scholarly journals Advanced time domain wave‐number sensing for structural acoustic systems. Part III. Experiments on active broadband radiation control of a simply supported plate

1995 ◽  
Vol 98 (5) ◽  
pp. 2613-2621 ◽  
Author(s):  
J. P. Maillard ◽  
C. R. Fuller
Keyword(s):  
Time Domain ◽  
Wave Number ◽  
Simply Supported ◽  
Radiation Control ◽  
Broadband Radiation

An inverse scattering method in time-domain electromagnetics

1981 ◽  
Vol 59 (10) ◽  
pp. 1348-1353
Author(s):  
Sujeet K. Chaudhuri
Keyword(s):  
Inverse Scattering ◽  
Time Domain ◽  
Random Noise ◽  
Power Series Expansion ◽  
Inverse Scattering Method ◽  
Wave Number ◽  
Moment Condition ◽  
Scattering Method ◽  
Fourth Moment ◽  
Rayleigh Coefficient

An inverse scattering model, based on the time-domain concepts of electromagnetic theory is developed. Using the first five (zeroth to fourth) moment condition integrals, the Rayleigh coefficient and the next higher order nonzero coefficient of the power series expansion in k (wave number) of the object backscattering response are recovered. The Rayleigh coefficient and the other coefficient thus recovered are used (with the ellipsoidal assumption for the object shape) to determine the dimensions and orientation of the object.Some numerical results of the application of this coefficient recovery technique to conducting ellipsoidal scatterers are presented. The performance of the software system in the presence of normally distributed random noise is also studied.

Vibrations of rotating cylindrical shells with functionally graded material using wave propagation approach

2018 ◽  
Vol 232 (23) ◽  
pp. 4342-4356 ◽  
Author(s):  
Muzammal Hussain ◽  
M Nawaz Naeem ◽  
Aamir Shahzad ◽  
Mao-Gang He ◽  
Siddra Habib
Keyword(s):  
Wave Propagation ◽  
Natural Frequencies ◽  
Volume Fraction ◽  
Cylindrical Shells ◽  
Functionally Graded ◽  
Wave Number ◽  
Type I ◽  
Rotating Speed ◽  
Simply Supported ◽  
Fundamental Frequencies

Fundamental natural frequencies of rotating functionally graded cylindrical shells have been calculated through the improved wave propagation approach using three different volume fraction laws. The governing shell equations are obtained from Love’s shell approximations using improved rotating terms and the new equations are obtained in standard eigenvalue problem with wave propagation approach and volume fraction laws. The effects of circumferential wave number, rotating speed, length-to-radius, and thickness-to-radius ratios have been computed with various combinations of axial wave numbers and volume fraction law exponent on the fundamental natural frequencies of nonrotating and rotating functionally graded cylindrical shells using wave propagation approach and volume fraction laws with simply supported edge. In this work, variation of material properties of functionally graded materials is controlled by three volume fraction laws. This process creates a variation in the results of shell frequency. MATLAB programming has been used to determine shell frequencies for traveling mode (backward and forward) rotating motions. New estimations show that the rotating forward and backward simply supported fundamental natural frequencies increases with an increase in circumferential wave number, for Type I and Type II of functionally graded cylindrical shells. The presented results of backward and forward simply supported fundamental natural frequencies corresponding to Law I are higher than Laws II and III for Type I and reverse effects are found for Type II, depending on rotating speed. Our investigations show that the decreasing and increasing behaviors are noted for rotating simply supported fundamental natural frequencies with increasing length-to-radius and thickness-to-radius ratios, respectively. It is found that the fundamental frequencies of the forward waves decrease with the increase in the rotating speed, and the fundamental frequencies of the backward waves increase with the increase in the rotating speed. This investigation has been made with three different volume fraction laws of polynomial (Law I), exponential (Law II), and trigonometric (Law III). The presented numerical results of nonrotating isotropic and rotating functionally graded simply supported are in fair agreement with parts of other earlier numerical results.

Eigenfrequencies of Continuous Plates With Arbitrary Number of Equal Spans

1979 ◽  
Vol 46 (3) ◽  
pp. 656-662 ◽  
Author(s):  
Isaac Elishakoff ◽  
Alexander Sternberg
Keyword(s):  
Arbitrary Number ◽  
Wave Number ◽  
Analytical Technique ◽  
Simply Supported ◽  
Isotropic Plates ◽  
Simple Support ◽  
Transcendental Equations ◽  
Rigid Supports ◽  
Numerical Complexity

An approximate analytical technique is developed for determination of the eigenfrequencies of rectangular isotropic plates continuous over rigid supports at regular intervals with arbitrary number of spans. All possible combinations of simple support and clamping at the edges are considered. The solution is given by the modified Bolotin method, which involves solution of two problems of the Voigt-Le´vy type in conjunction with a postulated eigenfrequency/wave-number relationship. These auxiliary problems yield a pair of transcendental equations in the unknown wave numbers. The number of spans figures explicitly in one of the transcendental equations, so that numerical complexity does not increase with the number of spans. It is shown that the number of eigenfrequencies associated with a given pair of mode numbers equals that of spans. The essential advantage of the proposed method is the possibility of finding the eigenfrequencies for any prescribed pair of mode numbers. Moreover, for plates simply supported at two opposite edges and continuous over rigid supports perpendicular to those edges, the result is identical with the exact solution.

Time-domain study of transient fields for a thin circular loop antenna

2002 ◽  
Vol 80 (9) ◽  
pp. 995-1003 ◽  
Author(s):  
S T Bishay ◽  
G M Sami
Keyword(s):  
Time Domain ◽  
Analytical Form ◽  
Loop Antenna ◽  
Inverse Laplace Transform ◽  
Wave Number ◽  
Earth Model ◽  
Circular Loop ◽  
Wave Forms ◽  
Displacement Currents ◽  
The Time Domain

The transient fields in the time-domain of a thin circular loop antenna on a two-layer conducting earth model are expressed in analytical form. In these expressions, the displacement currents both in the two-layer ground and in the air region are taken into consideration. The closed-form expressions of the time-domain are obtained as the inverse Laplace transform of the derived full-wave time-harmonic solution. These time-domain solutions are obtained as a summation of wave-guide modes plus contributions from branch cuts in the complex plane of the longitudinal wave number. Numerical examples are given to indicate the important features in the wave forms of the surface fields due to step and pulsed current excitation. These features provide the means of detecting the earth's stratification, measuring the overburden height, and determining the ratio of the conductivities of the layers. PACS Nos.: 41.20Jb, 42.25Bs, 42.25Gy, 44.05+e

Effect of Winkler and Pasternak elastic foundation on the vibration of rotating functionally graded material cylindrical shell

2018 ◽  
Vol 232 (24) ◽  
pp. 4564-4577 ◽  
Author(s):  
Muzamal Hussain ◽  
Muhammad Nawaz Naeem ◽  
Mohammad Reza Isvandzibaei
Keyword(s):  
Cylindrical Shell ◽  
Boundary Conditions ◽  
Elastic Foundation ◽  
Natural Frequencies ◽  
Cylindrical Shells ◽  
Functionally Graded ◽  
Radius Ratio ◽  
Wave Number ◽  
Simply Supported ◽  
Elastic Foundations

In this paper, vibration characteristics of rotating functionally graded cylindrical shell resting on Winkler and Pasternak elastic foundations have been investigated. These shells are fabricated from functionally graded materials. Shell dynamical equations are derived by using the Hamilton variational principle and the Langrangian functional framed from the shell strain and kinetic energy expressions. Elastic foundations, namely Winkler and Pasternak moduli are inducted in the tangential direction of the shell. The rotational motions of the shells are due to the Coriolis and centrifugal acceleration as well as the hoop tension produced in the rotating case. The wave propagation approach in standard eigenvalue form has been employed in order to derive the characteristic frequency equation describing the natural frequencies of vibration in rotating functionally graded cylindrical shell. The complex exponential functions, with the axial modal numbers that depend on the boundary conditions stated at edges of a cylindrical shell, have been used to compute the axial modal dependence. In our new investigation, frequency spectra are obtained for circumferential wave number, length-to-radius ratio, height-to-radius ratio with simply supported–simply supported and clamped–clamped boundary conditions without elastic foundation. Also, the effect of elastic foundation on the rotating cylindrical shells is examined with the simply supported–simply supported edge. To check the validity of the present method, the fundamental natural frequencies of non-rotating isotropic and functionally graded cylindrical shells are compared with the open literature. Also, a comparison is made for infinitely long rotating with the earlier published paper.

BENCHMARK SOLUTIONS FOR 3-D SCATTERING FROM CYLINDRICAL INCLUSIONS

2001 ◽  
Vol 09 (04) ◽  
pp. 1311-1327 ◽  
Author(s):  
ANTÓNIO J. B. TADEU ◽  
LUIS M. C. GODINHO ◽  
JULIETA M. P. ANTÓNIO
Keyword(s):  
Time Domain ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Wave Number ◽  
Simple Geometry ◽  
Nonaxisymmetric Wave ◽  
Cylindrical Inclusions ◽  
Boundary Elements Method ◽  
Scattered Fields ◽  
Benchmark Solutions

The solutions for two-dimensional diffracting objects with simple geometry such as a cylindrical inclusion are frequently used as benchmark solutions to test the accuracy of numerical schemes, such as the Finite Elements Method and the Boundary Elements Method, and to better understand the wave propagation around inclusions. The importance of having benchmark solutions available is greater in the case of the evaluation of three-dimensional scattered fields, given its increase in complexity. In this work, analytical-numerical solutions are used to evaluate the three-dimensional wave field elicited by monopole sources in the vicinity of a fluid-filled cylindrical cavity drilled through an unbounded homogeneous elastic medium. This model is used to assess the effects of the position of the source and receiver, on the propagation of both axisymmetric and nonaxisymmetric wave modes. Both frequency versus axial-wave number responses and time-domain transients are presented.

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