• 음성과학
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• 제8권4호
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• pp.87-98
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• 2001

Vocal nodule is one of the representative chronic diseases of vocal folds, and it can be cured by surgical removal or voice therapy. The aim of this study is to evaluate the effect of the accent method, one of the popular effective voice therapy, in the patients with vocal nodule. Authors executed the accent method in 17 patients with vocal nodule who visited the Voice & Speech Therapy Clinic, Pusan National University Hospital analysed the voice before and after treatment using the local findings, acoustic analysis and aerodynamic analysis MPT. The voice was analysed with MDVP of CSL and MPT was checked using stop watch. The parameters included Fo, Jitter, Shimmer and noise to harmonic ratio(NHR) as acoustic analysis. The results were obtained as follows. In the evaluation by the local findings, it was improved to 77% in the patients of vocal nodule. Jitter and Shimmer were shown to be improved significantly. In particular, it was shown to be improved significantly in patients with vocal nodule. As the result of this study, the improvement of aerodynamic aspect was more statistically significant than that of acoustic parameters. When I generalized the above mentioned results, we suggest that it is a useful voice therapy which can be helpful to the improvement of voice, applying the accent method to the vocal nodule patients, and there are currently many methods to be used in the voice therapy, but it is thought which the accent method is the good treatment as the alternatives of keeping the continuous medical treatment.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.790-798
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• 2008

Counter-rotating axial flow fan(CRF) consists of two counter-rotating rotors without stator blades. CRF shows the complex flow characteristics of the three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in CRF, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential to improve the aerodynamic characteristics and to reduce the aerodynamic noise level and vibration characteristics of the CRF. In this paper, experimental study on the three-dimensional unsteady flow of the CRF is performed at the design point(operating point). Flow fields in the CRF are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. The phase-locked averaged hot-wire technique utilizes the inclined hot-wire, which rotates successively with 120 degree increments about its own axis. Three-dimensional unsteady flow characteristics such as tip vortex, secondary flow and tip leakage flow in the CRF are shown in the form of the axial, radial and tangential velocity vector plot and velocity contour. The phase-locked averaged velocity profiles of the CRF are analyzed by means of the stationary unsteady measurement technique. At the mean radius of the front rotor inlet and the outlet, the phase-locked averaged velocity profiles show more the periodical flow characteristics than those of the hub region. At the tip region of the CRF, the axial velocity is decreased due to the boundary layer effect of the fan casing and the tip vortex flow. The radial and the tangential velocity profiles show the most unstable and unsteady flow characteristics compared with other position of rotors. But, the phase-locked averaged velocity profiles of the downstream of the rear rotor show the aperiodic flow pattern due to the mixture of the front rotor wake period and the rear rotor rotational period.

• 한국음향학회지
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• 제41권6호
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• pp.713-722
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• 2022

본 연구에서는 대상 원심팬 시스템에서 발생하는 유동 현상과 공력 음향 성능을 수치적/실험적으로 분석하고 다양한 수치 기법을 비교하여 평가하고자 하였다. 먼저 원심팬의 성능을 실험적으로 분석하기 위해 반무향실에서 음향 파워를 측정하였으며, 실험 결과를 통해 대상 원심팬 시스템에서 방사되는 소음 성능에 대한 유효 주파수 범위를 파악하고 이에 대한 수치 모사를 실시하였다. 수치적으로 유동 및 음향 파워를 분석하기 위해 Navier-Stokes 방정식과 Ffowcs Williams&Hawkings 방정식을 각각 유동장과 음향장의 지배방정식으로 사용하였으며, 음향장의 구현을 위해 가상의 음향 방사면을 설계하여 사용하였다. 고차 3차원 전산유체역학(Computational Fluid Dynamics, CFD)와 연계된 Hybrid-CAA 기법을 사용하여 모사한 음향 파워 레벨과 소음 실험을 통해 측정한 음향 파워 레벨의 비교를 통해 사용된 수치 기법의 정확도 및 수치적 특성을 평가하였다.

• Radiation Oncology Journal
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• 제23권1호
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• pp.17-21
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• 2005

목적 : 후두암에서 방사선 치료는 음성을 보존할 수 있기 때문에 조기 성문암의 일차적인 치료법으로 사용된다. 이에 T1a 병기 성문암에서 방사선 치료가 환자의 음성에 미치는 영향을 알아보고자 하였다. 대상 및 방법 : 조기 성문암(T1a)으로 진단 받고 방사선 치료를 받은 후 최소 1년이 지난 17명의 남자 환자들을 대상으로 객관적인 음성검사들(음향분석, 공기역학검사, 후두 스트로보스코피)을 이용하여 음성을 평가하였고, 이것을 성별과 연령을 맞춘 정상 대조군과 비교하였다. 음향분석으로는 평균 기본주파수(Fo), jitter, shimmer, 잡음 대 조화음 비율(Noise to Harmonics Ratio)을 측정하였다. 공기역학적 검사로는 최대발성지속시간, 평균호기류율, 음강도, 성문하압, 성문저항, 성문효율, 성문력을 측정하였다. 결과 : 방사선 치료를 받은 환자에서 음향분석의 shimmer만이 통계학적으로 의의 있게 높았다. 그 외 다른 검사나 공기역학검사에서는 두 군 간에 통계학적인 유의성이 없었다. 결론 : 본 연구에서는 단지 shimmer만이 방사선 치료 환자군에서 높았기 때문에 T1a 병기 성문암에서의 방사선치료는 음성의 질에 큰 영향을 미치지 않은 것으로 사료된다.

• 대한후두음성언어의학회지
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• 제16권1호
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• pp.23-27
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• 2005

Background and Objectives : Voice disorders can cause problems in patients with benign vocal cord lesions emotionally, physically, economically and functionally. Neither subjective nor objective voice examinations can evaluate such factors adequately. The Voice Handicap Index (VHI) subjectively evaluates voice disorders in terms of physical, functional, emotional factors and measures the patient's perception of the impact of voice disorder. The purpose of this study is to evaluate the usefulness of VHI in the patients with benign vocal cord lesions. Materials and Method : The authors evaluated 37 patients who experienced laryngeal microsurgery for benign vocal cord lesions from september 2003 to August 2004. The VHI was used to measure the postoperative changes of the patient's perception and acoustic analysis and aerodynamic tests were also done. Statistical analysis was done using paired t-test and Pearson's correlation. Results : The VHI scores showed statistically significant reductions postoperatively. In acoustic analysis, jitter and shimmer had statistically significant reductions after surgery but noise-to-harmonics ratio did not. A statistically significant change in the average MFR and MPT perioperatively was found. The relationship between VHI and acoustic, aerodynamic analysis attained statistical significance. Conclusion : The VHI is a useful assessment tool to monitor the patient's self-perception of voice change after the surgery of benign vocal cord lesions. The VHI measurement, when combined with acoustic and aerodynamic analyses, will be helpful in comparing functional outcomes after voice surgery.

• 한국소음진동공학회논문집
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• 제20권1호
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• pp.29-35
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• 2010

This paper studies causes of the L-1 blade damage of a low pressure turbine, which was found during the scheduled maintenance, in 500 MW fossil power plants. Many failures of turbine blades are caused by the coupling of aerodynamic forcing with bladed-disk vibration characteristics. In this study the coupled vibration characteristics of the L-1 turbine bladed-disk in a fossil power plant is shown for the purpose of identifying the root cause of the damage and confirming equipment integrity. First, analytic and experimental modal analysis for the bladed-disk at zero rpm as well as a single blade were performed and analyzed in order to verify the finite element model, and then steady stresses, natural frequencies and corresponding mode shapes, dynamic stresses were calculated for the bladed-disk under operation. Centrifugal force and steady steam force were considered in calculation of steady and dynamic stress. The proximity of modes to sources of excitation was assessed by means of an interference diagram to examine resonances. In addition, fatigue analysis was done for the dangerous modes of operation by a local strain approach. It is expected that these dynamic characteristics will be used effectively to identify the root causes of blade failures and to perform prompt maintenance.

• 항공우주기술
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• 제6권1호
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• pp.157-164
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• 2007

GPS 안테나는 위성발사체의 전 비행 구간에서 GPS 위성 신호를 정상적으로 수신하기 하여 발사체의 외피에 설치되어야 한다. 위성발사체의 표면 온도는 발사체가 대기권을 통과하면서 발생하는 열공력의 영향으로 급격하게 상승하며 발사체 외피에 설치되는 GPS 안테나는 극심한 고온 환경에 직접적으로 노출된다. 따라서 위성발사체의 외피에 설치되는 GPS 안테나에 대한 고온 환경 시험 규격은 발사체 내부 시스템의 고온 환경 시험 규격보다 더 가혹하게 설정되어야 한다. 본 논문에서는 KSLV-I 발사체에 탑재될 GPS 안테나의 고온 환경에서 성능 분석 절차 및 결과를 기술하며, GPS 안테나가 고온 환경에서 물리적인 변형이나 내부 LNA(Low Noise Amplifier)의 성능 저하 없이 정상적으로 동작하였을 보여주고 있다.

• Wind and Structures
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• 제26권5호
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• pp.331-341
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• 2018

A numerical study on the flow over a square cylinder in the vicinity of a wall is conducted for different Couette-Poiseuille-based non-uniform flow with the non-dimensional pressure gradient P varying from 0 to 5. The non-dimensional gap ratio L (=$H^{\ast}/a^{\ast}$) is changed from 0.1 to 2, where $H^{\ast}$ is gap height between the cylinder and wall, and $a^{\ast}$ is the cylinder width. The governing equations are solved numerically through finite volume method based on SIMPLE algorithm on a staggered grid system. Both P and L have a substantial influence on the flow structure, time-mean drag coefficient ${\bar{C}}_D$, fluctuating (rms) lift coefficient ($C_L{^{\prime}}$), and Strouhal number St. The changes in P and L leads to four distinct flow regimes (I, II, III and IV). Following the flow structure change, the ${\bar{C}}_D$, $C_L{^{\prime}}$, and St all vary greatly with the change in L and/or P. The ${\bar{C}}_D$ and $C_L{^{\prime}}$ both grow with increasing P and/or L. The St increases with P for a given L, being less sensitive to L for a smaller P (< 2) and more sensitive to L for a larger P (> 2). A strong relationship is observed between the flow regimes and the values of ${\bar{C}}_D$, $C_L{^{\prime}}$ and St. An increase in P affects the pressure distribution more on the top surface than on bottom surface while an increase in L does the opposite.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.441-447
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• 2002

KSR-III(Korea Sounding Rocket - III), which is being developed by Space Technology R&D Division of KARI(Korea Aerospace Research Institute) will be launched in late 2002. It is a three-stage, liquid propellant rocket which can reach 250 km altitude and will carry out observation of ozone layer and scientific experiments, such as microgravity experiment, and atmospheric measurement. KSR-III is believed to be an intermediate to the launch vehicle capable of carrying a satellite to its orbit. Space Test Department of KARI performed GVT(Ground Vibration Test) fer KSR-III EM at Rocket Test Building of KARI. GVT is very important for predicting the behavior of rocket in its operation, developing flight control program and performing aerodynamic analysis. This paper gives an introduction of rocket GVT configuration and information on test procedures, techniques and results of It. In this test. to simulate free-free condition, test object hung in the air laterally by 4 bungee cords specially devised. For the excitation of test object, pure random signal by two electromagnetic shakers was used and total 22 frequency response functions were achieved. Polyreference parameter estimation was performed to identify the modal parameters with MIMO(Multi-Input-Multi-Output) method. As the result of the test, low frequency mode shapes and modal parameters below 60Hz were identified

• 한국음향학회지
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• 제37권6호
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• pp.396-403
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• 2018

본 논문에서는 쾌적한 운전 환경을 제공하기 위해 자동차 시트를 냉각시키기 위한 고성능 및 저소음 원심팬을 개발하였다. 먼저 팬 성능 테스터 및 전산유체역학(Computational Fluid Dynamics, CFD) 시뮬레이션을 이용하여 기존 팬 장치의 유동 특성을 분석하였다. 예측한 유동장 분석을 통하여 팬 허브 팁 근처의 와류 및 팬 허브 상단의 정체된 유동 현상이 관측되었다. 이러한 와류 및 정체 유동을 줄이기 위해 두 가지 설계 요소를 고안하였다. 첫째, 팬 날개와 팬 하우징 최소 간극(cut-off)를 증가시켜 난류강도를 줄이고 그 결과로 전체적인 음압 레벨을 줄이고자 하였다. 둘째, 허브 형상은 정체 유동을 줄이기 위해 형상을 변경하였다. 제안된 설계의 타당성을 수치해석을 통해 확인하였다. 수치해석결과를 바탕으로 프로토타입을 제작하고 팬 테스터에서 측정한 성능 곡선(P-Q curve)과 반무향실에서 측정한 음압 레벨의 분석을 통해서 유동과 소음 성능의 향상을 확인하였다.