• Journal of Ocean Engineering and Technology
• /
• v.14 no.2
• /
• pp.53-59
• /
• 2000

A numerical method to predict responses of very large floating structures in wave is suggested using source-dipole distribution method. The deflection of the plate is calculated by the finite element method in terms of rigidity matrix of each node. The calculated results for a plate are compared with the experimental ones.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2015.05a
• /
• pp.143-144
• /
• 2015

Here we report the Ar-ion milling rates of ultrathin Si and GaAs single crystals. The thickness change is measured using convergent beam electron diffraction (CBED) technique with the help of Bloch wave simulation method. This study suggests the experimental procedures to determine the references for an etching rate to reduce a sample thickness or to remove the damaged sample surface using Ar-ion source.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.1
• /
• pp.261-267
• /
• 2015

The eigenvalue problems involving the diffraction of waves by multi-layered grating configurations can be explained by rigorous modal expansion terms. Such a modal solution can be represented by equivalent transmission-line networks, which are generalized forms of simple conventional circuits. This approach brings considerable physical insight into the grating diffraction process of the fields everywhere. In particular, the transmission-line representation can serve as a template for computational algorithms that systematically evaluate dispersion properties, radiation effects and other optical characteristics that are not readily obtained by other methods. To illustrate the validity of the present rigorous approach, the previous research works are numerically confirmed and the results agree well each other.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.11
• /
• pp.1209-1215
• /
• 2014

The Uniform Geometrical Theory of Diffraction(UTD) is an effective technique to analyze the radio wave by ray-based calculation of the diffraction coefficient and the reflection coefficient. In this paper, user body shadowing based on the UTD is investigated when the user is close to the mobile device. Two cases are introduced. One is that the user is calling with the mobile attached to the ear(Head Model). The other is that the mobile is located about 15cm away from the user's chest(Chest Model) Radiation Model and Scattering Model are applied to these cases presenting which model is applicable.

• Ocean Systems Engineering
• /
• v.9 no.4
• /
• pp.423-448
• /
• 2019

Very Large Floating Structures (VLFS) are one among the solution to pursue an environmentally friendly and sustainable technology in birthing land from the sea. VLFS are extra-large in size and mostly extra-long in span. VLFS may be classified into two broad categories, namely the pontoon type and semi-submersible type. The pontoon-type VLFS is a flat box structure floating on the sea surface and suitable in regions with lower sea state. The semi-submersible VLFS has a deck raised above the sea level and supported by columns which are connected to submerged pontoons and are subjected to less wave forces. These structures are very flexible compared to other kinds of offshore structures, and its elastic deformations are more important than their rigid body motions. This paper presents hydroelastic analysis carried out on an innovative VLFS called truss pontoon Mobile Offshore Base (MOB) platform concept proposed by Srinivasan and Sundaravadivelu (2013). The truss pontoon MOB is modelled and hydroelastic analysis is carried out using HYDRAN-XR^* for regular 0° waves heading angle. Results are presented for variation of added mass and damping coefficients, diffraction and wave excitation forces, RAOs for translational, rotation and deformational modes and vertical displacement at salient sections with respect to wave periods.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.05a
• /
• pp.257-262
• /
• 2002

Numerical model introduced in this study combines wave refraction-diffraction, breaking, bottom friction, lateral mixing, and critical shear stress and three sub-models for simulating waves, currents, and bottom change were briefly discussed. Simulations of beach processes and harbor sedimentation were also described at the coast neighboring Bangpo Harbor, Anmyundo, Chungnam, where the area has suffered from accumulation of drifting sand in a small fishing harbor with a wide tidal range. We also made model test for the case of a narrow tidal range at Nakdong river's estuary area to understand the effect of water level variation on the littoral drift. Simulations are conducted in terms of incident wave direction and tidal level. Characteristics of wave transformation, nearshore current, sediment transport, and bottom change are shown and analyzed. We found from the simulation that the tidal level impact to the sediment transport is very important and we should apply the numerical model with different water level to analyze sediment transport mechanism correctly. Although the model study gave reasonable description of beach processes and harbor sedimentation mechanism, it is necessary to collect lots of field observation data, including waves, tides and bottom materials, etc. for better prediction.

• Wind and Structures
• /
• v.18 no.3
• /
• pp.253-265
• /
• 2014

The platform and floating structure of spar type offshore wind turbine systems should be designed in order for the 6-DOF motions to be minimized, considering diverse loading environments such as the ocean wave, wind, and current conditions. The objective of this study is to optimally design the platform and substructure of a 3MW spar type wind turbine system with the maximum postural stability in 6-DOF motions as well as the minimum material cost. Therefore, design variables of the platform and substructure were first determined and then optimized by a hydrodynamic analysis. For the hydrodynamic analysis, the body weight of the system was considered, and the ocean wave conditions were quantified to the wave forces using the Morison's equation. Moreover, the minimal number of computation analysis models was generated by the Design of Experiments (DOE), and the design variables of the platform and substructure were finally optimized by using a genetic algorithm with a neural network approximation.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.17 no.1
• /
• pp.231-236
• /
• 2017

The space harmonics generated by a plane-wave incident upon a multi-layered dielectric grating can undergo strong resonance scattering variations known as GMR(guided-mode resonance). To clarify these effects, we examine the field propagation and dispersion curve inside the grating region by using a rigorous equivalent transmission-line theory(RETT). The results show that, at the peak of a scattering resonance, the reflected mode is almost identical to a leaky wave that can be supported by the grating structure. Thus, we confirm and generalize previous research that has occurred GMR effect associated with the free-resonant character of leaky waves at multi-layered dielectric gratings. Quantitative simulation results illustrating the behavior of typical gratings are given, and the special case of normal incidence is discussed for TM mode.

• Ocean Systems Engineering
• /
• v.8 no.3
• /
• pp.329-343
• /
• 2018

The inclination of seabed profile (sloped seabed) is one of the known topographic features which can be observed at different seabed level in the large offshore basin. A mooring system connected between the platform and global seabed is an integral part of the floating structure which tries to keep the floating platform settled in its own position against hostile sea environment. This paper deals with an investigation of the motion responses of an FPSO platform moored on the sloped seabed under the combined action of wave, wind and current loads. A three-dimensional panel discretization method has been used to model the floating body. To introduce the connection of multi-segmented non-linear elastic catenary mooring cables with the sloped seabed, a quasi-static composite catenary model is employed. The model and analysis have been completed by using hydrodynamic diffraction code AQWA. Validation of the numerical model has been successfully carried out with an experimental work published in the latest literature. The analysis procedure in this study has been followed time domain analysis. The study involves an objective oriented investigation on platform motions, in order to identify the effects of the slopped seabed, the action of the wave, wind and current loads and the presence of riser system. In the end, an effective analysis has been performed to identify a stable mooring model in demand of reducing structural responses of the FPSO.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.19 no.5
• /
• pp.502-510
• /
• 2007

The present study is to estimate the effect of diffracted wave fields inside a harbor, around harbor entrance and outer breakwater, when a navigation channel is dredged in the vicinity of the a harbor entrance. The wave field of the problem is considered to be two-dimensional plane and the configuration of the submarine pit on the sea bed is designated by a single rectangular type. The numerical simulation is performed by using the solution of the Greet function based on the boundary integral equation. The results of this study is illustrated by applying the normal incidence and partially reflecting boundaries.