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Journal articles on the topic 'Stochastic wave packets'

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Author: Grafiati

Published: 30 May 2022

Last updated: 31 May 2022

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1

MILLET, Christophe, Bruno RIBSTEIN, and Francois LOTT. "Infrasound scattering from stochastic gravity wave packets." Journal of the Acoustical Society of America 141, no. 5 (May 2017): 3628. http://dx.doi.org/10.1121/1.4987800.

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2

Osborne. "Breather Turbulence: Exact Spectral and Stochastic Solutions of the Nonlinear Schrödinger Equation." Fluids 4, no. 2 (April 15, 2019): 72. http://dx.doi.org/10.3390/fluids4020072.

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I address the problem of breather turbulence in ocean waves from the point of view of the exact spectral solutions of the nonlinear Schrödinger (NLS) equation using two tools of mathematical physics: (1) the inverse scattering transform (IST) for periodic/quasiperiodic boundary conditions (also referred to as finite gap theory (FGT) in the Russian literature) and (2) quasiperiodic Fourier series, both of which enhance the physical and mathematical understanding of complicated nonlinear phenomena in water waves. The basic approach I refer to is nonlinear Fourier analysis (NLFA). The formulation describes wave motion with spectral components consisting of sine waves, Stokes waves and breather packets that nonlinearly interact pair-wise with one another. This contrasts to the simpler picture of standard Fourier analysis in which one linearly superposes sine waves. Breather trains are coherent wave packets that “breath” up and down during their lifetime “cycle” as they propagate, a phenomenon related to Fermi-Pasta-Ulam (FPU) recurrence. The central wave of a breather, when the packet is at its maximum height of the FPU cycle, is often treated as a kind of rogue wave. Breather turbulence occurs when the number of breathers in a measured time series is large, typically several hundred per hour. Because of the prevalence of rogue waves in breather turbulence, I call this exceptional type of sea state a breather sea or rogue sea. Here I provide theoretical tools for a physical and dynamical understanding of the recent results of Osborne et al. (Ocean Dynamics, 2019, 69, pp. 187–219) in which dense breather turbulence was found in experimental surface wave data in Currituck Sound, North Carolina. Quasiperiodic Fourier series are important in the study of ocean waves because they provide a simpler theoretical interpretation and faster numerical implementation of the NLFA, with respect to the IST, particularly with regard to determination of the breather spectrum and their associated phases that are here treated in the so-called nonlinear random phase approximation. The actual material developed here focuses on results necessary for the analysis and interpretation of shipboard/offshore platform radar scans and for airborne lidar and synthetic aperture radar (SAR) measurements.

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3

Khazanov, G. V., D. G. Sibeck, A. A. Tel'nikhin, and T. K. Kronberg. "Stochastic acceleration of ions driven by Pc1 wave packets." Physics of Plasmas 22, no. 7 (July 2015): 072901. http://dx.doi.org/10.1063/1.4926823.

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4

RIGATOS, GERASIMOS G. "QUANTUM WAVE-PACKETS IN FUZZY AUTOMATA AND NEURAL ASSOCIATIVE MEMORIES." International Journal of Modern Physics C 18, no. 10 (October 2007): 1551–69. http://dx.doi.org/10.1142/s012918310701156x.

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In this paper the existence of quantum wave-packets in neural structures, such as automata and associative memories, is studied. The synaptic weights are considered to be stochastic variables, with probability density functions given by the solution of Schrödinger's equation. It is shown that the weights' update can be performed with the use of unitary operators, as indicated by the postulates of quantum mechanics. Moreover, it is proved that the number of attractors of quantum associative memories increases exponentially with respect to conventional associative memories. Finally, simulation tests are used to demonstrate the improved pattern storage capabilities of quantum associative memories.

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5

Telloni, Daniele. "Persistence of Ion Cyclotron Waves and Stochasticity of Kinetic Alfvén Waves in the Solar Wind." Atmosphere 12, no. 1 (December 30, 2020): 44. http://dx.doi.org/10.3390/atmos12010044.

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This paper investigates the nature of the physical processes underlying the origin of the Ion Cyclotron Waves (ICWs) and Kinetic Alfvén Waves (KAWs) in the solar wind, by studying their Waiting Time Distributions (WTDs). The results show that ICWs and KAWs do not share common statistical properties: while KAWs independently occur as stochastic, uncorrelated wave packets governed by Poisson statistics, ICWs are highly correlated, thus departing from the Poisson hypothesis. The results based on the WTD analysis may cast more light on the mechanisms actively at work in the generation of the two wave modes. Specifically, while the stochastic character of KAWs may be reminiscent of the random convection-driven jostling of the flux-tube foot-points that generates the Alfvén waves in the lower solar atmosphere, the correlations among the ICW events can be effectively explained on the basis of the persistent nature of the mechanism underlying the local origin of ICWs, namely the proton cyclotron instability. Alternative explanations for the observed distribution of ICW waiting times, based on a piecewise-constant Poisson process involving time-varying rates, are also reported.

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6

DE MARTINO, SALVATORE, SILVIO DE SIENA, and FABRIZIO ILLUMINATI. "A CLASS OF QUANTUM STATES WITH CLASSICAL-LIKE EVOLUTION." Modern Physics Letters B 08, no. 29 (December 20, 1994): 1823–31. http://dx.doi.org/10.1142/s0217984994001734.

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In the framework of the stochastic formulation of quantum mechanics we derive non-stationary states for a class of time-dependent potentials. The wave packets follow a classical motion with constant dispersion. The new states define a possible extension of the harmonic oscillator coherent states. As an explicit application, we study a sestic oscillator potential.

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7

Ono, Akira, and Hisashi Horiuchi. "Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of the Vlasov equation." Physical Review C 53, no. 6 (June 1, 1996): 2958–72. http://dx.doi.org/10.1103/physrevc.53.2958.

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8

McNeill, Lucy O., and Bernhard Müller. "Stochastic core spin-up in massive stars – implications of 3D simulations of oxygen shell burning." Monthly Notices of the Royal Astronomical Society 497, no. 4 (August 5, 2020): 4644–53. http://dx.doi.org/10.1093/mnras/staa2287.

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ABSTRACT It has been suggested based on analytic theory that even in non-rotating supernova progenitors stochastic spin-up by internal gravity waves (IGWs) during the late burning stages can impart enough angular momentum to the core to result in neutron star birth spin periods below $100\, \mathrm{ms}$, and a relatively firm upper limit of $500\, \mathrm{ms}$ for the spin period. We here investigate this process using a 3D simulation of oxygen shell burning in a 3 M⊙ He star. Our model indicates that stochastic spin-up by IGWs is less efficient than previously thought. We find that the stochastic angular momentum flux carried by waves excited at the shell boundary is significantly smaller for a given convective luminosity and turnover time than would be expected from simple dimensional analysis. This can be explained by noting that the waves launched by overshooting convective plumes contain modes of opposite angular wavenumber with similar amplitudes, so that the net angular momentum of excited wave packets almost cancels. We find that the wave-mediated angular momentum flux from the oxygen shell follows a random walk, but again dimensional analysis overestimates the random walk amplitudes since the correlation time is only a fraction of the convective turnover time. Extrapolating our findings over the entire lifetime of the last burning stages prior to collapse, we predict that the core angular momentum from stochastic spin-up would translate into long birth spin periods of several seconds for low-mass progenitors and no less than $100\, \mathrm{ms}$ even for high-mass progenitors.

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9

Sembiring, J., and K. Akizuki. "On The De-correlation of Stochastic Processes Using Wave Packets: Fractional Brownian Motion Case." Proceedings of the ISCIE International Symposium on Stochastic Systems Theory and its Applications 1996 (May 5, 1996): 47–52. http://dx.doi.org/10.5687/sss.1996.47.

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10

Bratus', E. N., S. A. Gredeskul, L. A. Pastur, and V. S. Shumeyko. "Quantum dynamics of quasiparticles in a stochastic field and nonlinear dissipation of wave packets." Physics Letters A 131, no. 7-8 (September 1988): 449–53. http://dx.doi.org/10.1016/0375-9601(88)90299-x.

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11

Haba, Zbigniew. "Quantum State Evolution in an Environment of Cosmological Perturbations." Universe 7, no. 5 (April 21, 2021): 117. http://dx.doi.org/10.3390/universe7050117.

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We study the pure and thermal states of quantized scalar and tensor perturbations in various epochs of Universe evolution. We calculate the density matrix of non-relativistic particles in an environment of these perturbations. We show that particle’s motion can be described by a stochastic equation with a noise coming from the cosmological environment. We investigate the squeezing of Gaussian wave packets in different epochs and its impact on the noise of quantized cosmological perturbations.

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12

Restrepo, Juan M., and Jorge M. Ramirez. "Transport due to Transient Progressive Waves." Journal of Physical Oceanography 49, no. 9 (September 2019): 2323–36. http://dx.doi.org/10.1175/jpo-d-19-0087.1.

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AbstractMaking use of a Lagrangian description, we interpret the kinematics and analyze the mean transport due to numerically generated transient progressive waves, including breaking waves. The waves are packets and are generated with a boundary-forced, air–water, two-phase Navier–Stokes solver. These transient waves produce transient transport, which can sometimes be larger than what would be estimated using estimates developed for translationally invariant progressive waves. We identify the critical assumption that makes our standard notion of the steady Stokes drift inapplicable to the data and explain how and in what sense the transport due to transient waves can be larger than the steady counterpart. A comprehensive analysis of the data in the Lagrangian framework leads us to conclude that much of the transport can be understood using an irrotational approximation of the velocity, even though the simulations use Navier–Stokes fluid simulations with moderately high Reynolds numbers. Armed with this understanding, it is possible to formulate a simple Lagrangian model that captures the mean transport and variance of transport for a large range of wave amplitudes. For large-amplitude waves, the parcel paths in the neighborhood of the free surface exhibit increased dispersion and lingering transport due to the generation of vorticity. We examined the wave-breaking case. For this case, it is possible to characterize the transport very well, away from the wave boundary layer, and approximately using a simple model that captures the unresolved breaking dynamics via a stochastic parameterization.

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13

Chhak, Kettyah C., Andrew M. Moore, Ralph F. Milliff, Grant Branstator, William R. Holland, and Michael Fisher. "Stochastic Forcing of the North Atlantic Wind-Driven Ocean Circulation. Part II: An Analysis of the Dynamical Ocean Response Using Generalized Stability Theory." Journal of Physical Oceanography 36, no. 3 (March 1, 2006): 316–34. http://dx.doi.org/10.1175/jpo2853.1.

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Abstract As discussed in Part I of this study, the magnitude of the stochastic component of wind stress forcing is comparable to that of the seasonal cycle and thus will likely have a significant influence on the ocean circulation. By forcing a quasigeostrophic model of the North Atlantic Ocean circulation with stochastic wind stress curl data from the NCAR CCM3, it was found in Part I that much of the stochastically induced variability in the ocean circulation is confined to the western boundary region and some major topographic features even though the stochastic forcing is basinwide. This can be attributed to effects of bathymetry and vorticity gradients in the basic state on the system eigenmodes. Using generalized stability theory (GST), it was found in Part I that transient growth due to the linear interference of nonnormal eigenmodes enhances the stochastically induced variance. In the present study, the GST analysis of Part I is extended and it is found that the patterns of wind stress curl that are most effective for inducing variability in the model have their largest projection on the most nonnormal eigenmodes of the system. These eigenmodes are confined primarily to the western boundary region and are composed of long Rossby wave packets that are Doppler shifted by the Gulf Stream to have eastward group velocity. Linear interference of these eigenmodes yields transient growth of stochastically induced perturbations, and it is this process that maintains the variance of the stochastically induced circulations. Analysis of the large-scale circulation also reveals that the system possesses a large number of degrees of freedom, which has significant implications for ocean prediction. Sensitivity studies show that the results and conclusions of this study are insensitive and robust to variations in model parameters and model configuration.

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14

Khazanov, G. V., A. A. Tel’nikhin, and T. K. Kronberg. "Stochastic electron motion driven by space plasma waves." Nonlinear Processes in Geophysics 21, no. 1 (January 10, 2014): 61–85. http://dx.doi.org/10.5194/npg-21-61-2014.

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Abstract. Stochastic motion of relativistic electrons under conditions of the nonlinear resonance interaction of particles with space plasma waves is studied. Particular attention is given to the problem of the stability and variability of the Earth's radiation belts. It is found that the interaction between whistler-mode waves and radiation-belt electrons is likely to involve the same mechanism that is responsible for the dynamical balance between the accelerating process and relativistic electron precipitation events. We have also considered the efficiency of the mechanism of stochastic surfing acceleration of cosmic electrons at the supernova remnant shock front, and the accelerating process driven by a Langmuir wave packet in producing cosmic ray electrons. The dynamics of cosmic electrons is formulated in terms of a dissipative map involving the effect of synchrotron emission. We present analytical and numerical methods for studying Hamiltonian chaos and dissipative strange attractors, and for determining the heating extent and energy spectra.

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15

Savaş, Ö. "On flow visualization using reflective flakes." Journal of Fluid Mechanics 152 (March 1985): 235–48. http://dx.doi.org/10.1017/s0022112085000672.

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An analysis of flow visualization using small reflective flakes is introduced. This rational analysis is based on a stochastic treatment of Jeffery's (1922) solution for the motion of ellipsoidal particles in a viscous fluid, wherein thin flakes tend to align with stream surfaces. The predicted light fields are confirmed by examples of parallel flows, the flow over a rotating disk, and the spinup from rest in a cylindrical cavity. The Tollmien–Schlichting wave packet trailing a turbulent spot is taken as an example to discuss the suitability of the technique for visualizing small-amplitude waves. Attenuation of light through a suspension is described.

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16

Raouak, A., D. Saifaoui, and A. Dezairi. "Chaos dynamique des particules relativistes accélérées dans un paquet d'ondes électrostatiques." Canadian Journal of Physics 82, no. 6 (June 1, 2004): 467–79. http://dx.doi.org/10.1139/p04-022.

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In this work, we study the diffusion of particle accelerated in an electromagnetic wave packet, through a numerical simulation of the relativistic standard map. We contribute to the field of stochastic diffusion of accelerated particles as a function of the stochastic parameter K, specially the transition between partial and global stochasticity, and we also compare our theoretical computation of the diffusion with numerical results.

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17

Brown, Robert C., and Robert E. Wyatt. "Quantum mechanical manifestation of cantori: Wave-packet localization in stochastic regions." Physical Review Letters 57, no. 1 (July 7, 1986): 1–4. http://dx.doi.org/10.1103/physrevlett.57.1.

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18

Popel, Sergey I., and Sergey V. Vladimirov. "Stochastic properties of the modulational interaction in packets of random waves." Physics Letters A 200, no. 2 (April 1995): 156–59. http://dx.doi.org/10.1016/0375-9601(95)00197-b.

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19

Serwatka, T., and J. C. Tremblay. "Stochastic wave packet approach to nonadiabatic scattering of diatomic molecules from metals." Journal of Chemical Physics 150, no. 18 (May 14, 2019): 184105. http://dx.doi.org/10.1063/1.5092698.

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20

O’Connell, R. F. "Stochastic methods in atomic systems and QED." Canadian Journal of Physics 87, no. 1 (January 1, 2009): 45–48. http://dx.doi.org/10.1139/p08-078.

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We show that treating the black-body radiation field as a heat bath enables one to utilize powerful techniques from the realm of stochastic physics (such as the fluctuation–dissipation theorem and the related radiation damping) to treat problems that could not be treated rigorously by conventional methods. We illustrate our remarks by discussing specifically the effect of temperature on atomic spectral lines, and the solution to the problem of runaway solutions in the equation of motion of a radiating electron. We also present brief discussions relating to anomalous diffusion and wave-packet spreading in a radiation field and the influence of quantum effects on the laws of thermodynamics.PACS Nos.: 31.30.jg, 05.40.–a

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21

Moralev, Ivan, Ilya Popov, Igor Selivonin, and Maxim Ustinov. "Stochastic forcing of the 2D boundary layer by DBD plasma actuator." Journal of Physics: Conference Series 2100, no. 1 (November 1, 2021): 012001. http://dx.doi.org/10.1088/1742-6596/2100/1/012001.

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Abstract The paper describes the results of the parametric study of the broadband velocity pulsations, induced by DBD plasma actuator in 2D subsonic boundary layer. The presented data include the analysis of the disturbance growth at various pressure gradients. It is assumed that the broadband pulsations are composed of the elementary disturbances, induced by an individual microdischarges, wandering along the electrode edge. These disturbances have a streak-like structure in a near field, and evolve into a fan of packets of Tollmien-Schliechting waves as one moves downstream. The streamwise length, needed for transition to modal behavior, depends on the stability properties of the boundary layer.

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22

Meglinski, Igor V., Vladimir L. Kuzmin, Dmitry Y. Churmakov, and Douglas A. Greenhalgh. "Monte Carlo simulation of coherent effects in multiple scattering." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 461, no. 2053 (January 8, 2005): 43–53. http://dx.doi.org/10.1098/rspa.2004.1369.

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Using a combination of the stochastic Monte Carlo technique and the iteration procedure of the solution to the Bethe–Salpeter equation, it has been shown that the simulation of the optical path of a photon packet undergoing an n th scattering event directly corresponds to the n th–order ladder diagram contribution. In this paper, the Monte Carlo technique is generalized for the simulation of the coherent back–scattering and temporal correlation function of optical radiation scattered within the randomly inhomogeneous turbid medium. The results of simulation demonstrate a good agreement with the diffusing wave theory and experimental results.

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23

Mikhailov, Y. A., L. A. Nikitina, G. V. Sklizkov, A. N. Starodub, and M. A. Zhurovich. "Relativistic electron heating in focused multimode laser fields with stochastic phase perturbations." Laser and Particle Beams 26, no. 4 (September 18, 2008): 525–36. http://dx.doi.org/10.1017/s0263034608000566.

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AbstractWe describe a direct model for simulation of relativistic electrons acceleration with a given electromagnetic field which is determined by wave packet parameters. The multimode time-spatial structure of a focused Nd-laser beam with stochastic phase disturbances of each spectral component is taken into account as a source of random forces. Electron energies of more than 10 MeV are obtained even at moderate flux densities of 1016 W/cm2. The developed numerical code makes it possible to obtain a quantitative energy distribution function in relation to both field intensity and the temporal bell-shape of the laser pulse. The efficient heating of electrons can be triggered in the presence of a counter propagating wave being reflected from the critical plasma area with a different reflection coefficient. The heating mechanism occurs with a delay relative to the beginning of the pulse when the laser fields exceed some threshold amplitudes. The qualitative comparison of simulation results with the experimental data is given as evidence that this mechanism is reasonable.

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24

Saalfrank, Peter. "Stochastic wave packet vs. direct density matrix solution of Liouville-von Neumann equations for photodesorption problems." Chemical Physics 211, no. 1-3 (November 1996): 265–76. http://dx.doi.org/10.1016/0301-0104(96)00178-4.

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25

Mandal, Souvik, Fabien Gatti, Oussama Bindech, Roberto Marquardt, and Jean-Christophe Tremblay. "Multidimensional stochastic dissipative quantum dynamics using a Lindblad operator." Journal of Chemical Physics 156, no. 9 (March 7, 2022): 094109. http://dx.doi.org/10.1063/5.0079735.

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In this paper, multidimensional dissipative quantum dynamics is studied within a system–bath approach in the Markovian regime using a model Lindblad operator. We report on the implementation of a Monte Carlo wave packet algorithm in the Heidelberg version of the Multi-Configuration Time-Dependent Hartree (MCTDH) program package, which is henceforth extended to treat stochastic dissipative dynamics. The Lindblad operator is represented as a sum of products of one-dimensional operators. The new form of the operator is not restricted to the MCTDH formalism and could be used with other multidimensional quantum dynamical methods. As a benchmark system, a two-dimensional coupled oscillators model representing the internal stretch and the surface–molecule distance in the O2/Pt(111) system coupled to a Markovian bath of electron–hole-pairs is used. The simulations reveal the interplay between coherent intramolecular coupling due to anharmonic terms in the potential and incoherent relaxation due to coupling to an environment. It is found that thermalization of the system can be approximately achieved when the intramolecular coupling is weak.

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26

Nuckelt, J., M. Schack, and T. Kürner. "Deterministic and stochastic channel models implemented in a physical layer simulator for Car-to-X communications." Advances in Radio Science 9 (August 1, 2011): 165–71. http://dx.doi.org/10.5194/ars-9-165-2011.

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Abstract. This paper presents a physical (PHY) layer simulator of the IEEE 802.11p standard for Wireless Access in Vehicular Environments (WAVE). This simulator allows the emulation of data transmission via different radio channels as well as the analysis of the resulting system behavior. The PHY layer simulator is part of an integrated simulation platform including a traffic model to generate realistic mobility of vehicles and a 3D ray-optical model to calculate the multipath propagation channel between transmitter and receiver. Besides deterministic channel modeling by means of ray-optical modeling, the simulator can also be used with stochastic channel models of typical vehicular scenarios. With the aid of this PHY layer simulator and the integrated channel models, the resulting performance of the system in terms of bit and packet error rates of different receiver designs can be analyzed in order to achieve a robust data transmission.

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27

Cavaletto, Stefano M., Daniel Keefer, Jérémy R. Rouxel, Flavia Aleotti, Francesco Segatta, Marco Garavelli, and Shaul Mukamel. "Unveiling the spatial distribution of molecular coherences at conical intersections by covariance X-ray diffraction signals." Proceedings of the National Academy of Sciences 118, no. 22 (May 28, 2021): e2105046118. http://dx.doi.org/10.1073/pnas.2105046118.

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The outcomes and timescales of molecular nonadiabatic dynamics are decisively impacted by the quantum coherences generated at localized molecular regions. In time-resolved X-ray diffraction imaging, these coherences create distinct signatures via inelastic photon scattering, but they are buried under much stronger background elastic features. Here, we exploit the rich dynamical information encoded in the inelastic patterns, which we reveal by frequency-dispersed covariance ultrafast powder X-ray diffraction of stochastic X-ray free-electron laser pulses. This is demonstrated for the photoisomerization of azobenzene involving the passage through a conical intersection, where the nuclear wave packet branches and explores different quantum pathways. Snapshots of the coherence dynamics are obtained at high frequency shifts, not accessible with conventional diffraction measurements. These provide access to the timing and to the confined spatial distribution of the valence electrons directly involved in the conical intersection passage. This study can be extended to full three-dimensional imaging of conical intersections with ultrafast X-ray and electron diffraction.

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28

O'CONNELL, R. F. "BLACKBODY RADIATION: ROSETTA STONE OF HEAT BATH MODELS." Fluctuation and Noise Letters 07, no. 04 (December 2007): L483—L490. http://dx.doi.org/10.1142/s0219477507004124.

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The radiation field can be regarded as a collection of independent harmonic oscillators and, as such, constitutes a heat bath. Moreover, the known form of its interaction with charged particles provides a "rosetta stone" for deciding on and interpreting the correct interaction for the more general case of a quantum particle in an external potential and coupled to an arbitrary heat bath. In particular, combining QED with the machinery of stochastic physics, enables the usual scope of applications to be widened. We discuss blackbody radiation effects on: the equation of motion of a radiating electron (obtaining an equation of motion which is free from runaway solutions), anomalous diffusion, the spreading of a Gaussian wave packet, and decoherence effects due to zero-point oscillations. In addition, utilizing a formula we obtained for the free energy of an oscillator in a heat bath, enables us to determine all the quantum thermodynamic functions of interest (particularly in the areas of quantum information and nanophysics where small systems are involved) and from which we obtain temperature dependent Lamb shifts, quantum effects on the entropy at low temperature and implications for Nernst's law.

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29

Zhang, Yafei, Bo Li, Q. S. Zheng, Guy M. Genin, and C. Q. Chen. "Programmable and robust static topological solitons in mechanical metamaterials." Nature Communications 10, no. 1 (December 2019). http://dx.doi.org/10.1038/s41467-019-13546-y.

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AbstractSolitary, persistent wave packets called solitons hold potential to transfer information and energy across a wide range of spatial and temporal scales in physical, chemical, and biological systems. Mechanical solitons characteristically emerge either as a single wave packet or uncorrelated propagating topological entities through space and/or time, but these are notoriously difficult to control. Here, we report a theoretical framework for programming static periodic topological solitons into a metamaterial, and demonstrate its implementation in real metamaterials computationally and experimentally. The solitons are excited by deformation localizations under quasi-static compression, and arise from buckling-induced kink-antikink bands that provide domain separation barriers. The soliton number and wavelength demonstrate a previously unreported size-dependence, due to intrinsic length scales. We identify that these unanticipated solitons stem from displacive phase transitions with periodic topological excitations captured by the well-known $${\varphi }^{4}$$φ4 theory. Results reveal pathways for robust regularizations of stochastic responses of metamaterials.

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30

Cavalieri, André V. G., Peter Jordan, and Lutz Lesshafft. "Wave-Packet Models for Jet Dynamics and Sound Radiation." Applied Mechanics Reviews 71, no. 2 (March 1, 2019). http://dx.doi.org/10.1115/1.4042736.

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Organized structures in turbulent jets can be modeled as wavepackets. These are characterized by spatial amplification and decay, both of which are related to stability mechanisms, and they are coherent over several jet diameters, thereby constituting a noncompact acoustic source that produces a distinctive directivity in the acoustic field. In this review, we use simplified model problems to discuss the salient features of turbulent-jet wavepackets and their modeling frameworks. Two classes of model are considered. The first, that we refer to as kinematic, is based on Lighthill's acoustic analogy, and allows an evaluation of the radiation properties of sound-source functions postulated following observation of jets. The second, referred to as dynamic, is based on the linearized, inhomogeneous Ginzburg–Landau equation, which we use as a surrogate for the linearized, inhomogeneous Navier–Stokes system. Both models are elaborated in the framework of resolvent analysis, which allows the dynamics to be viewed in terms of an input–ouput system, the input being either sound-source or nonlinear forcing term, and the output, correspondingly, either farfield acoustic pressure fluctuations or nearfield flow fluctuations. Emphasis is placed on the extension of resolvent analysis to stochastic systems, which allows for the treatment of wavepacket jitter, a feature known to be relevant for subsonic jet noise. Despite the simplicity of the models, they are found to qualitatively reproduce many of the features of turbulent jets observed in experiment and simulation. Sample scripts are provided and allow calculation of most of the presented results.

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31

Huang, Duruo, and Zhuo Wang. "Wavelet-Based Stochastic Model for Jointly Simulating Three-Component Ground Motions." Bulletin of the Seismological Society of America, April 14, 2022. http://dx.doi.org/10.1785/0120200290.

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ABSTRACT A large number of ground motions are needed in performance-based earthquake engineering. To date, most existing stochastic models are limited to simulating a single horizontal component of earthquake motions. This study proposes a wavelet-based stochastic method for jointly simulating three-component accelerograms using earthquake magnitudes, source-to-site distances, and site conditions as input. Based on the Pacific Earthquake Engineering Research Center Next Generation Attenuation (NGA)-West2 database, prediction equations are developed for wavelet-packet parameters of two horizontal and one vertical components. Correlations among these components are obtained to jointly simulate three-component motions based on earthquake scenarios. The simulated ground motions are systematically compared with existing ground-motion attenuation equations. The model has the capability to simulate the different frequency content of horizontal and vertical motions. The simulated vertical-to-horizontal spectral ratios are found to be consistent with observed strong-motion data. The model is applicable to shallow crustal earthquakes in an active tectonic region with a moment magnitude between 5 and 8, source-to-site distance from 0 to 100 km, and shear-wave velocity in the top 30 m (VS30) in the range of 150–1000 m/s. It can find important applications in 3D time-history analyses in performance-based earthquake engineering.

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32

Mousavi, S. V., and S. Miret-Artés. "Stochastic Bohmian mechanics within the Schrödinger-Langevin framework: A trajectory analysis of wave-packet dynamics in a fluctuative-dissipative medium." European Physical Journal Plus 134, no. 6 (June 2019). http://dx.doi.org/10.1140/epjp/i2019-12672-4.

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