An Efficient Sound Source Localization Technique via Boundary Element Method

The boundary element method (BEM) is a widely used technique in vibro-acoustics. This method is effective not only in the determination of exterior and interior sound fields but also for the sound source localization of complex systems. In this chapter, the Helmholtz integral equation formulation and its boundary element discretization are presented. Half-space algorithm and half-space-contact version of this algorithm feasible for most machine locations are introduced. Some theoretical examples, for a dilating sphere in half-space, are presented. The chapter continues with a case study: Sound source identification and characterization of a refrigerator, via a cost-effective and easy-to-use technique, based on surface velocity measurements and BEM computation of surface and field acoustic pressures

A modal impedance technique for mid and high frequency analysis of an uncertain stiffened composite plate

A modal impedance technique is introduced for mid frequency vibration analyses. The approach is mainly based on statistical energy analysis (SEA), however loss factors are determined by not only driving but also contributed by transfer mobilities. The mobilities are computed by finite element modal analysis. The technique takes geometrical complexity and boundary condition into account to handle their mid-frequency effects. It is applied to a stiffened composite plate having randomized mass, i.e., uncertain plate. For the verification, several numerical and experimental tests are performed. Internal damping of subsystems is evaluated using power injection and is then fed to finite element software to perform numerical analyses. Monte Carlo simulation is employed for the uncertainty analyses. To imitate plate mass heterogeneity, many small masses are used in both numerical and experimental analysis. It is shown that the proposed technique can reliably be used for vibration analyses of uncertain complex structures from mid to high frequency regions. (C) 2015 Elsevier Ltd. All rights reserved

Extreme-Value-Based Bounding of Low Mid And High Frequency Responses of A Forced Plate With Random Boundary Conditions

The problem of statistically bounding the response of an engineering structure with random boundary conditions is addressed across the entire frequency range: from the low, through the mid, to the high frequency region. Extreme-value-based bounding of both the FRF and the energy density response is examined for a rectangular linear plate with harmonic point forcing. The proposed extreme-value (EV) approach, previously tested only in the low frequency region for uncoupled and acoustically-coupled uncertain structures, is examined here in the mid and high frequency regions, in addition to testing at low frequencies. EV-based bounding uses an asymptotic threshold exceedance model of Type-I, to extrapolate the m-observational return period to an arbitrarily-large batch of structures. It does this by repeatedly calibrating the threshold model at discrete frequencies using a small sample of response data generated by Monte Carlo simulation or measurement. Here the discrete singular convolution (DSC) method a transfrequency computation approach for deterministic vibration - is used to generate Monte Carlo samples. The accuracy of the DSC method is first verified i) in terms of the spatial distribution of total energy density, and ii) across the frequency range, by comparison with a mode superposition method and Statistical Energy Analysis (SEA). EV-based bound extrapolations of the receptance FRF and total energy density are then compared with: i) directly-estimated bounds using a full set of Monte Carlo simulations, and ii) with total mean energy levels obtained with SEA. The paper shows that for a rectangular plate structure with random boundary conditions, EV-based statistical bounding of both the FRF and total energy density response is generally applicable across the entire frequency range

A modal impedance technique for mid and high frequency analysis of an uncertain stiffened composite plate

A modal impedance technique is introduced for mid frequency vibration analyses. The approach is mainly based on statistical energy analysis (SEA), however loss factors are determined by not only driving but also contributed by transfer mobilities. The mobilities are computed by finite element modal analysis. The technique takes geometrical complexity and boundary condition into account to handle their mid-frequency effects. It is applied to a stiffened composite plate having randomized mass, i.e., uncertain plate. For the verification, several numerical and experimental tests are performed. Internal damping of subsystems is evaluated using power injection and is then fed to finite element software to perform numerical analyses. Monte Carlo simulation is employed for the uncertainty analyses. To imitate plate mass heterogeneity, many small masses are used in both numerical and experimental analysis. It is shown that the proposed technique can reliably be used for vibration analyses of uncertain complex structures from mid to high frequency regions. (C) 2015 Elsevier Ltd. All rights reserved