• Tunnel and Underground Space
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• v.18 no.1
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• pp.44-57
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• 2008

In this study, a 2D finite-element analysis, using the SEEP/W program, was carried out to estimate the amount of groundwater flawing into a tunnel, as well as the groundwater tables around wetland areas during and after a tunnel excavation through rock mass. Four sites along the Wonhyo-tunnel in Cheonseong Mountain (Gyeongnam, Korea) were analysed, where the model damain of the tunnel included both wetland and fault zone. The anisotropy of the hydraulic conductivities of the rock mass was calculated using the DFN model, and then used as an input parameter for the cantinuum model. Parametric study on the influencing factors was perofrmed to minimize uncertainties in the hydraulic properties. Moreover, the volumetric water content and hydraulic conductivity functions were applied ta the model to reflect the ability of a medium ta store and transport water under both saturated and unsaturated conditions. The conductivity of fault zone was assumed ta be $10^{-5}m/sec\;or\;10^{-6}m/sec$ and the conductivity of grouting zone was assumed as 1/10, 1/50 or 1/100 of the conductivity of rock mass. Totally $6{\sim}8$ cases of transient flow simulation were peformed at each site. The hydraulic conductivities of fault zone showed a significant influence on groundwater inflow when the fault zone crossed the tunnel. Also, groundwater table around wetland maintained in case that the hydraulic conductivity of grouting zone was reduced ta be less than 1/50 of the hydraulic conductivity of rock mass.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.119-122
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• 1996

The case for a massive black hole in the center of the Galaxy is reassessed using improved modeling techniques and observational data. A dark mass of ${\~}{\times} 10^6$ Mo is present within 0.2 pc of the Galactic center. However, the available data can be modeled, without appealing to a massive black hole, using an extended distribution of dark stellar remnants (neutron stars and stellar mass black holes) provided that the stellar initial mass function in the central parsec is deficient in stars less massive than $\~$1 Mo. Such a situation may be a natural consequence of repeated gas build-up followed by starbursts in the central region. A clear distinction between this and the massive central black hole model cannot be made using red giant tracers outside 0.2 pc due to uncertainties in the radial velocity dispersion distribution. The cluster of massive early-type emission-line stars in the central parcsec more effectively probe the mass distribution close to Sgr A $\ast$, but their small number and partial rotational support complicate mass determinations. Proper motion determinations for stars within 0.5' of Sgr A$\ast$ may be the most effective means of unambiguously determining the mass distribution in the immediate vicinity of the Galactic center.

• Journal of Korean Association for Spatial Structures
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• v.20 no.4
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• pp.73-81
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• 2020

In this study, a tuned mass damper(TMD) was installed to control the displacement response to earthquakes by generalizing to six analysis models according to the shape of the upper structure based on the case of various large spatial structures around the world. The six analysis models are ribbed type, latticed type, elliptical type, gable type, barrel type, and stadium type composed of 3D arch trusses. In this paper, ribbed type, latticed type and elliptical type were analyzed. The mass of each TMD was set to 1% of the total structural mass. Result of analyzing the optimal number and position of the analysis model, the displacement response control was the most excellent in the model with 6 and 8 TMDs, and the displacement response decreased in most cases. The displacement response control was better with installing the TMD at the edge point than focusing the TMD at the center of the analysis model. However, when 10 or more TMDs are installed or concentrated in the center, large loads intensively act on the structure, resulting in increased displacement. Therefore, although it is slightly different depending on the shape, it is judged that the displacement response control is the best to install 6 and 8 TMDs at the close to the edge point.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.65.3-66
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• 2015

The determination of three dimensional parameters (e.g., radial speed, angular width, source location) of Coronal Mass Ejections (CMEs) is very important for space weather forecast. To estimate these parameters, several cone models based on a flat cone or a shallow ice-cream cone with spherical front have been suggested. In this study, we investigate which cone model is proper for halo CME morphology using 33 CMEs which are identified as halo CMEs by one spacecraft (SOHO or STEREO-A or B) and as limb CMEs by the other ones. From geometrical parameters of these CMEs such as their front curvature, we find that near full ice-cream cone CMEs (28 events) are dominant over shallow ice-cream cone CMEs (5 events). So we develop a new full ice-cream cone model by assuming that a full ice-cream cone consists of many flat cones with different heights and angular widths. This model is carried out by the following steps: (1) construct a cone for given height and angular width, (2) project the cone onto the sky plane, (3) select points comprising the outer boundary, (4) minimize the difference between the estimated projection points with the observed ones. We apply this model to several halo CMEs and compare the results with those from other methods such as a Graduated Cylindrical Shell model and a geometrical triangulation method.

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.1
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• pp.93-101
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• 1998

Numerical models have been widely used to understand the structure of coastal currents and the transport mechanisms in regard to the fate of pollutants. This study focuses on the development of a three-dimensional model of coastal circulation and mass transport. The model was used to calculate coastal currents and temperature distributions of the thermal plume discharged from a power plant. The model results were compared with field-observed data. They showed the relatively good agreements with the data. The model can be used to estimate the currents and its mass transport in coastal waters.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.96.1-96.1
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• 2011

Halo coronal mass ejections (HCMEs) are major cause of the geomagnetic storms. To minimize the projection effect by coronagraph observations, we consider two CME cone models: an ice-cream cone model and an asymmetric cone model. These models allow us to determine three dimensional parameters of HCMEs such as radial speed, angular width, and the angle between sky plane and cone axis. In this study, we compare these parameters obtained from both models using 50 well-observed HCMEs from 2001 to 2002. Then we obtain the root mean square error (RMS error) between measured projection speeds and estimated ones for the models. As a result, we find that the radial speeds obtained from the models are well correlated with each other (R=0.89), and the correlation coefficient of angular width is 0.68. The correlation coefficient of the angle between sky plane and cone axis is 0.42, which is much smaller than what is expected. The reason may be due to the fact that the source locations of the asymmetric cone model are assumed to be near the center. The average RMS error of the asymmetric cone model (86.2km/s) is slightly smaller than that of the ice-cream cone model (88.6km/s).

• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.1-18
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• 2014

Heave plates have been widely used to enhance viscous damping and thus reduces the heave response of Spar platforms. Single heave plate attached to the keel of the Spar has been reported in literature (Tao and Cai 2004). The effect of double heave plates on hydrodynamic response in random waves has been investigated in this study. The influence of relative spacing $L_d/D_d$ ($D_d$-the diameter of the heave plate) on the hydrodynamic response in random waves has been simulated in wave basin experiments and numerical model. The experimental investigation has been carried out using 1:100 scale model of Spar with double heave plates in random waves for different relative spacing and varying wave period. The influence of relative spacing between the heave plates on the motion responses of Spar are evaluated and presented. Numerical investigation has been carried out to investigate effect of relative spacing on hydrodynamic characteristics such as heave added mass and hydrodynamic responses. The measured results were compared with those obtained from numerical simulation and found to be in good agreement. Experimental and numerical simulation shows that the damping coefficient and added mass does not increase for relative spacing of 0.4 and the effect greater than relative spacing on significant heave response is insignificant.

• Journal of Korean Association for Spatial Structures
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• v.24 no.1
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• pp.89-98
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• 2024

In this study, we investigated the dynamic characteristics of three irregular building models to analyze the effectiveness of displacement response control with Tuned Mass Damper (TMD) installation in twisted irregular buildings. The three irregular models were developed with a fixed angle of twist per story at one degree, subjected to three historical seismic loads and resonant harmonic loads. By designing TMDs with linear and dashpot attributes, we varied the total mass ratio of the installed TMDs from 0.00625% to 1.0%, encompassing a total of 10 values. Two TMDs were installed at the center of the top story of the analysis model in both X and Y directions to evaluate displacement response control performance based on TMD installation. Our findings suggest that the top displacement response control performance was most effective when a 1.0% TMD was installed at the top layer of the analysis model.

• Clean Technology
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• v.28 no.1
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• pp.32-37
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• 2022

Food waste is produced from food factories, food services, and home kitchens. The generated mass reached 5.4 million tons/year in 2020. The basic management technology for such waste has been biological degradation under an anaerobic environment. However, the whole process is intrinsically slow and considerably affected by the inner physicochemical properties of the waste and other surrounding conditions, which makes optimization of the process difficult. The most promising options to counter this massive generation of waste are eco-friendly treatments or recycling. As a preliminary step for these options, attempts were made to evaluate the feasibility and usability of three simulative models based on reaction kinetics. Model (A) predicted relative changes over reaction time for reactant, intermediate, and product. Overall, an increased reaction rate produced less intermediate and more product, thereby leading to a shorter total reaction time. Particle diminishing model (B) predicted reduction of the total waste mass. The smaller particles diminished faster along with the dominant effect of microbial reaction. In Model (C), long-chain cellulose was predicted to transform into reducing sugar. At a standard condition, 48% of cellulose molecules having 10⁵ repeating units turned into reducing sugar after 100 h. Also it was found that the optimal enzyme concentration where the highest amount of remnant sugar was harvested was 1 mg L^-1.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.521-528
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• 2005

The evaluation process of rock mass properties intrinsically contains some uncertainty due to the inhomogeneity of rock mass and the measurement error. Although various empirical methods for the determination of rock mass properties were suggested, there is no way of integrating various information on rock mass properties except averaging. For these reasons, this research introduces evidence theory which can model epistemic uncertainty and yield reasonable rock mass properties through combining various information such as empirical equations, in-situ test results, and so on. Through the application of evidence theory to the real site investigation and in situ experiment results, an interval of deformation modulus, cohesion and friction angle of rock mass were obtained. The ratios between lower and upper bound of those properties ranges from 1.6 to 3.6. Numerical analyses of circular hole using the properties for TYPE-2 rock mass were carried out. The magnitude or size of plastic region and radial displacement in case of lower bound properties is about 4 times larger than that of upper bound properties.