Observation of Colloidal Particle Dynamics Near a Flat Wall by Using Oscillating Optical Tweezers

박혁규,하청일,Daniel Ou-Yang 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3

We study the hydrodynamics of a micron-sized spherical particle positioned nearby a flat wall by using oscillating optical tweezers that trap and oscillate the colloidal particle. In this situation,the presence of the flat wall complicates the flow field surrounding the particle, so the force felt by the moving particle is quite different from the three dimensional hydrodynamics drag force,known as Stokes’ drag. However, in biological processes, this condition is ubiquitous and governs the biological particle hydrodynamics. In this work, we describe observations of confined particles dynamics by using oscillation optical tweezers and compare the results with known theories and other experimental data.

GENERAL RELATIVISTIC RADIATION HYDRODYNAMICS: FREQUENCY-INTEGRATED RADIATION MOMENT FORMALISM

Park, Myeong-Gu The Korean Astronomical Society 2012 Journal of The Korean Astronomical Society Vol.45 No.4

I present here one approach to general relativistic radiation hydrodynamics. It is based on covariant tensor conservation equations and considers only the frequency-integrated total energy and momentum exchange between matter and the radiation field. It is also a mixed-frame formalism in the sense that, the interaction between radiation and matter is described with quantities in the comoving frame in which the interaction is often symmetric in angle while the radiation energy and momentum equations are expressed in the fixed frame quantities in which the derivatives are simpler. Hence, this approach is intuitive enough to be applied straightforwardly to any spacetime or coordinate. A few examples are provided along with caveats in this formalism.

Experiments on Surface Waves Interacting with Flexible Aquatic Vegetation

Luca Cavallaro,Antonino Viviano,Giovanni Paratore,Enrico Foti 한국해양과학기술원 2018 Ocean science journal Vol.53 No.3

Surface wave interaction with aquatic vegetation appears to play a key role in coastal hydro-morpho-dynamics. As an example, the presence of a dense meadow at intermediate water depth is usually associated with a stable and resilient shore. Wave-meadow interactions are investigated here by means of physical modelling, with a focus on wave height distribution and hydrodynamics. The central part of a wave flume is covered by flexible artificial seagrass, composed of polyethylene leaves. This vegetation is tested in both near emergent and submerged conditions. The wave height reduction is evaluated by means of a drag coefficient defined from linear wave theory, which contains all the unknowns of the adopted methodology. The behaviour of such a coefficient is investigated as a function of a wave related Reynolds number. The influence of the flexibility of the leaves is also considered, together with a wave frequency parameter. The results show a complex behaviour with three different trends for near rigid, intermediate or highly flexible leaves. Amplitudes of the orbital velocities are investigated and show a fairly good match with the linear wave theory. On the contrary, the mean velocity along the water column appears to be modified by the seagrass for submerged leaves.

Influence of high density particles in reduction of axial dispersion in liquid fluidized bed with residence time distribution curve studies

Jamshid Behin,Tahereh Shojaeimehr 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.3

Liquid phase RTD curves were investigated in classical fixed and fluidized bed regimes with high density particles. The effect of liquid velocity was studied on bed hydrodynamics. Using an impulse tracer injection technique in a column of 5 cm inner diameter and 1.2 m height, liquid RTD, mean residence time (MRT), axial dispersion coefficient (ADC) and vessel dispersion number (N_D) were determined. ADC increases with liquid superficial velocity. It varied from 4.63 to 20.7 cm^2/s for the particle Reynolds number of 43 to 279, respectively. The experimental results show that the hight density particles cause less ADC than the low density particles at an identical Reynolds number.

자성유체에 잠긴 비자성체 부상현상의 다중물리수치해석 및 실험

최홍순(Hong-Soon Choi) 대한전기학회 2013 전기학회논문지 Vol.62 No.1

In this paper, magnetic buoyancy force on nonmagnetic solid object submerged in magnetic liquid was simulated and measured. For the evaluation of the force, a multi-physics approach of hydrostatic equilibrium considering magnetic body force as well as gravity is presented. The magnetic body force should be regarded as an additional forcing term in the momentum equation of hydrodynamics. It is also shown that the virtual air-gap based Kelvin’s force formula is a useful method for the calculation of force distribution in the magnetic liquid. The experimental result which was performed by a load-cell measurement system agreed quantitatively well with the numerical one.

Hydrodynamics prediction of a ship in static and dynamic states

Du, P.,Ouahsine, A.,Sergent, P. Techno-Press 2018 Coupled systems mechanics Vol.7 No.2

The ship hydrodynamics in static and dynamic states were investigated using 3-dimensional numerical simulations. The static case simulated a fixed ship, while the dynamic case considered a ship with free sinkage and trim using the mesh morphing technique. High speed was found to increase the wave elevation around the ship. Compared with the static case, the dynamic case seemed to generate higher waves near the bow and after the stern. The frictional resistance was found be to more dominant. However, the pressure resistance became gradually important with the increase of the ship speed. The trim and sinkage were also analyzed to characterize the ship hydrodynamics in the dynamic state.

만곡 수로실험을 활용한 TELEMAC 수리모형 검증

심규현 ( Gyu Hyeon Sim ),이응섭 ( Eeong Seop Lee ),최정우 ( Jeong Woo Choi ),최윤영 ( Yun Young Choi ) 한국수처리학회 2015 한국수처리학회지 Vol.23 No.5

This study was purposed to validate the capability of the TELEMAC model for simulating bended flow of natural rivers. A laboratory hydrodynamic test was done with an open channel with 30o, 60o, and 90o bended sections, and the measured hydrodynamic data were compared with the simulation data of the TELEMAC model. The measured and simulation data (i.e. flow velocity and water depth) in the straight sections of the channel were similar to each other, without variation along the cross-section, because the straight sections were not under the centrifugal force. However, in the bended sections, under the centrifugal force, the measured and simulation data showed that water depth increased but flow velocity decreased from the inner to the outer bend. For both of the straight and bended sections, the errors between the measured and simulation data were less than 7 % error. Therefore, we concluded that the TELEMAC model can properly simulate hydrodynamics in the bended channel, and it can be a good hydrodynamic simulation program for planning, designing, and early warning of bended natural rivers.

Magneto-Hydrodynamics 수치기법을 추가한 축대칭 유체동역학 코드 연구

이민형(Minhyung Lee) 대한기계학회 2022 大韓機械學會論文集B Vol.46 No.5

자체 개발 in-house 3차원 ExLO 유체동역학코드에 MHD(magneto-hydrodynamics) 모듈을 추가 접목하는 연구를 수행하였다. 운동량 보존 식 및 에너지 보존 식에 추가 항을 포함하는 대체로 쉬운 접목방법을 채택하였다. 플라즈마 물성을 모사하기 위한 상태방정식을 테이블 형태로 획득하고 코드에 연동하였다. 검정 예제로 물속에서 세선(wire)이 폭발하는 현상을 수치 모사하였으며 자체 실험 결과와 비교하였다. 직경 200 um 구리선 양 끝단에 전압은 13 kV를 부과한 후 반경 방향 여러 위치에서 시간에 따라 충격파 및 플라즈마 경계면을 측정하였다. 수치해석이 시험 결과를 매우 유사하게 모사함을 확인함으로써 플라즈마 상태방정식 및 수치 모델이 잘 구현되었음을 확인하였다. ExLO is an arbitrary Lagrnagian-Eulerian (multimaterial) computer code that has been developed in Korea since 2000. To perform simulation with confidence, we included a variety of validated material models and the sophisticated modern numerical algorithms. Recently, we incorporated the magneto-hydrodynamics (MHD) into the code to offer new physics such as magnetics. The test problem we chose was the exploding wires immersed in a water environment, as the material transforms from a solid state to liquid and finally to gas phases. A new plasma equation of state (EOS) was obtained for this study. The shock and plasma fronts were captured in the several locations in water. Our MHD simulations showed excellent agreement with experiments.

A CFD Analysis on Hydrodynamics Characteristics of Gas-Liquid Ejector

Tony Suryo Utomo,Jin Zhenhua,ChungSeub Yi,Hyo Min Jeong,Han Shik Chung 한국동력기계공학회 2006 한국동력기계공학회 학술대회 논문집 Vol.- No.-

A CFD investigation on hydrodynamics characteristics of gas liquid ejector has been carried out to study the influence of gas liquid flow rates ratio on the performance and on the mass transfer characteristic of ejector. In this study, the ejector design was modeled using finite volume CFD techniques to resolve the flow dynamics in the ejectors. The CFD results were validated with available experimental data. Flow field analyses and predictions of ejector performance were also carried out. During validation, although there is a discrepancy between CFD and experimental results, however it has a good agreement in the trend of phenomena respect to experimental results. From the present analysis, it can be concluded that the efficiency of the ejector increases with respect to gas liquid flow rates ratio. It also can be seen that the volumetric mass transfer coefficient is higher when the gas flow rate increased.

Influence of gas liquid flow rate ratio on hydrodynamics and mass transfer characteristics of gas-liquid ejector

Tony Suryo Utomo,Jin Zhenhua,ChungSeub Yi,Hyo Min Jeong,Han Shik Chung 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

An investigation on hydrodynamics characteristics of gas liquid ejector has been carried out using to study the influence of gas liquid flow rates ratio on the performance and on the mass transfer characteristic of ejector. In this study, the ejector design was modeled using finite volume CFD techniques to resolve the flow dynamics in the ejectors. The CFD results were validated with available experimental data. Flow field analyses and predictions of ejector performance were also carried out. During validation, although there is a discrepancy between CFD and experimental results, however it has a good agreement in the trend of phenomena respect to experimental results. From the present analysis, it can be concluded that the efficiency of the ejector increases with respect to gas liquid flow rates ratio. It also can be seen that the volumetric mass transfer coefficient is higher when the gas flow rate increased.