• 한국전산유체공학회지
• /
• 제10권1호
• /
• pp.8-15
• /
• 2005

Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 추계 학술대회논문집
• /
• pp.22-25
• /
• 2006

Direct simulations of aerodynamic sound, especially sound emitted by rapidly rotating elliptic cylinder by the finite difference lattice Boltzmann method (FDLBM). Effect of pile-fabrics for noise reduction is also studied by the finite volume LBM (FVLBM) using an unstructured grid. Second order time integration and third order upwind scheme are shown to be enough for these simulations. Sound sources are detected to be doublets for both cases. For the elliptic cylinder, the doublet is generated in the interaction between the vortex and the edge. For the circular cylinders, they are generated synchronizing with the Karman vortex street, and it is also shown that the pile-fabrics covering the surface of the cylinder reduces the strength of the source.

• 음성과학
• /
• 제5권1호
• /
• pp.105-119
• /
• 1999

Cleft palate patients have general speech problems with resonance disorders and articulation disorders. The aim of this study is to find the aerodynamic and acoustic characteristics of the nasalization in cleft palate speakers. Thirteen control groups and three cleft palate patients pre- and post operation were selected for these studies. The test words are composed by polysyllabic words: consonants between high vowel /i/ analysis. The cleft palate patients repeated test words pre- and post-operation from one, three and six month periods. The subjects repeated test words on Macquirer and on Nasometer Model 6200-3. The aerodynamic and acoustic results of nasalization show as follows: (1) The nasal rate in overall airflow of aspirated consonant for cleft palate patients shows higher levels than that of the control group. It had decreased since one month after operation. (2) The overall airflow of cleft palate patients is higher than in the control group, however oral air pressure is lower than control group. (3) The nasal airflow and the nasal rate in overall airflow of cleft palate patients has higher than the control group, however its decreased after operation. (4) The nasalance scores of cleft palate patients were 40% higher than that of the control group. The scores did not decrease after operation. The nasalance score of lateral and fricative sounds did not decrease after operation.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1915-1920
• /
• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제26권4호
• /
• pp.414-421
• /
• 2000

The objective evaluation of velopharyngeal closure function is the key to diagnosis and therapy control of velopharyngeal incompetency. The aim of this study is to evaluate the aerodynamic and acoustic characteristics of the velopharyngeal closure function of patients who have developed velopharyngeal incompetency after management with speech aids. The test words were composed of sustained vowels /a/, /i/, /e/, /u/, /ja/, /je/, /wi/ and polysyllabic words /p'ap'i/, /siso/, /mami/ for measuring nasalance, The data was collected before the placement of the speech aids and one to three months after. The results were as follows: The nasalance score of the velopharyngeal incompetency speakers was higher than that of the normal control group, except for nasal sounds, and was decreased after placement of the speech aids, especially in high vowels /i/ (P<.01) and /wi/ (P<.05).

• 대한음성언어의학회:학술대회논문집
• /
• 대한음성언어의학회 2003년도 제19회 학술대회
• /
• pp.147-147
• /
• 2003

Recent aerodynamic and acoustic studies of VPI(velopharyngeal insufficiency) are non-invasive and safety, therefore, many researchers have used it to diagnose the hyper/hyponasality and articulation disorders of cleft palate patients. The purpose of this study was to estimate mainly the oropharyngeal air pressure and over all air flow in cleft lip and palate patients. The pressure-collecting catheter was positioned in the oropharyngel cavity around tongue base. Twelve adult control group and three cleft lip & palate patients were participated to this experimentation. Aerophone II was used to measure peak air flow, mean air flow, phonatory airflow, phonatory efficiency and resistance. The results were as follows: 1) Airflow of cleft lip ＆ palate patients group were higher than those of control group. Fricative sounds /s/ and /s'/ showed the statistic significance of mean airflow and volume data. 2) Intraoral air pressure of cleft lip ＆ palate patients was lower than those of control group.

• 한국해양공학회지
• /
• 제18권2호
• /
• pp.10-17
• /
• 2004

In this research, a numerical simulation for the acoustic sounds around a two-dimensional circular cylinder in a uniform flaw was developed, using the finite difference lattice Boltzmann model. We examine the boundary condition, which is determined by the distribution function concerning density, velocity, and internal energy at the boundary node. Pressure variation, due to the emission of the acoustic waves, is very small, but we can detect this periodic variation in the region far from the cylinder. Daple-like emission of acoustic waves is seen, and these waves travel with the speed of sound, and are synchronized with the frequency of the lift on the cylinder, due to the Karman vortex street. It is also apparent that the size of the sound pressure is proportional to the central distance to the circular cylinder. The lattice BGK model for compressible fluids is shown to be a powerful tool for the simulation of gas flaws.

• Journal of Advanced Marine Engineering and Technology
• /
• 제28권5호
• /
• pp.717-727
• /
• 2004

In this study, we simulate the aerodynamic sounds generated by a two-dimensional circular cylinder in a uniform flow are simulated by applying the finite difference lattice Boltzmann method (FDLBM). The third-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives. and the second-order-accurate Runge-Kutta scheme is applied for the time marching. The results show that we successively capture very small acoustic pressure fluctuations with the same frequency of the Karman vortex street compared with the Pressure fluctuation around a circular cylinder The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow For the downstream. on the other hand. it quickly Propagates. It is also apparent that the amplitude of sound Pressure is Proportional to $r^{-1/2}$, r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence furthermore a 2D computation of the tone noise radiated by a NACA0012 with a blunt trailing edge at high incidence and low Reynolds number is also investigated.

• 대한후두음성언어의학회지
• /
• 제9권1호
• /
• pp.53-58
• /
• 1998

Objectives : To compare the voice quality and voice problems of untrained professional voice user groups with that of normal control group without voice problem. Materials and Methods : The sustained vowel sounds of 13 male and 36 female teachers, 46 clergies and 15 telephone operators, and 40 normal male and 20 normal female persons were analyzed, using a videostroboscopy and acoustic analyzer. Together with these analyses, a questionnaire associated with risk factors for current and past voice problems was handed over to the patients. Results : The most common symptom in subjective groups was the voice fatigue. In stroboscopic examination, the professional voice user groups shelved functional voice disorder findings regardless of the Intensity of voice use. In the clergy and teacher using loud voice, vocal polyp, vocal nodule and hyperfunction of laryngeal muscle were frequently observed. In the clergy and telephone operator, jitter and shimmer were significantly increased. In the female teacher, the value of jitter, fundamental frequency variation and fundamental frequency were statiscally significant. However, the voice of male teacher showed no significant findings in the acoustic and aerodynamic studies. Conclusion : In the management of voice problems for untrained professional voice user groups, it is important to find the exact causes and patterns of voice problems, and to be individualized the management according to the causes.

• 동력기계공학회지
• /
• 제11권1호
• /
• pp.82-91
• /
• 2007

기존의 2차원 FDLB 모델(D2Q21)에서 비열비 ${\gamma}$는 공간의 차원수(D)에 의존한다. 즉, 2차원 공간의 계산에서는 ${\gamma}=(D+2)/D=2.0$밖에 취할 수 없으며, 공기와 같은 실체기체를 전산모사 하기에는 여러 어려움이 있다. 이러한 이유 때문에 문헌[1]의 LBM에서 제안된 조정 가능한 비열비 모델을 2차원 FDLB모델에 적용하여 자려발생 에지톤(edgetone)의 수치계산이 수행되었다. wedge의 선단각도가 ${\alpha}=23^{\circ}$(Case I) 및 $20^{\circ}$(Case II)를 갖는 2가지 모델이 설정되었으며, 노즐출구에서 wedge선단까지의 거리 w/d는 $3d{\sim}12d$사이에서 주어졌다. edgetone은 노즐로부터 나온 분류와 edge의 상호작용으로 이난 음압(sound pressure)의 차에 의해서 소음이 발생하며, 이 음압은 다시 상류의 분류에 영향을 미쳐 분류의 변동을 가져온다. w/d가 ??9d이하인 경우, 피드백(feedback) 메커니즘에 기인한 주기적인 운동이 발생하지만, w/d가 큰 ??9d이상인 경우에는 분류의 불안정성 때문에 규칙적인 분류의 운동은 보이질 않으며, 이는 기존의 연구결과들과 잘 일치함을 보였다. 본 연구에서 적용된 모델을 이용하여 공기와 같은 2원자 기체의 비열비 ??${\gamma}=1.4$를 갖는 유체에 있어서 공력 소음의 수치예측이 가능하다는 것을 확인하였다.