Simulating and Measuring Structural Intensity Fields in Plates Induced by Spatially and Temporally Random Excitation

2004 ◽  
Author(s):  
Michael J. Daley ◽  
Stephen A. Hambric
Keyword(s):  
Pressure Fluctuations ◽  
Laser Doppler Vibrometer ◽  
Practical Interest ◽  
Analytical Techniques ◽  
Random Excitation ◽  
Plate Structures ◽  
Scanning Laser Doppler Vibrometer ◽  
Structural Intensity ◽  
Bending Waves ◽  
Pressure Fields

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. All studies to date, however, have considered only the structural intensity induced by deterministic, localized drives. Since many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations, techniques for measuring and predicting the structural intensity patterns in plates excited by such fields are presented here. The structural intensity at various frequencies in a simply-supported, baffled, flat plate driven by a diffuse pressure field is simulated using analytical techniques and measured by post-processing data from a scanning laser Doppler vibrometer and reference accelerometer using finite differencing techniques. The measured and simulated fields are similar, and show intensity patterns different from those caused by deterministic point drives.

Simulating and Measuring Structural Intensity Fields in Plates Induced by Spatially and Temporally Random Excitation

2005 ◽  
Vol 127 (5) ◽  
pp. 451-457 ◽  
Author(s):  
Michael J. Daley ◽  
Stephen A. Hambric
Keyword(s):  
Pressure Fluctuations ◽  
Laser Doppler Vibrometer ◽  
Practical Interest ◽  
Analytical Techniques ◽  
Random Excitation ◽  
Flat Plates ◽  
Plate Structures ◽  
Scanning Laser Doppler Vibrometer ◽  
Structural Intensity ◽  
Bending Waves

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. All studies to date, however, have considered only the structural intensity induced by deterministic, localized drives. Since many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations, techniques for measuring and predicting the structural intensity patterns in flat plates excited by such fields are presented here. The structural intensity at various frequencies in a simply supported, baffled, flat plate driven by a diffuse pressure field is simulated using analytical techniques and measured by post-processing data from a scanning laser Doppler vibrometer and reference accelerometer using finite differencing techniques. The measured and simulated fields are similar, and show intensity patterns different from those caused by deterministic point drives. Specifically, no clear source regions are apparent in the randomly driven intensity fields, although the energy flow patterns do clearly converge toward a point damper attached to the plate.

A Method to Simulate Structural Intensity Fields in Plates and General Structures Induced by Spatially and Temporally Random Excitation Fields

2007 ◽  
Author(s):  
Michael J. Daley ◽  
Stephen A. Hambric
Keyword(s):  
Finite Difference ◽  
Pressure Fluctuations ◽  
Practical Interest ◽  
Random Excitation ◽  
New Method ◽  
Thin Plates ◽  
Finite Differencing ◽  
Structural Intensity ◽  
Bending Waves ◽  
Pressure Fields

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. Most studies to date, however, have considered only the structural intensity induced by deterministic, localized drives. Many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations. Additionally, such studies typically employ finite differencing techniques to estimate the shear, bending and twisting components of intensity, and are therefore only applicable to simple homogenous uniform structures such as thin plates and beams. Often, however, finite differencing techniques are not applicable to practical structures of interest. The present study introduces a new method to compute the structural intensity induced by spatially random pressure fields in general structures which does not require the use of finite differencing techniques. The results of this method are validated using those obtained using finite-difference based techniques in a thin plate. The simulated fields from the new analytic technique are shown to be similar to those estimated via finite difference-based techniques, thus validating this new method. Both methods show intensity patterns different from those caused by deterministic point drives. The new general method may be applied in the future to complex non-homogenous structures which include discontinuities and curvature.

A Method to Simulate Structural Intensity Fields in Plates and General Structures Induced by Spatially and Temporally Random Excitation Fields

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Michael J. Daley ◽  
Stephen A. Hambric
Keyword(s):  
Multiple Input Multiple Output ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Practical Interest ◽  
Random Excitation ◽  
Thin Plates ◽  
Analysis Techniques ◽  
Finite Differencing ◽  
Structural Intensity ◽  
Pressure Fields

The structure-borne power in bending waves is well understood, and has been studied by many investigators in ideal beam and plate structures. Most studies to date, however, have considered only the structural intensity induced by deterministic localized drives. Many structures of practical interest are excited by spatially random pressure fields, such as diffuse and turbulent boundary layer pressure fluctuations. Additionally, such studies typically employ finite differencing techniques to estimate the shear, bending, and twisting components of intensity, and are therefore only applicable to simple homogenous uniform structures such as thin plates and beams. Often, however, finite differencing techniques are not applicable to practical structures of interest. The present study introduces a new analytic method to compute the structural intensity induced by spatially random pressure fields in general structures, which does not require the use of finite differencing techniques. This method uses multiple-input multiple-output random analysis techniques, combining frequency response function matrices generated from analytic or finite element (FE) models with cross-spectral density matrices of spatially random pressure fields to compute intensities in structures. The results of this method are validated using those obtained using finite-difference-based techniques in a flat plate. Both methods show intensity patterns different from those caused by deterministic point drives. The new general method, combined with FE analysis techniques, may be applied in the future to complex nonhomogenous structures, which include discontinuities, curvature, anisotropic materials, and general three-dimensional features.

scholarly journals Measurement of Translational and Angular Vibration Using a Scanning Laser Doppler Vibrometer

1996 ◽  
Vol 3 (2) ◽  
pp. 141-152 ◽  
Author(s):  
A.B. Stanbridge ◽  
D.J. Ewins
Keyword(s):  
Frequency Response ◽  
Laser Doppler Vibrometer ◽  
Random Excitation ◽  
Laser Doppler ◽  
Scanning Laser ◽  
Scanning Laser Doppler Vibrometer ◽  
Straight Line ◽  
Angular Vibration ◽  
Freely Suspended ◽  
Drive Signals

An experimental procedure for obtaining angular and translational vibration in one measurement, using a continuously scanning laser Doppler vibrometer, is described. Sinusoidal scanning, in a straight line, enables one angular vibration component to be measured, but by circular scanning, two principal angular vibrations and their directions can be derived directly from the frequency response sidebands. Examples of measurements on a rigid cube are given. Processes of narrow-band random excitation and modal analysis are illustrated with reference to measurements on a freely suspended beam. Sideband frequency response references are obtained by using multiplied excitation force and mirror-drive signals.

Operational modal analysis of a rotating structure subject to random excitation using a tracking continuously scanning laser Doppler vibrometer via an improved demodulation method

2021 ◽  
pp. 1-30
Author(s):  
Linfeng Lyu ◽  
Weidong Zhu
Keyword(s):  
Image Processing ◽  
Laser Doppler Vibrometer ◽  
Random Excitation ◽  
Processing Method ◽  
Rotating Beam ◽  
Scanning Laser Doppler Vibrometer ◽  
Rotating Structure ◽  
Fan Blade ◽  
Measured Response ◽  
Demodulation Method

Abstract A new operational modal analysis (OMA) method that is based on a rigorous nonuniform rotating beam vibration theory and an image processing method is developed to estimate modal parameters (MPs) of a rotating structure (RS) under random excitation using an improved demodulation method. The solution to the governing equation of a nonuniform rotating beam is derived, which can be considered as the response of the beam measured by a continuously scanning laser Doppler vibrometer (CSLDV) system. A recently developed tracking CSLDV system can track and scan the RS. The image processing method determines the angular position of the RS so that the tracking CSLDV system can sweep its laser spot along a time-varying scan path on it. The improved demodulation method obtains undamped mode shapes (UMSs) of the RS by multiplying its measured response by sinusoidal signals with its damped natural frequencies (DNFs) obtained from the fast Fourier transform of the measured response. Experimental investigation of the OMA method using the tracking CSLDV system is conducted, and MPs of a rotating fan blade (RFB), including DNFs and UMSs, with different constant speeds and its instantaneous MPs with a non-constant speed are estimated. Estimated first DNFs and UMSs of the stationary fan blade and RFB are compared with those from the lifting method that was previously developed by the authors.

Operational Modal Analysis of a Rotating Structure Subject to Random Excitation Using a Tracking Continuously Scanning Laser Doppler Vibrometer via an Improved Demodulation Method

2021 ◽  
Author(s):  
Linfeng Lyu ◽  
Weidong Zhu
Keyword(s):  
Image Processing ◽  
Laser Doppler Vibrometer ◽  
Random Excitation ◽  
Processing Method ◽  
Rotating Beam ◽  
Scanning Laser Doppler Vibrometer ◽  
Rotating Structure ◽  
Fan Blade ◽  
Measured Response ◽  
Demodulation Method

Abstract A new operational modal analysis (OMA) method is developed for estimation of modal parameters (MPs) of a rotating structure (RS) subject to random excitation using a nonuniform rotating beam model, an image processing method, and an improved demodulation method. The solution to the governing equation of a nonuniform rotating beam is derived, which can be considered as the response of the beam measured by a continuously scanning laser Doppler vibrometer (CSLDV) system. A recently developed tracking CSLDV system can track and scan the RS. The image processing method determines the angular position of the RS so that the tracking CSLDV system can sweep its laser spot along a time-varying path on it. The improved demodulation method obtains undamped mode shapes (UMSs) of the RS by multiplying its measured response by sinusoids whose frequencies are its damped natural frequencies (DNFs) that are obtained from the fast Fourier transform of the measured response. Experimental investigation of the OMA method using the tracking CSLDV system is conducted, and MPs of a rotating fan blade (RFB), including DNFs and UMSs, with different constant speeds and its instantaneous MPs with a non-constant speed are estimated. Estimated first DNFs and UMSs of the stationary fan blade and RFB are compared with those from the lifting method that was previously developed by the authors.

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