• Journal of Ocean Engineering and Technology
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• v.37 no.3
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• pp.111-121
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• 2023

This paper intends to introduce the applicability of HydroQus to a problem of a tanker collision against a semi-submersible type floating offshore wind turbine (FOWT). HydroQus is a plug-in based on potential flow theory that generates interactive hydroforces in a commercial Finite element analysis (FEA) code Abaqus/Explicit. Frequency response analyses were conducted for a 10MW capacity FOWT to obtain hydrostatic and hydrodynamic constants. The tanker was modeled with rigid elements, while elastic-plastic elements were used for the FOWT. Mooring chains were modeled to implement station keeping ability of the FOWT. Two types of fracture models were considered: constant failure strain model and combined failure strain model HC-LN model composed of Hosford-Coulomb (HC) model & localized necking (LN) model. The damage extents were evaluated by hydroforces and failure strain models. The largest equivalent plastic strain observed in the cases where both restoring force and radiation force were considered. Stress triaxiality and damage indicator analysis showed that the application of HC-LN model was suitable. It could be stated that applications of suitable failure strain model and hydrodynamics into the collision simulations were of importance.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.11a
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• pp.150-152
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• 2019

In this study, the effects of the wave field changes due to the coastal structure on the hydrodynamic performance of the OWC wave energy, converter are analyzed using a three-dimensional numerical wave tank technique (NWT). The OWC device is simulated numerically by introducing a linear pressure drop model, considering the coupling effect between the turbine and the OWC chamber in the time domain. The flow distribution around the chamber is different due to the change of reflection characteristics depending on the consideration of the breakwater model. The wave energy captured from the breakwater is spatially distributed on the plane of the front of the breakwater, and the converted pneumatic power increased when concentrated in front of the chamber. The change of the standing wave distribution is repeated according to the relationship between the incident wavelength and the length of the breakwater, and the difference in energy conversion performance of the OWC was confirmed.

• Journal of Korea Water Resources Association
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• v.56 no.spc1
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• pp.1059-1069
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• 2023

Dam-break flow occurs when an elevated dam suddenly collapses, resulting in the catastrophic release of rapid and uncontrolled impounded water. This study compares laminar and turbulent closure models for simulating three-dimensional dam-break flows using OpenFOAM. The Reynolds-Averaged Navier-Stokes (RANS) model, specifically the k-ε model, is employed to capture turbulent dissipation. Two scenarios are evaluated based on a laboratory experiment and a modified multi-layered block obstacle scenario. Both models effectively represent dam-break flows, with the turbulent closure model reducing oscillations. However, excessive dissipation in turbulent models can underestimate water surface profiles. Improving numerical schemes and grid resolution enhances flow recreation, particularly near structures and during turbulence. Model stability is more significantly influenced by numerical schemes and grid refinement than the use of turbulence closure. The k-ε model's reliance on time-averaging processes poses challenges in representing dam-break profiles with pronounced discontinuities and unsteadiness. While simulating turbulence models requires extensive computational efforts, the performance improvement compared to laminar models is marginal. To achieve better representation, more advanced turbulence models like Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) are recommended, necessitating small spatial and time scales. This research provides insights into the applicability of different modeling approaches for simulating dam-break flows, emphasizing the importance of accurate representation near structures and during turbulence.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.45-53
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• 2009

A possibility of the drag coefficient estimation in numerical water basins was discussed where the numerical solution were calculated by the 3-dimensional hydro-dynamical model (FLOW-$3D^{(R)}$) with the RNG $k-{\varepsilon}$ turbulence model. On the known cases of the drag coefficients for a rectangle, the numerical drag coefficients got $1.34{\sim}1.52$ and the wind tunnel values were $1.3{\sim}1.5$. For a cylinder, the numerical values were calculated as $0.75{\sim}0.78$ in the range of 0.5

• Journal of the Korean Institute of Gas
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• v.10 no.3 s.32
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• pp.7-12
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• 2006

In this paper, a new evaluation scheme is suggested to estimate load-carrying capacities of wall thinned pipes. At first, computational fluid dynamics analyses employing steady-state and incompressible flow are carried out to determine pressure distributions in accordance with conveying fluid. Then, the variational pressures are applied as input condition of structural finite element analyses to calculate local stresses at the deepest point. The efficiency of proposed scheme was proven from comparison to conventional analyses results and it is recommended to consider the fluid structure interaction effect for exact integrity evaluation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.523-530
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• 2013

In this work, we study a heat transfer enhancement technology using fan-shaped small-scale fins. Fins having a thickness of 10 ${\mu}m$ move up-down by a pulsating flow. Owing to these motions, the heat transfer on a surface increases dramatically. The two-way FSI (fluid-structure interaction) method was applied for the analysis, and the analysis model was evaluated using a single fin model by comparing the experimental results. In summary, a maximum 40% increase in heat transfer capacity using a single and multiple small-scale fins was obtained in comparison with the results obtained without using fins. From this work, we believe that the proposed method can be a promising method for heat transfer enhancement in real applications.

• Wind and Structures
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• v.26 no.5
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• pp.267-277
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• 2018

Numerical simulations are performed of a long flexible cylinder undergoing vortex-induced vibration at a Reynolds number of 500. The cylinder is pinned at both ends, having an aspect ratio of 100 (cylinder length to cylinder diameter) and a mass ratio of 4.2 (structural mass to displaced fluid mass). Temporal and spatial information on the cross-flow (CF) and in-line (IL) vibrations is extracted. High modal vibrations up to the $6^{th}$ in the CF direction and the $11^{th}$ in the IL direction are observed. Both the CF and IL vibrations feature a multi-mode mixed pattern. Mode competition is observed. The $2^{nd}$ mode with a low frequency dominates the IL vibration and its existence is attributed to a wave group propagating back and forth along the span. Distributions of fluid force coefficients are correlated to those of the CF and IL vibrations along the span. Histograms of the x'-y motion phase difference are evaluated from the total simulation time and a complete vibration cycle representing the standing or travelling wave pattern. Correlations between the phase difference and the vibrations are discussed. Vortex structures behind the cylinder show an interwoven near-wake pattern when the standing wave pattern dominates, but an oblique near-wake pattern when the travelling wave pattern prevails.

• Korean Chemical Engineering Research
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• v.51 no.6
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• pp.760-765
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• 2013

Lysozyme crystallization was performed by using flow-focusing chip in droplet-based microfluidic system. Water-in-oil droplets were formed in the system and collected on petri-dish and cross type mold. Liquid-liquid reaction of lysozyme and sodium chloride occurred in the droplet and crystals were observed through microscope. Solution pH was varied as 4.8 and 7.2. Crystals of polyhedron and plate-like shape were obtained at pH 4.8, while needle structure crystals formed at pH 7.2. Lysozyme in single droplet for two pHs were crystallized with constant or decreased droplet size. However, crystals at pH 4.8 were only obtained in the droplet of which size was increased by the interaction between droplets. Droplet volume did not change at pH 7.2 and crystals formed in both droplets.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5371-5376
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• 2013

The role of a main starting air valve is to supply compressed air to the diesel engine for starting the stopped diesel engine of a ship and cut off the air during normal operation. In this study, the main starting air valve with 80mm size was designed based on the developed valve with 50mm size. The concept design of the 80A main starting air valve was completed by using CATIA. Then, fluid analysis was performed to investigate the flow characteristics such as pressure and velocity distribution. Sequentially, structural analysis using FSI was performed. In this study, ANSYS CFX and ANSYS Workbench are utilized. The heavy weight of the body can deteriorate the strength performance of neighbor elements, leading to undesirable effect on flow characteristics. Thus, in this research, a lightweight design of the body was suggested satisfying strength requirement. The weight of the suggested design was reduced by 7kg, and the strength satisfied its requirement.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.30-36
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• 2018

In the present study, we investigate the flow characteristics of a quadrotor UAV in a hovering mode by measuring multiple two-dimensional velocity fields in the wake. The experiment is conducted at Re = 24,000 in a chamber large enough to neglect the ground effect, where Re is the Reynolds number based on the rotor chord length and the rotor tip speed. The rotational speed of the rotor is determined by an optical tachometer so that the lift force can be balanced with the weight of the UAV. The velocity field measured on the center plane of the rotor shows that the vortices are shedding from the tip of the rotor, inducing large fluctuations in the streamwise velocity along the wake shear layer. The strength of the rotor-tip vortex shedding is asymmetric with respect to the rotor axis due to the interaction between the rotor and the wake centerline of each rotor is inclined to the center of the UAV due to the pressure difference caused by the induced velocity. The wake from each rotor moves closer to each other while traveling in the streamwise direction, and then is merged together inducing large fluctuations in the transverse velocity. Due to the wake merging, on the center plane of the UAV, the velocity increases in the streamwise direction showing two-peak structure in the streamwise velocity contours.