• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.12
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• pp.12-20
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• 1998

The non-uniform leaky wave structure of the slits in a parallel-plate waveguide is analyzed from the viewpoints of transmitting(receiving) leaky wave antenna and grating coupler. Period and slit width are simultaneously varied along the leaky wave structure to construct the leaky wave structure with a specific distribution of complex propagation constant. Some results for the equivalent magnetic current distributions over the slits and the radiation characteristics of the leaky wave structure with various source(equivalent magnetic current) distributions such as Gaussian, uniform, cosine, cosine-squared, and Taylor distributions are given and compared with each other.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.559-565
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• 2005

As the wave impinges on and overtops the structure, a large highly aerated region is created in front of the structure and water splashs on top of the structure. The broken wave in front of the structure and associated green water on top of the structure are highly aerated containing not only a large number of bubbles but also very large sizes of bubbles. In this paper, the velocity field of the highly aerated region and the splashing water on the top is measured using a modified PIV method incorporating the traditional PIV method with the shadowgraphy technigue by correlating the ' texture ' of the bubble images. The velocity fields of a plunging wave impacting on a structure in a two-dimensional wave flume is measured. It is found that the maximum fluid particle velocity in flout of the structure during the impinging process is about 1.5 times the phase speed of the wave, while the maximum horizontal velocity above the top is less than the phase speed, It is also found that the dam breaking solution does not work well in predicting the green water velocity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.5
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• pp.485-496
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• 2020

Submerged structures such as low-crested breakwaters and artificial reefs have been commonly used for coastal protection. In this study, two-dimensional laboratory experiments were conducted in a wave flume to investigate the wave transmission phenomena of permeable type submerged structures armored by Tetrapods. Different cases of the experimental conditions were included by relative crest depth, relative freeboard, relative crest width, wave steepness and so on. An empirical formula from the experimental data was proposed to predict the wave transmission coefficients over various specifications and structural designs of the permeable type submerged structure. The proposed formula successfully predicted the wave transmission coefficients. In this study, the proposed empirical formula of the wave transmission over the submerged structure was improved from the existing formula.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.5
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• pp.497-507
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• 2020

Two-dimensional laboratory experiments were conducted in a wave flume to investigate the wave transmission phenomena of rubble-mound type submerged structures armored with Tetrapods. Different experimental conditions were included by considering relative crest depth, relative freeboard, relative crest width, wave steepness, and so on. An empirical formula was proposed to predict the wave transmission coefficients over various specifications and structural designs of the partial perforated (rubble-mound) type submerged structure from the experimental results. The proposed formula successfully predicted the wave transmission coefficients. In this study, the proposed empirical formula of the wave transmission over the rubble-mound type submerged structure was improved from the existing formula.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.125.1-125.1
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• 2012

The wave number 4 (wave-4) and wave number 3 (wave-3) longitudinal structures in the thermospheric neutral mass density are understood as tidal structures driven by diurnal eastward-propagating zonal wave number 3 (DE3) and wave number 2 (DE2) tides, respectively. However, those structures have been identified using data from limited time periods, and the consistency and recurrence of those structures have not yet been examined using long-term observation data. We examine the persistence of those structures by analyzing the neutral mass density data for the years 2001-2008 taken by the CHAllenging Minisatellite Payload (CHAMP) satellite. During years of low solar activity, the amplitude of the wave-4 structure is pronounced during August and September, and the wave-4 phase shows a consistent eastward phase progression of $90^{\circ}$ within 24 h local time in different months and years. During years of high solar activity, the wave-4 amplitude is small and does not show a distinctive annual pattern, but the tendency of the eastward phase shift at a rate of $90^{\circ}$/24 h exists. Thus the DE3 signature in the wave-4 structure is considered as a persistent feature. The wave-3 structure is a weak feature in most months and years. The amplitude and phase of the wave-3 structure do not show a notable solar cycle dependence. Among the contributing tidal modes to the wave-3 structure, the DE2 amplitude is most pronounced. This result may suggest that the DE2 signature, although it is a weak signature, is a perceivable persistent feature in the thermosphere.

• Journal of Ocean Engineering and Technology
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• v.20 no.6 s.73
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• pp.41-53
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• 2006

This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles. The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interaction between the regular wave and the structure. The results shaw the vortex generated near the structure corners, which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, which presents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.508-513
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• 2000

Micro wave seeker detects micro wave signal reflecting from a object and modifies the angle of a antenna in the direction of a reflecting signal. Gimbal structure makes a motion in the direction of an elevation axis and an azimuth axis and change the direction of a missile toward a object. As before, Micro wave seeker is a important part of a missile. Especially, gimbal structure is designed to resist a external force generated by a strong propelling power. For that reason, it is essential to analyze a vibration feature of gimbal structure. In this paper, we analyze dynamic characteristics of a gimbal structure of a micro wave seeker. And we measure frequency response functions of a gimbal structure in order to investigate the effect of a pre-load on bearing.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.649-655
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• 2006

Waves progressing into the coastal area can be amplified, swashed and overtopped by a wave overtopping control structure, and it converts the kinetic energy of the waves to the potential energy with a hydraulic head above the mean sea level by conserving the overflow in a reservoir. Then the potential energy in the form of hydraulic head can be converted to electric power utilizing extremely low-head hydraulic turbine. This study aims to find the most optimal shape of wave overtopping structure which maximizes overtopping volume rate of sea water. Laboratory experiments for the performance evaluation of wave overtopping control structures were carried out in three dimensional wave tank, and the three dimensional structure models with planar wave concentration shapes(B/b) were manufactured into five classes, which were optimized by cross sectional parameters of the structure, ie, length of ramp(l), gradient of inclined ramp($cot{\phi}$) and freeboard height of the wave overtopping structure($h_e$) proposed by Shin and Hong(2005). The wave overtopping discharges were investigated with 20 incident wave conditions and wave directions of $0^{\circ},\;15^{\circ},\;30^{\circ}$.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.505-519
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• 2016

If the seabed is exposed to high waves for a long period, the pore water pressure may be excessive, making the seabed subject to liquefaction. As the water pressure change due to wave action is transmitted to the pore water pressure of the seabed, a phase difference will occur because of the fluid resistance from water permeability. Thus, the effective stress of the seabed will be decreased. If a composite breakwater or other structure with large wave reflection is installed over the seabed, a partial standing wave field is formed, and thus larger wave loading is directly transmitted to the seabed, which considerably influences its stability. To analyze the 3-D dynamic response characteristics of the seabed around a composite breakwater, this study performed a numerical simulation by applying LES-WASS-3D to directly analyze the wave-structure-soil interaction. First, the waveform around the composite breakwater and the pore water pressure in the seabed and rubble mound were compared and verified using the results of existing experiments. In addition, the characteristics of the wave field were analyzed around the composite breakwater, where there was an opening under different incident wave conditions. To analyze the effect of the changed wave field on the 3-D dynamic response of the seabed, the correlation between the wave height distribution and pore water pressure distribution of the seabed was investigated. Finally, the numerical results for the perpendicular phase difference of the pore water pressure were aggregated to understand the characteristics of the 3-D dynamic response of the seabed around the composite breakwater in relation to the water-structure-soil interaction.

• Journal of the Korea Safety Management & Science
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• v.11 no.4
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• pp.139-145
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• 2009

The present study is to investigate the effect of wave-structure interaction such as wave oscillation. The theoretical method is based upon the linear diffraction theory obtained by the boundary element method. The water depth and incident wave period in fluid region are assumed to be constant. To investigate the wave interaction due to offshore structures, the numerical program has been developed and the simulation has been carried out by varying the conditions of distance and width of offshore structures. This study can effectively be utilized for safety assessment to various breakwater systems and layout of offshore breakwater in the ocean and coastal field. It can give information for the safety to construct offshore structure and revetment in coastal region.