Effects Of Noise Control Research Articles

Preparation of microscale multi-layered viscoelastic polymers and analysis of their noise control effects on composite structures

Multi-layered design is an effective method to improve the damping performance of structures. The existing research focuses more on the multi-layered design of the structure from the macro-perspective, but lacks attention to the material itself from the micro-perspective. Thus, whether microscale multi-layered (MML) viscoelastic polymers have advantages in damping performance is not clear. Moreover, damping materials preparation and structural noise control is an interdisciplinary study. The noise and vibration control effect of MML viscoelastic polymers in actual composite structures needs to be further investigated. This paper conducts such a study on these issues. First, two different types of MML viscoelastic polymers, i.e., free damping (FD) and micro-constrained damping (MCD) composites, were prepared, and their material properties were characterized. Second, the frequency-dependent damping loss factors and elastic modulus of the different damping composites were identified. The influences of damping composite types and MML designs on material damping loss factor and elastic modulus were compared. Third, a prediction model of vibroacoustic behaviours of the honeycomb sandwich structure was established and validated to investigate the noise and vibration control effects of the MML damping composites on composite structures. The influences of the types, numbers of layers and application positions of the MML damping composites on the honeycomb sandwich structure were studied. The results indicated that MML design is helpful to improve the damping performance of viscoelastic polymers, but its influence on different damping composites is quite different. For noise control, MML-FD is more suitable for controlling airborne sound propagation, while MML-MCD is more suitable for controlling structural sound propagation.

Passive control on deep cavity noise at subsonic speeds by leading-edge grooves

Control effects of leading-edge grooves on deep cavity noise are investigated numerically. The length-to-depth ratio of the grooves are 0.5, 1, and 4, respectively. The freestream Mach number is equal to 0.16, corresponding to the Re based on the cavity length of 7.7 × 105. The Detached Eddy Simulations (DES) combined with Ffowcs Williams–Hawkings (FW-H) acoustic analogy are adopted to simulate the characteristic information of the flow field and the acoustic field. The analysis results show that all grooves investigated in this paper have a certain noise control effect, and the groove with the most obvious noise reduction effect is the groove with a length-to-depth ratio of 0.5, namely, the deep groove. Narrowband noise generated by the flow-acoustic feedback (100–700 Hz) and the acoustic resonance mechanism (above 300 Hz) and broadband noise caused by the turbulent disturbance in the shear layer of the cavity mouth significantly reduce when the deep groove is used for the noise control. The reason for the noise reduction is that the leading-edge grooves can effectively change the flow characteristics near the mouth of the downstream cavity. When the flow passes the grooves, the groove flow reduces the energy in the fluid, resulting in the significant decrease of flow velocity of the boundary layer of the incoming flow of the cavity. In addition, the use of the deep groove also promotes the vortex concentration position to move towards the bottom of the cavity, pushes the energy in the shear layer of the downstream cavity towards the front-edge as well as the bottom of the cavity, and stabilizes the development of the shear layer near the cavity mouth.

A position optimization strategy of the dynamic vibration absorber for the noise control of the power equipment

Power equipment shows obvious low frequency line spectrum noise characteristics due to the power frequency. The effective noise control of the power equipment can be achieved by installing dynamic vibration absorbers (DVAs) on the structure surface of electrical equipment. However, if DVAs are not installed properly, considering the cases that they are installed at the vibration mode node position, the low radiation vibration mode and the redistribution of the integrate vibration power, the vibration and noise absorbing performances of DVAs may degrade. In order to achieve efficient vibration absorption and noise reduction on the power equipment, this paper proposes a low-frequency noise reduction technology for power equipment based on DVAs. The position optimization of the DAVs using in the power equipment is studied for the first time. Aimed at the single frequency radiated sound power of equipment, the integrate radiated sound power of the equipment is minimized through adjusting the position parameters of DVAs. A numerical case is studied to verify the effectiveness of the proposed DVAs position optimization. The results show that the noise control effect of the power equipment with the optimized DVAs is significantly improved. The method proposed in this paper solves the noise problem of the power equipment, which provides reference for power noise control.

Active Control Algorithm of Hybrid Vibroacoustic for Vehicle Interior Sound Quality

Background: In some applications, retaining the residual noise at a specified frequency can provide a better vehicle interior sound quality for occupant’s driving experience. The hybrid vibro-acoustic adaptive noise equalizer (HVA-ANE) algorithm introduces a sound retention factor on the basis of the hybrid vibro-acoustic filter-u, and filter-x least mean square (HVA-FUXLMS) algorithm to achieve control of the sound quality, but it is not possible to retain varying degrees of different frequency bands. The hybrid vibro-acoustic empirical-mode-decomposition frequencydomain block adaptive noise equalizer (HVA-EBANE) algorithm introduces Empirical-Mode- Decomposition (EMD) and frequency domain block methods to achieve different degrees of retention of noise in different frequency bands but cannot deal with the irrelevant frequency components in the error signal. Objective: This paper proposes an improved active control algorithm for vehicle interior sound quality, the so-called hybrid vibro-acoustic EMD frequency-domain block FELMS (HVA-EBFELMS) algorithm. Methods: Based on the filtered error, the least mean square algorithm and the residual filter of the specific frequency band are designed according to the psychoacoustic parameters of each component. The filter filters the irrelevant frequency components in the residual signal, and only retains the frequency components that have a great influence on the sound quality so as to achieve the regulation of the desired sound quality. Results: In order to verify the effectiveness of our algorithm, we used the noise and vibration in the vehicle at idle speed as the object and compared the noise control effect with HVA-ANE and HVAEBANE algorithms considering the sound quality. The simulation experiment shows that our algorithm reduces the loudness of the ear-side noise by more than 40% while taking into account the noise and vibration control. Conclusion: The loudness control effect of hybrid vibro-acoustic EMD frequency-domain block FELMS (HVA-EBFELMS) algorithm is better than HVA-ANE and HVA-EBANE algorithms; it has a better effect of improving loudness as well.

Experimental study on noise reduction of multi-rotor by phase synchronization

Phase synchronization implies that the rotors are synchronized to the same rotation speed and different phases to minimize rotor noise in specific directions. In this study, the influence of phase synchronization on noise directivity and the reducing effect of a multi-rotor were studied experimentally. Based on the multi-rotor noise test platform built in the anechoic chamber, to study the noise control effect of phase synchronization, tests were performed on a small-scale dual-rotor and quadrotor. The influence of phase synchronization on the noise directivity and frequency characteristics was analyzed. Furthermore, the effectiveness of the proposed method was verified using noise-reduction experiments for the target points and regions. The experimental results revealed that: (1) phase synchronization is more advantageous for co-rotating rotors than counter-rotating rotors. Phase synchronization reduces the noise level in all azimuths for the co-rotating rotors, and only a few directions for the counter-rotating rotors. (2) Phase synchronization effectively reduces the sound pressure level in the low-frequency band and multiple harmonic frequencies for a single observation point, especially at the blade-passing frequency. (3) The regional noise is reduced by 1–5 dB and 1–11 dB for the counter-rotating and co-rotating dual-rotor, respectively. Therefore, the experiments show that phase synchronization has a significant advantage in noise control for multi-rotor aircraft.

Low frequency noise control in duct based on locally resonant membrane with attached resonators

In this paper, locally resonant membrane with attached resonators is introduced to duct system to achieve good noise control effect especially in low frequency range. A rigorous analytical model based on modal expansion method is developed to investigate the vibroacoustic coupling characteristic of proposed duct-membrane-resonator system. The corresponding theoretical results show a good agreement with numerical simulation. The velocity distribution, sound transmission loss curve, and the mechanism behind are discussed and explained deeply. It is found that the attached resonators on the membrane can lead to new transmission loss peak which is related to but not exactly equal to the resonance frequency of attached resonator itself. Correspondence between zero equivalent density mass and transmission loss peak is achieved at the non-antisymmetric modes. Compared to single resonator, multi-resonators system can realize more transmission loss peaks for better sound transmission effect. In principle, ultra-low frequency noise reduction and arbitrarily adjustable frequency can be achieved by changing the frequency, position, and number of exerted resonators, which provide a new approach for duct noise control.

Urban 110 kV indoor substation noise analysis and control schemes: A real case study

As an important node in urban city, power substation provides the clean energy to thousands of households, ensuring a stable and high quality of urban life. However, the influence of noise emission from substation is always underestimated. With the improvement of environmental consciousness, making the substations quietly hidden in urban cities becomes an urgent issue which should be thoroughly considered. A real case is presented in this paper to vividly reflect how such a comprehensive noise issue is faced and tackled through proper techniques and novel applications. Based on the low-frequency noise characteristics of 110 kV power transformers and the limited space features of indoor substation, integrated noise control schemes are proposed with consideration of low-noise design of ventilation and heat dissipation systems. Dynamic vibration absorber is firstly investigated and designed to minimize the vibration of transformer tank. After the practical implementation, the acoustic environment is reevaluated and the measurement results verified the noise control effect. Consequently, the acoustic environment quality within and out of substation is improved and the negative impact of urban substation is controlled.

Discussion on Substation Noise Control Target and Simulation Analysis

Substation noise engineering control is an important environmental protection content of current power grid companies. How to ensure the effectiveness of noise control and reduce environmental complaints and disputes has become an important subject for engineering and technical personnel. This paper analyzes and discusses the “Environmental Noise Emission Standards for Industrial Plants” (GB 12348-2008), and uses the simulation calculations and analysis cases of typical substation noise control to propose the principles and principles of sensitive targets and station boundaries in substation noise control. The analysis method in substation noise control provides reference and reference for the revision of substation noise engineering control technology and related standards.

Design of Tunable Acoustic Liner and Adaptive Control System

Traditional acoustic liners used in nacelles and fan ducts include a perforated face sheet bonded to a honeycomb core. A tunable acoustic liner with a piezoelectric substrate is developed to overcome the shortages of current liner such as unchangeable structure and uncontrollable bandwidth. After the piezoelectric panel deformed under the driving voltage, the resonant chamber changed, and the resonant frequency shifts. The finite element method is used to calculate the acoustic system’s resonant frequency and sound pressure distribution. The transmission loss measurement was carried out in an impedance tube to demonstrate the broadband noise control effect of the liner. The experiment result indicates that the TL peak frequency keeps linear with the driving voltage, and the sensitivity is measured to be 0.1 Hz/V. A DC amplified circuit using photo resistor is designed based on constructing the function of driving voltage and noise frequency. Benefit from the adaptive algorithm, when the noise frequency offsets from 756 to 788 Hz, the driving voltage can be automatically regulated from 110 to 420 V, and the liner always keeps resonating. Meanwhile, the sound level was reduced. The adaptive noise control is realized for broadband noise reduction.

Simulation and Analysis of Noise from Acoustic Hood of Micro Electric Vehicle Range Extender*

Aiming at the noise control requirements of micro electric vehicle(EV) range extender, the author designed an acoustic hood and base it to build a 3D model and make a modal analysis and acoustic simulation to analyze the effect of noise control. Verifying the design of acoustic hood is reasonable. At the same time, it’s one of the important reasons the natural frequency of the hood results in the difficulty of noise control which can supply reference for improving design of acoustic hood of range extend.

The effects of noise control in coffee tasting experiences

The present research investigates the general effect of auditory noise control in individual’s eating and drinking experiences. In particular, the study applied passive vs active commercial headphone noise control techniques to an urban drinking situation. Here, each participant drank twice the same coffee while exposed to a louder (~85 dBA) vs less loud (−20 dBs) version of the same background noise of a food court in busy hours. Note that by loud, louder, and less loud, we are referring to differences in the sound level of the noise.Results suggest that most consumers tend to be less sensitive to specific sensory and hedonic attributes of the coffee under louder noise (sweetness, bitterness, acidity, flavor/aroma intensity, flavor-liking, sound-liking, flavor-sound-matching), and less willing to pay and purchase the coffee, relative to less loud sounds. This was more evident concerning the perceived bitterness and aroma intensity of the coffee. The effects reported are mainly attributed to the differences in noise level during taste, and discussed based on theory on crossmodal correspondences, and attention (e.g., louder noise may diminish the ability to attend to specific elements of the experience). When thinking of public health, for example, these results suggest that differences in urban noise level may moderate behavior during food/drink situations (e.g., potentially modulating sugar intake).

Analysis and control of ventilation noise reduction for box-type transformer in urban area

Noise generated by outdoor box transformer in the working process has a certain impact on the production and life of the surrounding residents. Combining with the current situation of box transformer in 10kV urban area of a residential district, the paper analyses the problems and causes of noise transmission and control. According to the characteristics of noise sources and transmission ways of substation, the paper puts forward and implements ventilation, heat dissipation and sound insulation cover to reduce noise, improve room temperature and ventilation effect, and compares and compares them. The effect of noise control before and after modification is analyzed. The result shows that the effect of modification is obvious and the noise at boundary of box transformer meets the national standard.

Noise in the outpatient operating room.

Noise exposure in hospitals can negatively impact both patients and doctors. It can make patients feel more anxious or depressive and can impair doctors' concentration or judgment, potentially leading to poor decision-making or performance. In China, an increasing number of outpatient operating rooms have emerged in recent years for the convenience of patients planning to undergo minor surgery. In this study, we aimed to investigate the impact of noise exposure in the outpatient operating room and ways to deal with it. By monitoring noise at different locations in three hospitals, we analyzed the average noise exposure intensity affecting outpatient operative procedures. After noise monitoring, we made some constructive suggestions and other adjustments to reduce and lower the noise exposure in one outpatient operating room [the experimental operating room (EOR)] to observe the feasibility and effectiveness of noise control in and out of the outpatient operating room. Noise intensity in the outpatient operating room was significantly higher than that in the inpatient operating room (68.3±14.7 vs. 45.7±9.6, P<0.05). After noise control, the noise intensity in the EOR decreased significantly (74.5±16.6 vs. 59.2±13.4, P<0.05) but was still higher than that in the inpatient operating room (59.2±13.4 vs. 46.0±9.3, P<0.05) of the same hospital. Further analysis revealed that noise affecting outpatient operating room mainly originates from vehicles outside, medical machines, ambulances, crowds in the outpatient main hall, and communication devices. Noise exposure is a common and serious problem, but measures can be taken to deal with it effectively.

Study on noise control effect based on generalized Lorenz system

The suppression of ship radiation noise is studied through a generalized Lorenz system. The system integrates a classical Lorentz system with a time-delay feedback control and an external acoustic excitation. The output of the system can be categorized into three different states: the quasi-periodic state, the periodic state and the chaotic state. The output state is characterized by the trajectory, the bifurcation diagram and the Lyapunov exponent of the system. The dependence of the output state on different excitation parameters like amplitude, frequency, time delay and the number of external excitations are simulated. It is found that the chaotic state and noise suppression is largely dependent on the amplitude of the external excitation. The noise suppression in the generalized Lorenz system is characterized by the changes in power spectrum of the acoustic energy, which is investigated through Fourier transformation. The suppression is optimized by specified excitation parameters: an acoustic energy reduction up to 26.67 dB is realized with excitation source of small amplitude, high frequency, and a phase synchronized with the noise phase. The noise suppression through multiple excitations in the system is also investigated.

Effect of helical cables on cylinder noise control

This paper presents a parametric study on the far-field noise control effect of a circular cylinder with helical cables wrapping along cylinder span, aiming at finding an optimal operation condition for this treatment. Experimental results reveal that the noise control efficiency of this treatment is highly dependent on the non-dimensional thread pitch and cable density. The noise control efficiency gradually increases with the non-dimensional thread pitch and cable density increasing when both values are smaller than critical values. Further increasing the values of the two parameters, the control efficiency cannot increase any more. By choosing the optimal parameters of helical cables, both tonal and broadband noise can be remarkably suppressed, and the overall sound pressure level can be reduced by as large as 17dB.

Transmission loss analysis of thick perforated plates for valve contained pipelines

Valve contained pipelines have witnessed a great growth and there exists a lot of noise caused by valves. Thick perforated plates are especially used is valve contained pipelines for the noise control, but there are limited literatures about its noise control performances under different structural parameter of thick perforated plates, which limits its popularization and application. In this paper, transmission loss (TL) predictions of various thick perforated plates are carried out to analyze the noise control performances. Finite element method (FEM) is implemented to simulate the acoustic response, and TL is achieved by the sound pressure of four points on both sides of the thick perforated plates. Adopted numerical method shows good agreements with the existing research works and the results indicate that reducing the margin of the plates can enhance TL of some frequencies. Similar to chamber mufflers, the maximum TL depends on the area ratio and the frequency range with the best noise control performance is related to the plate thickness. Meanwhile, the low velocity flow does not affect the TL curve so much and in the situation of supersonic flow, and the TL curve turns into a periodic shape, which may weaken the effects of noise control. Besides, based on the analytical solution of TL for the chamber muffler, a linear correction formula of maximum TL is proposed for the thick perforated plate. This work can give several advices for similar perforated plates design works and someone who are dealing with decreasing the noise effects from the valves in pipelines.

Evaluation of the Dynamic Characteristics of AZ91D Crankcase Covers and Boxes

Dynamic tests are performed on similarly structured crankcase covers and boxes made of AZ91D magnesium and A380 aluminum alloys. The real vibration and noise control effect of an AZ91D magnesium alloy is evaluated, based on the behavior of the integral frequency response function, which is derived from the measured surface vibrations of the crankcase cover under operating conditions. The results indicate that crankcase covers and boxes made of AZ91D magnesium and A380 aluminum alloys with the same geometry possess similar normal characteristics. Both materials are interchangeable. However, the stiffness of AZ91D crankcase covers and boxes is poor. It is also difficult to obtain good engineering vibration and noise effects in the real structure due to an AZ91D high damping capacity. At the same excitation and frequency response at different structure characteristics, the measurement analysis of time-domain response indicates that methods to strengthen the crankcase box stiffness, such as embedding a main bearing steel sleeve, is favorable for improving the dynamic characteristics of an AZ91D crankcase box.

S056025 プラズマアクチュエータを用いた平板翼列から発生する空力音の制御

In order to reduce an aerodynamic noise generated from the flat plate cascade, we attempted to flow and noise control by using plasma actuator. In the case of non-resonance condition (such as the Aeolian tone noise generated from a single flat plate), aerodynamic noise levels increase by using PA. This is considered because that PA supply the momentum to the separated flow near the leading edge, flow separations are suppressed and the share flow becomes stronger than that of without PA. As a result, aerodynamic noise is increased by using PA in non-resonance condition. The effect of noise control is proportional to the supplied voltage and driven frequency of PA. On the other hand, in the case of resonance condition of flow and sound fields, sound level can be reduced by using PA. When the acoustic resonance occurs in flat plate cascade, phase of vortex shedding is locked by the generated sound. The experimental results showed that PA was control the phase and intensity of the vortex shedding near the reading edge, and it is less likely to become strong acoustic resonance field is formed. These facts indicate that the control of unsteady aerodynamic flow and sound field characteristics must be discussed when the effectiveness of noise control with PA is evaluated.

Research of Quantum Algorithm for Adaptive Active Noise Control System

Adaptive active noise control based on least mean square (LMS) algorithm is a linear adaptive filter so that it cannot obtain desired noise reduction. Quantum algorithm is combined with noise control to form quantum adaptive controller. Quantum adaptive algorithm is discussed completely and noise control system is simulated in order to analyze the effects of noise control.

Research of Quantum Algorithm for Adaptive Active Noise Control System

Adaptive active noise control based on least mean square (LMS) algorithm is a linear adaptive filter so that it cannot obtain desired noise reduction. Quantum algorithm is combined with noise control to form quantum adaptive controller. Quantum adaptive algorithm is discussed completely and noise control system is simulated in order to analyze the effects of noise control.