A self-sustained sound, more usually known as a whistle, refers to a distinct tonal noise created due to the interaction between the sound and flow field. When a positive feedback loop is formed between the two fields, the energy in the mean flow will be transferred into the sound wave, thus giving rise to a whistle. In engineering practice, whistles are destructive as they can produce high sound and vibration levels and may result in risk for mechanical failures. In this work, a flow-related high level tonal noise was found during a measurement on a particle agglomeration pipe, which is a quasi-periodic corrugated structure designed for the exhaust system of heavy-duty trucks. The purpose of the pipe is to enhance particle agglomeration to increase the size of exhaust gas particles. To investigate the origin of the detected tonal noise additional measurements were carried out. Based on the measurement result, the aero-acoustic coupling in the agglomeration pipe was analyzed, revealing that the pipe has a large potentiality to amplify the incident sound power in the presence of a mean flow. Furthermore, the Nyquist stability criterion was applied to confirm the existence of exponentially growing modes in the system at certain conditions.
{"title":"Experimental Analysis of Whistle Noise in a Particle Agglomeration Pipe","authors":"Zhe Zhang, H. Tiikoja, M. Åbom, H. Bodén","doi":"10.1115/NCAD2018-6116","DOIUrl":"https://doi.org/10.1115/NCAD2018-6116","url":null,"abstract":"A self-sustained sound, more usually known as a whistle, refers to a distinct tonal noise created due to the interaction between the sound and flow field. When a positive feedback loop is formed between the two fields, the energy in the mean flow will be transferred into the sound wave, thus giving rise to a whistle. In engineering practice, whistles are destructive as they can produce high sound and vibration levels and may result in risk for mechanical failures. In this work, a flow-related high level tonal noise was found during a measurement on a particle agglomeration pipe, which is a quasi-periodic corrugated structure designed for the exhaust system of heavy-duty trucks. The purpose of the pipe is to enhance particle agglomeration to increase the size of exhaust gas particles. To investigate the origin of the detected tonal noise additional measurements were carried out. Based on the measurement result, the aero-acoustic coupling in the agglomeration pipe was analyzed, revealing that the pipe has a large potentiality to amplify the incident sound power in the presence of a mean flow. Furthermore, the Nyquist stability criterion was applied to confirm the existence of exponentially growing modes in the system at certain conditions.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"326 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122333005","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}
Anna Schwendicke, Shuyue Cheng, Xudong Yu, M. Altinsoy
Whole-body vibrations are an integral part of daily life experience. A thorough understanding of human vibration perception is necessary, e.g., for both the design of multi-modal virtual environments as well as the evaluation of comfort in the automotive industry. In this study, intensity perception for whole-body vibrations near threshold has been measured using amplitude modulated signals as well as narrow band noises. Stevens’ exponents have been calculated showing a significant dependence on frequency between 31.5 Hz and 125 Hz with higher frequencies leading to lower Stevens’ exponents. Amplitude modulation does not have an effect on intensity perception. The use of narrow band noise leads to bigger differences among Stevens’ exponents compared to those of sinusoidal signals. It is concluded that perceptual data from experiments with sinusoidal signals can be used to model the intensity perception of modulated signals, but adjustments have to be made for noisy signals.
{"title":"Intensity Perception for Complex Vertical Whole-Body Vibration","authors":"Anna Schwendicke, Shuyue Cheng, Xudong Yu, M. Altinsoy","doi":"10.1115/NCAD2018-6144","DOIUrl":"https://doi.org/10.1115/NCAD2018-6144","url":null,"abstract":"Whole-body vibrations are an integral part of daily life experience. A thorough understanding of human vibration perception is necessary, e.g., for both the design of multi-modal virtual environments as well as the evaluation of comfort in the automotive industry. In this study, intensity perception for whole-body vibrations near threshold has been measured using amplitude modulated signals as well as narrow band noises. Stevens’ exponents have been calculated showing a significant dependence on frequency between 31.5 Hz and 125 Hz with higher frequencies leading to lower Stevens’ exponents. Amplitude modulation does not have an effect on intensity perception. The use of narrow band noise leads to bigger differences among Stevens’ exponents compared to those of sinusoidal signals. It is concluded that perceptual data from experiments with sinusoidal signals can be used to model the intensity perception of modulated signals, but adjustments have to be made for noisy signals.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124867694","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 resulting dynamic loading on machines, the environment and humans generated by vibration and noise is dependent on the vibro-insulating components and the quality of resilient materials used in the mounting of these components. Well-designed vibration isolation of vibrating sources can effectively reduce the transmission of vibro-acoustic energy into supporting and surrounding structures. Based on frequency spectrum, the vibro-isolation efficiency of various vibro-insulating components and their resilient materials is analysed. The solution of this problem is based on theoretical knowledge and methodology of the transmission of vibration-sound waves and measurement of the machines involved. Measurements of vibration at the sources and along the path of transmission, as well as sound measurements, were performed for different vibro-isolators to compare real results with theory. Measured components include; isolation of a recirculation fan in a heating plant, air-conditioning unit, and combustion engine of a passenger vehicle. For the detection of the vibro-acoustic energy the vibration and sound were measured and FFT analysis was applied. Finally, this paper suggests measures which can be taken to reduce undesirable vibro-acoustic energy on machines, the environment and bystanders.
{"title":"Analysis of the Impact of Different Types of Vibration Isolation on the Dynamic Loading of Machines and the Surrounding Environment","authors":"S. Ziaran, O. Chlebo, M. Musil","doi":"10.1115/NCAD2018-6135","DOIUrl":"https://doi.org/10.1115/NCAD2018-6135","url":null,"abstract":"The resulting dynamic loading on machines, the environment and humans generated by vibration and noise is dependent on the vibro-insulating components and the quality of resilient materials used in the mounting of these components. Well-designed vibration isolation of vibrating sources can effectively reduce the transmission of vibro-acoustic energy into supporting and surrounding structures. Based on frequency spectrum, the vibro-isolation efficiency of various vibro-insulating components and their resilient materials is analysed. The solution of this problem is based on theoretical knowledge and methodology of the transmission of vibration-sound waves and measurement of the machines involved. Measurements of vibration at the sources and along the path of transmission, as well as sound measurements, were performed for different vibro-isolators to compare real results with theory. Measured components include; isolation of a recirculation fan in a heating plant, air-conditioning unit, and combustion engine of a passenger vehicle. For the detection of the vibro-acoustic energy the vibration and sound were measured and FFT analysis was applied. Finally, this paper suggests measures which can be taken to reduce undesirable vibro-acoustic energy on machines, the environment and bystanders.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115498964","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}
Clarice C. Daga, Hetty N. C. C. Lobo, J. A. Lobo, Carlos E. L. Melo
The acoustic conditions in school spaces are fundamental for the success of the learning process. This article aims to present the results of acoustic comfort by the analytical method of 9 classrooms with different geometric characteristics of the University of Brasília. In classrooms the background noise limits are 40 to 50dBA and considering that the teacher’s voice reaches a certain 65 decibels we can highlight that it can be heard clearly by the students. However in an environment with a lot of reverberation of sounds the teacher will have to exert more effort to be understood. The sound perception in a room depends on the intensity and temporal relationship between the direct sound and the indirect sound reflected by the walls of the room, therefore, in the present study were verified two parameters namely the reverberation time and speech intelligibility. The results obtained were compared with the normative parameters of ANSI S12.60: 2010 and it was verified that all rooms are not suitable for teaching-learning activity. To guarantee an environment with better conditions of concentration and learning for the students, acoustic coverings were suggested in order to fit the normative limits.
{"title":"Acoustical Comfort in Classrooms: Case Study at the University of Brasília","authors":"Clarice C. Daga, Hetty N. C. C. Lobo, J. A. Lobo, Carlos E. L. Melo","doi":"10.1115/NCAD2018-6119","DOIUrl":"https://doi.org/10.1115/NCAD2018-6119","url":null,"abstract":"The acoustic conditions in school spaces are fundamental for the success of the learning process. This article aims to present the results of acoustic comfort by the analytical method of 9 classrooms with different geometric characteristics of the University of Brasília. In classrooms the background noise limits are 40 to 50dBA and considering that the teacher’s voice reaches a certain 65 decibels we can highlight that it can be heard clearly by the students. However in an environment with a lot of reverberation of sounds the teacher will have to exert more effort to be understood. The sound perception in a room depends on the intensity and temporal relationship between the direct sound and the indirect sound reflected by the walls of the room, therefore, in the present study were verified two parameters namely the reverberation time and speech intelligibility. The results obtained were compared with the normative parameters of ANSI S12.60: 2010 and it was verified that all rooms are not suitable for teaching-learning activity. To guarantee an environment with better conditions of concentration and learning for the students, acoustic coverings were suggested in order to fit the normative limits.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130140734","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}
Mitigating the propagation of low frequency noise sources in ducted flows represents a challenging task since wall treatments have often a limited area and thickness. Loading the periphery of a duct with a periodic distribution of side-branch Helmholtz resonators broadens the bandwidth of the noise attenuated with respect to a single resonator and generates stop bands that inhibit wave propagation. However, significant flow pressure drop may occur along the duct axis that could be reduced using micro-perforated patches at the duct-neck junctions. In this study, a transfer matrix formulation is derived to determine the sound attenuation properties of a periodic distribution of MPPs backed by Helmholtz resonators along the walls of a duct in the plane wave regime. In the no-flow case, it is shown that an optimal choice of the MPP parameters and resonators separation distance lowers the frequencies of maximal attenuation while maintaining broad stopping bands. As observed in the no-flow and low-speed flow cases, these frequencies can be further decreased by coiling the acoustic path length in the resonators cavity, albeit at the expense of narrower bands of low pressure transmission. The achieved effective wall impedances are compared against Cremer optimal impedance at the first attenuation peak.
{"title":"Sound Attenuation in a Flow Duct Periodically Loaded With Micro-Perforated Patches Backed by Helmholtz Resonators","authors":"T. Bravo, C. Maury","doi":"10.1115/NCAD2018-6103","DOIUrl":"https://doi.org/10.1115/NCAD2018-6103","url":null,"abstract":"Mitigating the propagation of low frequency noise sources in ducted flows represents a challenging task since wall treatments have often a limited area and thickness. Loading the periphery of a duct with a periodic distribution of side-branch Helmholtz resonators broadens the bandwidth of the noise attenuated with respect to a single resonator and generates stop bands that inhibit wave propagation. However, significant flow pressure drop may occur along the duct axis that could be reduced using micro-perforated patches at the duct-neck junctions. In this study, a transfer matrix formulation is derived to determine the sound attenuation properties of a periodic distribution of MPPs backed by Helmholtz resonators along the walls of a duct in the plane wave regime. In the no-flow case, it is shown that an optimal choice of the MPP parameters and resonators separation distance lowers the frequencies of maximal attenuation while maintaining broad stopping bands. As observed in the no-flow and low-speed flow cases, these frequencies can be further decreased by coiling the acoustic path length in the resonators cavity, albeit at the expense of narrower bands of low pressure transmission. The achieved effective wall impedances are compared against Cremer optimal impedance at the first attenuation peak.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"246 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133934550","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}
Amy Dowsett, Daniel O'Boy, S. Walsh, Stephen A. Fisher
An experimental investigation carried out on a luxury sedan door observed the effect of making small changes to trim boundary conditions by removing and replacing a series of small polymer clips that held the trim to the aluminium door. Structural testing was carried out by exciting the system with a shaker and recording the response with accelerometers placed at three different locations about the door. Acoustic response measurements were also taken with the use of a sound intensity probe. The study found that the removal of even a single clip could vary the response significantly for certain clip locations. The spread of structural data was also found to range by more than 15 dB for certain frequency bands. Similar large deviations were observed for the noise transfer response measurements. This is significantly large spread of data for what might be perceived as a relatively small change to the structure, highlighting the importance of reduced variability at material joints.
{"title":"A Study on How Small Changes to Vehicle Panel Boundary Conditions Vary the Overall System Response","authors":"Amy Dowsett, Daniel O'Boy, S. Walsh, Stephen A. Fisher","doi":"10.1115/NCAD2018-6126","DOIUrl":"https://doi.org/10.1115/NCAD2018-6126","url":null,"abstract":"An experimental investigation carried out on a luxury sedan door observed the effect of making small changes to trim boundary conditions by removing and replacing a series of small polymer clips that held the trim to the aluminium door. Structural testing was carried out by exciting the system with a shaker and recording the response with accelerometers placed at three different locations about the door. Acoustic response measurements were also taken with the use of a sound intensity probe. The study found that the removal of even a single clip could vary the response significantly for certain clip locations. The spread of structural data was also found to range by more than 15 dB for certain frequency bands. Similar large deviations were observed for the noise transfer response measurements. This is significantly large spread of data for what might be perceived as a relatively small change to the structure, highlighting the importance of reduced variability at material joints.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126145828","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}
Two significant causes of noise related to cavities are direct and indirect flow induced turbulence/vortex shedding mechanisms. Examples of induced noise can be found in many applications of both closed-flow and open-flow cavities — some with resonance of acoustic modes. An example is a flow valve with a cavity where flow along the cavity gives pulsations either trapped within the valve or exciting downstream piping acoustic modes. There are passive methods of mitigation besides detuning such as modification of the entrance to the cavity, blockage, and use of Helmholtz resonators. Natural frequencies of cavity acoustic modes can be irregular, but for many such as with circular, square, rectangular or axisymmetric shapes can give symmetry of modes. An example is a cavity at the sides of rotating disks, where transverse symmetrical modes having circular and diametric patterns are similar to structural vibratory modes for bladed disks. In the last decade it has been documented that for centrifugal compressors blade passing acoustic pressure pulsation due to Tyler-Sofrin spinning modes can add to alternating stress from non-uniform flow excitation, such as from stator wakes. Cavity acoustic mode excitation then has been termed “triple coincidence” or “triple crossing”, explaining rare documented impeller fatigue failures and likely a reason, at least partially, for some unexplained failures. A novel method described herein is to treat these and similar cavities as fluid-filled disks, then utilize or add blade-like elements within the cavities. The method described (patent application, PCT US1820880) to reduce response of these cavities is to intentionally mistune the elements as has been documented for bladed disk modes. Other applications of this method are possible for many other mechanisms. These modification(s) can alleviate concern for any mechanism having structural vibration excitation acoustically and/or for environmental noise issues.
{"title":"Review of Causes and Mitigation of Cavity Noise in Machinery and Other Mechanisms","authors":"Frank Kushner","doi":"10.1115/NCAD2018-6102","DOIUrl":"https://doi.org/10.1115/NCAD2018-6102","url":null,"abstract":"Two significant causes of noise related to cavities are direct and indirect flow induced turbulence/vortex shedding mechanisms. Examples of induced noise can be found in many applications of both closed-flow and open-flow cavities — some with resonance of acoustic modes. An example is a flow valve with a cavity where flow along the cavity gives pulsations either trapped within the valve or exciting downstream piping acoustic modes. There are passive methods of mitigation besides detuning such as modification of the entrance to the cavity, blockage, and use of Helmholtz resonators. Natural frequencies of cavity acoustic modes can be irregular, but for many such as with circular, square, rectangular or axisymmetric shapes can give symmetry of modes. An example is a cavity at the sides of rotating disks, where transverse symmetrical modes having circular and diametric patterns are similar to structural vibratory modes for bladed disks. In the last decade it has been documented that for centrifugal compressors blade passing acoustic pressure pulsation due to Tyler-Sofrin spinning modes can add to alternating stress from non-uniform flow excitation, such as from stator wakes. Cavity acoustic mode excitation then has been termed “triple coincidence” or “triple crossing”, explaining rare documented impeller fatigue failures and likely a reason, at least partially, for some unexplained failures. A novel method described herein is to treat these and similar cavities as fluid-filled disks, then utilize or add blade-like elements within the cavities. The method described (patent application, PCT US1820880) to reduce response of these cavities is to intentionally mistune the elements as has been documented for bladed disk modes. Other applications of this method are possible for many other mechanisms. These modification(s) can alleviate concern for any mechanism having structural vibration excitation acoustically and/or for environmental noise issues.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117145367","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}
Traffic noise is a major noise source in the study of environmental noise. Various noise generation mechanisms depict different spectral features. Some are wide-band noise, such as engine knocks; some have signature frequencies, such as gear transmissions; and some are in a certain frequency region, such as tire/road noise. These spectral features affect the façade design of a building in order to achieve sufficient exterior noise insulation and satisfactory interior noise due to the traffic noise. ISO standard 11819-1 specifies the measurement procedure of statistical pass-by tests. There are three ranges of vehicle speed: slow, medium, and fast. However, it requires that the vehicle must maintain constant speed when passing by the test point. Unfortunately, a vehicle tends to generate higher noise when accelerating, especially at low frequencies. Therefore, it is necessary to distinguish the noise levels at an intersection versus middle-points of the road between two intersections. Presumably, the traffic noise levels at an intersection would be higher. This research measured the traffic noise at various locations of different speed limits. Statistical analyses were conducted to compare the spectra at these locations. This is also an effort to refine the noise map.
{"title":"Spectral Comparison of Pass-By Traffic Noise","authors":"Zhuang Li","doi":"10.1115/NCAD2018-6149","DOIUrl":"https://doi.org/10.1115/NCAD2018-6149","url":null,"abstract":"Traffic noise is a major noise source in the study of environmental noise. Various noise generation mechanisms depict different spectral features. Some are wide-band noise, such as engine knocks; some have signature frequencies, such as gear transmissions; and some are in a certain frequency region, such as tire/road noise. These spectral features affect the façade design of a building in order to achieve sufficient exterior noise insulation and satisfactory interior noise due to the traffic noise. ISO standard 11819-1 specifies the measurement procedure of statistical pass-by tests. There are three ranges of vehicle speed: slow, medium, and fast. However, it requires that the vehicle must maintain constant speed when passing by the test point. Unfortunately, a vehicle tends to generate higher noise when accelerating, especially at low frequencies. Therefore, it is necessary to distinguish the noise levels at an intersection versus middle-points of the road between two intersections. Presumably, the traffic noise levels at an intersection would be higher. This research measured the traffic noise at various locations of different speed limits. Statistical analyses were conducted to compare the spectra at these locations. This is also an effort to refine the noise map.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115908874","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}
In this investigation, the free vibration analysis of laminated composite rectangular plates with general boundary conditions is performed with a modified Fourier series method. Vibration characteristics of the plates have been obtained via an energy function represented in the general coordinates, in which the displacement and rotation in each direction is described as an improved form of double Fourier cosine series and several closed-form auxiliary functions to eliminate any possible jumps and boundary discontinuities. All the expansion coefficients are then treated as the generalized coordinates and determined by Rayleigh-Ritz method. The convergence and reliability of the current method are verified by comparing with the results in the literature and those of Finite Element Analysis. The effects of boundary conditions and geometric parameters on the frequencies are discussed as well. Finally, numerous new results for laminated composite rectangular plates with different geometric parameters are presented for various boundary conditions, which may serve as benchmark solutions for future research.
{"title":"Vibration Analysis of Laminated Composite Rectangular Plates With General Boundary Conditions","authors":"Yu Fu, Jianjun Yao, Zhenshuai Wan, Gang Zhao","doi":"10.1115/NCAD2018-6106","DOIUrl":"https://doi.org/10.1115/NCAD2018-6106","url":null,"abstract":"In this investigation, the free vibration analysis of laminated composite rectangular plates with general boundary conditions is performed with a modified Fourier series method. Vibration characteristics of the plates have been obtained via an energy function represented in the general coordinates, in which the displacement and rotation in each direction is described as an improved form of double Fourier cosine series and several closed-form auxiliary functions to eliminate any possible jumps and boundary discontinuities. All the expansion coefficients are then treated as the generalized coordinates and determined by Rayleigh-Ritz method. The convergence and reliability of the current method are verified by comparing with the results in the literature and those of Finite Element Analysis. The effects of boundary conditions and geometric parameters on the frequencies are discussed as well. Finally, numerous new results for laminated composite rectangular plates with different geometric parameters are presented for various boundary conditions, which may serve as benchmark solutions for future research.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129682071","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 explores jet noise control using castellations at the exit of pipe-jets. Far-field acoustic measurements and schlieren visualizations are performed for two configurations of castellations; namely, two and four counts. The results are compared with that of pipe-jet without castellations. The nozzle pressure ratio range of the study is 1.5 to 4.5. With each configuration, the position and strength of vortices vary causing it to interact in different manners. For pipe with two castellations, the screech is amplified and the overall sound pressure level is higher than the reference jet in most of the nozzle pressure ratios under study. For pipe with four castellations, there is no noise variation in the azimuthal direction, and screech is eliminated at all nozzle pressure ratios.
{"title":"The Role of Castellations on Pipe Jet Noise","authors":"R. Anureka, K. Srinivasan","doi":"10.1115/NCAD2018-6129","DOIUrl":"https://doi.org/10.1115/NCAD2018-6129","url":null,"abstract":"This paper explores jet noise control using castellations at the exit of pipe-jets. Far-field acoustic measurements and schlieren visualizations are performed for two configurations of castellations; namely, two and four counts. The results are compared with that of pipe-jet without castellations. The nozzle pressure ratio range of the study is 1.5 to 4.5. With each configuration, the position and strength of vortices vary causing it to interact in different manners. For pipe with two castellations, the screech is amplified and the overall sound pressure level is higher than the reference jet in most of the nozzle pressure ratios under study. For pipe with four castellations, there is no noise variation in the azimuthal direction, and screech is eliminated at all nozzle pressure ratios.","PeriodicalId":104108,"journal":{"name":"ASME 2018 Noise Control and Acoustics Division Session presented at INTERNOISE 2018","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123151043","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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