Leak testing is a critical manufacturing quality control process. Unintended leaks in pressurized or evacuated containers may be detrimental to consumers, manufacturers, and/or the environment. This paper describes a leak detection and localization technique based on photoacoustic sounds produced by scanning a carbon dioxide laser over leaks emitting a photoactive tracer gas, sulfur hexaflouride. Photoacoustic signals are recorded in a bandwidth from 3 up to 110 kHz by multiple microphones. From these recorded signals, the presence or absence of a leak may be deduced by comparison with background noise levels. When a leak is present, its location is determined from a simple model of the acoustic environment and matched field processing (MFP). Current results show that a gas leak of 1 cm3 per day can be detected and localized to within ±1 mm in a few seconds using four microphones placed 0.41 m from the leak location and an incoherent average of the MFP ambiguity surfaces at twelve signal frequencies.
{"title":"Photoacoustic Leak Testing","authors":"S. H. Yonak, D. Dowling","doi":"10.1115/imece2000-1606","DOIUrl":"https://doi.org/10.1115/imece2000-1606","url":null,"abstract":"\u0000 Leak testing is a critical manufacturing quality control process. Unintended leaks in pressurized or evacuated containers may be detrimental to consumers, manufacturers, and/or the environment. This paper describes a leak detection and localization technique based on photoacoustic sounds produced by scanning a carbon dioxide laser over leaks emitting a photoactive tracer gas, sulfur hexaflouride. Photoacoustic signals are recorded in a bandwidth from 3 up to 110 kHz by multiple microphones. From these recorded signals, the presence or absence of a leak may be deduced by comparison with background noise levels. When a leak is present, its location is determined from a simple model of the acoustic environment and matched field processing (MFP). Current results show that a gas leak of 1 cm3 per day can be detected and localized to within ±1 mm in a few seconds using four microphones placed 0.41 m from the leak location and an incoherent average of the MFP ambiguity surfaces at twelve signal frequencies.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122880483","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 is concerned with improving the performance of a vibration neutraliser (absorber) by making it adaptive. To achieve this, the stiffness and damping of the device has to be controlled so that the impedance of the neutraliser is optimised at its operational frequency. The results of an experimental study are presented where real-time control of such a device is demonstrated. The stiffness is adjusted by changing the geometry, and damping is controlled with a velocity feedback system. Both these actions are achieved using a fuzzy logic controller.
{"title":"Improving the Performance of a Vibration Neutraliser by Controlling Its Stiffness and Damping","authors":"M. Brennan, M. Kidner","doi":"10.1115/imece2000-1626","DOIUrl":"https://doi.org/10.1115/imece2000-1626","url":null,"abstract":"\u0000 This paper is concerned with improving the performance of a vibration neutraliser (absorber) by making it adaptive. To achieve this, the stiffness and damping of the device has to be controlled so that the impedance of the neutraliser is optimised at its operational frequency. The results of an experimental study are presented where real-time control of such a device is demonstrated. The stiffness is adjusted by changing the geometry, and damping is controlled with a velocity feedback system. Both these actions are achieved using a fuzzy logic controller.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115871489","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}
Effects of moderate straining speed on the material and damage characteristics of beam samples of graphite/epoxy and E-glass/epoxy composites were investigated. The basic fiber architecture utilized was unidirectional, axial layup, but data was also obtained for the 45-degree orientation. Ultrasonic and acoustic emission (AE) inspections were utilized. The acoustic emission records show matrix cracking. The ultrasonic images revealed the regions of failure. The results show that in general, strain rate notably affects material and damage properties.
{"title":"Aspects of Strain Rate Effects on Some Composite Materials","authors":"E. Ayorinde","doi":"10.1115/imece2000-1639","DOIUrl":"https://doi.org/10.1115/imece2000-1639","url":null,"abstract":"\u0000 Effects of moderate straining speed on the material and damage characteristics of beam samples of graphite/epoxy and E-glass/epoxy composites were investigated. The basic fiber architecture utilized was unidirectional, axial layup, but data was also obtained for the 45-degree orientation. Ultrasonic and acoustic emission (AE) inspections were utilized. The acoustic emission records show matrix cracking. The ultrasonic images revealed the regions of failure. The results show that in general, strain rate notably affects material and damage properties.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133686814","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}
Sandwich composite constructions that possess several multi-functional benefits in addition to providing structural strength and stiffness have been investigated in the current work. In comparison to traditional foam and honeycomb cores, the Z-pin reinforced space core provides multi-functionality to route wires and rods, embed electronic assemblies, store fuel and fire-retardant foam and provide tailored damping in structures among other conceivable benefits. The present study deals with vibration characterization of Z-pin sandwich plates with hollow and foam-filled core. A finite element study has been conducted on hollow Z-pin core sandwich panels to investigate the stiffness reduction associated with Z-pin buckling.
{"title":"Vibration Response of Multi-Functional Z-Pin Space Core Sandwich Composites","authors":"U. Vaidya, Scott P. Nelson, C. Ulven, B. Mathew","doi":"10.1115/imece2000-1630","DOIUrl":"https://doi.org/10.1115/imece2000-1630","url":null,"abstract":"\u0000 Sandwich composite constructions that possess several multi-functional benefits in addition to providing structural strength and stiffness have been investigated in the current work. In comparison to traditional foam and honeycomb cores, the Z-pin reinforced space core provides multi-functionality to route wires and rods, embed electronic assemblies, store fuel and fire-retardant foam and provide tailored damping in structures among other conceivable benefits. The present study deals with vibration characterization of Z-pin sandwich plates with hollow and foam-filled core. A finite element study has been conducted on hollow Z-pin core sandwich panels to investigate the stiffness reduction associated with Z-pin buckling.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117221258","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}
The high-energy boiler feedwater pump is the heart of the steam-generation cycle in modern high-pressure boiler systems. These multi-stage centrifugal pumps are engineered to produce system pressures from 12 MPa (1800 lb/in2) to 45 MPa (6500 lb/in2) at temperatures ranging from 150°C (300°F) to 312°C (600°F). To optimize pump hydraulic performance, pump designers have focused on impeller and diffuser vane angles, hydraulic passageway shapes and minimized impeller-to-diffuser vane clearances to maximize performance within a narrow range of operation. This was the approach that had been applied successfully on lower energy pump design of an earlier era. However, in the mid-1980s, in response to market forces, operators began to cycle and operate plants over a wide range of loads, which was contrary to the original plant designs. This new operating paradigm has resulted in unacceptable vibration and acoustic emissions that are often attributable to impeller-to-diffuser vane interaction (a result of the minimized clearances referenced previously). Efforts to reduce these emissions by changing the design must always be balanced with the potential impact on hydraulic performance. This paper uses operating field data taken from boiler feedwater pumps to prove that by: • optimizing hydraulic passageways and • changing the internal geometry, specifically, impeller-to-diffuser vane combinations, vibration and acoustic emissions are reduced without compromising hydraulic performance.
{"title":"Field Demonstration of a Boiler Feedwater Pump Upgraded to Reduce Vibration and Acoustic Emissions Without Compromising Performance","authors":"John F. Marchi, R. F. Bush","doi":"10.1115/imece2000-1612","DOIUrl":"https://doi.org/10.1115/imece2000-1612","url":null,"abstract":"\u0000 The high-energy boiler feedwater pump is the heart of the steam-generation cycle in modern high-pressure boiler systems. These multi-stage centrifugal pumps are engineered to produce system pressures from 12 MPa (1800 lb/in2) to 45 MPa (6500 lb/in2) at temperatures ranging from 150°C (300°F) to 312°C (600°F).\u0000 To optimize pump hydraulic performance, pump designers have focused on impeller and diffuser vane angles, hydraulic passageway shapes and minimized impeller-to-diffuser vane clearances to maximize performance within a narrow range of operation. This was the approach that had been applied successfully on lower energy pump design of an earlier era.\u0000 However, in the mid-1980s, in response to market forces, operators began to cycle and operate plants over a wide range of loads, which was contrary to the original plant designs. This new operating paradigm has resulted in unacceptable vibration and acoustic emissions that are often attributable to impeller-to-diffuser vane interaction (a result of the minimized clearances referenced previously). Efforts to reduce these emissions by changing the design must always be balanced with the potential impact on hydraulic performance.\u0000 This paper uses operating field data taken from boiler feedwater pumps to prove that by:\u0000 • optimizing hydraulic passageways and\u0000 • changing the internal geometry, specifically, impeller-to-diffuser vane combinations,\u0000 vibration and acoustic emissions are reduced without compromising hydraulic performance.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129702935","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 finite element/boundary element design tool is used to perform a structural acoustic optimization on an eight-ply graphite epoxy cylindrical shell. The shell is subject to two external monopole sources vibrating at a single frequency. The goal of the optimization is the minimization of the sum of the squared pressure amplitudes within the enclosed acoustic cavity. The ply angles serve as the design variables in optimization. The optimal design was obtained after 15 iterations with a 2 dB reduction in the average interior sound pressure level. The ply angle orientation shifted from an initially symmetric lay-up to an unsymmetric lay-up in the final design.
{"title":"Structural Acoustic Optimization of a Composite Cylindrical Shell Using FEM/BEM","authors":"W. Johnson, K. Cunefare","doi":"10.1115/1.1473829","DOIUrl":"https://doi.org/10.1115/1.1473829","url":null,"abstract":"\u0000 A finite element/boundary element design tool is used to perform a structural acoustic optimization on an eight-ply graphite epoxy cylindrical shell. The shell is subject to two external monopole sources vibrating at a single frequency. The goal of the optimization is the minimization of the sum of the squared pressure amplitudes within the enclosed acoustic cavity. The ply angles serve as the design variables in optimization. The optimal design was obtained after 15 iterations with a 2 dB reduction in the average interior sound pressure level. The ply angle orientation shifted from an initially symmetric lay-up to an unsymmetric lay-up in the final design.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125956837","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 discusses the damping capabilities of polymer materials with mechanical characteristics which vary through the thickness. The case studied is that of a beam coated with a single layer of this material, which can be classified as a free layer damping coating. A simple mechanical model of the system is proposed, together with a suitable modelling of the gradient material. Simulation results based on realistic cases are presented for different types of distribution through the thickness and their damping performance is assessed.
{"title":"A Study on Gradient Polymer Materials Used as Damping Coatings: Focus on Free Damping Coatings","authors":"C. Remillat, G. Tomlinson","doi":"10.1115/imece2000-1641","DOIUrl":"https://doi.org/10.1115/imece2000-1641","url":null,"abstract":"\u0000 This paper discusses the damping capabilities of polymer materials with mechanical characteristics which vary through the thickness. The case studied is that of a beam coated with a single layer of this material, which can be classified as a free layer damping coating. A simple mechanical model of the system is proposed, together with a suitable modelling of the gradient material. Simulation results based on realistic cases are presented for different types of distribution through the thickness and their damping performance is assessed.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121551807","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}
It is well known that turbomachinery rotors produce low frequency forces when subjected to a turbulent inflow. Predictions to date have been based largely upon idealizations of radial blades operating in homogeneous isotropic turbulence. In the present work these models are slightly extended to include the effects of complex blade geometry. The credibility of the method is then tested through comparison to existing experimental data. These comparisons show that the method performs well regarding the shape of the frequency spectrum and the relative effects of complex blade geometries. However, the method tends to sometimes overestimate the absolute levels of the thrust spectra.
{"title":"Prediction of Turbulence Ingestion Forces for Rotors With Arbitrary Rake and Skew","authors":"J. Gavin, G. Lauchle, Michael L. Jonson","doi":"10.1115/imece2000-1608","DOIUrl":"https://doi.org/10.1115/imece2000-1608","url":null,"abstract":"\u0000 It is well known that turbomachinery rotors produce low frequency forces when subjected to a turbulent inflow. Predictions to date have been based largely upon idealizations of radial blades operating in homogeneous isotropic turbulence. In the present work these models are slightly extended to include the effects of complex blade geometry. The credibility of the method is then tested through comparison to existing experimental data. These comparisons show that the method performs well regarding the shape of the frequency spectrum and the relative effects of complex blade geometries. However, the method tends to sometimes overestimate the absolute levels of the thrust spectra.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127826895","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}
The calculation of acoustic radiation from finite wings using a 3D, time-domain Boundary Element Method (BEM) was investigated. Numerical convergence was studied and solutions obtained using an extrapolated convergence method were used to compare to 2D analytical solutions. Frequency-domain lift solutions were found to be accurate to less than 5% using relatively coarse grids (Δx ∼ 0.1) for reduced frequencies above 0.1 and less than approximately 3. The acoustic responses for high aspect ratio wings were found to agree well qualitatively with the 2D results. As an illustration of the capabilities of the method, a full-span, flapped wing configuration undergoing oscillatory motion was considered with a preliminary quantification of the aeroacoustic influence of the flap.
{"title":"Time-Dependent Calculation of Acoustic Radiation From Finite Wings Using BEM","authors":"T. Wood, S. Grace","doi":"10.1115/imece2000-1595","DOIUrl":"https://doi.org/10.1115/imece2000-1595","url":null,"abstract":"\u0000 The calculation of acoustic radiation from finite wings using a 3D, time-domain Boundary Element Method (BEM) was investigated. Numerical convergence was studied and solutions obtained using an extrapolated convergence method were used to compare to 2D analytical solutions. Frequency-domain lift solutions were found to be accurate to less than 5% using relatively coarse grids (Δx ∼ 0.1) for reduced frequencies above 0.1 and less than approximately 3. The acoustic responses for high aspect ratio wings were found to agree well qualitatively with the 2D results. As an illustration of the capabilities of the method, a full-span, flapped wing configuration undergoing oscillatory motion was considered with a preliminary quantification of the aeroacoustic influence of the flap.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126427561","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 sequence of high-order accurate radiation boundary conditions involving local differential operators of auxiliary functions on a circular boundary are implemented in a spectral finite element method with mixed time integration. The semi-discrete finite element equations are integrated explicitly in time while the auxiliary functions on the circular boundary are integrated using a semi-implicit time-integration method. An efficient algorithm results which avoids the need to update either the solutions for the field variable or the boundary functions at intermediate time steps. Using this mixed time integration approach, a very natural and efficient implementation of the high-order accurate, local boundary conditions is obtained without altering the local/sparse character of the finite element equations. Numerical studies of time-dependent scattering from an elliptic object demonstrate the rapid convergence and accuracy of the implementation.
{"title":"Implementation of Local, High-Order Accurate Boundary Conditions for Time-Dependent Acoustic Scattering","authors":"L. Thompson, D. He, R. Huan","doi":"10.1115/imece2000-1591","DOIUrl":"https://doi.org/10.1115/imece2000-1591","url":null,"abstract":"\u0000 A sequence of high-order accurate radiation boundary conditions involving local differential operators of auxiliary functions on a circular boundary are implemented in a spectral finite element method with mixed time integration. The semi-discrete finite element equations are integrated explicitly in time while the auxiliary functions on the circular boundary are integrated using a semi-implicit time-integration method. An efficient algorithm results which avoids the need to update either the solutions for the field variable or the boundary functions at intermediate time steps. Using this mixed time integration approach, a very natural and efficient implementation of the high-order accurate, local boundary conditions is obtained without altering the local/sparse character of the finite element equations. Numerical studies of time-dependent scattering from an elliptic object demonstrate the rapid convergence and accuracy of the implementation.","PeriodicalId":387882,"journal":{"name":"Noise Control and Acoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130800271","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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