• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.337-340
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• 2002

Monitoring of wave height is important primarily to reduce storm risks at sea and along the coast. Wave heights in recent years have increased 50% for the last 40 years, thus requiring intensive monitoring. Satellite altimetry offers a powerful tool for regular and extensive monitoring of the wave height. We extracted significant wave height (SWH) using several altimeter missions from 1987-1995 over the Northwest Pacific and compared with ECMWF reanalysis (ERA) products. For large wave heights > 2.5 m, the ERA wave heights are smaller than the altimetric ones, while for small wave heights the ERA wave heights are larger. Comparison in SWH between altimetric derivations and ERA model products shows the discrepancy of 0.46-0.21$\times$SWH(m).

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.632-639
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• 2011

In order to design a wave energy generate system, a 6-Degree of freedom motion analysis technique was applied to the three-Dimensional CFD analysis on two floating body and the behavior was interpreted according to the nature of the incoming wave. The waves are generated by the same type of wave in the model of tank using the piston type, but due to the shallow water that is generated from the bottom of the wave energy is attenuated by Ekman boundary layer. According to the wavelength of waves generated by the result of evaluating the behavior of floating body, it is concluded that 0.3m is the maximum amplitude of wavelength of 5m, and 0.15m is the minimum amplitude of wavelength of 1m. 1.06m is the maximum distance between the two floaters of wavelength of 6m.

• Journal of Navigation and Port Research
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• v.30 no.3 s.109
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• pp.181-187
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• 2006

In the wave spectrum distribution based on linear wave theory, the appearance of a giant wave whose wave height reaches to 30m has been considered next to almost impossible in a real sea However since more than 10 giant waves were observed in a recent investigation of global wave distribution which was carried out by the analysis of SAR imagines for three weeks, the existence of the giant waves is being recognized and it is considered the cause of many unknown marine disasters. The change of wave height distribution concerning a formation of wave train, nonlinear wave to wave interaction and so on were raised as the causes of the appearance of the giant waves, but the occurrence mechanism of the giant waves hasn't been cleared yet. In present study, we investigated appearance circumstances of the giant waves in real sea and its occurrence mechanism was analyzed based on linear and nonlinear wave focusing theories. Also, through a development of numerical model of the nonlinear $schr\"{o}dinger$ equation, the formations of the giant wave from progressive wave train were reproduced.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.591-598
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• 2015

A hydraulic characteristics in the surf zone such as wave breaking points, wave set-down, wave set-up, wave-induced currents and run-up heights are studied using the SWASH model during Typhoon NAKRI(1412) in Haeundae Beach. Incident wave conditions is obtained from one-hourly observed wave data by KHOA and irregular wave by JONSWAP spectrum is given as an open boundary condition in the model. A Wave-induced current patterns by the SWASH model is compared with the observed currents and sediment flux patterns in that areas, the calculated maximum wave run-up heights in the model is compared with the video monitoring data, the empirical formula by Stockdon et al. and Mase. A dominant longshore currents toward the east of the beach appears due to the effect of incident wave direction and the geographical features and some rip currents occurs at the central part of the beach. The maximum wave run-up height(1.15 m) by the SWASH model shows a similar pattern with the video monitoring data(1.26 m) and the magnitude shows a similar result(1.33m) by Stockdon et al.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.585-587
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• 2006

Generally, LPF(low pass filter) circuits are used for converting square wave to average value, but these are not used necessary for average value of square wave in real time because of time constant of LPF. This paper deals with acquiring method for average value of square wave in real tine in case of frequency of output voltage is fixed, waveform of output voltage is square wave and duty of output voltage is varied like as 1 quadrant or 4 quadrant chopper.

• Journal of Ocean Engineering and Technology
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• v.37 no.6
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• pp.238-246
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• 2023

This paper proposes an effective inertia coefficient (EIC) in the Morison equation for better wave-force calculations. The OC4 semi-submersible floating offshore wind turbine (FOWT) platform was considered to test the feasibility. Large diffraction at large Keulegan-Carpenter (KC) numbers and the interaction between columns can result in errors in estimating the wave force using the Morison equation with a theoretical inertia coefficient, which can be corrected by the EIC as a function of the wave period and direction. The horizontal and vertical wave forces were calculated using the Morison equation and potential theory at each column, wave period, and wave direction. The EICs of each column were then obtained, resulting in a minimal difference between the Morison inertia force and the wave excitation force by the potential theory. The EICs, wave forces, phase angles, and dynamic motions were compared to confirm the feasibility of an EIC concept under regular and random waves.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.145-150
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• 2004

Using the DGPS of high precision take in a bouy, the wave-induced currents were observed by Lagrange method at Bonggile beach of the East Sea. At June, the northward wave-induced currents were dominated by the SSW waves. And the southward flaws were appeared at September and November. When 0.2-0.4m wave heights attacked the beach, the mean speed of the wave-induced currents was 0.15-0.3m/s at June and September, when the 1.0-1.6m wave heights incidented at November, that was about 0.3-0.6m/s. On the other hand, the observed results were compared with the simulated results which were solved by the 2-D model, WICU-DIVAST. It was showed the reasonable agreements.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.42 no.2
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• pp.23-28
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• 2005

This study was to suggest the propagation path loss and predictive model of propagation path analysis in order to apply the frequency in the millimeter-wave band to the real time inter-vehicle communication system. This study was to suppose the case of inter-vehicle communication on the one-way two-lanes road in the big cites with a lot of traffic jams in order to analyze the effect by the reflected wave of multipath. As a simulation of suggested model, it found out that the propagation path by the reflected wave was about 0.1[m]$\sim$5.1[m] longer than the one by the direct wave during the transmission of 100[m] wave direct path. Also, as a result of comparing the propagation path loss, the loss would be about -0.8[dB]$\sim$-4.2[dB] larger in case of wall reflection and -0.8[dB]$\sim$-1[dB] vehicle reflection. From the result above, this researcher found out that the path loss of reflected wave produced by the walls was about -3.2[dB] larger than the path loss produced by the adjacent vehicles.

• Proceedings of the IEEK Conference
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• 2004.06b
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• pp.335-338
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• 2004

We suggest Q-band MEMS MIMIC (Millimeter wave Monolithic Integrated Circuit) HEMT Oscillator using DAML (Dielectric-supported Airgapped Mcrostrip Line) structure. We elevated the signal lines from the substrate using dielectric post, in order to reduce the substrate dielectric loss and obtain low losses at millimeter-wave frequency. These DAML are composed with heist of $10\;{\mu}m$ and post size with $20\;{\mu}m\;{\times}\;20\;{\mu}m$. The MEMS oscillator was successfully integrated by the process of $0.1\;{\mu}m$ GaAs PHEMTs, CPW transmission line and DAML. The phase noise characteristic of the MEMS oscillator was improved more than 7.5 dBc/Hz at a 1 MHz offset frequency than that of the CPW oscillator And the high output power of 7.5 dBm was measured at 34.4 GHz.

• The Journal of the Acoustical Society of Korea
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• v.26 no.1E
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• pp.33-38
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• 2007

Compressional wave velocity and shear wave velocity were measured for gassy sediments collected from Jinhae Bay, Korea. To distinguish inhomogeneities of gassy sediments, Computed Tomography (CT) was carried out for gassy sediment using CT Scanner. The cored sediments are composed of homogeneous and soft mud (greater than $8{\Phi}$ in mean grain size) containing clay content more than 50%. In depth interval of gassy sediments, compressional wave velocity is significantly decreased from 1480m/s to 1360m/s, indicating that the gas greatly affects compressional wave velocity due to a gas and/or degassing cracks. Shear wave velocity shows a slight increasing pattern from ${\sim}55\;m/s$ in the upper part of the core to ${\sim}58\;m/s$ at 320 cm depth, and then decreases to ${\sim}54\;m/s$ in the lower part of the core containing a small amount of gas. But shear wave velocity in the gassy sediments is slightly greater than that of non-gassy sediments in the upper part of the core. Thus, the Vp/Vs ratio is decreased (from 30 to 25) in gas charged zone. The Vp/Vs ratio is well correlated with shear wave velocity, but no correlation with compressional wave velocity. This suggests that low concentrations of gas have little affects on shear wave velocity. By CT images, the gas in the sediments is mostly concentrated around inner edge of core liner due to a long duration after sediment collection.