scholarly journals Far- and near-field approximation for diffraction radiation

2013 ◽  
Vol 309 ◽  
pp. 194-197
Author(s):  
V. Shpakov ◽  
S.B. Dabagov ◽  
M. Castellano ◽  
A. Cianchi ◽  
K. Honkavaara ◽  
...  
Keyword(s):  
Near Field ◽  
Field Approximation ◽  
Diffraction Radiation

Second-Order Difference-Frequency Loads on FPSOs by Full QTF and Relevant Approximations

2020 ◽  
Author(s):  
Espen Engebretsen ◽  
Zhiyuan Pan ◽  
Nuno Fonseca
Keyword(s):  
Near Field ◽  
Time Domain Analysis ◽  
Second Order ◽  
Difference Frequency ◽  
Irregular Waves ◽  
Mooring Line ◽  
Diffraction Radiation ◽  
Surface Integral ◽  
Order Difference ◽  
Order Diffraction

Abstract This paper investigates three different approximations of the full Quadratic Transfer Function (QTF) for calculating horizontal plane second-order difference-frequency loads on FPSOs, namely Newman’s approximation, full QTF without free surface integral and the white-noise approximation. Second-order excitation loads obtained from approximated QTFs are compared in frequency-domain with those obtained by the full QTFs computed from second-order diffraction/radiation analysis in WADAM. The comparison is performed for a new-build FPSO in a range of water depths and environmental combinations. The full QTFs from second-order diffraction/radiation analysis are further compared to empirical QTFs as identified from cross bi-spectral analysis of model test results in irregular waves. A mesh convergence study is presented for calculating full QTFs by the near-field approach in a second-order diffraction/radiation analysis. The importance of including viscous damping in heave, roll and pitch is illustrated for the mean wave-drift force in surge and sway. FPSO motions and mooring line tensions from fully-coupled time-domain analysis in OrcaFlex is compared when using approximated QTFs and full QTFs from second-order diffraction/radiation analysis.

scholarly journals Optical bistability in two-dimensional nonlinear composites of coated cylinders with nonlinear core and graded shell

2020 ◽  
Vol 7 ◽  
pp. 6
Author(s):  
Ya M. Wu ◽  
Guo Q. Chen ◽  
Wen C. Wu ◽  
Yi X. Wang ◽  
Yang Huang
Keyword(s):  
Optical Bistability ◽  
Near Field ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Geometrical Parameters ◽  
Core Radius ◽  
The Core ◽  
Nonlinear Composite ◽  
Incident Frequency

The intrinsic optical bistability of the nonlinear composite consisting of coated cylinders with nonlinear core and graded Drude shell is investigated with self-consistent mean-field approximation. We derive the nonlinear equation of near field for such graded composite in the quasistatic limit. We demonstrate that the bistability threshold and the bistable width are highly dependent on the core radius, the incident frequency, and the graded coefficient of the coated cylinder inclusion. It is found that the optical bistability appears only when the core radius and the incident frequency satisfy some specific conditions. Therefore, the optical bistability for nonlinear composite materials may be optimized by the suitable adjustment of the physical and geometrical parameters. Our results may be helpful for the design of the nonlinear device with appropriate bistability.

Numerical Evaluation of Free-Surface Green Functions

1994 ◽  
Vol 38 (03) ◽  
pp. 193-202
Author(s):  
B. Ponizy ◽  
F. Noblesse ◽  
M. Ba ◽  
M. Guilbaud
Keyword(s):  
Coordinate Transformation ◽  
Near Field ◽  
Finite Domain ◽  
Diffraction Radiation ◽  
Green Functions ◽  
Offshore Structure ◽  
Local Flow ◽  
Ship Waves ◽  
Function Transformation ◽  
Singular Functions

A very simple and efficient method for computing the nonoscillatory near-field terms in the expressions for the Green functions, and their gradients, for wave diffraction/radiation by an offshore structure and steady ship waves in deep water is presented. The Green functions are decomposed into three terms corresponding to simple (Rankine) singularities, wave fields, and nonoscillatory near-field (local) flow components. The method which is presented for approximating the latter nonoscillatory near-field components is based on the use of a coordinate-transformation and a function-transformation. The coordinate-transformation maps the unbounded domain of definition of the Green function into a finite domain (unit square or cube) of transformed coordinates. The function-transformation expresses the near-field components, which are singular at the origin, in terms of functions that are regular everywhere. Proper coordinate and function transformations reduce the problem of approximating singular functions in unbounded domains into that of approximating smoothly varying functions within finite domains. The latter task can be accomplished in a number of ways, including the use of linear table interpolation presented in the study.

Near Field Representations of the Acoustic Green's Function in a Shallow Ocean with Fluid-Like Seabed

2007 ◽  
Vol 14 (1) ◽  
pp. 109-123
Author(s):  
Robert Gilbert ◽  
Miao-Jung Ou
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Near Field ◽  
Sound Field ◽  
Hankel Transform ◽  
Field Approximation ◽  
Construction Scheme ◽  
Stratified Ocean ◽  
Asymptotic Representations ◽  
Layer Waveguide

Abstract In this paper, the near-field approximation of the acoustic Green's function in a two-layer waveguide is constructed by using a variation of the method of Ahluwalia and Keller [Exact and asymptotic representations of the sound field in a stratified ocean, Springer, 1977]. The relation between the constructed multiple-scattering representation (suitable for near-field) and the Hankel transform representation (suitable for mid-range) is also discussed in this paper. The construction scheme presented in this paper can be generalized for an N-layer waveguide.

Scattering by a surface inhomogeneity on an elastic half-space, with application to fluid-structure interaction noise

1990 ◽  
Vol 429 (1876) ◽  
pp. 203-226 ◽  
Keyword(s):  
Turbulent Flow ◽  
Half Space ◽  
Near Field ◽  
Elastic Solid ◽  
Viscous Sublayer ◽  
Elastic Half Space ◽  
Diffraction Radiation ◽  
Frequency Spectra ◽  
Low Mach Number ◽  
Surface Inhomogeneity

A harmonic point source is situated in fluid bounded by a nominally plane interface with an elastic half-space. The source is close to a small protrusion of the elastic medium into the fluid, and it is required to determine the interaction (‘diffraction’) radiation, i. e. the acoustic, elastic-body and surface (Scholte) waves produced by the scattering of the near field of the source by the protrusion. The solution of this canonical problem is applied to the prediction of acoustic and structural noise generated by low Mach number turbulent flow over an inhomogeneity on the boundary of an elastic solid. Estimates are presented of the frequency spectra of the power delivered to the various wave modes and their dependence on the elastic properties of the solid, and a comparison is made with empirical predictions of excitation of the same modes in the absence of the inhomogeneity. The scattered radiation can be significant even when the surface inhomogeneity does not penetrate beyond the viscous sublayer into the turbulent flow.

A method for determining the effective conductivity of dispersions of particles

1990 ◽  
Vol 430 (1879) ◽  
pp. 285-313 ◽  
Keyword(s):  
Effective Conductivity ◽  
Near Field ◽  
Field Approximation ◽  
Spherical Particles ◽  
Far Field ◽  
Particle Interactions ◽  
Stokesian Dynamics ◽  
System A ◽  
Method Formulation ◽  
Capacitance Matrix

A general method is developed to predict the effective conductivity of an infinite, statistically homogeneous suspension of particles in an arbitrary (ordered or disordered) configuration. The method follows closely that of ‘stokesian dynamics’, and captures both far-field and near-field particle interactions accurately with no convergence difficulties. This is accomplished by forming a capacitance matrix, the electrostatic analogue of the low-Reynolds-number resistance matrix, which relates the monopole (charge), dipole and quadrupole of the particles to the potential held of the system. A far-field approximation to the capacitance matrix is formed via a moment expansion of the integral equation for the potential. The capacitance matrix of the infinite system is limited to finite number of equations by using periodic boundary conditions, and the Ewald method is used to form rapidly converging lattice sums of particle interactions. To include near-field effects, exact two-body interactions are added to the far-field approximation of the capacitance matrix. The particle dipoles are then calculated directly to determine the effective conductivity of the system. The Madelung constant of cohesive energy of ionic crystals is calculated for simple and body-centred cubic lattices as a check on the method formulation. The results are found to be in excellent agreement with the accepted values. Also, the effective conductivities of spherical particles in cubic arrays are calculated for particle to matrix conductivity ratios of infinity, 10 and 0.01.

Infrared Radiative Properties of Thin Polyethylene Coating Pigmented With Titanium Dioxide Particles

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Mehdi Baneshi ◽  
Shigenao Maruyama ◽  
Atsuki Komiya
Keyword(s):  
Particle Size ◽  
Volume Fraction ◽  
Near Field ◽  
Field Approximation ◽  
Anisotropic Scattering ◽  
Radiative Properties ◽  
Emission Model ◽  
Tio2 Pigment ◽  
Pigmented Coatings ◽  
Thin Polyethylene

The infrared (IR) radiative properties of TiO2 pigment particles must be known to perform thermal analysis of a TiO2 pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO2 particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7–15 μm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings.

CHERENKOV RADIATION INDUCED BY COSMOGENIC NEUTRINOS IN NEAR-FIELD

2013 ◽  
Vol 28 (02) ◽  
pp. 1340006
Author(s):  
CHIA-YU HU ◽  
CHIH-CHING CHEN ◽  
PISIN CHEN
Keyword(s):  
Near Field ◽  
Fdtd Method ◽  
Field Approximation ◽  
High Energy ◽  
Dense Medium ◽  
Numerical Code ◽  
Peak Structure ◽  
Alternative Approach ◽  
Radiation Induced ◽  
Difference Time

The radio technique of cosmogenic neutrino detection, which relies on the Cherenkov signals coherently emitted from the particle showers in dense medium, has now become a mature field. We present an alternative approach to calculate such Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method that does not rely on the far-field approximation. We show that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, the generated Cherenkov signal will always be a bipolar and asymmetric waveform in the near-field regime regardless of the specific variations of the multi-peak structure, which makes it a generic and distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.

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