This paper proposes an improved optimal adaptive control algorithm to accelerate convergence for sine control of general multichannel coupled system, as well as enhance the stability. First of all, the convergence of traditional multi-input multi-output (MIMO) sine control method is analytically investigated in the presence of frequency response function (FRF) error. Then, the controller with the improved optimal adaptive control algorithm is developed, where a high-precision algorithm for amplitude and phase estimation is proposed to guarantee the accuracy of the response vector calculation. Numerical simulation results show that the proposed method possess excellent performance with fast convergence rate and strong robustness.
{"title":"An Improved Optimal Adaptive Control Method for MIMO Sine Vibration Control of a Multichannel Coupled System","authors":"Chao Li, Zhang-wei Chen, Hongfei Zu, Yugang Zhao","doi":"10.1115/IMECE2018-86983","DOIUrl":"https://doi.org/10.1115/IMECE2018-86983","url":null,"abstract":"This paper proposes an improved optimal adaptive control algorithm to accelerate convergence for sine control of general multichannel coupled system, as well as enhance the stability. First of all, the convergence of traditional multi-input multi-output (MIMO) sine control method is analytically investigated in the presence of frequency response function (FRF) error. Then, the controller with the improved optimal adaptive control algorithm is developed, where a high-precision algorithm for amplitude and phase estimation is proposed to guarantee the accuracy of the response vector calculation. Numerical simulation results show that the proposed method possess excellent performance with fast convergence rate and strong robustness.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132176503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ashkan Ghanbarzadeh-Dagheyan, J. Heredia-Juesas, Chang Liu, A. Molaei, J. Martinez-Lorenzo
Compressive sensing (CS) theory states that, if certain conditions are met, a signal can be retrieved at a sampling rate that is lower than what Nyquist theorem requires. Among these conditions are the sparsity of the signal and the incoherence of the sensing matrix, which is constructed based on how the sensing system is designed. One effective method to render the sensing matrix incoherent is to use random processes in its construction. Diverse approaches have been proposed to randomize the sensing matrix including transmission at random transmitter positions and spectral coding with the use of a physical structure that responds very differently at disparate frequencies. In this work, a holey cavity with various frequency modes is used to spectrally code the ultrasound wave fields. Then, with the use of CS theory and simulations, it is shown that the sensing system that is equipped with such a cavity performs meaningfully better than a regular system in terms of sensing capacity, beam focusing, and imaging. What is more, the validity of Born approximation is investigated in this work to show its extent of applicability in imaging relatively small targets. Due to computational limitations, the simulation domain has been selected to be comparatively small; yet, the achieved results evidently show the concept and warrant further studies on holey cavities in ultrasound imaging, including their fabrication and experimental corroboration. The decrease in the number of measurements necessary for correct image reconstruction can make ultrasound sensing systems more efficient in size and scan time in a variety of applications including medical diagnosis, non-destructive testing, and monitoring.
{"title":"A Holey Cavity for High-Capacity Ultrasound Imaging","authors":"Ashkan Ghanbarzadeh-Dagheyan, J. Heredia-Juesas, Chang Liu, A. Molaei, J. Martinez-Lorenzo","doi":"10.1115/IMECE2018-88028","DOIUrl":"https://doi.org/10.1115/IMECE2018-88028","url":null,"abstract":"Compressive sensing (CS) theory states that, if certain conditions are met, a signal can be retrieved at a sampling rate that is lower than what Nyquist theorem requires. Among these conditions are the sparsity of the signal and the incoherence of the sensing matrix, which is constructed based on how the sensing system is designed. One effective method to render the sensing matrix incoherent is to use random processes in its construction. Diverse approaches have been proposed to randomize the sensing matrix including transmission at random transmitter positions and spectral coding with the use of a physical structure that responds very differently at disparate frequencies. In this work, a holey cavity with various frequency modes is used to spectrally code the ultrasound wave fields. Then, with the use of CS theory and simulations, it is shown that the sensing system that is equipped with such a cavity performs meaningfully better than a regular system in terms of sensing capacity, beam focusing, and imaging. What is more, the validity of Born approximation is investigated in this work to show its extent of applicability in imaging relatively small targets. Due to computational limitations, the simulation domain has been selected to be comparatively small; yet, the achieved results evidently show the concept and warrant further studies on holey cavities in ultrasound imaging, including their fabrication and experimental corroboration. The decrease in the number of measurements necessary for correct image reconstruction can make ultrasound sensing systems more efficient in size and scan time in a variety of applications including medical diagnosis, non-destructive testing, and monitoring.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129188112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.
{"title":"Effect of Angular Acceleration and Unbalance Force Orientation on the Backward Whirl in Cracked Rotors","authors":"Fatima AlHammadi, M. Al-Shudeifat, Oleg Shiryayev","doi":"10.1115/IMECE2018-87476","DOIUrl":"https://doi.org/10.1115/IMECE2018-87476","url":null,"abstract":"Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116741025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mike Kheirallah, Abdallah Hamieh, B. Jawad, Liping Liu
The pressure fluctuation over the fan blades can generate unpleasant noises that affect the fan performance. Therefore, the noise control is considered as a significant factor in the design process. The purpose of this study is to estimate the total acoustic power of the surface on a cooling fan as a key function to improve design parameters. The design process of a cooling fan to achieve low acoustic power can be lengthy and expensive through prototyping and experiments. The Mesh Morpher Optimizer (MMO) in ANSYS Fluent in coupling with the Powell’s model was applied to estimate the acoustic power over a cooling fan surface at a low speed. The Powell’s model in ANSYS was proved successfully in reducing the total acoustic power on the surface of the cooling fan which is shown by the numerical results. Comparison of the base model and Powell’s model, the Acoustic Power Level was reduced from 23.68 to 21.69 dB. The Surface Acoustic Power Level dropped from 62.24 to 61.26 dB. Likewise, the Surface Acoustic Power decreased from 9.67e−5 to 5.24e−5 W/m2. Also, the contour visualization results verified the success of the Powell’s model in combination of the Mesh Morpher Optimizer (MMO) to evaluate the total acoustic power and propose a new model that will assist in the design process in minimizing the manufacturing process of a new design model.
{"title":"An Acoustic Analogy to Evaluate the Total Acoustic Power of a Cooling Fan Using Mesh Morpher Optimizer","authors":"Mike Kheirallah, Abdallah Hamieh, B. Jawad, Liping Liu","doi":"10.1115/IMECE2018-86873","DOIUrl":"https://doi.org/10.1115/IMECE2018-86873","url":null,"abstract":"The pressure fluctuation over the fan blades can generate unpleasant noises that affect the fan performance. Therefore, the noise control is considered as a significant factor in the design process. The purpose of this study is to estimate the total acoustic power of the surface on a cooling fan as a key function to improve design parameters.\u0000 The design process of a cooling fan to achieve low acoustic power can be lengthy and expensive through prototyping and experiments. The Mesh Morpher Optimizer (MMO) in ANSYS Fluent in coupling with the Powell’s model was applied to estimate the acoustic power over a cooling fan surface at a low speed. The Powell’s model in ANSYS was proved successfully in reducing the total acoustic power on the surface of the cooling fan which is shown by the numerical results. Comparison of the base model and Powell’s model, the Acoustic Power Level was reduced from 23.68 to 21.69 dB. The Surface Acoustic Power Level dropped from 62.24 to 61.26 dB. Likewise, the Surface Acoustic Power decreased from 9.67e−5 to 5.24e−5 W/m2. Also, the contour visualization results verified the success of the Powell’s model in combination of the Mesh Morpher Optimizer (MMO) to evaluate the total acoustic power and propose a new model that will assist in the design process in minimizing the manufacturing process of a new design model.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125029347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper experimentally investigates the performance of a long smooth seal (length-diameter ratio L/D = 0.65 and radial clearance Cr = 0.140 mm) under laminar flow conditions. Tests are carried out at shaft speeds ω up to 10 krpm, pressure drops PD up to 48.3 bars, exit pressure Pe = 6.9 bars, and inlet temperature Ti = 39.4 °C. The seal is centered. Since there is no validated friction formula published for a liquid seal in the transitional regime, this paper uses San Andrés’s bulk-flow model with laminar-flow friction formula to produce predictions. Test results show that under laminar flow conditions, increasing ω decreases measured direct stiffness K, increases measured cross-coupled stiffness k, barely changes measured direct damping C, and generally increases measured cross-coupled damping c. The model correctly predicts these trends, and the predictions of K, k, C, and c are reasonably close to test results. Measured direct virtual-mass M values are normally larger than predictions. This paper also judges two cases with high PD or high ω to be in the transitional regime. For these cases, the predictions of K, k, C, and c based on the laminar-flow friction formula are significantly different from test results. This discrepancy further strengthens the judgment that the flow in these cases is transitional. For all test cases, measured leakage mass flow rate ṁ and measured effective damping Ceff are not sensitive to changes in ω, but increase as PD increases. The model with the laminar-flow friction formula adequately predicts ṁ and Ceff even when the flow within the seal annulus is at the start of the transitional flow regime. Also, Ceff predictions are lower than test results, allowing a safe margin for the pump design.
{"title":"Experimental Study on the Leakage and Rotordynamic Coefficients of a Long Smooth Seal at Laminar Flow Conditions","authors":"Min Zhang, D. Childs","doi":"10.1115/IMECE2018-88717","DOIUrl":"https://doi.org/10.1115/IMECE2018-88717","url":null,"abstract":"This paper experimentally investigates the performance of a long smooth seal (length-diameter ratio L/D = 0.65 and radial clearance Cr = 0.140 mm) under laminar flow conditions. Tests are carried out at shaft speeds ω up to 10 krpm, pressure drops PD up to 48.3 bars, exit pressure Pe = 6.9 bars, and inlet temperature Ti = 39.4 °C. The seal is centered. Since there is no validated friction formula published for a liquid seal in the transitional regime, this paper uses San Andrés’s bulk-flow model with laminar-flow friction formula to produce predictions. Test results show that under laminar flow conditions, increasing ω decreases measured direct stiffness K, increases measured cross-coupled stiffness k, barely changes measured direct damping C, and generally increases measured cross-coupled damping c. The model correctly predicts these trends, and the predictions of K, k, C, and c are reasonably close to test results. Measured direct virtual-mass M values are normally larger than predictions.\u0000 This paper also judges two cases with high PD or high ω to be in the transitional regime. For these cases, the predictions of K, k, C, and c based on the laminar-flow friction formula are significantly different from test results. This discrepancy further strengthens the judgment that the flow in these cases is transitional.\u0000 For all test cases, measured leakage mass flow rate ṁ and measured effective damping Ceff are not sensitive to changes in ω, but increase as PD increases. The model with the laminar-flow friction formula adequately predicts ṁ and Ceff even when the flow within the seal annulus is at the start of the transitional flow regime. Also, Ceff predictions are lower than test results, allowing a safe margin for the pump design.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120836934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sonic Crystals are noise barriers wherein the incident sound waves are scattered multiple times by the periodically arranged scatterers placed inside a host fluid. Used as sound attenuators, sonic crystals attenuate sound over frequency bands known as bandgaps. Broadening and lowering the bandgaps is the primary objective of this work. Effect of changing the shape, size and orientations of the scatterers on the band characteristics have been reported here. Different shapes of the scatterers are found to affect the band characteristics of the sonic crystals. Adding local resonance to the scatterers introduce a new attenuation mechanism due to local acoustic resonances. A new type of double circle split-ring resonator is also proposed which use acoustic resonance to produce additional bandgaps. Size and orientation of the scatterers are also found to affect the bandwidth and center frequency of the bandgaps. The band diagram, transmission loss, eigenmodes are computed using finite element method. COMSOL Multiphysics, a commercially available finite element software has been used to implement FEM and model the two-dimensional unit cells and the sonic crystal arrays. Due to the large difference in impedance of the steel scatterer embedded in air, the scatterers are assumed to be sound hard (sound rigid) which imposes a condition where normal component of acceleration is zero.
{"title":"Broadening the Bandgaps of Sonic Crystals by Varying Shapes, Sizes and Orientations of the Scatterers","authors":"Debasis Panda, A. Mohanty","doi":"10.1115/IMECE2018-87398","DOIUrl":"https://doi.org/10.1115/IMECE2018-87398","url":null,"abstract":"Sonic Crystals are noise barriers wherein the incident sound waves are scattered multiple times by the periodically arranged scatterers placed inside a host fluid. Used as sound attenuators, sonic crystals attenuate sound over frequency bands known as bandgaps. Broadening and lowering the bandgaps is the primary objective of this work. Effect of changing the shape, size and orientations of the scatterers on the band characteristics have been reported here. Different shapes of the scatterers are found to affect the band characteristics of the sonic crystals. Adding local resonance to the scatterers introduce a new attenuation mechanism due to local acoustic resonances. A new type of double circle split-ring resonator is also proposed which use acoustic resonance to produce additional bandgaps. Size and orientation of the scatterers are also found to affect the bandwidth and center frequency of the bandgaps. The band diagram, transmission loss, eigenmodes are computed using finite element method. COMSOL Multiphysics, a commercially available finite element software has been used to implement FEM and model the two-dimensional unit cells and the sonic crystal arrays. Due to the large difference in impedance of the steel scatterer embedded in air, the scatterers are assumed to be sound hard (sound rigid) which imposes a condition where normal component of acceleration is zero.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131742629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nonlinear vibration of a simply-supported Euler-Bernoulli microbeam with fractional Kelvin-Voigt viscoelastic model subjected to harmonic excitation is investigated in this paper. For small scale effects the modified strain gradient theory is used. For take into account geometric nonlinearities the Von karman theory is applied. Beam equations are derived from Hamilton principle and the Galerkin method is used to convert fractional partial differential equations into fractional ordinary differential equations. Problem is solved by using the method of multiple scales and amplitude-frequency equations are obtained for primary, super-harmonic and sub-harmonic resonance. Effects of force amplitude, fractional parameters and nonlinearity on the frequency responses for primary, super-harmonic and sub-harmonic resonance are investigated. Finally results are compared with ordinary Kelvin-Voigt viscoelastic model.
{"title":"Nonlinear Vibration Analysis of a Fractional Viscoelastic Euler-Bernoulli Microbeam","authors":"F. Bakhtiari-Nejad, E. Loghman, M. Pirasteh","doi":"10.1115/IMECE2018-87061","DOIUrl":"https://doi.org/10.1115/IMECE2018-87061","url":null,"abstract":"Nonlinear vibration of a simply-supported Euler-Bernoulli microbeam with fractional Kelvin-Voigt viscoelastic model subjected to harmonic excitation is investigated in this paper. For small scale effects the modified strain gradient theory is used. For take into account geometric nonlinearities the Von karman theory is applied. Beam equations are derived from Hamilton principle and the Galerkin method is used to convert fractional partial differential equations into fractional ordinary differential equations. Problem is solved by using the method of multiple scales and amplitude-frequency equations are obtained for primary, super-harmonic and sub-harmonic resonance. Effects of force amplitude, fractional parameters and nonlinearity on the frequency responses for primary, super-harmonic and sub-harmonic resonance are investigated. Finally results are compared with ordinary Kelvin-Voigt viscoelastic model.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131148797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with non-negative time delays between lifted CSLDV measurements of two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, i.e., natural frequencies, modal damping ratios and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.
{"title":"Operational Modal Analysis and Damage Identification of Structures Undergoing Random Vibration Using a Continuously Scanning Laser Doppler Vibrometer System","authors":"Daming Chen, Y. Xu, W. D. Zhu","doi":"10.1115/IMECE2018-88058","DOIUrl":"https://doi.org/10.1115/IMECE2018-88058","url":null,"abstract":"A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with non-negative time delays between lifted CSLDV measurements of two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, i.e., natural frequencies, modal damping ratios and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127519060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Scussel, M. Brennan, J. Muggleton, Fabrício César Lobato de Almeida, A. Paschoalini
Detection and location of leaks in buried plastic fluid-filled pipes are topics of increasing concern for water distribution companies. Acoustic correlation techniques have been widely used to provide an accurate estimate of the position of a leak in order to reduce the wastage of water. However, this technique depends on an accurate estimate of the wave propagation speed along the pipe, which is heavily dependent on the type of soil in which the pipe is buried. The soil also affects the distance that leak noise will propagate along the pipe. This paper describes theoretical and experimental investigations into the way the coupling conditions between the pipe and the soil affects the propagation characteristics of the wave that propagates leak noise in the pipe. Two water pipe systems which have different soil properties are considered: one is in Brazil and the other one is in UK. For the Brazilian pipe system, it is found that the shear modulus rather than the bulk modulus of the soil, has a profound effect on the wave motion in the pipe since it is buried in a clay-like soil. In this case, only the shear wave in the soil propagates away from the pipe. For the UK pipe system, which has sandy soil, both compressional and shear waves propagate away from the pipe. An analysis of the physical effects of fluid-pipe-soil interface and their corresponding parameters on the pipe wave speed and attenuation is also carried out. The results show that the axial coupling between the pipe and the soil has an important effect in the UK pipe system, but has a negligible effect in the Brazilian pipe system.
{"title":"On the Dynamic Loading Effects of Soil on Plastic Water Distribution Pipes and its Significance for Leak Detection Using Acoustics","authors":"O. Scussel, M. Brennan, J. Muggleton, Fabrício César Lobato de Almeida, A. Paschoalini","doi":"10.1115/IMECE2018-87420","DOIUrl":"https://doi.org/10.1115/IMECE2018-87420","url":null,"abstract":"Detection and location of leaks in buried plastic fluid-filled pipes are topics of increasing concern for water distribution companies. Acoustic correlation techniques have been widely used to provide an accurate estimate of the position of a leak in order to reduce the wastage of water. However, this technique depends on an accurate estimate of the wave propagation speed along the pipe, which is heavily dependent on the type of soil in which the pipe is buried. The soil also affects the distance that leak noise will propagate along the pipe. This paper describes theoretical and experimental investigations into the way the coupling conditions between the pipe and the soil affects the propagation characteristics of the wave that propagates leak noise in the pipe. Two water pipe systems which have different soil properties are considered: one is in Brazil and the other one is in UK. For the Brazilian pipe system, it is found that the shear modulus rather than the bulk modulus of the soil, has a profound effect on the wave motion in the pipe since it is buried in a clay-like soil. In this case, only the shear wave in the soil propagates away from the pipe. For the UK pipe system, which has sandy soil, both compressional and shear waves propagate away from the pipe. An analysis of the physical effects of fluid-pipe-soil interface and their corresponding parameters on the pipe wave speed and attenuation is also carried out. The results show that the axial coupling between the pipe and the soil has an important effect in the UK pipe system, but has a negligible effect in the Brazilian pipe system.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130125236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Aircraft engines, aerospace rotating equipment, gas turbines, compressors, and rotors in several industrial and aerospace applications approach their nominal operational speeds after the passage through at least one of their critical rotational speeds. During the passage through the critical speeds, elevation in vibration amplitudes is usually observed due to the effect of residual unbalance in these real-life applications rotors. In all of the reported literature, the theoretical and numerical simulation results and the related Campbell diagrams suggest that the backward whirl (BW) zone should precede the passage through the critical forward whirl (FW) speed/speeds of such systems. Here, the existence of zones of rotational speeds at which BW orbits are expected to appear will be investigated immediately before and after the passage through the critical FW speed. Accordingly, startup operations of two different configurations of crack-free rotor-disk systems are considered in this numerical and experimental study. It is found out that there exist zone/zones of the shaft rotational speeds at which BW orbits are experimentally captured where these zones are localized immediately after the passage through the critical FW rotational speed during the startup operations. These BW zones are strongly affected by the acceleration of the shaft during the transient startup operations. These findings suggests that the BW should not necessarily precede the critical FW speed as suggested by the related Campbell diagrams.
{"title":"Capturing BW Zone in an Intact Rotor System","authors":"Fatima AlHammadi, M. Al-Shudeifat, Oleg Shiryayev","doi":"10.1115/IMECE2018-87480","DOIUrl":"https://doi.org/10.1115/IMECE2018-87480","url":null,"abstract":"Aircraft engines, aerospace rotating equipment, gas turbines, compressors, and rotors in several industrial and aerospace applications approach their nominal operational speeds after the passage through at least one of their critical rotational speeds. During the passage through the critical speeds, elevation in vibration amplitudes is usually observed due to the effect of residual unbalance in these real-life applications rotors. In all of the reported literature, the theoretical and numerical simulation results and the related Campbell diagrams suggest that the backward whirl (BW) zone should precede the passage through the critical forward whirl (FW) speed/speeds of such systems. Here, the existence of zones of rotational speeds at which BW orbits are expected to appear will be investigated immediately before and after the passage through the critical FW speed. Accordingly, startup operations of two different configurations of crack-free rotor-disk systems are considered in this numerical and experimental study. It is found out that there exist zone/zones of the shaft rotational speeds at which BW orbits are experimentally captured where these zones are localized immediately after the passage through the critical FW rotational speed during the startup operations. These BW zones are strongly affected by the acceleration of the shaft during the transient startup operations. These findings suggests that the BW should not necessarily precede the critical FW speed as suggested by the related Campbell diagrams.","PeriodicalId":197121,"journal":{"name":"Volume 11: Acoustics, Vibration, and Phononics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124521706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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