• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.3
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• pp.35-42
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• 1984

In this paper, the lateral motions of a ship in the time domain are treated by applying the Impulse Response Function Technique. The acceleration, and displacement of a ship in the time domain are needed for the purpose of such automatic controls as the fire control system and the auto-pilot of ocean-going vessels, etc. The response Amplitude Operators of a ship are calculated by the Strip Method of Salvesen-Tuck-Faltinsen, and the Pierson-Moskowitz Spectrum multiplied by spreading function is used to represent the short crested ocean waves. The ocean wave elevations in the time domain are simulated according to the Method of Borgman. Finally the rudder effect is considered by simply adding the force and moment due to the rudder to the wave exciting force. And the results of lateral motions with and without rudder are shown.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.795-805
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• 2006

Tuned Liquid damper and Tuned Liquid Column are kind of passive mechanical damper which relies on the sloshing of liquid in a rigid tank for suppressing structural vibrations. TLD and TLCD are attributable to several potential advantages - low costs ; easy to install in existing structures : effective even for small-amplitude vibrations. In this paper, the shaking table experiments were conducted to investigate the characteristics of water sloshing motion in TLD (rectangular, circular) and TLCD. The parameter obtained from the experiments were wave height, base shear force and energy dissipation. The shaking table experiments show that the liquid sloshing relies on amplitude of shaking table and frequency of tank. The TLCD was more effective control vibration than TLD.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.886-890
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• 2003

The etching characteristics of a LiNbO$_3$ single crystal have been investigated using helicon wave plasma source with bias power and the mixture of CF$_4$, HBr, SF$_{6}$ gas parameters. The etching rate of LiNbO$_3$ with etching parameters was evaluated by surface profiler. The etching surface was evaluated by Atomic Force Microscopy (AFM). The surface morphology of the etched LiNbO$_3$ changed with bias power and the mixture of CF$_4$/Ar/Cl$_2$, HBr/Ar/Cl$_2$, and SF$_{6}$/Ar/Cl$_2$ parameters. Optimum etching conditions, considering both the surface flatness and etch rate were determined.

• Steel and Composite Structures
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• v.31 no.6
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• pp.575-589
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• 2019

The main focus of this study is to numerically investigate the influence of strong earthquake and tsunami-induced wave impact on the response and behavior of a cable-stayed steel bridge with large caisson foundations, by assuming that the earthquake and the tsunami come from the same fault motion. For this purpose, a series of numerical simulations were carried out. First of all, the tsunami-induced flow speed, direction and tsunami height were determined by conducting a two-dimensional (2D) tsunami propagation analysis in a large area, and then these parameters obtained from tsunami propagation analysis were employed in a detailed three-dimensional (3D) fluid analysis to obtain tsunami-induced wave impact force. Furthermore, a fiber model, which is commonly used in the seismic analysis of steel bridge structures, was adopted considering material and geometric nonlinearity. The residual stresses induced by the earthquake were applied into the numerical model during the following finite element analysis as the initial stress state, in which the acquired tsunami forces were input to a whole bridge system. Based on the analytical results, it can be seen that the foundation sliding was not observed although the caisson foundation came floating slightly, and the damage arising during the earthquake did not expand when the tsunami-induced wave impact is applied to the steel bridge. It is concluded that the influence of tsunami-induced wave force is relatively small for such steel bridge with large caisson foundations. Besides, a numerical procedure is proposed for quantitatively estimating the accumulative damage induced by the earthquake and the tsunami in the whole bridge system with large caisson foundations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.1
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• pp.20-36
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• 2024

In this study, probabilistic models for the wave- and lifting forces were derived directly from long-term in-situ wave data embedding the Korean marine environment characteristics varying from sea to sea based on the Three-Parameter Weibull distribution. Korean marine environment characteristics varying from sea to sea carved out their presence on the probability coefficients of probabilistic models for wave- and lifting forces. Energetic wave conditions along the southern coast of Korea distinguish themselves from the others with a relatively large scale coefficient, small location coefficient, and shape coefficient around 1.3. On the other hand, mild marine environment along the western coast has a small variability, leading to small scale-coefficient, large location coefficient and shape coefficient around 2.0. In the sea off Mokpo, near the boundary between the South- and West Seas, marine environment was characterized by small scale-coefficient, large location coefficient, and shape coefficient around 1.2, implying that marine environments characteristics of the South-and West Sea coexist in the sea off Mokpo.

• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.13-27
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• 2018

To study how stable the rubble mound breakwaters are, one can look to the research of wave induced seepage flow through the pores of the rubble mound. Seepage flow is generally generated by the difference between the water level around the breakwater during a typhoon. The existing stability analysis method of the rubble mound is the static analysis which simply considers the force equilibrium taking into account the horizontal force acting on the concrete block induced by a wave (calculated by Goda equation) and the vertical force induced by the weight inclusive of the concrete block, quarry run, filter, and armor layer above the slipping plane. However, this static method does not consider the wave-induced seepage flow in the rubble mound. Such seepage may decrease the stability of the rubble mound. The stability of a rubble mound breakwater under the action of seepage was studied based on the results of CFD software (OpenFOAM) and Limit Equilibrium Method (GeoStudio). The numerical analysis result showed that the seepage flow decreased the stability of the rubble mound breakwaters. The results of the numerical analyses also revealed the stability of the rubble mound was varied with time. Especially, the most critical state happened at the condition of overtopping the concrete block, acting strong uplift pressure raising along side and underneath the concrete block, and generating high pore pressure inside rubble mound due to seepage flow. Therefore, it may be necessary to conduct a dynamic analysis considering the effect of wave-induce seepage flow together with the static analysis.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.214-214
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• 2003

During a model test of Hutton TLP, a "ringing" response was first observed about 20 years ago. This phenomenon is a resonant build up over the time of wave period and this burst-like motion can cause the extreme load on the TLP tether. It is often detected in the large and steep irregular waves but the generation mechanism leading to the "ringing" is not yet well understood. According to the research since then, the higher order harmonic components may account for the "ringing" on the floating offshore structures. The main purpose of the present research is, thus, to measure the higher harmonic forces exerted on a vertical truncated circular column and to compare them with available data. A vertical truncated cylinder with a diameter of 3.5inch and a draft of 10.5inch is used as a test structure, which is a scaled model of ISSC TLP column. The cylinder is installed at a distance of 45ft from the wave maker in order to avoid parasitic waves created in the wave flap. Attached to the upper part of the cylinder are two force gages to measure the horizontal (surge) and vertical (heave) forces on the cylinder. The incoming waves are Stokes waves with a slope ranging from 0.06 to 0.24. The forces and waves are measured for 60 seconds with a sampling rate of 50 Hz. Among the recorded data, the first 10 waves are excluded because of transient behavior of the waves and the next The horizontal and vertical forces are analyzed up to 5th order harmonics. The horizontal forces are then compared to the values from the theoretical model called "FNV model". In addition, force transfer functions are also investigated. Major findings in this research are below. 1) The first order forces measured are slightly larger than the theoretical values of "FNV model" 2) The "FNV model" considerably overpredicts the second order forces. 3) The larger the amplitude and more extreme the wave slope, the smaller the predictions are compared to the experimental. 4) The higher harmonic forces are significantly smaller than the first harmonic force for all wave parameters. 5) The normalized forces vs. waves slopes are almost constant in the lower harmonics but vary a lot in the higher harmonics. 6) The trend of forces is more nonlinear in the horizontal forces than in the vertical forces as the wave slope increases. 7) The part of the results above is also observed by other researchers and confirmed again through the present work.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.209-218
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• 2011

The present study proposes a new estimation relationship for the transmission rate of the steel breakwater which is expected to make up for the weakness points in existing hard solution for shore protection. The steel breakwater consists of the wave dissipator of the dual horizontal plates, the supporting columns and their foundations, and thus its respective designs should also be conducted one by one. Furthermore, the breakwater has to ensure both functions of shore protection and structure stabilization. The study produced experimental data for the stability and safety investigation of the steel breakwater. The forces acting on the steel breakwater were classified into two categories, one is vertical up and down loads for the pile resistance and the other was maximum difference of the vertical load acting on horizontally different position for the torsion. The study applied the stability force produced by the summation of maximum pressure at each point and the safety force acting on each point simultaneously. The regular wave corresponding to the significant wave was utilized for measuring wave pressure and force. The study showed the method for the proper position of submerged upper plate by considering occurrence frequency of tide level. The design process finally determined by trial and error is proposed in the present study.

• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.1-6
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• 2011

The installation of a topside structure can be categorized into the following stages: start, pre-lifting, lifting, lifted, rotating, positioning, lowering, mating, and end of installation. The transfer of the module onto the floating spar hull occurs in the last three stages, from lowering to the end. The coupled multi-body motions are calculated in both calm water and in irregular waves with a significant wave height (1.52m). The effects of the hydrodynamic interactions between the heavy lifting vessel and the spar hull during the lowering and mating stages are considered. The internal forces caused by the load transfer and ballasting are derived for the mating phases. The results of the internal forces for the calm water condition are compared with those in the irregular sea condition. Although the effect of the pitch motion on the relative vertical motion between the deck of the floating structure and the topside module is significant in the mating phases, the internal force induced pitch motion is too small to have this influence. However, the effect of the internal force on the wave-induced heave responses in the mating phases is noticeable in the irregular sea condition because transfer mass-induced draught changes for the floating structure are observed to have higher amplitudes than the external force induced responses. The impacts of the module on the spar hull in the mating phase are investigated.