• 한국음향학회:학술대회논문집
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• 한국음향학회 2002년도 하계학술발표대회 논문집 제21권 1호
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• pp.469-474
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• 2002

In recent years, modularization of engine parts has increased the application of plastic products in air intake systems. Plastic intake manifolds provide many advantages including reduced weight, contracted cost, and lower intake air temperatures. These manifolds, however, have some weakness when compared with customary aluminium intake manifolds, in that they have low sound transmission loss because of their lower material density. This low transmission loss of plastic intake manifolds causes several problems related to flow noise, especially when the throttle is opened quickly. The physical processes, responsible for this flow noise, include turbulent fluid motion and relative motion of the throttle to the airflow. The former is generated by high-speed airflow in the splits between the throttle valve and the inner-surface of the throttle body and surge-tank, which can be categorized into the quadrupole source. The latter induces the unsteady force on the flow, which can be classified into the dipole source. In this paper, the mechanism of noise generation from the turbulence is only investigated as a preliminary study. Stochastic noise source synthesis method is adopted for the analysis of turbulence-induced, i.e. quadrupole noise by throttle at quick opening state. The method consists of three procedures. The first step corresponds to the preliminary time-averaged Navier-Stokes computation with a $k-\varepsilon$ turbulence model providing mean flow field characteristics. The second step is the synthesis of time-dependent turbulent velocity field associated with quadrupole noise sources. The final step is devoted to the determination of acoustic source terms associated with turbulent velocity. For the first step, we used market available analysis tools such as STAR-CD, the trade names of fluid analysis tools available on the market. The steady state flows at three open angle of throttle valve, i.e. 20, 35 and 60 degree, are numerically analyzed. Then, time-dependent turbulent velocity fields are produced by using the stochastic model and the flow analysis results. Using this turbulent velocity field, the turbulence-originated noise sources, i.e. the self-noise and shear-noise sources are synthesized. Based on these numerical results, it is found that the origin of the turbulent flow and noise might be attributed to the process of formulation and the interaction of two vortex lines formed in the downstream of the throttle valve. These vortex lines are produced by the non-uniform splits between the throttle valve and inner cylinder surface. Based on the analysis, we present the low-noise design of the inner geometry of throttle body.

• 한국음향학회지
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• 제40권4호
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• pp.320-329
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• 2021

본 논문에서는 선박 수중방사소음 저감을 위한 에어마스커의 기포크기 추정 모델을 제시하였다. 제시된 모델은 Rayleigh의 제트 불안정 모델과 연속 조건을 이용하여 유도된 기존 모델에 공기의 제트유속을 도입함으로써 저속유동 조건에서 발산하는 단점을 보완 하였다. 공기의 제트유속은 유동이 없는 경우 기포의 크기를 이용하여 추정하였다. 유동이 없는 매질에서 기포의 크기는 분사된 공기의 레이놀즈수를 기반으로 층류구간, 천이구간, 그리고 난류구간으로 나누어 경험적 방법으로 추정 하였다. 제시된 기포크기 추정 모델은 Computational Fluid Dynamics(CFD) 해석결과 그리고 기존 문헌의 실험결과와 비교하여 잘 일치함을 확인하였다. 끝으로, 음향 역산법을 활용하여 대형터널에서 수행된 에어마스커 공기분사 실험의 계측된 삽입손실로부터 기포의 분포를 추정하였다. 역산된 기포분포와 기포크기 추정 모델의 추정 결과를 비교하였다.

• 한국철도학회논문집
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• 제15권6호
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• pp.531-536
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• 2012

판토그라프 팬헤드의 공력소음 발생의 주요 인자와 영향을 미치는 변수를 분석하였다. 팬헤드 주변의 유체 유동과 결과적인 소음 방사를 분석하기 위해, 수치해석적인 방법 중 하나인 격자볼츠만 방법으로 팬헤드 단순모델을 사용했다. 풍동실험을 통해 측정된 결과로 시뮬레이션 결과를 검증했다. 와흘림이 주요한 공력소음 발생원인이며 Strouhal수, 유체의 속도 및 판토그라프의 형상에 영향을 받았다. 이 논문에 사용된 직사각형 형상을 통해 양력의 발생을 증가시키면서 방사 소음을 줄이는 팬헤드의 설계가 가능함을 제시하였다. 또한 통로나 유선 형상을 이용해 와흘림을 최소로 줄이면, 방사 소음을 크게 저감하는 형상의 설계가 가능함을 구축된 해석모델을 이용하여 검증하였다.

• International Journal of Aeronautical and Space Sciences
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• 제17권4호
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• pp.518-525
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• 2016

This paper presents the characteristics of non-fundamental multi-mode combustion instability and the effects of high-harmonic components on the Rayleigh criterion. Phenomenological observations of multi-harmonic-mode dynamic pressure waves regarding the intensity of harmonic components and the source of wave distortion have been explained by introducing examples of second- and third-order harmonics at various amplitudes. The amplitude and order of the harmonic components distorted the wave shapes, including the peak and the amplitude, of the dynamic pressure and heat release, and consequently the temporal Rayleigh index and its integrals. A cause-and-effect analysis was used to identify the root causes of the phase delay and the amplification of the Rayleigh index. From this analysis, the skewness of the dynamic pressure turned out to be a major source in determining whether multi-mode instability is driving or damping, as well as in optimizing the combustor design, such as the mixing length and the combustor length, to avoid unstable regions. The results can be used to minimize errors in predicting combustion instability in cases of high multi-mode combustion instability. In the future, the amount of research and the number of applications will increase because new fuels, such as fast-burning syngases, are prone to generating multi-mode instabilities.

• 한국임상수의학회지
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• 제28권1호
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• pp.163-172
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• 2011

Subcutaneous foreign body causes recurrent problems such as chronic soft tissue swelling and discharge. Wooden foreign body is one of the most common foreign bodies found in subcutaneous region including face, interdigit, and thoracic or abdominal area. This report demonstrated three dogs with wooden foreign body located in subcutaneous region of thoracic wall, abdominal wall and upper eyelid, respectively. Three dogs showed prominent soft tissue swelling adjacent the foreign body. A sinus or drainage tract was developed in two of these dogs. Ultrasonography revealed that hyperechoic linear structure accompanied acoustic shadow in all dogs, and which was diagnosed as a subcutaneous foreign body. Anechoic or hyperechoic fluid and hypoechoic tissue circumscribed the foreign body. A subcutaneous foreign body in case 3 was removed by clamp under ultrasound-guide with sedation. Sinography was performed in case 1 and clarified that the wooden foreign body did not perforate the thoracic wall and there was no direct communication into thoracic cavity. Ultrasonography and sinography can be used to identify the subcutaneous foreign body and evaluate the inflammatory reaction and relationship between foreign body and adjacent structures.

• 한국추진공학회지
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• 제21권5호
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• pp.54-60
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• 2017

연소불안정 연구의 일환인 화염전달함수에서 나타나는 gain의 특성을 파악하기 위하여 비연소상태에서의 전달함수를 도입하여 화염전달함수에서의 특성과 비연소전달함수의 특성에 대한 원인을 파악하고자 하였다. 비연소 전달함수를 획득하기 위하여 질소와 이산화탄소를 활용하였으며, 입력값과 출력값을 계측하기 위하여 열선풍속계를 이용하였다. 비연소 전달함수에서의 gain과 주파수의 peak는 비활성기체의 밀도와 유량에 대하여 영향을 받는 것을 확인하였다. 또한 연료공급라인에서의 음향학적 공진주파수가 peak 주파수에 영향을 주는 것을 확인하였다.

• 한국항공우주학회지
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• 제43권8호
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• pp.677-683
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• 2015

하이브리드 로켓은 특정한 연소조건에서 10~30Hz 저주파수 연소불안정이 나타난다. 후연소실의 와류 흘림 현상이 저주파수 불안정 발생과 직접적인 관련이 있는 것으로 판단되며, 이를 확인하기 위하여 발광하는 연소가스의 후연소실 내부유동을 직접 촬영하여 광도 분석과 유동 가시화를 시도하였다. 저주파수 연소불안정이 발생하면 일정한 주기(~18Hz)를 갖는 광도 변화가 나타났으며, 압력교란(p')의 위상(phase)이 거의 일치하고 있어 비-음향 불안정임에도 불구하고 압력과 연소교란이 상호 간섭하고 있음을 확인하였다. POD에 의한 유동 모드 분석결과 안정한 연소가 발생하면 후연소실 유동은 공간적으로 상하 대칭 모드 형태를 이루지만 불안정 연소에서는 수직방향 경사각을 이루는 대칭축을 중심으로 변화하는 유동모드가 나타난다. 특히 3번 모드는 불안정 연소가 발생하는 경우에만 나타나는 유동 모드이다. 불안정 연소가 발생하는 경우에 수직선을 대칭으로 변하는 모드가 나타나는 것은 저주파수 연소불안정이 발생할 때 와류 흘림인 것으로 판단할 수 있다.

• 상하수도학회지
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• 제20권6호
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• pp.911-918
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• 2006

This study was conducted to evaluate the effect of the launder type on settling performance and hydrodynamic behavior within the two certain full-scale sedimentation basins (each flow rate/one basin; $10,000m^3/d$); one is the transverse typed launder(existing basin) and the other is building the finger type launder in combination with the longitudinal baffle. Comparative experimental investigations have been carried out through residual turbidity and particle concentration measurements in each effluent from two basins with the transverse and the finger type launders, respectively. From the experimental results, we could observe that turbidity removal rate in the finger type launder basin (modified basin) is about 30% higher than that in the transverse type launder basin (existing basin). Also, from the measurement of total particle concentration in each effluent, the removal efficiency was improved about 27% within modified basin compared to the existing basin. In order to explain the comparative experimental results and investigate the hydridynamic behavior within each basin in more detail, we conducted computational fluid dynamics (CFD) simulation and verified simulation results with acoustic Doppler velocimetry (ADV) technique. From the CFD simulation, it was investigated that extreme upward flow occurs underneath of the transverse launder. On the other hand, in the case of modified basin, the upward flow, which occurred in the beneath of launder, was much less than that in the existing basins.

• 한국안전학회지
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• 제35권6호
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• pp.32-45
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• 2020

The problem of determining the discharge rates of gases from pressurized vessels through pressure relief devices was dealt with comprehensively. First, starting from basic fluid flow equations, detailed modeling procedures were presented for isentropic nozzle flows and frictional flows in a pipe, respectively. Meanwhile, physical explanations were given to choking phenomena in terms of the acoustic velocity, elucidating the widespread use of Mach numbers in gas flow models. Frictional flows in a pipe were classified into adiabatic, isothermal, and general flows according to the heat transfer situation around the pipe, but the adiabatic flow model was recommended suitable for gas discharge through pressure relief devices. Next, for the isentropic nozzle flow followed by adiabatic frictional flow in the pipe, two equations were established for two unknowns that consist of the Mach numbers at the inlet and outlet of the pipe, respectively. The relationship among the ratio of downstream reservoir pressure to upstream pressure, mass flux, and total frictional loss coefficient was shown in various forms of MATLAB 2-D plot, 3-D surface plot and contour plot. Then, the profiles of gas properties and velocity in the pipe section were traced. A method to quantify the relationship among the pressure head, velocity head, and total friction loss was presented, and was used in inferring that the rapid increase in gas velocity in the region approaching the choked flow at the pipe outlet is attributed to the conversion of internal energy to kinetic energy. Finally, the Levenspiel chart reproduced in this work was compared with the Lapple chart used in API 521 Standatd.

• 대한기계학회논문집A
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• 제41권2호
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• pp.87-94
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• 2017

프로펠러와 같은 수중운동체 주변에서 발생하는 공동 현상은 물체를 부식시키고 소음을 발생시키므로, 공학적 측면에서 중요한 문제로 다루어지고 있다. 따라서 본 연구에서는 Clark-Y 수중익형에서 발생하는 공동 현상과 이로 인한 유동 소음을 예측하였다. 공동 예측 결과를 정량적으로는 수중익형 표면의 압력 분포, 정성적으로는 수중익형 주변 공동의 체적분율 변화 양상을 이용하여 비교하였으며, 실험결과 및 선행 연구와 비슷한 경향을 가짐을 확인하였다. 이러한 공동에 의한 유동 소음을 예측하기 위하여 음향상사법을 이용하였으며, 시간에 따른 체적분율 변화를 단극자 소음원으로, 수중 익형 표면에서의 비정상 압력섭동을 이극자 소음원으로 모델링하였다. 소음 예측 결과는 SPL과 방향성을 통해 분석하였고, 계산된 전체 주파수 영역에서 비정상 압력섭동에 의한 소음원이 지배적임을 확인하였다.