Modeling fluid-structure-acoustic interaction is a highly challenging task and currently there is a lack of available benchmark datasets. For instance, to understand the processes of human phonation, ...it is essential to fully understand the fluid-structure-acoustic interaction process. In this article, a synthetic human phonation model is presented for benchmarking numerical methods in the field of aerodynamics, aeroacoustics and the highly-complex fluid-structure-acoustic interaction process of the voice production. The objective is to present the wide range of experimental data available, including the model geometry, the material characteristics, quantitiesreferred to the vocal fold dynamics, fluid mechanical quantities and the acoustic field. Firstly, the experimental setup is specified. Secondly, the experimental data is described in detail, accompanied by illustrations. Having the dataset in hand, finally, it is shown how to use this data to validate a computational phonation model called simVoice successfully. In conclusion, this benchmarking dataset offers the opportunity to validate structural dynamics, aerodynamics and aeroacoustics of a highly-complex fluid-structure-acoustic interaction simulation, obtained from different mathematical formulations and numerical procedures.
The flow-induced sound sources of human voice production are investigated based on a validated voice model. This analysis is performed using a hybrid aeroacoustic workflow based on the perturbed ...convective wave equation. In the first step, the validated 3D incompressible turbulent flow simulation is computed by the finite volume method using STARCCM+. In a second step, the aeroacoustic sources are evaluated and studied in detail. The formulation of the sound sources is compared to the simplification (neglecting the convective sources) systematically using time-domain and Fourier-space analysis. Additionally, the wave equation is solved with the finite element solver openCFS to obtain the 3D sound field in the acoustic far-field. During the detailed effect analysis, the far-field sound spectra are compared quantitatively, and the flow-induced sound sources are visualized within the larynx. In this contribution, it is shown that the convective part of the sources dominates locally near the vocal folds (VFs) while the local time derivative of the incompressible pressure is distributed in the whole supra-glottal area. Although the maximum amplitude of the time derivative is lower, the integral contribution dominates the sound spectrum. As a by-product of the detailed perturbed convective wave equation source study, we show that the convective source term can be neglected since it only reduces the validation error by 0.6%. Neglecting the convective part reduces the algorithmic complexity of the aeroacoustic source computation of the perturbed convective wave equation and the stored flow data. From the source visualization, we learned how the VF motion transforms into specific characteristics of the aeroacoustic sources. We found that if the VFs are fully closing, the aeroacoustic source terms yield the highest dynamical range. If the VFs are not fully closing, VFs motion does not provide as much source energy to the flow-induced sound sources as in the case of a healthy voice. As a consequence of not fully closing VFs, the cyclic pulsating velocity jet is not cut off entirely and therefore turbulent structures are permanently present inside the supraglottal region. These turbulent structures increase the broadband component of the voice signal, which supports research results of previous studies regarding glottis closure and insufficient voice production.
Acoustic emissions play a major role in the usability of many product categories. Therefore, mitigating the emitted sound directly at the source is paramount to improve usability and customer ...satisfaction. To reliably predict acoustic emissions, numerical methods such as the boundary element method (BEM) are employed, which allow for predicting, e.g., the acoustic emission into the free field. BEM algorithms need appropriate boundary conditions to couple the sound field with the structural motion of the vibrating body. In this contribution, firstly, an interpolation scheme is presented, which allows for appropriate interpolation of arbitrary velocity data to the computational grid of the BEM. Secondly, the free-field Helmholtz problem is solved with the open-source BEM software framework NiHu. The forward coupling between the device of interest and BEM is based on the surface normal velocities (i.e., a Neumann boundary condition). The BEM simulation results are validated using a previously established aeroacoustic benchmark problem. Furthermore, an application to a medical device (knee prosthesis frame) is presented. Furthermore, the radiated sound power is evaluated and contextualized with other low-cost approximations. Regarding the validation example, very good agreements are achieved between the measurements and BEM results, with a mean effective pressure level error of 0.63 dB averaged across three microphone positions. Applying the workflow to a knee prosthesis frame, the simulation is capable of predicting the acoustic radiation to four microphone positions with a mean effective pressure level error of 1.52 dB.
In low Mach number aeroacoustics, the well-known disparity of scales allows applying hybrid simulation models using different meshes for flow and acoustics, which leads to a fast computational ...procedure. The hybrid workflow of the perturbed convective wave equation involves three steps: (1) perform unsteady incompressible flow computations on a subdomain; (2) compute the acoustic sources and (3) simulate the acoustic field, using a mesh specifically suited. These aeroacoustic methods seek for a robust, conservative and computational efficient mesh-to-mesh transformation of the aeroacoustic sources. In this paper, the accuracy and the application limitations of a cell-centroid-based conservative interpolation scheme is compared to the computationally advanced cut-volume cell approach in 2D and 3D. Based on a previously validated axial fan model where spurious artifacts have been visualized, the results are evaluated systematically using a grid convergence study. To conclude, the monotonic convergence of both conservative interpolation schemes is demonstrated. Regarding arbitrary mesh deformation (for example, the motion of the vocal folds in human phonation), the study reveals that the computationally simpler cell-centroid-based conservative interpolation can be the method of choice.
This paper presents a hierarchical distributed control strategy for multiple refrigeration units (RUs). The main target is to create a modular architecture that provides the thermal demand of the ...central plant in a multi-agent framework. Combined with the model predictive control method, a robust and effective framework is developed that aims to minimize the energy consumption while reducing latency times and switching of the RUs. The upper layer model predictive control is identical for all RUs, while in a lower layer a mixed-integer optimization using the decentralized Frank–Wolfe algorithm secures optimal switching of the RUs. The operational behavior can be easily and transparently adjusted in a wide range. Furthermore, availability and quick replacement of faulty units is guaranteed by the concept. A simulation example consisting of an insulated cool box on a truck demonstrates the versatility and performance of the proposed approach.
•Distributed hierarchical optimization for multiple refrigeration units is presented.•Model predictive control with mixed-integer optimization is employed.•Multiple refrigeration units maximize availability for the central plant.•Transparent weighting factors enable wide variety of operating patterns.
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Many numerical simulation tools have been developed and are on the market, but there is still a strong need for appropriate tools capable of simulating multi-field problems, especially in ...aeroacoustics. Therefore, openCFS provides an open-source framework for implementing partial differential equations using the finite element method. Since 2000, the software has been developed continuously. The result is openCFS (before 2020, known as CFS++ Coupled Field Simulations written in C++). In this paper, we present pyCFS-data, a data processing framework written in Python to provide a flexible and easy-to-use toolbox to access and manipulate, pre- and postprocess data generated by or for usage with openCFS.
Efficient numerical simulation of the human voice Maurerlehner, Paul; Schoder, Stefan; Freidhager, Clemens ...
Elektrotechnik und Informationstechnik,
06/2021, Volume:
138, Issue:
3
Journal Article
Peer reviewed
Open access
The process of voice production is a complex process and depends on the correct interaction of the vocal folds and the glottal airstream inducing the primary voice source, which is subsequently ...modulated by the vocal tract. Due to the restricted access to the glottis, not all aspects of the three-dimensional process can be captured by measurements without influencing the measurement object. Hence, the application of a numerical tool capturing the physical process of phonation can provide an extended database for voice treatment and, therefore, can contribute to an increased effectiveness of voice treatment. However, such numerical models involve complex and demanding procedures to model the material behavior and the mechanical contact of the vocal folds and to realize moving boundaries of the involved physical domains. The present paper proposes a numerical model called
simVoice
, which circumvents these computational expenses by prescribing the experimentally obtained vocal fold motion within the simulation. Additionally, a hybrid approach for sound computation further enhances the computational efficiency and yields good agreement with acoustic measurements. An analysis of the computational workloads suggests that the key factor for a further increase in efficiency is an optimized flow simulation and source term computation.
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This article presents an aeroacoustic workflow (pipeline) to generate a flow and acoustic dataset for studying flow-induced sound in the context of a cylinder in cross flow. The numerical simulations ...are performed using OpenFOAM (v9 or v10, or v2306) for the flow and openCFS for acoustics using the perturbed convective wave equation (PCWE) and the dilatation equation of Ribner. The workflow involves several steps, including the flow simulation, the acoustic simulation, and post-processing of the results in Python 3.9. The simulation steps are presented in all their details to verify your own segregated aeroacoustic solver. The analysis focuses on the acoustic characteristics of the flow, including sound pressure levels, frequency spectra, and directivity patterns. The results show good agreement with literature benchmarking datasets. The article concludes by discussing applications of the workflow for different cases that involve flow-induced sound generation.
Efficient numerical simulation of the human voice Maurerlehner, Paul; Schoder, Stefan; Freidhager Clemens ...
E & I. Elektrotechnik und Informationstechnik/Elektrotechnik und Informationstechnik,
01/2021, Volume:
138, Issue:
3
Journal Article
Peer reviewed
Open access
The process of voice production is a complex process and depends on the correct interaction of the vocal folds and the glottal airstream inducing the primary voice source, which is subsequently ...modulated by the vocal tract. Due to the restricted access to the glottis, not all aspects of the three-dimensional process can be captured by measurements without influencing the measurement object. Hence, the application of a numerical tool capturing the physical process of phonation can provide an extended database for voice treatment and, therefore, can contribute to an increased effectiveness of voice treatment. However, such numerical models involve complex and demanding procedures to model the material behavior and the mechanical contact of the vocal folds and to realize moving boundaries of the involved physical domains. The present paper proposes a numerical model called simVoice, which circumvents these computational expenses by prescribing the experimentally obtained vocal fold motion within the simulation. Additionally, a hybrid approach for sound computation further enhances the computational efficiency and yields good agreement with acoustic measurements. An analysis of the computational workloads suggests that the key factor for a further increase in efficiency is an optimized flow simulation and source term computation.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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