High-frequency analysis of Gaussian beam scattering by a two-dimensional parabolic contour of finite width

Radio Science ◽  
1995 ◽  
Vol 30 (3) ◽  
pp. 493-503 ◽  
Author(s):  
Hristos T. Anastassiu ◽  
Prabhakar H. Pathak
Keyword(s):  
Gaussian Beam ◽  
Frequency Analysis ◽  
High Frequency ◽  
Finite Width ◽  
Two Dimensional ◽  
Beam Scattering

Transient Vibrations of Two-Dimensional Beam Frames at Mid- and High-Frequencies

2019 ◽  
Author(s):  
Yichi Zhang ◽  
Bingen Yang
Keyword(s):  
Frequency Analysis ◽  
High Frequency ◽  
Transfer Functions ◽  
Flexible Structures ◽  
Frame Structure ◽  
Inverse Laplace Transform ◽  
Two Dimensional ◽  
Beam Structure ◽  
Element Analysis ◽  
High Frequencies

Abstract Transient vibrations of flexible structures at mid- and high-frequencies have important applications in aerospace, civil, auto and ship engineering. In this paper, a new method is developed for the determination of the transient vibration solutions of two-dimensional beam frames in mid- and high-frequency regions. In the development, the governing equations of a beam frame structure are formulated by an augmented Distributed Transfer Function Method (DTFM), without the need for discretization and approximation. The augmented DTFM differs from the traditional DTFM in that it does not contain the singularities of subsystem transfer functions, which is crucially important in a mid- or high-frequency analysis. The proposed method delivers exact eigensolutions of a beam structure from low- to high-frequencies without numerical instability. With the platform provided by the augmented DTFM, the transient response of a beam structure can be conveniently estimated by either modal expansion or the residue formula for inverse Laplace transform. A highlight of the augmented DTFM lies in that detailed information at mid- and high-frequencies, such as local displacement, slope, bending moment and shear force at any point, can be obtained, which otherwise may be difficult with conventional methods for mid- and high-frequency analysis. The proposed method is illustrated on several examples and is computationally efficient and stable from low- to high-frequency regions. In the numerical simulation, the augmented DTFM is shown to produce more accurate results than traditional finite element analysis (FEA). The proposed method is extensible to three-dimensional beam structures.

A New Approach to Transient Vibration Analysis of Two-Dimensional Beam Structures at Medium and High Frequencies

2020 ◽  
Vol 15 (9) ◽  
Author(s):  
Bingen Yang ◽  
Yichi Zhang
Keyword(s):  
Frequency Analysis ◽  
High Frequency ◽  
Vibration Analysis ◽  
Local Information ◽  
Two Dimensional ◽  
Transient Vibration ◽  
Beam Structures ◽  
High Frequencies ◽  
Analysis Tools ◽  
Internal Forces

Abstract Transient analysis of medium-frequency (mid-frequency) and high-frequency vibrations plays an important role in the research and development of complex structures in aerospace, automobile, civil, mechanical, and ship engineering. Low-frequency analysis tools, like the finite element methods, do not work well for mid- and high-frequency problems because they require a huge number of degrees-of-freedom and consequently costly computation, and are sensitive to material properties and boundary conditions. High-frequency analysis tools, such as the statistical energy analysis (SEA) and its variations, are unsuitable for midfrequency problems because they describe the vibrational behaviors of multibody structures in a global manner and cannot provide detailed local information about displacements and internal forces. In this paper, a new method, which is called the augmented distributed transfer function method (DTFM), is proposed for transient vibration analysis of two-dimensional beam structures at medium and high frequencies. Without the need for discretization and numerical integration, the augmented DTFM consistently delivers analytical transient solutions from low to high-frequency regions. A unique feature of the proposed method is that it can provide local information about system response, such as the displacements and internal forces of a structure, at any point and in any frequency region. Additionally, the proposed method provides a platform for model reduction, by which, a balance of efficiency and accuracy in mid- and high-frequency analyses can be achieved. The proposed method is demonstrated in numerical examples.

Despeckling of Sar Images Using Shrinkage of Two-Dimensional Discrete Orthonormal S-Transform

2020 ◽  
pp. 2150023
Author(s):  
Priya R. Kamath ◽  
Kedarnath Senapati ◽  
P. Jidesh
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Relevant Information ◽  
Detection Algorithm ◽  
Two Dimensional ◽  
Sar Images ◽  
S Transform ◽  
Processing Step ◽  
Frequency Components ◽  
Shock Filter

Speckles are inherent to SAR. They hide and undermine several relevant information contained in the SAR images. In this paper, a despeckling algorithm using the shrinkage of two-dimensional discrete orthonormal S-transform (2D-DOST) coefficients in the transform domain along with shock filter is proposed. Also, an attempt has been made as a post-processing step to preserve the edges and other details while removing the speckle. The proposed strategy involves decomposing the SAR image into low and high-frequency components and processing them separately. A shock filter is used to smooth out the small variations in low-frequency components, and the high-frequency components are treated with a shrinkage of 2D-DOST coefficients. The edges, for enhancement, are detected using a ratio-based edge detection algorithm. The proposed method is tested, verified, and compared with some well-known models on C-band and X-band SAR images. A detailed experimental analysis is illustrated.

High Frequency Analysis of the Vivaldi Antenna Parameters

2020 ◽  
Author(s):  
Claudia Constantinescu ◽  
Calin Munteanu ◽  
Laura Grindei ◽  
Adina Giurgiuman ◽  
Claudia Pacurar ◽  
...  
Keyword(s):  
Frequency Analysis ◽  
High Frequency ◽  
Vivaldi Antenna
Sign in / Sign up

Export Citation Format

Share Document