Insertion loss of periodic cylindrical shells with helical slit

2021 ◽  
Vol 69 (3) ◽  
pp. 199-208
Author(s):  
Karisma Mohapatra ◽  
Dibya Prakash Jena
Keyword(s):  
Band Structure ◽  
Insertion Loss ◽  
Cylindrical Shells ◽  
Slit Width ◽  
Sharp Peak ◽  
Acoustic Attenuation ◽  
High Frequencies ◽  
Local Resonance ◽  
Resonance Band

We propose periodic shells with helical slit to overcome the lacuna in periodic C scatterers, where the first Bragg band is considerably reduced on increasing width of the slit. The key discovery of this research indicates that, by changing the upright slit of the C scatterers to helical slits, larger insertion loss (IL) is achieved around the first Bragg band without compromising the local resonance band. Comparing the performance of periodic shells without slit or cylindrical scatterers, it is found that IL becomes larger at first Bragg band. The pitch, thickness of the shell and width of helical slit can be altered to adjust the resonance of the proposed shells. On decreasing the pitch or increasing the slit width, the resonance band shifts toward high frequencies without much alteration in acoustic attenuation of bandwidth. Additionally, below threshold pitch, the said peak merges with first Bragg band and broadens with prominent IL. The calculated band structure authenticates the bandwidth of the first Bragg band, and the additional sharp peak in IL can be attributed to local resonance of the periodic scatterers.

Acoustic and Vibration Characteristics of Stiffened Finite Cylindrical Shells in Water under Multiple Axial-Excitations

2013 ◽  
Vol 662 ◽  
pp. 721-725
Author(s):  
Qi Zheng Zhou ◽  
De Shi Wang ◽  
Sheng Yao Gao
Keyword(s):  
Analytical Solution ◽  
Shell Theory ◽  
Acoustic Pressure ◽  
Acoustic Radiation ◽  
Cylindrical Shells ◽  
High Frequencies ◽  
Acoustic Coupling ◽  
Coupling Equations ◽  
Vibration And Sound Radiation ◽  
Thin Shell Theory

A research on the vibration and acoustic radiation of stiffened finite cylindrical shells in water under a multiple axial-excitations driven was presented. The vibro-acoustic coupling equations of shell under multiple axial-excitations based on Flügge thin shell theory were established. The displacements, surface acoustic pressure and stiffener impedances were expressed in terms of the numbers of normal modals and modes, and considering multiple excitations, the forces were expressed in terms of the numbers of normal modals and modes. Then analytical solution was derived for the vibration and sound radiation from the stiffened shell under multiple excitations. Based on the analytical solution, the influences of excitations’ positions to the vibration and acoustic radiation were investigated. The results show that for double excitations, at high frequencies, the distance between excitations was more large, the average velocity was more low. The results could be used to control the underwater vehicle’s vibration and acoustic radiation.

Research on local resonance and Bragg scattering coexistence in phononic crystal

2017 ◽  
Vol 31 (11) ◽  
pp. 1750127 ◽  
Author(s):  
Yake Dong ◽  
Hong Yao ◽  
Jun Du ◽  
Jingbo Zhao ◽  
Jiulong Jiang
Keyword(s):  
Band Gap ◽  
Mass Density ◽  
Resonance Effect ◽  
Phononic Crystal ◽  
Broad Band ◽  
Low Frequency ◽  
Bragg Scattering ◽  
Low Frequencies ◽  
Local Resonance ◽  
Resonance Band

Based on the finite element method (FEM), characteristics of the local resonance band gap and the Bragg scattering band gap of two periodically-distributed vibrator structures are studied. Conditions of original anti-resonance generation are theoretically derived. The original anti-resonance effect leads to localization of vibration. Factors which influence original anti-resonance band gap are analyzed. The band gap width and the mass ratio between two vibrators are closely correlated to each other. Results show that the original anti-resonance band gap has few influencing factors. In the locally resonant structure, the Bragg scattering band gap is found. The mass density of the elastic medium and the elasticity modulus have an important impact on the Bragg band gap. The coexistence of the two mechanisms makes the band gap larger. The band gap covered 90% of the low frequencies below 2000 Hz. All in all, the research could provide references for studying the low-frequency and broad band gap of phononic crystal.

Effectiveness of neoprene pad vibration isolators at high frequencies

2021 ◽  
Vol 263 (4) ◽  
pp. 2172-2183
Author(s):  
Jerry Lilly
Keyword(s):  
Natural Frequency ◽  
Insertion Loss ◽  
Dynamic Stiffness ◽  
Degree Of Freedom ◽  
Frequency Wave ◽  
Single Degree Of Freedom ◽  
High Frequencies ◽  
Vibration Isolators ◽  
Single Degree ◽  
Wide Range

The natural frequency, dynamic stiffness, and insertion loss of commercially available neoprene pad vibration isolators have been measured in a simple, single degree of freedom system over a wide range of pad loadings out to a maximum frequency of 10 kHz. The results reveal that dynamic stiffness can vary significantly with pad loading as well as the durometer of the material. It will also be shown that insertion loss follows the theoretical single degree of freedom curve only out to a frequency that is about 5 to 10 times the natural frequency, depending upon the pad durometer rating. Above that frequency wave resonances in the material cause the insertion loss to deteriorate significantly out to a frequency near 1 kHz, above which the insertion loss maintains a relatively constant value, again depending upon the pad durometer rating. In some instances the insertion loss values can approach 0 dB or even become negative at specific frequencies in the frequency region that is 10 to 20 times the natural frequency of the system.

Wave Motion in Periodic Flexural Beams and Characterization of the Transition Between Bragg Scattering and Local Resonance

2011 ◽  
Vol 79 (1) ◽  
Author(s):  
Liao Liu ◽  
Mahmoud I. Hussein
Keyword(s):  
Wave Propagation ◽  
Band Structure ◽  
Band Gap ◽  
Frequency Band ◽  
Band Gaps ◽  
Flexural Wave ◽  
Propagation Mechanism ◽  
Bragg Scattering ◽  
Frequency Spectra ◽  
Local Resonance

Band gaps appear in the frequency spectra of periodic materials and structures. In this work we examine flexural wave propagation in beams and investigate the effects of the various types and properties of periodicity on the frequency band structure, especially the location and width of band gaps. We consider periodicities involving the repeated spatial variation of material, geometry, boundary and/or suspended mass along the span of a beam. In our formulation, we implement Bloch’s theorem for elastic wave propagation and utilize Timoshenko beam theory for the kinematical description of the underlying flexural motion. For the calculation of the frequency band structure we use the transfer matrix method, derived here in generalized form to enable separate or combined consideration of the different types of periodicity. Our results provide band-gap maps as a function of the type and properties of periodicity, and as a prime focus we identify and mathematically characterize the condition for the transition between Bragg scattering and local resonance, each being a unique wave propagation mechanism, and show the effects of this transition on the lowest band gap. The analysis presented can be extended to multi-dimensional phononic crystals and acoustic metamaterials.

A Study of Axisymmetric Vibrations of Cylindrical Shells as Affected by Rotatory Inertia and Transverse Shear

1956 ◽  
Vol 23 (2) ◽  
pp. 255-261
Author(s):  
T. C. Lin ◽  
G. W. Morgan
Keyword(s):  
Transverse Shear ◽  
Circular Tube ◽  
Cylindrical Shells ◽  
Rotatory Inertia ◽  
High Frequencies ◽  
Additional Mode ◽  
Velocity Of Propagation

Abstract An analysis is presented of the problem of the propagation of axisymmetric waves in an elastic circular tube. The theory includes the effects of rotatory inertia and transverse shear in the same manner as does Timoshenko’s theory of the vibrations of bars. These effects are of importance for waves at high frequencies; they tend to decrease the velocity of propagation and introduce an additional mode due to shear.

Resonance identifications in Saturn’s rings

1984 ◽  
Vol 75 ◽  
pp. 349-359
Author(s):  
M.E. Wiesel ◽  
F.A. Franklin
Keyword(s):  
Band Structure ◽  
Resonance Band ◽  
Saturn’S Rings ◽  
F Ring ◽  
Saturn's Rings

AbstractWhen Saturn’s oblateness perturbations are included, a single classical resonance splits into a resonance band structure. We have derived expressions for resonance location, libration region width, and the maximum librator range. We compare these predictions to areas of the C and B rings, the Cassini division, and the F ring, and offer some thoughts on possible mechanisms involved.

The Use of Rigidity Properties in Cylindrical Shells for Noise Reduction

2006 ◽  
Vol 113 ◽  
pp. 259-264
Author(s):  
R. Butkus ◽  
J. Deikus ◽  
Danielius Gužas ◽  
A. Šarlauskas
Keyword(s):  
Dynamic Theory ◽  
Cylindrical Shells ◽  
Variable Coefficients ◽  
Theory Of Elasticity ◽  
Theoretical Research ◽  
Sound Insulation ◽  
Slight Reduction ◽  
Low Frequencies ◽  
High Frequencies ◽  
Radiated Noise

The present paper deals with methods aimed at developing calculation models of sound insulation of various cylindrical shells, making it possible to estimate the shell-radiated noise levels. The proposed methodology is based on the mathematical analysis of the cylindrical shell as an element that is subordinated to the equation of dynamic theory of elasticity of thin-walled constructions of variable rigidity. The work provides the corresponding controls of dynamic theory of elasticity in partial derivatives with variable coefficients. Theoretical research and calculations carried out show that sound insulation under analysis at low frequencies is quite high. A slight reduction of sound insulation at high frequencies conditioned by wave processes is also considered.

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