Propagation Regime Research Articles

MHD flow of submerged jets behind the inlet disturbance

AbstractIn a broad variety of configurations in technology and industrial applications, the properties of liquid metal flows subjected to strong magnetic fields, are largely governed by the dynamics of coherent structures, known to settle several basic types, such as thin shear layers, forming near the walls or within the fluid domain, vortices extended along the field, or planar and round jets. In some cases, these structures are created by the design, like a submerged jet formed by a sudden expansion from the nozzle into a blanket channel, or jets formed behind some flow obstruction. In the other cases this may be due to instability and evolution of secondary structures, for example, descending and ascending jets appearing as a result of convective instability in blanket channels. In this study, we undertake an attempt to affect liquid metal flow via inlet disturbance formed by a simple rod placed along the magnetic induction lines. The disturbance can generate flat jets behind the rod and, furthermore, a sustainable flow of anisotropic vortical perturbations further downstream the flow. We seek to analyze the most important mechanisms of the flow dynamics and effects of magnetic field on the integral system properties of enhancing mixing, mass and heat transport for such flow. The most optimal regimes of vortex generation are found to be governed by the magnetic interaction parameter (Stuart number). The exact ratio of the optimal Stuart number is found to be in a range between 20 and 40, based on the channel double width as a characteristic size. The observed vortices attain quasi‐2D shape and exist at a length of dozens of duct calibers, being the strongest at higher flow rates. The obtained flow regimes and their turbulent properties are also found to resemble significant similarity to the results on quasi‐2D turbulence found in prior studies of channel and duct flows under spanwise magnetic field.

Solitary Waves in Two-Layer Fluid with Piecewise Exponential Stratification

The problem on internal stationary waves in a two-layer fluid with density, depending exponentially on the depth inside the layers and having a jump at the interface, is considered. A non-linear equation of the second-order long-wave approximation is derived, and their asymptotic submodels, describing solitary waves of finite amplitude, are discussed. Dispersive properties and wave propagation regimes depending on dimensionless parameters of the background piecewise constant flow are studied.

Fatigue Phase‐field Modeling for Elastomeric Materials

AbstractFatigue failure prediction of elastomeric materials plays a crucial role in engineering applications, e.g., rolling tires. Experimental investigations, as a straightforward evaluation of fatigue failure, do not enable an efficient insight due to significant time consumption. Therefore, several numerical approaches are developed to model fatigue fracture or damage behavior of material components subjected to cyclic loading. Inspired by [1], the work at hand incorporates a degrading fracture toughness into a promising phase‐field method. As a smeared crack representation, the phase‐field model does not depend upon any explicit criterion for crack evolution, e.g., crack initiation and propagation. Furthermore, this work proposes a novel algorithm, which is based on a post‐processing technique, to evaluate the energy release rate for PARIS' parameters during the stable crack propagation regime. The methodology is implemented into the Finite Element framework and a demonstrative numerical example is simulated.

Investigation of Heterogeneous Detonation Wave Interaction with Porous Medium

ABSTRACT Mathematical model of aluminum heterogeneous detonation interaction with inert porous media was developed. Main regimes of interaction of heterogeneous detonation wave of stoichiometric mixture of aluminum particles in oxygen with porous inserts were studied. One- and two-dimensional calculations for micron and submicron particles and comparison of these calculations were made. Main regimes of detonation interaction with porous zone and critical conditions of detonation attenuation in porous zones were obtained. Calculations show that for micron particles reducing the diameter of burning particles lead to increasing the volume concentration of inert phase in the porous body that needs for detonation attenuation. Main difference of the propagation regimes for micron and submicron aluminum particles was found.

On Classification of Water-in-Oil and Oil-in-Water Droplet Generation Regimes in Flow-Focusing Microfluidic Devices

The objective of this research work is to propose a phase diagram that can be used to find a proper operating condition for generating droplets of different types. It is found that the phase diagram of QR versus CaD can effectively classify the droplet generation into three vivid regimes: dripping, jetting and tubing. For the dripping regime, its operating condition is in the range of either CaD < 10−4 and QR < 50 or 10−3 < CaD < 10−4 and QR < 1. For the jetting regime, its operating condition is in the range of either CaD < 1.35 × 10−2 and QR > 100 or CaD > 1.35 × 10−2 and QR > 1. For the tubing regime, its operating condition is in the range of CaD > 1.35 × 10−2 and QR < 1.

Self-similarity in transient stimulated Raman scattering in CO2-filled hollow-core fiber

We demonstrate experimentally the complex and extensive spectro-temporal dynamics of stimulated Raman scattering in C O 2 -filled hollow-core photonic crystal fiber, pumped by a single infrared microchip laser; namely, the cascading transient Raman process and self-similar behaviors in the regime of higher-order Stokes wave generation. Our measurements are in good agreement with the numerical simulations based on the nonlinear Schrödinger equation.

Numerical simulation of interaction of cellular detonation wave with systems of inert porous filters

Numerical modeling of the interaction of cellular detonation in a hydrogen-air mixture with several systems of porous filters covering part of the channel was carried out. The main regimes of detonation propagation and the critical conditions for detonation failure in the filter systems were obtained for each system. A map of detonation regimes was constructed, from which it follows that with an increase in the concentration of particles in the filters, it is possible to increase the distance between the filters or reduce the number of filters in the system necessary to successfully suppress detonation. A comparison of various filter systems in terms of blockage ratio and the total surface area of particles was made, from which it was concluded that the system of two filters was the most efficient to suppress detonation.

Tuning the directionality of spin waves generated by femtosecond laser pulses in a garnet film by optically driven ferromagnetic resonance

Excitation of spin waves of a required frequency and directional spectrum is among the crucial tasks in optomagnonics. Here we investigate the generation of spin waves in an iron garnet thin film by a train of femtosecond laser pulses with ultimately high repetition rate of up to 10 GHz and compare it with the case of 1-GHz repetition rate. The periodic optical excitation with repetition rate close to the frequency of the ferromagnetic resonance amplifies spin waves with particular phase velocity and wavelength, which are tunable across a wide range by small variations of the frequency detuning, and can be adjusted by the magnitude of the applied external magnetic field. For pulses of the same fluence, the 10-GHz pulse rate provides a significant resonant increase of the spin-wave amplitude by 11.5 times with respect to single-pulse excitation while the 1-GHz pulse rate provides only a 1.5 times advancement. Moreover, variation of the detuning frequency provides different regimes of the spin-wave propagation: short- and long-distance propagation along the magnetic field direction and appearance of an ``X'' line shape in the directionality pattern, making the considered optical approach of spin-wave generation promising for designing magnonic devices.

Particle acceleration in colliding flows: Binary star winds and other double-shock structures.

A shock wave propagating perpendicularly to an ambient magnetic field accelerates particles considerably faster than in the parallel propagation regime. However, the perpendicular acceleration stops after the shock overruns a circular particle orbit. At the same time, it may continue in flows resulting from supersonically colliding plasmas bound by a pair of perpendicular shocks. Although the double-shock acceleration mechanism, which we consider in detail, is not advantageous for thermal particles, preenergized particles may avoid the premature end of acceleration. We argue that if their gyroradius exceeds the dominant turbulence scale between the shocks, these particles might traverse the intershock space repeatedly before being carried away by the shocked plasma. Moreover, entering the space between the shocks of similar velocities u_{1}≈u_{2}≈c, such particles start bouncing between the shocks at a fixed angle ≈35.3^{∘} to the shock surface. Their drift along the shock fronts is slow, V_{d}∼|u_{2}-u_{1}|≪c, so that it will take N∼Lc/|u_{2}-u_{1}|d≫1 bounces before they escape the accelerator (here, L is the size of the shocks and d is the gap between them). Since these particles more than tenfold their energy per cycle (two consecutive bounces), we invoke other possible losses that can limit the acceleration. They include drifts due to rippled shocks, the nonparallel mutual orientation of the upstream magnetic fields, and radiative losses.

Morphology influence on the acoustics of permeo-elastic media

This paper deals with the acoustics of permeo-elastic media. These media consist of a rigid porous skeleton on which flexible elastic films are fixed and interact with the fluid saturating the pores. They can correspond to foams, the thin membranes playing the role of films and the rigid structure being formed by the struts. The acoustics of permeo-elastic media can deviate from that of conventional porous media due to the fluid/film interaction at the pore scale. This introduces an elastic component in the energy that interacts with viscous and inertial effects. The actual behavior is established by the two-scale asymptotic homogenization method. It is shown that the film effects depend strongly on the pores and the film arrangement. Different wave propagation regimes are identified depending on the nature of the local flow. Consider- ing (i) fully connected, i.e., no pores are closed by the films, (ii) unconnected, i.e., all pores are closed, and (iii) partially connected, i.e., some pores are closed by the films, the study re- veals under which conditions the fluid-film interaction significantly influences the macroscopic acoustic behavior. Depending on the morphology, the permeability or compressibility (or both) can exhibit singularities or anomalous properties due to inner resonance or anti-resonance.

Nonlinear photonics with metasurfaces

Nonlinear optics is a well-established field of research that traditionally relies on the interaction of light with macroscopic nonlinear media over distances significantly greater than the wavelength of light. However, the recently emerged field of optical metasurfaces provides a novel platform for studying nonlinear phenomena in planar geometries. Nonlinear optical metasurfaces introduce new functionalities to the field of nonlinear optics extending them beyond perturbative regimes of harmonic generation and parametric frequency conversion, being driven by mode-matching, resonances, and relaxed phase-matching conditions. Here we review the very recent advances in the rapidly developing field of nonlinear metasurface photonics, emphasizing multi-frequency and cascading effects, asymmetric and chiral frequency conversion, nonperturbative nonlinear regimes, and nonlinear quantum photonics, empowered by the physics of Mie resonances and optical bound states in the continuum.

Wavelength and pulse width programmable mode-locked Yb fiber laser.

To the best of our knowledge, this study is the first demonstration of a mode-locked polarization-maintaining Yb fiber laser that incorporates a liquid-crystal-on-silicon-based electrically programmable filter into the cavity. The intracavity filter continuously tunes pulse characteristics, such as a wavelength tunable range of 1018-1065 nm and pulse width tunable range of 0.3-2.6 ps. Further, numerical simulations of the laser oscillator results were consistent with the experimental results and confirmed the mode-locked pulse generation regime. The proposed technique is expected to have great potential as a seed laser for multifunctional ultrashort-pulse lasers.

Regimes of optical propagation through turbulence: theory and direct numerical simulations

Classical work provides an analytical framework to predict distortions of an electromagnetic wave as it interacts with turbulence. However, there seems to be virtually no systematic validation of these predictions and assessment of the assumptions behind the theory. In this work, we present numerical results of optical distortions based on highly-resolved direct numerical simulations of turbulence at a range of conditions, and new theory which accounts for more realistic representations of turbulent fluctuations. This leads to a number of new results. First, we discover two new scaling regimes for the variance of phase and log-amplitude at propagations comparable to Kolmogorov scales. Second, our theory highlights and overcomes limitations of classical work including the effects of finite outer-scale, non-Kolmogorov intermittency corrections, and a more general representation of small scales. Third, we propose a new universal refractive-index structure parameter in terms of three non-dimensional parameters involving turbulence and optical scales. This yields a universal presentation of all scaling regimes in a new phase space. Finally, high-fidelity direct numerical simulations which resolve all turbulent scales are used to perform the first systematic assessment of classical and new scaling regimes. Excellent agreement is found between simulations and theoretical findings.

Wave propagation in random media: beyond Gaussian statistics

In this paper we review some aspects of wave propagation in random media. In the physics literature the picture seems simple: for large propagation distances, the wavefield has Gaussian statistics, mean zero, and second-order moments determined by radiative transfer theory. The results for the first two moments can be proved under general circumstances by multiscale analysis. The Gaussian conjecture for the statistical distribution of the wavefield can be proved in some propagation regimes, such as the white-noise paraxial regime that we address in the first part of this review. It may, however, be wrong in other regimes, such as in randomly perturbed open waveguides, that we address in the second part of this review. In the third and last part, we reconcile the two results by showing that the Gaussian conjecture is restored in randomly perturbed open waveguides in the high-frequency regime, when the number of propagating modes increases.

Polarization Simultons in CARS by Polaritons

The system of shortened Maxwell’s equations simulating the processes of evolution of the stimulated Raman scattering (SRS) by polaritons in anisotropic dipole-active crystals is obtained. The theory was developed for the case of cubic crystals which become anisotropic due to the deformation of the dielectric constant by the linearly polarized pump wave. The pump field is a linearly polarized plane electromagnetic wave. We report the results of the theoretical investigation of the possibility of the existence of a regime of pulse propagation as simultaneous travel of solitary waves in coherent anti-Stokes stimulated Raman scattering by polaritons in anisotropic crystals. The emphasis was made on the existence of both Stokes and anti-Stokes pulses propagating with two stable and perpendicular to the direction of travel polarizations. We showed the theoretical possibility of simultaneous propagation of pulses not only at frequencies of Stokes and anti-Stokes waves but the pump frequency as well. We obtained the expression for the gain factor g. It is also shown that the expression for g is consistent with the experimental results for the spectra of ZnS.

Фазовые эффекты при вынужденном рассеянии Мандельштама-Бриллюэна

In the study of stimulated Brillouin scattering (SBS) in the constant intensity approximation, the spatial behavior of the intensity of the Stokes scattering wave in a medium was investigated. It was found that as a result of nonlinear interaction of waves, the period of spatial beats changes. The intensity of the Stokes scattering component is considered as a function of the phase mismatch, pump and acoustic wave intensities. It is found that the efficiency of the scattering of the backward Stokes wave is affected by the total length of the nonlinear medium. According to the analytical expressions obtained in this work, the choice of the optimal parameters of the problem makes it possible to implement the regime of efficient generation of the Stokes scattering component in SBS. The process of generation and amplification of the Stokes scattering component is compared with experiment. By varying the pump intensity, one can control and manipulate the intensity of the output radiation of the Stokes component.

Phase effects at stimulated Brillouin scattering

In the study of stimulated Brillouin scattering (SBS) in the constant intensity approximation, the spatial behavior of the intensity of the Stokes scattering wave in a medium was investigated. It was found that as a result of nonlinear interaction of waves, the period of spatial beats changes. The intensity of the Stokes scattering component is considered as a function of the phase mismatch, pump and acoustic wave intensities. It is found that the efficiency of the scattering of the backward Stokes wave is affected by the total length of the nonlinear medium. According to the analytical expressions obtained in this work, the choice of the optimal parameters of the problem makes it possible to implement the regime of efficient generation of the Stokes scattering component in SBS. The process of generation and amplification of the Stokes scattering component is compared with experiment. By varying the pump intensity, one can control and manipulate the intensity of the output radiation of the Stokes component. Keywords: SBS, backward Stokes scattering wave, constant intensity approximation.

«Палеозойская» нефть Урманского месторождения (юго-восток Западной Сибири)

This paper presents the results of applying paleotemperature modelling for determination possible sources, which form hydrocarbon deposits in the pre-Jurassic basement in the southeast of Western Siberia. Discovery of light oil deposits below the depth of 7000 m in the Tarim basin indicates the possibility of existence favourable temperature regime for generation and conservation of hydrocarbon deposits even at such great depths. According to some estimates about 40 % of the total proved oil and gas reserves in the world are distributed in the superdeep strata. Russian scientists also have extensive prospects for the Paleozoic sedimentary basins of Western Siberian Plate. These basins formed on betwixt mountains, where favourable environment for accumulation of dispersed organic matter and its transformation into hydrocarbons persisted for a long geological time. There are two concepts of “the main source” for oil accumulated in the Paleozoic reservoirs. The first suggests deposit formation via upward migration, while the second supports the idea of downward interstratal migration of hydrocarbons from the Jurassic source rocks. The aim of this study is to determine possible sources for the Paleozoic hydrocarbon deposits in the Urman field via modelling of thermal history of the Phanerozoic oil-source rocks. The first experience of performing such research is related to the Ostanino group of fields. The research is continued for the Chuzic-Chizhapka group of fields, which is located on the tectonic unit of the same name. Both groups are associated with the Nyurol sedimentary basin. It was found that the Paleozoic reservoir of the Urman field accumulates partially preserved gas generated by the Paleozoic source-rocks and oil representing a mixture of the Jurassic oil of marine and terrigenous origin.

Near-Field Localization for Holographic RIS Assisted mmWave Systems

In this letter, we envision the integration of holographic reconfigurable intelligent surface (HRIS) into a millimeter-wave (mmWave) localization system. The large aperture of HRIS in the mmWave band allows the system to operate in the near-field propagation regime, where the wavefront tends to be spherical and contains distance information. To investigate the fundamental limits of localization accuracy of the proposed system, we obtain the Fisher information matrix (FIM) and Cramér-Rao lower bound (CRLB) taking into account the radiation patterns of antennas. The analytical results reveal that the FIM quadratically increases with the size of HRIS. Then, to explore the potential of HRIS passive beamforming for improving localization quality, we formulate the HRIS phases optimization problem to minimize a worst-case CRLB with respect to an uncertainty set of user equipment (UE) positions. To address this formulated problem, an iterative entropy regularization (IER) based method is proposed. Numerical results evaluate the effect of key parameters on the squared position error bound and verify the effectiveness of the proposed IER-based method.

Guided electromagnetic discharge pulses driven by short intense laser pulses: Characterization and modeling

Strong electromagnetic pulses (EMPs) are generated from intense laser interactions with solid-density targets and can be guided by the target geometry, specifically through conductive connections to the ground. We present an experimental characterization by time- and spatial-resolved proton deflectometry of guided electromagnetic discharge pulses along wires including a coil, driven by 0.5 ps, 50 J, 1019 W/cm2 laser pulses. Proton-deflectometry allows us to time-resolve first the EMP due to the laser-driven target charging and then the return EMP from the ground through the conductive target stalk. Both EMPs have a typical duration of tens of ps and correspond to currents in the kA-range with electric-field amplitudes of multiple GV/m. The sub-mm coil in the target rod creates lensing effects on probing protons due to both magnetic- and electric-field contributions. This way, protons of the 10 MeV-energy range are focused over cm-scale distances. Experimental results are supported by analytical modeling and high-resolution numerical particle-in-cell simulations, unraveling the likely presence of a surface plasma, in which parameters define the discharge pulse dispersion in the non-linear propagation regime.