Mutual Validation of a Fast Solver Based on the Multilevel Nonuniform Grid Approach and an Asymptotic Approximation for High-Frequency Scattering by Strongly Elongated Spheroids

2020 ◽  
Author(s):  
Evgeny V. Chernokozhin ◽  
Ivan V. Andronov ◽  
Amir Boag
Keyword(s):  
High Frequency ◽  
Asymptotic Approximation ◽  
Nonuniform Grid ◽  
Fast Solver ◽  
Grid Approach

A uniform asymptotic approximation for high-frequency unsteady cascade flow

1995 ◽  
Vol 449 (1935) ◽  
pp. 177-186 ◽  
Keyword(s):  
High Frequency ◽  
Asymptotic Approximation ◽  
Model Problem ◽  
Noise Generation ◽  
Flat Plates ◽  
Infinite Products ◽  
Cascade Flow ◽  
Reduced Frequency ◽  
Physical Insight ◽  
Exact Factorization

The scattering of harmonic gusts by a two-dimensional, infinite cascade of flat plates is a model problem which is relevant to the prediction of noise generation by rotating turbomachinery. The problem can be solved analytically using the Wiener‒Hopf technique, and the key step involves the exact factorization of a certain generic kernel function, K , using infinite products. An approximate fac­torization, based on the realistic asymptotic limit of large reduced frequency, has been derived by Peake, and this approach has the advantages of both providing more physical insight and being significantly easier to compute than the exact factors. An important limitation of Peake’s approximation, however, is that it be­ comes invalid when any of the acoustic modes in the system are close to cut-off, and in this paper we therefore present new asymptotic factors which overcome this non-uniformity. The accuracy of this new approximation, across a whole range of operating parameters, is demonstrated by comparison with the exact results, with typical errors of the order of only 3% even for very modest values of the reduced frequency.

scholarly journals CFD Research on the Hydrodynamic Performance of Submarine Sailing near the Free Surface with Long-Crested Waves

2022 ◽  
Vol 10 (1) ◽  
pp. 90
Author(s):  
Kai Dong ◽  
Xianzhou Wang ◽  
Donglei Zhang ◽  
Liwei Liu ◽  
Dakui Feng
Keyword(s):  
Free Surface ◽  
High Frequency ◽  
Control Strategies ◽  
Response Spectrum ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
High Frequency Region ◽  
Irregular Wave ◽  
Grid Approach ◽  
Calm Water

The simulations of submarine sailing near the free surface with long-crested waves have been conducted in this study using an in-house viscous URANS solver with an overset grid approach. First, the verification and validation procedures were performed to evaluate the reliability, with the results showing that the generation of irregular waves is adequately accurate and the results of total resistance are in good agreement with EFD. Next, three different submerged depths ranging from 1.1D to 3.3D were selected and the corresponding conditions of submarine sailing near calm water were simulated, the results of which were then compared with each other to investigate the influence of irregular waves and submerged depths. The simulations of the model near calm water at different submerged depths demonstrated that the free surface will cause increasing resistance, lift, and bow-up moments of the model, and this influence decreases dramatically with greater submerged depths. The results of the irregular wave simulations showed that irregular waves cause considerable fluctuations of hydrodynamic force and moments, and that this influence remains even at a deeper submerged depth, which can complicate the control strategies of the submarine. The response spectrum of hydrodynamic forces and moments showed slight amplitudes in the high-frequency region, and the model showed less sensitivity to high-frequency excitations.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

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