scholarly journals Investigation of damping effects on low-frequency steady-state acoustical behaviour of coupled spaces

2020 ◽  
Vol 7 (8) ◽  
pp. 200514
Author(s):  
Mirosław Meissner ◽  
Krzysztof Wiśniewski
Keyword(s):  
Steady State ◽  
Sound Pressure ◽  
Low Frequency ◽  
Sound Field ◽  
Expansion Method ◽  
Modal Expansion ◽  
Modal Expansion Method ◽  
Computational Data ◽  
The Mean ◽  
Complex Valued

In the low-frequency range, the acoustical behaviour of enclosed spaces is strongly influenced by excited acoustic modes resulting in a spatial irregularity of a steady-state sound field. In the paper, this problem has been examined theoretically and numerically for a system of coupled spaces with complex-valued conditions on boundary surfaces. Using a modal expansion method, an analytic formula for Green’s function was derived allowing to predict the interior sound field for a pure-tone excitation. To quantify the spatial irregularity of steady-state sound field, the parameter referred to as the mean spatial deviation was introduced. A numerical simulation was carried out for the system consisting of two coupled rectangular subspaces. Eigenfunctions and eigenfrequencies for this system were determined using the high-accuracy eigenvalue solver. As was evidenced by computational data, for small sound damping on absorptive walls the mean spatial deviation peaks at frequencies corresponding to eigenfrequencies of strongly localized modes. However, if the sound damping is much higher, the main cause of spatial irregularity of the interior sound field is the appearance of sharp valleys in a spatial distribution of a sound pressure level.

Computational studies of steady-state sound field and reverberant sound decay in a system of two coupled rooms

Open Physics ◽  
2007 ◽  
Vol 5 (3) ◽  
Author(s):  
Mirosław Meissner
Keyword(s):  
Steady State ◽  
Sound Pressure ◽  
Low Frequency ◽  
Sound Field ◽  
Coupled System ◽  
Reverberation Time ◽  
Acoustic Characteristics ◽  
Acoustical Properties ◽  
Forced Oscillator ◽  
Calculation Results

AbstractThe acoustical properties of an irregularly shaped room consisting of two connected rectangular subrooms were studied. An eigenmode method supported by a numerical implementation has been used to predict acoustic characteristics of the coupled system, such as the distribution of the sound pressure in steady-state and the reverberation time. In the theoretical model a low-frequency limit was considered. In this case the eigenmodes are lightly damped, thusthey were approximated by normal acoustic modes of a hard-walled room. The eigenfunctions and eigenfrequencies were computed numerically via application of a forced oscillator method with a finite difference algorithm. The influence of coupling between subrooms on acoustic parameters of the enclosure was demonstrated in numerical simulations where different distributions of absorbing materials on the walls of the subrooms and various positions of the sound source were assumed. Calculation results have shown that for large differences in the absorption coefficient in the subrooms the effect of modal localization contributes to peaks of RMS pressure in steady-state and a large increase in the reverberation time.

Analytic solutions of the scattering by two multilayered dielectric spheres

1992 ◽  
Vol 70 (9) ◽  
pp. 696-705 ◽  
Author(s):  
A-K. Hamid ◽  
I. R. Ciric ◽  
M. Hamid
Keyword(s):  
Boundary Conditions ◽  
Cross Sections ◽  
Plane Electromagnetic Wave ◽  
Expansion Method ◽  
Analytic Solutions ◽  
Addition Theorem ◽  
Modal Expansion ◽  
Modal Expansion Method ◽  
Dielectric Spheres ◽  
Scattered Fields

The problem of plane electromagnetic wave scattering by two concentrically layered dielectric spheres is investigated analytically using the modal expansion method. Two different solutions to this problem are obtained. In the first solution the boundary conditions are satisfied simultaneously at all spherical interfaces, while in the second solution an iterative approach is used and the boundary conditions are satisfied successively for each iteration. To impose the boundary conditions at the outer surface of the spheres, the translation addition theorem of the spherical vector wave functions is employed to express the scattered fields by one sphere in the coordiante system of the other sphere. Numerical results for the bistatic and back-scattering cross sections are presented graphically for various sphere sizes, layer thicknesses and permittivities, and angles of incidence.

Vibration Control of a Multi-Layer Piezoelectric Cylindrical Shell

1997 ◽  
Author(s):  
Jinhao Qiu ◽  
Junji Tani
Keyword(s):  
Cylindrical Shell ◽  
Feedforward Control ◽  
Equations Of Motion ◽  
Good Control ◽  
Expansion Method ◽  
Piezoelectric Sensor ◽  
State Equation ◽  
Integrated Sensor ◽  
Modal Expansion ◽  
Modal Expansion Method

Abstract Equations of motion for multi-layer piezoelectric cylindrical shells and the equations of the integrated piezoelectric sensors are derived. The state equation is obtained by solving the equations of motion with modal expansion method. The feedback control, feedforward control, and their combination are applied in the control of forced vibration of the piezoelectric cylindrical shell with integrated sensor and actuators. The simulation and experimental results show that good control effectiveness can be obtained by using the integrated piezoelectric sensor and actuators in conjunction with the combination of feedback and feedforward control methods.

Modal expansion method of analysis for slot-coupled microstrip antenna

1989 ◽  
Vol 25 (20) ◽  
pp. 1338 ◽  
Author(s):  
A. Ittipiboon ◽  
R. Oostlander ◽  
Y.M.M. Antar
Keyword(s):  
Microstrip Antenna ◽  
Expansion Method ◽  
Modal Expansion ◽  
Modal Expansion Method

Evaluating actuator distributions in simply supported truncated thin conical shell with embedded piezoelectric layers

2018 ◽  
Vol 29 (12) ◽  
pp. 2641-2659 ◽  
Author(s):  
Rasa Jamshidi ◽  
Ali A Jafari
Keyword(s):  
Conical Shell ◽  
Piezoelectric Layer ◽  
Cone Angle ◽  
Expansion Method ◽  
Longitudinal Direction ◽  
Modal Expansion ◽  
Simply Supported ◽  
Modal Expansion Method ◽  
Layer Segmentation ◽  
Distributed Actuator

In this investigation, distributed modal actuator forces of simply supported truncated conical shell embedded by a piezoelectric layer are studied. Piezoelectric layer is distributed on the conical shell surface as actuators. Three types of distributions are considered: longitudinal, circumferential, and diagonal distributions. First, electromechanical equations of the conical shell with embedded piezoelectric actuator layer are extracted. Then modal expansion method is used to define independent modal characteristics of the conical shell. For each kind of distribution, three case studies are considered and evaluated. Results showed that in the longitudinal and diagonal distributed actuator, membrane force in the longitudinal direction is the dominant force and in the circumferential distributed actuator, the membrane force in the circumferential direction is the dominant force. The effects of cone angle, piezoelectric thickness, and piezoelectric layer segmentation on modal forces of each distributed actuator are also studied. In circumferential distributed actuator, modal forces increase as the cone angle increases. This phenomenon in the longitudinal and diagonal distributed actuator is almost reversed. The piezoelectric layer segmentation effect on the modal forces distribution is also evaluated, and it showed that this phenomenon has a critical effect on the modal forces distribution.

Hybrid finite-element-modal-expansion method for matched magic T-junction

2002 ◽  
Vol 38 (2) ◽  
pp. 385-388 ◽  
Author(s):  
Zhongxiang Shen ◽  
Choi Look Law ◽  
Cheng Qian
Keyword(s):  
Finite Element ◽  
Expansion Method ◽  
Modal Expansion ◽  
Hybrid Finite Element ◽  
Modal Expansion Method

Modelling of a single-link flexible manipulator system: theoretical and practical investigations

Robotica ◽  
1996 ◽  
Vol 14 (1) ◽  
pp. 91-102 ◽  
Author(s):  
M. O. Tokhi ◽  
A. K. M. Azad
Keyword(s):  
Expansion Method ◽  
Practical Investigations ◽  
Flexible Manipulator ◽  
Experimental Investigations ◽  
Model Parameters ◽  
Modal Expansion ◽  
Modal Expansion Method ◽  
Lagrange’S Equation ◽  
Equivalent Time ◽  
Single Link

SummaryThis paper presents theoretical and experimental investigations into modelling a single-link flexible manipulator system. An analytical model of the manipulator, characterised by an infinite number of modes, is developed using the Lagrange's equation and modal expansion method. This is used to develop equivalent time-domain and frequency-domain working models of the system in state-space and transfer function forms respectively. The model parameters are then estimated experimentally using system's measured input/output data. The model thus obtained is validated through experimentation and results including the effect of payload on system characteristics presented and discussed.

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