The Effects of Modal Coupling on the Acoustic Power Radiation From Panels

1987 ◽  
Vol 109 (1) ◽  
pp. 48-54 ◽  
Author(s):  
R. F. Keltie ◽  
H. Peng
Keyword(s):  
Acoustic Radiation ◽  
Low Frequency ◽  
Acoustic Power ◽  
Resonant Excitation ◽  
One Dimensional ◽  
Simply Supported ◽  
Radiation Coefficient ◽  
Modal Coupling ◽  
End Conditions ◽  
Power Radiation

The effects of modal coupling on the acoustic power radiated from line forced panels of unit width with s-s (simply supported-simply supported) and c-c (clamped-clamped) end conditions have been studied. The expressions for the power radiated by the total square terms and by the coupling terms in these two one-dimensional problems were derived using Heckl’s power integral. A qualitative and quantitative discussion regarding the properties of Pmn (the power radiation coefficient of the m- and nth modes) and Dmn (the wavenumber cross-spectrum of modal velocities) for the s-s panel are presented. Numerical calculations (for both s-s and c-c cases) were carried out to investigate the relative importance of the modal coupling in the acoustic radiation. The results show that if the panel is under resonant excitation or if the driving force is at high frequency, then the effects due to modal coupling are negligible. At low frequency, however, or if the panel is under off-resonant excitation, then the contributions due to the modal coupling may be important.

Soil Effect on the Finite Simply Supported Plate Vibration

2012 ◽  
Author(s):  
Bernard Laulagnet
Keyword(s):  
Fourier Transforms ◽  
Acoustic Radiation ◽  
Homogeneous Medium ◽  
Low Frequency ◽  
Plate Vibration ◽  
Radiation Problem ◽  
Vibration Prediction ◽  
Modal Coupling ◽  
Cousin Problem ◽  
The One

We are interested in the vibration prediction for a finite flexural plate lying on a semi-infinite soil, whose surface is free, except under the plate. Both the plate equation and the Navier equations are solved, using their bidimensional spatial Fourier Transforms. A cousin problem is the one of the acoustic radiation of the unbaffled plate, a one velocity problem. In this soil problem, two velocities are taken into account, the soil shear and dilatation velocities, considered as a visco-elastic homogeneous medium. Finally, expanding the plate displacement on its modes, linear systems in plate displacement amplitude are solved. As for the unbaffled acoustic radiation problem, equivalent vibratory radiation impedances set is proposed, totally new, describing the modal coupling between the plate modes and the soil. It is shown, contrary to the acoustic one velocity problem that the sign of the imaginary part of the complex vibratory radiation terms is negative at very low frequency, and positive above, meaning that the soil adds stiffness to the plate at low frequency and mass above. The soil effect on the plate vibration is of first importance, highly decreasing the plate vibration by more than 30 dB even for thick concrete plates.

Analytical Sensitivity of Acoustic Power Radiated from a Closed Structure Based on the Theory of Acoustic Radiation Modes

2012 ◽  
Vol 518-523 ◽  
pp. 3834-3837
Author(s):  
Hai Jun Kou ◽  
Zhe Jiang
Keyword(s):  
Finite Elements ◽  
Acoustic Radiation ◽  
Sound Radiation ◽  
Acoustic Power ◽  
Analytical Sensitivity ◽  
Analytical Expression ◽  
Sensitivity Coefficients ◽  
Design Variables ◽  
Closed Structure ◽  
Power Radiation

A general formulation to obtain the analytical expression for the sensitivity of the acoustic power radiation by a vibrating closed structure to one its design variables is described. The formulation is based on finite elements and the theory of acoustic radiation modes. The sensitivity coefficients indicate the effect of changing various designs or modeling parameters on the acoustic power and can be used to optimize the structure for minimum sound radiation. Putting a rectangle case as an example and verifying the feasibility of this method.

The Effect of Flow Induced Coupling on Sound Radiation From Convected Fluid Loaded Plates

2004 ◽  
Author(s):  
Kenneth D. Frampton
Keyword(s):  
Structural Dynamics ◽  
Acoustic Radiation ◽  
Sound Radiation ◽  
Structural Dynamic ◽  
Fundamental Physics ◽  
Simply Supported ◽  
Modal Coupling ◽  
Vibrating Plates ◽  
Flow Speeds ◽  
Fluid Convection

Recent investigations concerning the effects of fluid convection on structural acoustic radiation have noted that radiation efficiency increases with increasing flow speeds. However, most of these studies based this conclusion on simulations which neglected flow induced coupling between the structural modes. Yet, flow induced modal coupling is know to have dramatic effects on structural dynamics including static and dynamic instabilities, and should therefore be expected to significantly affect sound radiation. The purpose of this investigation is to quantify the effects that fluid flow has on the sound radiated from rectangular vibrating plates when flow-induced structural modal coupling is considered. The discussion includes a description of the fundamental physics associated with a simply supported, vibrating, rectangular plate imbedded in an infinite baffle and radiating into a semi-infinite, convected fluid. This is followed by a discussion of the effect that flow-induced coupling has on the structural dynamic behavior. Finally, numerical results are presented which demonstrate the effect that such coupling has on the sound power radiated from a plate.

Numerical Study of Vibro-Acoustic Performance of Composite and Sandwich Shells with Viscoelastic Core

2017 ◽  
Vol 727 ◽  
pp. 249-256 ◽  
Author(s):  
Bo Tong ◽  
Xi Zhu ◽  
Yong Qing Li ◽  
Yan Bing Zhang
Keyword(s):  
High Frequency ◽  
Acoustic Radiation ◽  
Numerical Study ◽  
Low Frequency ◽  
Sound Field ◽  
Acoustic Vibration ◽  
Acoustic Power ◽  
Sandwich Composite ◽  
Steel Shell ◽  
Viscoelastic Core

In order to effectively evaluate the acoustic vibration characteristics of viscoelastic sandwich composite cylindrical shell, based on FEM and BEM method, the vibration acoustic radiation of the viscoelastic sandwich panel and metal shell are calculated, and the results agree well with the experimental results. The dynamic mechanical parameters of viscoelastic core are obtained by dynamic thermodynamic experiments and the equivalent principle of temperature and frequency. The finite element method is used to simulate the coupling of water and shell. Finally, the indirect boundary method is used to calculate the radiated sound field under point excitation and the results show that the average and peak value of the acoustic power of the viscoelastic sandwich composite shell is 21.2dB and 46.4dB lower than that of the steel shell. In the range of low frequency,the radiation sound power is sensitive to the change of the layer angle,which is opposite in the range of high frequency. In the range of high frequency,the shear loss of the viscoelastic core is relatively obvious,which is opposite in the range of low frequency.

Asymptotic derivation of a refined equation for an elastic beam resting on a Winkler foundation

2021 ◽  
pp. 108128652110238
Author(s):  
Barış Erbaş ◽  
Julius Kaplunov ◽  
Isaac Elishakoff
Keyword(s):  
Ad Hoc ◽  
Moving Load ◽  
Low Frequency ◽  
Elastic Beam ◽  
Winkler Foundation ◽  
One Dimensional ◽  
Beam Equations ◽  
Dimensional Equation ◽  
Phase And Group Velocities ◽  
Group Velocities

A two-dimensional mixed problem for a thin elastic strip resting on a Winkler foundation is considered within the framework of plane stress setup. The relative stiffness of the foundation is supposed to be small to ensure low-frequency vibrations. Asymptotic analysis at a higher order results in a one-dimensional equation of bending motion refining numerous ad hoc developments starting from Timoshenko-type beam equations. Two-term expansions through the foundation stiffness are presented for phase and group velocities, as well as for the critical velocity of a moving load. In addition, the formula for the longitudinal displacements of the beam due to its transverse compression is derived.

scholarly journals Resonant excitation of acoustic waves in one-dimensional exciton-polariton systems

2019 ◽  
Vol 100 (4) ◽  
Author(s):  
A. V. Yulin ◽  
V. K. Kozin ◽  
A. V. Nalitov ◽  
I. A. Shelykh
Keyword(s):  
Acoustic Waves ◽  
Resonant Excitation ◽  
One Dimensional

Acoustic Radiation From Thick Laminated Cylindrical Shells With Sparse Cross Stiffeners

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Xiongtao Cao ◽  
Chao Ma ◽  
Hongxing Hua
Keyword(s):  
Cylindrical Shell ◽  
Radial Displacement ◽  
Acoustic Radiation ◽  
Periodic Structures ◽  
Cylindrical Shells ◽  
Acoustic Power ◽  
Acoustic Energy ◽  
Parallel Plates ◽  
Wavenumber Domain ◽  
Laminated Cylindrical Shells

A general method for predicting acoustic radiation from multiple periodic structures is presented and a numerical solution is proposed to find the radial displacement of thick laminated cylindrical shells with sparse cross stiffeners in the wavenumber domain. Although this method aims at the sound radiation from a single stiffened cylindrical shell, it can be easily adapted to analyze the vibrational and sound characteristics of two concentric cylindrical shells or two parallel plates with complicated periodic stiffeners, such as submarine and ship hulls. The sparse cross stiffeners are composed of two sets of parallel rings and one set of longitudinal stringers. The acoustic power of large cylindrical shells above the ring frequency is derived in the wavenumber domain on the basis of the fact that sound power is focused on the acoustic ellipse. It transpires that a great many band gaps of wave propagation in the helical wave spectra of the radial displacement for stiffened cylindrical shells are generated by the rings and stringers. The acoustic power and input power of stiffened antisymmetric laminated cylindrical shells are computed and compared. The acoustic energy conversion efficiency of the cylindrical shells is less than 10%. The axial and circumferential point forces can also produce distinct acoustic power. The radial displacement patterns of the antisymmetric cylindrical shell with fluid loadings are illustrated in the space domain. This study would help to better understand the main mechanism of acoustic radiation from stiffened laminated composite shells, which has not been adequately addressed in its companion paper (Cao et al., 2012, “Acoustic Radiation From Shear Deformable Stiffened Laminated Cylindrical Shells,” J. Sound Vib., 331(3), pp. 651-670).

scholarly journals MULTIDIMENSIONAL REPRESENTATION OF AUTOMATIC DOSING DEVICE SIGNALS

2018 ◽  
pp. 26-32
Author(s):  
Denis Borisovich Fedosenkov ◽  
Anna Alekseevna Simikova ◽  
Boris Andreevich Fedosenkov ◽  
Stanislav Matveevich Kulakov
Keyword(s):  
Fourier Transform ◽  
Wigner Distribution ◽  
Low Frequency ◽  
Stationary Flow ◽  
Complex Model ◽  
Signal Spectrum ◽  
One Dimensional ◽  
Time Frequency ◽  
Cohen's Class ◽  
Discrete Values

The article describes the development of a special approach based on using multidimensional wavelet distributions principle to monitor and control the feed dozing processes in the mix preparation unit. As a key component, this approach uses the multidimensional time-frequency Wigner-Ville distribution, which is the part of Cohen's class distributions. The research focuses on signals characterizing mass transfer processes in the form of material flow measuring signals in relevant points of the unit. Wigner-Ville distribution has been shown in time terms as Fourier transform of products of multiplied parts of the signal under consideration for past and future time moments; corresponding distribution for the frequency spectrum is shown as Fourier transform of the products of signal parts for high-frequency and low-frequency fragments of the signal spectrum. It has been noted that when using a complex model of a dozing signal, discrete values (samples) of the latter are considered as its real values. The description of the signal parameters (amplitude, phase, frequency) has been carried out with the help of Hilbert transform. In Cohen's class distributions which represent one-dimensional non-stationary flow signals, the concept of ‘instantaneous frequency’ has been introduced. A graphical explanation for the transformation of a process flow signal from a one-dimensional time domain to a time-frequency 2 D/ 3 D -space is presented. The technology of developing a multidimensional image in the form of Wigner distribution for one-dimensional signals of continuous spiral or screw-type feeders has been examined in detail. There have been considered the features to support Wigner distribution, which allow to guess the presence or absence of time-frequency distribution elements in the interval of signal recording. There has been demonstrated how Wigner distribution can be obtained for a continuous-intermittent feeding signal. It has been concluded that for a certain types of the signal for zero fragments of the latter, non-zero time-frequency elements (i.e. virtual, anomalous ones) appear on the distribution. In addition to Wigner distribution, two other distributions - of Rihachek and Page - are considered. They display the same signal and also contain virtual elements, but in different domains of the time-frequency space. A generalized multidimensional compound signal distribution with a so-called distribution kernel available in it is presented, which includes a correction parameter that allows controlling the intensity of the virtual signal energy.

scholarly journals Tunable Omnidirectional Band Gap Properties of 1D Plasma Annular Periodic Multilayer Structure Based on an Improved Fibonacci Topological Structure

2021 ◽  
Author(s):  
Hong-Mei Peng ◽  
Bao-Fei Wan ◽  
Peng-Xiang Wang ◽  
Dan Zhang ◽  
Hai-Feng Zhang
Keyword(s):  
Band Gap ◽  
Plasma Frequency ◽  
Incident Angle ◽  
Low Frequency ◽  
Interesting Phenomenon ◽  
Azimuthal Mode ◽  
One Dimensional ◽  
Theoretical Support ◽  
Omnidirectional Band Gap ◽  
High Reflection

Abstract In this paper, the characteristics of the omnidirectional band gap (OBG) for one-dimensional (1D) plasma cylindrical photonic crystals (PCPCs) are based on an improved Fibonacci topological (IFT) structure are studied. The influences of the azimuthal mode number, incident angle, plasma thickness, and plasma frequency on the OBG are discussed. It is concluded that increasing the azimuth modulus can significantly expand the bandwidth of the OBG, and the OBG can be moved to the low-frequency direction by increasing the plasma frequency. In addition, an interesting phenomenon can be found that when the number of azimuthal modes is equal to 2, the TM wave can produce an extra high reflection zone. It provides a theoretical support for designing the narrowband filters without introducing any physical defect layers in the structure.

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