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The muffler shell of an automotive exhaust system can cause numerous NVH (Noise,Vibration and Harshness) issues such as radiated noise, buzzing, rattling and implosion. In general, the problems are detected and solved after the mufflers are built and assembled in a vehicle, which are expensive and time consuming to correct at that stage. It would be beneficial to develop an analytical technique to predict the vibration behavior of a muffler shell during the early stages of exhaust system design. In this paper, shell vibration theories are investigated by comparing the solutions with the results from modal tests and finite element analysis. Utilizing these theories, an analytical model to predict the natural frequencies and mode shapes of muffler shells with circular cross section, elliptical cross section and cross section with two constant radii has been developed. A novel approach for accurately predicting the natural frequencies of muffler sections with two constant radii is also presented in this paper. Case studies are presented to demonstrate that the theoretical analysis can be applied effectively to predict and solve NVH issues of muffler shells. [ABSTRACT FROM AUTHOR]

An effective data analysis technique is presented in this paper for condition monitoring (CM) and fault diagnosis of a quayside container crane (QCC) by utilizing a combined empirical mode decomposition and wavelet packet quantization. The technique is used to extract useful features from the real-time, nonlinear vibration and temperature data from a lifting motor of a crane to improve the reliability in quayside container operation. It is found that the multiple correlation coefficient (MCC) extracted from the real-time CM data of the lifting motor using the proposed technique can be utilized for an accurate fault diagnosis of the motor. It is also shown that when the QCC motor is at healthy state, the MCC calculated from the vibration and temperature data is close to unity and the variation trends (i.e., the change of the signal energy) calculated from these CM data are similar. On the contrary, the variation trends of these CM data become different from each other when the motor has a fault and the MCC value calculated from these data is far less than unity. The study also shows that the feature extracted using wavelet packet quantization technique alone can lead to erroneous results. [ABSTRACT FROM AUTHOR]

In this paper, the free and forced in-plane vibration analysis of rectangular plates are performed for the first time using an improved Fourier series method, in which the boundary restraining spring stiffness can vary in any functional pattern along each edge. Two-dimensional improved Fourier series displacement forms are constructed with four supplementary polynomials introduced into the standard 2-D Fourier series to make the field functions sufficiently smooth in the whole solving domain. Energy formulations are employed to describe the in-plane dynamics of plate system, in which the in-plane concentrated point force is taken into account in the form of work term. All the unknown Fourier series coefficients are then solved through the Rayleigh-Ritz procedure. Several numerical examples are given to demonstrate the correctness and effectiveness of the proposed model through the comparison with those calculated via finite element analysis (FEA). The results show that these two results can agree very well with each other for various non-uniform boundary conditions. Based on the established model, the in-plane vibration response is also studied. Some curves and contours are obtained to illustrate how the boundary restraining stiffnesses affect the in-plane point and transfer mobility of rectangular plate structure. [ABSTRACT FROM AUTHOR]

In many countries, high frequency noise (ultrasonic noise) is included in the list of factors harmful to health in a working environment. For that reason it is necessary to assess risk arising from this type of noise. A previous paper showed that there is no clear and complete information on the factors influencing the result of a measurement of the sound pressure level for the frequency range above 20 kHz. This article presents the influence of measuring instrumentation on the result of a measurement of sound pressure in the range of 10-40 kHz. It discusses the factors associated with adjustment and calibration of the metre/analyser using a sound calibrator; the factors associated with the microphone's frequency response in the free field; the factors associated with uncorrected errors of the metre/ analyser, resulting from its operation; and the factors resulting from the effects of various physical factors (static pressure, temperature, humidity). It also presents the standard uncertainty values for all the above-mentioned factors, and determines the overall uncertainty values for individual frequency bands. Finally, the article outlines the need for introducing, into the measurement result, corrections associated with the microphone's protection grid and the data from a periodic metrological check. [ABSTRACT FROM AUTHOR]

The European Environmental Noise Directive END requires harmonized prediction methods for the major environmental noise sources. Currently two potential candidates are discussed for the modelling of aircraft noise: the 3rd edition of ECAC Doc.29 was published in 2005 describing a recommended method for the prediction of aircraft noise around civil airports. The German AzB model published in 2008 was developed as a tool for the enforcement of the revised German Act for Protection against Aircraft Noise that came into force in 2007. This paper gives a comparative overview on both methods, the underlying acoustic and aircraft performance models and their usability for different fields of application. [ABSTRACT FROM AUTHOR]

Artificial neural network models are simple to apply and have generated a great deal of interest in engineering. By considering the successfully application of artificial neural networks in complex engineering problems, in this paper, artificial neural network system based noise prediction models were developed for predicting far field noise levels due to operation of specific set of mining machinery. Multi-Layer Perceptron (MLP) and Radial Basis Function Network (RBFN) systems were used to predict the machinery noise in opencast mines. The proposed models were designed with VDI-2714 noise prediction model. It was taken due to simplicity, for design of artificial neural network system based noise prediction models for opencast mines. From the present investigations, it was observed that the RBFN model gave better noise predictions than the MLP model. [ABSTRACT FROM AUTHOR]

This paper first presents the analytical models of an ALSTOM simulation software, DIVA, which computes the vibratory and acoustic behavior of a variable-speed induction machine due to Maxwell forces. This radial magnetic pressure in the air-gap makes the stator vibrate in the audible range, creating the so-called magnetic noise characterized by high tonality. On the basis of these analytical models, the main magnetic vibrations due to slotting, pulse-width modulation (PWM) harmonics and their interaction are then analytically characterized. Their number of nodes, velocity and propagation direction are experimentally validated by visualizing the stator deflection shapes. Finally, some experimental validations of the simulation tool are presented. Both analytical results and simulations show that some quieter motors can be designed with motor geometry (especially slot numbers) and PWM strategy. [ABSTRACT FROM AUTHOR]

Broadband noise is a major part of the noise radiated by industrial and domestic fans. For low-speed fans broadband noise contribution to the overall A-weighted noise level is often much higher than that of the tonal noise at the blade passage frequency and its harmonics. One of the main mechanisms of broadband noise is trailing-edge noise, which is due to the convection of the turbulent flow past the blade trailing edge. This paper presents results of a research program in progress, which aims at validating a model that predicts broadband noise levels of rotating blades. Trailing-edge noise prediction is made using an analytical model deduced from an extension of Amiet's formulation. The input data to the model are the frequency spectrum and the spanwise correlation length scale of the wall pressure fluctuations on the blade suction side close to the trailing edge. This model was successfully validated on single fixed airfoils at different angles of attack in an anechoic wind tunnel. The input data were measured with wall pressure transducers on the airfoil suction side. In the present study, the validity of the trailing-edge noise model is assessed for a 800-mm axial flow fan which is used without casing in order to avoid the tip clearance noise contribution. Wall pressure fluctuations are measured with small pressure transducers flush mounted on two rotating blades, using a slip ring to transmit the pressure signals to the frequency analyser. A comparison of measured and predicted far-field sound pressure spectra at different observation angles is presented for two blade pitch angles 20° and 30°. The prediction proves to be quite good at 30° but strongly underestimates fan noise levels over a large frequency range at the lower blade angle. In this case another sound source related to the blade tip vortex is detected. [ABSTRACT FROM AUTHOR]

Vehicle noise, vibration and harshness (NVH) problems can be analyzed using numerical methods such as finite element and boundary element analyses that are generally complex and time consuming. In order to reduce the analysis time and calculation burden, this paper discusses the development, use and verification of an enhanced, simplified numerical acoustic cavity formulation for the analysis of vehicle NVH problems. The proposed simplified vehicle model can incorporate multiple acoustic cavities, such as an engine compartment, passenger compartment, and connecting bulkhead compartment, joined by several flexible panels. The damping matrix of the model is constructed from measured acoustic absorption data and panel properties. Utilizing this approach, both single-cavity and three-cavity models are created, different floor panel configurations are investigated, and transfer functions predicted by these models are compared with corresponding transfer functions from measured data. The comparison results show that the proposed simplified model can provide reasonable accuracy for the analysis and simulation of vehicle compartment acoustics. [ABSTRACT FROM AUTHOR]

The Herschel-Quincke Duct is the simplest implementation of the interference principle with attenuation purposes. Its acoustic behaviour is well known, and it is characterized by the presence of relatively narrow attenuation spikes which, depending on the precise geometrical definition, may give rise to an acceptable attenuation in wide frequency bands. Apart from the study of the influence of a mean flow on its acoustic performance, different modifications to the basic Herschel-Quincke tube have been previously explored, such as the consideration of multiple interfering paths, or the inclusion of a duct connecting the two main propagating paths in the basic configuration. In this paper, a different modification is considered, in which one of the ducts in the two-duct configuration does not have a constant cross-section. A one-dimensional linear model for this modified device incorporating mean flow effects is developed, which is subsequently used to explore the potential of the proposed configuration in order to improve the attenuation characteristics of the Herschel-Quincke tube. [ABSTRACT FROM AUTHOR]