Abstract:The physical variables involved in a flow field are of very different scales to those of the aeroacoustic field within the flow. Thus, direct aeroacoustic computations (DACs) require extremely small time steps to capture the fluctuations in the aeroacoustic field and stabilize the numerical scheme. As a result, the computation time for DACs can be very long. This paper describes an implicit Adaptively Switched Time Stepping (ASTS) scheme that enables the use of larger time steps when solving DAC problems. ASTS… Show more
“…Furthermore, the relation between the size of the velopharyngeal valve and the sound amplitude observed at the far-field was consistent with the previous studies 11 , 14 , 15 . Figure 5 The spectrogram during co-articulation and sibilant /s/ sound ( a ) by the current study ( b ) measurement for the subject of the CT scan 25 . …”
Section: Resultsmentioning
confidence: 91%
“… The spectrogram during co-articulation and sibilant /s/ sound ( a ) by the current study ( b ) measurement for the subject of the CT scan 25 . …”
Section: Resultsmentioning
confidence: 99%
“…However, SLTS method is not suitable for aeroacoustic simulations even when the convergence criteria are satisfied because of the Newton linearization error of the term . Hence, adaptively switched time stepping scheme (ASTS) 24 , 25 was applied to maintain the accuracy in the aeroacoustic simulation at the same time reducing the computational cost.…”
A numerical simulation of sibilant /s/ production with the realistically moving vocal tract was conducted to investigate the flow and acoustic characteristics during the articulation process of velopharyngeal closure and tongue movement. The articulation process was simulated from the end of /u/ to the middle of /s/ in the Japanese word /usui/, including the tongue elevation and the velopharyngeal valve closure. The time-dependent vocal tract geometry was reconstructed from the computed tomography scan. The moving immersed boundary method with the hierarchical structure grid was adopted to approach the complex geometry of the human speech organs. The acoustic characteristics during the co-articulation process were observed and consistent with the acoustic measurement for the subject of the scan. The further simulations with the different closing speeds of the velopharyngeal closure showed that the far-field sound during the co-articulation process was amplified with the slower closing case, and the velum closure speed was inverse proportional to the sound amplitude with the slope value of − 35.3 dB s/m. This indicates possible phonation of indistinguishable aeroacoustics sound between /u/ and /s/ with slower velopharyngeal closure.
“…Furthermore, the relation between the size of the velopharyngeal valve and the sound amplitude observed at the far-field was consistent with the previous studies 11 , 14 , 15 . Figure 5 The spectrogram during co-articulation and sibilant /s/ sound ( a ) by the current study ( b ) measurement for the subject of the CT scan 25 . …”
Section: Resultsmentioning
confidence: 91%
“… The spectrogram during co-articulation and sibilant /s/ sound ( a ) by the current study ( b ) measurement for the subject of the CT scan 25 . …”
Section: Resultsmentioning
confidence: 99%
“…However, SLTS method is not suitable for aeroacoustic simulations even when the convergence criteria are satisfied because of the Newton linearization error of the term . Hence, adaptively switched time stepping scheme (ASTS) 24 , 25 was applied to maintain the accuracy in the aeroacoustic simulation at the same time reducing the computational cost.…”
A numerical simulation of sibilant /s/ production with the realistically moving vocal tract was conducted to investigate the flow and acoustic characteristics during the articulation process of velopharyngeal closure and tongue movement. The articulation process was simulated from the end of /u/ to the middle of /s/ in the Japanese word /usui/, including the tongue elevation and the velopharyngeal valve closure. The time-dependent vocal tract geometry was reconstructed from the computed tomography scan. The moving immersed boundary method with the hierarchical structure grid was adopted to approach the complex geometry of the human speech organs. The acoustic characteristics during the co-articulation process were observed and consistent with the acoustic measurement for the subject of the scan. The further simulations with the different closing speeds of the velopharyngeal closure showed that the far-field sound during the co-articulation process was amplified with the slower closing case, and the velum closure speed was inverse proportional to the sound amplitude with the slope value of − 35.3 dB s/m. This indicates possible phonation of indistinguishable aeroacoustics sound between /u/ and /s/ with slower velopharyngeal closure.
<div class="section abstract"><div class="htmlview paragraph">In vehicle development, reducing noise is a major concern to ensure passenger comfort. As electric vehicles become more common and engine and vibration noises improve, the aerodynamic noise generated around the vehicle becomes relatively more noticeable. In particular, the fluctuating wind noise, which is affected by turbulence in the atmosphere, gusts of wind, and wake caused by the vehicle in front, can make passengers feel uncomfortable. However, the cause of the fluctuating wind noise has not been fully understood, and a solution has not yet been found. The reason for this is that fluctuating wind noise cannot be quantitatively evaluated using common noise evaluation methods such as FFT and STFT. In addition, previous studies have relied on road tests, which do not provide reproducible conditions due to changing atmospheric conditions. To address this issue, automobile manufacturers are developing devices to generate turbulence in wind tunnels. However, in wind tunnels, it is difficult to reproduce the large length-scale fluctuations of natural winds, and it could not sufficiently simulate the road conditions. In this study, we simulated the fluctuating wind that vehicles experience on the road and verified the fluctuating aerodynamic noise. We first reproduced wind noise under steady flow conditions and confirmed that the pressure fluctuation measured on the side window matched well with wind tunnel results up to 2 kHz. Furthermore, it was confirmed that using modulation power spectrum analysis, it is possible to quantitatively evaluate the fluctuating wind noise compared with FFT and STFT. From these results, we found that fluctuating wind noise is an acoustic phenomenon in which the aerodynamic noise generated around the vehicle is amplitude-modulated by fluctuations in the mainstream velocity. The technical challenge is to understand the separation flow around the A-pillar and side mirror, which generates fluctuating wind noise.</div></div>
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