Equivalent Source Model Research Articles

Simulation and Analysis of Multi-point Sound Source Model for Transformer

In order to evaluate the noise radiation level of substation accurately, a proper transformer acoustic model should be established. Multi - point source s equivalent model is an effective acoustic model of transformer, but how to determine the number of equivalent sound sources is always a difficult problem. In this aper, the noise of a substation is tested, and the multi - point acoustic models with different numbers of equivalent sound sources are established by using LMS Virtual . Lab software. The sound field of the transformer are calculated by using the established simulation models and the results at the corresponding field points are compared with the measured data, the reasonable number of equivalent sound source model is determined. It provides a reference to the research of transformer multi - point acoustic source s model.

Influences of ground saturation and thermal boundary condition on energy harvesting using geothermal piles

The paper highlights an important distinction between heat transfer mechanism in dry and saturated soil. The effects of two site-specific conditions (e.g., soil saturation and thermal insulation at ground surface) on pile-soil heat exchange and ground temperature response are investigated through a series of thermal tests under laboratory-controlled conditions. Soil temperature data recorded during model tests are compared with soil thermal response predicted using a numerical pile-soil heat exchange model. Moreover, effective thermal conductivity values for the pile-soil system are derived employing equivalent line source model that utilizes circulation fluid temperature recorded during the laboratory tests. Such derived effective thermal conductivity values are compared with soil thermal conductivity values obtained from element thermal conductivity tests. Analysis of recorded soil temperature data and readings from pore pressure transducers during the thermal loading tests identify the possibility of temperature-induced pore fluid flow and convective heat transfer in saturated soil surrounding a ground heat exchanger.

Assessment of the equivalent dipole layer source model in the reconstruction of cardiac activation times on the basis of BSPMs produced by an anisotropic model of the heart

Promising results have been reported in noninvasive estimation of cardiac activation times (AT) using the equivalent dipole layer (EDL) source model in combination with the boundary element method (BEM). However, the assumption of equal anisotropy ratios in the heart that underlies the EDL model does not reflect reality. In the present study, we quantify the errors of the nonlinear AT imaging based on the EDL approximation. Nine different excitation patterns (sinus rhythm and eight ectopic beats) were simulated with the monodomain model. Based on the bidomain theory, the body surface potential maps (BSPMs) were calculated for a realistic finite element volume conductor with an anisotropic heart model. For the forward calculations, three cases of bidomain conductivity tensors in the heart were considered: isotropic, equal, and unequal anisotropy ratios in the intra- and extracellular spaces. In all inverse reconstructions, the EDL model with BEM was employed: AT were estimated by solving the nonlinear optimization problem with the initial guess provided by the fastest route algorithm. Expectedly, the case of unequal anisotropy ratios resulted in larger localization errors for almost all considered activation patterns. For the sinus rhythm, all sites of early activation were correctly estimated with an optimal regularization parameter being used. For the ectopic beats, all but one foci were correctly classified to have either endo- or epicardial origin with an average localization error of 20.4 mm for unequal anisotropy ratio. The obtained results confirm validation studies and suggest that cardiac anisotropy might be neglected in clinical applications of the considered EDL-based inverse procedure.

Spectral decomposition of turbulent mixing and broadband shock-associated noise from a high-performance military aircraft

Sound from high-performance military aircraft originates primarily from the turbulent mixing noise, but at smaller inlet angles, broadband shock-associated noise (BBSAN) is present. The similarity spectra of the two components of turbulent mixing noise developed by Tam et al. [AIAA Paper 96–1716 (1996)] represent noise associated with fine and large-scale turbulent structures and provide reasonable fits for ideally expanded, supersonic jet noise. For non-ideally expanded jet flow, BBSAN contributions to the spectral shape need to be included in spectral decompositions in the sideline and forward directions. A model proposed by Tam et al. [J. Sound Vib. 140, 55–71 (1990)] and later simplified by Kuo et al. [AIAA Paper 2011–1032 (2011)] provides a spectral function that models the BBSAN spectral shape. The ability of the BBSAN and similarity spectra shapes to account for the measured spectra is evaluated for ground-based microphones that covered a spatial aperture from 35 to 152 degrees. Spectral decompositions at low and high engine powers are compared. Using turbulent mixing noise similarity spectra decomposition in conjunction with BBSAN empirical fits, a better equivalent source model can be developed. [Work supported by the Office of Naval Research and the F-35 JPO. Distribution A: Approved for public release; distribution unlimited.]

Building air-infiltration quantification based on sound transmission loss calculated using nearfield acoustic holography

This talk will demonstrate the abilities of nearfield acoustic holography (NAH) to detect and quantify leakages in building envelopes. A tonal sound source was placed inside a building model which has known leakages and microphone array measurements were obtained from the outside. Equivalent sources model based NAH was applied on the measured data to reconstruct the sound pressure field on the wall of the building model. Present results show that the NAH method was able to successfully locate the major leakages. A single microphone was used to measure the sound pressure level inside the building model which was used as a reference for quantification calculations. The difference between the inner and outer sound pressure levels was related to the area of the leakage. Various sizes of pinholes and rectangular cracks were investigated, and the detection limits of the current method were explored.

Dynamic determination of equivalent CT source models for personalized dosimetry

Abstract With improvements in CT technology, the need for reliable patient-specific dosimetry increased in the recent years. The accuracy of Monte-Carlo simulations for absolute dose estimation is related to scanner specific information on the X-ray spectra of the scanner as well as the form filter geometries and compositions. In this work a mobile measurement setup is developed, which allows both to determine the X-ray spectra and equivalent form filter of a specific scanner from just one helical scan in less than 2 minutes.

Prediction of sound fields radiated by finite-size sources in room environments by using equivalent source models: three-dimensional simulation and validation

The use of equivalent source models (ESM) has recently been extended, with appropriate modifications, from its original application in acoustical holography to room acoustics simulations. This approach can serve as an alternative that is less computationally intense than the boundary element method and which is more flexible than traditional ray-tracing models in terms of dealing with non-compact sources and lower frequencies where the ray approximation is no longer accurate. Such room acoustics ESMs are based on the assumption that the room component of the total sound field can be represented by a number of equivalent sources of certain types, and that the total sound field can be predicted, with given free-space source information, by estimating the strengths of these equivalent sources based on a least-square match of the impedance boundary conditions on both the source and the room surfaces. However, to-date, the room acoustics ESMs have only been formulated and validated for two-dimensional cases. In the current work, the ESM formulation has been extended to three dimensions by replacing the two-dimensional equivalent sources with their three-dimensional counterparts, and its applications in a realistic three-dimensional room environment has been validated by successfully comparing the ESM and boundary element predictions.

An experimental comparison of various methods of nearfield acoustic holography

An experimental comparison of four different methods of nearfield acoustic holography (NAH) for planar acoustic sources is presented in this study. The four NAH methods considered in this study are based on: (1) spatial Fourier transform, (2) equivalent sources model, (3) boundary element methods and (4) statistically optimized NAH. Two dimensional measurements were obtained at distances ranging from one-half to sixteen microphone spacings away from a sound source and the NAH methods were used to reconstruct the sound field at the source surface. Reconstructed particle velocity and acoustic pressure fields presented in this study showed that the equivalent sources model based algorithm along with Tikhonov regularization provided the best localization of the sources. Reconstruction errors were found to be smaller for the equivalent sources model based algorithm and the statistically optimized NAH algorithm. The effects of hologram distance on the performance of various algorithms are discussed in detail. The study also compares the computational time required by each algorithm to calculate the reconstruction. Four different regularization parameter choice methods were compared. The L-curve method provided more accurate reconstructions than the generalized cross validation and the Morozov discrepancy principle at larger measurement distances. The performance of fixed parameter regularization was comparable to that of the L-curve method.

Measurement extension limits of patch nearfield acoustic holography

Patch nearfield acoustic holography is widely used when the measurement aperture is smaller than the area of the sound source. This paper discusses the factors affecting the limit of aperture extension. One step patch nearfield acoustic holography based on equivalent sources model was considered in this study. Available literature provide constant estimations on the ratio of measurement area to the area of the source. However, the present study shows that this extension limit is a variable depending on a few parameters. Wave number, hologram distance and choice of regularization technique were found to affect the extended area of reconstruction significantly. By choosing the right combination of these parameters, accurate reconstructions were achieved even when the measurement area was only ten percent of the source surface in size. This paper provides a systematic comparison of reconstruction errors for cases with various parameter combinations. A model relating the parameters and the extension limit is under development.Patch nearfield acoustic holography is widely used when the measurement aperture is smaller than the area of the sound source. This paper discusses the factors affecting the limit of aperture extension. One step patch nearfield acoustic holography based on equivalent sources model was considered in this study. Available literature provide constant estimations on the ratio of measurement area to the area of the source. However, the present study shows that this extension limit is a variable depending on a few parameters. Wave number, hologram distance and choice of regularization technique were found to affect the extended area of reconstruction significantly. By choosing the right combination of these parameters, accurate reconstructions were achieved even when the measurement area was only ten percent of the source surface in size. This paper provides a systematic comparison of reconstruction errors for cases with various parameter combinations. A model relating the parameters and the extension limit is ...

Determining Equivalent Dipoles Using a Hybrid Source-Reconstruction Method for Characterizing Emissions From Integrated Circuits

An efficient emission model for radiation problems in integrated circuits (ICs) is required at the early phase of industrial design. Traditional source-reconstruction methods rely exclusively on near-field scanning and lack the flexibility needed to handle varying IC work conditions. The proposed hybrid model can build a physical connection to the IC's inherent electric properties; therefore, after simple parameter adjustments, it can be applied to any mode of operation. The complete model consists of two sets of equivalent dipoles; one is converted directly from the current/voltage information distributed along the IC package, while the other initially is solved from linear equations that describe the relationship between the dipoles and scanned fields. Then, they are multiplied by a scaling factor to adapt to varying IC work conditions. The emission behavior of an 8-bit commercial microcontroller was reasonably simulated in full-wave solver under various working conditions. The proposed hybrid equivalent source model correctly predicted the simulated reference fields at each operation mode. The feasibility and flexibility of the proposed modeling method have been well validated.

Identifying equivalent sound sources from aeroacoustic simulations using a numerical phased array

An application of phased array methods to numerical data is presented, aimed at identifying equivalent flow sound sources from aeroacoustic simulations. Based on phased array data extracted from compressible flow simulations, sound source strengths are computed on a set of points in the source region using phased array techniques assuming monopole propagation. Two phased array techniques are used to compute the source strengths: an approach using a Moore-Penrose pseudo-inverse and a beamforming approach using dual linear programming (dual-LP) deconvolution. The first approach gives a model of correlated sources for the acoustic field generated from the flow expressed in a matrix of cross- and auto-power spectral values, whereas the second approach results in a model of uncorrelated sources expressed in a vector of auto-power spectral values. The accuracy of the equivalent source model is estimated by computing the acoustic spectrum at a far-field observer. The approach is tested first on an analytical case with known point sources. It is then applied to the example of the flow around a submerged air inlet. The far-field spectra obtained from the source models for two different flow conditions are in good agreement with the spectra obtained with a Ffowcs Williams-Hawkings integral, showing the accuracy of the source model from the observer's standpoint. Various configurations for the phased array and for the sources are used. The dual-LP beamforming approach shows better robustness to changes in the number of probes and sources than the pseudo-inverse approach. The good results obtained with this simulation case demonstrate the potential of the phased array approach as a modelling tool for aeroacoustic simulations.

Research and verification for parabolic equation method of radio wave propagation in obstacle environment

In recent years, the two-way parabolic equation method (2WPE) has been widely utilized for studying the tropospheric ground-wave propagation under the irregular terrain. This algorithm can deal with the influences of the irregular terrain characteristic and the different electromagnetic parameters of the surface structure on wave propagation. However, there are still some defects in 2WPE method. Firstly, the method considers the irregular terrain and obstacles as a whole, so it cannot deal with the situation where the medium parameters of obstacles and the ground are different. Secondly, its calculation precision is limited with the inclination of the undulating terrain: if there are obstacles the upper bound of the inclination is easily broken through. Therefore, in this paper, a novel two-way parabolic equation method is proposed for analyzing the radio wave propagation in obstacle environment. According to the principle of domain decomposition, the obstacle zones are divided into two domains in the new algorithm, and the two subdomains are calculated, respectively. Meanwhile, in order to avoid the calculation error caused by the abrupt truncation of the obstacle zone, the field at the upper boundary of obstacles is modified to ensure the continuity of tangential field. To further improve the accuracy of the new algorithm, according to the historical transmission paths, we exactly retrieve the phases of each forward and backward wave, especially when stepping in and out of the obstacles. Furthermore, the method of moment (MoM) is used to verify the calculation accuracy of the new algorithm in obstacle environment. Although the accuracy of the MoM is very high, it also requires a great deal of calculation resources: it can only be employed to compute the fields in short distance. To overcome the difficulty, we use the image principle in the obstacle environment and do not subdivide the ground into segments; therefore the verification accuracy can be improved. On this basis, to unify the source setting of the new algorithm and the MoM, the equivalent source model is used to set the initial field. Finally, through numerical experiments, the simulation results of both methods agree very well, so the effectiveness of the boundary correction and the phase correction which are presented in this paper are both verified. The accuracy and superiority of the new algorithm in obstacle environment are also demonstrated. To sum up, the novel two-way parabolic equation method can be used to accurately calculate the field of the space in the obstacle environment, and lays the foundation for the field calculation of radio wave propagation in real environment.

An equivalent source to describe realistic synchrotron hard X-rays

An equivalent source model was used to describe realistic third-generation synchrotron hard X-rays to avoid simplifying the light source model excessively or introducing too many variables from optical elements into quantitative calculation. By using particle swarm optimization, through secondary source with different slit apertures, the direct beam diffraction patterns on the detection plane propagated from the simulated equivalent source were in great agreement with the measured patterns. This study is hoped to reduce the difficulty of calculation and improve the accuracy of various coherent imaging or metrology measurements.

Wavepacket source modeling of high-performance military aircraft jet noise from cross-beamforming analysis

Wavepacket models provide a convenient representation of jet noise source phenomena because of the extended, partially correlated nature of the turbulent mixing noise. When treated as an equivalent source model, they are useful to estimate features of both the radiated noise as well as the source characteristics to assist in jet noise reduction efforts. In this study, advanced cross-beamforming techniques are applied to measurements in the vicinity of a high-performance military aircraft. These results are then decomposed into an azimuthally-averaged multi-wavepacket representation of the data, which can then be treated as an equivalent source. Estimates of the field levels and coherence properties using the equivalent source are compared with measurements, and results from the multi-wavepacket model show good agreement with benchmark measurements over a range of frequencies that contribute significantly to the overall radiation. The capabilities and limitations of the model to estimate field properties are quantified with respect to benchmark measurements in the mid and far fields as a function of frequency. Results indicate that the multi-wavepacket representation is an improvement over single-wavepacket models, which do not incorporate spatiotemporal features of the radiation. [Work supported by ONR and USAFRL through ORISE.]

Self-similarity of level-based wavepacket modeling of high-performance military aircraft noise

Construction of the equivalent acoustic source model for high-performance military aircraft noise presented in this paper begins with a decomposition of sound levels, from ground-based microphones 11.7 m from a high-performance military aircraft, into portions matching the similarity spectra associated with large-scale and fine-scale turbulent mixing noise (LSS and FSS). [Tam et al. AIAA Paper 96-1716 (1996)]. A Fourier transform of the spatial distribution of the decomposed levels yields frequency-dependent wavenumber spectra [Morris, Int. J. Aeroacoust. 8, 301-316 (2009)]. Each LSS-educed wavenumber spectrum corresponds to a wavepacket, consisting of a spatially varying amplitude distribution with a constant axial phase relationship. This wavepacket model produces a directional, coherent sound field. However, the asymmetry in the LSS-educed wavenumber spectra may indicate that a nonuniform phase relationship is a more physical choice that could be correlated to the axial variation in convective speed. The FSS component is modeled with a line of incoherent monopoles whose amplitude distribution is related to the FSS-educed wavenumber spectrum. While this level-based model is limited, the addition of the FSS-related source yields a better match to the noise environment of a high-performance military aircraft than is found using a single coherent wavepacket. [Work supported by ONR.]

Spatial variation in similarity spectra decompositions of a Mach 1.8 laboratory-scale jet

The primary source of noise from supersonic jets is turbulent mixing noise. Tam et al. [AIAA Paper 96-1716 (1996)] proposed similarity spectra for a two-source model of turbulent mixing noise corresponding to noise from omnidirectional fine-scale turbulence structures and directional large-scale turbulent structures. These empirical similarity spectra have been compared with reasonable success to the spectra of both military and laboratory-scale jets. Most application have looked at the variation in angle: fine-scale similarity spectra matches sideline of the jet nozzle, large-scale in the maximum radiation lobe, and a combination needed in between. A similarity spectra decomposition of from an ideally expanded, Mach 1.8 laboratory-scale jet allows for a spatial comparison between the near and far-field spectra. The sound from the convergent-divergent nozzle was collected at the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo at a variety of near, mid, and far field locations. Comparison of similarity spectra decompositions over distance yield insights into the sound propagation from this supersonic jet. In addition, results from a preliminary wavenumber eduction technique to build a wavepacket-based equivalent source model of the large-scale turbulent mixing noise. [Work supported by Office of Naval Research grant.]

Energy harvesting from electromagnetic interference induced in the human body

Energy harvesting using the human body as an antenna is presented. Low-frequency interference, mainly in the 40–60 kHz range, was generated from electronic ballast of a fluorescent light. Radiated electromagnetic energy was induced in a human body and a rectifier circuit converted induced energy into DC power. An input matching network of the diode rectifier was designed based on an equivalent source model of interference. A wristband-type harvesting module comprising a metal electrode designed to be in contact with the human skin was implemented. A power of −8.5 dBm was harvested from the body of a person with a height of 180 cm made to stand 60 cm below a fluorescent light with two 32 W lamps in a hemi-anechoic chamber. The proposed system can supply energy to the sensors used in body area networks.

Prediction of flat-bottom hole signals received by a spherically focused transducer for an ultrasonic pulse echo immersion testing

The spherically focused transducer has been widely used for nondestructive evaluation of micrometer-scale inner defects in material and microelectronic devices due to its outstanding transverse resolution and high beam intensity. In this paper, by combining the beam model, the flaw scattering model and the system efficiency factor, an ultrasonic measurement model is developed for the spherically focused transducer in an ultrasonic pulse-echo immersion testing and is used to predict the ultrasonic flaw signal for flat bottom hole (FBH). The multi-Gaussian beam (MGB) model and the Gaussian beam equivalent point source (GBEPS) model are extended to evaluate the beam fields radiated by the spherically focused transducer in water and transmitted into solid through a planar interface. Results show that the MGB model is more excellent considering both the accuracy and efficiency. Experiments are performed to determine the system efficiency factor and the experimental measured flaw signal is compared with the model predictions to validate the accuracy of the proposed model. Effects of the depth and size of the FBH are further studied using the established model.

Radiation Noise Source Modeling and Application in Near-Field Coupling Estimation

Near-field coupling in mixed digital/RF circuit design is critical to system sensitivity for modern high speed electronic systems. This paper presents radiation noise source modeling methods and applies equivalent noise source models to near-field coupling estimations. The noise source can be either modeled by physics-based dipole moment model or Huygens's equivalent model with data obtained from near-field scanning. The fundamental principles of both methods are first studied by simulation. A clock buffer integrated circuit is first modeled as a dipole moment model. The tangential fields on Huygens's box can be calculated by a dipole moment model with negligible multiple scattering effect assumption. The noise coupling then can be obtained by surface integration of Poynting vector at the RF antenna receiving port by full-wave simulation.

Broadband shock-associated noise near-field cross-spectra

The cross-spectral acoustic analogy is used to predict auto-spectra and cross-spectra of broadband shock-associated noise in the near-field and far-field from a range of heated and unheated supersonic off-design jets. A single equivalent source model is proposed for the near-field, mid-field, and far-field terms, that contains flow-field statistics of the shock wave shear layer interactions. Flow-field statistics are modeled based upon experimental observation and computational fluid dynamics solutions. An axisymmetric assumption is used to reduce the model to a closed-form equation involving a double summation over the equivalent source at each shock wave shear layer interaction. Predictions are compared with a wide variety of measurements at numerous jet Mach numbers and temperature ratios from multiple facilities. Auto-spectral predictions of broadband shock-associated noise in the near-field and far-field capture trends observed in measurement and other prediction theories. Predictions of spatial coherence of broadband shock-associated noise accurately capture the peak coherent intensity, frequency, and spectral width.