Wyniki wyszukiwania - BazTech

1

Edge waves over a shelf

Dolai P., Dolai D. P.

International Journal of Applied Mechanics and Engineering

|

2019

|

Vol. 24, no. 2

453--460

EN

The problem considered in this paper is the derivation of properties of edge waves travelling along a submerged horizontal shelf. The problem is formulated within the framework of the linearized theory of water waves and Havelock expansions of water wave potentials are used in the mathematical analysis to obtain the dispersion relation for edge waves in terms of an integral. Appropriate multi-term Galerkin approximations involving ultra spherical Gegenbauer polynomials are utilized to obtain a very accurate numerical estimate for the integral and hence to derive the properties of edge waves over a shelf. The numerical results are illustrated in a table and curves are presented showing the variation of frequency of the edge waves with the width of the shelf.

2

Properties of low frequency TE-electromagnetic wave in ternary plasma photonic crystal

Dehnavi Z. N., Askari H. R., Malekshahi M., Dorranian D.

Optica Applicata

|

2017

|

Vol. 47, nr 3

457--470

EN

In this study, the oblique incident of the electromagnetic waves with frequencies lower than plasma frequency in one dimensional ternary plasma photonic crystal has been investigated. The unit cell of crystal contains a plasma layer that is embedded in two different dielectric layers. Using the wave equation, Bloch theory, and boundary condition, the dispersion relation, the group velocity and the reflection relation of the structure have been obtained. Numerical results are presented in the form of dispersion curves. The dependence of photonic band gap characteristics on plasma frequency is discussed. One attempt has been made to show how the photonic band gap characteristic of a particular structure changes when the dielectric material of the unit cell is replaced by other dielectric materials or when the incident angle of the electromagnetic wave is changed. Results show that plasma layer characteristics has a significant effect on band gaps and wave propagation characteristics; also the results show that the proposed multi-layered structure can act as a tunable photonic crystal which can be controlled by the external parameters.

3

Modeling and seismic migration in anisotropic media as a function of azimuthal angle – HTI(Ψ)

Kostecki A., Żuławiński K.

Nafta-Gaz

|

2016

|

R. 72, nr 9

679--690

EN

In this paper, we present a new way of modeling in an anisotropic medium based on a pseudo-acoustic one-way equation, derived from the full equations system of elasticity using eigenvalues of dispersion equation – time-frequency. The method was shown on the examples of signals propagation in anisotropic medium HTI(Ψ) (Horizontal Transverse Isotropy) as function of azimuthal angle Ψ and zero-offset time sections for anticline model. The correctness of the modeling results was verified by new migration MG(F-K) in wavenumbers (K) – frequency (F) domain with a depth operator of extrapolation, which uses a vertical wavenumber derived from dispersion relation.

PL

W artykule przedstawiono nowy sposób modelowania w ośrodkach anizotropowych, bazujący na jednostronnym równaniu falowym wyprowadzonym z pełnego systemu równań sprężystości i stosującym wartości własne równania dyspersyjnego tj. czasową częstotliwość. Metoda została zaprezentowana na przykładach propagacji w ośrodkach HTI(Ψ) (Horizontal Transverse Isotropy) w funkcji kątów azymutalnych Ψ oraz na sekcjach zero-offset dla modelu antykliny. Poprawność rezultatów modelowania została zweryfikowana za pośrednictwem migracji MG(F-K) w dziedzinie liczb falowych (K) i częstotliwości (F) stosującej operator głębokościowej ekstrapolacji z użyciem pionowej liczby falowej wyprowadzonej z relacji dyspersyjnej.

4

Estimation of acoustically induced refractive index perturbation in silicon and germanium slab for optical applications

Sharma G., Kumar S., Kumar D., Singh V.

Optica Applicata

|

2015

|

Vol. 45, nr 4

491--500

EN

In-plane displacement field and refractive index variation for silicon and germanium in the presence of Lamb wave is estimated for optical applications. The required dispersion equation in a thin silicon and germanium plates is obtained using the method of potentials with boundary conditions involving the bulk and surface stress of the materials considered. The eigen-values thus obtained are used to compute the Lamb wave modes for the slab of silicon and germanium at same thickness. The fundamental anti-symmetric and symmetric plate modes and their overtones are observed due to confinement of acoustic energy within the slab thickness. In addition, the excited symmetric modes in silicon have longer wavelengths than those of germanium at a fixed frequency. Therefore, the refractive index modulation through the Lamb wave in silicon is always larger as compared to that of germanium. This refractive index modulation can be treated as periodic sinusoidal refractive index variation and may be considered as a tunable one-dimensional photonics crystal.

5

The pseudo-acoustic equations of the scalar wavefield in anisotropic media

Kostecki A., Żuławiński K.

Nafta-Gaz

|

2015

|

R. 71, nr 11

811--815

EN

In this paper we present a new formulation of scalar pseudo-acoustic wave equation in arbitrary anisotropic media TI (Transverse Isotropy) type for 2D and 3D cases. These equations, based on precise dispersion relation, determine eigenvalue – temporal frequency as the function of wavenumber and anisotropy parameters. Here we present a few snapshots obtained for different signals by one-way equation.

PL

W artykule przedstawiono nowe sformułowanie skalarnych pseudospektralnych równań falowych w dowolnych ośrodkach anizotropowych typu TI (Transverse Isotropy) dla przypadków 2D i 3D. Równania bazują na dyspersyjnych relacjach wyznaczających wartości własne – częstotliwości w funkcji liczb falowych i parametrów anizotropii na podstawie pełnego systemu równań akustycznych. Zaprezentowano kilka przypadków propagacji falowej określonej jednostronnym równaniem w formie migawkowych zdjęć dla różnych typów sygnału.

6

Plasmonic abilities of gold and silver spherical nanoantennas in terms of size dependent multipolar resonance frequencies and plasmon damping rates

Kolwas K., Derkachova A.

Opto-Electronics Review

|

2010

|

Vol. 18, No. 4

429-437

EN

Absorbing and emitting optical properties of a spherical plasmonic nanoantenna are described in terms of the size dependent resonance frequencies and damping rates of the multipolar surface plasmons (SP). We provide the plasmon size characteristics for gold and silver spherical particles up to the large size retardation regime where the plasmon radiative damping is significant. We underline the role of the radiation damping in comparison with the energy dissipation damping in formation of receiving and transmitting properties of a plasmonic particle. The size dependence of both: the multipolar SP resonance frequencies and corresponding damping rates can be a convenient tool in tailoring the characteristics of plasmonic nanoantennas for given application. Such characteristics enable to control an operation frequency of a plasmonic nanoantenna and to change the operation range from the spectrally broad to spectrally narrow and vice versa. It is also possible to switch between particle receiving (enhanced absorption) and emitting (enhanced scattering) abilities. Changing the polarization geometry of observation it is possible to effectively separate the dipole and the quadrupole plasmon radiation from all the non-plasmonic contributions to the scattered light.

7

The properties of coupled waves propagating in long suspended cables

Snamina J.

Journal of Theoretical and Applied Mechanics

|

2008

|

Vol. 46 nr 4

973-992

EN

In this paper, the properties of coupled waves travelling along a long cable are analysed. Since the tension and curvature in the equilibrium position of the cable are slowly varying functions of the arc co-ordinate, the problems concerning the travelling waves can be solved using the Wentzel-Kramers-Brillouin (WKB) method. The waves propagating in the plane of the equilibrium curve are coupled. The wave associated with displacements perpendicular to the plane is uncoupled from the remaining waves. Applying the WKB method, the dispersion relation and equations describing the amplitudes of waves are determined. For a longitudinal-dominated pair of waves, there exist two cut-off frequencies depending on the arc co-ordinate. The results of calculations of wavelengths and amplitudes are presented in the form of plots.

PL

W pracy przedstawiono analizę własności fal mechanicznych rozprzestrzeniających się w linach o znacznej długości. W liniowej teorii fale rozchodzące się w płaszczyźnie zwisu są ze sobą sprzężone, a fala wywołująca przemieszczenia punktów liny w kierunku prostopadłym do płaszczyzny zwisu rozprzestrzenia się niezależnie od pozostałych fal. W rozważaniach uwzględniono wolno-zmienną zależność siły osiowej i krzywizny od współrzędnej łukowej, w położeniu równowagi statycznej liny. Zagadnienia dotyczące przemieszczających się wzdłuż przewodu fal rozwiązano metodą WKB (Wentzel-Kramers-Brillouin).Wyznaczono związki dyspersyjne charakteryzujące ruch falowy w linach, wyprowadzono prędkości fazowe i grupowe z uwzględnieniem sprzężenia fal rozchodzących się w płaszczyźnie zwisu. Analizie poddano zależność liczb falowych oraz amplitud od współrzędnej łukowej. W rozważaniach wykorzystano symetrię ruchu fal. Wyniki obliczeń zostały zobrazowane na szeregu wykresach.

8

Efficient calculations of dispersive properties of phonic crystals using the transmission line matrix method

Romo G., Smy T.

Optica Applicata

|

2005

|

Vol. 35, nr 1

139-154

EN

In this paper, we present an analysis of the accuracy and efficiency of different approaches for the simulation of photonic crystals using the transmission line matrix method. The approaches that we present can be divided into two categories: complex- and real-valued algorithms using a uniform mesh, and complex- and real-valued algorthms using a multigrid mesh. The adventages and disadvantages of each approach are discussed and a brief comparision between these methods is made from the points of view of computqtional expense and accuracy. It is found that a combination of a real-valued method in a multigrid mesh results in the most efficient algorithm. However, while the complex-valued formulation is valid for the analysis of any phonic crystal, the applicability of the real-valued formulation is limited by structural constraints requiring cell symmetries. It is also found that a multigrid approach can considerably reduce the computational cost required for simulating phonic crystals and our results indicate that a good compromise between accuracy and computational cost can be found. Various photonic crystals are simulated by applying these approaches, and the results are validated using alternative methods.

9

The influence of wave-noise on wave speeds and amplitudes of surface-gravity waves

Murawski K., Zawada A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2004

|

Vol. 8, No 3

321-326

EN

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.

10

Instability and the formation of bubbles and the plugs in fluidized beds

Schulz P.

Opuscula Mathematica

|

2004

|

Vol. 24, no. 1

133-159

EN

This is an review paper, particulary concentrate on results not many researches by reason that are explain in the text. We consider stability of disperse, two-phase flow (gas-solid particles or liquid-solid particles) linear and non-linear. In particular we discuss the result of Anderson, Sundareson and Jackson (1995) [3] that for vertical dispersion flow one- and two-dimensional, they attack problem growing disturbances directly by numerical integration of equations of motion from given initial conditions (using computer Cray C-90). In principle, this would allow authors to explore all aspects of dynamical behaviour of fluidized beds. It is interesting mechanism of periodic plug describing by Anderson et al. and attest by other researchers. Second part of paper is more general, dedicate the problem of linear stability of uniformly fluidized state ("fluidized bed"). We make the most important stages of calculations (after to Jackson (2000) [23]) and demonstrate that the majority (but not all) of fluidized beds with parameters having technical importance is unstable, or stable in narrow interval of wave numbers k.