Sound Power Radiation Research Articles

방사소음 및 투과소음에 대한 승용차량 대시패널의 설계인자 별 영향도 분석

While a dash panel component, close to passengers, plays a very important role to protect heat and noise from a power train, it is also a main path that transfers vibration energy and eventually radiates acoustic noise into the cavity. Therefore, it is important to provide optimal design schemes incorporating sound packages such as a dash isolation pad and a floor carpet, as well as structures. The present study is the extension of the previous investigation how design variables affect sound radiation, which was carried out using the simple plate and framed system. A novel FE-SEA hybrid simulation model is used for this study. The system taken into account is a dash panel component of a sedan vehicle, which includes front pillars, front side members, a dash panel and corresponding sound packages. Design variables such as panel thicknesses and sound packages are investigated how they are related to two main NVH indexes, sound radiation power(i.e. structure-borne) and sound transmission loss(i.e. air borne). In the viewpoint of obtaining better NVH performance, it is shown that these two indexes do not always result in same tendencies of improvement, which suggests that they should be dealt with independently and are also dependent on frequency regions.

Acoustic Radiated Calculation of a Finite Cylindrical Shell and Interface Design of the Programs

Based upon the vibratory equation and sound radiation impedance of a cylindrical shell, the sound field distribution of a finite cylindrical shell simply-supported at two infinite rigid cylindrical shells were resolved with considering the structural loss. An interface containing some buttons connected with all the programs was designed by using Matlab, and their data were all stored in a file. It has been shown that the sound radiation power of the cylindrical shell decreases and the radiation efficiency increases with increasing of structural damping loss factors; when the frequency of the driving force is low, the sound field shapes “∞” directivity pattern; When the frequency of the driving force grows higher the sound directivity pattern becomes complex due to superposition of axial modes and circumferential modes; Only when the radiation of the end plates is much weaker than the cylindrical shell the analytical results of the shell simply-supported at two infinite rigid cylindrical shells can be utilized to illustrate the sound radiation by a finite cylindrical shell with two end plates.

Calculation of Sound Radiation Power at Two Ends of Duct System

A method to calculate the radiation sound power from the sound source characteristic of the duct component is developed here; The relationship between the sound source characteristic and the acoustical boundary conditions of the duct ends is also researched by the experiment. Based on the two-port model, the sound source characteristic and the sound transfer matrix of the duct component can be obtained by the numerical or experimental methods. The calculation model to predict the radiation sound power at the end of the duct system is deduced from the sound source characteristic of the duct component. A simple experimental duct system to validate the calculation model is setup and the measurement and calculation results are compared here as well.

Comparison of sound power radiation from isolated airfoils and cascades in a turbulent flow

An analytical model of the sound power radiated from a flat plate airfoil of infinite span in a 2D turbulent flow is presented. The effects of stagger angle on the radiated sound power are included so that the sound power radiated upstream and downstream relative to the fan axis can be predicted. Closed-form asymptotic expressions, valid at low and high frequencies, are provided for the upstream, downstream, and total sound power. A study of the effects of chord length on the total sound power at all reduced frequencies is presented. Excellent agreement for frequencies above a critical frequency is shown between the fast analytical isolated airfoil model presented in this paper and an existing, computationally demanding, cascade model, in which the unsteady loading of the cascade is computed numerically. Reasonable agreement is also observed at low frequencies for low solidity cascade configurations.

Sound reduction of a vibrating plate via dimpling design.

The vibroacoustic performance of plates can be altered by different methods known as structural dynamic modification methods. One of these methods is the shape modification of plate surface. In this study, a method for reducing the sound radiation of vibrating plates is presented. The method based on creating dimples on the surface of a plate. The dimple can be defined as a local modification in the surface of a structure, which has a spherical shape. The dimples change the local stiffness of the plate without changing its mass. Also, they alter the mode shapes so as to reduce sound power, i.e., the radiated sound at some modes is inefficient due to low net volume velocity. The design method couples finite element method, for predicting plate vibration response, with optimization technique based on a genetic algorithm to minimize sound power radiation. The sound radiation is minimized either at a single frequency, or over a broad frequency band. The results show that dimples forming on the plate can achieve effective reductions in radiated sound power.

Intensity Potential Approach for Modeling High-Frequency Sound Fields

This paper proposes the intensity potential approach for prediction of high-frequency sound power radiation. The approach is based on the Helmholtz decomposition of the vector field of time-averaged sound intensity into its irrotational and rotational components. The local power balance in a lossless medium is expressed in terms of the irrotational component only, and results in the Poisson equation for a scalar intensity potential of this component only. The approach gives an exact expression for the sound power through any closed surface in terms of the irrotational component, provided that the boundary conditions are correct. The approach is evaluated by exploring the two intensity components in three canonical examples, and by comparison to measured data with special focus on directivity aspects. It is concluded that the intensity potential approach is relevant, in particular for high-frequency sound fields from multiple sources that are uncorrelated and broadbanded. However, the intensity is generally overestimated in the shadow zones and underestimated in the directly exposed regions. Further, peaks in narrow frequency bands associated with interference of waves are ignored.

Comparison of decentralized velocity feedback control for thin homogeneous and stiff sandwich panels using electrodynamic proof-mass actuators

Theoretical and experimental work is presented to compare the effect of decentralised velocity feedback control on thin homogeneous and sandwich panels. The decentralised control system consists of five control units, which are composed of a proof-mass electrodynamic actuator with an accelerometer underneath its footprint and an analogue controller. The stability of the feedback loops is analysed by considering the sensor-actuator open-loop frequency response function of each control unit and the eigenvalues of the fully populated matrix of open-loop frequency response functions between the five sensors and five actuators. The control performance is then analysed in terms of the time-averaged total kinetic energy and total sound power radiated by the two panels. The results show that for a stiff sandwich panel higher stable feedback gains can be implemented than on a thin homogeneous panel of comparable weight per unit area. Moreover the implementation of decentralised velocity feedback can offset some of the undesirable sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.

Topology optimization of composite material plate with respect to sound radiation

In this paper, topology optimization of composite material plate with respect to minimization of the sound power radiation has been studied. A new low noise design method based on topology optimization is proposed, which provides great guidance for acoustic designers. The structural vibrations are excited by external harmonic mechanical load with prescribed frequency and amplitude. The sound power is calculated using boundary element method. An extended solid isotropic material with penalization (SIMP) model is introduced for acoustic design sensitivity analysis in topology optimization, where the same penalization is applied for the stiffness and mass of the structural volume elements. Volumetric densities of stiffer material are chosen as design variables. Finally, taking a simple supported thin plate as a simulation example, the sound power radiation from structures subjected to forced vibration can be considerably reduced, leading to a reduction of 20 dB. It is shown that the optimal topology is easy to manufacture at low frequency, while as the loading frequency increases, the optimal topology shows a more and more complicated periodicity which makes it difficult to manufacture.

Acoustic radiation from a simple structure in supersonic flow

It is well established that fluid flow can have significant effects on structural acoustic behavior, as is the fact that induced coupling between discrete modes of vibration becomes significant as flow velocity increases. To date, work in this area has been confined to subsonic flows, with the effects on sound radiation efficiency and sound power radiation quantified and compared for various subsonic flow speeds. The purpose of this work is to study the effects that supersonic flow has on these structural acoustic phenomena, along with an investigation of the uncoupled behavior of single modes in the transonic region. Theoretical development of the equations governing the vibration of a simply supported plate in an infinite baffle and an aerodynamic system that models a semi infinite flowing medium along with the method for coupling these systems is included. Computational results are presented illustrating the behavior of the uncoupled modes in the transonic region and the uncoupled and coupled effects on the structural response and sound power radiation as well as a study of the radiation efficiency of the coupled system.

Vibro-Acoustic Analysis of Functionally Graded Elliptic Disc under Thermal Environment

Parametric studies are carried out on the prediction of vibro-acoustic response from an elliptic disc made up of Functionally Graded Material with several cases of FGM index “n,” varying minor axis “a” and for different ceramic combinations with steel. Displacement, velocity, acceleration, radiated sound pressure, radiated sound power level and radiation efficiency of the elliptic disc are examined over a range of varying frequencies. Vibration response due to harmonic point load under thermal environment was computed by finite element method using a macro developed in Ansys Parametric Design Language by the authors, using available physics in ANSYS. Acoustic response of the FGM elliptic disc was computed by coupling the vibration data from the finite element method to the boundary element method using LMS SYSNOISE.

Effect of In-Plane Forces on Sound Radiation From Convected, Fluid Loaded Plates

The purpose of this work is to study the effects that plane stress has on the acoustic radiation from structures subjected to convected fluid loading. It is well established that fluid flow can have significant effects on structural acoustic behavior, along with the fact that induced coupling between discrete modes of vibration becomes significant as flow velocity increases. Work in this area has been confined to flows in air, over unloaded structures, with the effects on sound radiation efficiency, kinetic energy, and sound power radiation quantified and compared for various flow speeds. Theoretical development of the equations governing the vibration of a simply-supported plate subjected to in-plane forces in an infinite baffle and a semi-infinite flowing medium is presented along with a method for coupling these systems. Computational results are presented illustrating the effect of coupling on the sound power radiated from the plate in both subsonic and supersonic flows, for a variety of stress loading cases. It is shown that the state of stress in the plate affects the radiation efficiency of the plate, and that increasing stress eliminates a frequency shift in radiated sound power shown to exist for both subsonic and supersonic flow in previous work.

Sound Radiation of a Large Truck Oil Pan: Estimation and Experimental Investigation

The oil pan of large diesel engine trucks has been identified as a significant contributor to their external noise radiation. This undesired broadband noise is caused by the oil pan's structural vibration and can not be treated effectively by passive measures especially in the low frequency regime up to 500Hz. In order to address this challenge, an active structural acoustic control system consisting of structural sensors and actuators is suitable to alter the oil pans vibrations in a sound reducing manner. A first step is however to classify the broadband sound radiation such that it allows for a proper and efficient sound power estimation resulting from structural measurements. Therefore, an acoustical model was set up based on a geometrical surface scan of a serial production large truck oil pan mounted in a laboratory test stand. This model served for the numerical computation of a set of principle velocity patterns contributing independently to the active sound power, where its hybrid estimation has been performed employing additionally the measured structural response of the oil pan assembly due to a shaker excitation. Finally, the sound power radiation of the test stand has been measured in a reverberation room to validate this hybrid estimation.

Rectangular plate with velocity feedback loops using triangularly shaped piezoceramic actuators: Experimental control performance

This paper presents experimental results on the implementation of decentralized velocity feedback control on a new smart panel in order to produce active damping. The panel is equipped with 16 triangularly shaped piezoceramic patch actuators along its border and accelerometer sensors located at the top vertex of the triangular actuators. The primary objective of this paper is to demonstrate the vibration and sound radiation control using the new smart panel. Narrow frequency band experimental results highlight that the 16 control units can produce reductions up to 15 dB at resonance frequencies between 100 and 700 Hz in terms of both structural vibration and sound power radiation.

Near field placement of error sensors in an active noise control application of axial cooling fans using flow visualization techniques

The use of error sensors in the near field of an axial fan can be used to achieve global attenuation of the blade passage frequency and its harmonics. The pressure field produced by the minimized sound power radiation of the fan and control source configuration dictates possible locations of the error sensors by creating pressure nulls in the near field. By minimizing pressure at these locations, the minimized sound power field can be reproduced. Near field locations can be further investigated using qualitative flow visualization techniques including smoke visualization and quantitative particle image velocimetry (PIV). Analysis of the flow field will help to understand the presence of turbulent flow at the error sensors which can be a cause of a decreased signal to noise ratio. Optimal locations as well as mounting techniques for the error sensors will be discussed based on the flow field analysis. The effects of active noise control on the flow field produced by the fan will also be discussed.

The Modal Low Frequency Noise of an Elastically Supported Circular Plate

The modal low frequency noise generated by a vibrating elastically supported circular plate embedded into a flat infinite baffle has been examined. The main aim of this study is the analysis of the radiation efficiency. Low frequency approximated formulas have been presented. They are valid for all the limiting boundary conditions of the plate with its edge clamped, guided, simply supported or free as well as for all the intermediate axisymmetric boundary configurations. The formulas are expressed in the elementary form, useful for numerical computations. They are a generalization of some earlier published results. First, they are valid for axisymmetric and asymmetric modes since both kinds of modes play an important role in the low frequency range. Second, a single formula for the radiation efficiency, valid for all the axisymmetric boundary configurations, has been proposed. A numerical example for the sound power radiation has been given for some hatchway covers mounted on a ship deck.

Acoustic analysis of damping structure with response surface method

Analysis of vibro-acoustic systems is challenged by their highly non-linear and complex properties, especially for the damping structure. So, an approximate response surface method (RSM) method is utilized to analysis the effect of design parameters on the sound radiation from a vibrating panel. A simple case study was illustrated to demonstrate the capabilities of the developed procedure. In details, sound radiated from vibrating panel with a point force excitation has been analyzed by numerical method. The structure-born noise problem is approximated by a series of second-degree polynomials. Three analysis objectives are considered, namely, mean quadratic velocity, sound radiation power and system loss factor. In this way, the trend of sound radiation varying with design parameters can be obtained conveniently and effectively.

Vibro-acoustic analysis and optimization of damping structure with Response Surface Method

In order to reduce sound radiation, the effective ways are to modify the dimension and shape of structure, or cover the damping material. However, these methods base on the knowledge of qualitative and quantitative relationship between sound radiation and design parameters. It is very difficult to get this kind of function because of highly non-linear and complicated properties of vibro-acoustic problems. Therefore, in order to decrease the complexity of the analysis and reduce cost, approximate method is an effective method. In this study, Response Surface Method (RSM) is utilized to analysis and optimize the vibro-acoustic properties of the damping structure. A simple case was illustrated to demonstrate the capabilities of the developed procedure. In details, a structure-born noise problem is approximated by a series of polynomials using RSM. Three main performances are considered, i.e. sound radiation power, first-order modal frequency and system loss factor. In this way, the analysis and optimization of vibro-acoustic problems can be obtained conveniently and effectively.

The effect of in-plane forces on sound radiation from convected fluid-loaded plates

It is well established that fluid flow can have significant effects on structural acoustic behavior, along with the fact that induced coupling between discrete modes of vibration becomes significant as flow velocity increases. Work in this area has been confined to flows in air, over unloaded structures, with the effects on sound radiation efficiency, kinetic energy, and sound power radiation quantified and compared for various flow speeds. The purpose of this work is to study the effects that plane stress has on these structural acoustic phenomena. Theoretical development of the equations governing the vibration of a simply supported plate subjected to in-plane forces in an infinite baffle and an aerodynamic system that models a semi-infinite flowing medium along with the method for coupling these systems is included. Computational results are presented illustrating the behavior of the uncoupled coupled effects on the sound power radiation from the plate in both subsonic and supersonic flows, for a variety of loading cases.

Acoustic characterization of pneumatic percussion tools

Pneumatic powered percussion tools are extensively used in construction industry. They are one of the noisiest machines in the construction industry generating noise levels well above 110 dBA which are well beyond the permissible exposure limit (PEL) of 85 dBA. The paper presents comprehensive analysis of the noise generated from these percussion tools. Noise tests were carried out on different percussion tools ranging from small chipping hammers to rock drills from two major construction equipment manufacturing companies. These tests were carried out in an anechoic room as well as in simulated operating conditions to determine the overall sound power levels. A spherical array of microphones was used to obtain an accurate estimate of the overall sound power levels and the directivity. The overall sound power radiation was found to be in the range of 105–115 dBA. An advanced 63 microphone phased array was used to successfully locate and identify the major sources of noise from these tools. The outcome of the tests is illustrated in detail in the paper. Further the paper will suggest noise control methods to reduce overall sound power radiation and discuss potential performance levels.

351 圧電スピーカを用いた壁面透過騒音の能動制御

This paper proposes an active control system to reduce the sound transmission through walls without analysis of their characteristics of vibration. The system consists of the plural of control modules installed target walls which have piezo ceramic loudspeakers as a secondary source. Controling sound pressure near the wall and modules's structure make it possible that each circuit has single input and single output. As a result of the experiment of the verification that assumed application to the railway vehicle, we could recognize that the sound radiation power from the target wall was reduced over 4dB.