scholarly journals Faster Calculation of the Low-Frequency Radiated Sound Power of Underwater Slender Cylindrical Shells

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Rui Tang ◽  
He Tian ◽  
Dajing Shang
Keyword(s):  
Cylindrical Shell ◽  
Cylindrical Shells ◽  
Low Frequency ◽  
Sound Radiation ◽  
Sound Power ◽  
Radiation Characteristics ◽  
Calculation Process ◽  
Radiated Sound ◽  
Stiffened Cylindrical Shells ◽  
Radiated Sound Power

Based on the fact that beam-type modes play the main role in determining the sound radiation from an underwater thin slender (length-to-radius ratio L/a>20) elastic cylindrical shell, an equivalent-beam method is proposed for calculating the low-frequency radiated sound power of underwater thin slender unstiffened and stiffened cylindrical shells. The natural bending frequencies of the cylindrical shell are calculated by analytical and numerical methods and used to solve equivalent Young’s modulus of the equivalent beam. This approach simplifies the vibration problem of the three-dimensional cylindrical shell into that of a two-dimensional beam, which can be used to simplify the calculation process of radiated sound power. Added mass is used to approximate the fluid-structure coupling, further simplifying the calculation process. Calculation examples of underwater simply supported unstiffened and stiffened cylindrical shells verify the proposed method by comparison with analytical and numerical results. Finally, the effects of the size and spacing of the stiffeners on the sound radiation characteristics of underwater free-free stiffened cylindrical shells are discussed. The proposed method can be extended to the rapid calculation of the sound radiation characteristics of underwater slender complex cylindrical shells in the low-frequency range.

scholarly journals Prediction of Sound Radiation from Submerged Cylindrical Shell Based on Dominant Modes

2020 ◽  
Vol 10 (9) ◽  
pp. 3073 ◽  
Author(s):  
Chao Zhang ◽  
Sihui Li ◽  
Dejiang Shang ◽  
Yuyuan Han ◽  
Yuyang Shang
Keyword(s):  
Cylindrical Shell ◽  
Radiation Power ◽  
Cylindrical Shells ◽  
Low Frequency ◽  
Sound Radiation ◽  
Radiation Efficiency ◽  
Frequency Sound ◽  
Comparison Results ◽  
Sound Radiation Efficiency ◽  
Sound Radiation Power

A sound radiation calculation method by using dominant modes is proposed to predict the sound radiation from a cylindrical shell. This method can provide an effective way to quickly predict the sound radiation of the structure by using as few displacement monitoring points as possible on the structure surface. In this paper, modal analyses of a submerged cylindrical shell are carried out by taking the vibration mode of a cylindrical shell in a vacuum, as a set of orthogonal bases. The modal sound radiation efficiency and modal contributions to sound radiation power are presented, and comparison results show that a few modes dominantly contribute to the sound radiation power at low frequencies. These modes, called dominantly radiated structural modes in this paper, are applied to predict the sound radiation power of submerged cylindrical shells by obtaining the modal participant coefficients and sound radiation efficiency of these dominant modes. Aside from the orthogonal decomposition method, a method of solving displacement modal superposition equations is proposed to extract the modal participant coefficients, because few modes contribute to the vibration displacement near the resonant frequencies. Some simulations of cylindrical shells with different boundaries are conducted, and the number of measuring points required are examined. Results show that this method, based on dominant modes, can well predict the low-frequency sound radiation power of submerged cylindrical shells. In addition, compared with the boundary element method, this method can better reduce the number of required measuring points significantly. The data of these important modes can be saved, which can help to predict the low-frequency sound radiation of the same structure faster in the future.

Relation Between Structural Intensity-Based Scalars and Sound Radiation Using the Example of Plate-Rib Models

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Clarissa Schaal ◽  
Johannes Ebert ◽  
Joachim Bös ◽  
Tobias Melz
Keyword(s):  
Objective Function ◽  
Energy Flow ◽  
Vibrational Energy ◽  
Sound Radiation ◽  
Specific Region ◽  
Sound Power ◽  
Structural Intensity ◽  
Radiated Sound ◽  
Very High ◽  
Radiated Sound Power

The ability of the structural intensity (STI) to predict changes in the sound radiation of structures due to geometric modifications is investigated using the academic example of plate-rib models. All models consist of the same plate and are modified by attaching a rib, whose position, orientation, and length are varied. Various scalar quantities are derived from the STI and quantitatively compared to the equivalent radiated sound power (ERP) for each model. Based on this comparison the relation between the STI-based scalars and the ERP is studied to determine an STI-based scalar that can serve as the objective function for numerical structural optimizations. The influence of the rib parameters on the most promising STI-based scalar is analyzed by means of a variance-based sensitivity analysis. The STI pattern of those models with very high and very low ERP values are additionally analyzed to describe the characteristics of STI. The results of this study indicate that the STI pattern of models with low ERP has paths and vortices that can be more clearly identified compared to those in models with high ERP. The angular orientation of the rib has by far the highest influence on changes in STI and ERP. The results reveal a correlation between the energy flow into a specific region of a structure, an STI-based scalar, and the ERP. Therefore, the vibrational energy flow can indeed serve as an objective function for numerical structural optimizations aiming at reducing the sound radiation.

Sound Radiation Response of a Rectangular Plate Having a Side Crack of Arbitrary Length, Orientation, and Position

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Tanmoy Bose ◽  
Amiya R. Mohanty
Keyword(s):  
Rectangular Plate ◽  
Ritz Method ◽  
Sound Radiation ◽  
Radiation Efficiency ◽  
Sound Power ◽  
Cracked Plate ◽  
Side Crack ◽  
Radiated Sound ◽  
Radiated Sound Power ◽  
Element Method

Here, sound radiation characteristics of a rectangular plate having a side crack of different crack lengths, orientations, and positions are studied considering clamped boundary conditions. First, a free and forced vibration response analysis of a cracked plate is done using the Ritz method. Orthogonal polynomials are used for faster convergence and some corner functions are used to generate the effect of a crack. Radiated sound power and radiation efficiency of the cracked plate are computed by the quadruple integration. A convergence test of radiation efficiency is carried out to fix the number of polynomials and corner functions in the analysis. It is found that the radiation efficiency and radiated sound power computed by the Ritz method are close to the same obtained from the boundary element method (BEM). The natural frequencies computed using the Ritz method are also found to be close to that obtained from the finite element method (FEM). The radiation efficiency curves of different modes are shown for a change in crack length, orientation and position. Finally, the variations of normalized sound power are shown to be due to a change in the crack parameters.

Sound Radiation From Beams Under the Action of Moving Line Forces

1988 ◽  
Vol 55 (4) ◽  
pp. 849-854
Author(s):  
R. F. Keltie ◽  
H. Peng
Keyword(s):  
Low Frequency ◽  
Sound Radiation ◽  
Sound Power ◽  
Fluid Loading ◽  
Moving Force ◽  
Asymptotic Expressions ◽  
Line Force ◽  
Applied Forces ◽  
Radiated Sound ◽  
Moving Line

The topic of sound radiation from beams under the action of harmonic line forces moving at subsonic speeds is studied. The nondimensional sound power is formulated through integration of the surface acoustic intensity distribution over the entire beam. Asymptotic expressions for the sound power in the low frequency region are derived depending upon the characteristics of the fluid loading and the spatial extent of the applied forces. Numerical integrations have been performed to determine the effects on the radiated sound power of the Mach number, M, the acoustic length of line force, KoL, and the wavenumber ratio, γ. The results show that for beams under heavy fluid loading, the effect of the speed of the moving force is not pronounced, while for beams under light fluid loading, the unique coincidence radiation peak at γ ∼ 1 for a stationary force (M = 0̸) is split into two coincidence peaks (located in the frequency regions γ<1 and γ>1 respectively) due to the effects of the Doppler shift. The values of KoL that suppress the coincidence peaks are also changed due to the motion of the line force.

Active control of radiated sound power of a smart cylindrical shell based on radiation modes

2016 ◽  
Vol 114 ◽  
pp. 218-229 ◽  
Author(s):  
Ali Loghmani ◽  
Mohammad Danesh ◽  
Moon K. Kwak ◽  
Mehdi Keshmiri
Keyword(s):  
Cylindrical Shell ◽  
Active Control ◽  
Sound Power ◽  
Radiated Sound ◽  
Radiated Sound Power

scholarly journals Sound Radiation Characteristics of a Rectangular Duct with Flexible Walls

2016 ◽  
Vol 2016 ◽  
pp. 1-15
Author(s):  
Praveena Raviprolu ◽  
Nagaraja Jade ◽  
Venkatesham Balide
Keyword(s):  
Analytical Model ◽  
Power Level ◽  
Sound Radiation ◽  
Rectangular Duct ◽  
Radiation Characteristics ◽  
Vibration Displacement ◽  
Flexible Walls ◽  
Radiated Sound ◽  
Radiated Sound Power ◽  
Element Method

Acoustic breakout noise is predominant in flexible rectangular ducts. The study of the sound radiated from the thin flexible rectangular duct walls helps in understanding breakout noise. The current paper describes an analytical model, to predict the sound radiation characteristics like total radiated sound power level, modal radiation efficiency, and directivity of the radiated sound from the duct walls. The analytical model is developed based on an equivalent plate model of the rectangular duct. This model has considered the coupled and uncoupled behaviour of both acoustic and structural subsystems. The proposed analytical model results are validated using finite element method (FEM) and boundary element method (BEM). Duct acoustic and structural modes are analysed to understand the sound radiation behaviour of a duct and its equivalence with monopole and dipole sources. The most efficient radiating modes are identified by vibration displacement of the duct walls and for these the radiation efficiencies have been calculated. The calculated modal radiation efficiencies of a duct compared to a simple rectangular plate indicate similar radiation characteristics.

Experimental Analysis of Vibration and Radiated Sound Power Reduction Using an Array of Acoustic Black Holes

2015 ◽  
Author(s):  
Philip A. Feurtado ◽  
Stephen C. Conlon
Keyword(s):  
Black Hole ◽  
Experimental Analysis ◽  
Low Frequency ◽  
Mode Shapes ◽  
Design Parameters ◽  
Laser Vibrometer ◽  
Sound Power ◽  
Radiated Sound ◽  
Bending Wave ◽  
Radiated Sound Power

The Acoustic Black Hole (ABH) has been developed in recent years as an effective, passive, and lightweight method for attenuating bending wave vibrations in beams and plates. The acoustic black hole effect utilizes a local change in the plate or beam thickness to reduce the bending wave speed and increase the transverse vibration amplitude. Attaching a viscoelastic damping layer to the ABH results in effective energy dissipation and vibration reduction. Surface averaged mobility and radiated sound power measurements were performed on an aluminum plate containing an array of 20 two-dimensional ABHs with damping layers and compared to a similar uniform plate. Detailed laser vibrometer scans of an ABH cell were also performed to analyze the vibratory characteristics of the individual ABHs and compared with mode shapes calculated using Finite Elements. The diameter of the damping layer was reduced in successive steps to experimentally demonstrate the effect of damping layer distribution on the ABH performance. The experimental analysis demonstrated the importance of low order ABH modes in reducing the vibration and radiated sound power of plates with embedded ABHs. The results will be useful for designing the low frequency performance of future ABH systems and describing ABH performance in terms of design parameters.

scholarly journals Investigation of Low-Frequency Sound Radiation Characteristics and Active Control Mechanism of a Finite Cylindrical Shell

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Shaohu Ding ◽  
Chunyang Mu ◽  
Yang Gao ◽  
Hong Liu ◽  
Maoqiang Li
Keyword(s):  
Cylindrical Shell ◽  
Active Control ◽  
Physical Mechanism ◽  
Sound Power ◽  
Radiation Characteristics ◽  
Low Frequencies ◽  
Acoustic Control ◽  
Radiated Sound ◽  
Finite Cylindrical Shell ◽  
Structural Acoustic Control

In this paper, the radiation characteristics and active structural acoustic control of a submerged cylindrical shell at low frequencies are investigated. First, the coupled vibro-acoustic equations for a submerged finite cylindrical shell are solved by a modal decomposition method, and the radiation impedance is obtained by the fast Fourier transform. The modal shapes of the first ten acoustic radiation modes and the structure-dependent radiation modes are presented. The relationships between the vibration modes and the radiation modes as well as the contributions of the radiation modes to the radiated sound power are given at low frequencies. Finally, active structural acoustic control of a submerged finite cylindrical shell is investigated by considering the fluid-structure coupled interactions. The physical mechanism of the active control is discussed based on the relationship between the vibration and radiation modes. The results showed that, at low frequencies, only the first several radiation modes contributed to the sound power radiated from a submerged finite cylindrical shell excited by a radial point force. By determining the radiation modes that dominate the contribution to the radiated sound, the physical mechanism of the active control is explained, providing a potential tool to allow active control of the vibro-acoustic responses of submerged structures more effectively.

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