scholarly journals Performance Analysis of Piezoelectric Actuators in Railway Wheel Squealing Noise Mitigation

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Seyed Rahim Marjani ◽  
Davood Younesian
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Pressure Level ◽  
Contact Forces ◽  
Railway Track ◽  
Noise Mitigation ◽  
Method Performance ◽  
The Time Domain ◽  
Squeal Noise ◽  
Railway Wheels

Application of a shunted piezoelectric system in reduction of the squeal noise level in railway wheels is studied. A wheel squeal model including the railway track, wheel, and nonlinear interaction contact forces is taken into account in the time domain. Consequent vibration of the wheel is calculated at incident of sharp curve passing. The sound pressure level (SPL) of the noise is then calculated by an analytical method. Performance of different shunt circuits including the R (resistance) and RL (resistance inductance) is evaluated in different frequency ranges. A new methodology is proposed to achieve multimode damping. According to results, the SPL of wheel squeal noise can effectively get reduced by the proposed method, up to 5 dB at near-field and 10 dB at far-field.

LES of the Flow and Acoustics Generated by an Aircraft Fan Running in the Vicinity of the Ground

2005 ◽  
Author(s):  
Dragos¸ Moroianu ◽  
Arne Karlsson ◽  
Laszlo Fuchs
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Pressure Level ◽  
Velocity Variation ◽  
Noise Generation ◽  
Fan Noise ◽  
Blade Passage ◽  
Homogeneous Wave ◽  
Sound Spectrum ◽  
Homogeneous Wave Equation

An important component of the aircraft generated noise, especially ahead of it, is the fan noise created by the high velocity variation near the blades and the interaction of the rotating fan with the fluid. In order to predict the sound, the method used involves the acoustical analogy developed by Ffowcs Williams and Hawkings. Computation of the flow field is performed in the incompressible LES framework, while the noise is evaluated using a non-homogeneous wave equation. In this work the influence of the angle between the fan and ground, on the total sound spectrum, the noise generation and the noise propagation is investigated. It is found that the near field is dominated by the blade passage frequency and an upward inclination of the fan will produce a slightly different sound pressure level than a horizontal or downward inclination.

Travelers’ exposure to vibrations and noise depending on the type of transport – the results of pilot research

2019 ◽  
Vol 570 (3) ◽  
pp. 23-27
Author(s):  
Magdalena Matys ◽  
Kamil Piotrowski ◽  
Dominik Mleczko ◽  
Paweł Pawlik
Keyword(s):  
Air Pollution ◽  
Time Domain ◽  
Public Transport ◽  
Sound Pressure ◽  
Heavy Traffic ◽  
Pressure Level ◽  
Point Of View ◽  
Vibration Acceleration ◽  
Passenger Cars ◽  
The Time Domain

For some time residents of big cities have been encouraged to change their means of transport, that is, to swap passenger cars for public transport vehicles. This is meant to help to reduce the problems associated with heavy traffic and air pollution. The authors of the article decided to check if such a change is also beneficial from the point of view of comfort and health of a person who uses public transport. For this purpose values of vibration acceleration and sound pressure level to which Cracow’s commuters are exposed to have been analyzed, depending on the type of vehicle they choose. In this respect measurements have been carried out for passenger cars, buses and trams. Two vehicle models of each type, significantly different from each other (old and new) have been selected for the tests. The measurements during a few trips in each type of vehicle on a predetermined route have been conducted. This article presents a comparison of measured values of vibroacoustic parameters in the time domain. It attempts to assess vibration and noise parameters, taking into account their impact on the health and comfort of the traveler.

Noise Prediction for Multi-Element Airfoil Based on FW-H Equation

2011 ◽  
Vol 52-54 ◽  
pp. 1388-1393
Author(s):  
Jun Tao ◽  
Gang Sun ◽  
Ying Hu ◽  
Miao Zhang
Keyword(s):  
Flow Field ◽  
Sound Pressure ◽  
Near Field ◽  
Pressure Level ◽  
Aerodynamic Noise ◽  
Noise Prediction ◽  
Far Field ◽  
Acoustic Analogy ◽  
Acoustic Information ◽  
Good Agreement

In this article, four observation points are selected in the flow field when predicting aerodynamic noise of a multi-element airfoil for both a coarser grid and a finer grid. Numerical simulation of N-S equations is employed to obtain near-field acoustic information, then far-field acoustic information is obtained through acoustic analogy theory combined with FW-H equation. Computation indicates: the codes calculate the flow field in good agreement with the experimental data; The finer the grid is, the more stable the calculated sound pressure level (SPL) is and the more regularly d(SPL)/d(St) varies.

Noise Abatement From Large Size Electric Generators

2005 ◽  
Author(s):  
Wei Tong
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Near Field ◽  
Cost Effective ◽  
The United States ◽  
Pressure Level ◽  
Environmental Sound ◽  
Industrial Noise ◽  
Large Size ◽  
Electric Generators

Growing environmental sound concerns and recognition that lengthy unprotected exposure to high industrial noise levels can be detrimental to man have resulted in increased attention to reducing industrial noise. In the United States, it is required by law that all turbomachinery manufacturers must provide acoustic guarantees to their customers. For instance, for majority of generators, the near field sound pressure level is usually guaranteed not to exceed 85 dBA. To accomplish this goal, a number of methods of noise reduction have been developed in power industry. As one of the most practical and cost-effective solutions, acoustic blankets have been designed and tested for using on large size electric generators to efficiently reduce their sound pressure levels. This work has successfully demonstrated the potential of acoustic blankets for improve the passive acoustic transmission characteristics from generators. The acoustic data obtained from a field test have shown that the blankets can reduce the overall sound pressure level from large size generators about 4 to 6 dBA.

Reconstruction of the Force Applied to a Plate in the Time Domain From Sound Pressure Measurements

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Chuan-Xing Bi ◽  
Long Hu ◽  
Yong-Bin Zhang ◽  
Xiao-Zheng Zhang
Keyword(s):  
Time Domain ◽  
Sound Pressure ◽  
Microphone Array ◽  
Near Field ◽  
Impulse Response Function ◽  
Time History ◽  
Pressure Measurements ◽  
Concentrated Force ◽  
Vibration Responses ◽  
The Time Domain

Abstract This paper provides a non-contact approach to reconstruct the distributed or concentrated force applied to a plate in the time domain. This approach is based on sound pressure measurements and is realized by coupling the techniques of real-time near-field acoustic holography (RT-NAH) and force reconstruction. A microphone array is used to measure the sound pressures in the near field of the plate. The measured sound pressures are taken as the inputs of the RT-NAH to reconstruct the vibration responses, including the normal acceleration, velocity, and displacement, on the surface of the plate. With the reconstructed vibration responses, the equation of motion governing the forced vibration can be further processed to reconstruct the force applied to the plate in the time domain. In the process of reconstructing the vibration responses, a displacement–pressure impulse response function is derived for the first time and is used in the RT-NAH. Results of numerical simulations as well as experiments demonstrate that the proposed approach can identify the location of the force accurately and reconstruct the time history of the force effectively, thereby helping to diagnose the mechanical cause of the radiated noise.

scholarly journals Noise Source Identification and Noise Directivity Analysis of Bladeless Fans by Combined CFD and CAA Method

2020 ◽  
Author(s):  
Ang Li ◽  
Jun Chen ◽  
Yangfan Liu ◽  
J. Stuart Bolton ◽  
Patricia Davies
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Noise Source ◽  
Near Field ◽  
Low Noise ◽  
Pressure Level ◽  
Design Stage ◽  
Source Analysis ◽  
Far Field ◽  
Computational Domain

Abstract The bladeless fan is a new concept of fan that does not have visible impellers. It features low noise level, uniform airflow, and improved safety. It has been widely applied in household appliances. Since the customers are particularly sensitive to the noise generated by the fan, the aeroacoustics performance of the fan needs to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the aeroacoustics performance and identify the major noise source of the bladeless fan. A prototype of the bladeless fan, including a wind channel, a base cavity, a rotor and a stator inside the base, is set in a computational domain of 4m × 2m × 2m and the airflow through the fan is simulated. The hybrid mesh is generated, the unstructured mesh in the near field, and the structured at the far field. To compute the flow field, steady RANS simulation (standard k–ε turbulence model) and Large Eddy simulation (Smagorinsky-Lilly model) are carried out. Ffowcs Williams and Hawkings (FW-H) analogy is used to predict the acoustic field. Experiments, including air velocity measurement and sound pressure measurement, are conducted to validate simulation results. Sound pressure level results at the near-field receiver illustrate that the blade passage frequency can be captured by combined CFD and CAA method. Noise source analysis shows that the combination of the rotor and stator contributes most to the noise produced by the bladeless fan. The wind channel is the secondary source. Sound pressure level contours at different distances and different heights are generated to investigate the directivity pattern of the noise generated by the bladeless fan. At the near field, the produced noise at the front and the back of the bladeless fan are louder than those at left and right; at the far field, the noise at the front is much larger than the other three sides. In addition, at the near field, with the increase of the height, two separated hotspots appear over 2,500Hz and the sound pressure level at these two hotspots increases; at the far field, the noise distribution at different heights is similar and the peak near 3,000Hz can be estimated. A possible reason to cause this peak is vortex shedding at the trailing edge of the rotor’s blades. The aeroacoustics analysis is helpful to develop strategies to reduce noise and guide the improved design of the bladeless fan.

scholarly journals Noise Reduction Mechanisms of an Airfoil with Trailing Edge Serrations at Low Mach Number

2019 ◽  
Vol 9 (18) ◽  
pp. 3784 ◽  
Author(s):  
Hui Tang ◽  
Yulong Lei ◽  
Yao Fu
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Sound Source ◽  
Sound Pressure ◽  
Pressure Level ◽  
Source Distribution ◽  
Noise Mitigation ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Trailing Edge Serrations

Trailing-edge serrations have proven to be valid applications of trailing edge noise mitigation for an airfoil, while the physical noise reduction mechanism has not been adequately studied. We performed simulations employing Large-eddy simulation and the Lighthill–Curle method to reveal the variation in the hydrodynamic field and sound source due to the trailing edge serrations. The grid resolution and computational results were validated against experimental data. The simulation results show that: the trailing edge serrations impede the growth of spanwise vortices and promote the development of streamwise vortices near the trailing edge and the wake; the velocity fluctuations in the vertical cross-section of the streamwise direction near the trailing edge are reduced for the serrated airfoil, thereby obviously reducing the strength of the pressure fluctuations near the trailing edge; and the trailing edge serrations decrease the distribution of the sound source near the trailing edge and reduce the local peak value of sound pressure level in a specific frequency range as well as the overall sound pressure level. Moreover, we observed that, in the flow around the NACA0012 airfoil, the location where the strong sound source distribution begins to appear is in good agreement with the location where the separated boundary layer reattaches. It is therefore effective to reduce trailing edge noise by applying serrations on the upstream of the reattachment point.

scholarly journals Aerodynamic noise radiating from the inter-coach windshield region of a high-speed train

2018 ◽  
Vol 37 (3) ◽  
pp. 590-610 ◽  
Author(s):  
Wen-Qiang Dai ◽  
Xu Zheng ◽  
Zhi-Yong Hao ◽  
Yi Qiu ◽  
Heng Li ◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
High Speed ◽  
Sound Pressure ◽  
Near Field ◽  
Acoustic Power ◽  
Pressure Level ◽  
Aerodynamic Noise ◽  
Dominant Factor ◽  
High Speed Train ◽  
Frequency Range

The aerodynamic noise has been the dominant factor of noise issues in high-speed train as the traveling speed increases. The inter-coach windshield region is considered as one of the main aerodynamic noise sources; however, the corresponding characteristics have not been well investigated. In this paper, a hybrid method is adopted to study the aerodynamic noise around the windshield region. The effectiveness of simulation methods is validated by a simple case of cavity noise. After that, the Reynolds-averaged Navier–Stokes simulation is used to obtain the characteristics of flow field around the windshield region, which determine the aerodynamic noise. Then the nonlinear acoustic solver approach is employed to acquire the near-field noise, while the Ffowcs-Williams/Hawking equation is solved for far-field acoustic propagation. The results indicate that the windshield region is approximately an open cavity filled with severe disturbance flow. According to the analysis of sound pressure distribution in the near-acoustic field, both sides of the windshield region appear symmetrical two-lobe shape with different directivities. The results of frequency spectrum analysis indicate that the aerodynamic noise inside inter-coach space is a typical broadband one from 100 Hz to 5k Hz, and most acoustic power is restricted in the low-medium frequency range (below 500 Hz). In addition, the acoustic power in the low frequency range (below 100 Hz) is closely related to the cavity resonance with the resonance peak frequency of 42 Hz. The overall sound pressure level at different speeds shows that the acoustic power grows approximately 5th power of the train speed. Two forms of outside-windshields are designed to reduce the noise around the windshield region, and the results show the full-windshield form is better in noise reduction, which apparently eliminates interior cavity noise of inter-coach space and lessens the overall sound pressure level on the sides of near-field by about 13 dB.

scholarly journals Investigation of the effect of a noise barrier on a railway track in the Kysuce region

2020 ◽  
Vol 313 ◽  
pp. 00035
Author(s):  
Alžbeta Pultznerová ◽  
Juraj Grenčík
Keyword(s):  
Wave Propagation ◽  
Sound Wave ◽  
Sound Pressure ◽  
Pressure Level ◽  
Railway Track ◽  
Propagation Path ◽  
Noise Barriers ◽  
Noise Barrier ◽  
Barrier Efficiency

Purpose of the noise barriers is to create an acoustically sufficient impermeable obstacle located on the sound wave propagation path, thereby creating a shadow of the sound pressure level behind the barrier. The paper is focused on the analysis of measured noise values at specific selected points of the railway track in the region of Kysuce without noise barrier and on the determination of noise barrier efficiency. The observed values are compared with the permissible noise values specified by the Slovak legislation

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