Numerical Simulation Of Propagation Research Articles

Higher-dimensional exceptional points and peakon dynamics triggered by spatially varying Kerr nonlinear media and PTδ(x) potentials.

Higher-dimensional PT-symmetric potentials constituted by delta-sign-exponential (DSE) functions are created in order to show that the exceptional points in the non-Hermitian Hamiltonian can be converted to those in the corresponding one-dimensional (1D) geometry, no matter the potentials inside are rotationally symmetric or not. These results are first numerically observed and then are proved by mathematical methods. For spatially varying Kerr nonlinearity, 2D exact peakons are explicitly obtained, giving birth to families of stable square peakons in the rotationally symmetric potentials and rhombic peakons in the nonrotationally symmetric potentials. By adiabatic excitation, different types of 2D peakons can be transformed stably and reciprocally. Under periodic and mixed perturbations, the 2D stable peakons can also travel stably along the spatially moving potential well, which implies that it is feasible to manage the propagation of the light by regulating judiciously the potential well. However, the vast majority of high-order vortex peakons are vulnerable to instability, which is demonstrated by the linear-stability analysis and by direct numerical simulations of propagation of peakon waveforms. In addition, 3D exact and numerical peakon solutions including the rotationally symmetric and the nonrotationally symmetric ones are obtained, and we find that incompletely rotationally symmetric peakons can occur stably in completely rotationally symmetric DSE potentials. The 3D fundamental peakons can propagate stably in a certain range of potential parameters, but their stability may get worse with the loss of rotational symmetry. Exceptional points and exact peakons in n dimensions are also summarized.

Imaging and Mode Content Analysis of the Wave Beam From a Short-Pulse High-Power Gyrotron Using the Millimeter-Wave-Induced Gas Breakdown Initiated by a Metal–Dielectric Screen

The wave beam of a sub-terahertz (THz) gyrotron with a pulsed magnetic field was imaged in a single pulse using a microwave-induced gas breakdown initiated by a metal–dielectric (MD) screen. Images of sub-THz beams, which were recorded at the output of a quasi-optical mode converter, were compared with data obtained by numerical simulation of propagation and transformation of the wave beam from the gyrotron. The analysis of the waveguide mode content in the gyrotron was done. Based on experimental and simulation data, it was shown that the distortion of the sub-THz wave beam is caused by the deformation of the Teflon window at the gyrotron output. Based on the results of the study, the gyrotron was modified, and the quality of its wave beam was improved.

Turbulence effects on shaped booms: Finite impulse response filter development

Numerical simulations of propagation through turbulent atmospheres can quantify effects on ground waveforms, but such simulations are computationally expensive. To enable quick turnaround analyses as required by NASA’s Quesst Mission, updating the N-wave filtering approach developed by researchers at The Pennsylvania State University to include shaped booms is proposed as an alternative method for estimating turbulence effects on acoustic metrics more quickly. Beginning with a nearfield pressure cylinder modeled after the on-design X-59 configuration, a database of propagation results at 45 turbulence conditions was compiled using nonlinear turbulence propagation modeling code (KZKFourier) and used as input to a process for generating finite impulse response (FIR) filters. Ground waveforms distorted by turbulence were selected to represent mean and mean±standard deviation levels for six metrics, and corresponding FIR filters were generated through a matrix deconvolution process. In order to evaluate how well the FIR filters perform, additional KZKFourier verification cases were devised with different input conditions, and results used as a benchmark. Convolution of shaped boom waveforms modeled using nonturbulent propagation simulations with the new FIR filters showed better agreement on average with KZKFourier statistical results than the N-wave-based FIR filters.

Nonlocal soliton in non-parity-time-symmetric coupler

Parity-time (PT) symmetric is not a necessary condition for achieving a real spectrum and some studies about realizing real spectra in non-PT-symmetric systems with arbitrary gain–loss profiles have been presented recently. By tuning the free parameters in non-PT-symmetric potentials, phase transition could also be induced. Above phase transition point, discrete complex eigenvalues bifurcate out from continuous real eigenvalues in the interior of the continuous spectrum. In this work, we investgate the existence and stability of solitons in nonlocal nonlinear couplers with non-PT-symmetric complex potentials both below and above phase transition. There are several discrete eigenvalues in the linear spectra of the non-PT-symmetric system used here. With the square-operator iteration method, we find that different continuous families of solitions can bifurcate from different discrete linear eigenvalues. Moreover, linear-stability analysis collaborated with direct numerical propagation simulations demonstrates that the nonlocal solitions can be stable in a range of parameter values. we first address the cases below the phase transition. To be specific, when we fix the coupling coefficient and vary the degree of nonlocality, it’s found that fundamental solitons, dipole solitons, tripolar solitons, quadrupole solitons bifurcate from the largest,the second-largest, the third-largest and the fifth-largest discrete eigenvalue, respectively. These nonlocal solitons are all stable in the low power region. With an increase of the degree of nonlocality, the stability region shrinks for the fundamental solitons while it widens for the dipole and multiplole solitons. At the same time, the power of all the stable solitons increases with the increase of the degree of nonlocality. By varying the coupling coefficient, the arrangement of soliton families emerging in the discrete interval of the linear spectrum can be changed. For example, the dipole solitons bifurcate from the third-or fourth-largest discrete eigenvalue while the tripolar solitons bifurcate from the fifth largest discrete eigenvalue. Above phase transition,the fundamental solitons are unstable in the low and high power region but are stable in the moderate power region. The stability region shrinks with the increasing degree of nonlocality. We also find the family of dipole solitons bifurcates from the second-largest discrete eigenvalue, but all the dipole solitons are unstable. In addition, we find that the eigenvalues in linear-stability spectra of solitons emerge as conjugation pairs.

Experimental and numerical simulation of the propagation law of shock waves in corrugated steel-lined tunnels

Corrugated steel support structures are widely used in engineering tunnels owing to their rapid construction and high bearing performance, allowing for the complex propagation of shock waves. To clarify the propagation law of shock waves in a corrugated steel tunnel with interior lining, a 30-m-long straight tunnel was built to explore the propagation of an explosion shock wave, and three different tunnel inner walls were designed, namely, a concrete inner wall and two types of corrugated steel linings. Based on the data on the monitored shock wave, the propagation law of shock waves in the tunnel was obtained, and the influence of corrugated steel linings on the shock waves was analyzed. A finite element model of the channel was established to verify the results of experiment and determine the model and related parameters. This model was also used to perform a numerical simulation of explosion shock wave propagation in corrugated steel-lined tunnels of various sizes. Based on the experimental and numerical simulation results, a prediction model of shock wave overpressure in corrugated steel-lined tunnels was obtained. Research showed that the shock-wave energy of wavefronts near walls was diverted, the formation and propagation of waves reflected from walls was affected by corrugated steel linings, which effectively improved the attenuation efficiency of shock waves in tunnels.

Demonstration of a Real-Time 14 Tb/s Multi-Aperture Transmit Single-Aperture Receive FSO System With Class 1 Eye-Safe Transmit Intensity

To achieve a link budget capable of supporting high capacity free space optical communication (FSO), a high transmit power is required. However, the transmitter can become potentially hazardous to the human eye. For a C-band transmitter to be classified as Class 1 eye-safe, the transmit intensity should be limited such that the optical power passing through a 24.5 mm diameter area is below 10 dBm. In this work we used a 9-aperture transmit, single-aperture receive FSO system to reduce the transmit intensity. Wavelength division multiplexed (WDM) signals were divided into 9 groups and transmitted through 9 apertures as separate beams. The apertures were arranged in a 3 x 3 array at a 25 mm pitch, and the transmit power from each aperture was set to 10 dBm. As a validation of the system by numerical simulation of propagation over 220 m, we showed that the additional free space loss due to pointing errors for the beams transmitted through the off-center apertures was less than 7.4 dB, and that using multiple apertures can significantly increase the transmission capacity. In the outdoor demonstration we transmitted 35 WDM 400 Gb/s dual-polarization probabilistically shaped 16-ary quadrature amplitude modulation signals over 220 m. By distributing the WDM channels across the 9 apertures to suit the transmission loss from their positions in the 3 x 3 array, we demonstrated error-free real-time transmission of a record capacity of 14 Tb/s, while satisfying the requirements of the Class 1 laser safety standard.

STUDY ON EVOLUTION MODEL OF GASEOUS DETONATION WAVE IN PERIODIC INHOMOGENEOUS MEDIUM

The initiation, steady propagation and failure mechanism of gaseous detonation wave in periodic inhomogeneous media are very complex, and many physical mechanisms are still unclear, which is an active topic in detonation physics. Numerical simulation of propagation of gaseous detonations in the inhomogeneous medium is studied by using the reactive Euler equations coupled with a two-step chemical reaction model. The inhomogeneity is generated by placing artificial temperature perturbations with different wavelengths and amplitudes. The influence of temperature disturbance with different wavelength and amplitude on the structure of wave front is analyzed. The results show that, the transition of ZND detonation to cellular detonation under artificial temperature disturbance is mainly controlled by two competitive factors: one is the intrinsic instability of detonation wave, the other is the wavelength and amplitude of artificial disturbance, the former is the internal factor, the latter is the external factor. The existence of artificial temperature disturbance delays the evolution of ZND detonation to cellular detonation by suppressing the development of shear wave, and the increase of internal instability can slow down this delay phenomenon. This shows that the artificial temperature disturbance can restrain the development of cell instability in a certain range, but it cannot stop the process. The discontinuity of temperature makes the detonation wave front more distorted, which leads to the existence of a weak triple-wave structure near the shear wave, which is, the artificial disturbance increases the inherent instability of detonation wave and changes the propagation mechanism of detonation wave front. The propagation of detonation and the instability of detonation are restrained by the artificial temperature disturbance with large amplitude. The formation of detonation front cellular structure depends on the artificial temperature disturbance and its own instability.

Numerical Simulation of Propagation and Run-Up of Long Waves in U-Shaped Bays

Wave propagation and run-up in U-shaped channel bays are studied here in the framework of the quasi-1D Saint-Venant equations. Our approach is numerical, using the momentum conserving staggered-grid (MCS) scheme, as a consistent approximation of the Saint-Venant equations. We carried out simulations regarding wave focusing and run-ups in U-shaped bays. We obtained good agreement with the existing analytical results on several aspects: the moving shoreline, wave shoaling, and run-up heights. Our findings also confirm that the run-up height is significantly higher in the parabolic bay than on a plane beach. This assessment shows the merit of the MCS scheme in describing wave focusing and run-up in U-shaped bays. Moreover, the MCS scheme is also efficient because it is based on the quasi-1D Saint-Venant equations.

Numerical simulation of thermal wave propagation and collision in thin film using finite element solution

Numerical simulation of propagation and collision of thermal wave phenomena in the order of nanometer is carried out. The finite element procedure is developed for Cattaneo–Vernotte heat conduction equation. In this simulation, non-homogeneous boundary conditions are used. Newmark’s scheme and constant average acceleration method are used to solve second-order time derivatives. The non-dimensional results are compared with the analytical solutions of the same kind of problem solved by using superposition principle with solution structure theorems and experimental values. It is noted that this current procedure had good agreement with the results given by analytical and experimental solutions. In this study, the finite element modeling of hyperbolic equation is solved for thermal wave propagation and collision of thermal waves. The transition of hyperbolic to parabolic nature of thermal wave propagation for different layer lengths and the characteristics of nodal temperatures near to the boundary are discussed. Also this work examined the temperature variation at the center of the layer at all collisions, which shows the increase in temperature after the first collision when time is 0.5 and then propagates toward boundary with further increase in temperature. This is well above the applied boundary temperature and decrease in temperature at boundary for subsequent collisions. The transition of thermal waves from hyperbolic to parabolic nature is analyzed and is found that the transition happens for the film thickness greater than 5. This phenomenon is repeated until it reaches steady state when time is 5 for hyperbolic whereas 1.5 for parabolic mode.

Vortex solitons in fractional systems with partially parity-time-symmetric azimuthal potentials

We address the propagation dynamics of topological states in the framework of nonlinear fractional Schrodinger equation modulated by a partially parity-time ( $$\mathcal {PT}$$ )-symmetric azimuthal potential. While the eigenvalue spectra in a $$\mathcal {PT}$$ system experience a symmetry breaking, the p $$\mathcal {PT}$$ system exhibits entirely real spectra. The variation of Levy index impacts the properties of nonlinear vortex states evidently, including the existence domain, power, and stability. Unlike nonlinear vortices in conservative systems, vortex solitons with opposite charges exhibit different features, due to the nonequivalence of the gain–loss distribution along the azimuthal direction. Linear-stability analysis collaborated with direct numerical propagation simulations demonstrates that stable vortex solitons are possible only when their components are connected as a whole entity. Higher-charged vortex solitons are shown to be more stable than those with lower charges. We, thus, put forward the first example of stable vortex solitons in fractional configurations.

Baza dannyh nablyudeniy vnutrennih voln v Mirovom okeane

Purpose. The purpose of the paper is to describe the permanently updated public database containing the information on observations of the internal waves, as well as the scientific sources on the corresponding themes. The observations are based on the data obtained by remote sensing and direct contact measurements in various areas of the World Ocean and in the inland basins (lakes, reservoirs). Methods and Results. The data from 503 literature sources on the observations of internal waves are structured. The structure, format, volume and current content of the database are considered; the stored information is analyzed. Described is the process of adding and viewing the records using the IGWAtlas web application (the online project for working with the database of the observations of internal waves in the oceans and for public access to observations and sources that has an intuitive user interface). Geographical distribution of the recorded observations and their dependence on a season are illustrated. The examples of images of various types of records contained in the database, as well as their distribution according to the types of observations are given. The considered in the paper database is integrated into the IGWResearch software package intended for numerical simulation of propagation and transformation of the internal waves in the World Ocean. Conclusions. The database contains the materials for 1972–2018 on 2296 recorded manifestations of the internal waves, which correspond to 2465 images, namely device records, satellite images, graphs, maps and tables. The database scope includes geographic information systems, statistical analysis, knowledge bases, web-services for the tasks of the World Ocean research.

Experimental study and numerical simulation of propagation and coalescence processes of pre-existing flaws in a transparent rock-like material

Flaws in the rock play an important role in the failure of rock engineering. In this article, some rock-like specimens prepared by transparent resin material were used to investigate the propagatio...

Numerical simulation of oblique and multidirectional wave propagation and breaking on steep slope based on FEM model of Boussinesq equations

• A FEM model is established based on modified Boussinesq equations to simulate wave propagation and breaking. • The incident wave heights increase for different periods to catch different kinds of wave breaking. • Oblique regular and irregular incident waves and multidirectional waves are considered. • The initial breaking threshold parameter should take different values for oblique and multidirectional waves. Creating a representative numerical simulation of the propagation and breaking of waves along slopes is an important problem in engineering design. Most studies on wave breaking have focused on the propagation of normal incident waves on gentle slopes. In practice, however, waves on steep slopes are obliquely incident or multidirectional irregular waves. In this paper, the eddy viscosity term is introduced to the momentum equation of the improved Boussinesq equations to model wave dissipation caused by breaking and friction, and a numerical model based on an unstructured finite element method (FEM) is established based on the governing equations. It is applied to simulate wave propagation on a steep slope of 1:5. Parallel physical experiments are conducted for comparative analysis that considered a large number of cases, including those featuring of normal and oblique incident regular and irregular waves, and multidirectional waves. The heights of the incident wave increase for different periods to represent different kinds of waves breaking. Based on examination, the effectiveness and accuracy of the numerical model is verified through a comprehensive comparison between the numerical and the experimental results, including in terms of variation in wave height, wave spectrum, and nonlinear parameters. Satisfactory agreement between the numerical and experimental values shows that the proposed model is effective in representing the breaking of oblique incident regular waves, irregular waves, and multidirectional incident irregular waves. However, the initial threshold of the breaking parameter η t ( I ) takes different values for oblique and multidirectional waves. This needs to be paid attention when the breaking of waves is simulated using the Boussinesq equations.

Aeroptical Effects Caused by Supersonic Airflow around an Ogival Body

An optical model of a shock wave generated due to supersonic airflow around a body of an ogival form is developed. Mean values of airflow parameters were calculated from the Navier–Stokes equations using the CFD Fluent 6.0 software package accounting for the gas compressibility. It is shown that the maximum values of the structure parameters are several orders of magnitude larger than the values typical for an unperturbed shock wave in the atmosphere. Results of numerical simulation of propagation of an optical beam which crosses the shock wave at the beginning of a path and then propagates through a homogeneous medium are presented. It is shown that an increase in the aircraft speed increases the transverse dimensions of the beam due to diffraction. The angular deviation of the beam from rectilinear propagation under the impact of the shock wave depends only on the altitude above the Earth’s surface where the shock wave is generated. The impact of the shock wave on the crossing beam weakens as the altitude increases.

Numerical Simulation of Propagation of Unsteady Tribrachial Flames in Laminar Non-Premixed Jets

The characteristics of propagating Tribrachial Flames in non-premixed laminar jets have been investigated computationally, using a two dimensional model in ANSYS FLUENT 16.0. The edge of the propagating flame in a laminar jet regime has a Tribrachial flame structure: a lean premixed flame, a rich premixed flame, and a diffusion flame, all extending from a single location. This is usually observed in non-premixed combustion such occurring in burners. Such flames are important in the interaction of heat and mass transfer with chemical reactions in gas turbines and commercial burners. A computational study has been performed to assess the laminar tribrachial flame propagation in methane jets and to compare the tribrachial flame propagation for various flow rates. With an increase in the fuel jet Reynolds number, the tribrachial point is found to move closer to the nozzle. Additionally the tribrachial point is found to become larger with an increase in the Reynolds number.

A DNS Study of Sensitivity of Scaling Exponents for Premixed Turbulent Consumption Velocity to Transient Effects

3D Direct Numerical Simulations of propagation of a single-reaction wave in forced, statistically stationary, homogeneous, isotropic, and constant-density turbulence, which is not affected by the wave, are performed in order to investigate the influence of the wave development on scaling (power) exponents for the turbulent consumption velocity UT as a function of the rms turbulent velocity u′, laminar wave speed SL, and a ratio L11/δF of the longitudinal turbulence length scale L11 to the laminar wave thickness δF. Fifteen cases characterized by u′/SL = 0.5,1.0,2.0,5.0, or 10.0 and L11/δF = 2.1, 3.7, or 6.7 are studied. Obtained results show that, while UT is well and unambiguously defined in the considered simplest case of a statistically 1D planar turbulent reaction wave, the wave development can significantly change the scaling exponents. Moreover, the scaling exponents depend on a method used to compare values of UT, i.e., the scaling exponents found by processing the DNS data obtained at the same normalized wave-development time may be substantially different from the scaling exponents found by processing the DNS data obtained at the same normalized wave size. These results imply that the scaling exponents obtained from premixed turbulent flames of different configurations may be different not only due to the well-known effects of the mean-flame-brush curvature and the mean flow non-uniformities, but also due to the flame development, even if the different flames are at the same stage of their development. The emphasized transient effects can, at least in part, explain significant scatter of the scaling exponents obtained by various research groups in different experiments, thus, implying that the scatter in itself is not sufficient to reject the notion of turbulent burning velocity.

Determination of large-size liner impedance based on numerical simulation of sound propagation in a duct with specified azimuthal modal structure

A study of determining impedance of a large-size sound-absorbing liner with azimuthal acoustic modes propagating in a duct was conducted on the basis of numerical simulation. The first stage of the study consisted in developing a method of impedance eduction on the basis of a simple cylinder model with microphones installed outside the sound-absorbing liner section. The full-scale experiment was replaced by numerical simulation of the propagation of a specified azimuthal noise structure in a cylindrical duct with known impedance wall (direct problem). As a result of solving the direct problem, the values of acoustic pressures are determined at those points where microphones are to be installed during the realization of the full-scale experiment. The results obtained are used to find the initial impedance value (inverse problem). The solution of the inverse problem using the procedure of minimizing the discrepancy between the acoustic pressures of the direct and inverse problems showed good accuracy of finding the impedance. It was also found that the accuracy of impedance eduction practically does not vary with the angle of installation of the linear array of microphones. The second stage of the study consisted in applying the developed approach to the model of a facility for testing large-size sound-absorbing liners. Acceptable accuracy of determining the impedance was achieved with certain quality of the finite element mesh. It has also been checked that, to save the computational time, for some acoustical modes acceptable accuracy of impedance eduction is possible in an axisymmetric statement. Thus, the possibility of using the proposed approach based on numerical simulation for the eduction of sound-absorbing liner impedance was confirmed.

Chislennoe modelirovanie rasprostraneniya chernomorskih i azovomorskih tsunami cherez Kerchenskiy proliv

Chislennoe modelirovanie rasprostraneniya chernomorskih i azovomorskih tsunami cherez Kerchenskiy proliv

Universality of phonon transport in nanowires dominated by surface roughness

We analyze, both theoretically and numerically, the temperature dependent thermal conductivity \k{appa} of two-dimensional nanowires with surface roughness. Although each sample is characterized by three independent parameters - the diameter (width) of the wire, the correlation length and strength of the surface corrugation - our theory predicts that there exists a universal regime where \k{appa} is a function of a single combination of all three model parameters. Numerical simulations of propagation of acoustic phonons across thin wires confirm this universality and predict a d 1/2 dependence of \k{appa} on the diameter d.

Vertical Distribution of a Demodulated Low-Frequency Field in the Disturbed Low-Latitude Ionosphere

Numerical simulation of propagation of a demodulated beam of low-frequency electromagnetic waves at low latitudes in the presence of latitudinal gradients of the equatorial anomaly has been performed under the condition that the signal is recorded in the vertical direction, for example, with the use of sounding rockets. It has been shown that the wave beam has small spatial dimensions and, therefore, the amplitude distribution of the electromagnetic field in this beam is nonuniform owing to the interference effects under competitive action of the plasma density gradients and plasma anisotropy in the presence of a nonuniform geomagnetic field. Under these measurement conditions, the measurements usually conducted with the use of the instruments carried by an Earth satellite may become insufficient.