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Interaction of acoustic waves generated by coupled finite fluidloaded plates
 Date Issued:
 1993
 Summary:
 The response of fluidloaded plates has been extensively studied in the past. However, most of the work deals with either infinite plates or finite plates with particular boundary conditions and the results are generally presented only in the limit of small wavelengths compared with the dimensions of the plates. Furthermore, the problem of coupled finite plates where both the acoustic interaction and structural interaction are included in the solution has not been considered. In this dissertation the response of two coupled finite plates set in two alternative configurations is considered. The plates are simply supported on two edges, with arbitrary boundary conditions on the remaining two edges. The solutions obtained for the response of the plates include both the structural interaction at the common junction and the acoustic interaction due to the scattered pressure from each of the two plates. The results are presented in terms of the vibrational power flow into and out of each plate component. The solution is based on a formulation developed in the wavenumber domain combined with the Mobility Power Flow method. Using this approach, different substructural elements coupled under different boundary conditions to form a complex global structure can be considered. The detailed spatial and temporal scales of the structure response are not lost when using this method. In obtaining the solution for the scattering from the fluidloaded plates, a modal decomposition in the direction normal to the simply supported edge is used. A spatial Fouriertransform decomposition is used in the other direction. Due to the finiteness of the plate, eight unknowns parameters are obtained in the transformed result. The solution for these eight unknown parameters is obtained from the boundary conditions and the condition that the response must remain finite. Two analytical approaches are used to solve the final plate integral equation. The first approach consists of an approximation method which obtains a solution based on the solution of the corresponding infinite plate problem. The second approach is a more accurate solution based on the Projection Method for the solution of integral equations. Both of the approaches used in the solution provide accurate predictions at high frequencies. At low frequencies especially for low structural damping or for heavy fluid loading, only the Projection Method gives reliable results. This is attributed to the fact that at low frequencies, the influence of the edges of the plates on the scattering is significant. The overall results obtained from this analysis indicate that the fluid loading and the plate characteristics have a significant influence on the acoustic scattering properties, especially in the case of heavy fluid loading. The application of the method to coupled fluidloaded plates indicates that the junction enhances the scattering properties. The acoustical interaction between the coupled plates increases the contribution to scattering from subsonic wavenumber components. In the absence of the interaction, only supersonic wavenumbers contribute to the scattering. Inclusion of acousticlal interaction requires both supersonic and subsonic components. The significance of the contribution from the subsonic wavenumber components is dependent on the type of the fluid loading.
Title:  Interaction of acoustic waves generated by coupled finite fluidloaded plates. 
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Name(s): 
Kaina, Rachid. Florida Atlantic University, Degree grantor Cuschieri, Joseph M., Thesis advisor College of Engineering and Computer Science Department of Ocean and Mechanical Engineering 

Type of Resource:  text  
Genre:  Electronic Thesis Or Dissertation  
Issuance:  monographic  
Date Issued:  1993  
Publisher:  Florida Atlantic University  
Place of Publication:  Boca Raton, Fla.  
Physical Form:  application/pdf  
Extent:  144 p.  
Language(s):  English  
Summary:  The response of fluidloaded plates has been extensively studied in the past. However, most of the work deals with either infinite plates or finite plates with particular boundary conditions and the results are generally presented only in the limit of small wavelengths compared with the dimensions of the plates. Furthermore, the problem of coupled finite plates where both the acoustic interaction and structural interaction are included in the solution has not been considered. In this dissertation the response of two coupled finite plates set in two alternative configurations is considered. The plates are simply supported on two edges, with arbitrary boundary conditions on the remaining two edges. The solutions obtained for the response of the plates include both the structural interaction at the common junction and the acoustic interaction due to the scattered pressure from each of the two plates. The results are presented in terms of the vibrational power flow into and out of each plate component. The solution is based on a formulation developed in the wavenumber domain combined with the Mobility Power Flow method. Using this approach, different substructural elements coupled under different boundary conditions to form a complex global structure can be considered. The detailed spatial and temporal scales of the structure response are not lost when using this method. In obtaining the solution for the scattering from the fluidloaded plates, a modal decomposition in the direction normal to the simply supported edge is used. A spatial Fouriertransform decomposition is used in the other direction. Due to the finiteness of the plate, eight unknowns parameters are obtained in the transformed result. The solution for these eight unknown parameters is obtained from the boundary conditions and the condition that the response must remain finite. Two analytical approaches are used to solve the final plate integral equation. The first approach consists of an approximation method which obtains a solution based on the solution of the corresponding infinite plate problem. The second approach is a more accurate solution based on the Projection Method for the solution of integral equations. Both of the approaches used in the solution provide accurate predictions at high frequencies. At low frequencies especially for low structural damping or for heavy fluid loading, only the Projection Method gives reliable results. This is attributed to the fact that at low frequencies, the influence of the edges of the plates on the scattering is significant. The overall results obtained from this analysis indicate that the fluid loading and the plate characteristics have a significant influence on the acoustic scattering properties, especially in the case of heavy fluid loading. The application of the method to coupled fluidloaded plates indicates that the junction enhances the scattering properties. The acoustical interaction between the coupled plates increases the contribution to scattering from subsonic wavenumber components. In the absence of the interaction, only supersonic wavenumbers contribute to the scattering. Inclusion of acousticlal interaction requires both supersonic and subsonic components. The significance of the contribution from the subsonic wavenumber components is dependent on the type of the fluid loading.  
Identifier:  12341 (digitool), FADT12341 (IID), fau:9243 (fedora)  
Collection:  FAU Electronic Theses and Dissertations Collection  
Note(s): 
College of Engineering and Computer Science Thesis (Ph.D.)Florida Atlantic University, 1993. 

Subject(s): 
Finite element method Plates (Engineering) Acoustic emission SoundTransmission 

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Persistent Link to This Record:  http://purl.flvc.org/fcla/dt/12341  
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Host Institution:  FAU  
Is Part of Series:  Florida Atlantic University Digital Library Collections. 