• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.12-16
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• 2009

In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.375-385
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• 2016

Given the rapid progress made in understanding the dynamics of an offshore floating body in an ocean environment, the present study aimed to simulate ocean waves in a small-sized wave flume and to observe the motion of a cylindrical floating body placed in an offshore environment. To generate regular ocean waves in a wave flume, we combined a wave generator and a wave absorber. In addition, to precisely visualise the oscillation of the body, a set of light-emitting diode illuminators and a high-speed charge-coupled device camera were installed in the flume. This study also focuses on the spectral analysis of the movement of the floating body. The wave generator and absorbers worked well to simulate stable regular waves. In addition, the simulated waves agreed well with the plane waves predicted by shallow-water theory. As the period of the oncoming waves changed, the movement of the floating body was substantially different when tethered to a tension-leg mooring cable. In particular, when connected to the tension-leg mooring cable, the natural frequency of the floating body appeared suddenly at 0.391 Hz as the wave period increased.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.78.2-78.2
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• 2021

We present high resolution spectroscopic observations of transverse magnetohydrodynamic (MHD) waves in mottles located near the solar disk center. Different from previous studies that used transversal displacements of the mottles in the imaging data, we investigated the line-of-sight (LOS) velocity oscillations of the mottles in the spectral data. The observations were carried out by using the Fast Imaging Solar Spectrograph of the 1.6 meter Goode Solar Telescope of Big Bear Solar Observatory. Utilizing the spectral data of the Hα and Ca II 8542 Å lines, we measure the LOS velocity of a quiet region including the mottles and rosettes that correspond to the footpoints of the mottles. Our major findings are as follows: (1) Alfvénic waves are pervasive in the mottles. (2) The dominant period of the waves is 2 to 4 minutes. (3) From the time-distance maps of the three-minute filtered LOS velocity constructed along the mottles, it is revealed that the transverse waves in the mottles are closely related to the longitudinal waves in the rosettes. Our findings support the notion that Alfvénic waves can be generated by mode conversion of the slow magnetoacoustic waves as was shown in sunspot regions by Chae et al. (2021).

• Journal of Ocean Engineering and Technology
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• v.33 no.6
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• pp.573-580
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• 2019

A submerged breakwater is a coastal structure built under water with excellent landscape. The depth of the crest of the breakwater should be maintained at more than a certain level in order for the submerged breakwater to control waves properly. This means that the effect of blocking waves deceases sharply at high tide in coastal areas with large tidal differences. In this study, we proposed a Tide-Adapting Submerged Breakwater (TA-SB) to overcome this problem, and then we conducted hydraulic model experiments to evaluate the performance of the TA-SB for controlling waves. The experimental results showed that the tapered wings attached to the crest of the TA-SB helped induce forced breaking waves. In particular, they were very effective in blocking waves and attenuating wave energy at high tide. In addition, the wave control performance of the proposed TA-SB was far superior to the Tide-Adapting Low-Crested Structure (TA-LCS) of the previous study.

• Fisheries and Aquatic Sciences
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• v.11 no.1
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• pp.41-49
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• 2008

Internal waves and internal tides occur frequently along the eastern coast of Korea. During the spring-tide period in April 2003, the East Korean Warm Current (EKWC) flowed near the Korean East Coast Farming Forecast System (KECFFS; a moored oceanographic measurement system), creating a strong thermocline at the intermediate layer. Weakened stratification and well-mixed water appeared frequently around the KECFFS, with duration of approximately 1 day. The results suggest the following scenario. Baroclinic motion related to the internal tide generated high frequency internal waves around the thermocline. The breaking of those waves then created turbulence around the thermocline. After well-mixed water appeared, a current component with perpendicular direction to the EKWC appeared within the inertial period. The change in stratification around the KECFFS locally broke the geostrophic balance as a transient state. This local vertical mixing formed an ageostrophic current within the inertial period.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.807-814
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• 2004

Land seismic reflection survey has been increasingly demanded in various civil engineering works because of its own ability to delineate layers, water table, to detect cavities or fracture zones, to estimate seismic velocities of each layer. However, our shallow subsurface structures are very complex. The relatively thin layer(mostly soil) to the wavelength directly followed by a basic rock with high impedance used to generate complicated surface waves, kind of channel waves with high amplitude that is dominate in entire seismograms and hence the useful reflection events will be almost hopelessly immersed in the undesired surface waves. Thus, it would seem that the use of traditional seismic survey could not be likely to provide in itself a satisfactory information about our exploration targets. This paper hence introduces an efficient measuring strategy illustrating a properly controlled arrangement of the vertical single force sources commonly used, yielding a very sharply elongated form of P-energy with a minimum of S radiation energy, what we call, P-beam source. Abundant experiments of physical modeling showed that in that way the surface waves could be enormously reduced and the reflection events would be additive and thus reinforced. Examples of field data are also illustrated. The contribution of P-beam source will be great in civil engineering area as well as in general geological exploration area.

• The Mathematical Education
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• v.55 no.3
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• pp.383-396
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• 2016

This study investigated highschool students' brain waves on functional tasks such as a transition(F task) from equation to graph and the other transition(G task) vice versa. A total of 39 students participated in the study who attended a high school located in Gyunggi province. These students were divided into two groups, HMA and LMA by MASS test revised by Ko, & Yi (2012). The functional tasks for the stroop task to measure EEG were provided from a previous study, Seok(2015). The results indicated two groups on G tasks showed deeper and wider brain waves which demonstrated G tasks were more difficult than F tasks. However, HMA group had an effect of the non-psychological program which had given more chances on G tasks rather than F tasks within Students' Zone of Proximal Development. Also, HMA group's brain waves had more ranges in amplitude and width of waves. These results imply that the characteristics of students' brain waves with math anxiety are consistent to the previous studies.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.9
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• pp.648-655
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• 1999

In this study, a relationship between DC discharge and the radiated electromagnetic waves is investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The characteristics of frequency spectrum ofthe radiated electromagnetic waves was measured at the atmospheric pressure in Liquid Nitrogen $(LN_2)$ during partial discharges in nonuniform and uniform electric field depend on positive DC power. From this experiment results, it was confirmed that when partial discharge was produced in Liquid Nitrogen and Air, the signal of partial discharge was detected by this experiment and the analysis method. It is considered thatthese results obtained from this investigation may be used as fundamental data for diagnosis and prediction of insulation on the equipments ultra-high voltage, superconducting and cryogenic applications.

• Journal of the Korean Institute of Navigation
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• v.1 no.1
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• pp.45-62
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• 1977

The advanced researches of the ship's motion in the seaway can predict the heaving, pitching and slamming of ship's motion. The researches as of today are that of displacement type such as a small typical fishing boat and U, UV and V bow ship forms under low speed. In recent day, the study of behaviours of high speed planning boat in the regular waves has been carried out by Bessho [5]. The calculation about behaviours of a high speed vessel in the longitudinal regular waves is calculated by Ordinary Strip Method in this paper. The data of the results were discussed and compared with Bessho's results. The conclusions deduced from this study are as follow, (1) The acceleration of motion calculated by the O.S.M. is similar with Bessho's data for the Fn 0.5 (2) The amplitudes of the behaviours of motions take peak at 1.0<λ/L<1.4.

• Journal of the Korean Institute of Navigation
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• v.3 no.2
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• pp.1-19
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• 1979

The advanced researches of the ship's motion in the seaway can predict the heaving, pitching and slamming of ship's motion. The researches as of today are that of displacement type such as a small typical fishing boat and U, UV and V bow ship forms under low speed. In recent day, the study of behaviours of high speed planning boat in the regular waves has been carried out by Bessho [5]. The calculation about behaviours of a high speed vessel in the longitudinal regular waves is calculated by Ordinary Strip Method in this paper. The data of the results were discussed and compared with Bessho's results. The conclusions deduced from this study are as follow, (1) The acceleration of motion calculated by the O.S.M. is similar with Bessho's data for the Fn 0.5 (2) The amplitudes of the behaviours of motions take peak at 1.0<λ/L<1.4.