Clark-Y 수중익형 캐비테이션 유동 소음 특성 분석

구가람(Garam Ku),김상현(Sanghyoen Kim),정철웅(Cheolung Cheong),하콩투(Cong Tu Ha),박원규(Warn-Gyu Park) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4

In this study, computational fluid dynamics techniques are applied to simulate cavitation flow and the noise caused by cavitation is predicted by applying the acoustic analogy to the predicted flow. The predicted results of cavitation flows are compared with the measurement and other prediction obtained from references available in terms of surface pressure distribution and the variation of periodic cavitation pattern. There are good agreements between these results. The noise sources are modeled as monopole and dipole sources. Then, the predicted noise results are analyzed in terms of directivity and SPL spectrum. Since the lift of the hydrofoil is higher than the drag, dipole source is dominant in the direction normal to the mean flow while monopole source is dominant in the direction parallel to the mean flow.

맥문동(麥門冬)의 증숙(蒸熟)에 따른 항산화 효능 및 고지혈증 유발 흰쥐에 대한 효능 연구

구가람 ( Garam Ku ),이현인 ( Hyun-in Lee ),김수지 ( Suji Kim ),신미래 ( Mi-rae Shin ),이아름 ( Ahreum Lee ),박해진 ( Hae-jin Park ),노성수 ( Seong-soo Roh ),서영배 ( Young Bae Seo ) 대한본초학회 2018 大韓本草學會誌 Vol.33 No.5

Objectives : This study is aimed to compare the changes in Antioxidative capacity of Liriopis Tuber by steaming process and to compare the effects in hyperlipidemia induced rats fed high cholesterol diet between Simvastatin and Liriopis Tuber by steaming process. Methods : The SD rats were divided into six groups: normal diet (Nor), high cholesterol diet (Veh), high cholesterol diet plus Simvastatin 5 ㎎/㎏ (Sim), high cholesterol diet plus LT0 extract 200 ㎎/㎏ (LT0), high cholesterol diet plus LT6 extract 200 ㎎/㎏ (LT6) and high cholesterol diet plus LT9 extract 200 ㎎/㎏ (LT9). We compared the total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL) contents and reactive oxygen species (ROS) from each serums. Protein expression in liver tissues related to antioxidant and cholesterol was analyzed. Results : The Antioxidant activity of Liriopis Tuber increased by steaming process. In vivo, TC, TG, LDL-c, atherogenic index (AI) and cardiac risk factor (CRF) decreased and HDL-c increased with increasing steaming frequency. aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, and blood urea nitrogen (BUN) decreased with increasing steaming frequency. ROS decreased only in LT9, and SOD, catalase and glutathione peroxidase (GPx) increased with increasing steaming frequency. phospho-AMP-activated protein kinase (p-AMPK) increased and sterol regulatory element-binding protein 2 (SREBP-2), Phospho-Acetyl-CoA Carboxylase (p-ACC) and HMG-CoA reductase (HMGCR) decreased with increasing steaming frequency. Liver staining showed a decrease in hepatic fat accumulation of LT9. LT9 showed significant results in all experiments. Conclusions : LT9 showed significance of anti-lipid effect and improved fatty liver of hyperlipemia induced rats fed on high cholesterol diet, In conclusion, LP9 can be effectively used for the treatment of hyperlipidemia.

오매(烏梅)와 증숙오매(蒸熟烏梅)의 생리활성 연구

구가람 ( Garam Ku ),권오준 ( Ojun Kwon ),노성수 ( Seong-soo Roh ),서영배 ( Young-bae Seo ) 대한본초학회 2016 大韓本草學會誌 Vol.31 No.3

Objectives:Presently Mume Fructus (MF) undergoes fumigation, which produces benzo[a]pyrene. As a primary analysis with the aims to minimize the production of benzo[a]pyrene and to suggest standards for processing the MF, the steaming method was chosen among the various processing methods, and reviewed through a series of experiments. Methods:Pitted and un-pitted MF were steamed and processed into samples. After testing level of benzo[a]pyrene, the samples were analyzed for amount of polyphenol and flavonoids. Scavenging activities of the samples for the DPPH and ABTS radicals were tested. In order to measure anti-inflammatory effects of the samples, cell survival rate was investigated using CCK-8 Assay. Also, water extracts of dried and steamed MF were administered to the RAW 264.7 cells to compare expressions of NO, PGE2, IL-1β, and TNF-α. In addition, anti-diarrhea effects of the herbal medicine were tested on animal models with diarrhea induced by MgSO4 and Castor oil. Results:Regardless of pitting, processed MF contained no benzo[a]pyrene. Anti-oxidation effect increased in relation to the frequency of steaming process. However, extracts of dried and steamed MF suppressed different kinds of inflammation factors, and extract of dried MF showed superior anti-diarrhea effect than extract of steamed MF. Conclusions:It is suggested that steaming method of MF is recommended for processing the herbal medicine without the production of benzo[a]pyrene. But regarding that dried and steamed MF showed differences in their anti-oxidative, anti-inflammatory, and anti-diarrhea effects, it is recommended to perform further researches on different efficacies of MF according to their processing methods.

Clark-Y 수중익형 주변 공동 현상에 의한 유동장과 소음 예측에 대한 수치적 연구

구가람(Garam Ku),정철웅(Cheolung Cheong),김상현(Sanghyeon Kim),하콩투(Cong-Tu Ha),박원규(Warn-Gyu Park) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.2

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. Because the cavitation flow driven by an underwater propeller corrodes the materials around it and generates a high level of noise, it has become an important topic in engineering research. In this study, computational fluid dynamics techniques are applied to simulate cavitation flow, and the noise in the flow is predicted by applying the acoustic analogy to the predicted flow. The predicted results are compared with measurement results and other predictions in terms of surface pressure distribution and the temporal variation in liquid volume fraction. The predicted results are found to be in good agreement with the measured results. The source of the noise attributed to the time rate of change in the liquid volume fraction around the hydrofoil is modeled as a monopole source, and the source of the noise due to unsteady pressure perturbations on the hydrofoil surface is modeled as a dipole source. Then the predicted noise results are analyzed in terms of directivity and SPL spectrum. The noise caused by unsteady pressure perturbations was dominant in the entire frequency range considered in the study.

Clark-Y 수중익형 주변 캐비테이션 유동장에 대한 수치적 고찰

구가람(Garam Ku),정철웅(Cheolung Cheong),하콩투(Cong Tu Ha),박원규(Warn-Gyu Park) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Cavitation can be produced by localized pressure drop around a device which runs at a high speed in the water and generate stronger noise than non-cavitation flow. In this study, as a prior task to predict flow noise due to cavitation, basic numerical methods are developed to simulate cavitation flow and are applied to predict cavitation flow around a Clark-Y hydrofoil for the validation purpose. The prediction results are compared with the experiment and the simulation result obtained from the references available in terms of surface pressure distribution and the variation of periodic cavitation pattern. There are good agreements beween these results.

고압 배관 내 감압밸브 유동소음에 대한 수치적 연구

구가람(Garam Ku),이송준(Songjune Lee),김극수(Kuksu Kim),정철웅(Cheolung Cheong) 한국소음진동공학회 2017 한국소음진동공학회 학술대회논문집 Vol.2017 No.4

파수-주파수 분석을 통한 고압 배관 내 수축 확장 노즐의 유동 소음원에 대한 수치적 연구

구가람,이송준,김극수,정철웅,Ku, Garam,Lee, Songjune,Kim, Kuksu,Cheong, Cheolung 한국음향학회 2017 韓國音響學會誌 Vol.36 No.5

일반적으로 감압밸브는 고압 가스에 의한 배관 파손을 방지하기 위해 설치된다. 그러나 감압 밸브를 지나면서 발생하는 급격한 압력 저하는 음향파의 형태로 전파되는 큰 음향 에너지를 발생 시키며, 하류 방향으로 전파되면서 배관의 벽면을 진동시키는 가진원으로 작용하여 배관의 파손을 유발한다. 따라서, 본 연구에서는 단순 수축-확장 배관을 대상으로 LES(Large-Eddy Simulation)기법과 파수-주파수 분석을 통해 유동장 내 비압축성 압력섭동과 압축성 압력 섭동을 분리하고, 밸브 유동에 의한 내부 유동소음을 예측하였다. 수치해석의 수렴성을 향상시키기 위해 먼저 정상상태 Reynolds-Averaged Navier-Stokes 방정식을 해석하여, 고정확도의 비정상 LES해석의 초기 값으로 활용하였으며, 비정상 유동장 결과로부터 파수-주파수 분석을 실시하였다. 파수-주파수 분석을 통해 비압축성 압력섭동과 압축성 압력섭동을 분리하였으며, 이를 통해 배관 내 음향유기진동에 의한 소음원 정보를 정확히 제공할 수 있음을 확인하였다. A pressure relief valve is generally used to prevent piping systems from being broken due to high pressure gas flows. However, the sudden pressure drop caused by the pressure relief valve produces high acoustic energy which propagates in the form of compressible acoustic waves in the pipe and sometimes causes severe vibration of the pipe structure, thereby resulting in its failure. In this study, internal aerodynamic noise due to valve flow is estimated for a simple contraction-expansion pipe by combining the LES (Large-Eddy Simulation) technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. In order to increase the convergence, the steady Reynolds-Averaged Navier-Stokes equations are numerically solved. And then, for the unsteady flow analysis with high accuracy, the unsteady LES is performed with the steady result as the initial value. The wavenumber-frequency analysis is finally performed using the unsteady flow simulation results. The wavenumber-frequency analysis is shown to separate the compressible pressure fluctuation in the flow field from the incompressible one. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of a piping system.

사중극자 보정 Ffowcs Williams and Hawkings 방정식을 이용한 수중 익형 공동 유동소음에 대한 수치적 고찰

구가람,유서윤,정철웅,Ku, Garam,Ryu, Seo-Yoon,Cheong, Cheolung 한국음향학회 2018 韓國音響學會誌 Vol.37 No.5

외부 유동소음 문제를 다루는 대부분의 산업현장에서 FW-H(Ffowcs Williams and Hawkings) 방정식을 이용한 복합전산공력음향 기법이 수치적인 효율성으로 인하여 널리 사용되고 있다. 그러나 사중극자항을 무시한 면적분 형태의 FW-H 방정식을 사용할 때 경우에 따라 무시할 수 없는 비물리적인 소음이 발생한다고 알려져 있다. 특히, 수중 프로펠러와 같이 날개 끝 와류 공동(tip vortex cavitation)이 하류방향으로 길게 형성되는 유동에 대해서는 적절하게 모델링하지 않으면 소음 예측의 정확도가 떨어지게 된다. 따라서 본 연구에서는 사중극자 보정항을 추가하여 적분면에서 FW-H 방정식으로부터 발생하는 비물리적인 음향을 저감시키고자 하였다. 먼저 FW-H 방정식에 기초하여 개발한 내부 예측코드의 정확성을 확인하기 위하여 에어컨 실외기에 사용되는 축류팬을 대상으로 검증을 수행하였으며, ANSYS Fluent의 결과와 비교하여 잘 일치하는 것을 확인하였다. 사중극자 보정항의 효과를 확인하기 위하여 등엔트로피 와류 전파에 대한 소음 해석을 수행하였으며, 사중극자 보정항에 의한 오차의 저감 효과가 발생하는 것을 확인하였다. 마지막으로 Clark-Y 수중익형에서 발생하는 공동 유동장을 대상으로 소음 해석을 수행하였으며, 공동이적분면을 통과할 때 발생하는 오차를 사중극자 보정항을 이용하여 저감할 수 있다는 것을 확인하였다. In most industry fields concerning external flow noise problems, the hybrid computational aeroacoustic techniques based on the FW-H (Ffowcs Williams and Hawkings) equation are widely used for its numerical efficiency. However, when the surface integral form of FW-H equation is used without volume quadrupole sources, it is known to generate significant non-physical noise in a certain case. Especially, in the case of a flow in which the tip vortex cavitation is formed in the distant downstream direction such as flow driven by an underwater propeller, the accuracy in noise prediction becomes poor unless it is not properly modelled. Therefore, in this study, the nonphysical acoustic waves caused by the surface integral form of FW-H equation is reduced by adding the quadrupole correction term. First, to verify the accuracy of the in-house code of FW-H equation, the noise by an axial fan used in the outdoor unit of air conditioner was calculated and compared with the results of ANSYS Fluent. In order to verify the effects of the quadrupole correction term, the noise prediction for isentropic vortex convection is performed and it is confirmed that the error is reduced by the quadrupole correction term. Finally, the noise prediction is performed for the flow field generated by the Clark-Y hydrofoil in underwater. It is confirmed that the error caused by the cavitation passing through the integral surface can be reduced by the quadrupole correction term.

다공판을 이용한 고압 가스 배관 내 밸브 유동 소음 저감에 대한 수치적 고찰

김규남,구가람,정철웅,강웅,김극수,Kim, Gyunam,Ku, Garam,Cheong, Cheolung,Kang, Woong,Kim, Kuksu 한국음향학회 2021 韓國音響學會誌 Vol.40 No.1

In this study, a numerical methodology is proposed for evaluating valve flow noise in a pipe conveying high pressure gas, and the effects of perforated plates on reduction of such valve flow noise are quantitatively analyzed. First, high-accurate unsteady compressible Large Eddy Simulation techniques are utilized to predict flow and flow noise by a valve in a high-pressure pipe. The validity of the numerical result is confirmed by comparing the predicted wall pressure spectrum with the measured one. Next, the acoustic power of downstream-propagating acoustic waves due to the valve flow is analyzed using an acoustic power formula for acoustic waves propagating on mean flow in a pipe. Based on the analysis results, perforated plates are designed and installed downstream of the valve to suppress the valve flow noise and the acoustic power of downstream-going acoustic waves is predicted by using the same numerical procedure. The reduction by 9.5 dB is confirmed by comparing the predicted result with that of the existing system. Based on these results, the current numerical methodology is expected to be used to reduce valve flow noise in an existing system as well as in a design stage.

선박 추진시스템 유동 소음원 상대적 기여도 분석

하준범,구가람,정철웅,설한신,정홍석,정민석,Ha, Junbeom,Ku, Garam,Cheong, Cheolung,Seol, Hanshin,Jeong, Hongseok,Jung, Minseok 한국음향학회 2022 韓國音響學會誌 Vol.41 No.3

In this study, each component of flow noise source of underwater propeller installed to the scale model of the KVLCC2 is investigated and the effect of each noise source on underwater-radiated noise is quantitatively analyzed. The computation domain is set to be the same as the test section of the large cavitation tunnel in the Korea Research Institute of Ship and Ocean Engineering. First, for the high-resolution computation of flow field which is noise source region, the incompressible multiphase Delayed Detached Eddy Simulation is performed. Based on flow simulation results, the Ffowcs Williams and Hawkings integral equation is used to predict underwater-radiated noise and its validity is confirmed through the comparison with the tunnel experiment result. For the quantitative comparison on the contribution of each noise source, the spectral levels of sound pressure and power levels predicted using propeller tip-vortex cavitation, blade surface and rudder surface as the integral region of noise sources are investigated. It is confirmed that the cavitation which is monopole noise source significantly contributed to the underwater-radiated noise than propeller blades and rudder which is dipole noise source, and the rudder have more contribution than propeller blades due to the influence of the propeller wake.