Modal analysis method and apparatus therefor

• US 20020183942A1
• Filed: 05/13/2002
• Published: 12/05/2002
• Est. Priority Date: 05/14/2001
• Status: Active Grant

• Current Assignee: Centre de recherche industrielle du Québec
• Original Assignee: Centre de recherche industrielle du Québec
• Inventors: Thomas, Marc, Lafleur, Francois, Laville, Frederic
• Granted Patent: US 6,763,310 B2
• Time in Patent Office: Days
• US Class Current: 702/56
• CPC Class Codes: G01M 7/00 Vibration-testing of structures; Shock-testing of structures G01M9/00 takes precedence

Abstract

A modal analysis method and apparatus for acoustically determining dynamic vibration characteristics of a structure, including natural frequencies, mode shapes and damping factors, is based on a Multiple-Input-Single-Output (MISO) model. The method and apparatus involve generation of an acoustic excitation signal toward n spatially distributed locations associated with the structure while the latter is held to allow vibration thereof, one of the locations being chosen as a reference location. A series of microphones are disposed at the locations to produce m complementary sets of n input acoustic pressure-related electrical signals, one of these being chosen as a reference signal associated with the reference location. A Fourier analysis is performed on the sets of input acoustic pressure-related electrical signals to provide corresponding sets of correlated input acoustic pressure-related data in the frequency domain including reference data associated with the reference signal. A vibration transducer such as an accelerometer is used to sense induced output vibration in response to the acoustic excitation at a reference point on the excited structure corresponding to the reference location to produce m complementary sets of output vibration response electrical signals, which are then converted through Fourier analysis into corresponding sets of output vibration response data in the frequency domain. Then, from relations between m corresponding complementary sets of n input transfer functions characterizing the correlation between each set of input acoustic pressure-related data and the reference data from one hand, and m sets of output vibration response data on the other hand, the structural transfer functions characterizing each said set of input acoustic pressure-related data are obtained. Finally, the dynamic vibratory characteristics of the acoustically excited structure are derived from the resulting structural transfer functions through usual calculation techniques.

Claims

1. A modal analysis method for determining dynamic vibration characteristics of a structure under acoustic excitation, said method comprising the steps of:

providing m complementary sets of correlated input acoustic pressure-related data in the frequency domain representing m complementary acoustic excitation signals, all said sets of data being provided according to n spatially distributed locations associated with the structure with m≧

n, each said set including reference input acoustic pressure-related data provided according to a reference one of said locations;

providing m corresponding complementary sets of output vibration data in the frequency domain in response to said acoustic excitation at a reference point on the excited structure corresponding to the reference location;

providing m corresponding complementary sets of n input transfer functions characterizing the correlation between each said set of input acoustic pressure-related data and the reference input acoustic pressure-related data;

obtaining n structural transfer functions characterizing each said set of input acoustic pressure-related data from relations between said m sets of n input transfer functions and said m sets of output vibration response data; and

deriving from the structural transfer functions the dynamic vibratory characteristics of the acoustically excited structure.

2. A modal analysis method for acoustically determining dynamic vibration characteristics of a structure, said method comprising the steps of:

a) generating an acoustic excitation signal toward n spatially distributed locations associated with the structure while the latter is held to allow vibration thereof, one of said locations being a reference location;

b) sensing the acoustic excitation signal at said locations to produce a corresponding set of n correlated input acoustic pressure-related electrical signals, one of said electrical signals being a reference signal associated with said reference location;

c) converting said set of n correlated input acoustic pressure-related electrical signals into a set of correlated input acoustic pressure-related data in the frequency domain including reference data associated with said reference signal;

d) sensing induced output vibration in response to said acoustic excitation at a reference point on the excited structure corresponding to the reference location to produce an output vibration response electrical signal;

e) converting said output vibration response electrical signal into a set of output vibration response data in the frequency domain;

f) providing n input transfer functions characterizing the correlation between said input acoustic pressure-related data and the reference data;

g) performing said steps a) to f) for m−

1 complementary acoustic excitation signals with m≧

n, to produce m−

1 complementary sets of input acoustic pressure-related data and to produce m−

1 complementary sets of output response vibration data;

g) obtaining n structural transfer functions characterizing each said set of input acoustic pressure-related data from relations between said m sets of n input transfer functions and said m sets of output vibration response data; and

h) deriving from the structural transfer functions the dynamic vibratory characteristics of the structure.

3. A modal analysis apparatus for determining dynamic vibration characteristics of a structure, comprising:

acoustical source means capable of generating m complementary sets of correlated acoustic excitation signals toward n spatially distributed locations associated with the structure, one of said locations being a reference location;

a structure holder provided with attachment means for holding the structure while allowing thereof to vibrate under said acoustic excitation signals;

acoustic sensor means responsive to the acoustic excitation signal at said locations to produce m complementary sets of n correlated input acoustic pressure-related electrical signals, one of said electrical signals being a reference signal associated with said reference location;

Fourier transform means for converting said sets of correlated input acoustic pressure-related electrical signals into sets of correlated input acoustic pressure-related data in the frequency domain including reference data associated with said reference signal;

vibration sensing means responsive to induced output vibration in response to said acoustic excitation at a reference point on the excited structure corresponding to the reference location to produce m complementary output vibration electrical signals;

Fourier transform means for converting said output vibration electrical signals into m sets of output vibration data in the frequency domain; and

data processor means responsive to said sets of correlated input acoustic pressure-related data and to said sets of output vibration data for providing n input transfer functions characterizing the correlation between each said set of acoustic pressure-related data and the reference data, for obtaining n structural transfer functions characterizing each said set of input acoustic pressure-related electrical data from relations between said m sets of n input transfer functions and said m sets of output vibration response data, and for deriving from the structural transfer functions the dynamic vibratory characteristics of the structure.