• Journal of Ocean Engineering and Technology
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• v.36 no.1
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• pp.11-20
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• 2022

Generally, tsunamis are generated by the rapid crustal movements of the ocean floor. Other factors of tsunami generation include landslides on coastal and ocean floor slopes, glacier collapses, and meteorite collisions. In this study, two numerical analyses were conducted to examine the formation, propagation, and deformation properties of landslide tsunamis. First, LS-DYNA was adopted to simulate the formation and propagation processes of tsunamis generated by dropping rigid bodies. The generated tsunamis had smaller wave heights and wider waveforms during their propagation, and their waveforms and flow velocities resembled those of theoretical solitary waves after a certain distance. Second, after the formation of the landslide tsunami, a tsunami based on the solitary wave approximation theory was generated in a numerical wave tank (NWT) with a computational domain that considered the stability/steady phase. The comparison of two numerical analysis results over a certain distance indicated that the waveform and flow velocity were approximately equal, and the maximum wave pressures acting on the upright wall also exhibited similar distributions. Therefore, an effective numerical model such as LS-DYNA was necessary to analyze the formation and initial deformations of the landslide tsunami, while an NWT with the wave generation method based on the solitary wave approximation theory was sufficient above a certain distance.

• Earthquakes and Structures
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• v.24 no.1
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• pp.65-79
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• 2023

A simplified analytical solution for seismic response of tunnel cross section in horizontally layered ground subjected to oblique incidence of SH wave is deduced in this paper. The proposed analytical solution consists of two main steps: free-field response in layered field and tunnel response. The free field responses of the layered ground are obtained by one-dimensional finite element method in time domain. The tunnel lining is treated as a thick-wall cylinder to calculate the tunnel response, which subject to free field stress. The analytical solutions are verified by comparing with the dynamic numerical results of two-dimensional ground-lining interaction analysis under earthquake in some common situations, which have a good agreement. Then, the appropriate range of the proposed analytical solution is analyzed, considering the height of the layered ground, the wavelength and incident angle of SH wave. Finally, by using the analytical solutions, the effects of the ground material, burial depth of the tunnel, and lining thickness and the slippage effect at the ground-lining interface on the seismic response of tunnels are investigated. The proposed solution could serve as a useful tool for seismic analysis and design of tunnels in layered ground.

• Economic and Environmental Geology
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• v.34 no.5
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• pp.447-460
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• 2001

The geothermal waters from the Busan area belong to Na-CI type and are characterized by much higher EC (921 ~6,520${\mu}$S/cm) and TDS (608-3,390 mg/L) than other geothermal waters in Korea. The concentration of majorions shows a weakly positive relationship with temperature except for Mg ion. The concentrations of the major cat ions have the order of Na>Ca>K>Mg. Ca ion is enriched and Mg ion is depleted compared with seawater. All Br concentrations of geothermal water are lower than those of seawater, showing a positive relationship with temperature. Generally geochemical characteristics of geothermal waters of the Busan area indicate that these waters have relatively increased Ca and Sr contents and depleted Mg, Na and K contents caused by seawater interaction with wall rock at depth during deep circulation of seawater. Base on the relationship between major ions and temperature, saline geothermal waters are diluted and are cooled by mixing of groundwaters during ascent. Isotope study and reaction path modeling of the overall geochemical system are required in order to better quantify the evolution and origin of geothermal waters in the Busan area.

• Economic and Environmental Geology
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• v.55 no.5
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• pp.465-475
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• 2022

The seafloor massive sulfide deposits are important mineral resources for base and precious metals, and their ore genesis and metal contents are mainly controlled by wall-rock leaching process and/or magmatic volatile input from the underlying magma chamber. However, the contribution of two different metal sources to the seafloor hydrothermal mineralization significantly varies in diverse geological settings and thus still remains controversial. In this review, mineralogical and geochemical characteristics of SMS deposits from mid-ocean ridges (MORs) and volcanic arcs were investigated to understand the contribution from different metal sources and to suggest future challenges that need to be addressed. As a result, the genetic occurrences of enargite and cubanite, galena and barite indicate the effects of magmatic input and water-rock interaction, respectively. Also, the distributional behaviors of Co, As, and Hg in pyrite and FeS content of sphalerite could be useful empirical indicators to discriminate the significant roles of different metal sources between MOR and Arc settings. To date, as most studies have focused on sulfide samples recovered from the seabed, further studies on magmatic sulfides and sulfate minerals are required to fully understand the genetic history of SMS deposits.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.91-93
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• 2003

A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.309-316
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• 2015

Numerical analysis and experimental verification of a thermal liquid mass flow meter (LMFM) were performed. The configuration of the LMFM was the same as a gas mass flow meter (GMFM), but the opposite results in temperature difference between upstream and downstream thermistors occurred. In the case of the gas, the convection depending on the flow of thermal mass was small and comparable to the conduction through the sensor tube wall. The temperature difference was proportional to the mass flow rate due to their interaction. For the liquid flow, the convection overwhelmed the wall conduction because of the large flow of thermal mass caused by high density. The temperature difference in this case was inversely proportional to the mass flow rate. The tube diameter and heater wiring width are important design parameters, and the optimized sensor can be used to measure and control the infinitesimal liquid flow rate.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.4
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• pp.282-289
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• 2020

Purpose: The aim of this in vitro study was to evaluate the accuracy of three different intraoral scanners (IOSs) on digital impressions of different types of endocrown cavity preparations. Materials and methods: Two human mandibular molar teeth were prepared with different endocrown abutment designs: one with a buccal wall (Class 2) and the other without a buccal wall (Class 3). Both cavity designs were scanned using a reference desktop scanner (E3) and three different intraoral scanners: Trios3 (TRI group), Cerec Omnicam (CER group), and i500 (I5 group). The obtained Standard Tessellation Language (.stl) datasets were exported to metrology software. The precision was evaluated based on deviations among repeated scan models recorded by each IOS. The trueness was evaluated based on deviations between the reference data and repeated scans. For detecting interaction, data were statistically analyzed using a univariate analysis of variance (ANOVA) and for analyzing the comparison of the test groups data were analyzed by one-way ANOVA and post-hoc Tukey test at the significance level of .05. Results: The deviation values for both cavity designs in the I5 group were significantly lower than those in the other IOS groups in terms of trueness. For both cavity designs, the TRI group exhibited better precision than the other IOS groups. Conclusion: Different technologies of IOS device's and different endocrown prepration designs affected the accuracy of the digital scans.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.14-17
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• 2007

Magnetic properties of transition metal doped $La_{0.5}Ca_{0.5}(Mn_{0.98}TM_{0.02})O_3$(TM=Cr and Ti) are studied. The samples are synthesized by the conventional solid-state method. Using vibrating sample magnetometer magnetization-temperature measurement were carried out with zero field cooling and field cooling at 50 Oe. Cr-doped sample shows cluster or spin glass like behavior while Ti doped does not. Curie temperature obtained were decreased from that of LCMO(245.5 K). Curie temperatures of Cr-doped and Ti-doped samples are 235.5 K and 232.7 K, respectively. The temperature-dependent coercivity $H_c(T)$ was also measured. The coercive force continuously decreases with the substitution of Cr and Ti, The result can be understood in terms of the interaction between defect and domain wall.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.619-627
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• 2018

As ships become faster, larger and are required to meet higher standards, the importance of flow noise is highlighted. However, unlike in the aeroacoustics field for airplanes and trains (where flow noise is considered in design), acoustics are not considered in the marine field. In this study, analysis procedures for hull-induced flow noise are established to investigate the flow noise characteristics of a wave-piercing hull form that can negate the effect of wave-breaking. The principal mechanisms behind hull-induced flow noise are fluid-structure interactions between complex flows underneath the turbulent boundary layer and the hull. Noise induced by the turbulent boundary layer was calculated using wall pressure fluctuation and energy flow analysis methods. The results obtained show that noise characteristics can be distinguished by frequency range and hull region. Also, the low-frequency range is affected by hull forms such that it is correlated with ship speed.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.67-75
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• 2008

It is interesting to note that distinct element method has been used extensively to model the response of micro and discontinuous behavior in geomechanics. Impressive advances related to response of distinct particles have been conducted and there were difficulties in considering fluid effect simultaneously. Current distinct element methods are progressively developed to solve particle-fluid coupling focused on fluid flow through soil, rock or porous medium. In this research, numerical simulations of fluid injection into particulate materials were conducted to observe cavity initiation and propagation using distinct element method. After generation of initial particles and wall elements, confining stress was applied by servo-control method. The fluid scheme solves the continuity and Navior-Stokes equations numerically, then derives pressure and velocity vectors for fixed grid by considering the existence of particles within the fluid cell. Fluid was injected as 7-step into the assembly in the x-direction from the inlet located at the center of the left boundary under confining stress condition, $0.1MP{\alpha}\;and\;0.5MP{\alpha}$, respectively. For each simulation, movement of particles, flow rate, fluid velocity, pressure history, wall stress including cavity initiation and propagation by interaction of flulid-paricles were analyzed.