• Environmental Engineering Research
• /
• 제11권4호
• /
• pp.201-207
• /
• 2006

A simple empirical model with good quantitative prediction of inter-particle and intra-particle distance in a cake layer with respect to ionic strength was developed. The model is an inverse length scale with functions of interaction energy and hydrodynamic factor and it explains that the inter-particle and intra-particle distance in a cake is directly related to the effective size of particles. Particle compressibility with respect to ionic strength was also predicted by the model. The model corroborated very well with experimental results of polystyrene microsphere latex particles microfiltation in a dead end operation. From the results of the model, specific cake resistance could be controlled by the same variables affecting the height of particle energy barrier described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.

• 한국해양공학회지
• /
• 제8권2호
• /
• pp.80-92
• /
• 1994

The dynamic response characteristics of a floating ocean city are examined for presenting the basic data for the design of huge offshore structures supported by a large number of floating bodies in waves. The numerical approach which is accurate in linear system is based on combination of a three dimensional source distribution method, wave interaction theory and the finite element method of using the space frame element. The hydrodynamic interactions among the floating bodies are taken into account in their exact form within the context of linear potential theory in the motion and structural analysis. The method is applicable to an arbitrary number of three dimensional bodies having any individual body geometries and geometrical arrangement with the restriction that the circumscribed, bottom-mounted. Imaginary vertical cylinder for each body does not contain any part of the other body. The validity of this procedure was verified by comparing with experimental results obtained in the literature.

• International Journal of Ocean System Engineering
• /
• 제3권2호
• /
• pp.77-89
• /
• 2013

The propeller performance has been investigated using a benchmark Duisburg Test Case ship with RANSE. First, the hydrodynamic characteristics of propeller in case of open water have been analyzed by a commercial CFD program and the results are compared with those of experimental data. Later, the flow around the bare hull has been solved and the frictional resistance value and form factor of the ship have been obtained and compared with those of ITTC57 formulation and experimental results for validation. The free surface effect has been ignored. A good agreement has been obtained between the results of RANSE and experiments at both stages. Then the ship - propeller interaction problem was solved by RANSE and the differences in thrust, torque and efficiency of propeller as compared with the open-water numerical results have been discussed.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2001년도 학술발표회 논문집(II)
• /
• pp.1133-1138
• /
• 2001

The focus of this paper is on the numerical investigation of obliquely incident wane interactions with a system composed of full submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing. The fully submerged systems allow surface and bottom clearances to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of fille second kind) tat satisfy the Helmholz governing equation. Using this computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, clearances. spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters call, if it is properly tuned to the coming waves, have good performances ill reflecting the obliquely incident waves over a tilde range of wave frequency and headings.

• 대한기계학회논문집B
• /
• 제41권6호
• /
• pp.373-380
• /
• 2017

본 연구에서는 레이놀즈 평균 나비어-스톡스(Reynolds-averaged Navier-Stokes, RANS) 방정식을 적용하여 스러스터(thruster) 상호작용에 대한 점성 유동 CFD 해석을 수행하였다. 수치해석은 상용 프로그램인 STAR-CCM+를 이용하였으며, 프로펠러와 No.19a 덕트로 스러스터 모델을 구성하였다. 프로펠러의 회전에 의한 동적인 움직임의 해석을 위해 슬라이딩 격자(sliding mesh)기법을 사용하였으며, 격자구성은 다중영역으로 구분하여 육면체 격자(hexahedral element)로 구성하였고, 계산 시간의 경제성을 고려하여 비등각(non-conformal) 격자를 이용하였다. 스러스터 배치를 그대로 유지한 상태에서 상류방향 스러스터의 방위각(azimuth angle)과 축 기울기에 따라 스러스터 상호작용이 크게 변화하였다. 이러한 결과를 통해 축 기울기와 방위각이 추진성능에 중요한 영향을 미치는 것을 확인하였다.

• Ocean Systems Engineering
• /
• 제7권2호
• /
• pp.121-141
• /
• 2017

The purpose of this paper is to understand and model the slow current (~2 m/s) effects on the global response of a floating offshore platform in waves. A time-domain numerical simulation of full wave-current-body interaction by a quadratic boundary element method (QBEM) is applied to compute the hydrodynamic loads and motions of a floating body under the combined influence of waves and current. The study is performed in the context of linearized potential flow theory that is sufficient in understanding the leading-order current effect on the body motion. The numerical simulations are validated by quantitative comparisons of the hydrodynamic coefficients with the WAMIT prediction for a truncated vertical circular cylinder in the absence of current. It is found from the simulation results that the presence of current leads to a loss of symmetry in flow dynamics for a tension-leg platform (TLP) with symmetric geometry, resulting in the coupling of the heave motion with the surge and pitch motions. Moreover, the presence of current largely affects the wave excitation force and moment as well as the motion of the platform while it has a negligible influence on the added mass and damping coefficients. It is also found that the current effect is strongly correlated with the wavelength but not frequency of the wave field. The global motion of a floating body in the presence of a slow current at relatively small encounter wave frequencies can be satisfactorily approximated by the response of the body in the absence of current at the intrinsic frequency corresponding to the same wavelength as in the presence of current. This finding has a significant implication in the model test of global motions of offshore structures in ocean waves and currents.

• Journal of Advanced Research in Ocean Engineering
• /
• 제1권2호
• /
• pp.73-84
• /
• 2015

The turbine is one of the most important components in the tidal current power device which can convert current flow to rotational energy. Generally, a tidal turbine has two or three blades that are subjected to hydrodynamic loads. The blades are continuously deformed by various incoming flow velocities. Depending on the velocities, blade size, and material, the deformation rates would be different that could affect the power production rate as well as turbine performance. Surely deformed blades would decrease the performance of the turbine. However, most studies of turbine performance have been carried out without considerations on the blade deformation. The power estimation and analysis should consider the deformed blade shape for accurate output power. This paper describes a fluid-structure interaction (FSI) analysis conducted using computational fluid dynamics (CFD) and the finite element method (FEM) to estimate practical turbine performance. The loss of turbine efficiency was calculated for a deformed blade that decreased by 2.2% with maximum deformation of 216mm at the blade tip. As a result of the study, principal causes of power loss induced by blade deformation were analysed and summarised in this paper.

• 한국해양공학회지
• /
• 제15권2호
• /
• pp.11-21
• /
• 2001

The focus of this paper is on the numerical investigation of obliquely incident wav interactions with a system composed of fully submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing between two systems. The fully submerged two systems allow surface and bottom gaps to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of the second kind) that satisfy the Helmholz governing equation in fluid domains. A boundary element program for three fluid domains based on a discrete membrane dynamic model and simple source distribution method is developed. Using this developed computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, gaps, spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters can, if it is properly tuned to the coming waves, have good performances in reflecting the obliquely incident waves over a wide range of wave frequency and headings.

• Nuclear Engineering and Technology
• /
• 제55권6호
• /
• pp.2325-2334
• /
• 2023

To study the lubrication performance of tilting-pad thrust bearing (TPTBs) during start-up in nuclear pump, a hydrodynamic lubrication model of TPTBs was established based on the computational fluid dynamics (CFD) method and the fluid-structure interaction (FSI) technique. Further, a mesh motion algorithm for the transient calculation of thrust bearings was developed based on the user defined function (UDF). The result demonstrated that minimum film thickness increases first and then decreases with the rotational speed under start-up condition. The influence of pad tilt on minimum film thickness is greater than that of collar movement at low speed, and the establishment of dynamic pressure mainly depends on pad tilt and minimum film thickness increases. As the increase of rotational speed, the influence of pad tilt was abated, where the influence of the moving of the collar dominated gradually, and minimum film thickness decreases. For TPTBs, the circumferential angle of the pad is always greater than the radial angle. When the rotational speed is constant, the change rate of radial angle is greater than that of circumferential angle with the increase of loading forces. This study can provide reference for improving bearing wear resistance.

• 한국해양공학회지
• /
• 제25권2호
• /
• pp.29-35
• /
• 2011

In order to effectively control waves in a coastal zone, Multi-Cylinder Piles have been suggested as economic structures. A numerical analysis was conducted using the Delft-3D: WAVE module based on SWAN, which considered wave shoaling and refraction. Moreover, irregular waves were used to investigate the hydrodynamic characteristics of the wave interaction with the structure. In this paper, a numerical analysis was carried out to research the effect of wave control through a wave height analysis concerning an existing, concrete wave breaker and multi-cylinder piles placed at the same location. As a result, the effect of the wave control is shown using the wave breaker, multi-cylinder piles, and existing data.