• Wind and Structures
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• v.15 no.3
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• pp.247-261
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• 2012

Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.711-716
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• 2011

Today, high-speed trains enjoy wide acceptance as fast, convenient and environment-friendly means of transportation. However, increase in the speed of the train entails a concomitant increase in the aerodynamic noise, adversely affecting the passenger comfort. At the train speed exceeding 300 km/h, the effects of turbulent flows and vortex sheddding are greatly amplified, contributing to a significant increase in the aerodynamic noise. Drawing a biomimetic analogy from low-noise flight of owl, a method to reduce aerodynamic noise at inter-coach space of high-speed trains is investigated. The proposed method attempts to achieve the noise reduction by modifying the turbulent flow and vortex shedding characteristics at the inter-coach space. To determine the aerodynamic noise at various train speeds, wind tunnel testing and numerical CFD (Computational Fluid Dynamics) simulation for the basic inter-coach spacing model are carried out, and their results compared. The simulation and experimental results reveal that there are discrete frequency components associated with turbulent air flow at constant intervals in the frequency domain

• Journal of Aerospace System Engineering
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• v.4 no.2
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• pp.10-15
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• 2010

Aerodynamic noise is becoming the major source of annoyance for modern cars recently and is caused by many different noise sources in a car. Appropriate CFD technologies, therefore, have been developed to resolve the noise problems related with aerodynamics. It is necessary for designers to fully understand the relationship between vehicle aerodynamics and wind noise acoustics. In this study, we simulate the flow fields around two different shapes of side mirror models of passenger car and analyze the noise phenomena around one side mirror model that has lower drag than the other model using Fluent 6.3.

• Journal of Aerospace System Engineering
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• v.3 no.4
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• pp.1-6
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• 2009

Aerodynamic noise is becoming the major source of annoyance for modern cars recently and is caused by many different noise sources in a car. Appropriate CFD technologies, therefore, have been developed to resolve the noise problems related with aerodynamics. It is necessary for designers to fully understand the relationship between vehicle aerodynamics and wind noise acoustics. In this study, we simulate the flow fields around two different shapes of side mirror models of passenger car and analyze the noise phenomena around one side mirror model that has lower drag than the other model using Fluent 6.3.

• Speech Sciences
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• v.7 no.1
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• pp.109-141
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• 2000

Acoustic and aerodynamic characteristics of Cheju consonants were examined with the focus on the well-known three-way distinction among stops (i.e., lenis, fortis, aspirated) and the two-way distinction between sand s*. Acoustic parameters examined for the stops included VOT, relative stop burst energy, Fo at the vowel onset, H1-H2, and H1-F2 at the vowel onset. For the fricatives s and s*, acoustic parameters were fricative duration, Fo, centroid of the fricative noise, RMS energy of the frication, H1-H2 and Hl-F2 at the onset of the following vowel. In investigating aerodynamics, intraoral pressure and oral flow were included for the bilabial stops. Results indicate that, although Cheju and Korean are not mutually intelligible, acoustic and aerodynamic properties of Cheju consonants are very similar in every respect to those of the standard Korean. Among other findings there are three crucial points worth recapitulating. First, stops are systematically differentiated by the voice quality of the following vowel. Second, stops are also differentiated by aerodynamic mechanisms. The aspirated and fortis stops are similar in supralaryngeal articulation, but employ a different relation between intraoral pressure and flow. Finally, our study suggests that the fricative s is better categorized as 'lenis' than as 'aspirated' in terms of its phonetic realization.

• Speech Sciences
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• v.6
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• pp.145-161
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• 1999

21 normal Korean native speakers participated as subjects to investigate the acoustic and aerodynamic study of Korean fricatives and affricates and to make good use of the results for the patients with articulation problems. Their productions of [sa], [s'a], [ca], [$c^{h}a$], [c'a], [asa], [as'a], [aca], [$ac^{h}a$], and [ac'a] were analyzed with CSL and AP II instruments. The results are as followings: (1) Fricatives showed higher frequency in minimum and maximum frequency and longer duration than affricates. (2) Fricatives showed higher peak flow rate and longer rise time than affricates. (3) When we compared the different phonemes with each other, their differences were usually statistically significant, but when we compared CV and VCV syllables, they did not show significant difference, even VCV's showed higher and longer values than CV syllables. (4) Normaly, lax fricatives and affricates showed lower frequency and higher peak flow rate, shorter frication duration, and longer rise time.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.8 no.2
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• pp.178-184
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• 1997

Vocal nodule due to vocal hyperfunction is one of the representative chronic diseases of vocal folds, and it can be cured by surgical movement, and/or voice therapy. The present study is, focusing on the latter, to compare the acoustic and aerodynamic results of the pretreatment with those of posttreatment, and then to investigate the objective date on the efficiency of the voice therapy for the patients with vocal nodules. 11 females(age : 7-49) and 5 males(age : 8-40), total 16 patients wi vocal nodules treated by voice therapy were participated as subjects. Six measurements and comparisons of pretreatment and posttreatment of the results were performed : litter, shimmer, and noise-to-harmonic ratio as acoustic analyses ; maximum phonation time, mean flow rate, and the subtraction of mean flow rate from maximum flow rate as aerodynamic analyses. As a result, 14 of 16 subjects showed improvement at more than 4 of 6 measurements, and in group data, every measurements of posttreatment was improved significantly than the pretreatment. On the whole, the improvement of aerodynamic aspects was more statistically significant than that of acoustic ones.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.713-722
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• 2022

In this paper, the flow performance and aero-acoustic noise generated by the target centrifugal fan system were investigated numerically and experimentally. Also, the numerical method for Computational Aero-Acoustics were evaluated by comparing each method. To analyze the performance of the centrifugal fan experimentally, the acoustic power level was measured in the semi-anechoic chamber using microphones, and the active frequency range for the noise performance was identified and that frequency range was applied for Computational Aero-Acoustics (CAA) techniques as sampling frequency. Then, Navier-Stokes equation and the Ffowcs Williams&Hawking equations were used to analyze the flow and sound power numerically, respectively, and a virtual acoustic radiation plane was designed and used for the implementation of the sound field. The accuracy and numerical characteristics of the numerical methods were validated by comparing simulated acoustic power levels with acoustic power levels measured.

• Speech Sciences
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• v.15 no.2
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• pp.145-156
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• 2008

The purpose of this study was to investigate the reason why puberphonia patients revisit hospitals after completion of its treatment and the effect of visual voice therapy on voice improvement. The subject the study included are two puberphonia patients who had been diagnosed by laryngologists. The patients who were diagnosed as puberphonia by the laryngologist and treated by the a speech pathologist, completed their treatment and revisited hospital. The study used laryngoscopy, acoustic and aerodynamic analysis before and after voice treatment to investigate what change happens and why generalization of treatment effect did not occur naturally in the daily life. Their voices of pre-therapy and post-therapy were analyzed on the aspects of acoustics, aerodynamics and laryngeal endoscopy. As a result, it was found that fundamental frequency(Fo) was significantly lowered in respect of acoustic change and maximum phonation time(MPT) was increased to some extent in respect of aerodynamic change. In addition, there was a laryngoscopic change and commissure glottic chink disappeared generally in the phonation. The reason why the generalization did not occur naturally in one’s daily routine was mainly due to the fact that high-pitched voicing was used for a long time. Other than that reason, negative reaction or attitude of surrounding people and lack of confidence were to blame for failure of generalization.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4E
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• pp.183-196
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• 2003

General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curl's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method penn its generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.