Reduction Of Structure-borne Noise Research Articles

Study on Structure-borne Noise Characteristics and Noise Reduction of " Integrated Station-Bridge " High-Speed Railway Station

Study on Structure-borne Noise Characteristics and Noise Reduction of " Integrated Station-Bridge " High-Speed Railway Station

Mid-frequency propagation path analysis on vehicle body using structural intensity

With the penetration of electric vehicles, reduction of structure-borne road noise gets important issue to realize comfortable vehicles for customers.Sound generation mechanism of structure-borne road noise on vehicle body is analyzed basically by modal analysis in low-frequency range. On the other hand, as frequency increases, modal analysis cannot clarify vibration mechanism because vibration wavelength gets shorter, mode density gets high and mode shape gets complicated. Therefore, it is difficult to identify efficient countermeasure parts and inefficient damping materials are added to response panels in mid-frequency range. So alternative analytical methods in mid-frequency range are under research to understand vibration mechanism. In this paper, Structural intensity (SI) analysis is introduced to clarify sound propagation mechanism. This analysis method makes it possible to clarify the main energy propagation path from input point to vibrating panels on vehicle body. The results show that SI analysis unveils the main energy propagation path and gives the opportunity to reduce the panel vibration efficiently by controlling the energy propagation path in body frame structure without damping materials.

Long-Term Efficient Control of Structure-Borne Noise Inside Buildings Caused by Underground Railways by Using Novel Damping Fasteners

Damping fasteners provide vibration isolation to railway tracks because of their low vertical stiffness and improve the in-service performance of the tracks. In this paper, a new type of high lateral stiffness and vertical damping fastener is developed. First, the vibration suppression frequency band of the new fastener was determined from a field test, the design vertical stiffness was determined by calculating the P2 resonance frequency, and the vertical stiffness before and after a fatigue load test was found. Then, field experiments were carried out in buildings with known excessive subway train-induced vibration problems to assess the effectiveness of the proposed fastener, which showed that the damping fasteners reduced the vertical and transverse vibrations of the tunnel wall by 10 dB without increasing the transverse displacements of the rail. Furthermore, the structure-borne noise reduction in all measured buildings exceeded 3 dB. The study demonstrated that the replacement of novel damping fasteners is a feasible solution for controlling vibrations and noise in buildings adjacent to subway lines.

A new method for location of the main contribution modes by the decomposed sound pressure

The control of loud structure-borne noise inside car cabins is commonly by analyses such as panel acoustic contribution analysis, sensitivity analysis, and optimization analysis, to find suitable and practical structural modifications. However, these analyses are usually repeated dozens of times before accessing effective structural modifications, which requires more computation and time. This paper presents a new way to decompose sound pressure and quickly locate structural and acoustic modes of the main contribution for efficient access of feasible structural modifications. The decomposition process of the sound pressure inside structure-acoustic coupled systems was summarized by analyzing specific mathematical formulas. The details for locating the structural and acoustic modes of the main contribution by the decomposed sound pressure were investigated, taking a typical structure-acoustic coupled system of a rigid box with one flexible wall at bottom as an example. To evaluate the correctness of the main contribution modes, modifications were suggested in the structural modes of the main contribution, based on the mechanics of structure-acoustic coupling. The results indicated that the interior sound pressures of structure-acoustic coupled systems are decomposed into matrices by certain mathematical formulas. The main contribution modes are located by analyzing larger data in the decomposition matrices. The modifications in the structural modes of the main contribution reduce the corresponding sound pressure, which shows the correctness of the main contribution modes found. Furthermore, one way for quick suggestion of effective structural modifications was proposed, which offers a potential option for the reduction of structure-borne noise inside car cabins.

Reduction of structure-borne noise in hydraulic power unit with elastic mounting by evaluating structural acceleration level

Reduction of structure-borne noise in hydraulic power unit with elastic mounting by evaluating structural acceleration level

A novel interval analysis method to identify and reduce pure electric vehicle structure-borne noise

The interior noise of a pure electric vehicle (EV) is quieter than that of a traditional internal combustion engine vehicle (ICEV). However, if the noise masking effect of an ICEV is not employed, structure-borne noise from the suspension in an EV will become prevalent, although the interior noise weakens when the EV is driven at a moderate speed. Identifying the sources of suspension structure-borne noise is necessary to reduce the interior noise in an EV and improve the vehicle sound quality. However, the suspension system comprises many components and noise sources, making the identification and reduction of suspension structure-borne noise in an EV a challenging task. In this paper, a new noise source identification method based on interval analysis is proposed. This method can not only accurately identify the sources of noise but also provide details regarding modification methods for reducing interior noise. To implement this method, a test EV was used for measurement, and 15 tests constructed through experimental design were carried out to record the interior noise and vibrations of suspension components. The results showed that the suspension structure-borne noise of the test vehicle was distributed mainly below a frequency of 400 Hz. The feasible intervals and noise source contributions were calculated via the interval analysis method, and the front spring and rear shock absorber were identified as the major sources of suspension structure-borne noise. In addition, component parameters were optimized through the interval analysis method. In accordance with the suggested modification method, a verification test was implemented, illustrating that the EV interior noise quality was improved and validating the effectiveness of the proposed method. The presented approach may be regarded as a promising method for identifying and optimizing vehicle noise sources.

Suppression of Structure-Borne Noise in a Rectangular Enclosure

To date, there is few study on the relation of the structure mode and noise mode as most of researches are only focusing on the modal analysis of the structure-borne noise. This paper presents the extension of study of structure-borne noise analysis in a developed rectangular enclosure which comprises the reduction of structure-borne noise in the enclosure by mitigation method. The suppression of structure-borne noise is significant due to its agonizing effect of causing annoyance and dizziness thus affecting one’s life productivity. The vibrational and sound responses acquired from the modal and sound analysis performed on the enclosure using LMS Spectral Testing. Mitigation is executed by placing the stiffeners made up of aluminum sheet metal perpendicularly to the surface of aluminum sheet-metal of the enclosure. The research purpose is to diagnose the relationship between the structural and noise mode that is obtained from acoustic modal experiment. Resonance between the vibration and noise spectrum needs to be avoided to reduce the structure-borne noise in the enclosure. Before the reduction, the frequency from vibration spectrum is 57.8 Hz while from the noise spectrum is 60.3 Hz. It is found that both of the frequencies are close to each other, thus resulting the occurrence of resonance. After the suppression has been made, the frequency from vibration has declined to 38.8 Hz while the frequency from noise spectrum has increased to 72.8 Hz. The large gap between the frequencies from vibration and noise spectrum indicates that the resonance has been avoided. Therefore, the suppression of the structure-borne noise has successfully attained.

Overview of vibroacoustic isolators used in railway tracks

The paper presents an overview of vibroacoustic isolators used in railway tracks to reduce negative effects from railway traffic. These include single components or their assemblies, with different material characteristics and location in the track structure due to track structure type (ballasted or ballastless track system). The reduction of negative effects relates mainly to the reduction of vibration and structure-borne noise. The practical solutions for railway structures include various components that perform different functions at the same time: vibroacoustic isolation and mechanical function to ensure safe and durable use of rail track (i.e. rail fastening systems, rail supporting structures). The main goals of this paper are systematization and description of basic material characteristics of vibroacoustic isolators applied sufficiently close to the place of vibration generation during the movement of rail vehicles.

동조질량감쇠기를 이용한 탄성지지 래프트 시스템의 구조소음 저감

동조질량감쇠기를 이용한 탄성지지 래프트 시스템의 구조소음 저감

Reduction of Structure-borne Noise of a Building due to Elastic Road Pavement

Reduction of Structure-borne Noise of a Building due to Elastic Road Pavement

Naval-vessel on board equipment base to minimize structure-borne noise

In order to reduce the structure-borne noise of naval-vessel onboard equipment to meet imposed standards, the equipment exciting force should be restricted and additional anti-vibration devices such as resilient mounts and bellows should be applied. Since the structure-borne noise is dependent on the design of the equipment base, the realization of a low-vibration base design is important. In this study, a typical pump base is optimized using Design of experiment (DOE) and Computer-aided engineering (CAE) techniques, in order to minimize the vibration transferred from the equipment base to the floor. In addition, a sandwich panel consisting of a steel plate and rubber material is applied to the pump base between an anti-vibration mount and the base, so as to reduce the vibration transferred from the pump using the double-mounting-system principle. Consequently, the structure-borne noise reduction achieved by applying the proposed base design is verified via experiment.

Value-added recycling of construction waste wood into noise and thermal insulating cement-bonded particleboards

Large amounts of waste wood formwork from construction sites end up with landfill disposal every day. This study aims to develop a practicable technology for recycling construction waste wood into formaldehyde-free cement-bonded particleboards that have value-added features of high strength, light weight, and thermal/noise insulation for reuse in building and construction applications. The mineralogy and microstructure of particleboards were characterized by X-ray diffraction, thermogravimetry, and mercury intrusion porosimetry analyses. Among the mineral admixtures, chloride accelerated precipitation of oxychlorides while sulphate produced calcium sulphoaluminate for promoting early strength development. The use of 2% CaCl2 proved to be sufficient for improving the wood-cement compatibility. At wood-to-cement ratio of 3:7 by weight (i.e., 3:1 by volume), cement hydrates in the porous structure ensured acceptable dimensional stability (<2% swelling). By adjusting the water-to-cement ratio to 0.3 and density of the particleboards to 1.54gcm−3, the volume of capillary pores was effectively reduced from 0.16mLg−1 to 0.02mLg−1. The more compact microstructure contributed to high fracture energy at 6.57Nmm−1 and flexural strength of 12.9MPa. Using the above optimal production conditions, the particleboards complied with the International Standard (9MPa) while enabling reuse as light-weight structure. The particleboards also manifested outstanding structure-borne noise reduction (at 32–100Hz) and low thermal conductivity (0.29Wm−1K−1), suggesting potential application as acoustic and thermal insulating materials. Preliminary cost-benefit analysis illustrated economic viability of the proposed approach. Therefore, technological innovation is crucial for delivering an eco-friendly solution to waste wood recycling for the building and construction industry.

An Experimental Analysis of the Structure-Borne Noise Reduction on Electrical Equipment

본 논문은 전자장비의 구조기인소음 (structure-borne noise)의 실험적 저감방안 검토에 대한 내용을 다루었다. 수냉식 전자장비의 유일한 소음원인 냉각장치를 목업(mock-up)으로 제작하여 소음 특성을 파악하였으며, 전원에 의한 영향, 구조체 강성에 의한 영향, 팬 고정부위의 절연에 의한 효과, 마운트의 공진주파수가 미치는 영향 등에 대한 검토를 수행하였다. 이를 반영하여 제작된 전자장비 프로토타입의 소음 특성을 파악하였으며, 구조기인소음을 저감시키기 위하여 작동회전수(rpm) 조합, 마운트 종류 및 설치방법 등에 대하여 검토하였다. 냉각팬 작동 주파수의 1차, 4차 성분에 의하여 소음이 크게 발생하며, 구조체 강성증가, 팬 고정부위 절연, 마운트 공진주파수 저하, 작동회전수조합, 마운트 선정방법 등에 의하여 전자장비의 구조소음을 저감시킬 수 있음을 확인하였다. In this paper, the structure-borne noise reduction on electrical equipment is discussed by the experimental analysis. The water cooling system in electrical equipment is the only noise source, so the mock-up was made to measure noise characteristics. Effects of power supply, stiffness, isolation of noise source and natural frequency determined by resilient mounts are investigated using the mock-up. The console prototype was made referring to noise reduction technique by the mock-up. The structure-borne noise level of a console prototype was measured and some experiments to reduce the noise was undertaken. The <TEX>$1^{st}$</TEX> and <TEX>$4^{th}$</TEX> harmonics of operating frequency of cooling fans causes highest structure-borne noise levels. The control of operating speeds of several DC cooling fan groups was tried. Also types and installation layouts of resilient mounts were investigated. To reduce structure-borne noise, followings can be applied: increase of stiffness, isolation of source, decrease of natural frequency of mount, combination of operating speed of fans, selection of mounts, and so on.

Interior structure-borne noise reduction by controlling the automotive body panel vibration

The adoption of a numerical method to perform vibration and acoustic analyses is attracting increasing attention because of its merits in saving costs and time. The analysis flow chart of structure-borne noise reduction by controlling the vehicle body panel vibration is proposed. A finite element analysis of a body in white is performed according to this flow chart, using MSC. Nastran, and the experimental modal analysis of a body in white is also carried out. To verify the finite element model, a correlation analysis between the test and the finite element results is performed. After the acoustic boundary element model with seats has been constructed, the acoustic transfer vector is calculated using LMS software. A transfer path analysis is performed to estimate the powertrain and exhaust pipe operational forces at idle. Then the forces are input into the acoustic boundary element model to calculate the body panel velocity. By combining the acoustic transfer vector and the body panel velocity, the interior acoustic response can be obtained. The simulation results are verified by tests. To determine the main contribution panels for the interior sound pressure level, a panel acoustic contribution analysis is based on the boundary element method. Finally, constrained damping treatments are adopted to control the main panel vibration based on the results of the panel acoustic contribution analysis. The test results indicate that the sound pressure level of the interior noise at idle is reduced obviously before and after treatments, which has proved the correctness of the results from the panel acoustic contribution analysis. Therefore it is believed that the proposed analysis method is feasible for reducing interior structure-borne noise.

Environmental and architectural acoustics

Fundamentals of Sound Waves and Hearing. Sound Waves. Speed of Sound. Impetence. Noise and Vibration - Measurement and Rating. Measurement of Sound/Noise. Noise Rating. Measurement of Vibration. Room Acoustics. Sound Field in a Room. Normal Modes of Vibration in Rooms. Reverberation Time. Sound Absorption - Materials and Construction. Types of Sound Absorption Mechanisms. Measurement of Absorption Coefficient and Acoustic Impetence. Characteristics of Porous Sound Absorber. Airborne Sound Insulation. Propagation and Transmission of Airborne Sound. Measurement and Rating of Airborne Sound Insulation. Mass Law for Sound Insulation of a Single Wall. Isolation of Structure-borne Noise and Vibration. Propagation and Radiation of Structure-borne Sound. Reduction of Structure-borne Noise. Measurement and Rating of Impact Sound Insulation. Noise and Vibration Control in the Environment. Basic Strategy. Determination of Required Reduction. Plan for Dealing with Noise and Vibration Sources. Acoustic Design of Rooms. Design Target. Design of Room Shape. Planning the Reverberation. Electro-acoustic systems. Function and Aim of Electro-acoustic Systems. Reinforcement Systems and Architectural Design. Prevention of Howling. Agenda. Wave Equation. Analogues in Electrical, Mechanical and Acoustic Systems and Time Constant. Fourier Transformation and Correlation Functions.

Performance of a restrained-interface substructuring FE model for reduction of structural-acoustic problems with poroelastic damping

This work deals with numerical computation of structural-acoustic applications including dissipative interfaces, in the context of structure-borne noise reduction. It focuses on the need to propose efficient solution strategies for costly finite element modelling. As such, a restrained-interface component mode synthesis is applied to the conservative parts of structural-acoustic applications. The method description being general and computational-oriented, it is straightforwardly applicable to a wide range of problems. The aim is to establish the efficiency as well as the limitations in the use of such a reduced model for harmonic solutions to dissipative structural-acoustic applications including 3D modelling of porous media.

Multiphysics Modeling and Experimental Validation of the Active Reduction of Structure-Borne Noise

This paper presents a fully coupled multiphysics modeling and experimental validation of the problem of active reduction of noise generated by a thin plate under forced vibration. The plate is excited in order to generate a significant low-frequency noise, which is then reduced by actuators in the form of piezoelectric patches glued to the plate with epoxy resin in locations singled out earlier during finite element (FE) analyses. To this end, a fully coupled FE system relevant for the problem is derived. The modeling is very accurate: The piezoelectric patches are modeled according to the electromechanical theory of piezoelectricity, the layers of epoxy resin are thoroughly considered, and the acoustic-structure interaction involves modeling of a surrounding sphere of air with the nonreflective boundary conditions applied in order to simulate the conditions found in anechoic chamber. The FE simulation is compared with many experimental results. The sound pressure levels computed in points at different distances from the plate agree excellently with the noise measured in these points. Similarly, the computed voltage amplitudes of controlling signal turn out to be very good estimations.

Estimation of Structure-Borne Noise Reduction Effect of Steel Railway Bridge Equipped with Floating Ladder Track and Floating Reinforced-Concrete Deck

Estimation of Structure-Borne Noise Reduction Effect of Steel Railway Bridge Equipped with Floating Ladder Track and Floating Reinforced-Concrete Deck

Interior sound field refinement of a passenger car using modified panel acoustic contribution analysis

Panel acoustic contribution analysis (PACA) is a practical engineering tool for the reduction of interior structure-borne noise in passenger cars. In this study, the current PACA method has been improved for sound field refinement of the entire interior. Two new parameters, the “acoustic contribution sum” and the “total sound field contribution”, are introduced to analyze the interior sound field characterized with multiple field points and sound pressure peaks, and to evaluate the integrated acoustic contributions of auto body panels. In addition, a systematic methodology for automotive interior sound field refinement is also proposed on the basis of the modified PACA method. An example of a passenger car model demonstrates the application of the sound-field-refinement methodology and shows the advantage of using damping layers at optimum locations on the auto body. The example also shows that the modified PACA method has practical significance for refining the interior sound field and decreasing added mass in accord with the trend towards lightweight auto bodies.

선박 격실 mock-Up을 이용한 뜬바닥구조의 소음.진동 저감효과 계측에 관한 연구

In this paper, noise and vibration reduction for floating-floored ship cabin is studied. A mock-up is built by using 6 mm steel plate, and two identical cabins are made for simulation of ship cabins. When a speaker is used as a sound and vibration sources, it is shown that floating floor is more effective in isolating sound than bare deck by 2-5 dB. It is also shown that structure-borne noise of the bare deck is greater than that of floating-floored deck by 3-10 dB. For tapping machine excitation, it is found that the effect of floating floor in airborne noise and structure-borne noise reduction reaches up to 40-50 dB for high frequency ranges.