• The Journal of the Acoustical Society of Korea
• /
• v.25 no.1
• /
• pp.1-6
• /
• 2006

The Possibility of using acoustic impedance as an input Parameter for computation of underwater acoustic field in shallow waters was investigated. Analysis of the acoustic reflection from the ocean bottom with shear wave effect showed that acoustic impedances below the critical grazing angle have nearly angle-independent property and could be approximated with a single value of near-grazing impedance $Z_0$. Computations of the Propagation loss based on the concept of 'effective depth' indicate that near-grazing bottom acoustic impedances could be used as an input parameter for simulation of the acoustic fields in shallow waters.

• Tribology and Lubricants
• /
• v.31 no.5
• /
• pp.213-220
• /
• 2015

This study evaluates the effect of grooves on the stem part of a plunger on the lubrication characteristics of a fuel injection pump (FIP) by using hydrodynamic lubrication analysis. The current study uses the two-dimensional Reynolds equation to evaluate the changes in lubrication characteristics with variations in clearance, viscosity, and grooves for a laminar, incompressible, and unsteady state flow. This study investigates the lubrication characteristics by comparing the dimensionless minimum film thickness or the film parameter, which is the ratio of the minimum film thickness to surface roughness. The analysis method for the groove section differs depending on the depth of the groove. For instance, in the case of a shallow groove, the film thickness equation considers the depth of the groove, while in the case of a deep grove, it considers the flow continuity. The lubrication characteristics of the FIP are more sensitive to changes in the groove width than to changes in other design variables. Moreover, the application of a groove is more effective under low viscosity conditions. The smaller the distance from the edge of the stem part to the first groove in the case of shallow grooves, the better are the lubrication characteristics of the FIP. In contrast, in the case of deep grooves, the lubrication characteristics of the FIP improve as the distance increases. The application of shallow grooves is more effective for improving the lubrication characteristics than the application of deep grooves.

• Journal of Forest and Environmental Science
• /
• v.29 no.4
• /
• pp.314-323
• /
• 2013

To examine surface erosion and sediment export patterns on a hillslope, which was devastated by a shallow landslide and which was slowly revegetating by natural plant species, we surveyed variations in surface erosion depth on the upper-, middle- and lower-section of the hillslope, and subsequent sediment yield from the whole hillslope. The result showed that, with the passing of year, surface erosion on the devastated hillslope was regulated by higher rainfall intensity due to the supply-limitation of exportable sediment, and its variation range decreased. In addition, surface erosion on the upper-section with steep slope was regulated by higher rainfall intensity, which might result in raindrop erosion, compared to it on the lower-section with relatively gentle slope. Besides, the sediment yield from the devastated hillslope had nonlinear relationship with surface erosion depth on the hillslope because sediments on the hillslope are exported downwards while repeating their cycle of transport and redistribution. Our findings suggest the establishment of management strategy to prevent sediment-related disasters occurred during torrential rainfall events, which was based on the continuous field investigation on the hillslope devastated by landslides.

• Journal of the Korea Computer Graphics Society
• /
• v.25 no.5
• /
• pp.21-30
• /
• 2019

We propose a physical simulation method based on the shallow water equation(SWE) to represent water surface effectively. In this paper, the water which can be represented has a much larger width compared to the depth does not have a large vertical direction flow. In order to calculate the water flow efficiently, we start with the shallow water equation as the governing equation, which is a simplified version of the Navier-Stokes equation. In order to numerically calculate the advection term of the SWE, we introduce a new conservtive USCIP(CUSCIP) method which improves the Constrained Interpolation Profile (CIP) method to preserve the physical quantity while increasing the numerical accuracy. The proposed method is based on Kim et. al.'s Unsplit Semi-lagrangian CIP[9], and calculates advection term with additional constraints on term that consider integral values. The experimental results show that the CUSCIP method is robust to the loss of physical quantity due to numerical dissipation, which improves wave detail and persistence.

• Journal of Korean Society of Water and Wastewater
• /
• v.25 no.5
• /
• pp.627-634
• /
• 2011

In the present study, the flow behaviors of square jets surface discharged and submerged discharged into shallow water were each simulated using computational fluid dynamics, and the results were compared. As for the verification of the models, the results of the hydraulic experiment conducted by Sankar, et al. (2009) were used. According to the results of the verification, the present application of computational fluid dynamics to the flow analysis of square jets discharged into shallow water was valid. As for the wall jet, which is one form of submerged discharges, at the bottom wall boundary, the peak velocity of the jet rapidly moved from the center of the jet to the bottom wall boundary due to the restriction of jet entrainment and the no-slip condition of the bottom wall boundary, and, as for the surface discharge, because jet entrainment is limited on the free water surface, the peak velocity of the jet moved from the center of the jet to the free water surface. This is because jet entrainment is restricted at the bottom wall boundary and the surface so that the momentum of the central core of the jet is preserved for considerable time at the bottom wall boundary and the surface. In addition, due to the effect of the bottom wall boundary and the free water surface, the jet discharged into shallow water had a smaller velocity diminution rate near the discharge outlet than did the free jet; at a location where it was so distant from the discharge outlet that the vertical profile of the velocity was nearly equal (b/x =20~30), moreover, it had a far smaller velocity diminution rate than did the free jet due to the effect of the finite depth.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.31 no.2
• /
• pp.127-141
• /
• 1995

The distribution of water mass in Deukryang Bay was investigated using observational data obtained on July 12 (spring tide) and 19 (neap tide) in 1994. In characteristics of water mass at the bay the area is divided into three ones by a vertical attenuation coefficient k and a stratification parameter, log sub (10) (H/U super (3)), was H is depth, and U mean velocity in the bay. The contour of k=0.6 has a similar distribution to the isobath of 10m depth in spring tide, and of 5m depth in neap tide, respectively. This indicates that the water mass in the area between the isobath of 5m and 10m depth is changed by tidal periods. The stratification parameter corresponding to k=0.6 was 2.1~2.2. In the shallow water of 5m depth the characteristics of water mass was distributed in temperature of 25.5~31.$0^{\circ}C$ and salinity of 32.8~33.8PSU(Practical Salinity Unit), the temperature was high and the salinity distributed widely. In the deep water of 10m depth it was the temperature of 22.0~29.5$^{\circ}C$ and the salinity of 33.0~33.6PSU, the temperature was low and the salinity distributed narrowly. In the middle depth water of 5m to 10m depth, the temperature of 22.0~30.$0^{\circ}C$ and the salinity of 32.8~33.5PSU, its values showed the middle between the values of the deep area and the values of the shallow area.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.12 no.4
• /
• pp.328-336
• /
• 2007

A piston core (587 cm long) was recovered from the upper slope of a seamount in the Korea Plateau. Three episodes of sedimentation were identified based on sedimentary facies, grain size distribution, carbonate constituents and initial $^{87}Sr/^{86}Sr$ ratio of carbonates. The lower part of the core, Unit I-a (core depth $465{\sim}587cm$) is composed of shallow marine carbonate sediments the deposited by storm surges, and is about $13{\sim}15Ma$ (Middle Miocene) based on $^{87}Sr/^{86}Sr$ initial ratio. This suggests that the depositional environment was relatively shallow enough to be influenced by storm activities. Unit I-b (core depth $431{\sim}465cm$) is mostly composed of turbidites, and Sr isotope ages of bivalves and planktonic formaminifera are about $11{\sim}14\;and\;6{\sim}13Ma$, respectively. This indicates that the Korea Plateau maintained shallow water condition until 11 Ma, and began to subside since then. However, planktonic foraminifera were deposited after 11 Ma and redeposited as turbidites as a mixture of planktonic foraminifera and older shallow marine carbonates about 6 Ma ago. Unit II (core depth $0{\sim}431cm$) is composed of pelagic sediments, and the Sr isotope age is younger than 1 Ma, thus the time gap is about 5 Ma at the unconformity. About 1 Ma ago, the Korea Plateau subsided down to a water depth of about 600 m. The sampling locality was intermittently influenced by debris flows and/or turbidity currents along the slope, resulting the deposition of re-transported coarse shallow marine and volcaniclastic sediments.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.23 no.6
• /
• pp.613-619
• /
• 2017

Recently, the size of container ships has been progressively increasing, and much attention is required for safe navigation in shallow areas such as coastal waters and ports due to increases in draft. It is necessary to understand the characteristics of ship motion not only in still waters but also with waves. Especially in shallow regions, squat due to the vertical movement of the ship can be an important evaluation factor for the safe navigation, and wave drift force acting in the horizontal direction can have a great influence on the maneuverability of a ship. In this study, a numerical simulation using computational fluid dynamics has been performed for the wave exciting force acting in the vertical direction and the wave drift force acting in the horizontal direction for a very large container vessel sailing in shallow zone. As a result, it was found that total resistance in still waters greatly increased in shallow water. Wave drift force was shown to decrease given longer wavelengths regardless of water depth. It was observed that the wave exciting force in shallow water was considerably larger than at other water depths. As wave height against the central part of the ship lowered, the aft side rose.

• Geophysics and Geophysical Exploration
• /
• v.8 no.1
• /
• pp.26-33
• /
• 2005

Inversion of multi-mode surface-wave phase velocity for shallow engineering site investigation has received much attention in recent years. A sensitivity analysis and inversion of both synthetic and field data demonstrates the greater effectiveness of this method over employing the fundamental mode alone. Perturbation of thickness and shear-wave velocity parameters in multi-modal Rayleigh wave phase velocities revealed that the sensitivities of higher modes: (a) concentrate in different frequency bands, and (b) are greater than the fundamental mode for deeper parameters. These observations suggest that multi-mode phase velocity inversion can provide better parameter discrimination and imaging of deep structure, especially with a velocity reversal, than can inversion of fundamental mode data alone. An inversion of the theoretical phase velocities in a model with a low velocity layer at 20 m depth can only image the soft layer when the first higher mode is incorporated. This is especially important when the lowest measurable frequency is only 6 Hz. Field tests were conducted at sites surveyed by borehole and PS logging. At the first site, an array microtremor survey, often used for deep geological surveying in Japan, was used to survey the soil down to 35 m depth. At the second site, linear multichannel spreads with a sledgehammer source were recorded, for an investigation down to 12 m depth. The f-k power spectrum method was applied for dispersion analysis, and velocities up to the second higher mode were observed in each test. The multi-mode inversion results agree well with PS logs, but models estimated from the fundamental mode alone show f large underestimation of the depth to shallow soft layers below artificial fill.

• Structural Engineering and Mechanics
• /
• v.47 no.4
• /
• pp.559-573
• /
• 2013

Geometrically non-linear axisymmetric bending of a shallow spherical shell with a clamped or a simply supported edge under axisymmetric load was investigated numerically. The partial load was introduced by the Heaviside step function, and the solution was obtained by the finite difference and the Newton-Raphson methods. The thickness of the shell was considered to be uniform and the material was assumed to be homogeneous and isotropic. Sensitivity analysis was made for three geometrical parameters. The accuracy of the algorithm was checked by comparing the central deflection, the radial membrane stress at the edge, or the transverse shear force with the solutions of plates and shells in the literature and good agreement was obtained. The main findings of the study can be outlined as follows: (i) If the shell is fully loaded the central deflection of a clamped shell is larger than that of a simply supported shell provided that the shell is not very shallow, (ii) if the shell is partially loaded the central deflection of the shell is sensitive to the parameters of thickness, depth, and partial loading but the influence of the boundary conditions is negligible.