation of powerful high-voltage pulses with a duration on the order of a nanosecond or less in large-scale transmission lines in an atmosphere of various gases make it possible to solve a wide range of fundamental and applied problems, from modeling the passage of electromagnetic pulses (EMPs) through the atmosphere to estimating the electrical strength of elements of pulsed high-voltage gas-filled systems. At the Institute of Applied Physics, Russian Academy of Sciences, experiments with strip lines with a length of up to 5 m were conducted using the Krot and Sprait setups. When EMP propagates with an electric field strength level of up to 100 kV/m in a rarefied gas, effects such as the formation of inhomogeneous and significantly nonstationary glow structures, nonlinear absorption, and dispersive transformation of the shape of high-power pulses caused by gas ionization in the EMP field are studied.

An approach to the development of a dynamic model of one of the key stages of the flight of rocket and space systems is presented: the separation of large-sized structures. The importance of taking into account the elastic properties of separated objects is justified. Based on the assumptions typical of the process under study (small angular velocities of relative motion during separation compared to the lower frequencies of the separated objects), the partial differential equations of elastic vibrations are replaced with a system of ordinary differential equations describing the excitation of a limited number of lower order modes, which made it possible to formulate an efficient approach that allows a clear mechanical interpretation: the general motion during separation is decomposed into a transport motion (rotational and translational as a whole) and small elastic relative vibrations, described in a universal modal formulation. The process of separation of an aerospace aircraft and a launch vehicle is analyzed. The effect of loss of the relative separation velocity due to elastic vibrations is revealed, and a recommendation for the rational arrangement of separation tools is formulated.

This study is devoted to generalization of the traditional approach for the description of photon scattering on free electrons in the case of ultrashort laser pulses. In the framework of the second order of quantum mechanical perturbation theory with the use of the Klein–Nishina formula, we derived an expression for the total scattering probability during the whole time of the pulse action that is applicable in the relativistic limit. The redshift of scattered pulse spectra under an increase in the scattering angle in the relativistic case was studied. The trends of the total scattering probability on the duration of ultrashort laser pulses were categorized.

A method for generating solutions of the Burgers equation, which describe the interaction of waves in a nonlinear dissipative medium with a linearly growing wavefront, is proposed. The exact solutions describing these interactions and symmetry properties of the equation are used. It is shown that the rising wavefront is able to compete with the dissipation and compress the signal in time. On the contrary, the wavefront with the decreasing steepness “stretches” the signal.

The damping characteristics of hybrid composites reinforced with spherical and fibrous elastic inclusions with viscoelastic coatings are studied. It is shown that, in the composites with the particle morphology, a significant increase in the dissipation loss can be implemented and the effective loss of a composite can exceed the dissipation loss of viscoelastic coatings by a factor of more than 20. Analytical estimates of the optimum parameters of hybrid composites are proposed. The effect of possible imperfections of the composite structure on the effective dissipation properties of the composites is analyzed.

Active synchronized antenna arrays generating ultra-wideband radiation with an electric field strength of about 1 V/m at a distance of several hundred kilometers have been studied. They are designed to study the passage of ultra-wideband signals in the surface layer of the atmosphere and through the ionosphere. Synchronous antenna arrays with four and nine radiating modules have been created. Their radiation has a symmetrical radiation pattern along the x and y axes with a pulse duration at half-height of about 100 ps. They have a pulse energy potential (E × R) of about 60 and 150 kV, with a gross weight of 50 and 100 kg, respectively. Such characteristics allow these arrays to be placed on air carriers. The option of using air balloons under irradiation in the surface layer of the atmosphere and the option of placing meteorological rockets under irradiation from a height of 300 km to the Earth’s surface is considered.

The results of the main research in the field of self-ignition theory are summarized. For symmetrical vessels, the following are presented: critical conditions of spontaneous ignition in dimensional coordinates, temperature distribution in the vessel, pre-explosive heating of fuel, and the critical size of the vessel at the time of explosion. It is noted that the self-ignition conditions for various vessels differ only by a digital multiplier, which indicates that the shape of the vessel does not affect the physicochemical processes going on in the fuel at the time of the explosion. Each singular point, being a bifurcation point, determines a number that allows finding a single critical condition of self-ignition from the set of solutions to the heat equation. This condition, in the coordinates of its variables, represents a multidimensional surface separating the zone of stationary existence of a combustible system from the zone of “no return,” where a combustible system cannot exist.

In this paper, we present the results of direct numerical modeling of the process of susceptibility of a supersonic boundary layer over an unswept wing with a thin parabolic profile to acoustic noise of various intensities. It was demonstrated that acoustic noise can cause a laminar–turbulent transition over the unswept wing of a supersonic passenger aircraft.

Samples of the Dhajala meteorite (ordinary chondrite, type H3.8) were kept isothermically in a specially designed device in the temperature range from 300 to 800°C for 90 minutes. The composition and content of the released gases were studied on a gas chromatograph. The following were detected: CO, CO₂, and H₂O in concentrations of 10–60 µg/g of the sample; in addition, H₂, CH₄, and H₂S in concentrations of 0.3–2 µg/g. The total nitrogen content during degassing increased quasi-linearly over time from 1–2 to 10–12 µg/g at each fixed temperature. Based on experimental observations of the change in the rate of nitrogen release depending on temperature, it was concluded that the effect of phase transitions depends on the permeability of the mineral matrix.