• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.413-422
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• 2001

In this study, the effect of hydrodynamic masses is investigated in the dynamic characteristics and earthquake response analyses of the submerged HANARO flow tubes. First, the consistent hydrodynamic masses of the surrounding water are obtained by finite element method. Then, modal analyses and response spectrum analyses are performed and verified by comparing the results with those measured from an experiment. Arbitrary cross-sections of submerged structures and boundary conditions of the surrounding fluid can be considered by using the general benefits of a finite element method comparing with the conventional analytical methods. Practical criteria based on parametric studies are proposed to evaluate the dynamic characteristics of HANARO flow tubes including the hydrodynamic masses.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.512-519
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• 2023

Noise pollution poses significant challenges to human well-being and marine ecosystems. It is primarily caused by the flow around ships and marine installations, emphasizing the need for accurate noise evaluation of flow noise to ensure environmental safety. Existing flow noise analysis methods for underwater environments typically use a hybrid method combining computational fluid dynamics and Ffowcs Williams-Hawkings acoustic analogy. However, this approach has limitations, neglecting near-field effects such as reflection, scattering, and diffraction of sound waves. In this study, an alternative using direct method flow noise analysis via the lattice Boltzmann method (LBM) is incorporated. The LBM provides a more accurate representation of the underwater structural boundaries and acoustic wave effects. Despite challenges in underwater environments due to numerical instabilities, a novel DM-TS LBM collision operator has been developed for stable implementations for hydroacoustic applications. This expands the LBM's applicability to underwater structures. Validation through flow noise analysis in pipe orifice demonstrates the feasibility of near-field analysis, with experimental comparisons confirming the method's reliability in identifying main pressure peaks from flow noise. This supports the viability of near-field flow noise analysis using the LBM.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.408-412
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• 2006

단면평균 1차원 수치모형의 수중구조물 표현방식으로 흔히 사용되는 월류공식의 유량계수를 범용 난류유동 수치모형인 FLUENT를 사용하여 완전월류와 불완전월류의 전구간에 걸쳐 구하고 공식화한 결과를 제시한다. 수중구조물은 고무댐과 Ogee형 월류보의 2가지를 대상으로 하였다.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.963-969
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• 2002

In this studies, methly celluloes was used as antiwashout admixture and when considering the physical properties and economical efficiencies of Underwater Concrete as the results of making an experiencing slump flow, flow loss, setting time, suspension and pH also compressive strength and underwater/an air compressive strength ratio according to the adding amount changes 5, 7, 9, 11 kg/$m^3$ to Underwater Concrete of melamine superplasticizer, the using amount of melamine superplasticizer in Underwater Concrete approximately represents 9 kg/$m^3$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.21-24
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• 2006

공동 현상은 난류와 이상 유동으로 인해 그 해석에 어려움이 따르게 된다. 따라서 본 연구에서는 Pressure based 알고리즘을 이상 유동 포착 기법 중, volume fraction모델에 Kunz의 공동 현상 모델을 이용, 공동 현상을 해석할 수 있는 코드를 개발하였다. 이를 통해 2차원의 수중익 주위의 정상유동 해석을 통하여 수중익 주위의 압력 분포를 비교, 코드의 검증을 마쳤다. 또한 2차원 수중익 주위의 비정상 해석을 통해 재진입 영역의 발달에 따른 공동의 생성 및 붕괴를 모사하여 실험 결과와 비교하였다.

• Magazine of the Korea Concrete Institute
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• v.13 no.2
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• pp.38-43
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• 2001

교량 하부구조 특히 교각 및 기초의 경우는 지반 또는 수중에 묻혀 있기 때문에 손상을 발견하기도 어렵고 또한 손상의 보수 및 보강이 곤란한 경우가 많다. 하부구조의 손상은 지반의 마모, 침하, 측방유동토압, 하상세굴, 홍수류, 선박 및 유하물에 의한 충격, 지진 등의 여러 원인에 의하여 발생된다. 이러한 손상은 지표수 및 지하수 배제공, 성토공, 지반개량공, 단면보수공, 세굴방지공, 내진보강공 등에 의하여 보수 및 보강이 행하여 진다. 본 고에서는 이러한 하부구조의 보수.보강공법 중 수중부에 실시되는 방법에 대하여 소개하고자 한다.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.293-300
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• 2007

Turbulent boundary layer over an underwater vehicle is formed when it moves underwater and wall pressure fluctuation within the turbulent boundary layer generates flow-induced noise by exciting the elastic hull of the underwater vehicle. One of the methods to reduce this flow noise is to attach a compliant layer on the surface of the vehicle. In order to observe the possibility of noise reduction in the water when the compliant layer treatments are applied on the surface, three types of specimens those are a bare steel plate, a steel plate coated with neoprene and a steel plate with polyurethane coating material are tested at various flow speeds in a low noise cavitation tunnel. This paper presents the results of measurements and analysis of wall pressure fluctuations which is a main source of flow noise, within the turbulent boundary layer on three specimens. Its results could be shown that about 10dB reduction of wall fluctuation pressure at high frequencies was achieved due to the dissipation of turbulent energy by the compliant coating while it makes the turbulent boundary layer thicker and changes the behavior of turbulent flow in the layer.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.167-170
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• 2004

본 논문에서는 수중익 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 거동 및 소음을 Eulerian-Lagrangian 기법을 이용하여 수치적으로 해석하였다. Eulerian-Lagrangian 기법은 캐비테이션 버블이 유동장에 미치는 영향이 거의 없다는 가정하에 유동장과 캐비테이션 거동을 일방으로 연계하여 해석하는 방식이다. 수중익 버블 캐비테이션 해석을 위한 유동장은 비압축성 RAMS 방정식을 해석하여 구하고 날개 끝 볼텍스 캐비테이션 유동장은 일반적 CFD 기법의 큰 수치 소산으로 그 특성이 잘 나타나지 않으므로 Sculley 볼텍스 모델을 이용하여 해석한다. 해석한 유동장 정보를 입력치로 하고 버블의 지배 방정식인 Rayleigh-Plesset 방정식과 Newton의 제2법칙에 근거한 궤적 방정식을 연계하여 캐비테이션의 성장-붕괴와 운동을 예측한다. 계산된 거동 정보를 이용하여 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 소음을 예측하였다. 본 연구는 수중 운동체에서 발생하는 캐비테이션의 거동과 소음의 특성을 파악하고 그에 따른 대비책을 마련하는 기본 연구로서 활용할 수 있을 것이다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.12
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• pp.913-919
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• 2015

A supercavitating vehicle has a speed of more than 300 km/h in water. A numerical analysis of the flow around a supercavitating vehicle must deal with a multiphase flow consisting of the water, vapor and exhaust gas because the vehicle is powered by roket propulsion. The effect of the exhaust gas on the vehicle is an important part in the study of the performance of the supercavitating vehicle. In the present study, the effect of the exhaust gas on the drag of vehicle was investigated by conducting numerical analysis. When there is no exhaust gas, drag of vehicle is affected by re-entrant. In the case with rocket propulsion, the exhaust gas reduces the influence of re-entrant. The exhaust gas also creates Mach disk and it changes drag profile.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.37-44
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• 2000

An experimental study has been carried out at circulating water channel to investigate the viscous flow around breaking waves generated by a submerged hydrofoil(NACA0012). Detailed flow measurements were made at several critical points including an incipient wave-breaking point and a fully-developed wave breaker. Particle Image Velocimetry(PIV) was employed to visualize the flow field very close to the breaker as well as at the near- and far-wake of the breaker. Generation, development and decay of the wave breaker have been investigated. It is found that PIV technique could be well applied to the complex flow field, including the vortical structures near the free surface as well as the wake of the hydrofoil.