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    Wyświetlanie 1-6 z 6
    Tytuł:
    Surface Waves along the Martian Ionopause
    Autorzy:
    Chmielewski, P.
    Murawski, K.
    Kumar, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1400415.pdf
    Data publikacji:
    2013-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    94.20.wh
    96.30.Gc
    Opis:
    We study the behaviour of surface waves propagating along the ionopause of the planet Mars and derive the onset criteria for unstable Kelvin-Helmholtz modes and negative energy waves at the Martian ionopause. Growth rate of unstable Kelvin-Helmholtz mode decreases with wavelength. The backward propagating waves became negative energy waves for the ionosheath velocity higher than critical velocity. It is found that short wavelength surface waves propagating along the Martian ionopause are less dispersive than long waves.
    Źródło:
    Acta Physica Polonica A; 2013, 123, 1; 156-161
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    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
    Tytuł:
    Impulsively Generated Linear and Non-Linear Alfvén Waves in the Coronal Funnels
    Autorzy:
    Chmielewski, P.
    Srivastava, A.
    Murawski, K.
    Musielak, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1195963.pdf
    Data publikacji:
    2014-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    96.60.P-
    96.60.pc
    Opis:
    We present simulation results of the impulsively generated linear and non-linear Alfvén waves in the weakly curved coronal magnetic flux-tubes (coronal funnels) and discuss their implications for the coronal heating and solar wind acceleration. We solve numerically the time-dependent magnetohydrodynamic equations to find the temporal signatures of the small and large-amplitude Alfvén waves in the model atmosphere of open and expanding magnetic field configuration with a realistic temperature distribution. We compute the maximum transversal velocity of both linear and non-linear Alfvén waves at different heights of the model atmosphere, and study their response in the solar corona during the time of their propagation. We infer that the pulse-driven non-linear Alfvén waves may carry sufficient wave energy fluxes to heat the coronal funnels and also to power the solar wind that originates in these funnels. Our study of linear Alfvén waves shows that they can contribute only to the plasma dynamics and heating of the funnel-like magnetic flux-tubes associated with the polar coronal holes.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 1; 158-164
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    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 the effect of time-dependent random mass density field on frequencies of sound waves
    Autorzy:
    Murawski, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955804.pdf
    Data publikacji:
    2001
    Wydawca:
    Politechnika Gdańska
    Tematy:
    numerical simulations
    convection - Sun
    oscillations - turbulence
    time-dependent random mass density field
    space-dependent random field
    Opis:
    Numerical simulations of the effect of random mass density field on frequencies of sound waves are considered for driven and impulsive sound waves which are described by one-dimensional hydrodynamic equations, with the ponderomotive force which depends stochastically both on space and time. The numerical results reveal frequency increase for short waves and both wave damping and amplification for the overall range of wavenumbers. Moreover, a space- and time-dependent random field leads to a generation of a wide frequency spectrum which contains both retarded and speeded up waves.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2001, 5, 2; 229-238
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-6 z 6

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