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    Wyświetlanie 1-5 z 5
    Tytuł:
    Numerical simulations of sound wave generation in a random medium
    Autorzy:
    Murawski, K.
    Selwa, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955700.pdf
    Data publikacji:
    2004
    Wydawca:
    Politechnika Gdańska
    Tematy:
    sound waves
    random waves
    frequency shift
    amplitude alteration
    Opis:
    In turbulent media, both sound wave sources and the speed of sound can be stochastic variables. By means of numerical simulations of one-dimensional Euler equations with random source terms we have studied two cases in a homogeneous stochastic random medium for which the speed of sound and sound sources are: (1) correlated and (2) uncorrelated. The numerical simulations indicate that, if the source and the speed of sound fluctuations are uncorrelated, the acoustic field is incoherent, with a zero expectation value. The mean field is non-zero in the correlated case. The correlated and uncorrelated cases are clearly distinguishable by the mean field, but also - to some extent - in the power spectrum, which displays a modified Lorentzian profile with a shift in frequency.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2004, 8, 1; 109-114
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Sound waves in a wave noise
    Autorzy:
    Murawski, K.
    Tarnowski, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955702.pdf
    Data publikacji:
    2004
    Wydawca:
    Politechnika Gdańska
    Tematy:
    sound waves
    random waves
    frequency shift
    amplitude alteration
    Opis:
    We examine by analytical and numerical means sound waves which propagate in a space- and time-dependent random mass density field in the form of dispersionless wave noise of its spectrum E(kappa,omega) ~ E(kappa) delta (omega-crk), where cr is a random speed. Numerical simulations are in agreement with the analytical theory which shows that at cr=omega/k resonance occurs and the cyclic frequency omega tends to infinity. For values of cr which are close to the resonance point, the sound waves are slowed down and attenuated (accelerated and amplified) for cr < omega/k (cr > omega/k).
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2004, 8, 1; 103-108
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Numerical simulations of Alfv´en waves in the solar atmosphere with the PLUTO code
    Autorzy:
    Wołoszkiewicz, P.
    Murawski, K.
    Musielak, Z. E.
    Mignone, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/205850.pdf
    Data publikacji:
    2014
    Wydawca:
    Polska Akademia Nauk. Instytut Badań Systemowych PAN
    Tematy:
    MHD
    Alfv´en waves
    Opis:
    With an adaptation of the PLUTO code, we present a 2.5-dimensional Cartesian magnetohydrodynamic model with the invariant (∂/∂z = 0) coordinate z of propagating magnetohydrodynamic- gravity waves in the solar atmosphere, permeated by curved magnetic field and constant gravity field g = −gˆy. This code implements second-order accurate Godunov-type numerical scheme and MPI for high level of parallelization. We show that the inhomogeneous grid, originally built in the code, resolves well the system dynamics, resulting from the localized pulse initially launched in the transverse component of velocity Vz. We consider two cases for background magnetic field Be = [Bex,Bey,Bez] with its transverse component: (a) Bez = 0 and (b) Bez 6= 0. In case (a), the initial pulse triggers only Alfv´en waves, described solely by Vz. These waves drive by ponderomotive forces the magnetoacoustic waves, associated with perturbations in Vx and Vy. As a result of Bez 6= 0, in the (b) case, Alfv´en waves are coupled to their magnetoacoustic counterparts and all three velocity components are perturbed. We show that in this case the PLUTO code is accurate, its order being 1.97 and the numerically induced flow is of magnitude ≈ 0.1 km s−1, i.e. by a factor of at least ≈ 103 lower than the characteristic (Alfv´en) speed of the system. The errors, associated with the selenoidal condition, are low with the max |∇ ・ B| ≈ 1.3 ・ 10−10 Tesla km−1. We conclude that the PLUTO code copes well with resolving all spatial and temporal scales that appear in this numerically challenging system.
    Źródło:
    Control and Cybernetics; 2014, 43, 2; 321-335
    0324-8569
    Pojawia się w:
    Control and Cybernetics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The influence of wave-noise on wave speeds and amplitudes of surface-gravity waves
    Autorzy:
    Murawski, K.
    Zawada, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1954094.pdf
    Data publikacji:
    2004
    Wydawca:
    Politechnika Gdańska
    Tematy:
    random waves
    dispersion relation
    wave-noise
    Opis:
    We have analytically examined surface-gravity waves which propagate in space- and time-dependent random velocity fields. Using a perturbative method, we have derived a dispersion relation which is solved for the case of wave-noise whose spectrum E(k,omega) ~ E(k)delta(omega-crk), where delta is Dirac's delta-function and cr is the random phase speed. We have found that for a dispersionless noise resonance occurs when cr is equal to the group velocity cg of the surface-gravity wave. In this resonance the real part of the wave frequency is finite, but its imaginary part exhibits the characteristic 1/x singularity. The wave-noise interacts with a packet of the surface-gravity waves in such a way that the waves are attenuated for cr < cg and are amplified for cr > cg. As the real part is positive for high values of k, the surface-gravity waves are accelerated by the wave-noise.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2004, 8, 3; 321-326
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Numerical simulations of acoustic waves with the graphic acceleration GAMER code
    Autorzy:
    Murawski, K.
    Schive, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/201677.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    numerical simulation
    acoustic waves
    graphic acceleration GAMER code
    Opis:
    We present results of numerical simulations of acoustic waves with the use of the Graphics Processing Unit (GPU) acceleration GAMER code which implements a second-order Godunov-type numerical scheme and adaptive mesh refinement (AMR). The AMR implementation is based on constructing a hierarchy of grid patches with an octree data structure. In this code a hybrid model is adopted, in which the time-consuming solvers are dealt with GPUs and the complex AMR data structure is manipulated by Central Processing Units (CPUs). The code is highly parallelized with the Hilbert space-filling curve method. These implementations allow us to resolve well desperate spatial scales that are associated with acoustic waves. We show that a localized velocity (gas pressure) pulse that is initially launched within a uniform and still medium triggers acoustic waves simultaneously with a vortex (an entropy mode). In a flowing medium, acoustic waves experience amplitude growth or decay, a scenario which depends on a location of the flow and relative direction of wave propagation. The amplitude growth results from instabilities which are associated with negative energy waves.
    Źródło:
    Bulletin of the Polish Academy of Sciences. Technical Sciences; 2012, 60, 4; 787-792
    0239-7528
    Pojawia się w:
    Bulletin of the Polish Academy of Sciences. Technical Sciences
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-5 z 5

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