Numerical Modeling of Head-Related Transfer Functions Using the Boundary Source Representation

2006 ◽  
Vol 128 (5) ◽  
pp. 594-603 ◽  
Author(s):  
Mingsian R. Bai ◽  
Teng-Chieh Tsao
Keyword(s):  
Transfer Functions ◽  
Human Head ◽  
Memory Storage ◽  
Computational Time ◽  
Minimal Amount ◽  
Virtual Source ◽  
Layer Potential ◽  
Source Method ◽  
Boundary Source ◽  
Human Listener

A technique based on the virtual source representation is presented for modeling head-related transfer functions (HRTFs). This method is motivated by the theory of simple layer potential and the principle of wave superposition. Using the virtual source representation, the HRTFs for a human head with pinnae are calculated with a minimal amount of computation. In the process, a special regularization scheme is required to calculate the equivalent strengths of virtual sources. To justify the proposed method, tests were carried out to compare the virtual source method with the boundary element method (BEM) and a direct HRTF measurement. The HRTFs obtained using the virtual source method agrees reasonably well in terms of frequency response, directional response, and impulse response with the other methods. From the numerical perspectives, the virtual source method obviates the singularity problem as commonly encountered in the BEM, and is less computationally demanding than the BEM in terms of computational time and memory storage. Subjective experiments are also conducted using the calculated and the measured HRTFs. The results reveal that the spatial characteristics of sound localization are satisfactorily reproduced as a human listener would naturally perceive by using the virtual source HRTFs.

Rankine Source Method for Seakeeping Predictions

2012 ◽  
Author(s):  
Heinrich Söding ◽  
Alexander von Graefe ◽  
Ould el Moctar ◽  
Vladimir Shigunov
Keyword(s):  
Steady Flow ◽  
Potential Flow ◽  
Transfer Functions ◽  
Stokes Equations ◽  
Computational Time ◽  
Ship Motions ◽  
Periodic Flow ◽  
Source Method ◽  
Rankine Source ◽  
Rankine Source Method

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations. Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.

scholarly journals Levels of detail analysis of microwave scattering from human head models for brain stroke detection

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e4061 ◽  
Author(s):  
Awais Munawar Qureshi ◽  
Zartasha Mustansar
Keyword(s):  
Scattering Problem ◽  
Human Head ◽  
Computational Time ◽  
Head Model ◽  
Microwave Scattering ◽  
Levels Of Detail ◽  
Realistic Head Model ◽  
Different Types ◽  
Brain Stroke ◽  
Brain Tissues

In this paper, we have presented a microwave scattering analysis from multiple human head models. This study incorporates different levels of detail in the human head models and its effect on microwave scattering phenomenon. Two levels of detail are taken into account; (i) Simplified ellipse shaped head model (ii) Anatomically realistic head model, implemented using 2-D geometry. In addition, heterogenic and frequency-dispersive behavior of the brain tissues has also been incorporated in our head models. It is identified during this study that the microwave scattering phenomenon changes significantly once the complexity of head model is increased by incorporating more details using magnetic resonance imaging database. It is also found out that the microwave scattering results match in both types of head model (i.e., geometrically simple and anatomically realistic), once the measurements are made in the structurally simplified regions. However, the results diverge considerably in the complex areas of brain due to the arbitrary shape interface of tissue layers in the anatomically realistic head model.After incorporating various levels of detail, the solution of subject microwave scattering problem and the measurement of transmitted and backscattered signals were obtained using finite element method. Mesh convergence analysis was also performed to achieve error free results with a minimum number of mesh elements and a lesser degree of freedom in the fast computational time. The results were promising and the E-Field values converged for both simple and complex geometrical models. However, the E-Field difference between both types of head model at the same reference point differentiated a lot in terms of magnitude. At complex location, a high difference value of 0.04236 V/m was measured compared to the simple location, where it turned out to be 0.00197 V/m. This study also contributes to provide a comparison analysis between the direct and iterative solvers so as to find out the solution of subject microwave scattering problem in a minimum computational time along with memory resources requirement.It is seen from this study that the microwave imaging may effectively be utilized for the detection, localization and differentiation of different types of brain stroke. The simulation results verified that the microwave imaging can be efficiently exploited to study the significant contrast between electric field values of the normal and abnormal brain tissues for the investigation of brain anomalies. In the end, a specific absorption rate analysis was carried out to compare the ionizing effects of microwave signals to different types of head model using a factor of safety for brain tissues. It is also suggested after careful study of various inversion methods in practice for microwave head imaging, that the contrast source inversion method may be more suitable and computationally efficient for such problems.

scholarly journals The wavelet transfer function of a human body–seat system

2018 ◽  
Vol 38 (2) ◽  
pp. 817-825 ◽  
Author(s):  
Andrzej Błażejewski ◽  
Sebastian Głowiński ◽  
Igor Maciejewski
Keyword(s):  
Transfer Function ◽  
Human Body ◽  
Wavelet Transforms ◽  
Transfer Functions ◽  
Mechanical Vibration ◽  
Angular Position ◽  
Control Program ◽  
Human Head ◽  
Two Dimensions ◽  
Time Shift

In the analysis of vibration systems, classical transfer functions are used. Usually, it is the ratio of Fourier or Laplace transforms. The wavelet transfer function is proposed in this work. In this paper, the wavelets transfer function is the ratio of output and input wavelet transforms. It is considered as a distinctive correlation of the output and input system signals. The wavelet transform consists of coefficients, where the first is a scale and second time shift. To get input and output signals in the human body–seat system the dedicated test stand was made. The stand consists of a seat, moved by special shaker, which is used as a mechanical vibration device. The control program included in the source file is taken to imitate angular position of the engine. Motor shaft is connected with exciter’s moving parts and stand base, which influences directly on the seat position. The disturbance signal usually simulates a horizontal road influence on a driver. It can be considered as a low-frequency signal. It is measured by accelerometers called inertial sensors, which are placed on the platform of the shaker. The output signal is measured by an accelerometer placed on a seat and on the human head. Both signals are recorded by the Inertia Studio software wireless in the real time. After the measurement, the signals are transformed into wavelet coefficients by using Matlab package functions. The transfer function and its visualization are presented in two dimensions scale-time. The scale is related to frequency (pseudo-frequency). By the transfer function it is possible to analyze the systems, evaluate safety, compare the systems, and many more.

On the fundamentals of the virtual source method

Geophysics ◽  
2006 ◽  
Vol 71 (3) ◽  
pp. A13-A17 ◽  
Author(s):  
Valeri Korneev ◽  
Andrey Bakulin
Keyword(s):  
Green’S Function ◽  
Direct Measurement ◽  
Green's Function ◽  
Velocity Model ◽  
Practical Approach ◽  
Virtual Source ◽  
Processing Stage ◽  
Source Method ◽  
Complex Part ◽  
Seismic Images

The virtual source method (VSM) has been proposed as a practical approach to reduce distortions of seismic images caused by shallow, heterogeneous overburden. VSM is demanding at the acquisition stage because it requires placing downhole geophones below the most complex part of the heterogeneous overburden. Where such acquisition is possible, however, it pays off later at the processing stage because it does not require knowledge of the velocity model above the downhole receivers. This paper demonstrates that VSM can be viewed as an application of the Kirchhoff-Helmholtz integral (KHI) with an experimentally measured Green’s function. Direct measurement of the Green’s function ensures the effectiveness of the method in highly heterogeneous subsurface conditions.

scholarly journals Stochastic modeling error reduction using Bayesian approach coupled with an adaptive Kriging-based model

2014 ◽  
Vol 33 (3) ◽  
pp. 856-867 ◽  
Author(s):  
Ahmed Abou-Elyazied Abdallh ◽  
Luc Dupré
Keyword(s):  
Inverse Problem ◽  
Stochastic Modeling ◽  
Approximation Error ◽  
Memory Storage ◽  
Computational Time ◽  
Problem Solution ◽  
Content Type ◽  
Inverse Problem Solution ◽  
Bayesian Approximation ◽  
Adaptive Kriging

Purpose – Magnetic material properties of an electromagnetic device (EMD) can be recovered by solving a coupled experimental numerical inverse problem. In order to ensure the highest possible accuracy of the inverse problem solution, all physics of the EMD need to be perfectly modeled using a complex numerical model. However, these fine models demand a high computational time. Alternatively, less accurate coarse models can be used with a demerit of the high expected recovery errors. The purpose of this paper is to present an efficient methodology to reduce the effect of stochastic modeling errors in the inverse problem solution. Design/methodology/approach – The recovery error in the electromagnetic inverse problem solution is reduced using the Bayesian approximation error approach coupled with an adaptive Kriging-based model. The accuracy of the forward model is assessed and adapted a priori using the cross-validation technique. Findings – The adaptive Kriging-based model seems to be an efficient technique for modeling EMDs used in inverse problems. Moreover, using the proposed methodology, the recovery error in the electromagnetic inverse problem solution is largely reduced in a relatively small computational time and memory storage. Originality/value – The proposed methodology is capable of not only improving the accuracy of the inverse problem solution, but also reducing the computational time as well as the memory storage. Furthermore, to the best of the authors knowledge, it is the first time to combine the adaptive Kriging-based model with the Bayesian approximation error approach for the stochastic modeling error reduction.

Improving the virtual‐source method by wavefield separation

2007 ◽  
Author(s):  
Kurang Mehta ◽  
Andrey Bakulin ◽  
Jonathan Sheiman ◽  
Rodney Calvert ◽  
Roel Snieder
Keyword(s):  
Virtual Source ◽  
Source Method ◽  
Wavefield Separation

RELATIONSHIP BETWEEN DETECTING PITCH VIA BONE-CONDUCTED ULTRASOUND AND EIGENFREQUENCIES OF HUMAN HEAD

2006 ◽  
Vol 14 (03) ◽  
pp. 369-378 ◽  
Author(s):  
YOH-ICHI FUJISAKA ◽  
SEIJI NAKAGAWA ◽  
MITSUO TONOIKE
Keyword(s):  
Auditory Cortex ◽  
Frequency Dependence ◽  
Speech Intelligibility ◽  
Transfer Functions ◽  
Hearing Aid ◽  
Human Head ◽  
Hearing Impaired ◽  
Head Model ◽  
Human Head Model ◽  
The Relationship

This paper describes the relationship between the eigenfrequencies of CT scanned realistic human head model and the subjective detecting pitch, which is given by providing the bone-conducted ultrasound. Our goal is to develop the optimal bone-conducted ultrasonic hearing aid for profoundly hearing-impaired persons. An ascent of a speech intelligibility is the requirement of hearing aid. To improve it, the perception mechanism of the bone-conducted ultrasound must be clarified, but the conclusive agreement of it has not been reached yet, although many hypotheses were reported. The authors feel an interest in the detecting pitch of bone-conducted ultrasound with no frequency-dependence and predict that the cochleae are related to the perception mechanism for bone-conducted ultrasound, since it has been verified that the auditory cortex responds to bone-conducted ultrasound by MEG study. In this paper, waves propagating from the mastoid to both cochleae are numerically analyzed and the characteristics of transfer functions are estimated as a first step to clarifying the perception mechanism for detecting pitch of bone-conducted ultrasonic stimuli.

Virtual shear source makes shear waves with air guns

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. A7-A11 ◽  
Author(s):  
Andrey Bakulin ◽  
Albena Mateeva ◽  
Rodney Calvert ◽  
Patsy Jorgensen ◽  
Jorge Lopez
Keyword(s):  
Shear Wave ◽  
Shear Waves ◽  
Shear Velocity ◽  
Velocity Profiles ◽  
Virtual Source ◽  
S Wave ◽  
Converted Wave ◽  
Source Method ◽  
Vsp Data ◽  
Walkaway Vsp

We demonstrate a novel application of the virtual source method to create shear-wave sources at the location of buried geophones. These virtual downhole sources excite shear waves with a different radiation pattern than known sources. They can be useful in various shear-wave applications. Here we focus on the virtual shear check shot to generate accurate shear-velocity profiles in offshore environments using typical acquisition for marine walkaway vertical seismic profiling (VSP). The virtual source method is applied to walkaway VSP data to obtain new traces resembling seismograms acquired with downhole seismic sources at geophone locations, thus bypassing any overburden complexity. The virtual sources can be synthesized to radiate predominantly shear waves by collecting converted-wave energy scattered throughout the overburden. We illustrate the concept in a synthetic layered model and demonstrate the method by estimating accurate P- and S-wave velocity profiles below salt using a walkaway VSP from the deepwater Gulf of Mexico.

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