• 환경생물
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• 제32권4호
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• pp.297-305
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• 2014

부산시 강서구 낙동강 하구에서 채집한 방사무늬김(Porphyra yezoensis Ueda)의 용존산소 생산율은 $68.8{\pm}46.0{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, 질산염과 인산염 흡수율은 각각 $2.5{\pm}1.8{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, $0.18{\pm}0.11{\mu}mol\;{g_{FW}}^{-1}h^{-1}$ 그리고 용존무기탄소 흡수율은 $87.1{\pm}57.3{\mu}mol\;{g_{FW}}^{-1}h^{-1}$이었다. 용존산소 생산율과 질산염, 인산염, 용존무기탄소 흡수율은 각각 음의 선형관계를 보여, 광합성활동에 의한 결과물임을 파악할 수 있었다. 김의 생중량에 따른 이들 성분의 생산/흡수율은 로그함수적으로 감소하여, 성체(>~0.3 g)보다는 어린 엽체의 광합성효율이 매우 높은 것으로 나타났으며, 이는 질소부족으로 인한 황백화가 양식초기에도 발생할 수 있음을 제시하였다. 우리나라 시도 단위로 월별 생산되는 김 생산량과 양식면적을 바탕으로 질소요구량과 탄소흡수율을 산정한 결과, 생산량이 가장 높은 전라남도보다 부산(경상남도 포함)과 전라북도의 단위면적당 질소요구량이 높았다. 최근 김 황백화가 빈발하는 전라북도는 좁은 면적에서의 과밀 생산과 최대수확기가 육상과 저층으로부터 영양염 공급이 부족한 12~1월인 점 등이 황백화의 원인인 것으로 추정된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.763-766
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• 2002

A BEM is highly efficient method in the sense of economic computation. However, boundary integration is not easy for the complex and moving surface e.g. in a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element depending on its acoustic characteristics. In this study, an axial fan is assumed to have loading noise as a dominant source. Dipole sources can be computed based on the FW-H equation. Acoustic field is then computed by changing Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.83-91
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• 2003

Pantograph design Process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings(FW-H) equation is used to calculate the flow induced sound pressure level in aeroacoustics. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25 m away from Pantograph. Based on aerodynamic(CFD) and aeroacoustic(FW-H) analysis data, the optimal sizing and Positioning of panhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. In this paper, two-step optimization method is used as a parameter design procedure. It is executed using signal to noise(S/N) ratio and analysis of means(ANOM) method. So Thus, an optimal level of design parameters Is extracted to minimize the disconnection ration between contact strips and catenary system, and reduce the far-field aeroacoustic noise.

• Ocean Systems Engineering
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• 제13권2호
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• pp.147-172
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• 2023

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near- and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.

• 한국수산과학회지
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• 제43권6호
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• pp.679-686
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• 2010

To investigate the contribution of macroalgae to biogeochemical nutrients and carbon cycles, we measured the uptake rates of nutrients and $CO_2$ by Undaria pinnatifida using an incubation method in an acrylic chamber. From January to March 2010, U. pinnatifida was sampled at Ilkwang, a well-known area of macroalgae culture in Korea. The initial and final concentrations of nutrients, dissolved oxygen, total alkalinity, and pH of the chamber water were measured, and production/uptake rates were calculated using concentration changes, chamber volume, and incubation time. The production rate of dissolved oxygen by U. pinnatifida (n = 32) was about $5.4{\pm}4.0\;{\mu}mol\;g_{fw}^{-1\;}h^{-1}$. The uptake rate of total dissolved inorganic carbon (TDIC), calculated by total alkalinity and pH, was $7.9{\pm}6.5\;{\mu}mol\;g_{fw}^{-1}\;h^{-1}$. Nutrients uptake averaged $141.7{\pm}119.2$ nmol N $g_{fw}^{-1}\;h^{-1}$ and $15.0{\pm}9.1$ nmol P $g_{fw}^{-1}\;h^{-1}$. A positive linear correlation ($r^2$ = 9.6) existed between the production rate of dissolved oxygen and the uptake rate of total dissolved inorganic carbon, suggesting that these two factors serve as good indicators of U. pinnatifida photosynthesis. The relationships between fresh weight and uptake rates of nutrients and $CO_2$ suggested that younger specimens (<~50 g fresh weight) are much more efficient at nutrients and $CO_2$ uptake than are specimens >50 g. The amount of carbon uptake by the total biomass of U. pinnatifida in Korea during the year of 2008 was about 0.001-0.002% of global ocean carbon uptake. Thus, more research should be focused on macroalgae-based biogeochemical cycles to evaluate the roles and contributions of macroalgae to the global carbon cycle.

• 대한기계학회논문집B
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• 제27권6호
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• pp.701-713
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• 2003

The BEM is a highly efficient method in the sense of economical computation. However, boundary integration is not easy for the complex geometry and moving surface, e.g. a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element according to their acoustic characteristics. In this study, an axial fan is assumed to have unsteady loading noise as a dominant source. Dipole sources can be modeled to solve the FW-H equation. Acoustic field is then computed by determining Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it. The optimal shape and the location of Kirchhoff surface are discussed by comparing with experimental data acquired in an anechoic chamber.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1235-1241
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• 2001

Pantograph design process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore Pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings (FW-H) equation is used to calculate the flow induced sound pressure level. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25m away from panhead contact strips. Based on aerodynamic (CFD) and aeroacoustic (FW-H) analysis data, the optimal sizing and positioning ofpanhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. Using a parameter design procedure associated with signal-to-noise (SIN) ratio and sensitivity analysis, an optimal level of design parameters are extracted to minimize the disconnection ratio between contact strips and catenary system, and reduce the far-field aeroacoustic noise.

• 해양환경안전학회지
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• 제24권7호
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• pp.930-938
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• 2018

잠수함에서 발생하는 수중방사소음은 적함의 소나에 의해 피탐될 확률과 직결되며, 잠수함 저소음화 방안은 생존성 향상을 위해 필수적이다. 최신 잠수함의 경우 기계류 소음저감 및 고속/대형화가 진행됨에 따라 선체 주위에 발생하는 유동소음에 대한 관심이 높아지고 있다. 본 연구에서는 자유수면의 효과를 고려하여 잠수함 형상 주위에 발생하는 유동소음 수준을 예측할 수 있는 소음해석기법을 개발하였다. 잠수함이 자유수면 근처 운항시에 잠수함 주위 유동장의 교란에 의해 발생하는 난류유동소음과 쇄파버블에 의한 소음이 발생한다. 먼저 잠수함 주위 유동장 해석을 위해, VOF법 기반의 비압축성 이상유동(two-phase flow)해석을 수행하여 잠수함 주위 자유수면 형상과 유동장 정보를 도출하였다. 이후 난류유동소음해석을 위해 음향상사기법인 Permeable FW-H를 적용하였고, 쇄파버블 소음해석을 위해 유동해석에서 도출된 난류운동에너지 분포결과를 기반으로 쇄파버블 소음모델을 적용하였다. 최종적으로 개발된 유동소음 해석기법은 선박해양플랜트연구소(KRISO)의 대형캐비테이션터널(LCT)에서 수행된 잠수함 모형 유동소음계측 실험결과와 비교를 통해 검증을 수행하였다.

• 한국소음진동공학회논문집
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• 제26권6_spc호
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• pp.705-713
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• 2016

Underwater noise produced by ships has been becoming an increasing issue. A dominantly contributing noise source is a ship propeller. Therefore, it is important to predict the propeller noise at the propeller design stages. This study applied the acoustic analogy based on Ffowcs Williams equation for the prediction of the marine propeller BPF noise. A marine propeller BPF noise is investigated experimentally as well as numerically. Propeller BPF noise measurement and propeller cavitation observation tests are performed in the KRISO medium size cavitation tunnel. Numerical prediction schemes of marine propeller BPF noise are presented together with the noise measurement method. Propeller BPF noise predictions and experiments are performed under the various propeller operating conditions including non-cavitating and caveating conditions. Numerical and experimental results are compared and analyzed. It is shown that numerical prediction results are generally in good agreement with the measured data.

• 항공우주시스템공학회지
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• 제17권2호
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• pp.26-37
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• 2023

도시 교통 혼잡과 환경 문제에 대한 대안으로 차세대 비행체 Urban Air Mobility(UAM) 항공기 개발이 주목받고 있다. 이를 위해, UAM 항공기가 수직이착륙할 수 있는 플랫폼인 버티포트(Vertiport) 역시 논의되고 있다. 버티포트로 인한 지면 효과는 UAM 항공기의 공력과 소음 특성에 직접적인 영향을 미친다. UAM 항공기는 인구가 밀집된 도심에서 운용되므로 엄격한 소음 규제가 예상되므로, 설계단계에서 공기역학적 현상과 공력 소음의 정밀한 예측이 요구된다. 본 연구에서는 Lattice-Boltzmann Method(LBM) 시뮬레이션과 투과면 기반의 Ffowcs Williams and Hawkings(FW-H) 음향상사법을 이용하여 지면 효과에 대한 공력, 유동장, 원거리 소음 방사 특성을 분석하였다.