Near‐field ray acoustic response of submerged elastic spherical shells

1994 ◽  
Vol 96 (1) ◽  
pp. 525-535 ◽  
Author(s):  
Jin‐Meng Ho
Keyword(s):  
Near Field ◽  
Acoustic Response ◽  
Spherical Shells

Theoretical and Numerical Investigations of Acoustic Response of a Multiperforated Plate for Combustor Liners

2015 ◽  
Author(s):  
V. Popie ◽  
E. Piot ◽  
S. Tordeux ◽  
F. Vuillot
Keyword(s):  
Film Cooling ◽  
Near Field ◽  
Perforated Plate ◽  
Combustion Instabilities ◽  
Acoustic Response ◽  
Combustion Chambers ◽  
Perforated Plates ◽  
Numerical Investigations ◽  
Definition Of ◽  
Physical Quantities

Multiperforated plates are used in combustion chambers for film cooling purpose. As the knowledge of the acoustic response of the chamber is essential for preventing combustion instabilities, the acoustic behaviour of the perforated plates has to be modeled. This can be done either by considering the transmission impedance of the plates, or their Rayleigh conductivity. In this paper, the link between these two values is given in the frame of matched asymptotic expansions. Especially the far-field or near-field nature of the physical quantities used in the definition of the impedance and Rayleigh quantity is enlighted. Direct numerical simulations of the propagation of an acoustic plane wave through a perforated plate are performed and post-treated so that the assumptions underlying the definitions of impedance and Rayleigh conductivity are checked.

A Linearized Unsteady Aerodynamic Analysis for Real Blade Supersonic Cascades

1997 ◽  
Vol 119 (4) ◽  
pp. 686-694
Author(s):  
M. D. Montgomery ◽  
J. M. Verdon ◽  
S. Fleeter
Keyword(s):  
Flat Plate ◽  
Numerical Stability ◽  
Near Field ◽  
Axial Flow ◽  
Acoustic Response ◽  
Unsteady Aerodynamic ◽  
Field Solution ◽  
Blade Cascade ◽  
Impulsive Loads ◽  
Blade Row

The prediction capabilities of a linearized unsteady potential analysis have been extended to include supersonic cascades with subsonic axial flow. The numerical analysis of this type of flow presents several difficulties. First, complex oblique shock patterns exist within the cascade passage. Second, the acoustic response is discontinuous and propagates upstream and downstream of the blade row. Finally, a numerical scheme based on the domain of dependence is required for numerical stability. These difficulties are addressed by developing a discontinuity capturing scheme and matching the numerical near-field solution to an analytical far-field solution. Comparisons with semi-analytic results for flat plate cascades show that reasonable predictions of the unsteady aerodynamic response at the airfoil surfaces are possible, but aeroacoustic response calculations are difficult. Comparisons between flat plate and real blade cascade results show that one effect of real blades is the impulsive loads due to motion of finite strength shocks.

On the Influence of a Rigid Circular Inclusion on the Twisting and Shearing of a Shallow Spherical Shell

1980 ◽  
Vol 47 (3) ◽  
pp. 586-588 ◽  
Author(s):  
E. Reissner
Keyword(s):  
Near Field ◽  
Circular Inclusion ◽  
Interior Solution ◽  
Far Field ◽  
Stress Concentrations ◽  
Spherical Shells ◽  
Edge Zone ◽  
Field Behavior ◽  
Membrane Type ◽  
Rigid Circular Inclusion

Known results for plates with rigid inclusions are complemented by explicit asymptotic solutions of the corresponding problems for sufficiently thin spherical shells. An important element of the analysis is recognition of the fact that in addition to the distinction between interior and edge zone solution contributions there is a significant distinction between near-field and far-field behavior of the interior solution, with the nature of this distinction depending on the nature of the boundary conditions which are prescribed. In the event that near-field behavior is of the membrane type and far-field behavior of the inextensional bending type, or vice versa, much higher stress concentrations occur than without such change in interior solution behavior.

scholarly journals A Linearized Unsteady Aerodynamic Analysis for Real Blade Supersonic Cascades

1996 ◽  
Author(s):  
Matthew D. Montgomery ◽  
Joseph M. Verdon ◽  
Sanford Fleeter
Keyword(s):  
Flat Plate ◽  
Numerical Stability ◽  
Near Field ◽  
Axial Flow ◽  
Acoustic Response ◽  
Unsteady Aerodynamic ◽  
Field Solution ◽  
Blade Cascade ◽  
Impulsive Loads ◽  
Blade Row

The prediction capabilities of a linearized unsteady potential analysis have been extended to include supersonic cascades with subsonic axial flow. The numerical analysis of this type of flows presents several difficulties. First, complex oblique shock patterns exist within the cascade passage. Second, the acoustic response is discontinuous and propagates upstream and downstream of the blade row. Finally, a numerical scheme which is based on the domain of dependence is required for numerical stability. These difficulties are addressed by developing a discontinuity capturing scheme and matching the numerical near-field solution to an analytical far-field solution. Comparisons with semi-analytic results for flat plate cascades show that reasonable predictions of the unsteady aerodynamic response at the airfoil surfaces are possible, but aeroacoustic response calculations are difficult. Comparisons between flat plate and real blade cascade results show that one effect of real blades is the impulsive loads due to motion of finite strength shocks.

Near-field scanning optical microscopy

1986 ◽  
Vol 44 ◽  
pp. 642-643
Author(s):  
E. Betzig ◽  
A. Harootunian ◽  
M. Isaacson ◽  
A. Lewis
Keyword(s):  
Near Field ◽  
Optical Microscope ◽  
Visible Radiation ◽  
Field Methods ◽  
Optical Elements ◽  
Optical Region ◽  
Order Of Magnitude ◽  
Nondestructive Imaging ◽  
Scanning Optical Microscopy ◽  
Near Field Scanning

In general, conventional methods of optical imaging are limited in spatial resolution by either the wavelength of the radiation used or by the aberrations of the optical elements. This is true whether one uses a scanning probe or a fixed beam method. The reason for the wavelength limit of resolution is due to the far field methods of producing or detecting the radiation. If one resorts to restricting our probes to the near field optical region, then the possibility exists of obtaining spatial resolutions more than an order of magnitude smaller than the optical wavelength of the radiation used. In this paper, we will describe the principles underlying such "near field" imaging and present some preliminary results from a near field scanning optical microscope (NS0M) that uses visible radiation and is capable of resolutions comparable to an SEM. The advantage of such a technique is the possibility of completely nondestructive imaging in air at spatial resolutions of about 50nm.

Principles of Planar Near-Field Antenna Measurements

2007 ◽  
Author(s):  
Stuart Gregson ◽  
John McCormick ◽  
Clive Parini
Keyword(s):  
Near Field ◽  
Antenna Measurements
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