• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.1
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• pp.102-111
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• 1998

Ocean monitoring facilities are divided into two types, fixed type and floating type. This paper deals with wane load calculation and mooring system for a floating monitoring facility. Wave load and drift forces are calculated for an example case of floating monitoring buoy To enlarge holding power of anchor, circular pile model test was performed. A program for horizontal force of circular pile in sand was made and the calculated result showed fairy good agreement with the result of model test. It is expected that this method will provide good estimation for the holding power of the prototype of circular pile anchor which is relied upon SCUBA activity for installation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.69-74
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• 2000

Linear and nonlinear motion responses of a Tension Leg Platform(TLP) was investigated by model tests. The model tests were carried out at KRISO's Ocean Engineering Basin which has a deep pit of which diameter and depth are 5 meters and 12.5 meters, respectively. Optical sensors were used for measuring drift motions, and a set of accelerometers were employed for analyzing wave frequency motions. ISSC TLP was chosen as the model for the present study. Scale ratio was 1/65 and elastic modelling of tether system were conducted. Very good agreement was obtained between experimental results and theoretical calculations not only in linear motion responses but tension responses, nonlinear wave drift force and double frequency excitations.

• Journal of Navigation and Port Research
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• v.27 no.1
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• pp.55-61
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• 2003

The maneuvering equations of motion are derived to express the motion of a ship. The wave forces in the time domain analysis are generated from the frequency transfer function calculated by 3-D source distribution method. The linear wave forces whose periods are equal to those of incident waves and the nonlinear wave forces that make long period drift forces are computed for the simulation. The consideration of irregular waves and nonlinear wave force effects on the slew motion are carried on the analyzing the motion of ship in the regular and irregular waves.

• Journal of Ocean Engineering and Technology
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• v.28 no.6
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• pp.508-516
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• 2014

A numerical method to investigate the non-linear motion characteristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodynamic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous drag force acting on the platform and tendons is also considered by using Morison’s drag. The results of the present numerical method are compared with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morison's formula.

• Journal of Korean Port Research
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• v.10 no.1
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• pp.25-36
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• 1996

Generally, it is pointed out that a nonlinear analysis is needed to estimate accurately the water surface fluctuation and dynamic responses of a floating structure in case of large wave reflection. In this study, a frequency-domain method is applied and newly developed to analyze the nonlinear characteristics of the air-chamber floating breakwater. The air-chamber floating breakwater in this study can control well the wave transformation, motions of the structure and its natural frequency by adjusting the air depth in the chamber. Experiments are carried out to verify the numerical results. It is appeared that the mean water level is setup in the anti-node and setdown in the node, while the nonlinearity in wave profile is larger in the node than in the anti-node. Because of vertical mooring system, the sway, especially the time-independent nonlinear component, plays predominant role in the motion. On the other hand, the time-dependent component, as well as the time-independent one to the tensile force of mooring line contributes greatly, and the time averaged value presents tensional force oriented to the onshore side due drift force.

• Earthquakes and Structures
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• v.24 no.1
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• pp.53-64
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• 2023

Earth fissures with several kilometers will inevitably approach or cross the metro line, significantly threatening the safety of the underground structure in the earth fissure site. However, the influence of the earth fissure site's amplification effect on the metro station's dynamic response is still unclear. A representative earth fissure in Xi'an was taken as an example to establish a numerical model of a metro station in the earth fissure site. The dynamic response characteristics of the metro stations at different distances from the earth fissure under various seismic waves were calculated. The results show that the existence of the earth fissure significantly amplifies the dynamic response of the nearby underground structures. The responses of the axial force, shear force, bending moment, normal stress, horizontal displacement, inter-story drift, and relative slip of the metro station were all amplified within a specific influence range. The amplification effect increases with the seismic wave intensity. The amplification effect caused by the earth fissure has relatively weak impacts on the axial shear, shear force, bending movement, normal stress, and horizontal movement; slightly larger impacts on the inter-story drift and acceleration; and a significant impact on the relative slip. The influence ranges of the axial force and normal stress are approximately 20 m. The influence ranges of the acceleration and inter-story drift can reach 30 m. Therefore, the seismic fortification level of the underground structure in the earth fissure site needs to be improved.

• Ocean Systems Engineering
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• v.9 no.1
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• pp.97-109
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• 2019

Accurate calculation of the mean drift forces and moments is necessary when studying the higher order excitations on the floater in waves. When taking the time average of the second order forces and moments, the second order potential and motion diminish with only the first order terms remained. However, in the results of the first order forces or motions, the irregular frequency effects are often observed in higher frequencies, which will affect the accuracy of the calculation of the second order forces and moments. Therefore, we need to pay close attention to the irregular frequency effects in the mean drift forces. This paper will discuss about the irregular frequency effects in the calculations of the mean drift forces and validate our in-house program MDL Multi DYN using some examples which are known to have irregular frequency effects. Finally, we prove that it is necessary to remove the effects and demonstrate that the effectiveness of the formula and methods adopted in the development of our program.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.79-82
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• 2003

An aquaculture system for feeding the caged fishes in the open water is suggested for ocean application. Survival and operation conditions are defined at the conceptual design. Wave and current drag forces are discussed to determine the proper dimension of the aquaculture system and the related mooring system. Second order wave drift force at the survival condition is the dominant force, which be reduced by minimizing the superstructure open to the surface. Automation in feeding, sorting, cleaning is introduced to use the ongoing technology for quality product. The suggested system has advantage compared to onshore culturing, but not to shallow water culturing system. There is room for real application in future by the countries, such as Korea and Japan, which are in short of fish supply and have willingness to venture towards the ocean aquaculture.

• 한국기계연구소 소보
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• s.14
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• pp.135-144
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• 1985

A method is described to obtain the first order force and second order steady force on the fixed two dimensional submerged or semisubmerged cylinders at infinite depth of water due to regular waves. The first order diffraction wave velocity potential which describes the flow diffracted by a body is obtained numerically using source distribution method on the mean wetted surface. And a technique to remove the irregular frequency phenomena of the source distribution method is also applied. The second order steady force is calculates by means of direct integration of the pressures on the body as derived from the first order velocity potential and is also computed by means of reflection wave height derives from momentum conservation theory. The results are compared with those of published works, and show good agreement.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.275-294
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• 2013

Side-by-side offloading operations are widely utilized in engineering practice. The hydrodynamic interactions between two vessels play a crucial role in safe operation. This study focuses on the coupled effects between two floating bodies positioned side-by-side as a shuttle tanker-FPSO (floating production, storage and offloading) system. Several wave directions with different side-by-side distances are studied in order to obtain the variation tendency of the horizontal hydrodynamic coefficients, motion responses and mean drift forces. It is obtained that the coupled hydrodynamics between two vessels is evidently distinguished from the single body case with shielding and exaggerating effects, especially for sway and yaw directions. The resonance frequency and the peak amplitude are closely related with side-by-side separation distance. In addition, the horizontal hydrodynamics of the shuttle tanker is more susceptible to coupled effects in beam waves. It is suggested to expand the gap distance reasonably in order to reduce the coupled drift forces effectively. Attention should also be paid to the second peaks caused by hydrodynamic coupling. Since the horizontal mean drift forces are the most mainly concerned forces to be counteracted in dynamic positioning (DP) system and mooring system, prudent prediction is beneficial in saving consumed power of DP system and reducing tension of mooring lines.