• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.1
• /
• pp.34-44
• /
• 1992

A numerical model using Hybrid Element Method(HEM) is presented for the prediction of wave agitations in a harbor which are induced by the intrusion and transformation of incident short-period waves. A linear mild-slope equation including bottom friction is used as the governing equation and a partial absorbing boundary condition is used on solid boundaries. Functional derived in the present paper is based on the Chen and Mei(1974)'s concept which uses finite element net in the inner region and analytical solution of Helmholtz equation in the outer region. Final simultaneous equations are solved using the Gaussian Elimination Method. The model appears to be reasonably good from the comparison of numerical calculation with hydraulic experimental results of short-wave diffraction through a breakwater gap(Pos and Kilner, 1987). The problem of requring large computational memory could be overcome using 8-noded isoparametric elements.

• Journal of Korea Water Resources Association
• /
• v.30 no.3
• /
• pp.225-233
• /
• 1997

The nonlinear effects on the statistical properties of wave groups in terms of the average nomber of waves in a group and the mean number of waves in a high run is studied in this paper utilizing the complex envelope and total phase function, random variable transformation technique and perturbation method. It tures out that the phase distribution is modified significantly by nonlinearities and it show systematic excess of values near the mean phase and the corresponding symmetrical deficiency on both sides away from the mean. for the case of threshold crossing rate, it turns out that threshold crossing rate reaches its maxima just below the mean water level rather than zero and considerable amount of probability mass is shifted toward the larger values of water surface elevation as nonlinearity is getting profound. Furthermore, the mean waves in a high run associated with nonlinear wave are shown to have larger values than the linear counterpart. Similar trend can also be found in the average number of waves in a group.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.6
• /
• pp.350-360
• /
• 2016

In order to investigate characteristics of waves and currents varying in space in the Haeundae coast in winter, numerical simulations by using a 2-D spectral wave model(SWAN) and 2-DH hydrodynamic model(Delft3D) were carried out in this study. The results of numerical simulations were validated with the field data collected at several different locations in the study area in February, 2014. From the numerical simulations, it was found that waves and currents were significantly influenced in terms of direction and magnitude by bottom topography characterized by straggling rock crops covered with sea grasses. The coupling of SWAN and Delft3D models also revealed that alongshore currents directing from the east to the west were developed in the nearshore, due to the influence of larger waves with the main incident direction from the east.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.21 no.2
• /
• pp.123-130
• /
• 1985

This paper was conducted for the purpose of evaluating the accuracy of the observed time difference in Loran-C when the ground wave propagated on the surface included both land sea. The time difference of X and Y station in North East Pacific Chain GRI 5970 was measured at 25 points in Cheju areas. The results obtained are as follows: (1) The errors of time difference for M-X pair are increased when the Loran-C wave propagates above 500m heights of Hanla mountain on propagation path between the observed point and master or X, Y slave station. (2) The errors of time difference for M-X pair are able to decrease by way of correction for the propagation velocity and the geodetic datum, but errors of the time difference for M-Y pair very irregularly because irregular terrain include in propagation path from X station and propagation path from Y station is twice longer than X station. (3) It is confirmed that accuracy of Loran-C fix can elevate by the way of all correction for a geodetic datum transformation, the propagation velocity with refractive index of radio wave and the propagation velocity over land.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.8
• /
• pp.967-975
• /
• 2012

This paper presents a method to measure reflection coefficients of microwave devices or antennas based on time domain analysis with sampling oscilloscopes. The reflection coefficients were extracted by the Fourier transformation of echo pulses from devices with respect to the 20 GHz incident pulse signals. The three-error terms, which are commonly used for the correction of a microwave network, were determined using a 3.5 mm calibration kit. In addition, a modified error-correction model associated with a directional coupler for reflection coefficient measurements is introduced. The results were compared with those of measured with a commercial vector network analyzer.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.10 no.1
• /
• pp.1-9
• /
• 1998

Among the phenomena of water-wave transformation, the wave diffraction is prominent for waves insidc the harbor. It is important to study how accurately the diffraction can be resolved by the numerical model. Three parabolic mild-slope equations, i.e., simple, wide-ang1e, three-parameter parabolic equations, are compared in view of the diffraction of water-waves around a semi-infinite breakwater. To avoid reflections at lateral boundaries, we apply the perfect boundary condition of Dalrymple and Martin (1992) in case of simple parabolic equation. The numerical results for the case of a semi-infinite breakwater are compared with the analytical solution of Penney and Price (1952). All the results are very accurate when waves attack the breakwater normally. When waves attack the breakwater obliquely, however, the simple parabolic equation yields the worst solution and the three-parameter parabolic equation yields the most accurate solution.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.23 no.3
• /
• pp.248-257
• /
• 2011

In the present study, we proposed a new numerical wave tank model to analyze the vertical tension-leg circular floating bodies, using a 2-D Navier-Stokes solver. An IBM(Immersed Boundary Method) capable of handling interactions between waves and moving structures with complex geometry on a standard regular Cartesian grid system is coupled to the VOF(Volume of Fluid) method for tracking the free surface. Present numerical results for the motions of the floating body were compared with existing experimental data as well as numerical results based on FAVOR(Fractional Area Volume Obstacle Representation) algorithm. For detailed examinations of the present model, the additional hydraulic experiments for floating motions and free surface transformations were conducted. Further, the versatility of the proposed numerical model was verified via the numerical and physical experiments for the general rectangular floating bodies. Numerical results were compared with experiments and good agreement was archived.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.249-252
• /
• 2008

The solutions are expressed in terms of a double integral transformation over wavenumber and frequency. The complete solution is considered in such a full wave theory approach. This method can handle a larger number of plane layers. Therefore, the result of FK method is very similar to real data. Using the models that were modified in velocity and Q value with depth by iterative process from a model (Kang and Park, 2006) and considered as one of the best models in Korean Peninsula, the synthetic data are simulated for explosions and earthquakes of North Korea. This study notes that the wave shape of the synthetic data is very dependent on Q value, velocities, and thickness of sedimentary layers. Comparing between the real and the synthetic, fitting well in arrival time of first arrival and wave shape causes us to arrive at an indication that the model is very close representation of upper crustal structure and simulations are well done in amplitude fitting and in identification of phases of local and regional waves.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.6
• /
• pp.298-304
• /
• 2006

This paper proposes a ray-based forward modeling scheme which is suitable for the shallow water acoustic wave propagation simulations. The proposed model comprises of ray tracings for the layered media of which sound speed profiles are interpolated linearly. considerations of plane and spherical wave reflection coefficients. and calculations of the phases and the amplitudes of eigen rays. The main characteristic of the scheme is fast simulation time due to direct calculation of the broad-band time signals in the time-domain, i.e. without transformation of the frequency-domain solutions to the time si 밍 131s. Finally, we applied the model to 4-types of test environments and compared the resulting signals with those of ORCA and Ram in order to validate the proposed model.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
• /
• v.12 no.1
• /
• pp.25-50
• /
• 2001

Using Fourier transformation and wavelet analysis, we compared the auditory event-related potentials of the patients with attention deficit-hyperactivity disorders(abbr. ADHD, 13 boys) and normal control children(8 boys). Amplitudes of the event-related potentials which were calculated via Fourier transformation were compared between the groups and between conditions(non-target versus target) in each group. To the non-target stimuli, the patients with ADHD showed significantly greater amplitudes across almost all of the electrode sites and frequencies. To the target stimuli, the incidents which ADHD patients showed much higher amplitudes than normal controls significantly decreased, while those of the reverse results increased significantly. These results were consistent with the comparison results about negative difference wave(abbr. Nd wave) using Fourier transformation. In summary, it was proved that non-target stimulus which should be ignored elicited more robust electrical response from the patients with ADHD than normal children, but the target stimulus which reguired active processing did much less electrical activity in the patients. For the patients, they showed much inhibited electrical response to the target stimuli in some electrodes and frequency ranges. Normal children were more strongly stimulated by the target stimuli in almost all electrodes and frequency ranges than the patients, but less in prefrontal leads and frontal leads. Wavelet analysis results proved that early responses(0-300msec) to the nontarget stimuli of the patients were significantly greater than the normal controls in prefrontal, anterior frontal, some parts of temporal, and occipital lobes and that late response(300-370msec) were significantly lesser than normal children in parietal and central electrodes. Target stimuli elicited significantly higher electrical activity in both group than non-target stimuli did. Prefrontal and frontal lobes showed stronger responses in the patients than normal children irrespective of stimulus condition, but parietal and temporal lobes did higher activities in normal children than the patients only to the target stimuli. In conclusion, the patients with ADHD showed much greater responses to the stimuli which should be ignored, but failed to activated the necessary processes to the target stimuli. Also, we found that the frequency-dimension analysis and wavelet analysis were useful for the signal processing such as event related potentials.