• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.562-568
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• 2009

Hull form generation and variation methods to be mainly discussed in this study are based on the fairness optimized B-Spline form parameter curves (FOBFC). These curves can be used both as indirect modification function for variation and as geometric entities for hull form generation. The flexibility and functionality of geometric control technique play the most important role for the success of hull form optimization. This study shows the hydrodynamic optimization process and the characteristics of optimum design hull forms of a 14,000TEU containership and 60K LPG carrier. SHIPFLOW has been used as a CFD solver and FS-Framework as a geometric modeler and optimizer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.10 s.253
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• pp.1003-1011
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• 2006

Droplets are ejected onto a substrate through a nozzle by pushing liquids in flow channels of drop-on-demand devices. The behavior of ejection and formation of droplets is investigated to enhance the physical understanding of the hydrodynamics involved in inkjet printing. The free surface phenomenon of a droplet is described using $CFD-ACE^{TM}$ which employs the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC). Droplet formation characteristics are analyzed in various flow regimes with different Ohnesorge numbers. The computational results show that the droplet formations are strongly dependent on the physical properties of working fluids and the inlet flow conditions. In addition, the wetting characteristics of working fluids on a nozzle influence the volume and velocity of a droplet produced in the device. This study may provide an insight into how a liquid droplet is formed and ejected in a piezoelectric inkjet printing device.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.7
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• pp.992-1001
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• 2023

OWEC (Overtopping Wave Energy Converter) is a wave power generation system using the wave overtopping. The performance and safety of the OWEC are affected by wave characteristics, such as wave height, period. To mitigate this issue, optimal OWEC designs based on wave characteristics must be investigated. In this study, the environmental conditions along the Ulleungdo coast were used. The hydraulic efficiency of the OWEC was calculated using SPH (Smoothed Particle Hydrodynamics) by comparing 4 models that changed the substructure. As a result, it was possible to change the substructure. Through design optimization, a new truss-type structure, which is a substructure capable of carrying the design load, was proposed. Through a case study using member diameter and thickness as design variables, structural safety was secured under allowable stress conditions. Considering wave load, the natural frequency of the proposed structure was compared with the wave period of the relevant sea area. Harmonic response analysis was performed using wave with a 1-year return period as the load. The proposed substructure had a reduced response magnitude at the same exciting force, and achieved weight reduction of more than 32%.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.29-33
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• 2005

The accuracy of predicting wave transformation in the nearshore is very important to wave hydrodynamics, sediment transport, and design of coastal structures. Numerical experiments are conducted to identify the shoaling and breaking characteristics of a fully nonlinear Boussinesq equation-based model. Simulated shoaling showed good agreement with the Shouto's formula, and the results of the breaking experiment agreed well with experimented data, over several beach profile.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.1
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• pp.168-174
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• 2022

In a wave power generation system, the overtopping system is known as an overtopping wave energy converter (OWEC). The performance of an OWEC is affected by wave characteristics such as height and period because its power generation system is sensitive to those characteristics; these, as well as wave direction, depend on the sea. As these characteristics vary, it is hard for the OWEC to produce power in a stable manner. Therefore, it is necessary to find an appropriate shape for an OWEC, according to the characteristics of the sea it is in. This research verified the effect of the design of the OWEC ramp on the hydraulic efficiency using the smoothed particle hydrodynamics (SPH) particle method. A total of 10 models were designed and used in simulations performed by selecting the design parameters of the ramp and changing the attack angle based on those parameters. The hydraulic efficiency was calculated based on the rate of discharged water obtained from the analysis result. The effect of each variable on the overtopping performance according to the shape of the ramp was then confirmed. In this study, we present suggestions for determining the direction for an appropriately shaped OWEC ramp, based on a specific sea area.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.39-46
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• 2019

A three-dimensional flow simulation model for high flow concrete was developed using Incompressible Smoothed Particle Hydrodynamics (ISPH), which can solved Navier-Stokes equation with the assumption of a fluid to be incompressible. For the simulation, a computer program code for ISPH was implemented with MATALB programming code. A piecewise cubic spline function was used for the kernel function of ISPH. Projetion method was used to calculate the velocity and pressure of particles as a function of time. Fixed ghost particle was used for wall boundary condition. Free surface boundaries were determined by using virtual density of particles. In order to validate the model and the code, the simulation results of slump flow test, $T_{500}$ test and L-box test were compared with experimental ones. The simulation results were well matched with the experimental results. The simulation described successfully the characteristics of the flow phenomenon according to the change of the viscosity and yield stress of high flow concrete.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2817-2822
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• 2007

The purpose of this paper is to study the influence of operating condition and ejector geometries on the hydrodynamics and on the mass transfer characteristic of ejector. The CFD results were validated with available experimental data. Flow field analyses and predictions of ejector performance were also carried out. Variation on the operating conditions was made by varying the gas-liquid flow rate ratio in the range of 0.2 to 1.2. The ejector configuration was also varied on the length to diameter ratio of mixing tube ($L_M/D_M$) in the range of 4 to 10. CFD studies show that at $L_M/D_M$ 5.5, the volumetric mass transfer coefficient increases with respect to gas flow rates. Meanwhile, at $L_M/D_M$ 4, the plot of volumetric mass transfer coefficient to gas-liquid flow rates ratio reach maximum at gas-liquid flow rates ratio of 0.6. This study also shows that volumetric mass transfer coefficient decrease with respect to the increase of mixing tube length.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.1
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• pp.1-13
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• 2015

Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and landward-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. In this paper, combined wave overtopping and storm surge overflow of a levee embankment strengthened with high performance turf reinforcement mat (HPTRM) system was studied in a purely Lagrangian and meshless approach, two-dimensional smoothed particle hydrodynamics (SPH) model. After the SPH model is calibrated with full-scale overtopping test results, the overtopping discharge, flow thickness, flow velocity, average overtopping velocity, shear stress, and soil erosion rate are calculated. New equations are developed for average overtopping discharge. The shear stresses on landward-side slope are calculated and the characteristics of soil loss are given. Equations are also provided to estimate soil loss rate. The range of the application of these equations is discussed.

• Korean Chemical Engineering Research
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• v.58 no.2
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• pp.307-312
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• 2020

Fluidized bed reactors operated in subatmospheric pressure has been focused because several industrial applications such as vacuum drying and plasma cvd requires reduced pressure fludization. However, the hydrodynamics of fluidized beds in subatmospheric pressure has not been extensively investigated. The pressure drop in the fluidized bed has been measured with variation of downstream pressures from 1.33 to 101.3 kPa in the shallow and deep fluidized beds under the sub-atmospheric pressures. The obtained minimum fluidization velocity of powders is a function of pressure due to the changes of gas density and mean free path. We can experimentally determine the critical Knudsen number and the critical pressure to define the slip regime significantly to influence the hydrodynamics of fluidized beds.

• Journal of Ocean Engineering and Technology
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• v.36 no.3
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• pp.143-152
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• 2022

To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water.