• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.3
• /
• pp.139-145
• /
• 1992

In this paper, a technique to separate the incident and reflected waves in the flume tests is investigated. Using a least squares method, the separation technique has been formulated systematically. This method is applicable to the regular and irregular wave conditions. To illustrate its validity and applicability, numerical experiments have been carried out for both regular and irregular wave conditions. It was found that the method gives perfect results for the conditions without signal noises, and yields reasonable results even for the conditions with 30% signal noises of incident wave height. Hydraulic experiments have been also performed to prove its applicability of the method for real situations.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.29 no.6
• /
• pp.286-304
• /
• 2017

In this study, we proposed a new-type of circular perforated caisson breakwater consisting of a bundle of latticed blocks that can be applied to a small port such as a fishing port, and numerically investigated the hydraulic characteristics of the breakwater. The numerical method used in this study is OLAFOAM which newly added wave generation module, porous media analysis module and reflected wave control module based on OpenFOAM that is open source CFD software published under the GPL license. To investigate the applicability of OLAFOAM, the variations of wave pressure acting on the three-dimensional slit caisson were compared to the previous experimental results under the regular wave conditions, and then the performance for irregular waves was examined from the reproducibility of the target irregular waves and frequency spectrum analysis. As a result, a series of numerical simulations for the new-type of circular perforated caisson breakwaters, which is similar to slit caisson breakwater, was carried out under the irregular wave actions. The hydraulic characteristics of the breakwater such as wave overtopping, reflection, and wave pressure distribution were carefully investigated respect to the significant wave height and period, the wave chamber width, and the interconnectivity between them. The numerical results revealed that the wave pressure acting on the new-type of circular perforated caisson breakwaters was considerably smaller than the result of the impermeable vertical wall computed by the Goda equation. Also, the reflection of the new-type caisson breakwater was similar to the variation range of the reflection coefficient of the existing slit caisson breakwater.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.5 no.3
• /
• pp.182-190
• /
• 1993

A numerical technique is presented to calculate the motions of 6 d.o.f and mooring tensions for a catenary moored floating breakwater. The breakwater may be subjected to the 3-D combination of regular or irregular waves and stationary forces. The added mass coefficients at the infinitive frequency of input wave and the variations of damping and exciting force coefficients are calculated using the source distribution method. The coefficients are used to constitute motion equations in time domain which are solved by WiIson-$\theta$ method. The solutions agree quite well with either static displacement determined from Newton method under the stationary force only or 6 d.o.f determined from the frequency domain analysis under regular wave only. An example analysis is also done for a floating breakwater to demonstrate its applicability.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.2
• /
• pp.122-134
• /
• 2020

On the many coasts of South Korea, including the eastern side, it has been recently increasing the coastal disaster such as the severe coastal erosion and road damage swept away by the wave. As one of the alternatives to prevent the coastal disaster, it has been widely studied the coastal disaster reduction method by the Low-Crested Structure (LCS) in the many countries including several European countries. In this study, the olaFLow model is used to simulate the permeable LCS and wave field of the LCS through the three-dimensional irregular waves numerical analysis on the basis of the previous research. From the numerical analysis, it is evaluated the H_rms, nearshore current and time-averaged turbulent kinetic energy. In addition, the pattern of nearshore current and spatial distribution of time-averaged turbulent kinetic energy are compared with the case of submerged breakwater under the irregular wave fields. As one of significant results, it is confirmed that the pattern of nearshore current is different with the case of submerged breakwater.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.19 no.2
• /
• pp.193-199
• /
• 2013

Course keeping ability of ships under wave are analyzed with wave. The simulation with three degrees of freedom is developed and 3-D source distribution method is applied to get wave force for the simulation. The simulation is conducted with the restriction of maximum rudder angle and time delay of control and regular wave and irregular wave are considered as the source of external forces. Simulations with ships which have different maneuverability with tuned hydrodynamic coefficients are developed to assess the variation of the course keeping ability depending on the ship's maneuvering characteristics. The course Keeping ability is evaluated by comparison of distance while the ships are simulated with autopilot control.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.2
• /
• pp.90-103
• /
• 1997

A numerical procedure is described for predicting the motion and structural responses of the very large floating offshore structures supported by multiple 3-D floating bodies of arbitrary shape in multi-directional irregular waves. The developed numerical approach taking into account of the hydrodynamic interactions among the multiple floating bodies is based on a combination of the 3-D source distribution method, the wave interaction theory, the finite element method and the spectral analysis method to get the significant values of the dynamic responses in the multi-directional irregular waves. The effects of wave interactions and directionality on the dynamic responses of a very large offshore structure, which is semisubmersible ring type, are numerically examined.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.18 no.5
• /
• pp.388-397
• /
• 2012

In this study, 3D-NIT(3-Dimensional Numerical Irregular wave Tank) model in which regular wave as well as stable irregular wave can be generated in 3-dimensional numerical irregular wave tank was proposed. To verify validity, the following steps need to be conducted: 1) comparative analysis between calculated waveforms and targeted waveforms at the wave generating point, 2) comparative analysis with the existing experimental values of overtopping volume estimated, targeting shore protection structures installed on a slope bed, 3) comparison with the existing numerical and hydraulic experimental results through application in the analysis on the wave deformation by structures and wave force acting on the vertical cylindrical structures. Based on the results, characteristics of the breaking wave forces according to incident waves and interval distance of structures were identified through application of 3D-NIT model in the analysis on the breaking wave forces acting on the cylindrical structures installed on a slope bed, and reflection and overtopping was reviewed through application in the special breakwaters on the domestic fields. The numerical results obtained the 3D-NIT model are in good agreement with experimental results, and its applicaion to the complex-shpaed coastal structures is verified.

• Journal of Navigation and Port Research
• /
• v.29 no.10 s.106
• /
• pp.839-845
• /
• 2005

A rudder roll control system is developed and analyzed to control the yawing and rolling motion of ship in irregular waves. The 4-DOF maneuvering equations of motion are derived to carry out the simulation of the motion of a ship and the wave forces are considered as the external forces of a ship in the simulation. The wave forces in the time domain analysis are generated from the frequency transfer function calculated by 3-D source distribution method. The rudder roll control system is developed by linear combination of PD rudder controllers of yawing and rolling motion. Rudder rate speed and Schilling rudder are considered to increase the roll reduction efficiency.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2005.10a
• /
• pp.55-61
• /
• 2005

A rudder roll control system is developed and analyzed to control yawing and rolling motion of ship in irregular waves. The 4-DOF maneuvering equations of motion are derived to carry out the simulation of the motion of a ship and the wave forces are considered as the external forces of a ship in the simulation. The wave forces in the time domain analysis are generated from the frequency transfer function calculated by 3-D source distribution method. The rudder roll control system is developed by linear combination of PD rudder controllers of yawing and rolling motion Rudder rate speed and Schilling rudder are considered to increase roll reduction efficiency.

• Journal of Ocean Engineering and Technology
• /
• v.8 no.1
• /
• pp.23-32
• /
• 1994

A numerical procedure is described for simultaneously predicting the motion and structural responses of tension leg platforms (TLPs) in multi-directional irregular waves. The developed numerical approach is based on a combination of a three dimensional source distribution method, the finite element method for structurally treating the space frame elements and a spectral analysis technique of directional waves. The spectral description for the linear responses of a structure in the frequency domain is sufficient to completely define the responses. This is because both the wave inputs and the responses are stationary Gaussian ran dom process of which the statistical properties in the amplitude domain are well known. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural analysis. The effect of wave directionality has been pointed out on the first order motion, tether forces and structural responses of a TLP in multi-directional irregular waves.