Acoustic Resonance Scattering by Submerged Elastic Shells

1990 ◽  
Vol 43 (8) ◽  
pp. 171-208 ◽  
Author(s):  
G. C. Gaunaurd ◽  
M. F. Werby
Keyword(s):  
High Frequency ◽  
Asymptotic Methods ◽  
Resonance Region ◽  
Acoustic Resonance ◽  
Resonance Scattering ◽  
Elastic Shells ◽  
Acoustic Wave Scattering ◽  
Elastic Bodies ◽  
Unbounded Media ◽  
Numerical Approaches

We review a number of instances in which classical acoustic wave scattering from submerged elastic shells can be analyzed in the resonance region of their spectra. We recently reviewed (Refs 42, 43, 12) the cases dealing with acoustic resonance scattering from solid elastic bodies, or with elastic resonance scattering from fluid or solid inclusions in elastic media. It only remains for us to address the works dealing with submerged shells, which we analyze here. We study scattering by bare or viscoelastically coated spherical and cylindrical shells in water, by means of (exact) normal-mode solutions, and by spheroidal shells by numerical approaches, particularly via the T-matrix method. We consider the shell responses mostly in unbounded media and when the interrogating waves are plane and c.w., although some recent findings valid for pulsed incidences and in the vicinity of environmental boundaries are also included. We use the methodology of the resonance scattering theory (RST) as much as possible, emphasizing its post-1981 results. High-frequency findings, obtained by asymptotic methods, are extrapolated to lower frequencies, to confirm RST predictions for the intermediate spectral regions in which the most important structural resonances are known to reside. A large number of bibliographical entries are collected and discussed in connection with our approach.

Elastic and Acoustic Resonance Wave Scattering

1989 ◽  
Vol 42 (6) ◽  
pp. 143-192 ◽  
Author(s):  
Guillermo C. Gaunaurd
Keyword(s):  
Wave Scattering ◽  
Target Identification ◽  
Resonance Region ◽  
Acoustic Resonance ◽  
Resonance Scattering ◽  
Incident Radiation ◽  
Scattering Problems ◽  
Acoustic Wave Scattering ◽  
Resonance Wave ◽  
Time Domains

The present article addresses classical elastic and/or acoustic wave-scattering problems for situations in which the pertinent targets are penetrable. In contrast to impenetrable scatterers, penetrable bodies admit interior fields coupled to the external fields through suitable (sets of) boundary conditions. When the wavelength of the incident radiation is either very long or very short, the scattered echoes returned to an interrogating active sensor can be described in a relatively simple way. This is not the case in the resonance region of the scattering cross section of any penetrable body. This region is sandwiched in between the long-wavelength (Rayleigh) region and the short-wavelength (geometrical) spectral regime. For penetrable (viz, acoustic, elastic, viscoelastic) structures, the resonance region becomes very broad, and results within it are quite difficult to describe analytically, to compute numerically, or to confirm experimentally. Resonance scattering (by definition) implies that the situation at hand occurs within that most troublesome of spectral regimes. We describe a technique particularly useful to simplify and interpret predictions and measurements in the resonance region. This technique exploits the presence of certain “features” clearly observable in the echoes returned by the targets that scatter them. It is by means of these (resonance) features that, for example, different submerged structures can be remotely distinguished from one another. The natural resonances of the structure, not in vacuum, but accounting for its fluid-loaded condition, are communicated to its returned echo in a unique fashion that unambiguously characterizes it as a “fingerprint.” It is always these echoes that we investigate for their “resonance” contents, either in the frequency or time domains. The resonance technique described here, often called the resonance scattering technique (RST), is a linear approximation that makes the understanding of resonance signatures from scatterers not only easier, but possible at all. Results obtainable from strictly classical approaches are so cluttered with information that it is difficult to use them. One simply “cannot see the forest for the trees.” The applications of the RST to various separable and nonseparable configurations are shown. Validating experiments are described, and a bibliography emphasizing the recent target-identification and target-camouflaging aspects of the technique is provided.

Problems of Nonlinear Multiple-Mode Vibrations of Thin Elastic Shells of Revolution

2000 ◽  
Author(s):  
Veniamin D. Kubenko ◽  
Piotr S. Kovalchuk
Keyword(s):  
Degrees Of Freedom ◽  
Asymptotic Methods ◽  
Nonlinear Resonance ◽  
Shells Of Revolution ◽  
Elastic Shells ◽  
Resonance Amplitude ◽  
Multiple Degrees Of Freedom ◽  
Free And Forced Vibrations ◽  
Multiple Mode ◽  
Averaged Equations

Abstract A method is suggested for the calculation of nonlinear free and forced vibrations of thin elastic shells of revolution, which are modeled as dynamic systems of multiple degrees of freedom. Cases are investigated in which the shells are characterized by two or more closely-spaced eigenfrequencies. Based on an analysis of averaged equations, obtained by making use of asymptotic methods of nonlinear mechanics, a number of new first integrals is obtained, which state a regular energy exchange among various modes of cylindrical shells under conditions of nonlinear resonance. Amplitude-frequency characteristics of multiple-mode vibrations are obtained for shells subjected to radial oscillating pressure.

scholarly journals Flame response to high-frequency oscillations in a cryogenic oxygen/hydrogen rocket combustor

2019 ◽  
Author(s):  
N. Fdida ◽  
J. Hardi ◽  
H. Kawashima ◽  
B. Knapp ◽  
M. Oschwald ◽  
...  
Keyword(s):  
High Frequency ◽  
Acoustic Resonance ◽  
High Amplitude ◽  
Operating Conditions ◽  
Test Facility ◽  
Response Analysis ◽  
Rocket Engines ◽  
Acoustic Oscillations ◽  
Spatially Resolved ◽  
Flame Response

Experiments presented in this paper were conducted with the BKH rocket combustor at the European Research and Technology Test Facility P8, located at DLR Lampoldshausen. This combustor is dedicated to study the effects of high magnitude instabilities on oxygen/hydrogen flames, created by forcing high-frequency (HF) acoustic resonance of the combustion chamber. This work addresses the need for highly temporally and spatially resolved visualization data, in operating conditions representative of real rocket engines, to better understand the flame response to high amplitude acoustic oscillations. By combining ONERA and DLR materials and techniques, the optical setup of this experiment has been improved to enhance the existing database with more highly resolved OH* imaging to allow detailed response analysis of the flame. OH* imaging is complemented with simultaneous visible imaging and compared to each other here for their ability to capture flame dynamics.

Simulation And Development Of Electronic Ballast for High Pressure Discharge Lamps

2021 ◽  
pp. 86-92
Author(s):  
Vladimir G. Kulikov ◽  
Albert A. Ashryatov
Keyword(s):  
High Pressure ◽  
High Frequency ◽  
Acoustic Resonance ◽  
High Frequency Current ◽  
Electronic Ballast ◽  
Advantages And Disadvantages ◽  
Test Operation ◽  
Pressure Discharge ◽  
Frequency Current ◽  
High Pressure Discharge

The advantages and disadvantages of using electromagnetic ballasts for power supply of high pressuredischarge lamps (HPDL) are considered. The advantages of using electronic ballasts for supplying HPDL are shown. The analysis is fulfilled of the operation of the HPDL when powered by a high-frequency current, in particular, high-pressure sodium lamps (HPSL). It is indicated that when high-pressure discharge lamps are supplied with a high-frequency current, acoustic resonance may appear. The basic requirements to be met by electronic ballasts for HPSL have been determined. The topology of construction of electronic ballasts for supplying HPDL with a capacity of up to 1 kW has been selected. It has been established that half-bridge converters with inductive ballast and active power factor corrector (PFC) allow maintaining a stable power on the lamp while changing its parameters and efficiency. Mathematical modelling of the electronic ballast based on a half-bridge converter and an ignition device for the sodium discharge lamps DNaT type has been carried out. According to the proposed topology, the electronic ballast was developed for a DNaT 600 lamp powered from the 380 V network. Test operation of the lamps confirmed the reliability of the proposed electronic ballast topology.

The effects of material attenuation on acoustic resonance scattering from cylindrical tubes

Ultrasonics ◽  
1996 ◽  
Vol 34 (7) ◽  
pp. 737-745 ◽  
Author(s):  
Jong Po Lee ◽  
Ji Ho Song ◽  
Myoung Seon Choi
Keyword(s):  
Acoustic Resonance ◽  
Resonance Scattering ◽  
Cylindrical Tubes

A design methodology for acoustic resonance-free, high-frequency, dimmable electronic ballast for high-pressure sodium-vapour lamps

2019 ◽  
Vol 52 (4) ◽  
pp. 524-539
Author(s):  
B Gupta Bakshi ◽  
B Roy
Keyword(s):  
High Pressure ◽  
High Frequency ◽  
Design Methodology ◽  
Power Level ◽  
Harmonic Distortion ◽  
Acoustic Resonance ◽  
Electrical Characteristics ◽  
Electronic Ballast ◽  
Lamp Current ◽  
Sodium Vapour

This paper presents a methodology to design acoustic resonance-free, high-frequency, dimmable electronic ballasts for high-pressure sodium vapour (HPSV) lamps having a range of rated wattage (70–400 W). After estimation of the ‘quiet window’ of an HPSV lamp, the proposed iterative algorithm is able to determine the acoustic resonance-free driving frequencies of a design ballast corresponding to 50%–100% power level. On the other hand, a developed wattage and voltage independent HPSV lamp model facilitates finding the required electrical characteristics of HPSV lamps without performing laboratory experimentation. Using the estimated driving frequencies of a design ballast and the synthesized electrical characteristics of the lamp, the design circuit parameters of an electronic ballast are determined. Performance evaluation of the designed ballasts, carried out on the Matlab–Simulink platform, indicates several important attributes, viz. higher power control accuracy (deviation ≤3.69%), near-unity lamp power factor (≥0.98), lower lamp current crest factor (<1.7) and lower lamp current total harmonic distortion (≤12.63%). Results establish the effectiveness of the proposed design methodology to design lightweight and compact electronic ballasts for HPSV lamps with less effort than conventional design practice.

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